Environmentally-Compatible Food Packaging (Woodhead Publishing Series in Food Science, Technology and Nutrition)

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Author: Emo Chiellini

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Environmentally compatible food packaging

© 2008, Woodhead Publishing Limited

Related titles Handbook of waste management and co-product recovery

in food processing (ISBN 978-1-84569-025-0) Millions of tonnes of waste are produced every year by the agri-food industry. Disposal by landfill or incineration is already expensive and the industry faces increasing costs for the removal of refuse and remnants. The costs of energy and water are also significant for food businesses and savings can be made in these areas if the quantity of energy and water used is limited. Methods to recycle and reduce the need for disposal are therefore increasingly of interest. This comprehensive collection reviews recent research in the field, covering optimisation of manufacturing procedures to decrease waste, reduction of energy and water expenditure, methods to valorise refuse by co-product recovery and techniques to deal with wastewater and solid waste. Novel food packaging techniques (ISBN 978-1-85573-675-7) With its distinguished international team of contributors, Novel food packaging techniques summarises the key developments in the field. The first part of the book discusses general issues such as packaging design, consumer attitudes to novel packaging and the legislative context. Part II looks at new techniques such as the use of oxygen and other scavengers, freshness indicators and antimicrobial packaging. The final part of the book discusses packaging materials and considers how packaging can be used with other preservation techniques to improve the quality of particular foods. Environmentally friendly food processing (ISBN 978-1-85573-677-1) With increasing regulation and consumer pressure, the food industry needs to ensure that its production methods are sustainable and sensitive to environmental needs. This important collection reviews ways of analysing the impact of food processing operations on the environment, particularly life cycle assessment (LCA), and techniques for minimising that impact. The first part of the book looks at the application of LCA to the key product areas in food processing. Part II then discusses best practice in such areas as controlling emissions, waste treatment, energy efficiency and biobased food packaging. Details of these books and a complete list of Woodhead’s titles can be obtained by: • visiting our web site at www.woodheadpublishing.com • contacting Customer Services (e-mail: [email protected]; fax: +44 (0) 1223 893694; tel.: +44 (0) 1223 891358 ext. 130; address: Woodhead Publishing Ltd, Abington Hall, Granta Park, Great Abington,

Cambridge CB21 6AH, England)


Environmentally compatible food packaging Edited by Emo Chiellini

WPTF3007

Cambridge England


Published by Woodhead Publishing Limited, Abington Hall, Granta Park, Great Abington, Cambridge CB21 6AH, England www.woodheadpublishing.com Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW, Suite 300, Boca Raton, FL 33487, USA First published 2008, Woodhead Publishing Limited and CRC Press LLC © 2008, Woodhead Publishing Limited The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials. Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing Limited. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress. Woodhead Publishing ISBN 978-1-84569-194-3 (book) Woodhead Publishing ISBN 978-1-84569-478-4 (e-book) CRC Press ISBN 978-1-4200-7789-6 CRC Press order number: WP7789 The publishers’ policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp which is processed using acidfree and elementary chlorine-free practices. Furthermore, the publishers ensure that the text paper and cover board used have met acceptable environmental accreditation standards. Typeset by SNP Best-set Typesetter Ltd., Hong Kong Printed by TJ International Ltd, Padstow, Cornwall, England


Contents

Contributor contact details........................................................................... xiii Preface............................................................................................................ xviii Part I 1

2

Biobased food packaging materials: new directions

State-of-the-art biobased food packaging materials........................ G. Robertson, University of Queensland, Australia 1.1 Introduction: biobased packaging, the food industry and the environment................................................................. 1.2 Classification of biobased food packaging materials ............ 1.3 Properties of biobased food packaging materials................. 1.4 Assessing the biodegradability of biobased materials for food packaging................................... 1.5 Applications and challenges for biobased food packaging .......................................................... 1.6 Future trends .............................................................................. 1.7 Sources of further information and advice ............................ 1.8 References .................................................................................. Types, production and assessment of biobased food packaging materials.............................................................................. S. Imam, G. Glenn, B.-S. Chiou, J. Shey, R. Narayan and W. Orts, USDA-ARS-PW-WRRC, USA


3 3 7 14 19 21 22 23 24 29

vi

Contents 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12

3

4

Introduction: rationale and need for biobased food packaging .......................................................... The environmental impact of conventional food packaging........................................................................... Opportunities for renewable polymers .................................. Production of biobased food packaging materials................ Hybrid blends and composites ................................................ New developments in the production of packaging from recycled lignocellulosic fiber and renewable materials........................................................... Assessing the biodegradability of renewable materials in food packaging ...................................................................... Biodegradable packaging life cycle assessment .................... Food safety concerns, applications and adoption by the industry ........................................................................... Future trends .............................................................................. Sources of further information and advice ............................ References ..................................................................................

Thermoplastic nanobiocomposites for rigid and flexible food packaging applications .......................................... J. Lagaron and M. Sanchez-Garcia, Institute of Agrochemistry and Food Technology, Spain; E. Gimenez, ESID, University Jaume I, Castellon, Spain 3.1 Introduction: plastic food packaging, sustainable materials and barrier properties ......................... 3.2 ‘Barrier properties’ limit the use of plastics in monolayer packaging............................................................ 3.3 Novel developments in barrier polymeric structures ........... 3.4 Polymer blends: the case of permeable fillers ....................... 3.5 Nanocomposites: the case of impermeable fillers ................. 3.6 Nanobiocomposites for monolayer packaging: polylactic acid, polycaprolactone, polyhydroxyalkanoate and starch ........................................... 3.7 Future trends and outlook ....................................................... 3.8 Nomenclature............................................................................. 3.9 References .................................................................................. Improved fibre-based packaging for food applications................... J. Poustis, JPC Packaging Institute, France 4.1 Introduction................................................................................ 4.2 Properties and uses of fibre-based food packaging .............. 4.3 Innovative methods to improve fibre-based packaging for food applications .................................................................


29 30 32 37 41 44 46 52 53 55 56 57

63

63 65 69 71 73 78 82 82 83 90 90 93 95

Contents 4.4 4.5 4.6 4.7 4.8 5

6

Starch-based edible films..................................................................... Y. Zhang and Z. Liu, University of Manitoba, Canada; J. Han, Frito-Lay, Inc., USA 5.1 General properties and structure of starch............................ 5.2 History of edible films .............................................................. 5.3 Edible film materials and their previous applications.......... 5.4 Starch film-forming mechanisms – gelatinization and recrystallization .................................................................. 5.5 Appearance and physical properties of starch films............. 5.6 Plasticization of starch films..................................................... 5.7 Trends in starch research and applications ............................ 5.8 References .................................................................................. The use of chitin and chitosan for food packaging applications............................................................................................ I. S. Arvanitoyannis, University of Thessaly, Greece 6.1 Introduction................................................................................ 6.2 Mechanical properties............................................................... 6.3 Thermal properties .................................................................... 6.4 Gas permeability ....................................................................... 6.5 Water permeability .................................................................... 6.6 Conclusions ................................................................................ 6.7 References ..................................................................................

Part II 7

Suitability of new fibre-based packaging materials for food packaging .................................................................... Assessing the biodegradability of new fibre-based packaging materials for food packaging................................. Applications and future trends in the food industry............ Sources of further information and advice ............................ References ..................................................................................

vii 96 102 103 107 107 108 108 110 111 112 118 126 132 133 137 137 138 146 149 154 156 157

Using environmentally compatible packaging technologies in the food industry

Consumer attitude to food packaging and the market for environmentally compatible products ......................................... I. S. Arvanitoyannis and A. Kasaveti, University of Thessaly, Greece 7.1 Introduction................................................................................ 7.2 Packaging materials................................................................... 7.3 ‘Green’ packaging ..................................................................... 7.4 Disposal of packaging materials.............................................. 7.5 Recycling of packaging materials ............................................


161 161 163 164 164 166

viii

Contents 7.6 7.7 7.8 7.9 7.10

8

9

10

New packaging technologies.................................................... Food packaging regulation in the European Union ............. The study of consumer behaviour ........................................... Conclusions ................................................................................ References ..................................................................................

Environmental assessment of food packaging and advanced methods for choosing the correct materials.................... K. Verghese, RMIT University, Australia 8.1 Introduction................................................................................ 8.2 Modern day lifestyle conflicts and demands from the retail sector................................................................................. 8.3 Recognition of the environmental impacts of packaging in the food industry ........................................... 8.4 Environmental assessment of food packaging systems........ 8.5 Environmental assessment tools for food packaging systems ........................................................................................ 8.6 Sustainable packaging developments ..................................... 8.7 Implementing environmental assessment approaches into the product–packaging system development process......................................................................................... 8.8 Future trends .............................................................................. 8.9 Sources of further information and advice ............................ 8.10 References .................................................................................. Measuring the environmental performance of food packaging: life cycle assessment ......................................................... G. Parker, Ciba Expert Services, UK 9.1 Introduction................................................................................ 9.2 Environmental performance of biopolymers ........................ 9.3 Measuring environmental impacts: the science of life cycle assessment .................................................................. 9.4 Results of existing life cycle assessment studies of biopolymers ........................................................................... 9.5 Measuring the environmental performance of packaging: future trends ........................................................... 9.6 Sources of further information and advice ............................ 9.7 References .................................................................................. Eco-design of food packaging materials ........................................... H. Lewis, RMIT University, Australia 10.1 Introduction................................................................................ 10.2 Key drivers of eco-design of food packaging materials ....... 10.3 Eco-design strategies for food packaging materials ............. 10.4 Future trends .............................................................................. 10.5 Conclusions ................................................................................


168 170 171 178 179 182 182 183 185 188 190 204 204 204 205 209 211 211 212 217 229 234 236 237 238 238 239 241 258 258

Contents 10.6 10.7 11

12

13

ix

Sources of further information and advice ............................ 259 References .................................................................................. 259

Additives for environmentally compatible active food packaging...................................................................................... S. Irmak and O. Erbatur, Cukurova University, Turkey 11.1 Introduction................................................................................ 11.2 Antimicrobial/antioxidant agents incorporated into polymers...................................................................................... 11.3 Chemical preservatives ............................................................. 11.4 Peptides and proteins................................................................ 11.5 Polysaccharides .......................................................................... 11.6 Natural antimicrobial/antioxidant compounds from plant sources............................................................................... 11.7 Extraction and fractionation techniques for antimicrobial/antioxidant compounds from plant sources......................................................................................... 11.8 Antimicrobial and antioxidant tests ....................................... 11.9 Suitability of new coatings and adhesives for food packaging .................................................................... 11.10 Incorporation of antimicrobials/antioxidants into polymer materials...................................................................... 11.11 Applications in the food industry ........................................... 11.12 Future trends .............................................................................. 11.13 References .................................................................................. Recycling of food packaging materials: an overview ...................... D. Dainelli, Sealed Air Corporation, Italy and EuPC (European Plastics Converters Association), Belgium 12.1 Introduction................................................................................ 12.2 Regulation of recycling of food packaging materials ........... 12.3 Recycling paper food packaging: collection, separation and processing............................................................................ 12.4 Recycling plastic food packaging: collection, separation and recovery ........................................................... 12.5 Recycling of other materials .................................................... 12.6 Supply chain management to reduce packaging waste........ 12.7 Conclusions ................................................................................ 12.8 References ..................................................................................

263 263 265 265 266 268 270 273 276 279 280 282 283 284 294 294 295 299 305 314 319 322 324

Recycled plastics for food applications: improving safety and quality............................................................................................. 326 V. Komolprasert and A. Bailey, Food and Drug Administration, USA 13.1 Introduction................................................................................ 326 13.2 Plastic food packaging and the environment ........................ 327


x

Contents 13.3 13.4 13.5 13.6 13.7 13.8 13.9

14

Recycled paper and board for food applications: improving safety and quality............................................................... C. Nerín, I3A, CPS, University of Zaragoza, Spain 14.1 Introduction................................................................................ 14.2 The recyclability of paper and board...................................... 14.3 Improving the recyclability of paper and board packaging .................................................................................... 14.4 Testing the safety and quality of recycled paper and board.................................................................................... 14.5 Future trends .............................................................................. 14.6 Sources of further information and advice ............................ 14.7 References ..................................................................................

Part III 15

16

The recyclability of packaging plastics ................................... Recycling processes ................................................................... Improving the recyclability of plastic packaging for food use ................................................................................ The safety and quality of recycled plastics ............................ The use of recycled plastics in the food industry .................. Future trends .............................................................................. References ..................................................................................

328 330 331 336 345 346 347 351 351 352 358 359 364 365 367

Environmentally compatible food packaging for particular applications

Overview of environmentally compatible polymeric materials for food packaging............................................ E. Chiellini, A. Barghini, P. Cinelli and V. I. Ilieva, University of Pisa, Italy 15.1 Introduction................................................................................ 15.2 Polymers from renewable resources ....................................... 15.3 Multilayer packaging films ....................................................... 15.4 Technology for biobased polymer processing ....................... 15.5 Economic issues regarding biodegradable polymers...................................................................................... 15.6 Conclusions ................................................................................ 15.7 Sources of further information and advice ............................ 15.8 References ..................................................................................

371 371 372 376 377 379 388 389 390

Modified atmosphere packaging using environmentally compatible and active food packaging materials ............................. 396 C. Guillaume, P. Chalier and N. Gontard, University of Montpellier II, France 16.1 Introduction................................................................................ 396


Contents 16.2 Modified atmosphere packaging of fruit and vegetables: using proteins to control gas transport phenomena through paper-based materials ................................................ 16.3 Antimicrobial modified atmosphere packaging: antimicrobial properties of aroma compounds and their controlled release using the paper coating agent as an inclusion matrix....................................... 16.4 Future trends .............................................................................. 16.5 References .................................................................................. 17

18

19

Active environmentally compatible food packaging ....................... R. Catalá, P. Hernández-Muñoz and R. Gavara, IATA-CSIC, Spain 17.1 Introduction................................................................................ 17.2 Basic characteristics of active packaging ............................... 17.3 Biopolymer-based active materials for food packaging .................................................................................... 17.4 Future trends .............................................................................. 17.5 References .................................................................................. Biobased intelligent food packaging.................................................. P. Taoukis, National Technical University of Athens, Greece; M. Smolander, VTT Technical Research Centre of Finland, Finland 18.1 Introduction................................................................................ 18.2 Biobased tools for the detection of quality-indicating metabolites.................................................. 18.3 Biobased tools for the detection of pathogenic and microbial contamination ................................................... 18.4 Biobased indicators for monitoring the time–temperature history ......................................................... 18.5 Other intelligent packaging systems utilising biomolecules............................................................................... 18.6 Future trends .............................................................................. 18.7 References .................................................................................. Environmentally compatible packaging of fresh agricultural and horticultural produce.................................................................... C. Bishop and S. Hanney, Writtle College, UK 19.1 Introduction................................................................................ 19.2 Specific challenges for fresh produce packaging................... 19.3 Industry response ...................................................................... 19.4 Storage of packaging material ................................................. 19.5 Supply chain ...............................................................................


xi

397

403 414 415 419 419 420 422 432 433 439

439 440 444 446 450 451 452

459 459 463 464 468 470

xii

Contents 19.6 19.7 19.8

20

21

22

Reducing the environmental impact of secondary packaging – returnable plastic crates...................................... 471 Conclusions ................................................................................ 475 References .................................................................................. 476

Biobased packaging of dairy products .............................................. M. Jakobsen, University of Copenhagen, Denmark; V. Holm, Danish Technological Institute, Denmark; G. Mortensen, Danish Dairy Board, Denmark 20.1 Introduction................................................................................ 20.2 Properties required in relation to dairy products ................. 20.3 Current applications of biopackaging of dairy products ..... 20.4 Future trends .............................................................................. 20.5 Sources of further information and advice ............................ 20.6 References .................................................................................. Environmentally friendly packaging of muscle foods ..................... P. Dawson, K. Cooksey and S. Mangalassary, Clemson University, USA 21.1 Introduction................................................................................ 21.2 Types of meat packaging materials ......................................... 21.3 Source reduction ........................................................................ 21.4 Recyclable materials ................................................................. 21.5 Biobased materials .................................................................... 21.6 Future trends .............................................................................. 21.7 References .................................................................................. Legislation and certification of environmentally compatible packaging in the European Union..................................................... C. Enguix, A. Imbernon and J. Ferrer, AINIA – Instituto Tecnológico Agroalimentario, Spain 22.1 Introduction................................................................................ 22.2 Packaging waste legislation ...................................................... 22.3 Biodegradable waste ................................................................. 22.4 Legislation on materials and articles intended to come into contact with food .................................................... 22.5 Future trends for the legislation of materials and articles intended to come into contact with food ................. 22.6 References ..................................................................................


478

478 479 485 489 491 492 496 496 496 498 501 503 515 515 521 521 523 539 542 553 556

Contributor contact details

(* = main contact)

Chapter 2

Editor

S. Imam,* G. Glenn, B.-S. Chiou, J. Shey, R. Narayan and W. Orts Bioproduct Chemistry and Engineering Research USDA-ARS-PW-WRRC 800 Buchanan Street Albany CA 94710 USA

E. Chiellini Laboratorio Materiali Polimerici Bioattivi per Applicazioni Biomediche ed Ambientali UdR-Consorzio INSTM – Dipartimento di Chimica e Chimica Industriale University of Pisa Via Risorgimento 35 56126 Pisa Italy E-mail: [email protected]

E-mail: [email protected]

Chapter 3

G. L. Robertson School of Land and Food Sciences University of Queensland Brisbane QLD 4072 Australia

J. M. Lagaron* and M. D. Sanchez-Garcia Novel Materials and Nanotechnology Institute of Agrochemistry and Food Technology C.S.I.C. Apdo. Correos 73 46100 Burjassot Spain



Chapter 1


xiv


E. Gimenez Department of Engineering and Design (ESID) University Jaume I Campus del Riu Sec E-12080 Castelló de la Plana Spain Email: [email protected]

Chapter 4 J. Poustis CEO JPC Packaging Institute 3 allée de Saintonge 33600 Pessac France E-mail: [email protected]

Chapter 5 Y. Zhang and Z. Liu Department of Food Science University of Manitoba Winnipeg, MB Canada R3T 2N2 E-mail: [email protected] J. H. Han* Pepsico Fruit and Vegetable Research Center Frito-Lay, Inc. 7701 Legacy Dr. Plano, TX 75024 USA Emial: [email protected]


Chapter 6 I. S. Arvanitoyannis Department of Agriculture, Ichthyology and Aquatic Environment School of Agricultural Sciences University of Thessaly Fytoko Street 38446 Nea Ionia Magnesias Volos-Hellas, Greece E-mail: [email protected]

Chapter 7 I. S. Arvanitoyannis* and A. Kasaveti Department of Agriculture, Ichthyology and Aquatic Environment School of Agricultural Sciences University of Thessaly Fytoko Street 38446 Nea Ionia Magnesias Volos-Hellas, Greece E-mail: [email protected]

Chapter 8 K. Verghese Centre for Design RMIT University GPO Box 2476V Melbourne Victoria 3001 Australia E-mail: Karli.Verghese@rmit. edu.au


xv

Chapter 9

Chapter 12

G. Parker Ciba Expert Services Cleeve Road Leatherhead Surrey KT22 7RU UK

D. Dainelli Analytical Department and Regulatory Affairs Sealed Air Corporation Via Trento 7-20017 Passirana di Rho (Milano) Italy


E-mail: Dario.dainelli@ sealedair.com

Chapter 10 H. Lewis Centre for Design RMIT University GPO Box 2476V Melbourne Victoria 3001 Australia E-mail: [email protected]

Chapter 11 S. Irmak* and O. Erbatur Department of Chemistry Cukurova University Balcali 01330 Adana Turkey E-mail: [email protected]

Chapter 13 V. Komolprasert* and A. Bailey Division of Food Contact Notifications (HFS-275) Office of Food Additive Safety Center for Food Safety and Applied Nutrition Food and Drug Administration 5100 Paint Branch Parkway College Park, MD 20740 USA E-mail: Vanee.Komolprasert@fda. hhs.gov

Chapter 14 C. Nerín Research Institute of Engineering Research (I3A) Centro Politécnico Superior (CPS) Department of Analytical Chemistry University of Zaragoza María de Luna 3 50018 Zaragoza Spain E-mail: [email protected]


xvi


Chapter 15

Chapter 18

E. Chiellini,* A. Barghini, P. Cinelli and V. I. Ilieva Laboratorio Materiali Polimerici Bioattivi per Applicazioni Biomediche ed Ambientali UdR-Consorzio INSTM – Dipartimento di Chimica e Chimica Industriale University of Pisa Via Risorgimento 35 56126 Pisa Italy

P. S. Taoukis* National Technical University of Athens School of Chemical Engineering Heroon Polytechniou 5 15780 Zografou Greece


Chapter 16 C. Guillaume, P. Chalier and N. Gontard* UMR 1208 IATE Agropolymers Engineering and Emerging Technologies University of Montpellier II CC023, Pl. E. Bataillon, 34095 Montpellier Cedex 5 France E-mail: [email protected]

E-mail: [email protected] Maria Smolander VTT Technical Research Centre of Finland Tietotie 2, Espoo PO Box 1000 FI-02044 VTT Finland E-mail: [email protected]

Chapter 19 C. F. H. Bishop* and S. J. Hanney Writtle College Chelmsford Essex CM1 3RR UK E-mail: [email protected]

Chapter 17 R. Catalá, P. Hernández-Muñoz and R. Gavara* Institute of Agrochemistry and Food Technology IATA-CSIC Apdo. Correos 73 46100 Burjassot Spain

Chapter 20




M. Jakobsen* University of Copenhagen Department of Food Science Rolighedsvej 30 DK-1958 Frederiksberg C Denmark

Contributor contact details V. Holm Danish Technological Institute Holbergsvej 10 DK-6000 Kolding Denmark E-mail: Vibeke.Kistrup.Holm@ teknologisk.dk G. Mortensen Danish Dairy Board Frederiks Allé 22 DK-8000 Århus C Denmark E-mail: [email protected]

Chapter 21 Paul L. Dawson* Department of Food Science and Human Nutrition Clemson University 204 Poole Hall Clemson SC 29634-0316 USA E-mail: [email protected]


xvii

Kay Cooksey and Sunil Mangalassary Department of Packaging Science Clemson University Clemson SC USA E-mail: [email protected]

Chapter 22 C. Enguix,* A. Imbernon and J. M. Ferrer Dpto. Tecnologías de Envase AINIA – Instituto Tecnológico Agroalimentario Portal Agroalimentario Spain E-mail: [email protected]

Preface

The packaging sector plays an important role in industrial activity with an estimated economic impact in developed countries and in countries in transition of about 2.5% of the average gross national product. Europe has a market share of around 150 million euros, which is more than one-third of the worldwide packaging market. About 50% of this figure is represented by food packaging and projections for the future development of the sector indicate a continuous growth in size and performance improvement. Beyond the fashionable trend of current consumers – ever more inclined to purchase packaged food products that are easy to handle, prepare and consume, while maintaining the quality and freshness of the original produce – there is mounting public concern about the environmental impact of the post-consumer packaging waste that is being generated. On the other hand, the modern vision in food packaging development is no longer focused on the passive role of packaging exploitation in the processing and preservation of foodstuffs and ensuring food integrity and safety.Today, packaging design aims for: the one-step transfer of the produce directly ‘from the field to the table’, hence guaranteeing food freshness and safety; and the preparation of ‘ready-to-eat’ food portions in microwaveable packaging containers (bowls and trays), supplying the consumer with warm food dishes. Active and intelligent packaging can be considered as a further step in the optimization of packaging efficacy. Active packaging is able to modify the condition of the packed food without provoking any substantial variation in its quality and nutritional value, while improving its shelf-life and ultimately its safety. Intelligent packaging is meant to monitor the features of the packed food to provide indications of the quality status of the food during storage and handling. A combination of these two attributes in a single packaging material would then be desirable for the maintenance and quality control of the packed food.


Preface

xix

Among the wide variety of materials currently utilized in food packaging technology, polymeric materials are taking a major share because of the versatility of their processing methods – extrusion (bubble and cast), injection and compression moulding – and their interesting cost/performance ratios. There are various parameters determining the fortunes of natural, artificial or truly synthetic materials aiming to penetrate the food packaging market, notably parity of efficacy in food protection and hence cost/performance. One aspect that is assuming ever-increasing performance, is the environmental impact of these materials as well as the management of the post-consumer packaging waste. The present book primarily focuses on environmentally compatible packaging based on materials that are designed to achieve a low environmental burden during their formulation, processing and conversion to semi-finished and fully finished items, as well as at the end of the service life of the packaging, once it becomes a waste to be treated in appropriate infrastructures. According to the major scope of the book, its content is divided into three parts: • •

•

Part I, new directions in the utilization of biobased materials for food packaging. Part II, using environmentally compatible packaging technology in the food industry, including chapters focusing on the recycling technology related to food packaging and one chapter describing the use of additives for the development of active food packaging. Part III, environmentally compatible food packaging for particular applications, primarily the use of active and intelligent packaging systems.

The book should therefore be of interest to readers from research, industry and government institutions who are involved not only in the field of food packaging but also in the area of new materials design and the utilization of resources and technologies in keeping with the modern vision for sustainable industrial development. Finally, I wish to express my personal appreciation to all the contributors for their efforts and their willingness to share their expertise in the fields of materials science and technology, and food packaging, under the pressure of the tight schedules kindly but firmly imposed by personnel from Woodhead Publishing. Last, but not least, I wish to thank my Secretarial Assistants Maria G. Viola, Michela Bianchi and Maria Caccamo for their continuous help in keeping timely contacts with Woodhead Publishing staff and the contributors to the book. Emo Chiellini Editor


To my wife Teresa and my joyful grand-daughter Eugenia Emo Chiellini


Part I Biobased food packaging materials: new directions


1 State-of-the-art biobased food packaging materials G. Robertson, University of Queensland, Australia

1.1

Introduction: biobased packaging, the food industry and the environment

Biobased food packaging materials have been defined (van Tuil et al. 2000) as ‘materials derived from renewable sources’. A narrower definition (Haugaard & Mortensen 2003) which will be used in this chapter is ‘materials derived from primarily annually renewable sources’, thus excluding paper-based materials, since trees used for papermaking generally have a renewal time of 25–65 years depending on species and country. Paper-based materials have been used for food packaging for decades and account for approximately 50% of all municipal solid waste (MSW) in developed countries (wood accounts for a further 10%); they will not be discussed further in this chapter. At the beginning of the twentieth century, most non-fuel industrial products such as inks, dyes, paints, medicines, chemicals, clothing, synthetic fibres, flexible packaging and also plastics were made from biologically derived resources (Weber et al. 2002). During the twentieth century, petroleum-derived chemicals replaced these to a major extent, due largely to their better physical and chemical properties such as, in the case of packaging materials, strength, lightness and resistance to water and waterborne micro-organisms. Now at the beginning of the twenty-first century, increasing attention is being given to sustainability and the replacement of non-renewable resources (particularly those derived from petroleum) with those from renewable sources, essentially plant-derived products and byproducts from their fermentation (Mohanty et al. 2005).


4


It has become almost commonplace for introductory chapters in books on biobased polymers to include dire warnings about the consequences for life on Earth if a switch is not made immediately from conventional to biobased polymers. For example, Scholz and Khemani (2006) wrote ‘there is a growing general awareness among consumers and government agencies in most countries around the world that conventional plastic products, although useful, are causing tremendous damage to the environment, water supplies, sewer systems (sic) as well as to the rivers and streams’. Mohanty et al. (2005) wrote that ‘persistence of plastics in the environment, the shortage of landfill space, the depletion of petroleum resources, concerns over emissions during incineration, and entrapment by and ingestion of packaging plastics by fish, fowl and animals have spurred efforts to develop biodegradable/biobased plastics’. There is not space here to rebut these statements; a more balanced discussion of the issues can be found in Robertson (2006). A recent article (Royte 2006) questioned whether biodegradable packaging is really the answer to America’s throwaway culture and addressed various concerns about poly(lactic) acid (PLA) and in particular its inability to break down in home composting operations. Environmentalists such as Lester Brown, president of the Earth Policy Institute, question the morality of turning a foodstuff into packaging when so many people in the world are hungry. The recent increase in bioethanol production in the United States has resulted in the price of corn reaching the highest level in a decade and, as a consequence, a dramatic rise in the cost of the tortilla, a food staple in Mexico. The reality is that plastic packaging materials from petroleum sources are well established and play an essential role in the packaging of food. The global annual production of plastics exceeds 250 million tonnes and of this approximately 40% or 100 million tonnes are used for packaging. North America produces about 26 million tonnes of plastics for packaging; Europe about 28 million tonnes; Japan 7 million tonnes and Asia (excluding Japan) 34 million tonnes. Global consumption of biobased polymers was estimated to be 79 800 tonnes (starch, 44 800; PLA, 35 800) in 2005 with loose-fill foam packaging accounting for more than half of starch biopolymer volumes. By 2010, global consumption is forecast to reach 180 000 tonnes (starch, 89 200; PLA, 89 500), a compound annual growth rate of 17.7%. In 2005, global production capacity for biodegradable polymers was around 360 000 tonnes and is expected to reach 600 000 tonnes by 2008. Packaging (including rigid and flexible packaging, paper coating and food service) is the largest sector with 39% of total biodegradable polymer market volumes in 2005; loose-fill packaging was second with 24%, followed by bags and sacks with 21% (Platt 2006). Even with rapid expansion of manufacturing capacity (and assuming equivalent performance), it will be many years before the packaging industry can switch a significant quantity of its production to biobased materials.


State-of-the-art biobased food packaging materials

5

There are two main driving forces behind the development of biobased packaging materials. One driver is the ambition to replace non-renewable with renewable resources, thus leading to a more sustainable packaging industry. The other driver is a desire to reduce the amount of used packaging going to landfill by converting to biodegradable and compostable packaging. Retailers are playing a leading role in encouraging the switch to biobased packaging materials, presumably because that is what their customers want. For example, the UK Courtauld Commitment agreement took shape at a ministerial summit held at the Courtauld Gallery in March 2005, where the Environment Minister met with senior representatives from the majority of the leading UK grocery retailers, as well as the British Retail Consortium. The meeting focused on engaging support to find new packaging solutions and technologies, so that less rubbish ends up in the household bin. The retailers strongly supported the development of biopolymers and compostable packaging. In the United States, Wal-Mart released their Packaging Scorecard in 2006 with a commitment of reducing packaging across its global supply chain by 5% by 2013. Although renewability as such is not explicitly mentioned, the paper-based packaging sector is working to ensure that it receives proper weighting in the scorecard, since in their view renewability is just as important as recyclability when considering the environmental impact of raw materials. From a public point of view, the main drivers for the development of biodegradable packaging are the solid waste problem (particularly the perception of a lack of landfills), the litter problem which the public feel would be solved if biodegradable packaging were used and pollution of the marine environment by non-biodegradable plastics packaging. Despite the professed public preference for biodegradable or compostable packaging, more than 50% of MSW in the United States is biowaste such as yard trimmings, food scraps and paper products (Narayan 2006). This suggests that even if part of the current 15% of MSW that is plastics were to be replaced by biobased materials, there is no guarantee that such material would be composted rather than sent to landfill. A major stumbling block is the lack of composting facilities close to major cities and towns; only 113 such facilities have been identified nationwide in the United States (Royte 2006). An alternative approach is to construct bioreactors or biologically active landfills. The situation in Europe is quite different with European legislation being the key driver for national and regional policy on composting. The 1999 EU Landfill Directive (99/31/EC) contains ambitious targets for diverting biodegradable MSW from landfills; if the targets are met, the quantity of biodegradable waste going to landfill by 2016 will be only 35% of that produced in 1995. This legislation has led to significant developments in composting infrastructures across Europe where organic matter makes up 30–40% of MSW. In The Netherlands and Germany, more than 95% and 60% respectively of all households have access to industrial composting


6


plants (Platt 2006). In the United Kingdom, one-third of households actively compost their green waste at home and the potential is for more than 80% to do so. With the development of commercial composting facilities, food retailers in Europe are leading the switch to biodegradable packaging for fresh foods so that they can send ‘back of store’ waste such as product that has passed its ‘best by’ date straight to composting without the need for separation. Producing biodegradable plastics using annually renewable biomass feedstocks that end up in biodegradation infrastructures like composting is ecologically sound and promotes sustainability (Narayan 2006). Such an approach would be carbon neutral in that the inorganic carbon present in the atmosphere as CO2 is converted to organic carbon in plants using sunlight and then returned to the atmosphere as CO2 during biodegradation. However, given that the major contemporary environmental problem is an excess of CO2 in the atmosphere, a more helpful approach would be to sequester biobased packaging materials in sanitary landfills where, because of little or no moisture and negligible microbial activity, biodegradation is retarded. Landfills have been described as vast mummifiers with excavations finding that even after two decades of burial, about one-third to one-half of food and yard waste remains in a recognisable condition and newspapers can be easily read (Rathje & Murphy 1992). However, because there will be some anaerobic decomposition of organic materials in landfills leading to the production of landfill gas (c. 50% CH4 and 50% CO2), such gas should be captured using conventional gas wells and combusted to produce energy. Polyhydroxyalkanoates (PHAs) are well known to biodegrade under anaerobic conditions, in contrast with other condensation polymers including PLA and aliphatic polyesters which do not biodegrade in the absence of oxygen (Swift & Wiles 2004). The development of biobased packaging materials is predicated on a widely held belief that such materials will have lower environmental impacts than existing petroleum-derived materials. Without this advantage, there is less incentive for industry to adopt biobased packaging materials. Detailed life cycle assessment (LCA) studies on biobased products have been released and are discussed further in Chapter 9. A comparative review (Patel et al. 2003) of 20 published studies (7 dealing with starch polymers, 5 with PHAs, 2 with PLAs, 3 with other biobased polymers and 3 with composites based on natural fibres) provided some interesting conclusions. Of all the biobased polymers studied, starch polymers performed best in environmental terms, with some differences among the various types. Compared with starch polymers, the environmental benefits seemed to be smaller for PLA (LCA results were only available for energy and CO2). For PHA, the environmental advantages seemed to be very small compared with conventional polymers (LCA results were only available for energy use). For both PLA and PHA, the production method, scale of production and type of waste management treatment has a decisive influence on the



7

ultimate conclusion concerning overall environmental balance. Recently Patel and Narayan (2005) stated that available LCA studies and environmental assessments strongly support further development of biodegradable and biobased polymers. However, careful monitoring of various environmental impacts continues to be necessary both for decision makers in companies and policymakers in governments. Recently, Kim and Dale (2005) reported on a detailed LCA of PHAs derived from no-tilled corn and concluded that, under the current PHA fermentation technology, PHA from corn grain does not provide an environmental advantage over polystyrene (PS). The main reason that different LCA studies arrive at different conclusions is because of variations in the approaches used to allocate the environmental burdens. In an attempt to improve its environmental profile, NatureWorksTM announced in 2005 that it will achieve a greenhouse-gas-neutral position for its PLA, making it the first, and only, commercially available greenhouse-gas-neutral polymer in the industry. This will be achieved through the purchase of renewable energy certificates, which serve as an offset to cover all of the emissions from the energy used for the production of PLA. The net result will be a 68% reduction in fossil fuel use in the manufacture of PLA compared with traditional plastics.

1.2

Classification of biobased food packaging materials

Biobased food packaging materials can be classified in a number of ways, based on their chemical composition, origin, synthesis method, economic importance, application, etc. It is important to note that biodegradable polymers such as polycaprolactones (PCLs), polyglycolic acid and polyesteramides are made from petroleum feedstocks and therefore will not be included in the classification below since they are not derived from primarily annually renewable resources. Polymers from renewable resources are distinct from natural polymers in that their synthesis has been purposely initiated. Currently there is no industrial process in place that produces plastic materials solely from renewable resources (Scholz & Khemani 2006). Due to their natural origin (i.e. an enzyme-catalysed synthesis), all natural polymers are inherently biodegradable since for every polymerase enzyme whose action leads to a natural polymer, there is a depolymerase capable of catalysing the degradation of that polymer (Scholz & Khemani 2006). However, it has recently been shown that some recombinant strains of micro-organisms capable of PHA synthesis are also able to synthesise polymers of mercaptoalkanoic acids, which are generally referred to as polythioesters. They are distinguished from PHAs solely by the occurrence of sulphur atoms instead of oxygen atoms in the linkages of the polymer backbone and are non-biodegradable (Steinbüchel 2005).


8


The traditional way of classifying biobased packaging materials has been to divide them into three generations based on their historical development. A similar approach has been adopted below, with the third generation further subdivided into three main categories based on their origin and method of production. 1.2.1 First generation The first generation of biobased packaging materials were used for shopping bags and consisted of synthetic polymers such as low-density polyethylene (LDPE) with 5–15% starch fillers and pro-oxidative and auto-oxidative additives. Although these materials disintegrated or biofragmented into smaller molecules when composted, they did not biodegrade. This gave a very poor image to biodegradable products, leading to public outrage with many consumers feeling that they had been misled by the biodegradability claims. 1.2.2 Second generation Second-generation materials consist of a mixture of gelatinised starch (40–75%) and LDPE with the addition of hydrophilic copolymers such as ethylene acrylic acid, poly(vinyl alcohol) (PVOH) and vinyl acetate which act as compatibility agents. Complete degradation of the starch takes 40 days and degradation of the entire film a minimum of 2–3 years. Public reaction to these films has been similar to that described above for firstgeneration materials. 1.2.3 Third generation Third-generation materials consist of completely biobased materials and can be classified into three main categories according to their origin and method of production. 1 Polymers directly extracted from biomass. 2 Polymers produced by classical chemical synthesis from biomass monomers. 3 Polymers produced directly by natural or genetically modified organisms. A schematic presentation of these three categories is depicted in Fig. 1.1. Category 1: polymers directly extracted from biomass Most of the commonly available Category 1 polymers are extracted from marine and agricultural products: examples including polysaccharides such as cellulose, starch and chitin, and proteins such as collagen and soy. They



9

Third-generation biobased polymers

Category 2

Category 1

Category 3

Polymers synthesised Polymers directly extracted from biomass from bioderived monomers

Polysaccharides

Polymers produced directly by natural or genetically modified organisms

Proteins

Polylactates Plant

Animal

Other polyesters Collagen

Starches Potato Corn Wheat Rice

PHAs

Bacterial celluloses

Soy Chickpea Gluten

Hemicelluloses Barley

Others Chitin/chitosan

Fig. 1.1 Classification of third-generation biobased polymers used for food packaging based on their origin and method of production. Adapted from van Tuil et al. (2000).

can be used alone or in a mixture with a synthetic biodegradable polymer such as PCL or other biodegradable polyesters such as PLA. The most widely used food packaging material in this category is cellulose-based paper and board which will not be discussed further since the raw material (typically trees) is not annually renewable. Regenerated cellulose film (referred to as cellophane in many countries), which has been available for just over a century, and cellulose acetate will not be discussed for the same reason. There is on-going research into the use of hemicelluloses (the second most abundant plant biopolymers on Earth) for biobased food packaging materials (Gröndahl et al. 2006) using glucuronoxylan (the primary


10


hemicellulose in hardwood) and arabinoxylan (the primary hemicellulose in annuals such as barley). Of the annually renewable raw materials, those based on starch are the most commonly used. In nature starch is found as crystalline beads of about 15–100 µm in diameter and after extraction the crystalline structure must be destroyed by pressure, heat, mechanical work or plasticisers such as water, glycerol or other polyols to make the starch thermoplastic (Bastioli 2005). Plasticised starch (known as thermoplastic starch or TPS) is most commonly obtained after disruption (destructuration) and plasticisation of native starch with water and plasticiser by applying thermomechanical energy in a continuous extrusion process. TPS can be processed in the same way as traditional plastics but its sensitivity to water vapour and poor mechanical properties make it unsuitable for many applications. TPS properties reach equilibrium only after several weeks (Avérous & Boquillon 2004). Blending of starch with aliphatic polyesters improves their processability and biodegradability, PCL and its copolymers being particularly suitable (Bastioli 2005). The combination of starch with a water-soluble polymer such as PVOH has been widely studied since 1970 and is currently used to produce starch-based loose fillers as a substitute for expanded PS, as well as sheet extrusion and thermoforming (Bastioli 2005). Italian-based Novamont is the largest producer of biodegradable blends based on starch and synthetic polymers (Platt 2006). Chitin is the second most widespread polysaccharide resource after cellulose and is particularly abundant in the cell walls of insect cuticles, many fungal species and crustacean exoskeletons, the latter being a major source. Chitosan is the deacetylated derivative of chitin (β-[1-4]-poly-Nacetyl-d-glucosamine). Although both chitin and chitosan can be extruded to make films for packaging applications, there being 63 main producers (Clarinval & Halleux 2005), their main use is as an edible coating to extend the shelf-life of fresh fruits and vegetables (Zhao & McDaniel 2005). Films made only from chitosan lack water resistance and have poor mechanical properties. Recently Xu et al. (2005) prepared chitosan/starch composite films that had decreased water vapour transmission rates (WVTRs) and increased mechanical properties. Both chitin and chitosan have antimicrobial activity against a range of food-borne filamentous fungi, yeast and bacteria which can be a useful attribute in many food packaging applications to improve quality and extend shelf-life (No et al. 2007). Two of the more common plant proteins used to produce biodegradable plastic films are chickpea and soy protein isolates; other proteins used include those extracted from wheat, pistachio, sunflower and peas (Dean & Yu 2005). Many other protein-based polymers – such as casein, albumin, fibrinogen, silks and elastins – have been considered because of their inherent biodegradability but they have not yet found widespread use as packaging materials since they are difficult to process, do not melt without decomposition, are difficult to blend with most polymers because of



11

their incompatibility and are more expensive than most polysaccharides (Bhattacharya et al. 2005). Soy protein isolate films suffer from high moisture sensitivity and low strength. The addition of up to 25% stearic acid resulted in films with improved tensile and thermal properties as well as reduced moisture sensitivity (Lodha & Netravali 2005). Recently soy protein isolate, glycerol and gellan gum or κ-carrageenan were found to be suitable for the manufacture of biodegradable/edible soy-based packaging trays (Mohareb & Mittal 2007). However, a moisture barrier must be applied to the trays as they are hydrophilic in nature. Although protein materials have been studied extensively as food packaging materials with recent improvements in properties (Guilbert & Cuq 2005), a breakthrough leading to commercialisation has not yet eventuated. Collagen sausage casings remain the major commercial protein packaging material. Future packaging applications of proteins are likely to be as edible films. Category 2: polymers produced by classical chemical synthesis from biomass monomers Of all the possible biopolyesters that have been produced from biobased materials, PLA has shown the highest commercial potential and is now produced on a comparatively large scale. Lactic acid can be produced cheaply by the fermentation of glucose obtained from the starch in biomass such as corn or wheat, or from lactose in whey or sucrose in molasses. Recently, a novel oat-based biorefinery producing l(+)-lactic acid and various value-added coproducts was proposed (Koutinas et al. 2007). Lactic acid production was achieved via fungal fermentation of Rhizopus oryzae on pearled oat flour and could, it was claimed, lead to significant operating cost reduction as compared with current industrial practices for lactic acid production. The dimerisation of polycondensed lactic acid into lactide (dilactone of lactic acid) and the ring-opening polymerisation (ROP) thereof was reported by the American chemist Wallace Carothers and others from DuPont in 1932 (Södergård & Stolt 2002). However, because the polymer based on lactyl units was unstable at high humidities, it was not considered to have commercial potential until the 1960s when its advantages in medical applications became apparent (Zhang & Sun 2005). Lactic acid (2-hydroxypropanoic acid) is one of the smallest optically active molecules; it can be either an l(+) or a d(−) stereoisomer (Huang 2005). Lactide is formed by the condensation of two lactic acid molecules to give a combination of l-lactide (two l-lactic acid molecules); d-lactide (two d-lactic acid molecules) and meso-lactide (an l-lactic acid and d-lactic acid molecule). PLA can be prepared by both direct condensation of lactic acid and by the ROP of the cyclic lactide dimer. Because the direct condensation route is an equilibrium reaction, difficulties in removing trace amounts of water during the late stages of polymerisation generally limit


12


the ultimate molecular weight achievable by this approach. Most work has focused on the ROP, although Mitsui Toatsu Chemicals has patented an azeotropic distillation process using a high-boiling-point solvent to drive the removal of water in the direct esterification process to obtain high molecular weight PLA (Gruber & O’Brien 2003). NatureWorks® LLC has developed a patented, low-cost continuous process for the production of lactic acid-based polymers. The process starts with a continuous condensation reaction of aqueous lactic acid to produce low molecular weight PLA prepolymer which is converted into a mixture of lactide stereoisomers using tin catalysts. The molten lactide mixture is then purified by vacuum distillation. Finally, PLA high molecular weight polymer with a repeating unit of -[O-CH(CH3)-CO]- is produced using a tin-catalysed, ring-opening lactide polymerisation in the melt, completely eliminating the use of costly and environmentally unfriendly solvents. After the polymerisation is complete, any remaining monomer is removed under vacuum and recycled to the beginning of the process (Gruber & O’Brien 2003). Category 3: polymers produced directly by natural or genetically modified organisms Category 3 polymers consist mainly of the microbial polyesters known generally as PHAs. PHAs are a family consisting of renewable, biodegradable, biocompatible, optically active polyesters that were first identified in 1925 by the French microbiologist Maurice Lemoigne. They are produced in the form of intracellular particles by many commonly found microorganisms which accumulate PHAs as a carbon and energy sink when grown under nutrient stress in the presence of excess carbon (Iwata et al. 2006). Under controlled fermentation conditions, some species can accumulate up to 90% of their dry mass as polymer (Chen 2005). There are now over 100 different types of known molecular building blocks reported for various PHA copolymers (Noda et al. 2004). PHAs are linear aliphatic polyesters consisting of homo- or copolymers of β-hydroxyalkanoic acids that can be produced from the fermentation of sugars by, for example, Cupriavidus necator (originally known as Alcaligenes eutrophus and subsequently renamed Ralstonia eutropha and then Wautersia eutropha), the sugar to polymer conversion yield being about 33%. The polymers produced are biodegradable, and due to their characteristics are suitable for the production of packaging materials. Many different prokaryotic micro-organisms are known to accumulate PHAs intercellularly under growth-limiting conditions. By manipulating the growth medium, a random copolymer containing both 3-hydroxybutyrate (HB) and 3-hydroxyvalerate (HV) is obtained. After biomass separation, the polyester is extracted from the biomass and refined. In the PHA family, poly(hydroxybutyrate) (PHB) is the most common, and is classed as a short chain length PHA (scl PHA) with its monomers containing four to five



13

carbon atoms. Another important scl PHA is poly(hydroxybutyrate-cohydroxyvalerate) or PHBV. PHAs are degraded on exposure to bacteria or fungi in soil, compost or marine sediment. In composting trials up to 85% of the PHA samples degraded within 7 weeks, and PHA-coated paper was rapidly degraded and incorporated into the compost (Nayak 1999). PHAs were first developed industrially in the 1960s and commercialised by ICI in the late 1980s under the tradename Biopol®, the first commercial product being launched in Germany by Wella AG in 1990 as a biodegradable, injection blow-moulded bottle for hair and skin products; these products were introduced to the United States and Japanese markets in 1991 and 1992 respectively (Ramsay & Ramsay 2004). Monsanto acquired Biopol® technology in 1996 and focused on direct synthesis in transgenic plants but stopped production in 1998. The technology was acquired by Metabolix in 2001 who have formed a joint venture company with Archer Daniels Midland known as Telles; they will release a family of PHAs under the tradename MirelTM in late 2008. Biomer in Munich has produced PHB since 1994 using proprietary bacteria. Proctor & Gamble released NodaxTM (a family of PHA copolyesters consisting of scl HB and medium chain length (mcl) HAs) using a genetically modified Pseudomonas species in 2005 but have since withdrawn them from the market (Noda et al. 2005). Since bacterial synthesis is costly, the focus now is on producing PHA plastics and derived chemicals directly in genetically modified crops such as switchgrass, while concurrently providing biomass for alternative energy generation. Switchgrass grows with high yields in the United States on land of marginal use for other crops. It fixes 2 kg CO2 in its root system per 1 kg of biomass above ground. Sugar cane and soybean are also attractive crops for PHA production. Coproduction of energy and PHAs using biomass is seen as the most sustainable approach to biobased material production. It is hoped that direct production of PHAs in plants will achieve economics competitive with those of existing large-volume petrochemical polymers. However, the extraction of PHA accumulated in plant materials will not be as easy as extracting PHA from micro-organisms (Sudesh & Doi 2005). The numerous challenges, both technical and non-technical, associated with commercialising this technology have recently been discussed (Bohlmann 2006). One challenge is to achieve a high level of polymer production in the plant without a decrease in crop yield; another is to recover the polymer from the plant biomass economically. An analysis of the process economics for producing PHAs in agricultural crops such as soybean or switchgrass and the economics compared with those for PHA production by Escherichia coli fermentation are discussed by Bohlmann (2006). Another Category 3 polymer is bacterial cellulose which can be synthesised by bacteria belonging to the genera Acetobacter, Rhizobium, Agrobacterium and Sarcina. Its most efficient producers are the


14


Gram-negative, acetic acid bacteria Gluconacetobacter xylinus (previously Acetobacter xylinum) (Bielecki et al. 2003). It is considered to have enormous potential within the food packaging industry but so far is unexploited. The cellulose is identical in chemical and physical structure to the cellulose formed in plants but has the advantage that it is not combined with lignin, hemicelluloses and pectin, and so can be extracted without the need for harsh chemical treatment.

1.3

Properties of biobased food packaging materials

Before biobased materials can be successfully utilised by the food packaging industry, their physical and mechanical properties have to be within an acceptable range, as does their cost. The key properties of interest in food packaging are briefly reviewed below. 1.3.1 Barrier properties The poor barrier properties (especially under conditions of high humidity) of the traditional and most widely used biobased materials (paper and regenerated cellulose film or cellophane) are well known and it is necessary for them to be coated with synthetic polymers in order to achieve the desired barrier properties necessary for the packaging of many foods. Polysaccharide-based films are poor barriers against water vapour and other polar substances at high relative humidity but at low to intermediate relative humidity they are good barriers against oxygen and other non-polar substances such as aromas and oils (Dole et al. 2004). WVTRs of starchbased films are 4–6 times greater than those of conventional films made from synthetic polymers. Films based on arabinoxylan from annuals such as barley have low oxygen and carbon dioxide permeabilities but high water vapour permeability; they have been made less hydrophilic by surface fluorination but are not yet commercially available (Gröndahl et al. 2006). The barrier properties of some biobased and petroleum-derived polymers are shown in Table 1.1. The wide variation in the values reported are due in large part to the physical nature of the films (e.g. some are handmade; others are extruded commercially) and variations in test methodology rather than their inherent transmission properties. In addition, many values reported in the literature could not be included in the table since their units were incomplete. All the values in Table 1.1 should be used with caution. PLA has WVTRs 3–5 times higher than PET, LDPE, HDPE and OPS; PHAs have WVTRs similar to those of petroleum-derived polymers. PLA has better O2 barrier properties than PS but not as good as PET; PHB has better O2 barrier properties than PET and polypropylene (PP) (data not shown), and adequate fat and odour barrier properties for applications with


State-of-the-art biobased food packaging materials Table 1.1

15

Barrier properties of biobased and petroleum-derived polymers

Polymer OPLA

Water vapour Oxygen Temperature Thickness Source transmission transmission (ºC) (mm) a b rate rate 15.30

22

4.6

66c

23

0.1

PLLA-Mh

210d

25

0.25

P(LLA-DLA) (50:50) PLLAh

214d

25

0.25

31d

27

1

18d 34–40c

27 23

1 0.1

118c 118 146c 1.16

23 23 23 30

0.1 0.1 0.1 1

1.39

30

1

3.48

22

4.6

5.18 6c

22

4.6 0.1

7.9

38d

0.75

36.85

38d

0.75

PLA

PLLA + SiOx PLA/NCg PLA-PCLe PLA (IM)f PLA-PCL/NCg PHB PHBV (14% HV) PET OPS LDPE/APET

56.33 200

84–99 105 233 183

9.44 532 33

LDPE LDPE + 5% starch

Auras et al. (2005) Plackett et al. (2006) Tsuji et al. (2006) ″ Uemura et al. (2006) ″ Plackett et al. (2006) ″ ″ ″ Miguel and Iruin (1999) ″ Auras et al. (2005) ″ Plackett et al. (2006) Jagannath et al. (2006) ″

Abbreviations: OPLA, oriented PLA; PLLA-M, poly(l-lactic acid) middle molecular weight; P(LLADLA), poly(l-lactic acid) and poly(d-lactic acid); NC, nanoclay; PLA (IM), impact modified PLA; PCL, poly(caprolactone); PHB, poly(hydroxybutyrate); PHV, poly(hydroxyvalerate); PHBV, poly(hydroxybutyrate-co-hydroxyvalerate); PET, poly(ethylene terephthalate); OPS, oriented polystyrene; LDPE/APET, low-density polyethylene/amorphous poly(ethylene terephthalate). a Units: mL m−2 day−1 at 0% relative humidity (RH). b Units: g m−2 day−1 at 100% RH. c 37.8 ºC. d 90% RH. e 3–4% caprolactone. f Impact modified. g 5% nanoclay. h Poly(l-lactic acid).


16


short-shelf-life products. Although the gas barrier properties of most biobased materials depend on the ambient humidity, PLA and PHA are two notable exceptions (Auras et al. 2004b). Recently the sorption of ethyl acetate and d-limonene in PLA polymers has been determined (Auras et al. 2006). Ethyl acetate permeability coefficients in PLA are lower than those for PP and LDPE and slightly higher than PET. The permeability coefficient for d-limonene in PLA is much lower than for PET, PP and LDPE, thus confirming that PLA is a good aroma barrier when used in food packaging, as shown earlier in studies on orange juice (Haugaard et al. 2002). 1.3.2 Mechanical properties The mechanical properties of most biobased materials are similar to synthetic polymers as can be seen in Table 1.2. Polysaccharide film tensile

Table 1.2 Mechanical properties of biobased and petroleum-derived polymers Glass Young’s Tensile Elongation Melting transition modulus strength at break Source Polymer temperature, temperature, (Gpa) (Mpa) (%) Tm (ºC) Tg (ºC) Starcha

0.1–0.4

24–30

200–1000

Starchb Starch

110–115

—

0.2–2.0 0.6–0.85

20–30 35–80

20–500 580–820

PLA PHA PHB PHBV PHB

130–180 70–170 140–180 100–190 180

40–70 −30 to 10 0 0–30 4

3.5 0.7–1.8 3.5 0.6–1 3.5

48–53 18–24 25–40 25–30 43

30–240 3–25 5–8 7–15 5

PHBVc PET

145 245–265

1 73–80

1.2 2.8–4.1

20 48–72

50 30–300

PS LDPE LDPE

100 98–115 110

70–115 −100 −30

2.3–3.3 0.3–0.5 0.2

34–50 8–20 10

1.2–2.5 100–1000 620

PP

176

1.7

38

400

a b c

Film grade. Injection moulding grade. 20% HV.


0

Bastioli (2005) ″ Clarinval and Halleux (2005) ″ ″ ″ ″ Sudesh and Doi (2005) ″ Clarinval and Halleux (2005) ″ ″ Sudesh and Doi (2005) ″


17

strength and elastic modulus decrease with increasing plasticiser content, while film elongation normally increases. The mechanical properties of PLA are determined by the molecular weight of the polymer, chain architecture (linear versus branched) and degree of crystallinity, the achievable crystallinity being determined by the relative proportions of l-, d- and meso-lactide in the polymer backbone (Dorgan et al. 2006). Orientation of PLA improves mechanical strength and heat stability, and varying crystallinity and molecular weight results in films ranging from soft and elastic to stiff and high strength. Some limitations do still exist, including the low melt strength (extensibility without breaking of the molten state) and the relatively low temperature at which heat distortion begins to occur. Amorphous and low-crystalline PLA are clear with a high gloss, while highly crystalline PLA is an opaque white material (Dorgan 2006). PLA has a heat seal initiation temperature of 80 ºC, and mechanical properties similar to those of PET. Recently it has been shown (Holm et al. 2006) that hydrolysis of PLA ester linkages results in a 75% decrease in molecular weight and a 35% loss of tensile strength over 130 days at 25 ºC and 98% relative humidity; no decrease was observed at 5 ºC. The physical properties of PHA copolymers can be regulated by varying their molecular structures and copolymer compositions. In general PHB is a hard, highly crystalline thermoplastic polymer that most closely resembles isotactic PP with respect to mechanical behaviour. Although PHB homopolymer is relatively stiff and brittle, introduction of HV comonomers greatly improves its mechanical properties by reducing the level of crystallinity and the melting point, resulting in a decrease in stiffness but an increase in toughness or impact resistance (Bohlmann 2005). As a consequence, the PHA family of polyesters displays a wide variety of properties, from hard crystalline plastics to elastic rubbers with melting temperatures of 50–180 ºC (Sudesh et al. 2000). A random copolymer containing both 3-HB and 3-HV is thermoplastic, being able to be formed by the same techniques as those used for synthetic polymers. By changing the ratio of HV to HB, the resulting copolymer can be made to resemble either PP (low HV) or LDPE (high HV) with regard to flexibility, tensile strength and melting point. For example, the melting temperature decreases from 179 ºC for PHB with no HV to 137 ºC with 25% HV (Hocking & Marchessault, 1998). PHBV has good chemical and moisture resistance as well as good oxygen and aroma barrier properties. PHB has a different resistance to dynamic compression than PP, its deformation value being about 50% lower indicating a more rigid and less flexible material. Under normal freezing and refrigeration conditions the performance of PHB tended to be inferior to that of PP, whereas at higher temperatures PHB performed better than PP (Bucci et al. 2005). When amorphous PLA was blended with PCL it resulted in improved mechanical properties and thermal stability without significant decrease in barrier properties (Cabedo et al. 2006). The toughness of PLA has been


18


substantially increased without a reduction in optical clarity by blending a small amount of ductile PHA with PLA (Noda et al. 2004). 1.3.3 Current limitations The major limitations of most biobased packaging materials for food applications are their performance, processing and cost (Sorrentino et al. 2007). In particular, brittleness, low heat distortion temperature, poor resistance to protracted processing operations and (with the exception of PHAs) their barrier properties, in particular their barrier to water vapour, have limited their applications. Cost has declined in recent years and will decline further as production volume is increased and process optimisation and in-plant efficiencies are achieved. Limited availability is another issue although construction of additional production capacity will address this issue. However, it is unlikely that there will be sufficient PLA to meet food industry requirements for some time. 1.3.4 Methods to improve functionality It is possible to improve the barrier properties of biobased materials (as well as petroleum-derived polymers) using various techniques including plasma deposition of SiOx and the addition of nanocomposites from natural polymers and modified clays. The use of nanocomposites promises to expand the use of biobased packaging (Chiellini et al. 2004; Lagarón et al. 2005; Ray & Bousmina 2005, 2006; Lewitus et al. 2006; Okamoto 2006; Yu et al. 2006) and readers are referred to two recent reviews for details of the potential of bio-nanocomposites in food packaging applications (Rhim & Ng 2007a; Sorrentino et al. 2007). A detailed review of the current literature associated with the barrier properties of polymer/clay nanocomposites has recently been published (Sorrentino et al. 2006). To give just a few examples, an SiOx coating on PLA reduced the WVTR by 60% (Uemura et al. 2006); when 4% kaolinite nanofillers were blended with amorphous PLA, it resulted in an increase in oxygen barrier of 43% (Cabedo et al. 2006). Chang et al. (2003) reported that O2 permeability values were less than half when three types of nanoclays were incorporated into PLA. Results of a similar order of magnitude obtained by Plackett et al. (2006) are shown in Table 1.1 although they did not achieve the full potential for permeability reduction, possibly due to processing conditions, extruder characteristics and selection of the most appropriate nanoclay for a given polymer. Recently starch/clay nanocomposite films were prepared which showed improved mechanical properties (Avella et al. 2005). In a more traditional approach to improving film properties, Rhim et al. (2007b) coated a soy protein isolate film on both sides with PLA and reported up to a 6-fold increase in tensile strength and a 20- to 60-fold decrease in water vapour permeability compared with uncoated soy protein



19

isolate. Coating of paperboard with up to 3 w/v% PLA resulted in an improvement in water barrier properties (Rhim et al. 2007c).

1.4

Assessing the biodegradability of biobased materials for food packaging

Biodegradability is a much over-used and frequently misunderstood word and has no practical meaning unless the environment, timeframe and context are specified. Biodegradable polymers constitute a loosely defined family of polymers that are designed to be degraded by biological agents. Two key steps occur in the biodegradation of polymers. First is a depolymerisation or chain cleavage step (hydrolysis and/or oxidation may be responsible) which converts the polymer chain into smaller oligomeric fragments. The hydrolytic or oxidative processes may be promoted biotically (in biological pathways) and abiotically (in non-biological pathways), oxidation usually being a slower process than hydrolysis (Swift & Baciu 2006). The second step (known as mineralisation) occurs inside the cell where oligomeric fragments are converted into biomass, minerals and salts, water and gases such as CO2 and CH4 (Bohlmann 2005). Composting is the accelerated degradation of heterogeneous organic matter by a mixed microbial population in a moist, warm, aerobic environment under controlled conditions (Narayan 2006). Temperatures in a typical compost system are in the range 40–70 ºC. A standard definition for biodegradable plastics can be found in ISO 472 Plastics vocabulary and ASTM D883 Standard terms relating to plastics: ‘Biodegradable plastic: a degradable plastic in which the degradation process results in lower molecular weight fragments produced by the action of naturally occurring micro-organisms such as bacteria, fungi and algae’. As has been clearly pointed out (Scott 2005), the development of biodegradable polymers has been beset by misinterpretation of the way in which nature deals with its waste products. In particular, the importance of abiotic (non-living) processes has not been given sufficient emphasis in the process of bioassimilation, with the consequence that standards for biodegradable polymers tend to be based on folklore rather than scientific evidence since they ignore completely the environmental role of abiotic chemistry. A number of ASTM standards address important aspects of biodegradable plastics. For example, D5338 addresses CO2 generation in aerobic environments including controlled composting, while D5511 addresses CH4/CO2 evolution in anaerobic environments such as high solids anaerobic digestion, and D5526 accelerated landfill conditions. Other relevant standards include: D6002 for assessing the compostability of environmentally degradable plastics; D6400 for compostable plastics; D6868 for biodegradable plastics used as coatings on paper and other compostable substrates; D6954 for exposing and testing plastics that degrade


20


in the environment by a combination of oxidation and biodegradation; D7075 for evaluating and reporting the environmental performance of biobased products. Complete biodegradation of the product is commonly measured through respirometric tests such as ASTM D5338 which is equivalent to ISO 14852. In this method, the aerobic biodegradation of polymer materials is determined under controlled composting conditions. This test is more suitable for packaging materials as the inoculum is obtained from composted MSW. Difficulties associated with maintaining the complicated temperature profile of this test have been eliminated in ISO 14855, where a constant temperature of 58 ± 2 ºC is specified. This is the most widely used standard test method for the determination of the rate and degree of biodegradation of packaging materials under conditions simulating an intensive aerobic composting process (Jayasekara et al. 2005). The percent biodegradation does not include the carbon converted to cell biomass and not metabolised to CO2 during the course of the test. The European standard EN 13432 Requirements for packaging recoverable through composting and biodegradation – test scheme and evaluation criteria for final acceptance of packaging corresponds to D6400. It is worth noting that both the D6400 and EN 13432 standards were originally developed for starch-based biopolymers, or hydrobiodegradable polymers, where the mechanism inducing biodegradation is based on a reaction with water. The inherent biodegradation test measures the conversion of carbon to CO2 but there is one significant difference between the two standards: complete biodegradation in the compost is measured by CO2 evolution in 180 days in D6400 and 90 days in EN 13432 (Swift & Baciu 2006). The International Standards Organisation has developed ISO 17088 which specifies procedures and requirements for the identification and labelling of plastics, and products made from plastics, that are suitable for recovery through aerobic composting. It comes as a surprise to many people to learn that certain natural materials do not meet these standards, e.g. a leaf will not naturally biodegrade within the timeframe allotted by either D6400 or EN 13432. It is worth emphasising that ‘biobased’ refers to the feedstock used while ‘biodegradable’ refers to how a material acts during disposal. Of course biodegradation depends only on the chemical composition of the polymer and not on its origin (Scott 2005). A major problem with the above standards is that they evaluate samples of biodegradable materials under laboratory conditions rather than as a complete package under real commercial conditions. Recently, Kale et al. (2007b) determined the degradation process of two PLA packages (a bottle and a delicatessen container) over 30 days under real composting and ambient exposure conditions. Bottles made of 96% l-lactide exhibited less degradation than trays made of 94% l-lactide, mainly due to their highly ordered structure and, therefore, their higher crystallinity.



21

The procedure to have a package certified as ‘compostable’ is very elaborate (Kale et al. 2007a). As well as passing test method D5338 or ISO 14855, it must meet various other requirements such as the disintegration test, having heavy metals below certain limits and passing the plant growth test for ecotoxicity. An LCA evaluating the environmental impacts of solid waste management alternatives concluded that diversion of organic waste from landfill to composting reduced energy recovery and increased greenhouse gas emissions of the waste management system (Barlaz et al. 2003). However, the environmental consequences of composting could not be completely characterised due to lack of data.

1.5

Applications and challenges for biobased food packaging

Despite considerable research and development, the use of the newer biobased packaging materials for the packaging of food remains limited. The major scientific studies on the packaging of foods in (partly) biobased materials have been reviewed (Haugaard & Mortensen 2003). Although the number of published papers is few, they show that there are many potential applications. For example, thermoformed PLA cups and injection-moulded PHB cups were found to be as effective as HDPE cups in protecting an orange juice simulant and a dressing from quality changes during storage (Haugaard et al. 2003). The O2 permeability of the three containers was 0.21, 0.18 and 0.26 mL cup−1 day−1 respectively. The quality changes were primarily induced by light. PLA can be made into films, co-extruded into laminates, thermoformed and injection stretch blow moulded into bottles (Auras et al. 2004a). A major application to date has been as food service containers. For example, one-way beverage cups have been used, either as 100% PLA cups or paper cups coated with PLA, to promote an environmentally friendly image. Other current uses are for thermoformed packaging for bakery products, and bags for bread, fresh pasta and salads. Small niche markets for PLA trays and films have been found in Europe, often for organically grown food. Auras et al. (2005) evaluated OPLA for fresh food service containers and compared it with PET and OPS. At ambient conditions (22 ºC) they concluded that OPLA containers provided better mechanical properties than OPS and were comparable to PET. Although the OPLA WVTR was inferior to OPS (5 times greater), the oxygen transmission rate was 10 times less and it was concluded that OPLA could easily replace OPS for fresh food containers. PLA products are fully compostable in commercial composting facilities. Provided that production costs can be reduced, PLA is expected to find packaging applications in areas such as candy twist wraps, coatings for


22


paperboard beverage cartons, plastic film wraps for foods, blister packs and plastic windows in boxes. Recently Rhim et al. (2007c) showed that the optimum concentration of coating solution for improving the water resistance of paperboard was 3 w/v% of PLA solution; a reduction in water vapour permeability of almost 96% at 98% relative humidity was achieved. It was suggested that the improved water barrier properties of paperboard could be exploited in the preparation of water-resistant corrugated fibreboard boxes for storage and distribution of high-moisture foods such as fresh agricultural produce. A small but widely publicised niche market has been developed for a water-soluble, compostable, thermoformed starch tray in chocolate boxes, replacing polyvinyl chloride (PVC) and PET trays. A glassine ‘topper’ pad covers the chocolates in a paperboard box that is overwrapped with PVC film. The tray is manufactured by Plantic and is reputed to consume 50% less energy throughout its life cycle than the previous PVC tray; it has been adopted by the two major chocolate manufacturers in Europe. Haugaard and Mortensen (2003) suggested that, in the short term, biobased materials will be used for short-shelf-life foods stored at chill temperatures, due to the fact that the materials are biodegradable. Recently Holm et al. (2006) reported on the influence of temperature and humidity on the stability of copolymer PLA films with 1.8% PCL. They concluded that PLA films can be expected to be mechanically stable when packaging dry to moist foods at chill to ambient temperatures. Potential applications include fast food packaging of salads, egg cartons, fresh or minimally processed fruits and vegetables, dairy products such as yoghurt and organically grown foods. The high CO2 : O2 permeability ratio of certain biobased packaging materials suggests that they could find application in the packaging of respiring foods such as fruits and vegetables. The challenge for the successful use of biodegradable polymer products in food packaging is achieving the desired shelf-life followed by efficient biodegradation after disposal. Obviously, premature biodegradation and insect infestation must be avoided. In addition, it is imperative that biodegradable plastics do not contaminate the recycling stream for nonbiodegradable, petroleum-derived plastics.

1.6

Future trends

Numerous factors, including political and legislative changes as well as global demand for foods and energy resources, will influence the development and success of biobased packaging materials. However, there is no doubt that the use of biobased materials for food packaging will increase, partly as a result of improvements in mechanical and barrier properties, partly as a result of decreases in costs vis-à-vis petroleum-derived polymers,



23

and partly as a result of their improved environmental profiles. Major supermarket chains are already leading the way by encouraging their suppliers to use biobased packaging materials and this trend is likely to accelerate. Future biobased food packaging materials are likely to be blends of polymers and nanoclays (so-called bio-nanocomposites) in order to achieve the desired barrier and mechanical properties demanded by the food industry. Already important research has been undertaken in this area with some small commercialisation; the next decade will see significant production of bio-nanocomposites for food industry use. Cost is undoubtedly a limitation to the widespread adoption of biobased packaging materials but as production capacity increases, costs will fall. One barrier to reducing costs is the increase in the production of biofuels which in many cases are competing for the same raw materials (corn and maize) as biobased packaging, putting upward pressure on raw material costs. If PHA is to be competitive with synthetic plastics economically, it must be produced on a far larger scale than any other aerobically produced microbial product. In addition, since PHAs are intracellular products, there are physical limitations to the amount that can be produced per cell (Ramsay & Ramsay 2004). The biggest unanswered question from a commercial point of view is whether the use of biobased packaging materials will be enthusiastically embraced by consumers. Only time will tell if the majority of consumers are ready for environmentally sustainable food packaging materials, and if they are, whether they insist on them being composted rather than landfilled after use.

1.7

Sources of further information and advice

• Baillie C (2004), Green Composites Polymer Composites and the Environment, Cambridge, UK, Woodhead Publishing Ltd. • Bastioli C (2005), Handbook of Biodegradable Polymers, Shawbury, UK, Rapra Technology Ltd. • Bozell JJ, Patel MK (2006), Feedstocks for the Future: Renewables for the Production of Chemicals and Materials, ACS Symposium Series No. 921, Washington DC, American Chemical Society. • Kaplan DL (1998), Biopolymers from Renewable Resources, New York, Springer. • Khemani K, Scholz C (2006), Degradable Polymers and Materials: Principles and Practice, ACS Symposium Series No. 939, Washington DC, American Chemical Society. • Mai Y-W, Yu Z-Z (2006), Polymer Nanocomposites, Cambridge, UK, Woodhead Publishing Ltd.


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• Mallapragada SK, Narasimhan B (2006), Handbook of Biodegradable Polymeric Materials and Their Applications, vol. 1, Valencia, California, American Scientific Publishers. • Mattson B, Sonneson U (2003), Environmentally Friendly Food Processing, Boca Raton, Florida, CRC Press. • Mohanty AK, Misra M, Drzal LT (2005), Natural Fibers, Biopolymers, and Biocomposites, Boca Raton, Florida, CRC Press. • Smith R (2005), Biodegradable Polymers for Industrial Application, Cambridge, UK, Woodhead Publishing Ltd. • Weber CJ (2000), Biobased Packaging Materials for the Food Industry – Status and Perspectives, Copenhagen, The Royal Veterinary and Agricultural University, Department of Dairy and Food Science.

1.8

References

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2 Types, production and assessment of biobased food packaging materials S. Imam, G. Glenn, B.-S. Chiou, J. Shey, R. Narayan and W. Orts, USDA-ARS-PW-WRRC, USA

2.1

Introduction: rationale and need for biobased food packaging

Food packaging was initially created to facilitate trade and transportation of commodities over long distances. These commodities include both perishable as well as non-perishable foods. Paper, cardboard and cellulosic fibers – as well as glass, aluminum and tin – were the materials of choice for packages such as cartons, sacks, containers, bottles, etc. Over the last few decades, the packaging industry has transformed into a highly sophisticated and intelligent service industry, particularly for perishable foods; the industry has taken advantage of the state-of-the-art in material science, manufacturing and process engineering along with ever-advancing knowledge of food science (Truong et al., 2001; Ahvenainen, 2003; Robertson, 2005). Today, food packaging has many purposes. It is designed not only to contain and protect food, but also to keep food safe and secure, to retain food quality and freshness, and to increase its shelf-life. In addition, packaging should be affordable to consumers worldwide and, more importantly, it must be naturally biodegradable upon disposal. Undeniably, packaging has become the very core of the thriving businesses of fast-foods, ready meals, on-the-go beverages, snacks and manufactured foods, and is one of the fastest growing sectors of the global economy. Names are necessary to report factually on available data; however, the United States Department of Agriculture (USDA) neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may be suitable.


30


The packaged food industry experienced a tremendous growth in the later half of the twentieth century owing mostly to the advances made by the petrochemical industry offering new and innovative plastics with a wide range of useful properties. Such synthetic plastics not only offer large processing windows, but are physically strong, chemically and biologically inert, produced at a fraction of the cost of earlier plastics, and are adaptable to most plastic processing equipments. Of the petrochemical-based synthetic plastics, high- and low-density polyethylene (LDPE and HDPE), polypropylene (PP), polystyrene (PS), poly vinylchloride (PVC) and polyethylene terephthalate (PET), polyvinyl alcohol (PVA) and polycaprolactone (PCL) are among the major synthetic polymers routinely utilized by the food packaging industry. Synthetic plastics offer excellent barrier (to moisture and gas) and thermal insulation properties that are considered critical for packaged foods. Some examples of synthetic food-contact articles/packagings include grocery bags, packaging containers for fresh produce, dairy and meat products, clamshells for the food service industry, dinnerware and containers for hot and cold beverages. However, one drawback of synthetic plastics is that they are exceedingly recalcitrant to biodegradation, and because of that reason, these plastics have become a challenge for the municipal solid-waste (MSW) management companies, and are posing a real threat to the already rapidly shrinking capacities of landfills in the United States and Europe. Furthermore, in some developing countries, and in most under-developed countries, which lack sound MSW practices, the unregulated disposal of single-use plastic packaging has become a nuisance and is impacting the quality of life of the local populations and the health of the local environment.

2.2

The environmental impact of conventional food packaging

Synthetic plastics are the wonder material of today’s world, and life without them is unimaginable. Unfortunately, these same useful qualities are overshadowed by their steady contribution to litter worldwide and its negative consequences for the environment. The unrestricted volume generated by the single-use consumer packaging made from such plastics accumulates because they do not readily break down in nature. In fact, synthetic plastic disposed of today may still be around for hundreds of years. Because the cost of the virgin resins is so low, recycling is not an attractive option and is only limited to certain plastic types. The Food and Drug Administration (FDA) of the United States has raised many concerns regarding recycled plastics, particularly for re-use of these materials in food-contact articles. These concerns include: (a) the contaminants from the post-consumer material that may appear in the final food-contact product made from the recycled material, (b) incorporation of recycled


Types, production and assessment of biobased materials

31

post-consumer material that is not regulated for food-contact into foodcontact packaging and (c) assimilation of adjuvants/additives in the recycled plastic not approved for food-contact use. In view of the serious threat posed by synthetic plastics to marine life and the environment, in 1987 Congress enacted the Marine Plastic Pollution Research and Control Act. This law prohibits the dumping of plastics in all US waters. In an effort to further save the environment as well as marine life, in 1997 the US Congress signed the International MARPOL treaty (Marine Pollution Treaty) prohibiting all US and foreign vessels, both naval and commercial, from discarding any plastic waste overboard in US territorial waters unless it is shown to be completely biodegradable. It is estimated that about 1 million metric tons of plastics per year are dumped into the oceans and that in certain areas as many as 17 500 pieces of plastic are present per square kilometer (Narayan, 1994). The situation on land with respect to plastic waste is even worse. According to a US Environmental Protection Agency report published in 2005, roughly 24.2 million metric tons of MSW deposited in US landfills consisted of disposable consumer packaging used for both food and non-food purposes made mostly from non-renewable resources. On average, every American generates approximately 1500 pounds (680 kg) of waste per year, much of which is destined for landfills. Of this waste, single-use food and non-food consumer packaging made from synthetic polymers constitutes about 40–60% of the volume, which roughly represents about 20–30% of the size of a typical landfill. According to some estimates, industrialized nations alone generate quantities of packaging waste in a single day that if stacked-up together would fill up a space equivalent to the Sears Tower, which once was the world’s tallest building. Most of this packaging is made from synthetic plastics. The consequences of such irresponsible behavior will be of enormous proportions; continued production and accumulation of trash is not only detrimental to the environment but is also contributing to the depletion of our precious and finite natural resources. Currently, one sensible alternative is to produce biobased fuels and chemicals from renewable resources that can compete effectively with petroleum-derived synthetic chemicals in terms of both the overall cost and physical properties (Röpper and Koch, 1990; Swanson, et al., 1993; Shogren and Bagley, 1999; Chum and Overend, 2001; Chiellini et al., 2002; Stevens, 2002). This offers an excellent opportunity for biobased/renewable feedstock to be utilized as a raw material substitute for petrochemicals in the manufacturing of food packaging. Despite many challenges, there is a common belief among the scientific community worldwide that inherently biodegradable biopolymers with improved properties are poised to play a positive role in the development of environmentally compatible, single-use consumer packaging, as evidenced by the explosive increase in the number of scientific papers, patents and products that have surfaced in the last decade alone.


32

2.3


Opportunities for renewable polymers

Heightened fuel prices and the rising cost of petroleum-derived commodity chemicals have provided much of the impetus for the research and development in the field of biobased/renewable polymers. The availability of many renewable polymers in surplus quantities, problems associated with the disposal of recalcitrant plastic products and consumer demand for environmentally compatible, greener products – especially single-use packaged goods – have further helped to build the momentum to seek new uses for agriculturally derived polymers and byproducts. Generally, agriculturally derived polymers exhibit poor physical–mechanical properties, provide materials of inconsistent purity, present difficulties in material processing and perform poorly under extreme environmental conditions (Luzier, 1992; Swanson et al., 1993; Mayer and Kaplan, 1994). Nevertheless, these materials have an inherent advantage over their petroleum counterparts in that they are susceptible to biodegradation in the environment upon disposal. Renewables such as cellulose, starch, proteins, oils and, to a lesser extent, lignin, are among the most abundant agriculturally derived materials. In order to overcome many of the shortcomings in renewable materials, hybrid blends and composites, particularly made in conjunction with bio-derived and/or biodegradable polymers such as poly (lactic acid) (PLA), poly (hydroxyalcanoates) (PHAs) and PVA, along with other additives, plasticizers and compatibilizers, etc., have shown to be the most promising, and are expected to play a major role in food packaging. Figure 2.1 compares some plastic properties (modulus and elongation at break) of biopolymers with those of synthetic plastic polymers.

PHB

PLA

PS Modulus (MPa)

PET

PP HDPE STARCH LDPE Elongation (%)

Fig. 2.1 Comparison of the mechanical properties of biopolymers with those of synthetic polymers (shown in bold). PHB, poly(hydroxybutyrate).



33

2.3.1 Polymer properties Some relevant information about starch, poly (hydroxybutyrate) (PHB) and PLA polymers along with the factors that influence their properties is provided below. Starch is one of the most extensively studied biopolymers derived from renewable crops grown in surplus in the world, and is naturally biodegradable (Whistler et al., 1984). It is also one of the most abundant and versatile among natural polymers, and has been extensively researched as a raw material for the development of biodegradable hybrid composites and blends (Griffin, 1971; Otey et al., 1976, 1987; Doane et al., 1998). Its structure and some relevant properties are described in the following paragraphs. The starch polymer is composed of two major components, amylose and amylopectin. The amylose is mostly composed of linear α-d-(1→4)-glucan (Fig. 2.2), whereas, amylopectin is a highly branched α-d-(1→4)-glucan with α-d-(1→6) linkages at the branch points (Fig. 2.3). The linear amylose molecules constitute about 30% of common cornstarch and have molecular weights of 200 000–700 000, while the branched amylopectin molecules have molecular weights as high as 100–200 million.

HO

O

HO HO

HO

O

HO

O OH OH

OH O HO n

OH O HO

G Gn G

Fig. 2.2

Linear amylose molecule.

G G G G G G G G G G G G G G G

O HO

OH O

HO O HO

Fig. 2.3


O

HO O

OH O HO

O

HO

OH O HO

O OH O

Branched amylopectin molecule.

34


Starch is stored in plants as granules comprised of molecules of both amylose and amylopectin. The granules vary in size from a few micrometers to >50 µm, depending on their botanical source. Starch granules are hydrophilic since each starch monomer unit contains three free hydroxyl groups. Consequently, the moisture content of starch changes as relative humidity (RH) changes. Cornstarch granules retain about 6% moisture at 0% RH but contain 20% moisture at 80% RH. Starch granules are thermally stable when heated in an open atmosphere to about 250 ºC. Above this temperature, the starch molecules begin to decompose. Dry granules absorb moisture when immersed in water but retain their basic structure due to their crystallinity and hydrogen bonding within the granules. Native granular starch contains crystalline areas within the amylopectin (branched) component, but the linear amylose component is largely amorphous and can be mostly extracted in cold water. The granular structure is ruptured by heating in water or treating with aqueous solutions of reagents that disrupt crystalline areas and hydrogen bonding within the granules. The constituent molecules become completely soluble in water at 130–150 ºC and at lower temperatures in alkaline solutions. Starch granules that have been ruptured in aqueous media are commonly referred to as gelatinized or destructurized starches. The temperature at which starch granules are completely gelatinized is known as the gelatinization temperature, which varies depending on the botanical source of the starch. Application of high pressure and shear to starch granules permits disruption of the organized structure at lower water contents than is possible at atmospheric pressure. Gelatinized starch also tends to swell in water leading to its hydrolytic degradation. Starch granules can be disrupted by high pressure and low shear at moisture contents below 10% (Whistler, 1984; Swanson et al., 1993; van Soest, 1996; Shogren, 1998). Starch solutions are unstable at low temperatures. On standing in dilute solutions, the linear amylose component crystallizes. Many branches of amylopectin may also crystallize. Rapid cooling of concentrated starch dispersions creates stiff gels, which crystallize more slowly. Amylose, and to a lesser degree the outer branches of amylopectin, can assume helical conformations that have a hydrophobic core (Fig. 2.4). Each turn the helix comprises six monomer units. Iodine, fatty acids, lipids, alcohols and other materials may enter the core of the helix to form stable complexes with starch. Small amounts of crystalline amylose–lipid V-type complexes are usually found in starches such as corn and wheat, which contain free fatty acids and phospholipids (Galliard and Bowler, 1987; Chinnaswamy et al., 1989; Shogren, 1992; Imam et al., 1993). Starch molecules readily depolymerize into glucose monomer units when heated in acidic solutions or when treated with a variety of amylolytic enzymes. They are generally stable under alkaline conditions at moderate temperatures. When heated with amines under alkaline conditions, they undergo complex Maillard reactions to form brown-colored products with caramel-like odors. Upon mechanical injury that alters its surface


Types, production and assessment of biobased materials O

O

O

O

O

O O O

O O

O

O

O O

O

O O

O O

O O

O O

O O

O O O

O

O

O

O

O

35

O O

O O

Fig. 2.4 Helical conformation in amylose and the outer branches of amylopectin. Each turn of the helix comprises about six monomer units.

morphology causing starch to be exposed on the surface, starch degrades fairly quickly under ambient conditions. The presence of many hydroxyl groups on starch permits easy alteration of its properties through chemical derivatization. This provides the opportunity to improve starch properties for use in packaging. Modifications in starch polymers have yielded starches with improved properties. Acetate esters and carboxymethyl and hydroxypropyl ethers exemplify starch derivatives. Extruded acetylated starch (DS 2.23) foam, for example, has much-improved moisture barrier characteristics, mechanical properties and dimensional and thermal stability compared with unmodified starch (Xu et al., 2005). Several other starch derivatives with unique functionalities have also been reported (Imam and Harry-O’Kuru, 1991). Aging of the starch polymer at constant temperature and moisture levels results in starch embrittlement. Differential scanning calorimetric studies (Shogren, 1992) have shown that this phenomenon is due to structural relaxation of starch chains, leading to decreases in enthalpy and free volume with time. This type of aging is typical of most amorphous polymers (Hodge and Berens, 1982; Hutchinson and Kovacs, 1984). The rates of aging seem to vary with polymer structure but the reasons for such differences are not fully understood at present. In addition, starch can be crosslinked with compounds having many functional groups, such as formaldehyde, pyrophosphate and epichlorohydrin. Such modifications usually lead to improved polymer properties. In this regard, an increased tensile property and water resistance was observed in starch/cellulose/PVA crosslinked with hexamethoxymethylmelamine (Cymel 323) reagent (Imam et al., 1999b). Two other important biodegradable polymers in the context of biobased packaging are PHA and PLA. Both biopolymers have excellent physical properties, exhibit excellent compatibility with other natural polymers and,


36


more importantly, are completely biodegradable in a variety of environments. PHAs are linear polymers produced in nature and can be produced via bacterial fermentation of plant-derived feedstock such as sugars or lipids. A combination of a variety of different monomers can provide materials with variable and distinct properties. For example, with melting points ranging between 40 and 180 ºC the polymer can behave as a thermoplastic, as well as an elastomer. The most common of the PHAs is a homopolymer, PHB (Fig. 2.5), with properties quite similar to those of PP, albeit stiffer and much more brittle. A copolymer, poly (β-hydroxybutyrate-co-valerate) (PHBV) (Fig. 2.5), is ideal for packaging as it is less stiff and much tougher than PHB. PLA, on the other hand, is a condensation polymer of lactic acid produced via fermentation using renewable resources such as starch (Fig. 2.6). PLA has many useful properties similar to the petroleum-based plastics,

O

HC

CH2CH3 O

O

CH3

CH2C

HC

O

CH2C

n

n PHB

PHV

CH3 O

HC

O CH2C

CH2CH3 O O

CH

CH2C n

PHBV

Fig. 2.5

PHB and copolymer.

O H3C

Catalyst+ heat

O

O CH C

O

CH3

O Lactide

Fig. 2.6

CH3 O

CH3 O O CH C n

Polylactide

Ring opening polymerization of lactide to polylactide.



37

which makes it highly suitable for a variety of applications. PLA, certified as Generally Recognized As Safe by the US FDA, is a non-volatile, odorless, clear and naturally glossy polymer. It is a versatile polymer that can be processed using a variety of conventional techniques/equipments such as injection molding, blow molding, sheet extrusion, thermoforming, film forming and fiber spinning. Furthermore, its resistance to moisture and oils along with its gas barrier properties makes it ideal for food packaging. Both PHA and PLA are still relatively expensive compared with synthetic plastics. These polymers are starting to be noticed by the food packaging industry due to their plastic-like properties, but their market penetration will be dictated mainly by their cost and product performance. In order to achieve this market penetration, the overall objective would be to seek biobased substitutes for synthetic plastics in food packaging by engineering products from renewable materials that are stable, durable, provide the required mechanical and barrier properties, improve transportation and storage, and ensure that the product biodegrades effectively when disposed of after use. In this regard, efforts are being made worldwide, including at USDA laboratories, to improve and transform agriculturally derived materials to overcome the technological barriers that are restricting their commercial potential and consumer acceptance. Biochemical and engineering tools are being used to improve and optimize the properties of biopolymers. Approaches include: chemical crosslinking, chemical grafting, chemical substitutions/derivatizations, biocatalysis, plasticization, novel processing, blending and compatibilization with other polymers and additives. Research efforts on the use of starch-, PLA- and PHBV-based blends and hybrid composites for food packaging applications will be reviewed in the subsequent sections along with the future outlook for these materials.

2.4

Production of biobased food packaging materials

2.4.1

Production, properties and functionality of biobased food packaging materials Extrusion, baking, thermoforming, casting, blow molding, injection molding, lamination, calendaring and coating are some of the major plastic processing methods that are currently utilized by the plastic industry in producing food packaging, mostly from LDPE, HDPE, PP, PS, PET, PCL, etc. With few exceptions, renewable/biobased polymers generally exhibit a great deal of adaptability for many of these plastic processing methods requiring little or no adjustments (Röper and Koch, 1990; Tomka, 1991; Doane et al., 1998; Shogren, 1998; Bastioli, 2000). Some, however, have a narrow processing window and poor mechanical and thermal properties, causing materials to be rigid, stiff and dry; others lack good gas and moisture barrier properties.


38


These shortcomings in their properties need to be overcome before biobased packaging is successfully commercialized and accepted by the consumers (Zobel, 1988; van Soest, 1996). In order to overcome the brittleness and to improve the properties of biopolymers, biodegradable plasticizers are routinely used in formulations. Plasticizers include glycerol and other low molecular weight polyhydroxy compounds, polyethers and urea. During extrusion, the starch granular structure is disrupted due to high shear and temperature in the presence of plasticizers. This causes starch to plasticize and behave as a molten or viscous thermoplastic material. Plasticized starch could subsequently be used for injection-molding and for thermoforming into sheets. Thermoforming of starch into sheets for subsequent molding into products is somewhat challenging, and industrial applications are limited due to its moisture sensitivity and poor mechanical properties. Blending plasticized wheat starch with biodegradable polyester, however, has been shown to improve moisture resistance in injectionmolded packaging materials (Avérous and Fringant, 2001). In addition, blending plasticized wheat starch with cellulose fiber considerably improved stiffness and impact resistance, as well as aging behavior, of the extruded material. Such blends and composites, when processed on industrial-scale thermoforming equipment to produce packaging trays, exhibited much improved aging properties at storage temperatures ranging from ambient to 4 ºC (Avérous et al., 2001). The starch baking process is quite analogous to the process used in making waffles and wafer cookies. A predetermined amount of aqueous starch dough is placed into a preheated (120–200 ºC) mold cavity, after which the mold is closed. Upon heating, the starch in the dough is gelatinized, and steam serves as the foaming agent providing a starch product with properties similar to expanded polystyrene (EPS); the procedure is described in detail elsewhere (Glenn et al., 2001a; Shey et al., 2006). Tiefenbacher (1993) and Hass et al. (1996) demonstrated a baking process for making molded starch products as thin as 1.5 mm. An Austrian company, Biopack, was the first to produce starch-based foam trays commercially for food packaging. Currently, Apack in Germany is also producing starchbased food packaging made by a similar process. More notably, EarthShell Corporation in the United States had a much larger impact on the development of baked starch packaging as they have been able to successfully produce commercial, single-use, disposable baked trays, dinner plates, soup bowls and clamshells for the fast-food industry. These products have been sold in selected US markets for trials, and are currently being sold at Smart & Final stores. More recently, EarthShell has licensed its technology to Renewable Products, Inc. located in Lebanon, Missouri for manufacturing and distribution of EarthShell Packaging plates and bowls in the United States and to EarthShell Hidalgo S.A. de C.V. of Mexico for markets in Central and South America. As consumer demand for such products



39

increases, EarthShell is poised to take a leadership role in the disposable food container market worldwide. The properties of the baked starch foams are dependent on several factors such as moisture content, starch type and the additives used in the dough formulation (Andersen and Hodson, 1996; Shogren et al., 1998; Lawton et al., 1999). Although baked starch foams have decent mechanical properties and their thermal properties are quite comparable with PS-based commercial food containers, these products are susceptible to moisture and lack the required flexibility. Starch polymers and blends have been successfully baked into foamed articles with properties similar to those of an EPS. Under dry storage conditions, starch blends and composites lose water quickly and become brittle, yielding a matrix of low modulus. Under high-moisture conditions, starch can absorb moisture, yielding a loose and flexible matrix. Thus, to obtain a starch food packaging with improved properties, other substances such as fillers, compatible additives, plasticizers and a moisture-resistant coating are generally required. Incorporating cellulose fibers as a filler material in formulations has been shown to improve both the flexibility and the strength of baked starch foams (Andersen and Hodson, 1996). For example, addition of softwood pulp fiber improved flexural properties and lowered the foam density (Glenn et al. 2001a). Foam properties can be further improved by utilizing chemically modified starches and additives such as aspen fiber, PVA and monostearyl citrate (Shogren et al., 1997, 2002; Lawton et al., 2004). Modified starches improved flexibility and aspen fiber improved strength, whereas monostearyl citrate improved water resistance. Interestingly, not all fibers improve foam properties. The addition of corn fiber in formulations had a rather negative impact on starch foam packaging trays, as it tended to decrease the mechanical properties and cause an increase in the baking time and batter volume (Cinelli et al., 2006a). Trays produced with a high fiber ratio in conjunction with PVA, however, showed improved water resistance. The addition of PVA in the formulation was also effective in providing moisture resistance to the baked foam products (Shogren and Lawton, 1998). Alternatively, protective food grade, hydrophobic and thermostable polymer laminate could also be applied directly on to the baked product to provide an effective moisture barrier (Glenn et al. 2001b; EarthShell Corporation, 2002). More recently, Shey et al. (2006) used natural rubber latex as a moisture-resistant additive for baked starch foams. Moisture resistance in starch foams improved when a small amount of latex was added in the formulation in the presence of non-ionic additives. Latex also improved the flexibility of the foam product. Such approaches to improve moisture resistance, however, add to the overall cost of the product. Among all the biodegradable polymers, starch currently represents about 85–95% of the total market share in various single-use consumer products. Current applications are mostly limited to films, sacks, garbage


40


bags and as fillers. However, articles made from expanded starch foam and hybrid composites such as cups, bowls, cutlery, plates, wrapping, laminated paper and food containers are beginning to penetrate the market place (Bastioli, 2001). PLA-based hybrid materials, having properties similar to synthetic plastics like PET and PP, are well suited for processing on standard equipment used by the plastic industry. In particular, films, injection-molded and thermoformed articles such as food containers, and other types of packaging have been manufactured and are currently marketed in North America, Europe and Asia. Film wraps and containers for organic foods are two of the wellknown products made from PLA (Francia, 2000; Bastioli, 2001). CargillDow is currently the largest producer of PLA polymer under the brand name NatureWorksTM. Cargill-Dow’s new facility in Blair, Nebraska has a capacity to produce 140 000 metric tons of NatureWorksTM; expansion is expected in order to meet the demands of European and Asian markets. PLA offers a good moisture barrier, but its application in vacuumed packaged foods is limited due to its poor gas barrier properties. Because of its excellent compatibility with other biopolymers and synthetic polymers, this is not a serious impediment. DannonTM, the yogurt manufacturer, is already successfully marketing the thermoformed PLA-based yogurt containers in supermarkets in Europe and North America. Also included in the list of PLA-based products are single-use, food-contact packaging for readymade meals available in the frozen section of supermarkets. Food service wares including cups, plates and other containers laminated or extrusion-coated with PLA-based materials are available in the market for hot and cold beverages (Bastioli, 2001). These also include starch-based baked and molded soup bowls and dinner plates as well as cardboard cups laminated or coated with the PLA. Table 2.1 lists many of the commercial resins made

Table 2.1 List of major biobased/biodegradable polymers and blends produced commercially worldwide Biodegradable polymer

Trade name

Company

Starch Starch Modified starch Thermoplastic starch Starch/copolyester PHAs PHAs Copolyester Copolyester Copolyester Polylactc acid Cellulose acetate

Ecofoam Novon Evercorn Paragon Mater Bi Nature’s Plastic Nodax Ecoflex Biomax Bionelle NatureWorks ACEPLAST

National Starch, USA Ecostar GmbH, Germany Japan Corn Starch Co. Ltd Avebe, The Netherlands Novamont, Italy Metabolix, USA Proctor & Gamble, USA BASF, Germany Dupont, USA Showa Highpolymer, Japan NatureWorks (Cargill-Dow), USA Acetati, Italy



41

from biobased polymers and blends that are currently available for food packaging applications. The aliphatic polyester PHB and copolymer PHBV are commercially important biobased biodegradable plastics that are well positioned to fulfill many of the food packaging industry needs. Typically, PHB is a good thermoplastic material with high crystallinity, but PHAs of medium chain length behave more as an elastomeric material having considerably lower melting points and a relatively low degree of crystallinity. A very interesting property of PHAs in the context of food packaging is their low water vapor permeability, which makes them behave like LDPE. This polymer can be blow molded, extruded or injection molded into shapes such as films, bottles, food packaging containers, etc. PHAs have proven quite useful biomaterials in biomedical applications, e.g. tissue engineering and controlled-release carriers, owing to their properties such as biodegradability, optical activity and isotacticity (Köse et al., 2003). Because of its non-toxicity and biocompatibility in humans, PHB is also being used in implants, bone plates and surgical sutures. PHB has been utilized to produce packaging for some disposable products (Rosa et al., 2004a), but information with respect to its much broader application in food packaging is limited at this point. Major impediments in the successful commercialization of PHB are its production cost and brittleness, and the resulting intolerance to high impact. Nevertheless, companies worldwide are making efforts to produce this polymer and copolymer cheaply. Particularly, both Brazil and China claim to have used sugarcane bagasse and cornstarch, respectively, as a renewable carbon source to produce PHB inexpensively. PHB produces a transparent film above 130 ºC providing a much larger window of operation for plastic processing. Additionally, PHB offers low permeability and, more importantly, biodegrades completely without leaving any visible residue. The injectionmolded food containers made from PHB showed good potential for this material in food packaging (Bucci et al., 2005). These investigators found that under normal freezing and refrigeration conditions, the performance of PHB food containers was slightly inferior compared with PP, but at higher temperatures, the performance of PHB food packaging was much superior to that of PP packaging. Sensory evaluation of food packaged in PHB containers yielded positive and encouraging results.

2.5

Hybrid blends and composites

Renewable polymers are generally sensitive to moisture and do not provide effective gas barrier properties. Hybrid blends and composites, containing renewable polymers in conjunction with other biobased or synthetic polymers and additives, have shown great potential in making up for some of these shortcomings. In fact, the majority of the consumer food packaging currently available commercially worldwide is based on hybrid materials,


42


rendering the desirable properties and functionality for packaging a variety of foods such as fresh meats, dairy products, ready-meals, beverages, fruits and vegetables, snacks, and frozen and dry foods (Table 2.2). For example, multilayer films produced from plasticized wheat starch and various biodegradable aliphatic polyesters via flat film co-extrusion and compression, significantly improved mechanical performance and moisture resistance in melt blended wheat starch films (Martin et al., 2001). In this film, the properties were totally dependent on the compatibility between the respective materials without the use of any additives, compatibilizers or adhesives. Coatings of edible and biodegradable polymers have, in general, been used to achieve an improved moisture barrier and to prolong the shelf-life of perishable food products (Guilbert et al., 1996, 1997; Guilbert, 2000). Improved water permeation barrier properties were observed as a result of an in situ lamination process for baked starch foams with PVA and PVC. These foams had barrier properties similar to the EPS foams (Glenn et al., 2001a). With the addition of a small amount of cellulose fibers in wheat starchbased extruded films, increases in modulus, strength and temperature stability were observed with concomitant shifts in the glass transition (Tg) temperature. Thermoformed food trays from these hybrid blends showed greatly reduced aging compared with trays without added fibers (Averous et al., 2001). Similarly, products formed from hybrid composite foams prepared by baking granular starch in the presence of 10–30% aqueous PVA showed markedly improved strength, flexibility and water resistance (Shogren et al., 1998). More recently, these investigators have also shown that the addition of softwood fiber and monostearyl citrate in the formulations yielded baked products with sufficient flexibility and water resistance to function as clamshell-type, hot-sandwich food containers (Shogren et al., 2002); aspen fiber also had a similar effect (Lawton et al., 2004). A detailed work has been published recently on extruded and injection-molded hybrid blends and composites containing agriculturally derived fiber and PVA, and their impact on material properties (Chiellini et al., 2004, Cinelli et al., 2006a, 2006b). A laminate of chitosan-cellulose and PCL film has shown to be effective for modified atmospheric packaging of horticultural crops such as lettuce, broccoli, tomatoes and sweet corn within the 10–25 ºC temperature range (Makino and Hirata, 1997). PE film containing 6% starch has been recommended for storage of wet and dry low-lipid foods. However, significant loss of elongation was observed in these films due to possible interactions between the film and the free radicals developed during lipid oxidation in foods with higher fat content, such as ground beef, during storage under freezing conditions (Holton et al., 1994). It is interesting to note that PE– starch films neither impaired the heat sealing nor accelerated microbial growth in ground beef. Furthermore, there was no impact on color stability during refrigeration and frozen storage (Strantz and Zottola, 1992). In this


Table 2.2 Commercial food packaging from biobased polymers, blends and composites currently in use worldwide Packaging product

Properties

Biopolymer(s)

Packaged material

Company

Trays

Convenience, moisture barrier Oxygen and moisture barrier Convenience Convenience, insulation, moisture barrier Mechanical protection, moisture barrier, carbon dioxide barrier Moisture barrier, light barrier, grease barrier Containment

Virgin pulp

Beer, chicken

PE–starch (0–28%)

Ground meat

Pactiv, Omni-Pac, Germany Europe

Coated pulp and starch Powdered starch, foam, baked foam

French fries Hamburgers/sandwiches

Belgium Apack, Germany Earthshell, USA

Cardboard/PLA

Yogurt

Dannon, Europe/ North America/ Asia

PLA–copolyester, starch–PLA, PLA–polycaprolactone

Butter/margarine

Europe

Nets of starch-based plastics, pulp trays, corrugated board trays and transport boxes NatureSEAL™ (cellulose based) Starch/starch–polycaprolactone

Fruits and vegetables

Germany, Belgium/Europe

Variety of fruits and vegetables General purpose

Europe/USA/Asia

Wrapping films Tray/container Container clamshells/ plates, soup bowls, beverage cups, etc. Container

Packaging Packaging Packaging Bags

Moisture and gas barrier Biodegradable

Data are partly selected and condensed from Haugaard et al. (2001a, 2001b). © 2008, Woodhead Publishing Limited

Europe – Finland, Italy, Denmark

44


Table 2.3 Advantages and disadvantages of using cellulosic fiber in composites Advantages

Disadvantages

Renewable Strong Light weight Biodegradable Inexpensive

Poor dimensional stability Low biological resistance No thermal plasticity Low processing temperature Incompatible with hydrophobic thermoplastics

regard, an excellent review article has been written on the potential of biobased materials for food packaging (Petersen et al., 1999). Cellulose, one of the world’s most abundant and inexpensive raw materials, is problematic to use because of its hydrophilic nature, insolubility and crystalline structure. Because of its highly ordered structure, hydroxyl groups and strong hydrogen bonding yield highly crystalline microfibrils and fibers. Such fibers are already being used in numerous commercial packaging products made up of paper and cardboard. Fibers also make excellent biological fillers in many plastic wraps and films. Having biological filler in a plastic matrix is advantageous because the biological additive is readily attacked by microbes, which start the deterioration process leading to eventual composting. Waxed or PE-coated papers are commonly used in the food packaging industry. While cellulose fiber in blends offers many advantages, it can also have a negative impact on the matrix properties. Some of the advantages and disadvantages of using cellulose fiber are outlined in Table 2.3. The strengthening of the polymer matrix by the discontinuous fiber reinforcements is dependent upon the aspect ratio, geometry and orientation of the fibers, and the interface adhesion between the fiber and the matrix, as well as the microstructural features within the matrix. Dispersed microstructures offer higher elastic properties than equivalent aggregated microstructures due to the more efficient reinforcement of a dispersed system. Cellulose fibers have poor dimensional stability and offer little or no thermal plasticity. The addition of fiber in higher amounts generally results in processing difficulties and a reduction in viscosity. The strategies used to overcome this challenge are usually to increase the shear rate and to use lubricants or plasticizers to improve the flowability.

2.6

New developments in the production of packaging from recycled lignocellulosic fiber and renewable materials

Paper products – such as corrugated boxes, food wraps, bags and single-ply boxes – constitute the largest percentage of single-use items in the United States, and end up as the largest component in MSW streams. Even with



45

recycling (the United States recycles ∼27% of its MSW stream), lignocellulosic material (paper) accounts for 37–40% of our landfill materials. The need for using recycled materials and renewable non-wood pulps, rather than virgin wood pulp, is clear. New twists in the traditional slurry-pulp technology provide an outlet for this recyclable fiber, creating food packaging and wraps from 100% recycled and/or non-wood pulps, such as straw and bagasse. Slurry-pulp processing has been used for years to make egg cartons, drink trays and box in-lays. In slurry-pulping, screens in the shape of the finished product are dipped into a tank holding slurry-pulp, a mixture of water (99%) and recycled fiber (1%). As vacuum is applied to the molded screen, a thin layer of fiber forms on to the screen; upon drying, this thin fiber mat, which is in the shape of the contoured mold, is then separated. Innovations in slurry-pulp processing have provided tremendous flexibility in the size and shape range of products created by innovators such as Greg Gale and colleagues, as described elsewhere (Orts et al., 2003a, 2003b). In particular, two improvements stand out: (a) use of rapid prototyping to create molds within 2 days and (b) drying of the molded package on the mold, which prevents ‘slumping’ or sagging of the piece during drying. Rapid prototyping creates a mold using designs drawn in the latest computer aided design programs: these complex designs are then sent to the rapid prototype instrument. The rapid prototyping method produces the tool, one layer at a time by depositing a thin layer of a dry polymer powder followed by application of a laser beam that fuses that layer into a solid. Once one layer is complete, a second layer of powder is deposited and fused, similar to rastering methods used in a laser printer. This layering and fusing process is repeated until the complex mold takes shape, generally within hours or days. The second feature of improved slurry-pulp processing methods is the ability to dry the fiber product while it is still on the mold. In the traditional (egg carton) process, the carton is taken off the (metal) mold while wet and passed through a drying oven. Pieces must be relatively small or they will ‘slump’ and dry unevenly. Blowing hot air under pressure through the mold dries the fiber package evenly without any change in shape, preventing the piece from sagging during drying. With this innovation, shapes can be more extreme with heights exceeding 18 in. (45.7 cm). One example of the innovative shapes that are attainable is the wine packaging/bottle shipper and some other food packaging produced by Regale, Napa, California that prevents label scuffing during transportation. Ultimately, the economics of slurry-pulp processing depend on reducing drying times to minimize energy costs. Continuing experimentation with alternative fibers has shown that agriculturally derived, non-wood pulps – such as rice straw, wheat straw, grasses, cotton linters, chicken feathers, and fibers recovered from MSW – can be used. Molded fiber packages have been created from processing slurries containing anywhere from 5 to 60%


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straws and other agriculturally derived fibers, reducing drying times by as much as 22%. A key driving force behind using agriculturally derived fibers in packaging is the need to find novel economically viable uses for crop residues, especially straws and grasses which can no longer be burned in California due to legislation. Regale’s first plant obtains most of its recycling pulp by shredding wine boxes, office waste and brochures from its wineproducing neighbors in the Napa Valley.

2.7 Assessing the biodegradability of renewable materials in food packaging Biodegradation is a process in which organic material is decomposed via natural biological activity. In this process, biochemical breakdown of an organic compound leads to smaller products (oligomers or monomers) due to the action of microbes (bacteria, fungi, yeast) or their hydrolytic enzymes. Thus, under ideal conditions, biodegradation is generally a two-step process: the polymer is first hydrolyzed into intermediate compounds, where abiotic factors such as ultraviolet light, along with microbial enzymes, may facilitate this process. This step is then followed by further metabolism of such intermediates by microorganisms. Biodegradation can occur under both aerobic and anaerobic conditions. Under aerobic conditions, the final breakdown products are H2O, CO2 and residual biomass (byproducts). Under anaerobic conditions, biogas such as methane or hydrogen gas is produced in lieu of CO2. Eventual biodegradation of renewable polymers and blends is dependent upon a wide variety of factors. Parameters that influence the biodegradation process include environmental conditions like temperature, moisture, salinity and pH, as well as geometry and surface area of the material, inoculum size, type of environment and the availability of microbes. In addition, certain chemical structures are more susceptible to microbial breakdown than others. Availability and accessibility of specific enzymes to hydrolyze a certain polymer are also critical. For example, polymers such as starch, cellulose, protein and polyester will require amylases, cellulases, proteases and esterases, respectively, to hydrolyze these individual polymers. Therefore, in hybrid blends containing two or more polymers, degradation will be influenced by the presence of the right combination of microbes or enzymes in the disposal environment. In order to assess polymer biodegradation, packaging material is generally exposed to the testing environment (such as soil, compost, seawater, sewage, sludge, etc.) containing appropriate microbes and environmental conditions that are controlled for the duration of the experiment. Sample degradation can be assessed by measuring the deterioration in the physical–mechanical properties such as tensile strength, elongation at break and decrease in molecular weight of the testing material. However, more



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commonly, polymer degradation is assessed by measuring the production and accumulation of CO2 (under aerobic conditions) or CH4 (under anaerobic conditions) as a result of enzymatic hydrolysis of the material and further assimilation of intermediate byproducts. Collected data can be useful in determining both the rate and extent of the polymer degradation and, if the exact carbon values in the initial sample are known, theoretical yields can be calculated to determine overall carbon to CO2 or CH4 conversion. The reproducibility and reliability of the test method is critical. In order to test the reliability of the system and for comparative purpose, use of a background measurement, as well as positive and negative controls are also required. There are several international organizations that are actively involved in writing, examining and establishing standards for testing polymeric materials for biodegradability. The International Organization for Standardization (ISO), American Society for Testing Materials (ASTM), European Committee for Standardization (CEN), German Institute for Standardization (DIN), Organic Reclamation and Composting Association (Belgium based) and Institute for Standards Research (ISR) are some of the leading institutions playing a major role in defining and regulating the standards to assess polymer biodegradation. Standards pertaining to biodegradable plastics put forward by these organizations differ somewhat in their definitions and specific requirements, but the ultimate approach/goal is more or less the same. Great efforts have been made by international scientists to reconcile the European and American standards with international standards. The Sturm test (or modified Sturm test), BODIS test, composting test, anaerobic test, enzyme test, soil burial test and toxicity test are some of the most relevant tests pertaining to bioplastics. No attempt will be made to provide details on the standardized tests, and a list of the most commonly used tests is provided in Table 2.4. The only exception is the ASTM D533893 test for determining the compostability of the plastic materials. This test is quite important, as most of the biodegradable single-use food packaging in future will be sent to composting facilities. Furthermore, knowing the product’s compostability will be a desirable feature for commercialization and ultimately acceptance of the product. In order to apply the ASTM D5338-93 (composting) standard, composting materials need to have both the capacity to biodegrade and to physically disintegrate. Disintegration must lead to the physical collapse of the plastic matrix yielding visually indistinguishable fragments, a requirement for composting. To achieve total biodegradability, after disintegration, polymer chains must be first broken down by microbes and their enzymes, followed by their complete mineralization, i.e. polymer conversion into CO2, H2O and minerals. Mineralization rate, however, has to be high and compatible with the composting process. Materials having a biodegradation capacity equal to or more than that of cellulose are considered compostable under this testing standard.


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Table 2.4 A list of some of the important standard tests from various organizations used to determine the biodegradability of food packaging Standards/tests

Environment

ASTM D6400

Standard specifications for compostable plastics Controlled compost Aerobic biodegradation in soil Compost Aerobic, sewer sludge Anaerobic, sewage sludge High-solids anaerobic digestion Aerobic biodegradation under controlled conditions Aerobic biodegradation in aqueous environments Anaerobic biodegradation in a high-solids sewerage environment European standard for biodegradability for polymers and packaging; incorporates other standards and tests

ASTM 5338-98 (2003) = ISO 14852 ASTM D5988-03 = ISO 17556:2003 ISO CD 14855 ASTM D5209-91 ASTM D5210-92 ASTM D5511-94 ISO 14855 ISO 14852 ISO 15985 CEN 13432 ISO 14855; ISO 14855 (respirometric); ISO 14852; ASTM D5338-92; ASTM D5511-94; ASTM D5152-92; ASTM E1440-91; modified OECD 207; CEN TC 261/SC4/WG2

Specifically, the ASTM D5338-93 standard measures compostability of plastic materials. The test method determines the aerobic biodegradation of plastic materials under controlled composting conditions. In this method, plastic is mixed with stabilized and mature compost. The CO2 evolution is compared with unsupplemented compost. Biodegradation is determined by the rate and extent of material conversion into CO2 over time. The conversion should be accompanied by weight loss in the plastic material, visible disintegration and high biological activity in the compost. According to the standard, 90% of the disintegrated material must not have any adverse effect on the quality of the compost. In particular, it must not be toxic to other plants. ISO CD 14855 and the CEN test procedures are quite similar to ASTM D5338-92. The only difference is that both ISO and CEN protocols require that the temperature profile of the compost should be continuously at 58 ºC, whereas the ASTM procedure follows a temperature profile of 35–58–50–35 ºC. In addition, for packaging to turn into visibly indistinguishable fragments in compost, different standards have put forward different requirements regarding time limitations (Table 2.5). Scores of studies have been conducted to investigate the biodegradability of starch polymer and its hybrid blends containing both syntheic and/or renewable polymers and additives (Imam et al., 1992, 1995a, 1995b, 1999a, 1999b; Shogren 1992; Ramsay et al., 1993; Lawton, 1997; Avévous



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Table 2.5 Compliance requirements of various international standards for plastic degradation Standard organization

Percentage biodegradation

Time requirement

DIN ASTM CEN OECD

60% 60% 90% 60% (for chemicals)

6 months 6 months None 28 days

OECD, Organization for Economic Co-operation and Development.

et al., 2001; Lawton and Shogren, 2004). In the 1970s, investigators from the United Kingdom (Griffin, 1971, 1977) and the United States (Otey et al., 1976, 1987; Doane et al., 1998), for the first time reported on the production of starch–PE blown films where starch was totally accessible to microbial attack, leaving behind a decomposed matrix comprising mostly of recalcitrant PE; hence, the birth of the bioplastics. Since that time, scientists worldwide have developed a variety of novel hybrid plastics containing both biodegradable as well as non-biodegradable polymers and additives. They offer novel properties and are useful for single-use packaging applications. Starch, cellulose, PLA, PHBV, PVA, PE, PP, PET and PCL are among the most prominent materials of choice for the production of these hybrid plastics and plasticizers, compatibilizers and coating materials are also used as additives to improve properties. Most of the focus of these developments has been to achieve bioplastics that are mostly biodegradable or compostable. Several excellent articles have been written on this subject (Yasin et al., 1989; Luzier, 1992; Shogren et al., 1993; Mayer and Kaplan, 1994; Koenig and Huang, 1995; Cutter, 2000; Avérous and Fringant, 2001; Chiellini et al., 2002, 2004). Hybrid plastics are a multi-component polymeric system. It is possible that, when polymers are mixed and compounded, compatibilized, plasticized or surface modified to make a hybrid blend, the properties of the individual polymer(s) may also change. As a result, blends may have biodegradation properties distinct from their individual parent polymers. For example, in PE-based blown thin films containing up to 40% thermoplastic starch (dry weight basis), most of the starch readily degraded when films were disposed of in the environment (Imam et al., 1992, 1996). However, when a similar formulation was used to produce injection-molded articles, most of the starch was found to be encapsulated in the PE matrix, severly compromising the ability of microbes and/or their hydrolytic enzymes to access the starch substrate (Imam et al., 1995a, 1995b). This clearly indicated the influence of processing technique on the biodegradability of the polymer matrix. Packaging films where starch or cellulose fiber were used as fillers in a slow-degrading polymeric matrix, showed quick degradation of these fillers, which accelerated the deterioration of the otherwise slow-degrading


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polymer and allowed for rapid compostability (Bastioli, 2001). Due to the presence of starch in a starch–PHBV blend, a significant enhancement was observed in both the rate and extent of PHBV degradation in a compost environment (Imam et al., 1998). In similar blends, where starch was precoated with polyethylene oxide to increase the compatibility between starch and PHBV, starch degradation was negatively impacted. Many biodegradation studies of starch–PHBV hybrid blends in a variety of environments have shown that PHBV and starch both degraded, albeit at different rates and to different extents (Ramsay et al., 1993; Imam et al., 1995a, 1995b, 1999a, 1999b). Blends of the aliphatic polyester PCL or aliphatic-aromatic copolyesters with starch are another important group of biodegradable plastics suitable for food packaging; it has been found that thermal behavior is dominated mainly by PCL and mechanical properties are improved by blending with starch (Rosa et al., 2004, 2007; Dean et al., 2007). Biodegradability of this blend is heavily influenced by the complex interaction between starch and the polyester not only at the molecular level, but also in the surface properties. A good example of this is seen in modified natural polymers such as starch and cellulose acetates used to improve polymer properties via esterification of hydroxyl groups of sugar residues. The increased degree of substitution (esterification) improves the properties of polymers, but greatly reduces their biodegradability. Starch and cellulose acetates containing large amounts of plasticizers are available commercially and are claimed to be biodegradable. PLA is biodegradable in compost; however, information on its biodegradation in other environments is limited. Several studies have confirmed the degradation of PLA by a variety of microorganisms (Agarwal et al., 1998; Jarerat and Tokiwa, 2001, 2003; Jarerat et al., 2003; Masaki et al., 2005). Changes in environmental factors such as humidity and temperature have been shown to influence PLA degradation (Ho et al., 1999). In one study (Shogren et al, 2003), little or no degradation was observed in injection-molded PLA samples buried in soil for a 1 year period in the Midwestern United States. The reason for the slow breakdown of PLA and other polyester-based plastics may be that the environmental degradation of PLA requires a two-step process. First, high molecular weight polyester chains need to be hydrolyzed into low molecular weight oligomers. This is a rather slow step, but the reaction can be accelerated by acids or bases and is also affected by both temperature and moisture levels of the compost. In a second step, microbes and enzymes convert the low molecular weight components into CO2, H2O and residual biomass. The synthesis and assembly of the supra-macromolecular structure of biopolymers proceeds through distinct biosynthetic pathways, requiring specific biological building blocks joined together via specific linkages or chemical bonds. Thus, specific enzymes are required to disassemble or decompose each polymer. From a biodegradation standpoint, blends containing two biopolymers are interesting materials. In starch–PHBV blends, both polymers require different enzymes to degrade effectively. Starch



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needs microbial amylases that can attack both α-1→4 and α-1→6 linkages to completely break down the polymer. On the other hand, PHBV requires esterases to break down the ester linkages in the polymer to achieve degradation. Similarly, cellulose and lignocellulose would require cellulases and lignases and protein polymer would need proteases to attack polypeptide linkages. Certain chemical modifications might improve the properties of a polymer, but it would be challenging for natural microbes as they are programmed to degrade naturally occurring polymers. Assessing the de-gradation of individual polymers in a hybrid blend is challenging. Fourier transform infrared (FTIR) spectroscopy has shown to be a very powerful technique for this purpose in some blends because certain chemical group(s) in each polymer have a characteristic infrared absorption, and the decrease of these absorption peaks or changes in their peak ratios with time can provide useful information on the extent of polymer biodegradation. For example, a hybrid blend made up of PE–starch–protein will show distinguishable peaks that are characteristic of starch, such as the hydroxyl and the fingerprint region. Similarly proteins show the amide I and amide II peaks, and PE shows characteristic C–H stretching bands and a weaker C–H bending absorbance (Imam et al., 1992; Gordon et al., 1996). The CO2 evolution, loss of polymer weight and decrease in molecular weight and tensile properties in polymers all correlated well and were in excellent agreement with the FTIR data (Imam et al., 1992; Gordon et al., 1996). Polymer degradation occurs mainly through scission of the main chains or side chains of macromolecules. In nature, in addition to biological activity (enzymes), polymer degradation is also induced by several other processes, including thermal activation, hydrolysis, oxidation, photolysis and radiolysis. Although there is little evidence that PE can be attacked directly by microbial enzymes, there are many PE-based products available in the market place that are being sold as ‘biodegradable’ materials. The primary step in the degradation consists of a chemically or physically induced reduction of the polymer chain length. Chain length reduction in biodegradable PE has also been attributed to special additives, which trigger the thermal and/or photo-oxidation causing embrittlement of the plastic, followed by enzymatic degradation. Addition of biodegradable fillers like starch or cellulose can further help in the rapid defragmentation of the PE matrix. Such PEbased plastics are termed ‘oxobiodegradable plastics’. EPI Environmental Technologies Inc., based in Vancouver, Canada is the supplier of the product TDPATM (Totally Degradable Plastic Additive, a pro-oxidant). An extruded sample of LDPE containing TDPA additive, when first thermally degraded and subjected to mature compost in respirometric studies, showed that these samples were biodegraded by micro-organisms and the mineralization rates exceeded 60%, a level typical of several natural polymers. Moreover, the rate of biodegradation was comparatively slower (Chiellini et al., 2003). This additive can also be used with other thermoplastic polymers such as


52


PP, PVC, etc. Other investigators have also proposed that thermally degraded polyolefins can be mineralized by microorganisms in soil (Volke-Sepúlveda et al., 1999; Scott and Wiles, 2001). However, further research is needed; in particular, respirometric studies to confirm biodegradability and toxicity evaluations are required to ascertain the safety of the breakdown products. If the claims are confirmed, then this might be the breakthrough technology that would certainly benefit the packaging industry on a wider scale.

2.8

Biodegradable packaging life cycle assessment

A product’s life cycle starts from the moment when raw materials are harvested and processed, followed by the product’s manufacturing, transport, usage and disposal. At every stage of the life cycle, there are emissions of greenhouse gases and consumption of resources/energy. Life cycle assessment (LCA) documents the environmental profile over the life of the product, also known as ‘cradle to grave’ analyses of the environmental impact or the product’s ‘environmental footprint’. This information helps to evaluate the product’s (such as food packaging) overall sustainability and the entire environmental economy. LCA identifies and quantifies the environmental loads involved at every stage – e.g. the energy and raw materials consumed, including the emissions and wastes generated – evaluates the potential environmental impacts of these loads and assesses available options for reducing these environmental impacts. LCA is becoming so crucial that ISO has standardized this framework within the ISO 14040 series on LCA. In the future, all biodegradable packaging manufacturers will be required to conduct LCAs on their products. In this regard, Novamont in Italy has applied LCA to evaluate their product Mater-Bi bags, used for the collection of organic waste, and to compare it with paper bags and PE bags (Bastioli, 2001). Interestingly, paper bags, due to their weight, consumed much more energy in their production compared with Mater-Bi or PE bags. However, the Mater-Bi bags had a four times lower greenhouse effect than PE bags and a five times lower effect than paper bags. This is attributed to the presence of natural fillers in the MaterBi bags. Preliminary studies carried out under the European Climate Change Program indicated a primary CO2 savings potential equivalent to approximately 4 million metric tons of CO2 as a greenhouse gas. This figure is based on the assumption that the bioplastics market, given the appropriate supportive framework conditions, will have grown to around 1 million metric tons (www.european-bioplastics.org). Bioplastics, particularly for food packaging, are at a very early stage of their development, and therefore the information available on the LCA of biobased products is scarce. A comprehensive article on this subject has been published by Patel et al. (2003).



2.9

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Food safety concerns, applications and adoption by the industry

The safety of biobased food packaging has to be examined from a variety of perspectives in view of their overall LCA. Raw materials for bioplastics are derived from renewable crops and their monomers are naturally biodegradable and eventually get recycled back to the earth. Material handling, processing and product manufacturing is routine and does not raise any issues concerning workers’ health or environmental safety. The biggest concern, however, is public health, and safety and security of the packaged food. Petroleum-based packagings have contributed tremendously in this regard, improving the stability and safety of packaged foods. No less is expected from biobased packaging. With consumers demanding more environmentally friendly packaging, the question remains, can biobased polymers provide packaging products that can match the properties of petrochemical-based packaging, by delivering food safely to consumers? In this regard, some earlier developments in the biobased food packaging have already provided results that are quite encouraging. For example, with hybrid biobased packaging, improvements have been observed with regard to the handling of food, prevention of moisture loss, reduction in lipid oxidation, improvement in flavor, stabilization of microbial growth and retention of color in foods ranging from fresh fruits, vegetables, dairy products and meats, to processed food requiring modified atmospheric packaging (Petersen et al., 1999; Marron, et al., 2000; van Tuil et al., 2000; Haugaard et al., 2001a, 2001b; Weber et al., 2002). Numerous investigators have observed that biobased packaging technology improved the quality and safety of fresh processed muscle food (Cutter, 2000), enhanced color and storage life of fresh beef (Ayers, 1959; Baker et al., 1994) and provided enhanced barrier and antimicrobial properties to dairy products where stability of microbial environment and storage capacity is critical (Ahvenainen, 2003). Prolongation of the shelf-life of perishable foods using biodegradable films and coatings has also been reported (Ayers, 1959; Baker et al., 1994; Baldwin, 1995; Guilbert et al., 1996). Many biobased packagings have also been reported to offer fire-retardant capabilities. Interestingly, very few or no reports exist to indicate any negative impact on food quality resulting from biobased packaging. For example, concern has been raised with respect to petroleumbased plastics as containers (packaging) for foods that are cooked in microwave or conventional ovens. Plasticizers, unreacted monomers, mold release agents or other contaminants found in plastics may leach upon heating, and contaminants may get absorbed by foods. This may produce changes in food flavor and raise safety concerns (Brooker and Friese, 1989; Castle et al., 1992; McNeal and Hollifield, 1993). In contrast, such concerns have not been raised for the biobased packaging made of mostly renewable natural polymers.


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Biobased packaging has already been adapted and is in wide use by nonfood industries worldwide. Europe, North America and Asia have taken the lead in this regard. The items manufactured include garbage bags, shopping bags, laundry bags, agricultural mulch films, single-use consumer packaging and corrugated (KTM Industry, Lansing, MI) and loose-fill foams. KTM and Michigan State University are jointly developing ‘green’ technology-based novel industrial materials to provide innovative solutions for global packaging applications. Biodegradable starch foam packaging and insulation materials are now available commercially. Some automotive manufacturers (Toyota) as well as giant computer manufacturers (NEC) and other consumer electronics producers (HP and Dell) are using biobased packaging for their products. In particular, renewable polymers have found some useful applications in the field of biomedicine. Implants, prostheses, bone substitutes, sutures and drug delivery vehicles are examples of their applications. This is quite encouraging, as these materials have shown to be quite compatible with human tissues and blood, and no rejection of these materials or adverse effects of their use have been reported in a mammalian system. Adoption of these products by the food industry has been steady but slow due to obvious health and food safety concerns as well as regulatory hurdles. In the United States, for example, any food contact item has to pass through a stringent and lengthy process of evaluation before it can be approved by the US FDA for public use. The European Community also has similar protocols in place. For example, the EU Framework Directive 90/128/EEC requires that any biobased packaging for food contact must ensure food quality and safety. Another reason for the slow progress in incorporation of biobased packaging by the food industry concerns the fulfillment of unique and characteristic functionality requirements demanded by packaged food to provide a stable, healthy and safe food to consumers. Packaging biologically active materials in a space made up of mostly biologically active polymers is in itself a challenge. Factors such as modified atmospheres, provision of gas and water vapor barriers, microbial and thermal stability, retention of color, texture and flavor, as well as timecontrolled performance, are not trivial issues and need to be considered in the design of the food package. In the last decade, the science of biobased materials with respect to food packaging has advanced to the highest level and some great strides have been made by the food industry to embrace this new thinking on biobased food packaging. In addition, biobased packaging for foods has been reconsidered as a more environmentally responsible alternative compared with petrochemical-based counterparts. This factor, and the demand for environmentally friendly packaging from consumers and advocacy groups, concern for accumulating recalcitrant plastic waste in landfills and ever-increasing oil prices have all served as catalysts to bring about this change. Many companies worldwide are positioning themselves as leaders in developing biodegradable plastic resins as they foresee a bright future for applications of these materials (Table 2.1); this is evidenced by the food packaging products that are already in the market © 2008, Woodhead Publishing Limited


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place (Table 2.5). More details on this subject are provided elsewhere (Haugaard et al., 2001a, 2001b). There are several critically important determinants that will guide the success of renewable and biopolymers as raw materials for food packaging. First of all, the availability of material with consistent properties will be critical for the industry. Factors such as flooding, extended drought, frost, harvesting pattern and crop infestation could potentially have an impact on on both the quality and the quantity of the available raw materials. For example, harvesting a corn crop prematurely would certainly affect the quality of the starch. One consistent fear will be the presence of any chemical contaminants, or their byproducts, from the fertilizers, pesticides or herbicides used in industrialized countries. Although there seems to be no indication of this at the present time, this is one of the aspects that will be closely examined and monitored by regulatory agencies such as the FDA. Currently, most of the renewable crops are produced in surplus, and this seems to be the global trend. However, environmental factors, weather, climate change due to global warming and scarcity of water resources could change this scenario, and will threaten the abundant availability of raw materials. Yet another important aspect of renewable-based plastics is the fact that many renewable crops, for example corn and soybean, are also consumed as food. Many impoverished nations – particularly in Africa, Asia and South America – are dependent on these crops to provide food to their people. There is a fear that, when demand exceeds the supply, market forces will drive the food prices high and will place economic pressure on these countries. The world’s population is expected to double by the year 2050 and a big portion of agricultural land will presumably be lost to the urban development required to accommodate the population. This will, inevitably, provoke competition for renewable crops, i.e. crops grown for food and crops grown for use as raw materials for industrial products. One of the unintended consequences of this competition has already occurred. Many of the small family farms, once considered the backbone of American agriculture, have been replaced by corporate farming organizations. Large corporations with business interests and with intellectual property rights on many commercially important, genetically modified germplasms are positioning themselves to be the market players in the near future. The effort to produce biodegradable microbial polyesters in plants by NatureWorksTM is one such example.

2.10

Future trends

Judging from the R&D achievements of the past 10–15 years with respect to biopolymer-based plastics, the future of biobased polymers in food packaging looks quite promising. Many of the challenges posed by renewable materials have been and are being resolved, and the food industry in general is supporting the concept by moving towards the adoption of biobased packaging. Consumers have shown a strong acceptance on their part for © 2008, Woodhead Publishing Limited

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biobased products and are even willing to pay higher prices for the sake of the environment. These products will also be good for MSW management companies and composting facilities, which will generate extra revenues by converting these compostable materials into rich soil additives. This would also reduce pressure on the ever-shrinking landfill spaces. One obvious benefit will be the minimization of litter on land and sea: the litter is not only a nuisance but is also compromising the natural habitats for many animals, including marine life. Many countries and regions have already introduced legislation on the management of plastic waste and have placed incentives to promote biodegradable plastics. Likewise, many international organizations such as ASTM, ISO, CEN, DIN and OECD are coordinating testing standards, criteria and definitions for biodegradable packaging. Composting councils are active in defining what is acceptable for composting and what is not. The LCAs of several renewable and biobased products have shown very encouraging trends indicating a strong environmental benefit of such packaging. A recent EU study estimates a considerable reduction in the production of greenhouse gases as a result of the usage of biodegradable plastics (Patel, 2004). In the end, a combination of the desired properties and functionalities of the packaging materials and the commodity market price will dictate the successful adoption of renewable polymers in food packaging. If these packages do not perform at the level consumers are currently accustomed to, they will not be accepted or supported. In addition, raw materials have to be cost competitive, otherwise the industry will naturally revert to the petroleumbased chemicals. This is particularly critical for the PHB and PLA polymers, because despite having good properties, the current market price for these resins is not attractive and is keeping many manufacturers away. It is encouraging to note that consumer surveys in industrialized countries have repeatedly shown the willingness of consumers to pay a fractionally higher price for an environmentally friendly packaging derived from biodegradable and/ or renewable polymers. For now, there are strong factors in favor of renewables: an astonishing amount of per capita garbage generation in the industrialized world, rising oil prices and the production of crops in surplus quantities. This momentum needs to be sustained with commitment for the design and production of products with useful functionality, i.e., products that perform under a variety of storage conditions and that retain the ability to degrade after use. More efforts are needed globally to take advantage of the changing market trends with respect to biobased packaging.

2.11


Publications • Ahvenainen R (Ed.). Novel food packaging techniques. Woodland Publishing Limited, Cambridge, UK, 2003.



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• Petersen K, Væggemose Nielsen P, Bertelsen G, Lawther M, Olsen MB, Nilsson NH, Mortensen G. Potential of biobased materials for food packaging. Trends Food Sci. Technol., 1999, 10, 52–68. • Robertson GL (Ed.). Food packaging: principles and practice. CRC Press, Boca Raton, Florida, 2005. • Smith R (Ed.). Biodegradable polymers for industrial applications. Woodhead Publishing Limited, Cambridge, UK, 2005. • Truong D, Pham PSS, Dimov SS (Eds). Advances in manufacturing technology. Wiley & Sons, Hoboken, New Jersey, 2001. • Young RA, Rowell JK, Roweu RM (Eds). Paper and composites from agro-based resources. CRC Press, Boca Raton, Florida, 1996. Websites • American Society for Testing and Materials (ASTM) (www.astm.org). • European Committee for Standardization (CEN) (www.cenorm.be). • International Organization for Standardization (ISO) (www.iso.org).

2.12

References

agarwal m, koelling kw, chalmers jt. Characterization of the degradation of polylactic acid polymer in a solid substrate environment. Biotechnol. Prog. 1998, 14, 517–526. ahvenainen r. (Ed.) Novel food packaging techniques. Woodhead Publishing Limited, Cambridge, UK, 2003, p. 590. andersen pj, hodson sk. Molded articles having an inorganically filled organic polymer matrix. US Patent No. 5,545,450, 1996. avérous l, fringant c. Association between plasticized starch and polyesters: processing and performances of injected biodegradable systems. Polym. Engng Sci., 2001, 41, 727–734. avérous l, fringant c, moro l. Starch-based biodegradable materials suitable for thermoforming packaging. Starch/Stärke, 2001, 53, 368–371. ayers jc. Use of coating materials or film impregnated with chlortetracycline to enhance color and storage life of fresh beef. Food Technol., 1959, 13, 512–515. baker ra, baldwin ea, nisperos-carriedo no. Edible coatings and films for processed foods. In Edible coatings and films to improve food quality, Krochta JM, Baldwin EA, Nisperos-Carriedo MO (Eds). Technomic Publishing Company, Lancaster, Pennsylvania, 1994, pp. 89–104. baldwin ea, nisperos-carriedo mo, baker ra. Use of edible coatings to preserve quality of lightly (and slightly) processed products. Crit. Rev. Food Sci. Nutr., 1995, 35, 509–524. bastioli c. Industrial applications of bioplastics. Green Tech Conference, Utrecht, Holland, April 3–5, 2000. bastioli c. Global status of the production of biobased packaging materials. Starch/ Stärke, 2001, 53, 351–355. brooker jl, friese ma. Safety of microwave-interactive paperboard packaging materials. Food Technol., 1989, 31, 110–117. bucci dz, tavares lbb, sell i. PHB packaging for the storage of food products. Polym. Test., 2005, 24, 564–571.


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guilbert s, cuq b, gontard n. Recent innovations in edible and/or biodegradable packaging materials. Food Addit. Contam., 1997, 14, 741–751. hass f, hass j, tiefenbacher k. Process of manufacturing rottable thin-walled starchbased shaped elements. US Patent No. 5,576,049, 1996. haugaard vk, udsen am, mortensen g, høegh l, petersen k, monahan f. Potential food applications of biobased materials. In Biobased food packaging – status and perspectives, Weber C-J, (Ed.), Chapter 3. Royal Veterinary and Agricultural University, Copenhagen, 2001a, pp. 46–85. haugaard vk, udsen a-m, mortensen g, høegh l, petersen k, monahan f. Potential food applications of biobased materials. An EU-concerted action project. Starch/ Stärke, 2001b, 53, 189–200. ho k-lg, pometto iii al, hinz n. Effects of temperature and relative humidity on polylactic acid plastic degradation. J. Polym. Environ. Degrad., 1999, 7, 83–92. hodge im, berens ar. Effects of annealing and prior history on enthalpy relexation in glassy polymers: 2. Mathematical modeling. Macromolecules, 1982, 15, 762. holton ee, asp eh, zottola ea. Corn-starch-containing polyethylene film used as food packaging. Cereal Foods World, 1994, 39, 237–241. hutchinson jm, kovacs a. Effects of thermal history on structural recovery of glasses during isobaric heating. J. Polym. Engng. Sci., 1984, 24, 1087. imam sh, harry-o’kuru re. Adhesion of Lactobacillus amylovorus to insoluble and derivatized cornstarch granules. Appl. Envir. Microbiol., 1991, 57, 1128–1133. imam sh, gould jm, gordon sh, kinney mp, ramsey am, tosteson tr. Fate of starchcontaining plastic films exposed in aquatic habitats. Curr. Microbiol., 1992, 25, 1–8. imam sh, gordon sh, thompson ar, harry-o’kuru re, greene rv. The use of CP/MAS 13C-NMR for evaluating starch degradation in injection molded starch–plastic composites. Biotechnol. Tech., 1993, 7, 791–794. imam sh, gordon sh, burgess-cassler a, greene rv. Accessibility of starch to enzymic degradation in injection-molded starch–plastic composites. J. Environ. Polym. Degrad., 1995a, 3, 107–113. imam sh, gordon sh, shogren rl, greene rv. Biodegradation of starch–poly(βhydroxybutyrate-co-valerate) composites in municipal activated sludge. J. Environ. Polym. Degrad., 1995b, 3, 205–213. imam sh, gordon sh, greene rv. Starch biodegradation (in starch–plastic blends). In Polymeric materials encyclopedia, Salamone JC (Ed.), vol. 10. CRC Press, Boca Raton, FL, 1996, pp. 7892–7901. imam sh, chen l, gordon sh, shogren rl, weisleder d, greene rv. Biodegradation of injection molded starch–poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends in a natural compost environment. J. Environ. Polym. Degrad., 1998, 6, 91–98. imam sh, gordon sh, shogren rl, tosteson tr, govind ns, greene rv. Degradation of starch–poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) bioplastic in tropical coastal waters. Appl. Environ. Microbiol., 1999a, 65, 431–437. imam sh, mao l, chen l, greene rv. Wood adhesive from crosslinked poly(vinyl alcohol) and partially gelatinized starch: preparation and properties. Starch/Stärke, 1999b, 51, 225–229. jarerat a, tokiwa y. Degradation of poly (l-lactide) by a fungus. Macromol. Biosci., 2001, 1, 136–140. jarerat a, tokiwa y. Poly (l-lactide) degradation by Saccharothrix waywayandensis. Biotechnol. Lett., 2003, 25, 401–404. jarerat a, tokiwa y, tanaka h. Poly (l-lactide) degradation by Kibdelosporangiium aridum. Biotechnol. Lett., 2003, 25, 2035–2038. koenig mf, huang sj. Biodegradable blends and composites of polycaprolactone and starch derivatives. Polymer, 1995, 36, 1877–1882.


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köse gt, ber s, korkusuz f, hasirci v. Poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid) based tissue engineering matrices. J. Mater. Sci: Mater Med., 2003, 14, 121–126. lawton jw. Biodegradable coatings for thermoplastic starch. In Cereals: novel uses and processes, Campbell GM, Webb C, McKee SL (Eds). Plenum Press, New York, 1997, pp. 43–47. lawton jw, shogren rl, tiefenbacher kf. Effect of batter solids and starch type on structure of baked starch foams. Cereal Chem., 1999, 76, 682–687. lawton jw, shogren rl, tiefenbacher kf. Aspen fiber addition improves the mechanical properties of baked cornstarch foams. Ind. Crops Prod., 2004, 19, 41–48. luzier wd. Materials derived from biomass/biodegradable materials. Proc. Natl Acad. Sci. USA, 1992, 89, 839–842. makino y, hirata t. Modified atmosphere packaging of fresh produce with a biodegradable laminate of chitosan-cellulose and polycaprolactone. Postharvest Biol. Technol., 1997, 10, 247–254. marron v, saari l, floridi g, boelck c, innocenti f. The market of biobased packaging materials. In Biobased packaging materials for the food industry – status and perspectives, Weber CJ (Ed.). Report of EU Concerted Action Project, 2000, pp. 105–112. martin o, schwach e, avérous l, couturier y. Properties of biodegradable multilayer films based on plasticized starch. Starch/Stärke, 2001, 53, 372–380. masaki k, kamini nr, ikeda h, iefuji h. Cutinase-like enzyme from the yeast Cryptococcus sp. strain S-2 hydrolyzes polylactic acid and other biodegradable plastics. Appl. Environ. Microbiol., 2005, 71, 7548–7550. mayer jm, kaplan dl. Biodegradable materials: balancing degradability and performance. Trends Polym. Sci., 1994, 2, 227–235. mcneal tp, hollifield hc. Determination of volatile chemicals released from microwave-heat-susceptor food packaging. J. Assoc. Anal. Chem., 1993, 76, 1268–1275. narayan r. Impact of governmental policies, regulations and standards activities on an emerging biodegradable plastic industry. In Biodegradable plastics and polymers, Doi Y, Fukuda K. (Eds). Elsevier, Amsterdam, 1994, pp. 261–271. orts wj, ingelsby b glenn gm. Bringing bioproducts to market. Biocycle, 2003a, June, 25–27. orts wj, inglesby m, glenn gm. Cleaning up with bioproducts. Business, 2003b, March/April, 12–14. otey fh, westhoff rp, russell cr. Starch graft copolymers-degradable fillers for poly (vinyl chloride) plastics. Ind. Engng. Chem., Prod. Res. Dev., 1976, 15, 139–144. otey fh, westhoff rp, doane wm. Starch-based blown films. Ind. Engng. Chem. Res., 1987, 26, 1659–1663. patel m. Surfactants based on renewable raw materials: carbon dioxide reduction potential and policies and measures for the European Union. J. Ind. Ecol., Special Issue on Biobased Products, 2004, 7, 47–62. patel m, bastioli c, marini l, würdinger e. Life-cycle assessment of biobasedpolymers and natural fibers. In Biopolymers, Steinbüchel A (Ed.), vol. 10. WileyVCH, Weinheim, Germany, 2003, pp. 409–452. petersen k, væggemose nielsen p, bertelsen g, lawther m, olsen mb, nilsson nh, mortensen g. Potential of biobased materials for food packaging. Trends Food Sci. Technol., 1999, 10, 52–68. ramsay ba, langlade v, carreau pj, ramsay ja. Biodegradability and mechanical properties of poly(β-hydroxybutyrate-co-β-hydroxyvalerate)–starch blends. Appl. Environ. Microbiol., 1993, 59, 1242–1246.



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robertson gl (Ed.). Food packaging: principles and practice. CRC Press, Boca Raton, Florida, 2005, p. 568. röpper h, koch h. The role of starch in biodegradable thermoplastic materials. Starch/Stärke, 1990, 42, 123. rosa ds, lotto nt, lopez dr, guedes cgf. The use of roughness for evaluating poly-β-(hydroxybutyrte) and poly-β-(hydroxybutyrate-co-β-valerate). Polym. Test., 2004a, 23, 3. rosa ds, gliedes cgf, pedroso ag, calil mr. The influence of starch gelatinization on the rheological, thermal, and morphological properties of poly(ε-caprolactone) with corn starch blends. Mater. Sci. Engng C, 2004b, 24, 663–670. rosa ds, lopes dr, calil mr. The influence of the structure of starch on the mechani cal, morphological and thermal properties of poly (ε-caprolactone) in starch blends. J. Mater. Sci., 2007, 42, 2323–2328. scott g, wiles dm. Programmed-life plastics from polyolefins: a new look at sustainability. Biomacromolecules, 2001, 2, 615–622. shey j, imam sh, glenn gm, orts wj. Properties of baked starch foam with natural rubber latex. Ind. Crops Prod., 2006, 24, 34–40. shogren rl. Effect of moisture content on the melting and subsequent physical aging of cornstarch. Carbohydr. Polym., 1992, 19, 83. shogren rl. Complexes of starch with telechelic poly(ε-caprolactone) phosphate. Carbohydr. Polym., 1993, 22, 93–98. shogren rl. Starch: properties and material applications. In Biopolymers from renewable resources, Kaplan DL (Ed.). Springer-Verlag, Berlin, 1998, pp. 30–46. shogren rl, bagley eb. Natural polymers as advanced materials: some research needs and directions. In Biopolymers – utilizing nature’s advanced materials, ACS Symposium Series 723, Imam SH, Greene RV, Zaidi BR (Eds). ACS, Washington, DC, 1999, pp. 2–11. shogren rl, lawton jw. Enhanced water resistance of starch-based materials. US Patent No. 5,756,194, 1998. shogren rl, lawton jw, doane wm, tiefenbacher kf. Structure and morphology of baked starch foams. Polymer, 1997, 39, 6649–6655. shogren rl, lawton jw, tiefenbacher kf, chen l. Starch–poly (vinyl alcohol) foamed articles prepared by a baking process. J. Appl. Polym. Sci., 1998, 68, 2129–2140. shogren rl, lawton jw, tiefenbacher kf. Baked starch foams: starch modification and additives improve process parameters, structure and properties. Ind. Crops. Prod., 2002, 16, 69–79. shogren rl, doane wm, garlotta dv, lawton jw, willet jl. Biodegradation of starch/polylactic acid/poly(hydroxyester-ether) composite bars in soil. Polym. Degrad. Stabil., 2003, 79, 405–411. stevens es. Biopolymers. In Green plastics. Princeton University Press, New Jersey, 2002, pp. 83–103. stranz aa, zottola ea. Bacterial survival on lean beef and bologna wrapped with cornstarch-containing polyethylene film. Food Prod., 1992, 55, 782–786. swanson cl, shogren rl, fanta gf, imam sh. Starch–plastic materials – preparation, physical properties, and biodegradability (a review of recent USDA research), J. Polym. Environ., 1993, 1, 155–166. tiefenbacher k. Starch-based foamed materials – use and degradation properties. J. Macromol. Sci., Pure Appl. Chem., 1993, A30, 727–731. tomka i. Thermoplastic starch. Adv. Exp. Med. Biol., 1991, 302, 627. truong d, pham pss, dimov, ss (Eds). Advances in manufacturing technology. Wiley & Sons, Hoboken, NJ, 2001, p. 490. van soest jjg. Starch plastics structure–property relationship. PhD thesis, Utrecht University, The Netherlands, 1996.


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van tuil r, fowler p, lawther m, weber cj. Properties of biobased packaging materials. In Biobased packaging materials for the food industry – status and perspectives, Weber CJ (Ed.). Report of EU Concerted Action Project, 2000, pp. 8–33. volke-sepúlveda t, favela-torres e, manzur-guzmáan a, limón-gonzalez m, trejo-quintero g. Microbial degradation of thermo-oxidized low-density polyethylene. J. Appl. Polym. Sci., 1999, 73, 1435–1440. weber cj, haugaard v, festersen r, bertelsen g. Production and applications of biobased packaging materials for the food industry. Food Addit. Contam., 2002, 19 (Suppl.), 172–177. whistler rl. History and future expectation of starch use. In Starch chemistry and technology, Whistler RL, Bemiller JN, Paschall EF (Eds). Academic Press, San Francisco, California, 1984, pp. 1–9. xu yx, dzenis y, hanna ma. Water solubility, thermal characteristics and biodegradability of extruded starch acetate foams. Ind. Crops Prod., 2005, 21, 361–368. yasin m, holland sj, jolly am, tighe bj. Polymers for biodegradable medical devices. VI. Hydroxybutyrate–hydroxyvalerate copolymers: accelerated degradation of blends with polysaccharides. Biomaterials, 1989, 10, 400–412. zobel hf. Starch crystal transformations and their industrial importance. Starch/ Stärke, 1988, 40, 1.


3 Thermoplastic nanobiocomposites for rigid and flexible food packaging applications J. Lagaron and M. Sanchez-Garcia, Institute of Agrochemistry and Food Technology, Spain; E. Gimenez, ESID, University Jaume I, Castellon, Spain

3.1

Introduction: plastic food packaging, sustainable materials and barrier properties

Over the last few decades there has been a significant increase in the amount of plastics being used in packaging applications. In fact, the largest application for plastics today is packaging, and within the packaging niche, food packaging constitutes the largest plastics-demanding application. This is because plastics demonstrate enormous advantages, such as thermoweldability, flexibility in thermal and mechanical properties, lightness and low price.1–3 However, polymers do also have a number of limitations for certain applications when compared with more traditional materials such as metals and alloys or ceramics. Of these limitations, those relevant to this chapter are their impermeability to low molecular weight components, a comparatively low thermal resistance and a strong interdependence between the last two properties. In spite of this, use of plastic materials continues to expand and to replace the conventional use of paperboard, tinplate cans and glass, which have typically been used as monolayer systems. Initially, most plastic packaging was made of monolayer rigid or flexible materials but as the advantages of plastic packaging became more and more established and developed, the increasingly demanding product requirements found when plastics had to suit more and more different food products led, in conjunction with significant advances in plastic processing technologies, to more and more complex polymeric packaging formulations. This resulted in complex multicomponent structures such as the so-called multilayer packaging-based systems widely used today. However, there are significant advantages in terms of costs and other issues, such as ease of recycling, in


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developing packaging materials made of monolayer components. As a result, much research effort has been expended over the last decades in the study of material developments and material blends to reduce complexity in food packaging structures. On the other hand, the substantial increase in the use of plastics has also raised a number of environmental concerns from a waste management point of view. As a result, there is a strong research interest – driven by authorities at national and international levels, and a concomitant increasing demand from industry – in the development and use of materials that can disintegrate and biodegrade, through processes such as composting, into carbon dioxide and water. Among biodegradable materials, three families are usually considered. The first family are polymers directly extracted from biomass, such as the polysaccharides chitosan, starch and cellulose and proteins such as gluten and zein. A second family makes use of oil-based monomers or biomassderived monomers but uses classical chemical synthetic routes to obtain the final biodegradable polymer; this is the case for polycaprolactones (PCLs), polyvinyl alcohol (PVOH) and copolymers (ethylene vinyl alcohol, EVOH), and for sustainable monomers of polylactic acid (PLA).1–3 The third family makes use of polymers produced by natural or genetically modified microorganisms such as polyhydroxyalkanoates (PHAs) and polypeptides.4 The materials that are now attracting more commercial interest are some biodegradable polyesters, which can be processed by conventional processing equipment and are already being used in a number of monolayer and also multilayer applications, particularly in the food packaging and biomedical fields. The most widely researched thermoplastic, sustainable biopolymers for monolayer packaging applications are starch, PHA and PLA. Of these, starch and PLA biopolymers are without doubt the most interesting families of biodegradable materials because they have become commercially available (from, for instance, companies such as Novamont and Natureworks, respectively) and are produced on a large industrial scale, and also because they present an interesting balance of properties. Of particular interest in food packaging is the case of PLA due to its excellent transparency and relatively good water resistance. The water permeability of PLA is, for instance, much lower than that of proteins and polysaccharides but it is still higher than that of conventional polyolefins and polyethylene terephthalate (PET). Its relatively high stiffness is usually reduced by addition of plasticizers such as PCL and others, but these also lead to a decrease in oxygen barrier properties and in transparency. Thus, the main drawbacks of this polymer regarding performance are still associated with low thermal resistance, excessive brittleness and insufficient barrier to oxygen and to water compared with, for instance, other benchmark packaging polymers like PET. It is, therefore, of great industrial interest to enhance the barrier properties of this material while maintaining its inherently good properties such as transparency and biodegradability.5–11


Thermoplastic nanobiocomposites for rigid and flexible packaging

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Finally, there are also other biomaterials that show a lot of potential in food packaging applications; these materials are directly extracted from biomass, for example gluten, protein zein obtained from corn and the polysaccharide chitosan typically obtained from the crustaceous chitin. These materials have excellent barrier properties to oxygen under dry conditions and are transparent (albeit zein is slightly coloured). The main drawbacks of these families of materials is their inherently high rigidity, difficult processability using conventional processing equipment and the very strong water sensitivity arising from their hydrophobic character, which leads to a strong plasticization of many properties, including the excellent oxygen barrier, as relative humidity and water sorption increase in the material. The low water resistance of proteins and polysaccharides strongly handicap their use as monolayers in food packaging and apart from a few particular cases such as starch-based materials and, on a smaller scale, gluten and zein, most proteins and polysaccharides are better suited for coatings or multilayer systems. Nevertheless, chitosan and zein biopolymers exhibit two very interesting characteristics: one is that the chitosan displays antimicrobial properties12,13 and the other is that zein shows an unusually high water resistance compared with other similar biomaterials.14 Furthermore, zein in a resin form can also be heat processed. In spite of this, and from an application point of view, it is of great relevance to diminish the water sensitivity of proteins and polysaccharides and to enhance the gas barrier properties of thermoplastic biopolyesters to make them suitable for monolayer and also for multilayer food packaging applications. The outline of the current chapter is to first introduce the general concept of barrier properties and the need for these in food packaging applications and to describe briefly the phenomenology of transport in polymers. This is followed by presentation of novel plastic strategies and technologies for monolayer packaging. The next sections introduce and review the role of the nanocomposites, and in particular the nanobiocomposites, as the most promising monolayer technology currently available for enhancing barrier properties and designing sustainable and more efficient active and bioactive systems for current and future food packaging applications.

3.2

‘Barrier properties’ limit the use of plastics in monolayer packaging

From the above introduction, it is clear that enhancing or being able to tailor the barrier properties of conventional and biodegradable polymers, but especially the latter, is essential for their competitive implementation in food packaging applications as monolayers, or even in some cases in multilayer structures. Barrier properties are concerned with the ability of a plastic material to reduce the transport of low molecular weight compounds through it; these properties strongly influence relevant, and often


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undesirable, transport phenomena in food packaging, such as the sorption of food components or scalping, migration and permeability processes. ‘High barrier’ is without doubt a highly desirable property to be retained by polymeric materials intended to be used in many packaging applications. The term ‘high barrier’ is usually referred to as the low to very low permeability of a material to low molecular weight chemical species like gases, water vapour and organic compounds. However, this property has perhaps never received as much industrial attention as it has over the last few decades, when it began to be discussed in relation to modern food and beverage packaging technologies making use of plastic materials.15–17 In this respect, high barrier has been the subject of a great deal of recent industrial and social discussion, as it has become associated with topical issues such as food commercialization, food shelf-life extension, and food quality and safety. As a consequence, polymer scientists, engineers and technologists in industry and academia have invested a great deal of effort and resources to push the limits of plastics and bioplastics performance towards impermeability, chiefly due to the overwhelming pressure exerted by an industry keen to benefit from the numerous cited advantages associated with the use of plastics in high barrier monolayer and multilayer applications. 3.2.1 Phenomenology of transport in plastics According to the above, barrier properties in polymers are necessarily associated with their inherent ability to permit the exchange, to a greater or lesser extent, of low molecular weight substances through mass transport processes such as permeation. The permeation of low molecular weight chemical species through a polymeric matrix is generally envisaged as a combination of two processes, i.e. solution and diffusion.18 A permeate gas is first dissolved into the upstream face of the polymer film and then undergoes a molecular diffusion to the downstream face of the film where it evaporates into the external phase again. A solution–diffusion mechanism is thus applied, which can be formally expressed in terms of permeability (P), solubility (S) and diffusion (D) coefficients as follows P = DS

[3.1]

This permeability coefficient derives from application of Henry’s law of solubility to Fick’s first law of diffusion as follows J=

q S∆p ql ∂c ∆p = −D =D = DS ⇒ P = DS = At l l At∆p ∂x

[3.2]

The solubility coefficient (S) is thermodynamic in nature and is defined as the ratio of the equilibrium concentration of the dissolved penetrant in the polymer to its partial pressure (p) in the gas phase (Henry’s law). In polymers, Henry’s law is usually obeyed at low penetrant concentrations, i.e.



67

when S is independent of concentration (or of the partial pressure). D characterizes the average ability of the sorbed permeate to move through the polymer chain segments and is determined from Fick’s first law of diffusion, i.e. the flux of the permeant J (q is the amount of substance expressed in mass for condensable fluids or in volume for permeant gases and A is the surface area) is proportional to the local gradient of concentration (c) through the thickness of the polymer film (l). During sorption kinetic experiments, if Fickian transport (case I) is assumed, a linear relationship in the penetrant uptake versus t1/2 (t being time) curve at small times is usually observed.19 Case II diffusion is defined when a linear relationship is observed in the uptake versus t curve. This behaviour is observed in a number of systems and is associated with large uptakes and plasticization of the structure by the penetrant. When complex sorption relationships such as sigmoidal shapes are observed, it is usually assumed that an ‘anomalous’ or non-Fickian transport has occured. Nevertheless, from recent works a better rationalization of these ‘anomalous’ relationships has been achieved, where contributions from the effect of macroscopic elastic constraints arising during the swelling process (geometrical effects) in adsorption experiments have been pointed out.20,21 Concerning the mechanisms of the mass transport process through polymeric materials, two general approaches can be found, namely: (a) molecular models studying the specific penetrant and chain motions in conjunction with the corresponding intermolecular forces and (b) ‘free-volume’ models which pay attention to the relations between the transports coefficients and the free volume existent in the polymeric matrix, without consideration of molecular-scale mechanisms.22 The structural factors determining inherent high barrier properties in polymers are fundamentally related to the chemistry, but there are also other relevant factors making a significant impact on barrier properties for a given chemistry including polymer morphology (crystallinity, thermal history, molecular orientation, etc.), polymer molecular architecture (branches, molecular weight and tacticity), polymer plasticization and others. Table 3.1 presents typical data relating to permeability to oxygen and water vapour for conventional and novel biodegradable plastics used in packaging. The differences in gas permeability, which can vary between materials by more than six orders of magnitude, are primarily related to the influence of chemistry. Plastics are either semi-crystalline or amorphous materials. Polymer crystals in semi-crystalline materials not only provide support and rigidity to hold the supermolecular structure of the materials but are in general impermeable blocks that impose some constraints on molecular mobility to the surrounding amorphous phase. Thus, the presence of crystallinity, its morphology (for instance crystal width to thickness ratio) and orientation, bring in additional considerations in terms of permeability as the penetrant molecules have to circumvent the crystallites and, thereby, travel through


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Table 3.1 Water permeability (at 38 ºC and 90% relative humidity (RH) and oxygen permeability (23 ºC) of a number of commercial plastics and multilayer structures (data were gathered, unless otherwise stated, from Reference 11)

Material

PVOH EVOH PAN PAN (70% AN) PVDC PA6 aPA (amorph.) PET PP PC LDPE LCP PET–PVDC PA–PVDC PP–PVDC PET-met. PET–AlOx–PE PET–SiOx–PE PA–SiOx–PE PP–SiOx–PE 23 PLA 24 PLA 23 PHB 24 PHB 23 PHBV 23 PCL 25 PCL 26 PCL

Water permeability (1018 kg m/(m2 s Pa))

Oxygen permeability (1021 m3 m/(m2 s Pa)) 0% RH

75% RH

485 000 17 000 2420 8250 30.53 20 600 2420 2300 726 19 400 1200 10 170 160 43 58 21 16 32 13 12 600

0.17 0.77 1.9 10.5 4.5 52 83 135 6750 10 500 21 500 0.42 17.5 18.2 25 3.5 7 4.9 7.7 81 2250

900 91

1689

230

6900 26 600

1590 4380 934 1960

31 225 60

15

2209 1750 5100 3010 7850

For abbreviations, see Section 3.8.

a more tortuous diffusive path than in a fully amorphous material. This effect is usually accounted for in the calculations of the transport coefficients (see equation [3.3] below for diffusion in which c is the crystallinity fraction) by the so-called tortuosity, detour or geometrical impedance factor (t). Thus, the tortuosity factor is in essence the path length that a permeant has to travel across the material thickness divided by the actual thickness of the material. At this point it is relevant to realize that any additional impermeable elements, such as clays or other fillers, added to the molecular structure of the polymers have an immediate impact on the tortuosity or detour factor, as will be further explained later in the chapter. Furthermore,



69

and as commented above, the presence of crystalline blocks or other fillers also affects the surrounding conformationally disordered amorphous phase. The constraining effects imposed by crystals or fillers to the chain segments in the amorphous phase typically depend on factors such as crystal or particle surface area and penetrant size. This phenomenon is substantiated from extensive mechanical and transport data, which clearly indicate that the segmental mobility of the non-crystalline fraction is much less than that in the fully amorphous polymer or in unfilled materials.27,28 This effect is accounted for in the calculations of the transport coefficients (see equation [3.3]) by the so-called chain immobilization factor (b) Dsemi-crystalline =

Damorphous (1 − χ ) βτ

[3.3]

As a result of this, awareness of the effects of crystallinity or of the presence of fillers, and their morphology and distribution, on the barrier properties is, as a matter of fact, a very relevant issue, because by adequate processing (thermal history) of polymers these additional effects can be optimized to obtain specimens, based on the same matrix chemistry, with enhanced permeability.

3.3

Novel developments in barrier polymeric structures

Novel developments in plastic materials currently come mainly from five different sources, namely: (a) new synthetic polymers, (b) biomass-derived polymers, (c) polymer blends, (d) nanocomposites, and (e) surface or coating technologies. Polymeric materials for high barrier applications are challenged today with a broad range of stringent property requirements including: ease of processing; higher barrier properties to permanent gases, moisture and low molecular weight organic compounds; excellent chemical resistance; permselectivity; low relative humidity dependence for the barrier performance; and ease of recycling, biodegradability or compostability. Among the new high barrier polymers being developed are materials like the polyketone (PK) copolymers (aliphatic polyketones).30,31 These semi-crystalline materials have an outstanding range of mechanical, thermal and high barrier properties (comparable with some EVOH copolymers), chemical resistance and reduced relative humidity dependence for barrier properties, which give them significant commercial potential in a broad range of engineering, barrier packaging, fibre and blend applications. Another new range of promising materials currently being investigated for packaging applications are those derived from biomass, as mentioned above, which to a greater or lesser extent are easily biodegradable or compostable.24,32 These polymers can have excellent barrier properties to gases, as for example plasticized chitosan, albeit the barrier performance is dramatically reduced in the presence of moisture. However, other polymers


70


such as the PHAs have very high water barrier properties. Therefore, in principle, one could devise a biomass-derived, high barrier multilayer system where an inner layer of plasticized chitosan could be sandwiched between high moisture barrier PHA layers. An interesting property of some of these biobased polymers, e.g. PLA and starch, is that their permeability to carbon dioxide compared with that of oxygen (permselectivity) is higher than most conventional mineral oil-based plastics. This is of interest, for instance, in some food packaging applications where a high barrier to oxygen is required, but carbon dioxide generated by the product should be allowed to exit the package head space to avoid package swelling. Some of these materials, however, still suffer from high production costs and shortcomings in certain properties and so cannot compete with other conventional plastic materials now in the market. Figure 3.1 shows a general mastercurve representing oxygen permeability versus the fractional free volume/cohesive energy density ratio for a number of plastics and the gas barrier properties at dry conditions for the bioplastics families for comparison purposes. The data indicate that some proteins and polysaccharides have excellent barrier properties under dry conditions, comparable with EVOH; however, under humid conditions these properties deteriorate to a much larger extent than for EVOH. On the other hand, thermoplastic biopolymers such as PLA or PCL are not as strongly affected by moisture but have lower barrier properties than for instance the benchmark PET. It is therefore of great interest, as explained above, to make functional monolayer food packages that reduce the moisture sensitivity of proteins and polysaccharides and increase the gas barrier properties of thermoplastic biopolyesters.

100 Thermoplastic biopolymers

10 Dry proteins Polysaccharide

1

PET PO2

HDPE

1

PVC

PA

0.

PK

0.0

EVOH

High barrier

0.00 0

0.000

0.00

0.001

0.00

0.002

FFV/CED

Fig. 3.1 Oxygen permeability (PO2) (cc mm/m2 day atm) versus the fractional free volume(FFV)/cohesive energy density (CED) ratio for a number of polymers and biopolymers typically used in packaging applications.



71

There are also a significant number of technological developments making use of existing materials and associated with modern packaging technologies aiming to tailor designs to specific performance and packagedproduct requirements. These developments include: (a) multilayer systems comprising various polymeric materials and made by lamination, coextrusion or co-injection; (b) aluminium metallized polymeric films obtained by vacuum deposition technologies; and (c) oxide (AlOx or SiOx)-coated polymeric films. Multilayer systems in the food packaging field usually consist of high gas barrier polymers like EVOH or polyamide (PA) sandwiched between structural layers of other polymers which usually provide the assembly with a high barrier to moisture as well as with other properties such as thermal, mechanical, optical or processing properties, printability, thermosoldability, etc. Coating plastics with vacuumdeposited aluminium aims to increase barrier properties to gases, moisture and organic vapours; it results in better flexibility, greater appeal to consumers and lower environmental impact due to the reduction in metal consumption and better recyclability compared with conventional lamination with aluminium foil. On the other hand, the metal coating of polymeric films imposes reductions in flexibility, stretchability and thermoformability compared with the performance of the polymer films alone. Moreover, aluminium coatings render the package opaque and cannot be microwaved. In order to circumvent these problems, oxide-coated polymer films can be obtained that exhibit transparency and high barrier properties, albeit they the coating is susceptible to microcracking during processing or handling. Apart from coatings, blending with other polymers and nanocomposites are the most commonly considered technologies in the manufacture of more efficient monolayer barrier systems for packaging.

3.4

Polymer blends: the case of permeable fillers

The blending of polymers is a feasible route for achieving the desired balance of properties by controlling the polymer phase interaction and/or morphology in monolayer barrier systems.33 The most commonly used method is to blend polymers with other polymers that have higher barrier properties. The barrier properties of these blends seem to follow a relationship (see equation [3.4]) that is in good general agreement with that proposed by Maxwell and extended by Roberson (see equation [3.4] and Fig. 3.2)34 for spheres of a low oxygen barrier phase (amorphous PA (aPA) in Fig. 3.2), but with higher water resistance, dispersed in a high oxygen barrier (EVOH in Fig. 3.2), continuous matrix which has a lower water resistance.35 This simple model would appear to closely reflect, albeit with a slight positive deviation (due to orientation, see Fig. 3.2), the case of the dispersed morphology found for this EVOH–PA blend.


72


aPA Simple additivity O2

PO2 (m3m/m 2s Pa)

1 × 10–19

1 × 10–20

O2 O2

1 × 10–21 0.0

EVOH blends

Maxwell equation Co-extruded multilayer EVOH32 0.2

0.4

0.6

0.8

1.0

EVOH volume fraction in the blend

Fig. 3.2 Modelling of oxygen permeability (PO2) for various EVOH–aPA blend components facing the transport of oxygen gas and as a function of volume fraction of EVOH. As an example, experimental data (see arrow) for 80/20 EVOH–PA and EVOH–ionomer melt-mixed blends developed in our laboratories are also provided.

The EVOH–ionomer blend presents even better barrier properties than predicted from equation [3.4] due to the fact that the morphology of the particles is elongated (higher aspect ratio) in the machine direction and normal to the permeation direction.  P + 2PEVOH − 2VaPA ( PEVOH − PaPA )  PEVOH/aPA = PEVOH  aPA   PaPA + 2PEVOH + VaPPA ( PEVOH − PaPA ) 

[3.4]

The permeability of blends following equation [3.4] would then approach the permeability of a co-extruded multilayer (see equation [3.5]) system comprising two layers, one made of a lower barrier disperse phase and the other of a high barrier matrix; therefore, the overall permeability will be close to the permeability of the neat high barrier matrix for a sufficiently high volume fraction of the matrix (VEVOH). Equation [3.5] is a very favourable situation in terms of permeability for a non-miscible blend. PEVOH/aPA =

PEVOH PaPA VaPA PEVOH + VEVOH PaPA

[3.5]

The circles on the graph in Fig. 3.2 represent the values of permeability obtained by application of a simple additive rule (layers parallel to permeant flow, see equation [3.6]). This case would clearly be a very unfavourable situation in terms of permeability for blends.


Thermoplastic nanobiocomposites for rigid and flexible packaging PEVOH/aPA = PEVOHVEVOH + PaPAVaPA

73 [3.6]

Figure 3.2 shows, as an example, some modelling for the barrier properties of EVOH–aPA blends as a function of blend composition and the orientation of the blend constituents in relation to the direction of oxygen transport. High barrier blends of EVOH with an ionomer and an amorphous polyamide have recently been developed in our laboratories.36,37 These blends show excellent barrier properties to gases compared with neat EVOH (see experimental values for EVOH 80/20 blends in Fig. 3.2), and yet much better thermoformability than EVOH alone for the production of thermoformed multilayer rigid food containers.35 Curiously, when the EVOH–aPA blend, which under dry conditions presented a lower barrier to oxygen, was subjected to typical packaged food water vapour sterilization (at 120 ºC for 20 min), it demonstrated better oxygen barrier properties than EVOH due the decreased water sensitivity of the system. There are also a relatively large number of blends reported in the literature where a high gas barrier polymer like EVOH was added to improve the barrier properties of a low gas barrier material and, conversely, where a high water barrier polymer was added to a high gas barrier material to reduce the relative humidity dependence in the barrier properties of the latter.36

3.5

Nanocomposites: the case of impermeable fillers

More recently, however, there has been a significant increase in the number of research works devoted to enhancing relevant polymer properties, mainly mechanical and barrier properties – but also surface hardness, UV-VIS (ultraviolet–visible light) protection, thermal stability and fire-retardancy – by means of nanotechnology. Nanotechnology is by definition the creation and utilization of structures with at least one dimension in the nanometrelength scale and which demonstrate novel properties and phenomena otherwise not displayed by either isolated molecules or bulk materials. Among the various existing nanotechnologies available, the one that has attracted the most attention in the food packaging field is inorganic layered nanocomposites. It has been broadly reported in the scientific literature that the addition of low loadings of nanolayered particles, with thickness in the nanometre scale and with high aspect ratios, to a raw polymer can have a profound enhancing effect on some material properties – such as mechanical properties, thermal stability, UV-VIS protection, conductivity, and gas and vapour barrier properties. Figure 3.3 shows typical modelling examples of permeability reductions in nanocomposites as a result of the application of the Nielsen and Fricke models (equation [3.5]) with different aspect ratios (L/W) to layered particles. The Nielsen model38 (see equation [3.7]), and other ulterior refinements such as that of Fredrickson and Bicerano,39 describe systems in which the


74

Environmentally compatible food packaging 1.0

L/W = 400, Nielsen L/W = 100, Nielsen O2 at 80% RH L/W = 100, Fricke L/W = 250, Fricke L/W = 400, Fricke d-Limonene

0.9 0.8 0.7 P/P0

0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.00

0.02

0.04

0.06

0.08

0.10

Volume fraction of filler

Fig. 3.3 Theoretical permeability reduction and some experimental permeability reduction values to oxygen and limonene found in poly(hydroxybutyrate) (PHB) by the authors. RH, relative humidity. P0, permeability of the unfilled material.

layered – i.e. thin, flat and squared – particles are perfectly oriented with length and width perpendicular to the permeant transport direction and are homogeneously diluted in the polymer matrix. 1 − Vclay Pnano = Pneat 1 + L V clay 2W

[3.7]

where L/W is the aspect ratio of the platelets, Vclay is the volume fraction of the clay filler, Pnano is the permeability of the nanocomposite and Pneat is the permeability of the pure material. The Fricke model40 describes oblate randomly oriented spheroids uniformly distributed across the matrix. Pnano 1 − Vclay = τ Pneat W = L

[3.8] 1

Vclay / (τ − 1) 0.785 − 0.616 − [Vclay / (τ − 1)] + 3

[3.9]

In equation [3.8], t is the tortuosity factor, which increases with increasing impedance efficiency of the clay filler. Equation [3.9] shows, in this model, the relationship between the volume fraction of clay, the aspect ratio and the tortuosity factor.



75

In this regard, gas and water vapour permeabilities have been found to decrease, in some cases to a large extent, in the nanocomposites due increased tortuosity factors, among other factors.41 For example, an ethylene propylene diene monomer (EPDM)–clay nanocomposite with a 4 wt% loading was found to decrease N2 permeability by 30% compared with EPDM alone.42 Oxygen permeability decreased by a factor of three in polyester–clay nanocomposites at 2.5 wt% loading. A 60% reduction in the water permeability was measured in a 5 wt% loaded poly(vinyl alcohol)– sodium montmorillonite (MMT) nanocomposite and the material still retained its optical clarity.43 In EVOH nanocomposites, reductions in oxygen permeability of more than 75% across a range of relative humidity values have been reported44,45 and reductions in water permeability of over 90% have also been reported in some proteins and polysaccharides.46 However, in general, the experimentally measured reductions in permeability have not been in full agreement with the values expected from modelling work for most systems, due to lack of complete exfoliation, insufficient compatibility, morphological alterations, penetrant solubility effects and other factors. Figure 3.4 shows the microstructure of a nanocomposite of PE containing nanolayers of NanoterTM (clay-based, food-contact approved, commercial clay grade of NanoBioMatters Ltd, Spain), in which a myriad of highly dispersed nanoshields constitute a definitive barrier to the passage of nondesirable permeants. Depending on barrier requirements, different particulate aspect ratios and modifications should be used. These one-dimensional nanoscale structures can display a high surface to volume ratio, which is ideal for applications that involve composite materials, chemical reactions, drug delivery, controlled and immediate release of substances in active and

100 nm

Fig. 3.4

Transmission electron micrograph of nanocomposites of HDPE.


76


functional packaging technologies and energy storage, for instance in intelligent packaging.44 Until recently, the most interesting packaging technology based on blending to generate barrier properties was the so-called oxygen scavenger technology. This technology is known to lead to relatively low levels of oxygen in contact with the food because it traps permeated oxygen from both the headspace and the outside. However in, for example, carbonated beverages, a barrier to carbon dioxide is also required. As most commodity plastic packaging materials, e.g. PET and its main sustainable counterpart PLA, are not sufficient barriers to these gases, multilayer structures had to be devised in which one layer (made of EVOH, aliphatic polyamide resin (MXD6), polyethylenenaphthalate (PEN), nanocomposites of PA6, etc.) needed to be high barrier to carbon dioxide and to oxygen, while the scavenger reduces oxygen levels at the package headspace. Nanobiocomposites technology can overcome this in monolayer solutions since barrier properties usually appertain not only to oxygen but also to other gases and low molecular weight components such as water vapour and food aroma components. Despite the fact that multilayer solutions are currently needed in many food packaging applications, including the above-mentioned carbonated beverages, a monolayer solution would be of great interest for many reasons, including recyclability and technology and material costs. Nanocomposites technology can also make this possible by simple melt or solution blending routes. For example, in PET bottles, the reason that nanocomposites are still devised to be used in multilayer systems is because the PET nanocomposites are extremely difficult to obtain in a monolayer form due to the high temperatures needed to process the polymer, which cause degradation of the organophilic chemical modification of the layered clay particles. Some sort of modification of the inorganic layered particles is needed in nanocomposites to facilitate exfoliation of these into nanolayers during processing and also to enhance compatibility with the polymer. In spite of this, new commercial clay formulations exist that are capable of producing high barrier PET nanocomposites by direct blending without degradation issues, therefore making monolayer formulations for PET possible.47 Another situation where ultrahigh barrier properties are needed is in high barrier food packaging applications, such as aromatic products, retortable pouches, dehydrated products and vacuum and some modifiedatmosphere packaging applications. In these and other similar applications, aluminium, EVOH or other high barrier materials and technologies are being applied. However, all of the existing technologies have associated drawbacks of some kind. While this is so, it would for instance be highly desirable to enhance the barrier properties of EVOH by 10-fold across the whole humidity range, making the material virtually impermeable in dry



77

conditions and capable of acting as a substitute for typical impermeable materials or technologies in many applications where transparency or more simple packaging structures represent added value. It is also a very important concern that most of the nanocomposite formulations (first-generation nanocomposites) on the market are currently making use of non-food-contact-permitted ammonium salts as organophilic chemical modifiers, and have been devised to enhance the properties of engineering polymers in structural applications. However, for food packaging applications only food-contact-approved materials and additives should be used, and should be incorporated at below their corresponding threshold migration levels. In this context, only the so-called secondgeneration nanocomposites claim to comply with the current food-contact legislation.46,48 Second-generation nanocomposites are therefore referred to as ‘nanocomposite formulations’; they are specifically designed to comply with current regulations and at the same time are cost-effective and specifically formulated to target specific materials (including biopolymers), materials properties or production technologies. In essence, second-generation nanocomposites are materials with targeted specifications rather than widespectrum generic formulations. Most applications of nanocomposites in plastics have made use of laminar clays and carbon nanotubes. However, there are other types of reinforcing elements, such as biodegradable fibres obtained by electrospinning, that are showing promise in a number of application fields.49,50 The electrospinning method is a simple and versatile technology that can generate ultrafine fibres, typically in the range of 50–500 cm3, of many materials. The fibres produced have a very large surface to mass ratio (up to 103 higher than a microfibre), excellent mechanical strength, flexibility and lightness. The procedure for obtaining these fibres is not mechanical but electrostatic and is applied to the polymer in solution or to polymer melts. As a result of the latter, it is a very suitable technique for the generation of ultrafine fibres of biodegradable materials, which are in general easy to dissolve.51 It has been reported that around 100 different polymers (including biopolymers) and polymer blends have been nanofabricated by electrospinning. In spite of the fact that there is a significant body of scientific literature reporting the characterization of nanofibres, there are not as many works reporting on the properties of nanocomposites made from materials containing these fibres. One of the most interesting aspects of the electrospinning methodology is the possibility of incorporating various substances, including fillers such as clays and also bioactive agents, in the electrospun fibres. The advantages of this nanotechnology have already been considered in the controlled release of bioactive principles in the pharmaceutical and biomedical fields and can also be applied to the controlled release of active and bioactive food packaging applications.


78

3.6


Nanobiocomposites for monolayer packaging: polylactic acid, polycaprolactone, polyhydroxyalkanoate and starch

Of the polymer–clay nanocomposite technologies, the case of the biocomposites containing biopolymers and clays is one of the most significant novel developments. The biopolymers typically considered for thermoplastic monolayer and also multilayer applications are PLA, PCL, PHA and starch. These materials have, however, a number of property shortcomings in terms of barrier, thermal and mechanical performance when compared with the conventional plastics currently used. The use of clay-based nanoadditives to boost their performance, particularly in barrier properties, is perhaps one of the most active areas of current and future research and, therefore, we pay special attention to reviewing the current status of the literature regarding the enhancement of barrier properties of thermoplastic biocomposites. For PLA, two techniques are frequently used to produce nanocomposites of this material, namely solution casting52,53 and melt mixing.54–63 The reports claim that, compared with neat PLA, the PLA nanocomposites show improvements in material properties such as storage modulus, flexural modulus, flexural strength, and heat distortion temperature, and also show improvements in gas barrier properties.60–73 Maiti et al.64 postulated that the barrier properties of non-interacting gases in nanocomposites primarily depend on two factors: one is the dispersed silicate particles’ aspect ratio and the other is the extent of the dispersion of these particles within the polymer matrix. When the degree of dispersion of the layered organoclay is at a maximum, an exfoliated morphology is attained and the barrier properties solely depend on the particles’ aspect ratio. Table 3.2 summarizes the reported improvements in oxygen and water permeability of the nanocomposites of PLA and of other thermoplastic biopolymers. Recently, Sinha Ray et al.61 claimed reductions in oxygen permeability of c. 65% for PLA + 4 wt% synthetic fluorine mica prepared by melt mixing. Nanocomposites with similar clay contents (4–7 wt%), but using a different kind of clay, showed less improvement in oxygen permeability, i.e. ranging from 6 to 56%.45,60,61,70,72,73 In summary, the barrier properties of PLA were found to depend strongly upon clay type, organic modification of the clay, clay content, clay aspect ratio, clay interfacial adhesion and clay dispersion. In the case of PHAs, Gardolinski et al.77 described the formulation of PHB nanocomposites. However, due to the high thermal instability of the polymer, the commercial applications of PHB have been extremely limited (see Table 3.2). Sanchez-Garcia et al.74 prepared nanocomposites of PHB and PCL by melt mixing with layered phyllosilicates based on commercial organomodified kaolinite and MMT clay additives. The addition of the PCL component to the blend was seen to reduce oxygen permeability and stiffness but it was also found to stabilize the PHB polymer during processing



79

Table 3.2 Reductions (%) in oxygen and water vapour permeability reported for nanocomposites of thermoplastic biopolymers

Matrix

Type of clay

PLA60 PLA60 PLA60 PLA61 PLA61 PLA61 PLA61 PLA70 PLA44 PLA72 PLA73 PLA73 PLA73 PLA73

Organically modified MMT Organically modified MMT Organically modified MMT MMT MMT-modified Saponite Synthetic fluorine mica MMT-layered silicate MMT-modified Bentonite Hexadecylamine-MMT Hexadecylamine-MMT Hexadecylamine-MMT Dodecytrimetil ammonium bromide-MMT Dodecytrimetil ammonium bromide-MMT Dodecytrimetil ammonium bromide-MMT Cloisite 25A (organically modified MMT) Cloisite 25A (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) Organomodified kaolinite-MMT NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) Organically modified mica-type silicate Organically modified mica-type silicate Organically modified mica-type silicate Organically modified mica-type silicate Cloisite 30B (organically modified MMT)

PLA73 PLA73 PLA73 PLA73 PLA23,46 PLA23,46 PHB74 PHBV46 PHBV46 PHBV46 PCL75 PCL75 PCL75 PCL75 PCL76


Clay content (%)

Reduction in O2 permeability (%)

Reduction in H2O permeability (%)

4 5 7 4 4 4 4 5 5 5 4 6 10 4

12 15 19 14 12 40 65 48 46 6 42 56 58 41

6

55

10

58

6

45

10

56

1

20

27

5

32

54

4

46

Dwater 72

50

1

61

5

60

5

28

52

1.1

11

2.5

39

3.6

59

4.8

80

2

35

80


Table 3.2 Cont’d

Matrix

Type of clay

PCL76

Cloisite 30B (organically modified MMT) Cloisite 30B (organically modified MMT) Cloisite 93B (organically modified MMT) Cloisite 93B (organically modified MMT) Cloisite 93B (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT) NanoterTM (organically modified MMT)

PCL76 PCL76 PCL76 PCL76 PCL23,48 PCL23,48 PCL23,48

Clay content (%)

Reduction in O2 permeability (%)

5

50

10

57

2

21

5

34

10

44

Reduction in H2O permeability (%)

1

47

5

63

10

63

and led to a finer dispersion of the clay. The study found that MMT clays can facilitate the degradation of the material and have therefore no commercial interest whereas kaolinite-based clays influence the inherent instability of the polymer to a much lower extent and can lead to property-enhanced nanobiocomposites. The study indicated that nanocomposites of PHB– PCL–kaolinite had better barrier properties to oxygen than the petroleumbased counterpart PET. The oxygen permeability was seen to be reduced by c. 43% at 0% relative humidity and by c. 46% at 80% relative humidity. The diffusion coefficient of water in the biocomposite was seen to drop by c. 72% compared with the unfilled polymer blend and the composites also exhibited higher barrier properties to limonene. Due to the above-mentioned instability of the PBH copolymer, researchers have mainly used lower melting temperature copolymers of PHB, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with improved chemical stability and good physical properties but with lower barrier properties. Again, solution-casting78–80 and melt-mixing74,79,80–82 routes were explored for the nanocomposites of this biopolymer, Sanchez-Garcia et al.23,46,48 reported an improvement in oxygen permeability of c. 28% in melt-mixed and casting material, compared with the unfilled material. They also reported reductions in water permeability of c. 52 and 60% for films of PHBV with 1 and 5% clay, respectively. In the case of PCL, four methodologies have been used to prepare nanocomposites containing PCL, namely polymerization in situ,83–87 solution-



81

casting,88 melt mixing75,76,89–96 and the master batch method.97 Table 3.2 summarizes the reported oxygen and water barrier improvements for these nanocomposites. Gorrasi et al.94 prepared nanocomposites of PCL with MMT by melt mixing. The barrier properties were studied for water vapour and dichloromethane as an organic solvent. Although the water sorption increased with increasing MMT content, the diffusion parameters of the samples showed much lower values in exfoliated systems. Messersmith et al.75 prepared nanocomposites with an organically modified mica-type silicate. The nanocomposite exhibited a significant reduction in water vapour permeability, which showed a linear dependence with silicate content. The significant decrease in water permeability observed for this system is of great importance in evaluating PCL and PCL nanocomposites for use in food packaging, protective coatings and other applications where efficient polymeric barriers are needed. The significant improvements in both barrier and mechanical properties of PCL nanocomposites could be attributed to the fine dispersion state of organoclay in the PCL matrix and the strong interaction between the organic modifier and the matrix. In starch, solution casting98–100 and melt mixing101–106 are also the nanocomposite technologies applied. In most cases, given the higher sensitivity of this material towards water sorption, attempts have been made to reduce water sorption in starch nanocomposites. Park et al.101,102 prepared nanocomposites of starch–organoclays by melt intercalation, with different natural MMT (Na+ MMT, Cloisite Na+) and different organically modified MMTs. The barrier properties to water vapour in the nanocomposites were found to be better than in the pure starch. In general, for the preparation of nanocomposites by solution casting the addition of a plasticizer has been considered a necessary condition. Kampeerapappun et al.98 prepared starch–MMT films by casting, using chitosan as a compatibilizing agent in order to disperse the clay in a starch matrix. Other nanocomposites99,100 of starch were prepared via different addition sequences of plasticizer and clay (Na+ MMT) by the solution method. Nanocomposites of starch with clay generally led to a decrease in hydrophilicity for the systems. Huang et al.103 and Huang and Yu105 prepared nanocomposites of starch– ethanolamine-activated MMT by melt mixing. From the results, the water absorption of the nanocomposites was also found to be reduced. Bagdi et al.104 prepared nanocomposites of thermoplastic starch and layered silicates organophilized with different surfactants, by the melt-mixing method. The equilibrium water uptake in an atmosphere of 50% relative humidity decreased by about 0.5–1.0% for composites containing 5 vol% silicate. The largest decrease in water adsorption was observed in the case of the neat Na+ MMT, for which laminate exfoliation was reported. De Carvalho et al.106 prepared nanocomposites with varying amounts of kaolin in thermoplastisized starch and observed a decrease in the water uptake of the nanocomposites.


82

3.7


Future trends and outlook

Several nanotechnologies are being trialled by an increasing number of material manufacturers and packaging converters. Nevertheless, for their wide commercial implementation and success they need to comply with current and future legislation and be designed to reach specific targets in materials and properties in specific food packaging applications. It is clear that there is still a lot of missing information in the food packaging sector regarding their use and potential in finished articles. However, the various nanotechnologies being currently developed will certainly have a wide range of applications given the fact that they make use of relatively inexpensive raw materials and that can have a strong impact on, among other factors, barrier, thermal and mechanical properties, without significant losses in impact resistance and while maintaining clarity. In the future, the above nanotechnologies will also have enormous potentials and synergies in new developments, for instance in providing intelligent, active and bioactive properties in addition to the current role as a passive barrier with enhanced thermal and mechanical performance.

3.8

Nomenclature

aPA EPDM EVOH HDPE LCP LDPE LLDPE MMT PA PAN PA6 PC PCL PE PET PHA PHB PHBV PK PLA PMMA PP PS

amorphous polyamide ethylene propylene diene monomer ethylene vinyl alcohol copolymers high-density polyethylene liquid crystal polymer low-density polyethylene linear low-density polyethylene montmorillonite polyamide polyacrylonitrile polyamide 6 (Nylon) polycarbonate polycaprolactone polyethylene polyethylene terephthalate polyhydroxyalkanoates poly(hydroxybutyrate) poly(3-hydroxybutyrate-co-3-hydroxyvalerate) aliphatic polyketone copolymers polylactic acid polymethyl methacrylate polypropylene polystyrene


Thermoplastic nanobiocomposites for rigid and flexible packaging PVC PVDC PVOH

3.9

83

polyvinyl chloride polyvinylidene chloride polyvinyl alcohol

References

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4 Improved fibre-based packaging for food applications J. Poustis, JPC Packaging Institute, France

4.1

Introduction

Demand for packaging for foodstuffs has soared as the agro-food industry has filled the space between agriculture and the consumer, first in the location of food processing, for example the move of butter production from farm to factory and also, more recently, in the development of pre-cooked and ready-to-heat meals. The rise in the numbers of restaurants and fastfood outlets has led to further industrialization in the food production line, and to changes in the cooking equipment used in homes. The packaging sector in Europe is estimated to produce 3 million tonnes of material per annum, and is becoming increasingly important in the agro-food and mass retailing industries – the mainstays of the food and drink sector. Food safety and quality are of paramount importance to consumers, manufacturers and regulators. Both can be influenced by the appropriateness of the packaging used and its performance throughout the logistics chain. Further development in the sector is likely to be fuelled by the higher safety standards for food and drink packaging required by EU regulations. Plastics account for 42% of total packaging materials used in Europe, followed by paper and cardboard (30%), glass (10%), steel (9%), aluminium (4.5%) and wood (3.6%). The use of plastic packaging is constantly increasing. Glass is used primarily for the beer market, particularly in the accession states, and the use of wood packaging remains small in all countries (source: http://www.foodproductiondaily.com) Some examples of packaging, taken from reference 1, are shown in Figs 4.1 to 4.3. Security, product protection, longer shelf-life and presentation are the basic requirements for packaging in the food industry. Among plastics,


Improved fibre-based packaging for food applications

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Fig. 4.1 Packaging in microflute for beer cans.

Fig. 4.2

Large range of packaging used for pet foods, from Nestlé Purina.

shrink bags and thermoformed packaging meet all of these requirements. Shrink bags have perfect shrinkage even at low temperatures, form an impermeable barrier and have a high-gloss surface printable in up to eight colours on either side. Thermoformed packaging materials represent the latest sensation. They lend themselves to transparent or glossy colours and high-quality product presentation, creating outstanding differentiation on the shelf. They are microwaveable and pasteurizable, and provide a highly impermeable barrier. They promote a long shelf-life and come in customized shapes and colours. Fibre-based packaging fulfils two main functions: • it acts as a protective and/or structural entity, particularly important in the distribution of goods; • it can display printed information. The basic function of fibreboard packaging is to protect products during distribution, right up to the point that the product is removed from the


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Fig. 4.3

Palletization of boxes.

Fig. 4.4 Regular slotted container for bottles of mineral water.

package by the consumer or user. The growing use of palletization (see Fig. 4.3) in distribution requires corrugated boxes with good stackability. Corrugated board is by far the commonest type of paper-based packaging in terms of tonnage, and is suitable for achieving high stackability. It has a lightweight rigid structure composed of liners separated by corrugated fluting papers. The pack shown in Fig. 4.4 is known as a regular slotted container. Issues in designing packaging for transport include positioning of the products within the packaging and cost-effectiveness in relation to packing and distribution logistics. Fibre-based board boxes are erected and packed manually or automatically. The packaging can be erected, filled and closed, or formed around the product and closed. Packaging today is not just about protecting and transporting products, but also about advertising and brand promotion. Printing technologies have been developed for packaging to take advantage of its potential as a communication medium, carrying information and artwork. The attractiveness of the print can be decisive in catching the customer’s eye. Of the total European production of corrugated board, 32% is used for food packaging, including transport packaging. If beverage packaging is included, this rises to 40% of the total European production. A significant



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Others 16 % Bakery and confectionery 7 %

Meat 10 % Frozen 7 %

Fig. 4.5

Fruit and vegetables 60 %

Corrugated board packaging in contact with food, data for Europe (source: FEFCO, Avenue Louise 250 B, 1050 Brussels).

proportion is used in direct contact packaging, but most of the applications are for trays for fruit and vegetables (Fig. 4.5). The volumes of corrugated board used for contact packaging vary widely by country across Western Europe, but in some areas may be as high as 20% of total production. The proportion of corrugated board used for other direct food-contact applications are for fatty/aqueous foodstuffs (pizza, burgers, french fries as fast food, fresh meat, poultry and fish), and for dry/frozen foodstuffs (bread, frozen meat, poultry and fish). Although a significant proportion of the total tonnage is not covered by legislation on direct food contact, some of this proportion may still be used in applications where food safety is critical.

4.2

Properties and uses of fibre-based food packaging

4.2.1 Standard properties Paper properties The papers used in the board industry are made from wood virgin fibres or from recovered papers. Packaging papers are defined by their structural properties, their mechanical properties and their water sensitivities. The basic properties of papers used in corrugated board are described in Table 4.1. Packaging properties The basic function of paper-based packaging is the same as for any packaging, namely to protect products during distribution up until purchase and use. Performance in areas such as stacking height or content protection are evaluated through various measurements (see Fig. 4.6); the most wellknown of these are described in Table 4.2.


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Table 4.1 Basic properties of papers Properties

Characterization

Nature of fibre Grammage Thickness Sheet density Strength Surface Orientation Water sensitivity

Virgin or recycled Basis weight (g/m²) Microns Porosity, IBT Burst, stiffness, compression, etc. Smoothness, brightness, gloss, etc. Machine/crossdirection Cobb, repellancy, etc.

IBT, internal bond test. Source: Poastis (2005).2

Table 4.2 Basic properties of packaging papers Properties

Characterization

Design Weight Stability Strength Surface Communicative Water sensitivity

Dimensions Grammage (g) Creep, fatigue Burst, stiffness, vertical compression Brightness, gloss, etc. Bar code, RFID Absorbance

Radio-frequency identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is an object that can be applied to or incorporated into a packaging for the purpose of identification using radiowaves. Some tags can be read from several metres away and beyond the line of sight of the reader. Source: Poastis (2005).2

Fig. 4.6 Compression tester measuring the vertical compression resistance of boxes, to investigate stacking height at 23 ºC, 50% relative humidity.



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4.2.2 Permeability to gases, including water vapour Permeability to gases is measured using a diffusion system developed to measure environmental gases at diffusion rates ranging from 50 to 105 ml/m2 per day. Measurements are carried out at temperatures between 5 and 50 ºC and with relative humidity between 0 and 30–90%. 4.2.3 Other properties Corrugated board packaging can be created that will allow microwave heating of foods. Other functionalities can be integrated: moisture isolation, anti-microbial uses, thermosealing, etc.

4.3

Innovative methods to improve fibre-based packaging for food applications

Innovative methods to improve fibre-based packaging for food applications include the following technologies: • extrusion of molten polymer (e.g. polyethylene) on to a paper base stock; • dip impregnation of paper into an aqueous polymer emulsion, solution in a solvent or bath of molten material (e.g. wax); • laminating paper with an aluminium film polymer; • off-paper machine application by metering rod, air-knife or blade coater; • on-machine application at the paper machine wet-end, size press or in-line coater. There are a broad range of coating types (see Fig. 4.7), including highbarrier polymer coatings (e.g. ethylene vinyl alcohol), polyolefin coatings (e.g. low-density polyethylene, linear low density polyethylene, high-density polyethylene, polypropylene or polypropene), other polymer coatings (e.g. polyethylene terephtalate), surface active agents such as fluorochemicals, wax-based products, water-based barrier coatings (e.g. acrylics) and, most recently, biopolymer coatings.3 Several trends dominate the sector. From a cost-benefit point of view, Polyethylene (PE) is still considered the best material. Fluorochemicals are still key additives, but there is a lot of discussion and debate around using fluorine-based products. Wax use is in decline, but there is some evidence of market growth in Eastern Europe. Water barriers come in a wide range of systems including innovative materials such as silicone or backing papers. The latest approach is surface modification using nanoclays and incorporating biodegradable polymers (compostable) to obtain high-barrier biodegradable packaging systems. Hybrid systems where cellulose fibres


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Other film 1%

Fluorochemicals 8% Silicone Wax 4% 2%

Water based 2.5 %

HDPE 2% PP 2% PE 79.5 %

Fig. 4.7 European market distribution of chemical products used to enhance fibre-based packaging for food applications in 2004 (source: G. Moore and N. Jopson, In: Future of Food and Drink Packaging for the European Market, PIRA International, Randalls Road, Leatherhead, Surrey, UK). PP, polypropylene; HDPE, high-density polyethylene.

and nanoclays are incorporated in a biodegradable polymer (polylactic acid (PLA)) are also being investigated.

4.4

Suitability of new fibre-based packaging materials for food packaging

Optimal packaging can extend the range over which food products can be transported and can prolong shelf-life. Packaging protects the food from mechanical damage, and from microbial and chemical contamination. 4.4.1 Characterization of packaging properties Various methods and standards are used for testing fibre-based packaging material. Water absorbency for paper, cardboard and corrugated board is tested using the cobb test and is based on standards ISO 535 and DIN 53132. Bursting strength is tested against standards ISO 2759, DIN 53141 and TAPPI T 807, and stiffness is tested against standards ISO 2493, and DIN 55437 and 53121. Air permeability and surface roughness are tested using the Bendtsen method, against standards ISO 5636/3 and 8971/2, and DIN 53108 and 53120; water resistance of the glue bond is tested by time to failure on immersion in water, standard ISO 3038-1975. Permeability specifications 1 Oxygen permeability. Sensitivity from 0.005 to 155.000 cc/m2 day. Temperature range within the cell from 5 to 50 ºC. Relative humidity range within the cell, 0% or from 35 to 90% relative humidity. Standards ASTM F1927, ASTM D3985 plastics and ASTM F1307.



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Water vapour permeability. Sensitivity from 0.005 to 500.000 g/m2 day. Temperature range within the cell from 5 to 50 ºC. Relative humidity range within the cell 100% or from 35 to 90% RV. Standard ASTM F1249. 3 Combined permeability for carbon dioxide, oxygen and nitrogen. Sensitivity: carbon dioxide, from 0.10 to 10.000 ml/m2 per day; oxygen, from 0.01 to 10.000 ml/m2 per day, nitrogen, from 0.30 to 10.000 ml/m2 per day. Temperature range within the cell from 0 to 70 ºC. Various ISO, DIN and ASTM standards.

2

UV ageing Standards ISO 4892 Plastic; ASTM G154, D4587, D4329; BS 2982; SAE J2020; General Motors TM-58-10. Transport simulations Drop and shock tests for packages; standard NBN EN 22248. Hydraulic vibration tables are used for transport simulation tests on packages and other objects. Vibration ranges from 0 to 200 Hz, acceleration 2G, maximum speed 30 cm/s; standards ASTM 4728, D3580, NBN EN 22247 and 28318. Electro-dynamic shakers are used to test components at vibrations from 10 to 2000 Hz, with a maximal displacement of 12.7 mm, acceleration 100G, maximum speed 165 cm/s; standards MIL-STD-810E, IEC 68. 4.4.2 Safety testing Packaging papers that will be in contact with food must have their safety and quality certified within an overall Hazard Analysis and Critical Control Point analysis. Certification also promotes the development of new and improved methods to reduce or eliminate the presence of specific, potentially harmful substances. Heavy metals can be poisonous, and those relevant to packaging papers are chromium, cadmium, lead and mercury. Special equipment (see Fig. 4.8) is used to measure the migration of heavy metals from packaging into food contents, using chromatographic techniques. Water, iso-octane and ethanol are used to simulate the food for migration tests. Organic contamination includes compounds such as polychlorinated biphenyls (PCBs) and pentachlorophenol (PCP). Gas chromatography and mass spectrometry are used to analyse the amounts of these compounds in the packaging (see Fig. 4.9). For packaging that will be in contact with wet or fatty foods, the migration of toxins from packaging to food is of particular importance, and it must be demonstrated that the packaging is free from toxins such as phtalates, di-isopropylnaphthalene, PCB and others. When the presence of volatile compounds – such as bromoanisols (monobromoanisol CH3OC6H4Br, dibromoanisol CH3OC6H3Br2 and tribromoanisol CH3OC6H2Br3) – is measured, the analytical machinery must include a headspace


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Fig. 4.8

Equipment for measuring migration of heavy metals from packaging.

Fig. 4.9 Gas chromatograph and mass spectrometer.

injector to detect these compounds in the atmosphere around the packaging itself. Microbiological or bacteriological contamination is another critical area for food packaging safety that sees constant development and improvement in processes. Again, packaging for wet or fatty foods is of particular importance, and the paper must be demonstrated to be free from pathogenic micro-organisms (see Fig. 4.10). Laboratory tests include the quantification of bacteria, yeast and moulds in and on the surface of the



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Fig. 4.10 Sample of paper in a Petri dish for yeast and mould counts. The standard for yeast and moulds on the surface is DIN 54378.

paper, and identification of the most common pathogenic micro-organisms (Listeria, Salmonella, Bacillus, Clostridium perfringens, Escherichia coli, Staphylococcus, etc.). Microbial contamination can be measured using a continuous flow luminometer with auto-tracking which automatically monitors contamination, taking measurements in continuous and real time using adenosine triphosphate bioluminescence technology (see reference 4). Some paper mills monitor microbial contamination by measuring the presence of aerobic bacteria, anaerobic bacteria, yeast and mould, and also monitor dissolved oxygen, redox potential, pH and temperature in water, pulp and additives to keep a close check on any possible contamination. Biological problems with packaging can affect odour and taste, and some paper mills have water treatment plants to prevent the formation and growth of slimes and filamentous bacteria, which can contribute to odour and taste problems. 4.4.3 Regulations on packaging for food contact Suppliers and users of paper and board packaging must comply with national regulations implemented in each member state under the umbrella of the European Framework Directive. Users often ask producers to certify the suitability of their papers for food contact, and this is generally done with reference to the United States Food and Drug Administration Regulations and, in some countries, to the German Recommendations of the BgVV (No. 36). In order to improve the environmental performance of packaging products, various aspects have to be taken in account, as described below.


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European Directive 89/109/EC This directive concerns the laws of member states relating to materials and articles intended to come into contact with foodstuffs: the framework directive has been transposed into the legislation of each member state of the European Union. The framework directive envisages a specific directive for each material type, but so far only plastics, regenerated cellulose and ceramics are covered by the directive. It was replaced in 2004 by EC No. 1935/2004 (http://www.food.gov.uk/consultations/consultni/2005/foodcontactni2005). Paper and board have been the subject of work in the Council of Europe, which is now finalizing a Resolution or Policy Statement. The relevant technical documents are: • the Good Manufacturing Practice Guide, which refers to the implementation of good hygiene standards throughout the process. • the inventory of substances that may be used in board manufacturing (chemicals, additives, etc.). • guidelines on recycled fibres that restrict the use of recovered paper in papers that will be in contact with fatty or aqueous foodstuffs to classes of material not normally used in papers for corrugated packaging. In producing corrugated packaging for fruits and vegetables, all grades of waste paper can be used, the only requirement is a specification for the content of PCP, which must be below 150 ppb. For packaging that will be in contact with other dry foodstuffs, and those with no fatty contact, all grades of waste paper can be used, but they must comply with specifications regarding the level of PCP, phthalate, polycyclic aromatic hydrocarbons and benzophenone. Currently, the use of recycled papers in any of the layers of corrugated board for applications such as pizza boxes is not regulated. Some 160 000 tonnes of corrugated board is estimated to be used in Europe for such applications per year. European Directive 89/109 (21/12/1989) This directive concerns the use of active (treated) packaging that is in contact with food, and the inertia or resistance of the packaging to the substances used to confer the particular active properties. It defines the following for each compound: • list of substances regulated: positive list of substances permitted for use; • purity criteria of these substances; • particular conditions of use; • specific migration limit; • global migration limit. The development of active packaging has been limited. European Directive 89/109 has been amended to include active packaging systems within the current relevant regulations for food packaging in Europe.



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Legal requirement for traceability Traceability was included in a revision of Directive 89/109/EC (All Materials). The traceability of materials and articles must be ensured at all stages in order to facilitate and control the recall of defective products, consumer information and the attribution of responsibility. • Article 17(2) states that ‘. . . business operators shall have in place systems and procedures to allow identification of the businesses from which and to which materials or articles . . . used in their manufacture are supplied. That information shall be made available to the competent authorities on demand.’ • Article 17(3) states that ‘The materials and articles which are placed on the market in the Community shall be identifiable by an appropriate system which allows their traceability by means of labelling or relevant documentation or information.’ European Directive 94/62 (20/12/1994): management of packaging waste This directive permits reduction in the weight of the packaging but not in the weight of the individual papers. The tendency is towards lighter-weight papers, but lighter papers do not always meet performance requirements. The paper industry meets the maximum targets of use of recovered and recycled papers required under the current directive. The level of heavy metals is far below the 100 ppm specified in the same directive. Last but not least, paper packaging is easily recyclable and energy can be recovered. Essential notification requirements for the packaging include manufacturing and composition, re-use specifications, and recycling, energy recovery, composting and biodegradability information. 4.4.4 Environmental considerations Wood and paper products are part of an integrated cycle based on photosynthesis, in which water, carbon dioxide, nutrients and solar energy are converted into renewable woody biomass. After use, wood and paper products may start a new life as a secondary raw material or biofuel. Virgin and recycled fibre products are complementary, and are not used separately. The optimum level of recycling depends on a number of economic, social and environmental aspects, such as geographical location, potential for collection, technical limitations to recycling, etc. In addition, the long-term use of wood-based products represents a potential reservoir of carbon removed from the atmosphere. Technologies exist or are being developed for benchmarking and specific analysis to support Europe-wide regulations. Among these are specifications for the polymer contents of bag-in-box liquid packaging systems, research into new polymers for bag-in-box packaging, identification of the components responsible for specific odours in paper


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and quantification of traces of organic components as required by regulations.

4.5

Assessing the biodegradability of new fibre-based packaging materials for food packaging

4.5.1 Biodegradable packaging Definition Many materials decompose in the environment over a relatively long period of time and the production of biodegradable packaging is important. Thus it is essential to develop a cost-effective material that has good biocompatibility and the necessary mechanical properties for packaging use. The development of eco-friendly materials with the desirable mechanical properties must take into account deterioration due to environmental factors such as water, atmospheric oxygen, sunlight and biological agents. Cellulose polymer packing Cellulose composites from renewable resources show promise with regard to the above-mentioned factors. Pure cellulose polymers are of great interest due to their cheap availability and general environmental degradability. Figure 4.11 shows important benchmarking results for biodegradation with objective composting, comparing pure cellulose (Avicel), a standard kraft paper (SK), a dual-system starch–plastic (Mater Bi) and a standard synthetic-base plastic (ABA). Packaging used for the collection of agrofood wastes is shown in Fig. 4.12.

Biodegradation (%)

Composite plastic packaging Packaging suppliers have started introducing various forms of biodegradable plastics made from a variety of plants, in the main corn, based on projections for a growing demand for environmentally friendly packaging. 100 90 80 70 60 50 40 30 20 10 0

Avicel 0

Fig. 4.11

10

20

SK paper 30 Days

Mater-Bi 40

ABA 50

60

Biodegradation of different packaging materials. ABA, plastic grocery bag.



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Fig. 4.12 Bags for fermentable wastes. Composite paper coated with Sweamcoat® inside the bag, to create a barrier to liquids.

Biodegradable plastic packaging made from PLA is the ideal solution for customers, brandowners and retailers who wish to use bioplastics. The switch to biodegradable packaging is driven by environmentally conscious consumers and recycling regulations. Some companies are predicting that the market will grow by about 20% a year. The development of bioplastics is also being pushed by the recent escalation in the price of oil, which is bringing traditional, petroleum-based polymers into the same cost range as the previously more expensive bioplastics. Food packagers last year faced price hikes of 30–80% for conventional plastics due to the increased cost of petroleum. Like food products themselves, packaging materials are constantly evolving to meet the latest demands of the marketplace. Food scientists, materials specialists and others are continually attempting to improve current packaging materials and develop new ones with optimal barrier properties. Biodegradable films made from cellulose, pectin and starch are in development.

4.6

Applications and future trends in the food industry

4.6.1 General issues Improvement of barrier products A new barrier product named Sweamcoat® was developed in France in the 1990s. Figure 4.13 compares Sweamcoat® to other solutions. Nanocomposites Sustainable nanocomposites as barriers are being investigated, both as intermediates and end products. Important barrier properties include their thickness, weight, strength, conductivity/isolation and dynamic barrier and optical qualities. Nanofibres are manufactured from wood and non-wood cellulose materials, and compounds including nanocomposites from these


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Environmentally compatible food packaging NO coated 2000 g/m2 24 h

Vapour barrier (g/m2 × 24 h)

2000

38 °C’ 90 % RH 1500 Varnish 1000 g/m2 24 h 1000 Sweamcoat ® 120 g/m2 24 h

500

0

0

1

2

3

4

5

Barrier film 100 g/m2 24 h

PE extrusion

6 7 8 Dry deposit (g/m2)

9

10

11

12

Fig. 4.13 Permeabilility (moisture vapour transmission rate (MVTR)) of different barrier products versus amount deposited.

fibres and various polymeric matrices (both bulk and engineering plastics) are created in granules and multilayer sheets, optimizing the relationship between fibre–matrix compatibilization and mechanical properties like stiffness, strength and impact resistance. Controlled release and innovative coatings The controlled release of active substances, such as natural anti-microbials, can extend shelf-life or make the product more attractive (odour release), which contributes to marketing and selling the product. This activity can be integrated with innovative coatings. These coatings can be used for several other purposes, including barrier functions, strength and visual improvement of packaging layers. Modelling and simulation of packaging use In the case of microwave packaging, the thermodynamic behaviour of food products in a microwave can be simulated through detailed numerical models. These models can be used for package development (package form and material positioning) aimed at homogeneous product defrosting and re-heating in microwaves. For this purpose, the research institute Agro-Technology Organisation in The Netherlands has developed a numerical model that predicts temperature homogeneity for simple product shapes. Consumer-oriented design Consumer-oriented design aims at a total concept, which encompasses consumer behaviour, packaging, product quality, safety and distribution. Integrating these disciplines in the right modelling/software tool will



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increase the chance of creating packaging that will encourage the consumer to buy a new product. Logistics and supply chain management Packaging development also aims at logistics and supply chain management. This must be based on a knowledge-based system that contains models of agro-product and agro-process performance indicators (such as capacity use, service levels, queue behaviour, timeframes in cool-fresh production, etc.). Life cycle assessment and recycling strategies Life cycle assessment aims at integrating and designing the entire materials processing chain from manufacture, utilization and recycling to the final end destination. 4.6.2 Specificity of active packaging Active packaging offers more than simply protection. It interacts with the product and in some cases responds to environmental or product changes. Packaging meats The main criteria for selecting packaging for meats are how the fresh ingredients are processed and the required shelf-life. Automated processes significantly reduce human contact with the meats and so are more hygienic. The packs should be attractive, 100% leakage free and efficiently designed. Special gas-filled packaging can be used for extra long shelf-life for minced meat, burger products, enhanced meat and other cuts (see Fig. 4.14). Ready meals Consumers love convenience. Complete ready meals are gaining in popularity. Fully automated solutions for filling, dosing and packaging put these meals together in a smooth and efficient process, using either preformed or thermoformed trays. Preparation, processing and packaging takes place in one location, and the objective is to produce attractive, safe and tasty

Fig. 4.14 Meat packed in composite packaging (paper base and plastic bag).


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Fig. 4.15 Ready to prepare – cooking a composite meal.

Fig.4.16

Sliced portions of meat, cheese and sausage.

ready meals in striking packaging. Ready meal solutions apply to frozen and fresh meals, salads and pasta products. Meal components Snacks and other fully cooked products can be prepared safely and quickly if the packaging is designed to permit the correct heat treatment to ensure food safety. Meal component solutions may include coated products, sliced/ diced products (Fig. 4.15) natural poultry products, fully cooked roasted meat, burger products, and sausage products. Sliced products Sliced meat, fish and cheese are packaged in shingled, stacked or shaved presentations. The latter option ensures an airy, attractive presentation that also enhances the taste. Sliced products must be prepared and packaged under efficient and strictly hygienic conditions (see Fig. 4.16). 4.6.3 Future trends Consumer demands for convenience and health are the two trends fuelling growth in the food industry. Busy lifestyles are opening avenues for developing packaging solutions that are safe, easy to open and convenient to use. Manufacturers are focusing on developing packaging solutions that cater



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to single and two-person households. A steam-cooking valve can be incorporated into packaging for ready meals. The contents can be steam cooked in the microwave, thus retaining flavour, texture and vitamins. An integrated valve closure allows the food to be steamed under pressure, which shortens preparation time and ensures that the product remains moist. Another solution combines new sealing layers to provide high-barrier packaging, along with a surface that allows printing for a striking appearance. Strong seals permit the use of a method that removes oxygen and fills the packaging with more stable gases, which increases the shelf-life of fresh and refrigerated food products. This is an advantage when targeting consumers looking for convenience as well as freshness. Packaging that combines modified atmosphere packaging with a steamcooking valve is the latest technology, prolonging the shelf-life of refrigerated products packed in pouches or trays. This packaging is also suitable for the latest generation of autoclaving systems, which ensure precise pressure and temperature control in the retort process.

4.7


Other sources: European Directive 89/109/EC: European framework regulation for materials in food contact. European Directive 89/109(21/12/1989): Global Approach to conformity assessment. European Directive 94/62(20/12/1994): Management of packaging waste. Web addresses:

4.8

References

1 j. poustis, Issues and new challenges of paper and board packaging, ATIP Annecy Conference: Modelling, simulation and decision support systems for process optimisation and industrial competetiveness, 27–29 April (2005). 2 j. poustis, Corrugated fibreboard packaging, in Paper and Paperboard Packaging Technology, Ed. M. Kirwan, Blackwell Publishing, Oxford, UK, pp. 317–372, (2005). 3 sustainpack eu program, Innovation and Sustainable Development in the Fibre Based Packaging Value Chain, Newsletter Plus, Issue 3 January, 2006 (http://www. sustainpack.com/newsletters/sustainpack_newsletter_03.pdf). 4 j. poustis, A new method for microbial contamination control within the paper mill water system, 7th Pira Recycling Conference, Paper Technology, 44 (4), 29–32 (2003).


5 Starch-based edible films Y. Zhang and Z. Liu, University of Manitoba, Canada; J. Han, Frito-Lay, Inc., USA

5.1

General properties and structure of starch

Commercially important starch is obtained from corn, wheat, rice, potatoes, tapioca and peas. Starch is a polysaccharide that is produced in almost all plants by photosynthesis. Naturally occurring starch is present in the form of semicrystalline granules, which vary in shape (round, lenticular, polygonal), granule size (1–100 µm in diameter), size distribution (uni- or bimodal), association (individual or granule cluster) and chemical composition (α-glucan, lipid, moisture, protein and mineral content) (Tester et al., 2004; Mali et al., 2006). Starch consists of two components, namely amylose and amylopectin. Amylose is a mostly linear α-d-(1 → 4) glucan, the molar mass of which is several hundred thousand g/mol. Amylopectin is a highly branched α-d-(1 → 4) glucan, with α-d-(1 → 6) linkages at the branch points. The molar mass of amylopectin can be as high as 100 million g/mol. The content of amylose depends on the plant source and can vary from 14 to 27 mass%. For example, the ‘waxy’ starches contain less than 15% amylose, ‘normal’ starches contain 20–35% amylose and ‘high’ amylose starches contain more than 40% (Tester et al., 2004). Both amylose chains and branches of amylopectin can form double helices, which may in turn associate and form crystalline domains (Tester et al., 2004). The degree of crystallinity within starch granules has been historically determined with X-ray diffraction (XRD). Maize starch granules exhibit 43–48% crystallinity; wheat, 36–39%; potato, 23–53%; pea, 17–20%; normal barley, 2–24%; rice, 38% (Tester et al., 2004). The application of XRD can also reveal the types of crystallinity due to the amylose content of starch, the starch origin, the transformation process (thermomoulding, extrusion


Starch-based edible films

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A type B type

Water

Fig. 5.1

A- and B-type polymorphs of amylose (from Wu and Sarko, 1978).

or casting) and the additives. Three XRD patterns exist in native starch granules. Cereal starches (rice, wheat and corn) exhibit an A-type pattern, in which the double helices pack in an anti-parallel manner into an orthorhombic unit-cell (Fig. 5.1), resulting in nearly hexagonal close-packing. Tubers, fruit and high-amylose corn (>40%) starches show a B-type pattern, and retrogradation starch – in which the double helices pack also in an anti-parallel manner but into a hexagonal unit cell with two helices per cell, leaving an open channel that is filled with water molecules (Fig. 5.1). The C-type pattern, which is intermediate between the A and B types, is observed for legume seed starches (Abd-Karim et al., 2000; Liu, 2005). The A, B and C type of XRD patterns are shown in Fig. 5.2. Starch contains 2% integral lipids in the form of lysophospholipids and free fatty acids, 0.6% protein and 0.4% minerals (calcium, magnesium, phosphorus, potassium and sodium). Starch is hydrophilic; its moisture content depends on the relative humidity (RH) of the atmosphere in which it is stored. The moisture content of starch at equilibrium in ambient air ranges from 10–12% for cereal starch to 14–18% for starch from some roots and tubers (Tester et al., 2004). Starch has seen very wide applications, such as in thickeners, pastes, etc. One of its advantages is its renewability, since it is produced by plants annually. Starch is also biodegradable. Its properties can be changed and adjusted to meet various purposes. Many properties of starch are close to those of synthetic polymers. Therefore, it is possible to use the processing methods for synthetic polymers for the processing of starch. Starch has been used as biodegradable filler for commercial thermoplastic polymers. There has been a growing interest in obtaining thermoplastic starch containing relatively low amounts of additives. Thermoplastic starch can be used for the production of articles unlikely


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B

Intensity

A

(a) (a) (b) (b)

(c) 0

5

(c) 10

15

20

25

Diffraction angle (2θ°)

30 0

5

10

15

20

25

30


Fig. 5.2 XRD patterns for (a) A-type (wild-type maize), (b) B-type (wild-type potato) and (c) C-type (wild-type pea) starches, using a fixed-slit (A) and an automatic divergence slit (B) diffractometer (from Bogracheva et al., 1999).

to be recycled, such as trash and compost bags, mulch films and disposable diapers (Jovanovic et al., 1997). Most recently, starch-based films for food packaging have received increasing attention from food industries and food scientists.

5.2

History of edible films

Edible films and coatings were used hundreds of years ago. For example, wax has been applied to citrus fruits to delay their dehydration since the twelfth and thirteenth centuries in China (Debeaufort et al., 1998). Yuba obtained from the skin of boiled soy milk, essentially a protein film, was used to preserve the appearance of some foodstuffs in Asia in the fifteenth century (Debeaufort et al., 1998; Han and Gennadios, 2005). In the sixteenth century, fats were used to coat meat cuts to prevent shrinkage. Lard or wax was used to enrobe fruit and other foodstuffs in England (Miller and Krochta, 1997). Later, in the nineteenth century, gelatin films were used to cover meat stuffs. Also in the nineteenth century, sucrose was chosen as an edible protective coating on nuts, almonds and hazelnuts to prevent oxidation and rancidness (Debeaufort et al., 1998). In the last 30 years, petrochemical polymers, commonly called plastic, have been the most widely used materials for packaging because of their high performance and low cost (Callegarin and Quezada-Gallo, 1997). However, the serious environmental



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problems associated with their non-biodegradability have urged scientists to search for new alternative materials (Petersson and Stading, 2005). Thus, edible or biodegradable packagings made from various biological resources and their applications have recently been investigated. Shellac and wax coatings on fruits and vegetables, zein coatings on candies and sugar coatings on nuts are the most common commercial examples of edible coatings (Han and Gennadios, 2005). Cellulose ethers (carboxymethyl cellulose, hydroxypropyl and methylcellulose) have been used as ingredients in coatings for fruits, vegetables, meats, nuts, confectionery, bakery, grains and other agricultural products (Han and Gennadios, 2005).

5.3

Edible film materials and their previous applications

Environmental concern about the use of synthetic plastics for food packaging has led to increased interest in biodegradable and edible film research (McHugh et al., 1993; Lai and Padua, 1997). Both dehydration and growth of microbial organisms in food products have been delayed by using edible and biodegradable films and coatings. Moreover, the flavor, odor and overall organoletic characteristics were not modified. Many materials from biological resources have been used for edible or biodegradable film and coating formulations, such as polysaccharides, proteins, lipids or their mixtures (Debeaufort et al., 1998). Waxes and oils (mineral oils, paraffin, beeswax, shellac, etc.) were used largely as coatings on fruits, such as oranges, lemons, apples, pears, etc.; they create a really efficient barrier to water and can prevent weight loss. Polysaccharides used in edible or biodegradable films and coatings include cellulose, starch, pectin and algal gum. Proteins from various plant and animal sources – including wheat gluten (Kayserilioglu et al., 2001), soy protein, zein (Lai and Padua, 1997; Lai et al., 1997) and milk protein (Letender et al., 2002) – have also been used in edible films. Lipids and their derivatives are mainly used in films or coatings to improve their moisture barrier properties. The properties of edible films depend on the type of film-forming materials and especially on their structural cohesion. Additives – such as plasticizers, cross-linking agents, anti-microbial agents, anti-oxidants and texture agents – are used to alter the functional properties of the films. Among the natural polymers, starch has been considered as one of the most promising candidates for future materials because of the attractive combination of price, availability and thermoplasticity (Lai and Padua, 1997; Mali et al., 2005a). Starch-based resins have been made into compost bags, disposable food-service items (cutlery, plates, cups, etc.), packaging materials (loosefill and films), coatings and other specialty items (Lai et al., 1997). Edible films and coatings from starch mainly find applications in the meat, poultry, seafood, fruit, vegetable, grains and candies industries (Debeaufort et al., 1998).


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Currently, the use of edible films is still limited in practical applications due to their hydrophilic properties. Some efforts have been made to improve the moisture resistance and water barrier properties of the edible films by combining with synthetic polymers or lipids and biopolymers (Han et al., 2006). Protein and polysaccharide edible and biodegradable films present a good ratio between CO2 and O2 permeabilities at from 10 to 25; the ratios of plastic films are lower than 5. Therefore, these films can be served as modified atmosphere packaging (MAP) materials to control the ripening of fruits and vegetables. Indeed, the use of zein coatings has already been reported for tomatoes, with delayed color, weight and firmness changes (Debeaufort et al., 1998). For confectionaries, edible or biodegradable films and coatings were found to be very efficient at reducing lipid oxidation and permeability. Many functions of edible or biodegradable films and coatings are the same as those of synthetic packaging. However, the films and coatings must be chosen according to the specific application, the type of food product and its main deterioration mechanisms (Guilbert, 2005).

5.4

Starch film-forming mechanisms – gelatinization and recrystallization

Often, the first step in the production of starch films is heating starch in water. When heated at high water content, starch is gelatinized and transformed from a semicrystalline granular material into a system containing granular remnants, or to an amorphous paste with no structure at all (Smits et al., 2003). The process is termed gelatinization, which corresponds to an irreversible swelling and breakage of starch granules, and leaching of amylose and amylopectin into the solutions. A gradual dissolution of starch granules allows a further hydration up to a point where the whole structure of the starch granules is completely disintegrated (Endres et al., 1994). Often, non-crystalline swollen granular remnants named ‘ghosts’ remain even after a long period of gelatinization (Fig. 5.3) (Smits et al., 2003;

100 µm

Fig. 5.3 Remaining starch granules on the surface of pre-gelatinized pea starch films containing fructose (from Zhang and Han, 2006b).



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Mehyar and Han, 2004; Mathew et al., 2006; Zhang and Han, 2006b). Studies have shown that the presence of sugars in the water increases the gelatinization temperature of starch. Various mechanisms have been proposed to explain this, including the ability of sugar to compete for water against starch, and the ability of sugars to reduce water activity in the system, resulting in a reduction in the plasticizing effect of the sucrose–water solvent (Maaurf et al., 2001). At temperatures higher than the glass transition temperature (Tg), starch materials are in a rubbery state, and retrogradation (or recrystallization) occurs easily when gelatinized starch is stored at high RH or high plasticizer contents (Delville et al., 2003). In the rubbery state, high RH or high plasticizer content favor starch macromolecular mobility, which facilitates the development of crystallinity (Delville et al., 2003). Recently, the mechanism of starch retrogradation has been extensively investigated. Starch retrogradation occurs as a result of intermolecular hydrogen bonding between O-6 of d-glucosyl residues of amylose molecules and OH-2 of d-glucosyl residues of short side-chains of amylopectin molecules (Fig. 5.4) (Tako and Hizukuri, 2002). It can be attributed to intermolecular hydrogen bonding between OH-2 of d-glucosyl residues of amylose molecules and O-6 of d-glucosyl residues of short side-chains of amylopectin molecules (Fig. 5.5). In addition to intermolecular hydrogen bonding between amylose and amylopectin, hydrogen bonding between O-3 and OH-3 of d-glucosyl residues

AP

H O H2 C ω

O

O

H O H2 C ω

HO OH

O

H

O O H2 C ω

AY

OH O

O H

O

HO

O H2 C ω

HO OH O

O

HO OH O n

Fig. 5.4 Hydrogen bonding between amylose and amylopectin molecules (dashed lines represent hydrogen bonds; AY, amylose; AP, short side-chains of amylopectin molecules) (from Tako and Hizukuri, 2002).


114

Environmentally compatible food packaging H O H2 Cω O

AP O HO

OH

H

O O HO H2 Cω O

H O H2 Cω O

AY

OH O O H2 Cω O

H

O HO

OH

AP

O HO

O H HO O H2 Cω O

OH O H O H2 Cω O

OH O HO

OH O

Fig. 5.5 Retrogradation mechanism of starch (dashed lines represent hydrogen bonds; AY, amylose; AP, short side-chains of amylopectin molecules) (from Tako and Hizukuri, 2002).

on different amylopectin molecules may also occur (Fig. 5.6) (Tako and Hizukuri, 2002). Intramolecular association of amylopectin molecules was not suggested to exist, while intramolecular hydrogen bonding might take place between OH-6 and adjacent hemiacetal oxygen atoms of the dglucosyl residues within the amylose molecules (Tako and Hizukuri, 2002). The mechanism of starch retrogradation is commonly represented as shown in Fig. 5.7 (Delville et al., 2003). The scheme in Fig. 5.7 represents the crystalline cluster formation of amylopectin. The cluster formation begins with the formation of crystalline lamellae composed of double helices of amylopectin short chains (represented by rectangular boxes). Then, the packing of double helices forms crystalline clusters (Delville et al., 2003). The effect of various plasticizers on the crystallinity has been studied. Increased water content increases the degree of crystallinity and the kinetics of crystallization, while increased glycerol content slows the crystallization kinetics in starch amorphous rubbery amylopectin systems (Delville et al., 2003). Crystallites may act as physical cross-linking points that generate internal stresses or cracks which lead to damage of the starch products (Delville et al., 2003). Therefore, while crystallinity increases, elongation (E) decreases drastically, and tensile strength (TS) and modulus of elasticity (EM) increase. Reportedly, a B-type polymorph of the crystallite develops in the aged gel


Starch-based edible films AP

A

115

B2

A

A B3 B1 B1

A B1 A

B2

B1 AY A

B2

A AP

A B3

A

B1 B1

B1 A

B2

B1

AP

A A

B2 A B3

A

B1 B1

B1 A

B2

B1 AY A

B2

A AP

A B3

A

B1

B1

B1

A

B2

B1

Fig. 5.6 Association between amylose and amylopectin molecules (dashed lines represent the hydrogen bonding sites). Two or more short-chains of amylopectin molecules may interact with one amylose molecule. Self-association within amylopectin molecules may also take place (from Tako and Hizukuri, 2002).

of all starches, irrespective of their pattern of crystallinity in the natural state (Abd-Karim et al., 2000). However, the type of polymorph developed in aged cereal starch gel may also depend on water content. Samples containing more than 43% moisture develop the B-pattern on aging, whereas those containing less than 29% moisture develop the A-pattern (Abd-Karim et al., 2000). The crystallite structure of starch films is often analyzed using an X-ray diffractometer, equipped with a 1º divergence slit and a 0.1 mm receiving slit, between 2θ = 3º and 2θ = 40º or 60º (where θ is the angle between the


116


Fig. 5.7

Schematic diagrams of amylopectin retrogradation at the rubbery state (amylopectin double helices are represented as rectangles).

incident radiation and the diffracting plane.) with a step size of 2θ = 0.02º or 0.05º when using CuKα1 radiation (the wave length of the X-ray, λ = 0.154 10 nm), 40 kV and 40 or 50 mA (Mali et al., 2002, 2006; Myllarinen et al., 2002; Zimeri and Kokini, 2002; Romero-Bastida et al., 2005; Mathew et al., 2006). Film samples are first cut into rectangular shapes and clamped onto a quartz monochromator. The typical XRD patterns of starch films (Fig. 5.8) are characterized by sharp peaks associated with the crystalline diffraction and an amorphous zone. The amorphous fraction of the sample can be estimated by the area between the smooth curve drawn following the scattering hump and the baseline joining the background within the low- and high-angle points. The crystalline fraction can be estimated by the upper region above the smooth curve (Mali et al., 2006). Therefore, the crystallinity of the starch films can be calculated using the following equation: Crystallinity =

Ac × 100% Ac + Aa

[5.1]

where Ac is the crystalline area on the X-ray diffractogram and Aa is the amorphous area on the X-ray diffractogram (Yoo and Jane, 2002). The crystallinity of starch films is dependent on the processing conditions, such as: the completeness of amylose dissolution in water, drying



117

800 Ac, crystalline area

Relative intensity (counts/s)

700 600

Aa, amorphous area

500 400

Banana

300 Okenia

200

Mango

100 0

0

10

20

30

40

50

60

70


Fig. 5.8 XRD pattern (B-type) of starch (banana, okenia and mango, respectively) films made by thermal gelatinization at 60 days of storage at 25 ºC (from Romero-Bastida et al., 2005).

conditions (rate and temperature), plant origin of the starch, moisture content of the films and the temperature of storage (Mali et al., 2002). For example, when starch films are stored at temperatures below the Tg , the starch polymers are in a stable glassy state, and crystallization does not occur or is extremely slow. However, recrystallization of starch can occur at temperatures above Tg at a rate depending on the difference between Tg and the storage temperature (Mali et al., 2006). The crystallinity of the starch films increased with storage time. As storage time increases, the width of the XRD peak decreases but its peak intensity increases, showing an increase in crystallinity of the starch (Mali et al., 2002). Plasticizers were also found to affect the crystallinity of starch. According to Mali et al. (2006), glycerol limited crystal growth and recrystallization. Glycerol could interact with the polymeric chains and interfere with polymer chain alignment due to steric hindrances. However, Garcia et al. (2000) reported that plasticizers (glycerol and water) favored polymer chain mobility and allowed the development of more stable crystalline structure during shorter periods of storage. In contrast to the conclusions of Mali et al. (2006), Smits et al. (2003) found that starch films without plasticizers showed less recrystallinity than the plasticized starch films. They attributed this phenomenon to the mobility of starch polymer chains. Plasticized starch polymers could easily vibrate and align to form crystallites, while the unplasticized starch polymers interact with each other strongly and lose mobility.


118


5.5

Appearance and physical properties of starch films

The appearance of starch films depends on the additives added into the starch dispersion. Pure starch films without any additives are usually colorless and transparent, but brittle. Films with polyols – such as glycerol, ethylene glycol or sorbitol – are also colorless, but flexible. Films containing monosaccharides – such as fructose, mannose and glucose – as plasticizers are yellowish, with the extent of the color depending on the concentration of the plasticizers used in the films (Zhang and Han, 2006b). When the microstructure of starch films is observed under a light microscope, starch films reveal a characteristic surface pattern with representative withered ‘ghost’ granules (Fig. 5.3) (Mehyar and Han, 2004; Mathew et al., 2006). Starch films can also be observed by scanning electron microscopy (SEM). Under SEM observation, the surface of starch films is smooth and homogeneous.

5.5.1 Mechanical properties of starch films Starch films are often characterized by tensile tests, from which three mechanical properties are obtained: TS, EM and E. TS is a measurement of the strength of the film. It is calculated by dividing the force needed to break the film by the cross-sectional area of the initial specimen. The value of TS should not be affected by film thickness (Phan et al., 2005). The E value represents the flexibility of the film. It is defined as the percentage of the change in the length of the specimen relative to the original length. The EM value, also known as Young’s modulus or the elastic modulus, is the fundamental measurement of the film stiffness. It is calculated from the initial linear slope of the stress–strain curve (Fig. 5.9). The higher the EM values of the films, the stiffer the films are (Mali et al., 2005a). The test methods follow the procedure of ASTM D882-91 (ASTM, 1991). The Universal Testing Machine is widely chosen to test the film mechanical properties. According to the method, the initial grip distance is set at 5 cm. The choice of cross-head speed depends on the E value. Because of the hydrophilicity of starch films, it is necessary to condition the films in a certain RH prior to the tests. Usually, the conditioning RH is 50%, accomplished using saturated calcium sulfate solution in a well-sealed chamber at room temperarture. Typical force–deformation curves are shown in Fig. 5.9. Apart from the original source of the starch, four other factors were found to affect the mechanical properties of the films: plasticizer content, Tg, crystallinity, and ratio of amylose to amylopectin. During the last few years, the effect of plasticizers on the mechanical properties of films prepared from starch, amylose, amylopectin and mixtures of starch and other biopolymers have been widely studied (Myllarinen et al., 2002). Normally, plasticizers are used to increase E values and to decrease TS and EM. This


Starch-based edible films (a)

(b) 60

40 30

35 30

Am (0) Stress (MPa)

50 Stress (MPa)

119

Am (9) Am (19)

20

Am (29)

10 0 0

25

15 10 Strain (%)

20

Ap (10)

20 15

Ap (19)

10 5

5

Ap (0)

0 0

Ap (28) 5

10 Strain (%)

15

20

Fig. 5.9 Tensile stress–strain curves of amylose (Am) and amylopectin (Ap) films with various glycerol contents, measured at RH of 50% and at 20 ºC. Abbreviations: Am (9) denotes amylose films containing 9% glycerol; Ap (10), amylopectin films containing 10% glycerols (from Myllarinen et al., 2002).

is because plasticizers can increase the free volume in the amorphous phase and reduce interaction between the starch polymer chains. However, an antiplasticization effect of plasticizers was found when the plasticizer concentration was below a critical level (Godbillot et al., 2006). At a temperature above Tg, the starch films are in a rubbery state and are flexible and extendible because more free volume is available in the starch film matrix. In contrast, at temperatures below Tg, the films are in a glassy state and are brittle. As crystallinity increases, the TS and EM of starch films increase, but E decreases, because crystallites behave like hard particles or physical cross-linkers (Liu, 2005). Amylose and amylopectin films are mechanically different (Fig. 5.9) (Myllarinen et al., 2002). Pure amylose films are stronger, whereas pure amylopectin films are more brittle. Films made of a mixture of amylose and amylopectin were studied by Lourdin et al. (1995); the results showed that a preponderance of amylose in starch films leads to higher TS, whereas a preponderance of amylopectin leads to lower TS. This is presumably due to the higher degree of crystallinity in starch films containing more amylase (Liu, 2005). 5.5.2 Barrier properties of starch films Permeation, absorption and diffusion are typical mass transfer phenomena occurring in food packaging films (Han and Scanlon, 2005); their relationship is shown in Fig. 5.10. Therefore, three coefficients – namely permeability (P), solubility (S) and diffusion (D) coefficients – are used to characterize these three phenomena quantitatively. Generally, the gas barrier property of a film is characterized by the permeability coefficient, P (Del Nobile


120

Environmentally compatible food packaging L

Fig. 5.10

Permeation

Permeability (P)

Absorption

Solubility (S) and partition coefficient (K)

Diffusion

Diffusivity (D)

Mass transfer phenomena and their characteristic coefficients (adapted from Han and Scanlon, 2005).

et al., 2002), which is defined as (Roy and others, 2000; Han and Scanlon, 2005): P = DS

[5.2]

where P is permeability coefficient, D is diffusion coefficient, and S is solubility or sorption coefficient of gas in the film. The SI units of P, D and S are m2s−1Pa−1, m2s−1 and Pa−1, respectively. Combining sorption and diffusion processes, P can be described as follows (Han and Scanlon, 2005): P=

QgasVSTP L At ∆p

[5.3]

where Qgas is the amount of gas diffused through the film (mol or kg), VSTP is the volume occupied by 1 mole of the gas under standard temperature and pressure conditions (0 ºC and 1 atm), L is the thickness of the film, A is the cross-sectional diffusion area, t is time and ∆p is the partial pressure difference across the package film. Water vapor permeability (WVP) is one of the most important properties in the gas barrier performance of starch films. It indicates the ability of the films to control water vapor transportion between a food system and its surroundings. The most common method used to measure WVP is known as the ‘cup method’, although some variations of this method exist (Gennadios et al., 1994). In the cup method, an acrylic cup (5 cm inside diameter, 1 cm depth) with a wide rim is filled with a certain amount of distilled water or desiccant and covered with a film sample to be tested. Vacuum grease is applied to the rim in order to seal the film specimen between the cup and lid. The assembly is weighed and placed in a chamber



121

Table 5.1 Comparison of WVP values of biodegradable/edible and synthetic films Film formulation

WVP (g m−1 s−1 Pa−1)

Reference

Yam starch with glycerol Corn starch with glycerol Cassava starch with glycerol Pea starch with glycerol Pea starch with sorbitol Pea starch with fructose Pea starch with mannose Corn starch with sorbitol Cellophane

(0.96–1.81) × 10−10 (5.37–6.70) × 10−10 (4.02–6.25) × 10−10 (7.65–27.72) × 10−10 (7.26–18.63) × 10−10 (5.45–13.29) × 10−10 (6.31–12.87) × 10−10 1.75 × 10−10 8.4 × 10−11

Low-density polyethylene High-density polyethylene Nylon 6 Konjac glucomannan Calcium caseinate Whey protein isolate Muscle protein of Nile tilapia Wheat gluten with glycerol Pea protein with glycerol Corn zein with glycerol Methyl cellulose with glycerol Methyl cellulose with EG400

9.14 × 10−13 2.31 × 10−13 2.09 × 10−9 (1.15–1.92) × 10−9 (2.38–3.50) × 10−9 (3.76–4.17) × 10−9 1.67 × 10−10 3.8 × 10−11–4.1 × 10−7 (1.14–2.06) × 10−9 (4.7–8.9) × 10−10 (1.6–3.6) × 10−10 (0.494–0.598) × 10−10

Mali et al. (2002) Mali et al. (2006) Mali et al. (2006) Zhang and Han (2006a) Zhang and Han (2006a) Zhang and Han (2006a) Zhang and Han (2006a) Garcia et al. (2000) Shellhammer and Krochta (1997) Smith (1986) Smith (1986) Smith (1986) Cheng et al. (2002) Mei and Zhao (2003) Mei and Zhao (2003) Paschoalick et al. (2003) Roy et al. (2000) Choi and Han (2001) Koh et al. (2002) Koh et al. (2002) Turhan and Sahbaz (2004)

with controlled RH and temperature. Weight loss or gain of the cup assembly is measured periodically to determine the water vapor transmission rate (WVTR). The WVP is calculated by multiplying the WVTR by the thickness of the film and dividing by the partial water vapor pressure difference between the inside and the outside of the cup (equation [5.3]) (Zhang and Han, 2006a). The experimental WVP data are listed in Table 5.1. Generally, starch films have higher WVP than synthesis films due to the hydrophilicity of starch. Therefore, starch films are not good water vapor barriers. Theoretically, the WVP of a film should be a constant that is independent of the difference in the partial water vapor pressure across the film. However, this is not the case in starch films, because water molecules interact with hydroxyl groups in starch molecules, and in turn cause plasticization leading to an increase in WVP (Del Nobile et al., 2002). In addition, the thickness of the hydrophilic films affects the WVP; WVP increases as the thickness increases (Gennadios et al., 1994). Therefore, the use of the terms ‘effective permeability’ or ‘apparent permeability’ has been suggested by researchers (Gennadios et al., 1994; Roy et al., 2000). The poor water barrier performance of starch films can be improved by incorporation of lipid materials,


122


Table 5.2 O2 permeability of various starch-based films Film

O2 permeability

Reference

Soluble starch and methyl cellulose with glycerol Soluble starch and methyl cellulose with sorbitol Soluble starch and methyl cellulose with xylose Whey protein film

9.8 × 10−15–4.7 × 10−11

Arvanitoyannis and Biliaderis (1999) Arvanitoyannis and Biliaderis (1999) Arvanitoyannis and Biliaderis (1999) McHugh and Krochta (1994) Gnanasambandam et al. (1997) McHugh and Krochta (1994) McHugh and Krochta (1994) McHugh and Krochta (1994) McHugh and Krochta (1994)

8.8 × 10−14–5.7 × 10−11 9.9 × 10−14–6.5 × 10−11 (0.81–88.05) × 10−20

Rice bran film

(0.47–1.03) × 10−20

Low-density polyethylene High-density polyethylene Cellophane

2.16 × 10−17

Ethylene vinyl alcohol

1.16 × 10−21–1.39 × 10−19

4.94 × 10−18 2.92 × 10−18

such as neutral lipids, fatty acids and waxes (Petersson and Stading, 2005; Han et al., 2006). Bilayer films in which a hydrophobic lipid layer is laminated over a hydrophilic film, and emulsion films in which a lipid material is uniformly dispersed throughout the films, have been tested. Bilayer films have better water vapor barrier performance. However, emulsion films possess superior mechanical properties. Recently, starch-based films have been considered good candidates for MAP where very high WVP is required (Guilbert, 2000). O2 permeability is another very important transport property of edible and biodegradable films (Miller and Krochta, 1997). Starch films usually have impressive O2 barrier properties in dry conditions (Guilbert, 2000) because of their hydrophilic nature. Table 5.2 shows some O2 permeability values of various edible films. The O2 permeability of edible films is comparable with that of low-density polyethylene which is a well-known high O2 barrier material. Miller and Krochta (1997) summarized several factors affecting the gas barrier properties of the polymer films. These factors include film chemical structure, method of polymer preparation, polymer processing conditions, free volume, crystallinity, polarity, tacticity, crosslinking and grafting. Plasticizer content and moisture content can cause large changes in starch film structure, crystallinity, tacticity, etc. Therefore, they can substantially affect the O2 barrier properties of the starch films. In fact, increased plasticizer and moisture contents can increase the O2



123

permeability by increasing the free volume and decreasing crystallinity in the starch-based matrix. Because of the hydrophilic nature of the starch films, it is difficult for aroma compounds from the packed foodstuff to be absorbed into the starch matrix. Therefore, the aroma barrier property is usually proposed to be the last main barrier function of starch films. The aroma barrier properties of starch films have not been thoroughly examined (Miller and Krochta, 1997). Quezada-Gallo et al. (1999) studied the aroma barrier properties of methylcellulose films, and found that the transfer rate of volatile aromatic compounds increased with the chain length of the compounds, while their diffusion coefficient decreased. It was suggested that aroma molecules interact with the methylcellulose polymer and modify the film structure. 5.5.3 Sorption isotherm of starch films As discussed above, starch films are very sensitive to the environmental RH. They absorb or lose water, leading to changes in their mechanical and thermal properties. Therefore, the relationship between the water content of starch films and RH has been extensively studied. This relationship, at a constant temperature, is described by a moisture sorption isotherm (Srinivasa et al., 2003), typically shown as a sigmoidal curve (Fig. 5.11). The moisture sorption isotherm of starch films represents the integrated hydroscopic properties of individual components. There are more than 200 sorption isotherm models reported in the literature. However, no single equation has the ability to describe accurately the relationship of equilibrium moisture content and equilibrium RH for various starch films over a broad range of RH values and temperatures. The change in the sorption isotherm is a result of some modification in the composition or structure of the films (Sebti et al., 2003) and the fact that the water is associated with the starch matrix by different mechanisms in different water activity regions (Mali et al., 2005b). Therefore, for a specific starch film, there is a need to search for the most appropriate isotherm equation. The Guggenheim– Anderson–de Boer (GAB) isotherm equation has been widely used to describe the water sorption behavior of starch films (Mali et al., 2005b), since the model has an excellent fit for almost the entire sorption isotherm (Biliaderis et al., 1999). In addition to starch films, the GAB model was also found to be the best model in fitting the sorption isotherm data for films made from wheat gluten (Roy et al., 2000) and a chitosan–polyvinyl alcohol blend (Srinivasa et al., 2003). In addition to the GAB model, the Brunauer– Emmet–Teller (BET), Smith and Flory-Huggins models are also popular models used to fit sorption data (Cha et al., 2001; Srinivasa et al., 2003). These models are listed in Table 5.3. The BET isotherm was originally derived by Stephen Brunauer, Paul Emmet and Edward Teller with reference to gas adsorption on a crystalline surface. In fact, the GAB model is an extension of the BET model with a


124


Water content (g water/g solids)

(a)

20 g plasticizer/100 g starch

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.0 0.1

0.2

0.3 0.4

0.5 0.6 0.7 0.8 0.9 1.0

Aw (water activity) (b)

40 g plasticizer/100 g starch

Water content (g water/g solids)

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.0

0.1

0.2

0.3 0.4

0.5 0.6 0.7 0.8

0.9 1.0

Aw (water activity)

Fig. 5.11 Effect of plasticizers on sorption isotherm for cassava starch films at 25 ºC. Symbols represent: , films with glycerol; , films with a blend of glycerol and sorbitol (1 : 1, w : w); , films with sorbitol; +, films without plasticizer (from Mali et al., 2005b).

Table 5.3 Moisture sorption isotherm models Name

Model

Smith Flory–Huggins BET GAB

M = A − [B ln (1 − aw)] M = A exp(Baw) M = ABaw/{(1 − aw)[1 + (B − 1)aw]} M = (ABCaw)/[(1 − Baw)(1 − Baw + BCaw)]

M, equilibrium moisture content (g water/g dry matter); aw, water activity; A, B and C, constants. In the GAB model, A is the monolayer moisture content (dry basis); B is the Guggenheim constant which is a correction factor for the sorption properties of the first layer with respect to the bulk liquid; C is a correction factor for the properties of the multi-player with respect to the bulk liquid.



125

correction factor, B (Table 5.3), for the structural changes of starch films. The BET model does not take into account the effect of water on any structural changes in the starch films as a result of water adsorption. When moisture adsorption into the film and dissolution of the film structure occur, the BET model will not prove applicable for providing insight into the sorption process. Therefore, the BET model is usually restricted to use in RH ranges of 11–55% (Mathlouthi, 2001) where film destruction does not occur. However, structural changes of starch films usually occur when the films are conditioned at a RH above 70%. Therefore, the GAB model should be used so that parameter B can correct for the structural changes. Roy et al. (2000) claimed that the lower the B value from one, the lower the sorption of water. At RH values above 85%, the accuracy of moisture determination falls quickly as osmotic and capillary phenomena significantly affect water sorption due to structural changes of the films (Biliaderis et al., 1999). One valuable parameter that can be roughly evaluated from GAB and BET models is the value of monolayer water. The estimated monolayer concept is useful because of its relationship with the stability (physical and chemical aspects) of low- and intermediate-moisture films (Diab et al., 2001). At monolayer moisture content levels, the rates of film quality loss resulting from chemical reactions can be negligible (Zimeri and Kokini, 2002). The Flory–Huggins model fits the isotherm where the interaction between adsorbate and adsorbent (water and starch, in the case of starch films) is weaker than the interaction between adsorbate and adsorbate (water and water). The weak interaction between the adsorbate (water) and the adsorbent (starch) leads to low water uptake at low RH. However, once a water molecule has become adsorbed at a primary adsorption site in starch films, the water–water interaction, which is much stronger, becomes the driving force of the adsorption process, resulting in accelerated water uptakes at higher RH. The goodness of fit of each model is evaluated by the mean of the relative percentage difference between the experimental and predicted values of moisture content, also known as the mean relative deviation modulus, G: G = (100 / n)∑ ( Ma − Mb / Ma )

[5.4]

where n is the number of observations, Ma is the moisture content experimentally determined and Mp is the moisture content predicted by the model (Roy et al., 2000). A value of G lower than 5 corresponds to an extremely good fit, a value between 5 and 10 shows a reasonably good prediction, and a value greater than 10 is considered a poor prediction (Roy et al., 2000). The sorption isotherms of starch films from different sources – such as corn, rice, wheat and cassava – have been studied extensively (Biliaderis et al., 1999; Gaudin et al., 1999; Fang and Hanna, 2000; Cha et al., 2001; Mali et al., 2002, 2005b; Myllarinen et al., 2002). As mentioned previously,


126


the moisture sorption isotherm for starch films generally shows a sigmoidal shape and is influenced by the concentration and type of plasticizers (Mali et al., 2005b). Figure 5.11 shows the effect of glycerol and sorbitol on the sorption isotherms for cassava starch films at 25 ºC. Higher plasticizer levels increase the film moisture content due to the hydrophilicity of the plasticizers. The presence of hydroxyl groups in the plasticizers facilitates moisture absorption by their interaction with water molecules through hydrogen bonding (Mali et al., 2005b; Zhang and Han, 2006a).

5.6

Plasticization of starch films

5.6.1 Physical chemistry of plasticization In order to overcome the brittleness inherent in pure starch films, the incorporation of a plasticizer is required. Plasticizers are defined as low molecular weight, non-volatile, high boiling point and non-separating substances, which are added to polymers and are able to change the physical and/or mechanical properties of those polymers (Sothornvit and Krochta, 2005). Plasticizers for starch films must be compatible with the polymer (starch) and be able to reduce the intermolecular forces of the polymers by interacting through hydrogen bonding with glucose chains. As a result, the very strong inter- and intra-molecular interactions of starch polymers are loosened, and the mobility of polymer chains is increased (Romero-Bastida et al., 2005). The presence of plasticizers decreases the Tg and improves the flexibility of starch films. The Tg is defined as the temperature at which the forces holding the principal components (e.g. amylose and/or amylopectin) of an amorphous solid together are overcome, so that these components are able to undergo large-scale molecular motion. The glass transition is a transition that occurs in amorphous polymers. When the temperature drops below the Tg, the long-range segmental motion of the polymers grinds to a halt. The glass transition then occurs, and the polymer changes from being soft and pliable to being hard and brittle. Therefore, the Tg is one of the most important characteristics of starch films. Tg values can be affected by many factors, such as the original starch sources and additives in the starch matrix. Differential scanning calorimetry (DSC) and dynamic thermal mechanical analysis (DMA) are the technologies commonly used to measure the Tg of starch films. In DSC thermograms, Tg is characterized by a step change of heat flow. The mid-point of the change in slope is identified as the Tg of the starch film sample (Ribeiro et al., 2003). DMA measures the thermomechanical properties, such as storage modulus (E′), loss modulus (E″) and tan δ (E″/E′) of starch films. In the glass transition zone, E′ drops. Tg is defined as the mid-point between the onset and end of the fall in E′ (Zhang and Han, 2006a), as shown in Fig. 5.12. Normally, water acts as a plasticizer to a hydrophilic polymer and decreases its Tg. The Gordon–


Starch-based edible films 0.8

107

0.6 Tan δ

Modulus E′ (Pa)

127

106 0.4

0.2

105 313 333 353 373 393 413 433 453 473 493 513 Temperature (K)

Fig. 5.12

Typical dynamic thermal mechanical analysis (DMA) plot for dry wheat gluten proteins (from Pouplin et al., 1999).

Table 5.4 The values of Tg and ∆CPi for some starches and plasticizers (Liu, 2005)

Pea amylose (cast 100 ºC) Potato starch (cast 90 ºC) Waxy maize starch (cast 90 ºC) Glycerol Water Sodium lactate Sorbitol

Tg(K)

∆Cpi (J kg−1 K−1)

605 589 558 187 134 246 271

265 265 295 970 1830 1960 2450

Taylor equation has been used to predict Tg, as affected by plasticizer content, in many food polymers (Ribeiro et al., 2003): Tg =

x1Tg1 + (∆CP2 / ∆CP1 )x2Tg 2 x1 + (∆CP2 / ∆CP1 )x2

[5.5]

where xi is the weight fraction of the ith component (i = 1, 2, . . . ), Tgi is the glass transition temperature of the ith components and ∆CPi is the change in heat capacity at Tgi. For a multi-component system (e.g. starch–water– glycerol), Tg can be predicted using the Couchman–Karasz equation: Tg =

∑ x ∆C T ∑ x ∆C

Pi gi

i

i

[5.6]

Pi

Values of Tg and ∆CPi for some starches and plasticizers are listed in Table 5.4.


128


5.6.2 Common plasticizers and their functions in starch films The plasticizers most commonly used in starch films include water, glycerol, sorbitol and ethylene glycol (Mali et al., 2005a). The plasticizer with the closet resemblance in structure to the polymers is considered the most effective plasticizer (Mali et al., 2005a). Therefore, some monosaccharides – such as glucose, fructose and mannose – have also been investigated recently regarding their capability of plasticizing pea starch films (Zhang and Han, 2006a, 2006b). The size or the shape of plasticizer molecules, the number of hydroxyl groups in the plasticizer molecules and the compatibility of the plasticizers with the starch matrix are considered as the most important factors affecting starch plasticization. For example, water is the smallest of the commonly used plasticizers and provides 5.56 moles of hydroxyl groups per 100 g, compared with glycerol which provides 3.26 moles of hydroxyl groups per 100 g. It was reported that the Tg of starch films containing 21% water is close to room temperature, whereas the Tg of starch films containing the same amount of glycerol is 93 ºC (Liu, 2005). Zhang and Han (2006a, 2006b) reported a detailed comparison of the effects of various plasticizers upon starch films in terms of the number of hydroxyl groups available in the plasticizer molecules. Although water is a very good plasticizer, it is easily lost by dehydration at low RH (Han and Gennadios, 2005). Therefore, the addition of other chemical plasticizers to starch films is required. According to Zhang and Han (2006a, 2006b), these non-water plasticizers fall into two categories according to their working mechanisms: (a) plasticizers acting as agents that directly interact with polymers by forming hydrogen bonds so as to create some distance between polymer chains; (b) plasticizers acting as agents that attract and hold a large number of water molecules, serving to plasticize the polymers in the films. Sorbitol belongs to the first category, because sorbitol-plasticized films have water contents similar to pure starch films without any other chemical plasticizers. Glycerol belongs to the second category. Glycerol-plasticized films have moisture contents 2–4.5 times those of sorbitol-plasticized films, and as glycerol content increases, the moisture content of the films increases dramatically (Zhang and Han, 2006a, 2006b). These two different working mechanisms are supposedly due to the physiochemical properties of the plasticizer molecules. The glycerol molecule has a dielectric constant of 42.5 at 25 ºC, while sorbitol has a dielectric constant of 33.5 at 80 ºC (Zhang and Han, 2006b). Mali et al. (2005b) and Garcia et al. (2000) found the same results when plasticizing cassava and corn starch films with sorbitol and glycerol. They suggested that the chances of sorbitol molecules interacting with polymeric starch chains are higher, since sorbitol is more similar to the molecular structure of glucose units than glycerol. As a result, sorbitol molecules in the starch films show a lower capacity to interact with water.



129

Water content (% w/w)

30.00 25.00 20.00 15.00 D

E H

10.00 5.00 A

C

0.00 0

10

G

F B 30 20 40 Glycerol content (% w/w)

50

60

Fig. 5.13 Phase diagram of water sorption isotherms as a function of glycerol percentage at different RHs (, 11%; , 33%; , 44%; , 58%; ×, 68%; ∗, 80%). See Fig. 5.14 for explanation of letters A to H. In the shaded area, the water content of the starch films increased with the increase in the glycerol content. In the unshaded area, water content decreased with the increase in the glycerol content (from Godbillot et al., 2006).

Recently, Godbillot et al. (2006) investigated the mechanisms of water binding in glycerol-plasticized starch films, and created a phase diagram (Fig. 5.13) containing characteristic points distinguished by the composition, stoichiometric ratios and type of phases observed in the film. A schematic representation of the different types of molecular interactions between starch, water and glycerol in different phases is shown in Fig. 5.14. It can be seen from Fig. 5.13 that, below 58% RH, an increase in glycerol content up to a critical point leads to a decrease in water content, and the levels of hydration increase slightly as glycerol content increases. Above 58% RH, the level of hydration increases rapidly as RH increases. The minimum water content at around 50% RH and 20% glycerol was considered to correspond to the saturation of starch binding sites (Godbillot et al., 2006). When RH is low, the saturation of starch sites with glycerol occurs with high glycerol concentration, whereas saturation of starch sites with water occurs with low glycerol concentration. Figure 5.14 is a schematic representation of the binding between starch, glycerol and water. A model of starch representation involving a series of equivalent monomers of anhydro-glucose with three binding sites, one of which had a stronger binding capacity (CH2OH), was proposed as well as models for water and glycerol. Point A in Fig. 5.13 corresponds to the monomolecular layer of starch primary hydration (BET layer). The calculated stoichiometric ratio at 5.5% water content is equal to 0.5 mol H2O per mol anhydro-glucose. Point B is the point where the water content in the starch films is zero and glycerol content is about 23%, which is equivalent to a stoichiometric ratio of 0.5 mol glycerol per mol anhydro-glucose. Point D is assumed to be the complete saturation of three hydroxyl groups in anhydro-glucose (starch)


130

Environmentally compatible food packaging A

B

C

D

E

F

G

H

Fig. 5.14

Schematic representation of different types of binding between starch ( ), water (∧) and glycerol ( ) (from Godbillot et al., 2006).

with water. Point E is considered to be the glycerol saturation point with multi-layer, multi-plasticizer binding. The validity of using this mechanism to describe the way in which water, glycerol and starch bind may be debatable, but it gives a new method for food scientists to think about the plasticization of starch films. 5.6.3 Antiplasticization of starch films Antiplasticization is a well-known phenomenon for synthetic polymers. This phenomenon also exists in starch films and has received increasing attention recently (Chang et al., 2006). Glycerol, sorbitol and water are the most commonly used plasticizers in starch film production. However, these plasticizers serve as antiplasticizers when present at low concentrations and, as a result, the starch films become stiffer (Chang et al., 2006). Figure 5.15 shows the EM of tapioca starch films as a function of glycerol content at different



131

2.8

Tensile modulus EM (×10–9 Pa)

2.4

2.0

0 aw

1.6

0.11 aw 0.22 aw 0.43 aw 0.32 aw 0.56 aw

1.2

0

5

10

15

20

25

30

Glycerol content (%)

Fig. 5.15

EM of tapioca starch films as a function of glycerol content (from Chang et al., 2006).

water activity (aw) levels. The EM of tapioca starch films in the aw range from 0 to 0.22 showed a maximum at a glycerol content of 2.5%. However, when aw is greater than 0.32, increasing glycerol content results in a continuous decrease in EM. It appears, therefore, that glycerol at a low concentration in drier films can exert an antiplasticization effect on film EM (Chang et al., 2006). Water also has an antiplasticization effect on tapioca films. Figure 5.16 shows the tensile strength of tapioca starch films as a function of moisture content at various glycerol contents. Increasing hydration in starch films from a dry state strengthens the films until a maximum TS is reached at a critical aw or moisture content; afterwards, further hydration weakens the films (Chang et al., 2006). Different plasticizers have different antiplasticization effects on starch film, indicating differences in molecular characteristics of plasticizers and possible dissimilar interactions with the starch polymers (Chang et al., 2006).


132

Environmentally compatible food packaging 55

50

Tensile strength σ (×10–6Pa)

45 0% glycerol 40 2.5% glycerol 35 5% glycerol 30

25 15% glycerol 20

15 0.0

Fig. 5.16

5.7

20% glycerol

0.1

0.2

0.3

0.4 aw

0.5

0.6

0.7

TS of tapioca starch films as a function of water activity (aw) with different glycerol contents (from Chang et al., 2006).

Trends in starch research and applications

Edible films and coatings are very promising systems for the future improvement of food quality and preservation during processing and storage (Debeaufort et al., 1998). They could be used where plastic packaging can not be applied, and many additives – such as antioxidants, antimicrobials, etc. – can be added into the films or coatings to provide new functions. Their main advantage is that they can be eaten and hence no waste is created; or, if left in the environment, they are totally non-polluting. Therefore, more and more industries have recently become interested in the use of edible films (Callegarin and Quezada-Gallo, 1997). However, the industrial future for edible or biodegradable films and coatings is still under discussion. One of the main obstacles to the worldwide use of these films and coatings is the cost of commercially available products (Guilbert and Gontard, 2005). Their cost is 10- to 50-fold higher than those of polyethylene or



133

polypropylene films (Debeaufort et al., 1998). Another obstacle is the fact that edible films have lower barrier and mechanical properties than plastic films. Currently, edible film research is trying to find new formulations that contain lipids to improve biopackaging performance so that it can compete with classical synthetic packaging (Callegarin and Quezada-Gallo, 1997). Industrial users have also suggested that research results should be extended by carrying out feasibility studies for the commercial uses of edible films and coatings (Han and Gennadios, 2005).

5.8

References

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6 The use of chitin and chitosan for food packaging applications I. S. Arvanitoyannis, University of Thessaly, Greece

6.1

Introduction

In the USA, out of 400 000 tonnes of garbage generated daily, plastics make up 30% of the volume, and their disposal is causing new challenges. No suitable infrastructure is available yet to dispose of the plastic packaging films and materials. Traditional methods for handling post-consumer plastic wastes include land filling, incineration, depolymerization, and recycling (Srinivasa et al., 2007a). The raw materials for biodegradable packages are generally derived from either replenishable agricultural feed stocks (Fishman et al., 1994) or marine food processing industry wastes, and therefore capitalize on natural resource conservation in an environmentally friendly and safe atmosphere. An additional advantage of biodegradable packaging materials is that upon biodegradation or disintegration and composting they may act as fertilizer and soil conditioner, facilitating better crop yields. Although somewhat expensive, bio-packaging is the future for packaging, especially for high value added food products (Tharanathan, 1995, 2003; Srinivasa et al., 2007a). Chitin, poly (β-(1-4)-N-acetyl-d-glucosamine), is a natural polysaccharide of major importance, first identified in 1884. This biopolymer is synthesized by an enormous number of living organisms; and considering the amount of chitin produced annually in the world, it is the most abundant polymer after cellulose. Chitin occurs in nature as ordered crystalline microfibrils forming structural components in the exoskeleton of arthropods or in the cell walls of fungi and yeast. It is also produced by a number of other living organisms in the lower plant and animal kingdoms, serving in many functions where reinforcement and strength are required (Rinaudo, 2006).


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Chitin is identical to cellulose except that the secondary hydroxyl on the alpha carbon atom of the cellulose molecule is substituted with an acetamide group. Thus, although chitin is a different natural polymer to cellulose, it is closely related, and aspects of cellulose technology should be readily applicable to chitin. In addition, chitin is obtained from invertebrates and fungi, and plays the same skeletal role in these animals as cellulose does in plants. The natural source of chitin is the shells of crustaceans (lobsters, shrimp, etc.) or the broth from industrial fungal processes (e.g. citric acid production). That is, the natural sources of chitin would be the waste products of other industrial processes. Since waste disposal is becoming an acute problem, this seems a very desirable source of raw material. Chitosan is the deacetylated product of the alkali treatment of chitin (Samuels, 1981). Chitosan, a copolymer of d-glucosamine and N-acetyl-dglucosamine with β-(1–4) linkage, is obtained by alkaline or enzymatic deacetylation of chitin and is an abundant polymeric product in nature. Chitosan was first discovered by Rouget in 1859 when he heated chitin to boiling point in a concentrated KOH solution (Dunn et al., 1997). Chitosan is found in different morphological forms such as a primary, unorganized structure and crystalline and semi-crystalline forms. For different reasons, especially problems of environmental toxicity, these two biopolymers are considered interesting substances for producing polymers (Sorlier et al., 2001; Shahidi and Abuzaytoun, 2005). Chitosan is thus a generic name for a complicated product which must be identified in terms of its degree of deacetylation and molecular weight. While chitin is insoluble in water and many commercial solvents, chitosan is readily soluble in various acidic solvents – e.g. formic acid, acetic acid, etc. – and hence is more amenable to industrial applications. Studies have shown that chitosan can act as a thickener, stabilizer or suspending agent, and can form gels and films (Samuels, 1981). Chitin and chitosan are examples of highly basic polysaccharides, whereas most of the naturally occurring polysaccharides – e.g. cellulose, dextrin, pectin, alginic acid, agar, agarose and carrageenans, xanthan, and galactomannans – are neutral or acidic in nature (Lamim et al., 2006). Thus, since chitosan is also edible, it can be applied to fabricated foods, encapsulating agents, or packaging materials (Samuels, 1981).

6.2

Mechanical properties (Table 6.1)

6.2.1 Tensile strength Arvanitoyannis et al. (1998) prepared films of chitosan and gelatin by casting their aqueous solutions (pH < 4.0) at 60 ºC and evaporating at 22 or 60 ºC (low- and high-temperature methods, respectively). An increase in the total plasticizer content resulted in an increase of tensile strength, up to 50% of the original values when 30% plasticizer was added. Rhim et al.


Table 6.1 Mechanical properties of chitosan and its blends Puncture Stress test

Deformation Reference

Origin

Tensile strength

Young’s modulus

Elongation

Chitosan

32.9 ± 0.7 MPa

—

—

—

Na-MMT (unmodified montmorillonite) chitosan-based nanocomposite film Cloisite 30B (an organically modified MMT) chitosan-based nanocomposite film Nano-silver chitosanbased nanocomposite film Ag-Ion chitosanbased nanocomposite film

35.1 ± 0.9 MPa

—

Elongation at break, — 54.6 ± 3.0% Elongation at break, — 50.3 ± 11.7%

—

—

36.8 ± 3.3 MPa

—

Elongation at break, — 66.3 ± 5.3%

—

—

35.9 ± 1.9 MPa

—


—

—

38.0 ± 3.4 MPa

—


—

—

Rhim et al. (2006)

(Continued)


Table 6.1 Cont’d Origin

Tensile strength

Chitosan–gelatin plasticized with water or polyols

An increase in the An increase in the total plasticizer total plasticizer content resulted content resulted in a considerable in a considerable decrease of decrease of elasticity modulus tensile strength (up to 50% of the (up to 50% of original values the original when 30% values when 30% plasticizer was plasticizer was added) added)

Enzymatically synthesized amylase (ESA)– water-soluble chitosan (WSC) (small amounts)

The tensile strength The elastic modulus of ESA–WSC of ESA film was blend films are increased by the also somewhat addition of a larger than those small amount of of ESA and WSC WSC

Chitosan films (at Optimum value, 20 °C, 40% RH and 35.8 MPa a storage period of 7 days)


Young’s modulus

Optimum value for modulus of elasticity, 896.7 MPa

Puncture Stress test

Deformation Reference

An increase in the total plasticizer resulted in a increase of percentage elongation (up to 150% compared with the original values)

—

—

—

Arvanitoyannis et al. (1998)

Significantly increased elongation of blend films in comparison with films of each component alone

—

—

—

Suzuki et al. (2005)

Optimum value, 29.9%

—

—

—

Srinivasa et al. (2007b)

Elongation

Chitosan–PLA blends (100/0) Chitosan–PLA blends (90/10) Chitosan–PLA blends (80/20) Chitosan–PLA blends (70/30) Chitosan–PLA blends (0/100)

82.4 MPa

534 MPa

5.2%

—

—

—

72.7 MPa

470 MPa

4.9%

—

—

—

64.4 MPa

433 MPa

4.2%

—

—

—

54.5 MPa

406 MPa

4.1%

—

—

—

52.5 MPa

384 MPa

3.6%

—

—

—

Chitosan–PANI

Tensile strength was reduced by about 30% after doping with HCl

Young’s modulus was reduced by about 30% after doping with HCl

Elongation at break was reduced after doping with HCl

—

—

—

Thanpitcha et al. (2006)

R-PAN–chitin (6%) acrylonitrile R-PAN–chitosan (6%) A-PAN–chitin (12%) A-PAN–chitosan (20%) A-PAN–butyl acrylate + chitosan (6%)

52 MPa

3000 MPa

2.0%

—

—

—

48 MPa

3000 MPa

2.0%

—

—

—

Sidorovich et al. (2006)

55 MPa 45 MPa

2600 MPa 3500 MPa

2.2% 1.5%

— —

— —

— —

64 MPa

3300 MPa

1.8%

—

—

—

PLA, poly(lactic acid); PANI, polyaniline, PAN, polyacrylonitrile.


Suyatma et al. (2004)

142


(2006) developed four different types of chitosan-based nanocomposite films: an Na-MMT (unmodified montmorillonite) chitosan-based nanocomposite film; Cloisite 30B (organically modified MMT) chitosan-based nanocomposite film; a nano-silver chitosan-based nanocomposite film; and an Ag-ion chitosan-based nanocomposite film. The tensile strengths of these films were 35.1 ± 0.9, 36.8 ± 3.3, 35.9 ± 1.9, and 38.0 ± 3.4 MPa, respectively; this compares with a tensile strength, for chitosan of 32.9 ± 0.7 MPa. The tensile strength of ESA film increased with the addition of a small amount (up to 10%) of WSC and the tensile strength then seemed to approach that of WSC film (Suzuki et al., 2005). According to Srinivasa et al. (2007b) the tensile strength of chitosan films was influenced more significantly by temperature and relative humidity. The tensile strength varied between 5.5 and 40 MPa and it was found that at 20 ºC and 40% relative humidity, and a storage period of ~7 days, the optimum value for tensile strength was 35.8 MPa. Suyatma et al. (2005) showed that chitosan has a better performance than PLA. As a consequence, all blends show a decrease in tensile strength with an increase in PLA content (chitosan–PLA 90/10, 72.7 MPa; chitosan–PLA 80/20, 64.4 MPa). Increased PANI content in PANI–chitosan blend films resulted in an increase in tensile strength. On increasing the PANI content to 17 wt% the tensile strength increased due to a more uniform distribution of PANI in the polyvingl alcohol matrix, and the tensile strength decreased again after adding more PANI. After doping the blend films with HCl, the tensile strength decreased at all PANI compositions. Increases in HCl concentration (blend films with 0.1 and 0.5% (wt/v) HCl concentration had tensile strengths of 53.2 ± 3.0 and 52.2 ± 5.7 MPa, respectively) and doping time caused decreases in the tensile strength (0.5 and 2 s doping time showed tensile strengths of 53.0 ± 4.2 and 51.5 ± 4.0 MPa, respectively) (Thanpitcha et al., 2006). Composite films were prepared from PAN synthesized by anionic and radical polymerization (A-PAN and R-PAN, respectively), and combined with chitin or chitosan. Films with high deformation and strength characteristics were prepared from the polysaccharides chitin and chitosan, combined with polyacrylonitrile. Films of R-PAN–chitin (6%) acrylonitrile had 52 MPa tensile strength, and films of A-PAN–chitin (12%) had 55 MPa tensile strength (Sidorovich et al., 2006). Mathew et al. (2006) found that the tensile strength of chitosan–starch composite films increased with the addition of starch, with a maximum tensile strength of 37.5 MPa at a starch:chitosan ratio of 0.5 : 1, due to the formation of intermolecular hydrogen bonds between the NH3 of chitosan and hydroxyl groups of starch. The tensile strength decreased with further increases in the starch:chitosan ratio up to 1.5 : 1; this may be due to the formation of starch intramolecular hydrogen bonds rather than inter-


The use of chitin and chitosan for food packaging applications

143

molecular hydrogen bonds, resulting in a phase separation between the two main components. Chitosan–whey protein edible films with different protein concentrations were prepared in the absence or presence of microbial transglutaminase as a cross-linking agent. In the absence of the enzyme, the addition of whey proteins significantly reduced the mechanical resistance of the films obtained with chitosan alone. In contrast, a marked improvement in the mechanical resistance of chitosan–whey protein films was observed when they were prepared in the presence of transglutaminase (chitosan (9.2 mg cm−2) showed a tensile strength of 14.4 ± 0.58 MPa; chitosan–whey protein showed a tensile strength of 9.5 ± 0.6 MPa; chitosan–whey protein + transglutaminase showed a tensile strength of 26.2 ± 0.9 MPa) (Di Pierro et al., 2006). Li et al. (2006) studied the tensile strength of a pure konjac glucomannan film and found that it was 88.1 ± 1.2 MPa and much higher than that of chitosan (61.0 ± 3.6 MPa). When chitosan was added to the konjac glucomannan solution, the tensile strength of the resulting blend film increased with increasing chitosan content and reached a maximum at about 20 wt% chitosan, achieving 102.8 ± 3.8 MPa. When elongation at break was studied, there was no significant difference between the konjac glucomannan–chitosan (KC) blend films and the pure konjac glucomannan or chitosan films. The reason for this might be that the konjac glucomannan and chitosan polysaccharide molecular chains have approximately equal molecular flexibility (Li et al., 2006). Cassava starch–MMT composite films were prepared by casting; with the amount of MMT fixed at 5 wt%, the tensile strengths of starch films containing 5, 10, 15, and 20 wt% chitosan were 21.02, 22.49, 23.14, and 24.64 MPa, respectively (Kampeerapappun et al., 2007). Ban et al. (2006) studied starchbased–chitosan films and found that a tremendous tensile increase was achieved when the chitosan content composed 12.5% of the starch film. Compared with the original starch film, an almost 10-fold increase in tensile strength was reached with 28% chitosan in the film. Bangyekan et al. (2006) studied the effect of chitosan coating contents on tensile properties in both the machine direction and the transverse direction of chitosan-coated starch films. The tensile stress at maximum load in both directions tended to increase. For example, in the machine direction the tensile stress of 1 wt% chitosan-coated film was 8.27 MPa. When the chitosan coating solution reached 4 wt%, the tensile stress was found to be 14.47 MPa. In the transverse direction, the tensile stress of 1 wt% chitosancoated film was 5.08 MPa, whereas that of 4 wt% chitosan-coated film was 9.6 MPa. 6.2.2 Young’s modulus According to Arvanitoyannis et al. (1998) an increase in the total plasticizer content of chitosan and gelatine films (water or polyols) resulted in a con-


144


siderable decrease of elasticity modulus of up to 50% of the original values when 30% plasticizer was added. The elastic modulus of ESA–WSC blend films is somewhat larger than those of pure ESA and WSC films (Suzuki et al. 2005). According to Srinivasa et al. (2007b), the modulus of elasticity was influenced by all the three independent variables, i.e. temperature, relative humidity, and storage period. It was found that at 20 ºC, 40% relative humidity, and a storage period of ~7 days, the optimum value for modulus of elasticity was 896.7 MPa. According to Suyatma et al. (2005), chitosan has a better performance than PLA. As a consequence, all blends show a decrease in Young’s modulus with increasing PLA content (chitosan–PLA 90/10, 470 Mpa; chitosan–PLA 80/20, 433 MPa. PANI–chitosan blend films were successfully prepared by a solution casting method. After doping the blend films with HCl, the modulus decreased at all PANI compositions. Increases in HCl concentration (blend films with 0.1 and 0.5% (wt/v) HCl concentration had moduli of 2434 ± 316 and 2430 ± 434 MPa, respectively) and doping time (0.5 and 2 s doping time had moduli of 2236 ± 262 and 2149 ± 310 MPa, respectively) caused a decrease in the modulus (Thanpitcha et al., 2006). Films with high deformation and strength characteristics were prepared from polysaccharides chitin and chitosan, combined with A-PAN or R-PAN. Films of R-PAN–chitin (6%) acrylonitrile had Young’s modulus of 3000 MPa and films of A-PAN–chitin (12%) had Young’s modulus of 2600 MPa (Sidorovich et al. 2006). Cassava starch–MMT composite films were prepared by casting; with the MMT content fixed at 5 wt%, the tensile modulus values of starch films containing 5, 10, 15, and 20 wt% chitosan were 1111, 1111, 1124, and 1225 MPa, respectively. The percentage elongation values showed a similar trend (Kampeerapappun et al., 2007). Bangyekan et al. (2006) studied the effect of chitosan coating contents on tensile properties in both the machine direction and the transverse direction of chitosan-coated starch films. The tensile modulus in both directions tended to increase. For example, in the machine direction the tensile modulus of 1 wt% chitosan-coated film was 506.29 MPa. When the chitosan coating solution reached 4 wt%, the tensile modulus was 751.34 MPa. In the transverse direction, the tensile modulus of 1 wt% chitosan-coated film was 267.84 MPa, whereas that of 4 wt% chitosan-coated film was 657.0 MPa. 6.2.3 Elongation An increase in the total plasticizer content (water or polyols) of chitosan and gelatine films resulted in a considerable increase in elongation; up to 150% compared with the original values (Arvanitoyannis et al., 1998). In



145

the four different types of chitosan-based nanocomposite films developed by Rhim et al. (2006), the elongation values were as follows: Na-MMT (unmodified MMT) chitosan-based nanocomposite film, 50.3 ± 11.7%; Cloisite 30B (organically modified MMT) chitosan-based nanocomposite film, 66.3 ± 5.3%; nano-silver chitosan-based nanocomposite film, 46.3 ± 7.6%; Ag-ion chitosan-based nanocomposite film with elongation 38.9 ± 1.4%. Chitosan showed 54.6 ± 3.0% elongation. Suzuki et al. (2005) prepared amylose films blended with chitosan that were free from additives. The addition of a small amount of WSC to ESA film increased the elongation significantly, i.e. the blend films were stronger than were films formed from each component alone. According to Srinivasa et al. (2007a), the elongation properties of chitosan films were influenced more significantly by temperature and relative humidity. It was found that at 20 ºC and 40% relative humidity, and a storage period of ~7 days, the optimum value for percentage elongation was 896.7. Suyatma et al. (2005) showed that chitosan had a better performance than PLA. As a consequence, all blends showed a decrease in elongation at break with an increase in PLA content (chitosan–PLA 90/10, 4.9% elongation at break; chitosan– PLA 80/20, 4.2% elongation at break). Thanpitcha et al. (2006) found that in PANI–chitosan blend films the elongation at break decreases substantially on adding PANI, indicating that the blend films were more brittle than the pure chitosan films (0% PANI content film showed 17.02 ± 1.6% elongation at break and a 10% PANI film showed 7.58 ± 1.1% elongation at break). Composite films were prepared from PAN synthesized by anionic and radical polymerization and combined with chitin or chitosan. Films with high deformation and strength characteristics were prepared from chitin and chitosan, combined with PAN. Films of R-PAN–chitin (6%) acrylonitrile had 2% elongation and films of A-PAN–chitin (12%) had 2.2% elongation (Sidorovich et al., 2006). According to Mathew et al. (2006), the average elongation values of films studied increased from 27.95% for a chitosan film to a maximum of 49.12% for a 1.5 : 1 starch–chitosan composite film. The increase in the percentage elongation with increase in starch content was due to the reduction in the number of intermolecular cross-links and an increase in the intermolecular distance. Chitosan–whey protein edible films with different protein concentrations were prepared in the absence or presence of microbial transglutaminase as cross-linking agent. In the absence of the enzyme the addition of whey proteins significantly reduced the mechanical resistance of the films obtained with chitosan alone. In contrast, a marked improvement in the mechanical resistance of chitosan–whey protein films was observed when they were prepared in the presence of transglutaminase (chitosan (9.2 mg cm−2) showed elongation of 23.3 ± 2.9%; chitosan–whey protein showed


146


elongation of 14.4 ± 0.59%; chitosan–whey protein + transglutaminase showed elongation of 3.1 ± 0.3%) (Di Pierro et al., 2006). Bangyekan et al. (2006) studied the effect of chitosan coating contents on tensile properties in both the machine direction and the transverse direction of chitosan-coated starch films. The percentage elongation at break in both directions tended to decrease as chitosan content increased. For example, in the machine direction, the percentage elongation at break of a 1 wt% chitosan-coated film was 14.48%. When the chitosan coating solution constituted 4 wt% of the film, this value was found to be 9.8%. In the transverse direction, the percentage elongation at break of the 1 wt% chitosancoated film was 33.1%, whereas that of the 4 wt% chitosan-coated film was 20.26%.

6.3

Thermal properties (Table 6.2)

6.3.1 Glass transition Arvanitoyannis et al. (1998) showed that the addition of low-molecularweight compounds (polyols or water) to chitosan–gelatin blends lowered the glass transition point (Tg) proportionally to the plasticizer content of the blend (Tg = 57.4 ± 3.6 ºC with 5% glycerol; Tg = 21.7 ± 2.5 ºC with 15% glycerol). Suyatma et al. (2004) showed that chitosan and polylactic acid had a single Tg at 194 and 59 ºC, respectively. Since their blends showed two Tg values that were slightly different from those of chitosan and PLA alone, this indicated that chitosan and PLA were not miscible. Moreover, there are minor variations in the Tg with composition. A transition was observed in the chitosan film at 202 ºC in the second run, corresponding to its Tg (Mathew et al., 2006). 6.3.2 Melting point Arvanitoyannis et al. (1998) also found that the addition of low-molecularweight compounds (polyols or water) to chitosan–gelatin blends lowered the melting temperature (Tm) proportionally to the plasticizer content of the blend (Tm = 146.3 ± 1.8 ºC with 5% glycerol; Tm = 138.7 ± 2.5 ºC with 15% glycerol). Suyatma et al. (2004) determined that the Tm of chitosan and PLA were 97 and 147 ºC, respectively; three blend compositions of chitosan–PLA (90/10, 80/20, and 70/30) showed a slight decrease in melting temperature at about 93–94 ºC. There were minor variations in Tm with composition of blends, indicating that chitosan–PLA blends are not compatible. Thanpitcha et al. (2006) found that in PANI–chitosan blend films the degradation temperature (Td) increased with increasing PANI content. This indicated that there was an intermolecular interaction between PANI and chitosan chains. The blend film containing 50 wt% PANI exhibited two


Table 6.2 Thermal properties of chitosan and its blends Speed

Origin

Tg

Chitosan–starch

A transition was 20 °C min−1 from observed in the ambient chitosan film at 202 °C temperature in the second run, to 500 °C corresponding to its Tg Nitrogen was The method used used as the was differential purge gas at scanning calorimetry/ a flow rate of differential thermal 20 ml min−1. analysis (DTA) using a Perkin-Elmer Pyris DSC 6. Nitrogen at a rate of 30 ml min−1 was used as the purge gas


The addition of lowmolecular-weight compounds (polyols or water) to chitosan– gelatin blends was shown to lower the Tg proportionally to the plasticizer content of the blend High plasticizer contents were related to lower crystallinities and lower Tm and Tg values

2 °C min−1

Conditions/method

Physical properties

Reference

Thermogravimetric analyses (TGAs) were performed in a simultaneous DTATG apparatus (DTG60, Shimadzu, Kyoto, Japan)

Chitosan showed considerable reduction in thermal stability when it was in the film form with the decomposition peak maximum at 294 °C, which increased to 308 °C in the blend films with increasing starch content, indicating the formation of intermolecular interactions between the two components

Mathew et al. (2006)

A dynamic mechanical thermal analyser at 1 Hz

The addition of lowmolecular-weight compounds (polyols or water) to chitosan– gelatin blends was shown to lower the Tm proportionally to the plasticizer content of the blend. High plasticizer contents were related to lower crystallinities and lower Tm and Tg values


(Continued)


Table 6.2

Cont’d

Origin

Tg

Speed

Conditions/method

Physical properties

Reference

Chitosan–PLA blends

Chitosan and PLA have a single Tg at 194 and 59 °C, respectively. Their blends showed two Tg

10 °C min−1

The thermal characteristics of the blends were determined using a differential scanning calorimeter (DSC) (Thermal Analyzer, Dupont, FL, USA) cooled with liquid nitrogen circulation

A first scan was made from −30 °C to 190 °C, 1 min at 190 °C, then the sample was cooled rapidly to −30 °C, 3 min at −30 °C and a second scan to 250 °C (Quenching)

Suyatma et al. (2004)

Chitosan hydrogel– PANI doped with HCl

—

10 °C min−1 under a nitrogen atmosphere

TGA, temperature range studied was 30–600 °C

The Td of the blend films increases with increasing PANI content The blend film containing 50 wt% PANI exhibited two distinct degradation temperatures at approximately 295 and 500 °C, corresponding to the Td of chitosan and PANI, respectively The chitosan and blend films exhibited a lower Td compared with the undoped films

Thanpitcha et al. (2006)

10 °C min−1

DSC of the film samples (c. 10 mg each) was performed on a DSC model 200PC under a nitrogen atmosphere with a flow capacity of 25 ml/min

Td reached 265.89 °C

Li et al. (2006)

KC films (chitosan content, 20 wt%) KC films (chitosan content, 10 wt%) KC films (chitosan content, 40 wt%)


Td reached 260.80 °C Td reached 263.20 °C


149

distinct Td at approximately 295 and 500 ºC, corresponding to the Td of chitosan and PANI, respectively. This implied that a substantial phase separation was also present. Chitosan and blend films exhibited a lower Td compared with those of the undoped films (doping with HCl). This may be due to acid hydrolysis inducing chitosan chain scission during the doping process. Mathew et al. (2006) found that the peak maximum decomposition of starch powder was at 316 ºC and that of chitosan was close, with a peak maximum at 317 ºC. Chitosan showed considerable reduction in thermal stability when it was in the film form with the decomposition peak maximum at 294 ºC, which increased to 308 ºC in the blend films with increasing starch content, indicating the formation of intermolecular interactions between the two components. The decomposition temperature for KC films reached 265.89 ºC for KC2 (chitosan content 20 wt%) which is higher than that of KC1 (10 wt% chitosan, 260.80 ºC) or KC4 (40 wt% chitosan, 263.2 ºC); this proves that a stronger interaction between the konjac glucomannan and the chitosan in KC2 had occurred (Li et al., 2006).

6.4

Gas permeability (Table 6.3)

Despond et al. (2005) deposited a continuous layer of chitosan on a porous cellulosic substrate to improve the gas barrier properties in anhydrous conditions. A chitosan coating of 7 g m−2 was achieved, which led to interesting gas barrier properties in the anhydrous state. A decrease in the CO2 permeability from 1635 10−10 cm3(STP) cm/cm2 s cmHg, the permeability of the parchmentized paper, to 0.08 cm3(STP) cm/cm2 s cmHg for the chitosan–paper bilayer was obtained. Nevertheless, the hydrophilic character of both cellulose and chitosan did not allow the preservation of these properties in the hydrated state. A layer of carnauba wax was then coated on the chitosan side of the bilayer. Because of the hydrophobic character of this external layer, the water sorption in the multilayer decreased greatly, and CO2 and O2 permeability coefficients lower than 0.5 cm3(STP) cm/cm2 s cmHg were obtained in the hydrated state. Arvanitoyannis et al. (1998) found that an increase in the total plasticizer content (water, polyols) of chitosan–gelatin blends resulted in a proportional increase in their gas permeability, from 3.0 ± 0.4 × 10−15 to 6.4 ± 0.5 × 10−14 with 4% and 17% glycerol, respectively, for O2 (in cm2 s−1 Pa−1). In general, the presence of a polyol as a plasticizer in the chitosan–gelatin blends was shown to increase water permeation rates proportional to the total plasticizer content. Rhim et al. (2006) found that the water vapour permeability (WVP) value of the chitosan film was 1.31 ± 0.07 × 10−12 kg m/m2 s Pa and also that the WVP of the nanocomposite films decreased significantly (P < 0.05) by


Table 6.3

Gas permeability of chitosan and its blends Feeding solution

Permeation flux (g/m2 h)

Separation factor (α)

Conditions

O2/CO2 permeability

Chitosan–whey 3.24 ± 0.15 cm3 µm/ protein (CWP) m2 day kPa) films (thickness, 68 ± 0.9 mm) CWP + 0.88 ± 0.06 cm3 µm/ transglutaminase m2 day kPa) (TGase) (thickness 62 ± 2 mm) Paper–chitosan — films

—

—

—

25 °C

O2, 20.6 ± 0.7; CO2, 20.7 ± 0.95 (cm3 µm/m2 day kPa)

—

—

—

25 °C

8 wt %

—

—

Anhydrous state

Paper–chitosan– carnauba wax films

—

—

—

Hydrated state

—

—

—

Origin

Chitosan

WVTR

Water activity 0.7, 0.96, 1.0, 55, 423, 7650 barrer, respectively Water activity 0.7, 0.96, 1.0, 1900, 13 000, 78 500 barrer, respectively


Method

Reference

WVP of films was evaluated by a gravimetric test according to ASTM E96 O2, 7.8 ± 0.8; CO2, 8.3 (1993) by means ± 0.7 (cm3 µm/m2 of a Fisher/Payne day kPa) permeability cup

Di Pierro et al. (2006)

0.04 barrer O2, 0.08 barrer CO2 permeability. The gas barrier property was not preserved in the hydrated state O2, CO2 permeability coefficient lower than 0.5 barrer

Despond et al. (2005)

The permeation cell consisted of two compartments (the upstream and downstream compartments) separated by the studied membrane. The cell was thermostated at 20 ± 1 °C

Chitosan

WVP, 1.31 ± 0.07 × 10−12 kg m/m2 s Pa

Na-MMT, chitosan-based nanocomposite film Cloisite 30B, chitosan-based nanocomposite film Nano-silver, chitosan-based nanocomposite film Ag-ion, chitosan-based nanocomposite film

WVP, 0.98 ± 0.15 × 10−12 kg m/m2 s Pa

KC, mixing ratio 80/20

76.2 ± 1.4% relative humidity 78.8 ± 0.6% relative humidity

WVP, 0.92 ± 0.03 × 10-12 kg m/m2 s Pa

78.2 ± 0.2% relative humidity

WVP, 0.95 ± 0.12 × 10−12 kg m/m2 s Pa


WVP, 0.96 ± 0.05 × 10−12 kg m/m2 s Pa


4.64 ± 0.25 g H2O mm/h cm2

25 °C

WVTR determined gravimetrically using a modified ASTM method E 96-95

Rhim et al. (2006)

Water vapour transmission was determined according to ASTM E96-80 (ASTM, 1989)

Li et al. (2006)

(Continued)


Table 6.3

Cont’d

Origin

WVTR

MMT–chitosan

Results show that WVTR values of the composite film are between about 2000 and 1082 g m−2 day−1. The WVTR value of the composite film decreases significantly as the chitosan and MMTcontent increases


Water permeation rates were proportional to the total plasticizer content


Feeding solution

Permeation flux (g/m2 h)

Separation factor (α)

Conditions 38 ± 10 °C and relative humidity, 90 ± 2%

—

—

—

—

O2/CO2 permeability

Method

Reference

WVTR was investigated according to ISO 2528-1995E

Kampeerapappun et al. (2007)

Measurements of Low-temperature gas permeability preparation were carried out method resulted in using a a decrease, by one Davenport or two orders of apparatus magnitude, of CO2 and O2 connected to an permeability in the IBM/PC in chitosan–gelatin accordance with blends. An increase ASTM D1434-82 in the total (ASTM, 1982). plasticizer content WVP (water, polyols) of measurements these blends was were carried out found to be as reported proportional to an previously increase in their (Martin-Polo gas permeability et al., 1992)


ESA

25 °C

ESA–WSC

25 °C

Chitosan

25 °C and 0% relative humidity

Chitosan–PLA blends

Improvement in water barrier properties increased with the increase in PLA contents. However, the addition of 10 wt% PLA gives more important amelioration than 20 and 30 wt% PLA

WVTR, water vapour transmission rate. © 2008, Woodhead Publishing Limited

—

—

—

Showed a strong barrier to several gases Permeability of C2 H4, CO2, O2, and N2 rapidly increased upon the addition of a small amount of WSC (up to 10%) 0.57 O2 permeability (amol/m s Pa); 1.83 CO2 permeability (amol/m s Pa)

25 °C under — 90% relative humidity

Suzuki et al. (2005) Gas transmittance was measured using a highvacuum system

WVTRs values Suyatma et al. were measured (2004) using a MOCON Permatran-W3/31 (Modern Control, Inc., Minneapolis, MN, USA)

154


25–30% depending on the nanoparticles used – with Cloisite 30B having the lowest value (0.92 ± 0.03 × 10−12 kg m/m2 s Pa). Amylose films were blended with additive free chitosan. The presence of a small amount of chitin (less than 10%) in these films significantly increased the permeability of gases (N2, O2, CO2, C2H4) and then the permeability seemed to approach the values of WSC film with an increase in WSC concentration. This fact indicated that the blending of ESA and WSC did not produce a film having simply additive properties of the two components and, thus, they are miscible with each other (Suzuki et al., 2005). The WVTR of the KC films was calculated and the results indicated that, on the whole, an increase in chitosan content decreased the WVTR. However, the KC2 film (chitosan content 20 wt%) was shown to have a low WVTR value (4.64 ± 0.25 gH2O mm/h cm2), even lower than that of KC3 (chitosan content 30 wt%). This might indicate the existence of intermolecular interactions and a decrease in the mobility of both the konjac glucomannan and chitosan macromolecules when the mixing ratio was 4 : 1 (Li et al., 2006). Kampeerapappun et al. (2007) found that the WVTR values of a composite film (MMT–chitosan) were between 2000 and 1082 g m2 day−1. It was clearly observed that the WVTR value of the composite film decreased significantly as the chitosan (MMT–chitosan 2 : 1 ratio, 1790 g m2 day−1 WVTR; MMT–chitosan 1 : 1 ratio, 1669 g m2 day WVTR) and MMT contents increased (MMT–chitosan 1 : 2 ratio, 1583 g m2 day−1 WVTR; MMT– chitosan 3 : 2 ratio, 1173 g m2 day−1). The WVTR of the chitosan-coated cassava starch films decreased gradually as the concentration of chitosan coating solution increased from 1 to 4 wt%. Coating a 1 wt% chitosan solution onto a series of foundation starch films containing varying glycerol concentrations was carried out in order to investigate the effect of the plasticizer. The results showed that the WVTR values of the coated films were between 2290 and 3134 g m−2 day−1. The increase in WVTR values depended heavily upon the increasing amount of glycerol. The WVTR value of the chitosan-coated film reached its maximum value at 4 wt% glycerol (Bangyekan et al., 2006).

6.5

Water permeability (Table 6.4)

An increase in water content resulted in much softer chitosan films. When submerged in water, the films became very soft and highly elastic (Srinivasa et al., 2007a). In chitosan–PLA blends, the improvement in water barrier properties increased with the increase in PLA contents. The addition of 10 wt% PLA provided greater improvement than 20 or 30 wt% PLA. This means that the incorporation of PLA was more effective at improving the


Table 6.4

Water permeability of chitosan and its blends

Origin

H2O

Conditions

Method

Reference

Starch–chitosan

Water uptake increases with chitosan content. When the chitosan content reached one-third of the total film by mass, as much as a 2-fold increase in water uptake was observed when compared with that of a pure starch film

25 ºC, 95% relative humidity

Film samples were conditioned at 25 ºC in a desiccator containing sodium sulphate to ensure a relative humidity ratio of 95% for a designated time. The excess water was then dried with tissue paper applied to the film surface

Ban et al. (2006)

Chitosan-coated cassava starch film–2 wt% glycerol Chitosan-coated cassava starch film–3 wt% glycerol Chitosan-coated cassava starch film–4 wt% glycerol Chitosan-coated cassava starch film–5 wt% glycerol Chitosan-coated cassava starch film–6 wt% glycerol Chitosan films

35.7% (4 wt% chitosan)

Determination of water absorption of films was carried out by a 24-h immersion method according to ASTM D 570

Bangyekan et al. (2006)


49.0% (4 wt% chitosan) 49.6% (4 wt% chitosan) 73.7% (4 wt% chitosan) 74.8% (4 wt% chitosan) Water permeability coefficient greatly increases with relative pressure

After desorption The samples were introduced in a Setaram in vacuo B92 microbalance (2.1026 mbar) at a constant temperature (20 ± 1 ºC)

CO2 uptake is 0.03% and Despond et al. O2 uptake 0.001% for (2001) dry conditions. For 82% relative humidity, CO2 uptake is 6.21% and for 91% relative humidity, O2 uptake is 0.036%

156


barrier properties at low levels of PLA because of its poor miscibility with chitosan (Suyatma et al., 2004). Regarding cassava starch–MMT–chitosan composite film with a fixed MMT content of 10 wt%, the moisture absorption values decreased significantly from 125% to 95, 83, 74, and 61% for chitosan contents of 0, 5, 10, 15, and 20 wt%, respectively. The remarkable reduction in moisture uptake was seen with a composite film containing 20 wt% chitosan (Kampeerapappun et al., 2007). As chitosan content increased to 28%, the water uptake of the starch-based–chitosan film increased linearly. When the chitosan content reached one-third of the total film (33.3%) by mass, an increase in water uptake of as much as 2-fold was recorded compared with that of a pure starch film (Ban et al. 2006). Bangyekan et al. (2006) found that the plasticizer contents had a significant effect on the percentage water absorption values of free starch films and coated films. A remarkable reduction in water uptake was determined for a coated film containing 4 wt% chitosan coating. For example, at 2, 3, 4, 5, and 6 wt% glycerol, the water absorption values of 1 wt% chitosancoated films were 71.8, 78.4, 92.2, 113.8, and 125.4%, respectively; whereas those of the 4 wt% chitosan-coated films were much lower at 35.7, 49.0, 49.6, 73.7, and 74.8%, respectively. Despond et al. (2001) studied the water sorption of chitosan at 20 ºC. For partial pressures lower than 0.4, the amount of sorbed water was mainly due to random mixing, whereas at higher relative pressures, an additional contribution due to water clustering was observed; in this range of partial pressures, the diffusion coefficient was concentration-dependent.

6.6

Conclusions

In a few years the differences in environmental protection practices, qualitative and quantitative, carried by out organizations around the world are anticipated to be less extreme than they currently are. In view of the overwhelming pollution problems, overall environmental control is expected to improve substantially worldwide, thus evening out the existing competitive advantages. It is not over-optimistic to expect that compliance with ISO 14001 (an environmental management system) will be a requirement for doing business in the future (Boudouropoulos & Arvanitoyannis, 1999, 2000). Although recycling appears to be the most promising solution to environmental problems, natural biodegradable polymers such as chitin and chitosan are also promising solutions in various applications and, among these, food packaging stands out. Chitosan, in particular, is endowed with satisfactory mechanical and gas permeability properties (under dry conditions) and this, in conjunction with its antimicrobial properties, has meant that it has proved to be one of the most effective and widely studied materials both for edible films and food enrobing heavy metal complexation and pharmaceutical applications (Arvanitoyannis, 1999).



6.7

157

References

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mathew s., brahmakumar m. and abraham t.e. (2006). Microstructural imaging and characterization of the mechanical, chemical, thermal, and swelling properties of starch–chitosan blend films. Biopolymers 82: 176–187. rhim j.-w., hong s.-i., park h.-m. and perry k.w.n.g. (2006). Preparation and characterization of chitosan-based nanocomposite films with antimicrobial activity. Journal of Agricultural and Food Chemistry 54: 5814–5822. rinaudo m. (2006). Chitin and chitosan: properties and applications. Progress in Polymer Science 31: 603–632. samuels r.j. (1981). Solid state characterization of the structure of chitosan films. Journal of Polymer Science, Part B: Polymer Physics 19: 1081–1105. shahidi f. and abuzaytoun r. (2005). Chitin, chitosan, and co-products: chemistry, production, applications and health effects. Advances in Food and Nutrition Research 49: 94–135. sorlier p., denuziere a., viton c. and domard a. (2001). Relation between the degree of acetylation and the electrostatic properties of chitin and chitosan. Biomacromolecules 2: 765–772. srinivasa p.c., ravi r. and tharanathan r.n. (2007). Chitin/chitosan – safe, ecofriendly packaging materials with multiple potential uses. Food Reviews International 23: 53–72. srinivasa p.c., ravi r. and tharanathan r.n. (2007). Effect of storage conditions on the tensile properties of eco-friendly chitosan films by response surface methodology. Journal of Food Engineering 80: 184–189. suyatma n.e., copinet a. and tighzert l. (2005). Effects of hydrophilic plasticizers on mechanical, thermal, and surface properties of chitosan films. Journal of Agricultural and Food Chemistry 53: 3950–3957. suyatma n.e., copinet a., tighzert l. and coma v. (2004). Mechanical and barrier properties of biodegradable films made from chitosan and poly (lactic acid) blends. Journal of Polymers and the Environment 12(1): 31–36. sidorovich a.v., sazanov y.z., praslova o.e., bobrova n.v., novoselova a.v., kostycheva d.m. and nud’ga l.a. (2006). Thermomechanical properties of composite films of polyacrylonitrile with chitin and chitosan. Russian Journal of Applied Chemistry 79(8): 1329–1332. suzuki s., shimahashi k., takahara j., sunako m., takaha t., ogawa k. and kitamura s. (2005). Effect of addition of water-soluble chitin on amylose film. Biomacromolecules 6(6), 3238–3242. thanpitcha t., sirivat a., jamieson a.m. and rujiravanit r. (2006). Preparation and characterization of polyaniline/chitosan blend film. Carbohydrate Polymers 64: 560–568. tharanathan r.n. (1995). Starch – the polysaccharide of high abundance and usefulness. Journal of Scientific and Industrial Research 54: 452–458. tharanathan r.n. (2003). Biodegradable films and composite coatings – past, present and future. Trends in Food Science and Technology 14: 71–78.


Part II Using environmentally compatible packaging technologies in the food industry


7 Consumer attitude to food packaging and the market for environmentally compatible products I. S. Arvanitoyannis and A. Kasaveti, University of Thessaly, Greece

7.1

Introduction

More than 15 000 new food products are introduced annually in the United States, all of which require new packaging, even if the contents are just line extensions. Furthermore, an uncounted number of food products, perhaps about 1000, are repackaged annually, each requiring some attention (http://members.ift.org/NR/rdonlyres/2189B5E5-5744-4493-871484009FDEDED2/0/0606pack.pdf). Packaging is a subject that is attracting more and more attention, both from the public and the media (http://www. incpen.org/pages/userdata/incp/Consumerattitudestopackagingsurvey.pdf). It is noteworthy that the food industry, of all the manufacturing industries, has the largest demand for packaging, whether it is paper/board (including laminates), plastics, glass, or metal. Indeed, the food industry is responsible for around two-thirds of the total industrial usage. Finding or improvising ways to reduce this packaging quantity and the subsequent waste is a demanding task (Lillford & Edwards, 1997). Over the past decade, the goal of harnessing the power of the market in support of environmental objectives has passed through several stages, from strong enthusiasm, cautious optimism, disappointment, and a refocusing of efforts toward achievable goals and defined market segments. In this evolution, one fact remains at the centre of efforts to expand green markets: opinion polls in both developing and developed countries consistently show that public support for environmental protection is robust and unwavering (Commission for Environmental Cooperation, 1999). The main environmental challenges for food companies could be summarized as follows: water availability, wastewater discharge, air emissions, byproduct disposal or utilization, chemical


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residues, solid water disposal, and food packaging materials. Ensuring a safe food supply requires prolonged shelf-life of a food product and choice of appropriate packaging materials which may constitute a critical disposal problem (Boudouropoulos & Arvanitoyannis, 2000). According to the Environmental Protection Agency, the annual generation of municipal solid waste in the United States increased from 88 million tonnes in 1960 to 229 million tons in 2001. Containers and packaging made up almost one-third of those 229 million tonnes (http://www.bren.ucsb.edu/services/student/GP/ green_packaging.pdf). The total packaging waste generated by various countries is shown in Fig. 7.1. The environmental impact of product packaging and its waste is an issue of growing importance and concern worldwide. All companies use various quantities of materials and other resources to package their products so that they will survive distribution and other harmful elements. Nowadays, our natural environment is adversely affected by product packaging and packaging waste (http://www.bren.ucsb.edu/services/student/GP/green_ packaging.pdf). Research demonstrates that consumers in many European countries regard packaging as a serious source of environmental pollution (Dichter Institut, 1987; Holland et al., 1989; Faller, 1990). So far, however, there has been no study of the extent to which consumers’ concerns about the environmental consequences of packaging affects their purchase of pre-packed everyday products (Bech-Larsen, 1996). Currently, there are

5 tonnes/year 10 tonnes/year

18 tonnes/year

2 tonnes/year 75 tonnes/year

Fig. 7.1

USA

Belgium

UK

Taiwan

Germany

Total packaging waste generation by country (adapted from http://www. p2pays.org/ref/20/19395.pdf).


Consumer attitude to food packaging and the market for products

163

environmental packaging design requirements in more than 25 countries and package reporting and advanced disposal fees in 30 countries (soon to be 35). All these countries’ programmes vary in terms of material definitions, packaging definitions, kinds of packaging covered, and fee structures (http://www.bren.ucsb.edu/services/student/GP/green_packaging.pdf). Beginning in the 1970s, a significant amount of research was conducted on consumer behaviour towards environmentally friendly products. Many variables were shown to drive consumer choice with regard to purchasing environmentally friendly products. These variables can be grouped into values, beliefs/knowledge, needs and motivations, attitudes, and demographics (Bui, 2005). Since packaging waste is more visible than most other environmental problems, it can arguably be used as a catalyst to galvanize consumers into action. However, the results of the various studies carried out suggest that, despite the high visibility of packaging waste, consumers’ concern about the environmental consequences of packaging is like their concern about most other environmental problems (Bech-Larsen, 1996).

7.2

Packaging materials

The main purpose of food packaging is to protect the product from its surroundings. Another aim is to maintain the quality of the food throughout the product’s shelf-life. Product shelf-life is controlled by three factors: product characteristics, product properties, and storage and distribution conditions of the individual package (Harte & Gray, 1987; Petersen et al., 1999). Two other functions of packaging are information – such as details of contents, ‘best before’ dates, nutritional values for foods – and promotion; in a competitive market the promotional role of packaging is as important as advertising (http://www.incpen.org/pages/userdata/incp/Consumerattitudestopackagingsurvey.pdf). The main categories of basic materials used for food packaging are (Lord, 2005): • • • •

plastics; paper; metals; glass.

Plastics, paper, and metal are the most important contributors to the CO2 emissions from packaging. They are responsible for about 3.3% of the European CO2 emissions (http://www.chem.uu.nl/nws/www/publica/98080. pdf). The above materials are applied in three broad categories of packaging: •

primary packaging, which is in contact with the goods and is taken home by consumers;


164 • •


secondary packaging, which covers the larger packaging such as boxes, used to carry quantities of primary packaged goods; tertiary packaging, which refers to the packaging that is used to assist transport of large quantities of goods, such as wooden pallets and plastic wrapping (Davis & Song, 2006).

7.3

‘Green’ packaging

The ‘puzzle’ in explaining why green markets have not taken off in the light of strong public concern for environmental protection can be explained thus: public ‘concern’ and consumer behaviour are far from identical. Often the public expects strong regulatory intervention by governments to safeguard the environment, without drawing any strong links between their individual purchasing decisions and the overall state of their environment (Commission for Environmental Cooperation, 1999). ‘Green’ packaging causes less damage to the environment than other forms of packaging – it is ‘environmentally friendly’. There are three types of ‘green’ packaging: • • •

reusable packaging, such as glass bottles, which can be cleaned and reused; recyclable packaging, which is made of materials that can be used again, usually after processing – such as glass, metal, card, and paper; biodegradable packaging, which will easily break down and disappear into the soil or the atmosphere, without causing damage (http://www. bbc.co.uk/schools/gcsebitesize/design/foodtech/packaginglabellingrev4. shtml).

North America is finally beginning to acknowledge the potential of biodegradable polyesters in packaging. The continent is lagging behind Europe and Asia in finding packaging applications for these synthetic resins. In fact, global suppliers have been commercializing a wide range of these biodegradable polyesters for the past 5 years. Demand is increasing at a reported rate of 30% per year – although from a comparatively small base. However, an obstacle that this ‘green’ packaging must overcome is its high cost (http://news.thomasnet.com/IMT/archives/2002/10/green_packaging.html?t=archive). Surprisingly, the 40–50% of consumers who say they buy ‘green’ do so only on occasion (Scarlett, 1996).

7.4

Disposal of packaging materials

Packaging can be safely handled in any modern waste management system, whether it is recycled, composted, burned, or buried.



165

5%

31%

23%

43% Metal

Fig. 7.2

Paper

Glass

Plastic

Recycling rate of materials from household packaging waste in the United Kingdom (adapted from Davis & Song, 2006).

7.4.1 Recycling Recycling is often held up to be the universal panacea for used packaging and so has become more politically acceptable than other treatment methods. Recycling has many benefits under the right circumstances but is has its own environmental and financial costs (http://www.incpen.org/pages/ userdata/incp/Consumerattitudestopackagingsurvey.pdf). The recycling rate of materials from household packaging waste in the United Kingdom is shown in Fig. 7.2.

7.4.2 Landfill Landfilling is essential for handling non-recyclable and non-combustible wastes and incinerator ash (Kashmanian, 1989). Although landfill was traditionally selected by many communities because of its low cost, it is anticipated that it will become prohibitively expensive. The costs of landfill will rise, due to the decreasing number of landfill sites (Arvanitoyannis & Bosnea, 2001). Current landfill technology does not support degradation of any material to any appreciable degree; plastics last up to 500 years in landfill (Armistead, 1994).


166


7.4.3 Incineration An alternative method of waste disposal to landfill is waste incineration (Arvanitoyannis & Bosnea, 2001). Incineration is useful in reducing the volume of waste that must be landfilled and can also generate usable thermal and electrical energy (Kashmanian, 1989). Incineration is becoming a more popular method of final waste disposal in both Southern and Eastern Europe as bans on this highly polluting and inefficient technology become more common in Northern Europe and the United States. Already, Poland, the Canadian province of Ontario, and two German Bundesländer have banned or put long-term moratoriums on new municipal waste incinerators due to environmental considerations (http://www.zhaba.cz/uploads/ media/1994_packaging.doc).

7.4.4 Composting Composting is essentially a process to break down waste by biodegradation and this is considered the most attractive route for treatment of biodegradable (or, in this particular context, compostable) packaging waste (Davis & Song, 2006).

7.4.5 Reuse Reuse of packaging and other ‘disposable’ goods also enhances source reduction goals by lowering demand for, and consumption of, virgin materials. Each time an item is reused, a new one need not be manufactured, purchased, and ultimately disposed of (Kashmanian, 1989).

7.5

Recycling of packaging materials

Recycling is a relatively old method with a well-recorded history. Metals have been recycled since their discovery because of their high value, rarity, and properties that allow near indefinite reprocessing. The recycling of old textiles has an equally long history since they were used for the production of paper (Arvanitoyannis & Bosnea, 2001). Glass makes up 8.2% of gross discards of the municipal solid waste stream. Of this amount, approximately 8.5% is recovered (Kashmanian, 1989). Glass recycling is hindered by the different colours of glass used. Clear glass makes the most desired cullet. Green glass is the most common colour for packaging and yet currently there is no sizeable UK recycling market (Davis & Song, 2006). European glass recycling rates are shown in Table 7.1. Aluminium is most commonly used as a material for beverage cans, foils and laminates. In 2001 in the United Kingdom, 5 billion cans of product were consumed and 42% of these were recycled (Wasteonline, 2002).



167

Table 7.1 European glass recycling rates (%) (adapted from Arvanitoyannis & Bosnea, 2001; http://www.allbusiness.com/nonmetallic-mineral/glass-glassmanufacturing/637774-1.html; http://www.assurre.eu/uploads/documents/pub-34_ en-7f0a5b7c-0b0c-496e-a531-cc7f4790ae78.pdf; http://www.enfo.ie/leaflets/as3.htm) Year Country Germany France Italy United Kingdom Spain Austria Denmark Sweden Finland

1989

1991

1993

1994

1995

1996

1997

1999

2000

53% 38% 42% 17% 24% 54% 36% 34% 36%

55%

71% 46% 52% 29% 29% 68% 64% 54%

75% 48% 54% 28% 31% 76% 67% 56% 50%

82% 50%

85% 50% 53% 26% 35%

89%

81% 55% 41%

83.6% 49.7% 46.9% 33.2% 31.3% 97.3% 80.6% 86.1% 64.3%

21%

27%

26% 42% 84% 63%

72% 78%

In Europe there is strong competition between steel and aluminium for beverage cans. Almost all of the lids of European beverage cans are made out of aluminium while 50% of the bodies of the cans are made out of steel and the other 50% are made out of aluminium (http://www.chem.uu.nl/nws/ www/publica/98080.pdf). Aluminum makes up 1.5% of gross discards of the municipal solid waste stream, of which 25% is recovered (Kashmanian, 1989). Recovered paper is today the most important raw material for the production of paper, paperboard, and corrugated board. Paper recycling in Europe increased markedly throughout the 1990s. This means that the recycling rate (percentage of recovered paper use compared with total paper consumption) was 53.2% in 2003, compared with about 40% in 1990. The prime objective of recovered paper recycling is to utilize the fibres contained in prior post-consumed recovered paper (Onusseit, 2006). The recycling rates of paper and metals (aluminium and steel cans) are presented in Fig. 7.3. Plastics make up 6.5% of gross discards of the municipal solid waste stream. Approximately 1% of discarded plastics is recovered (Kashmanian, 1989). There is a wide range of products made from recycled plastic. This includes polyethylene bin liners and carrier bags; polyvinyl chloride sewer pipes, flooring, and window frames; building insulation board; video and compact disk cassette cases; fencing and garden furniture; water butts, garden sheds, and composters; seed trays; anoraks and fleeces; fibre filling for sleeping bags and duvets; and a variety of office accessories (http://www. wasteonline.org.uk/resources/InformationSheets/Plastics.htm). The total amount of plastic waste generated, recycled, and recovered in Western Europe is shown in Fig. 7.4.


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Recycling rates (%)

90 85 80 75 70 65 60 55 50 45 40 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Year Paper

Aluminium cans

Steel cans

Total plastic waste (’000 tonnes)

Fig. 7.3 Recycling rates of paper and metals (aluminium and steel cans) (adapted from http://web-japan.org/stat/stats/19ENV51.html).

25 000 20 000 15 000 10 000 5000 0 1993

1995

1997

1999

2001

2003

Year Total plastic waste Plastic waste for mechanical recycling Recovered plastic

Fig. 7.4

7.6

Total plastic waste generated, recycled, and recovered in Western Europe (adapted from Garforth et al., 2004).

New packaging technologies

Increasing consumer demand for microbiologically safer foods, greater convenience, smaller packages, and longer product shelf-life is forcing the industry to develop new food processing, cooking, handling, and packaging strategies (Cagri et al., 2004). There are many reasons for changing an existing package or developing a new package, such as (Doyle, 1996a): • •

achieving legal compliance; attracting shoppers’ attention;


Consumer attitude to food packaging and the market for products • • • • • • •

169

demonstrating social responsibility; increasing consumer satisfaction; improving safety perceptions or meeting safety standards; responding to consumer complaints; responding to changing consumer needs; responding to competitive pressure; combinations of the above.

A breakthrough in food packaging occurred in 2004 with the introduction of Biota (Biota Brands of America, Telluride, CO) bottled water in a commercially compostable material (Lingle, 2005). This material is polylactide (PLA), a renewable material made from corn and marketed under the trade name NatureWorks PLA (Cargill Dow, Minnetonka, MN) (Eilert, 2005). Encapsulation involves the incorporation of food ingredients, enzymes, cells, or other materials in small capsules. Applications for this technique have increased in the food industry because the encapsulated materials can be protected from moisture, heat, or other extreme conditions, thus enhancing their stability and maintaining viability (Jimenez et al., 2004). The immobilization of enzymes in materials has recently been used for packaging applications. The objective of these bioactive materials is to catalyse a reaction that is considered beneficial from a nutritional point of view, i.e. decreasing the concentration of a non-desired food constituent, and/or producing a food substance beneficial to the health of the consumer (e.g. β-galactosidase and cholesterol reductase in the package walls for the hydrolysis of lactose and cholesterol, respectively) (Lopez-Rubio et al., 2006). The corn-based polymer PLA is increasingly popular because, unlike other plastics, it is not derived from petroleum. Corn-based plastics are starting to look cheap, now that oil prices are so high. Producing corn-based polymer PLA uses 65% less energy than producing conventional plastics, generates 68% fewer greenhouse gases, and contains no toxins. Corn plastic has been around for 20 years, but the polymer was too expensive for broad commercial applications (http://stuff.mit.edu/afs/athena/course/3/3.064/ www/slides/Smithsonian_corn_plastic.pdf). Two of the pioneer companies in using PLA as a packaging material were Dannon and McDonald’s in Germany, in yoghurt cups and cutlery, respectively. In the last 5 years, the use of PLA as a packaging material has increased in Europe, Japan, and the United States, mainly in the area of fresh products where PLA is being used as a food packaging polymer – such as for fruit and vegetables – and package applications include containers, drinking cups, sundae and salad cups, overwrap and lamination films, and blister packages (Auras et al., 2004). One of the challenges facing the food packaging industry in its efforts to produce biobased primary packaging is to match the durability of the packaging with product shelf-life. The biologically based packaging material


170


Table 7.2 Applications of biopackaging in the food industry (adapted from Petersen et al., 1999) Food product

Biopackaging

Fresh mushrooms Shredded lettuce and cabbage, head lettuce, cut broccoli, whole broccoli, tomatoes, sweet corn and blueberries Lean beef and bologna inoculated with pathogenic bacteria Bread, broccoli, and ground beef

Glass jar covered with gluten film Laminate of chitosan (14.5% by weight)–cellulose (48.3%) and polycaprolactone (36.2% glycerol and 1.0% protein) Polyethylene with corn starch (final concentration 6%) Corn starch-containing polyethylene (final corn starch concentration 6%) Starch–polyethylene films containing corn starch (0–28%), low- or highmolecular weight oxidized polyethylene and pro-oxidant

Ground beef

must remain stable without changes in mechanical and/or barrier properties and must function properly during storage until disposal. Subsequently, the material should biodegrade efficiently (Petersen et al., 1999). Some applications of biopackaging in the food industry are summarized in Table 7.2.

7.7

Food packaging regulation in the European Union

Public concern has been growing for decades about the environmental and financial impacts associated with the management of packaging materials from consumer products (http://www.p2pays.org/ref/20/19395.pdf). Presenting the story of the genesis and development of the European laws and regulations relating to food packaging constitutes a significant challenge (Heckman et al., 2005). The premise for the first packaging materials Framework Directive (76/893/EEC) was that differences between the national laws relating to packaging materials and articles was impeding free movement of goods in the community, and could create unequal conditions of competition that would affect the functioning of the market (Heckman et al., 2005). The EU Packaging Directive from 1994 (EU Directive 94/62/EC) has been an important basis, both for promoting increased recycling and recovery rates of packaging materials, and encouraging waste reduction related to packaging. Nationally, several countries have established agreements between environmental authorities and the packaging sector to follow up the requirements of the Packaging Directive, e.g. The Netherlands, United Kingdom, Sweden, and Norway (Hanssen et al., 2003).



171

Moreover, the biopackaging field is regulated primarily by two EU directives: ‘Plastics Materials and Articles Intended to Come into Contact with Foodstuffs’ (90/128/EEC) with later amendments, and ‘Packaging and Packaging Waste Directive’ (94/62/EEC) (Petersen et al., 1999). EU Directive 2002/16/EC is applicable to materials and articles that, in the finished product state, are intended to come into contact or are brought into contact with food-stuffs and are intended for that purpose and which are manufactured with or contain one or more of the following substances: (a) 2,2-bis(4-hydroxyphenyl)propane bis(2,3-epoxypropyl) ether, and some of its derivatives; (b) bis(hydroxyphenyl)methane bis(2,3-epoxypropyl)ethers and some of their derivatives; (c) other novolacglycidyl ethers and some of their derivatives (Arvanitoyannis et al., 2005). COM(2003)0689 and COD(2003)0272 are proposals for a regulation of the European parliament and of the council on materials and articles intended to come into contact with food (Commision of the European Communities, 2003). The target of this Regulation is to ensure the effective functioning of the internal market in relation to materials and articles intended to come into contact with food-stuffs, while providing the basis for securing a high level of protection of human health and the interests of consumers (Arvanitoyannis et al., 2005).

7.8

The study of consumer behaviour

In consumer surveys, one of the key questions often asked is how many respondents should be recruited to give a statistically reliable survey. Moreover, the costs of the survey and indeed the time required to produce results tend to increase with increasing sample size (Wangcharoen et al., 2005). Consumer research is difficult for at least four reasons: • • • •

in consumer research, the goal is to predict consumer purchase decisions; in consumer research, individual differences between consumers are significant; consumers think and behave in a dynamic, complex, and intrusive competitor environment; individual promotional elements such as food colour strongly interact with all other aspects of the marketer’s promotional plan to influence the consumer (Garber et al., 2003).

The study of consumers helps companies to improve their marketing strategies by understanding issues, such as: • •

how consumers think, feel, and select between different alternatives; how the consumer is influenced by the environment (e.g. culture, family, media);


172 • • • •


the behaviour of consumers while shopping or making other marketing decisions; limitations in consumer knowledge or information influence decisions; how consumer motivation and decision strategies differ between products; how marketers can improve their marketing campaigns and strategies (http://www.consumerpsychologist.com/). The four types of consumer buying behaviour are listed below.

1. Routine response/programmed behaviour: buying frequently low-cost items; little searching needed; purchased automatically (e.g. drinks, snack foods, milk, etc.). 2. Limited decision making: buying product occasionally; requires a moderate amount of time for information gathering (e.g. clothes). 3. Extensive decision making/complex: high involvement; unfamiliar, expensive and/or infrequently bought products (e.g. cars, homes, computers, education). 4. Impulse buying: no conscious planning (http://www.udel.edu/alex/ chapt6.html). There are six stages in the buying process – need arousal, information search, information evaluation, purchase decision, purchase, and postpurchase behaviour (satisfaction, dissatisfaction) (Hisrich, 2000). Of course, not every purchase involves all the stages, and not all decision processes lead to a purchase (Fig. 7.5) (Hisrich, 2000; http://www.udel.edu/alex/chapt6. html). For example, in a routine purchase, where the consumer buys the same brand as before, there is no need for information search or evaluation of the collected information (Hisrich, 2000). In the consumer behaviour context, it is typically accepted that customers complain when they have exceeded their zone of tolerance for dissatisfaction. In other words, customers with relatively high levels of dissatisfaction are most likely to complain compared with those with neutral or positive experiences that lead to satisfaction or indifference (Goetzinger et al., 2006). 7.8.1 Consumer behaviour The study of consumer behaviour aims to elucidate how people process information, make decisions, and evaluate products and purchases (http:// www.lycos.com/info/consumer-behaviour.html). It attempts to understand the buyer decision making process, both individually and in groups. It studies characteristics of individual consumers such as demographics, psychographics, and behavioural variables in an attempt to understand people’s wants. It also tries to assess influences on the consumer from groups such as family, friends, reference groups, and society in general (http://en.wikipedia.org/wiki/Consumer_behavior).



173

Awareness of need

Information search

Information evaluation

Purchase decision

Purchase

Post-purchase behaviour (satisfaction or dissatisfaction)

Fig. 7.5 Six-stage model of the consumer buying process (adapted from Hisrich, 2000; http://www.udel.edu/alex/chapt6.html).

Consumers make their purchasing decisions based on a number of factors. In addition to the price of the product, factors such as appearance, convenience, and perceived quality determine the decisions made in the marketplace. Assuming the existence of an ideal world, consumers would base their choices on perfect information about product attributes and hence purchase foods that maximize their well-being. However, without perfect food safety information, the consumer is faced with a more difficult decision when buying food (http://www.uni-giessen.de/zeu/Papers/DiscPap5. pdf). It is important to consider the fact that purchases of food are not only influenced by consumer’s attitudes to the packaging, but also by many other factors, including the purchasing situation and the consumer’s attitudes to the other characteristics of the product (e.g. taste and nutrition) (Bech-Larsen, 1996). A large proportion of the population (66%) feels that in general products are over-packed. This view is generated to a great extent by the perception that products have too many layers of packaging – e.g. bag, box, and


174


Table 7.3 Consumer’s attitudes towards packaging (adapted from http://www. incpen.org/pages/userdata/incp/Consumerattitudestopackagingsurvey.pdf) Statement

Level of agreement (%)

Packaging protects the produce Packaging makes things attractive to buy Manufacturers put too much emphasis on packaging Overall there is too much packaging Packaging makes things available out of season

86 79 73 76 72

Table 7.4 Percentage of consumers who reported problems with various types of packaging material (adapted from Winder et al., 2002)

Not strong enough to open it Not obvious how to open it Cannot see where or how to start opening it Worried about spilling or wasting product Always open it wrongly so product does not leave packaging properly

Tinned goods

Cans

Plastic bottles/jars

Glass bottles/jars

Cartons/boxes

19.0

12.5

36.5

55.5

21.5

8.0

4.0

8.0

5.5

24.5

8.5

4.0

5.5

7.0

33.5

17.0

15.0

24.5

21.0

38.5

9.0

4.5

7.0

5.5

42.5

cellophane over-wrap – or that the packaging itself is too large or too grand for the goods contained inside (http://www.incpen.org/pages/userdata/incp/ Consumerattitudestopackagingsurvey.pdf). Table 7.3 presents consumers’ attitudes towards packaging. The importance of both complaints and compliments, and their interrelatedness, has received substantial attention within the consumer behaviour literature. A main point of discussion has been that the attributes leading to satisfaction are not the same as the attributes leading to dissatisfaction (Goetzinger et al., 2006). The percentage of consumers who reported problems with various types of packaging material is shown in Table 7.4.

7.8.2 Consumer behaviour regarding recycled packaging materials In the food industry alone, the consumer can choose from over 20 000 items; and new products are constantly being added to the large number of items



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already available (Hisrich, 2000). The environment is an important supporting issue in many purchasing decisions. It tilts rather than triggers purchases, playing an important but secondary role, second to safety, second to cost, second to freshness and quality preservation, even second to convenience and ease of use. Consumers feel very strongly that packaging should be more eco-friendly – even more strongly than they feel it should be easier or more convenient to open and re-close (Doyle, 1996b). Kellogg’s is one of the few cereal companies employing recycled material in its packaging. On the company’s box of Mueslix breakfast cereal, the following statement is stamped next to the recycle symbol with chasing arrows: ‘Carton made from 100% recycled paper, minimum 35% post-consumer content’; indicating the concern of food processors for environmental issues (Stauffer, 1997). Although consumers are concerned about packaging waste, they do not seem to think that the problem is insurmountable. This probably means that consumers can be motivated to make a personal effort, but it also means that there are limits to the size of the effort they are prepared to make (in terms of money, time, and the amount of information they are willing to absorb) (Bech-Larsen, 1996). The results of a survey of 400 customers proposing ideas to manufacturers regarding packaging materials are presented in Fig. 7.6. With regard to eco-labelling, consumers are confused due to inappropriate labelling. Research has shown that consumers do not always understand environmentally friendly labels attached to products (Kangun & Polonsky,

90%

84%

Number of customers (%)

80% 70% 70% 62%

62%

More tamper safe

Easier to open

60% 50% 40% 30% 20% 10% 0% More eco-friendly

Easier to re-close

Fig. 7.6 Survey of 400 customers proposing some ideas to manufacturers regarding packaging materials (adapted from Doyle, 1996b).


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1995). Eco-labels such as ‘biodegradable’, ‘sustainable’, ‘environmentally friendly’, and ‘recyclable’ are usually unfamiliar and/or unknown to consumers. In addition, merely recognizing a label does not mean that one understands the meaning of that label (Morris et al., 1995). Consumers must know and trust a label before they can use it to make purchasing decisions (Bui, 2005). France, The Netherlands, Germany, Denmark, Norway, and Sweden are all leaders in eco-labelling. Virtually all countries in Europe – including Central and Eastern Europe – the European Union, and the United Nations are considering eco-label legislation (http://www.zhaba.cz/ uploads/media/1994_packaging.doc). Studies investigating how knowledge affects consumers’ ecological behaviours have shown contradictory findings. In most cases, knowledge was found to be significantly related to how consumers gather, organize, and evaluate products (Alba & Hutchinson 1987), as well as being a significant predictor of environmentally friendly behaviour (Chan, 1999; Vining & Ebreo 1990). In self-reported behaviour surveys, consumers report that they are willing to spend extra money for a socially desirable concept like environmentalism, but purchasing data suggest that ‘green’ matters very little when compared with price, quality, and convenience; therefore, businesses have become sceptical about consumers’ responses to such surveys (Mainieri et al., 1997). However, economic arguments suggest that convenience, and more generally costs, may have a significant impact on recycling behaviour (Jenkins et al., 2003). Many studies also explore links between demographic characteristics, socioeconomic characteristics, and recycling, with mixed results. The most commonly examined variables are age, education, gender, and income; but dwelling type, ethnicity, family size, and political beliefs have also been considered (Saphores et al., 2006). Based on demographic profiling, ‘green’ consumers generally are (Bui, 2005): • • •

people with a high income; people with a higher level of education; pre-middle-aged females.

Ireland has a strong track record in recovering and recycling packaging waste. Packaging waste recovery levels were as low as 14% in 1998 and the European Union set targets of 25% for Ireland by 2001 and 50% by 2005. These were both achieved and with a recovery rate of nearly 60% in 2005, Ireland continues – for the third year in a row – to exceed its EU targets. In fact, Ireland had in 2005 reached the target set by the European Union for Ireland for 2011 (http://www.environ.ie/DOEI/DOEIPol.nsf/0/ c8f71c4e05251d8280256f0f003bc802/$FILE/National%20Waste%20Repor t%202005.doc). Consumers’ letter-writing campaigns encouraging companies to discontinue using a combination of plastic and metal cans, or to use recycled feedstock for all of their greeting cards (or else to not market virgin paper cards under their company name), not only demonstrate how many



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consumers are concerned, but also generate good or bad publicity for the targeted companies (Kashmanian, 1989). Environmental information should not be based on dire warnings about impending disaster. On the contrary, it should stress the positive contribution to the conservation/recreation of environmental qualities that consumers can make (Ellen et al., 1991). Furthermore, preferential consumer purchasing on a large scale can impart economic gains to a selected company or product line. Alternatively, consumer boycotts can inflict economic losses on corporations that do not heed consumer concerns (Kashmanian, 1989). The increased consumer demand for high-quality, long shelf-life, readyto-eat foods has initiated the development of only mildly preserved products that keep their natural and fresh appearance as far as possible (Guilbert et al., 1996). A survey showed that 72% of US shoppers are willing to pay more for improved food and beverage packaging that guarantees freshness and taste. Indeed, the desire for these two qualities was seen as more important than traditional factors such as price and convenience (Ingram, 2006). However, consumers tend to exaggerate when asked to provide self-reported data on their willingness to pay more for a product, underestimating their price sensitivity in real market conditions (Krystallis et al., 2006). Another survey showed that 44% of consumers reported nutritional issues as most important in their purchasing decisions, while 19% reported that price was the most significant determinant of their purchasing. Only 14% cited environmental characteristics as important. Evaluating the survey, the association commented that few grocery shoppers take the environmental consequences of packaging into account when they purchase food products (Scarlett, 1996).

7.8.3 Consumer behaviour regarding biodegradable packaging materials The term ‘biodegradable’ materials’ is used to describe those materials that can be degraded by the enzymatic action of living organisms (such as bacteria, yeasts, and fungi) and the ultimate end-products of the degradation process – these being CO2, H2O, and biomass under aerobic conditions and hydrocarbons, methane, and biomass under anaerobic conditions (Doi & Fukuda, 1994). The global annual production capacity for biodegradable materials is around 300 000 tonnes, with the majority of plants commissioned since 2000, according to figures from European Bioplastics (Carmichael, 2006). The use of biodegradable packaging materials has the greatest potential in countries where landfill is the main waste management tool (Petersen et al., 1999). The possibility of choosing biodegradable and non-polluting products is a good alternative to many consumers. The quality of water, countryside air, etc., may be affected if consumers choose biodegradable and non-polluting products. As a consequence the whole agribusiness sector should face the challenge to maintain the food quality and quantity supply with the mentioned restrictions (http://ejeafche.uvigo. es/2(4)2003/001242003f.htm).


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In 1999, the International Biodegradable Plastics Institute (BPI) was launched, with the mandate of promoting the production, use, and recovery of ‘truly biodegradable’ plastics. In cooperation with the US Composting Council, BPI developed a certification process and logo (http://www. f-k.com/2005/fabri-kals-greenware-cups-are-bpi-certified-91-72.html). However, it is not just relatively high prices that have delayed bio-plastics adoption until now, but also a lack of attention from legislators and some underperforming products. All French shopping bags will have to be biodegradable from 2010, thanks to new legislation (Carmichael, 2006). The worldwide consumption of biodegradable polymers has increased from 14 million kg in 1996 to an estimated 68 million kg in 2001. Target markets for biodegradable products include packaging materials (trash bags, wrappings, loose-fill foam, food containers, film wrapping, laminated paper), disposable non-woven (engineered fabrics) and hygiene products (diaper back sheets, cotton swabs), consumer goods (fast-food tableware, containers, egg cartons, razor handles, toys), and agricultural tools (mulch films, planters) (Gross & Kalra, 2002). Among commercially available biodegradable packaging materials based on natural raw materials, those based on polysaccharides (starch) are currently the front-runners. This is mainly attributable to the fact that starch is annually renewable, abundant, and inexpensive (Davis & Song, 2000). An example of biodegradable packaging material is the moulded-pulp kiwi pack made from palm fibre that biodegrades in a few months; the film covering and package label are also biodegradable (Ingram, 2006). To date, poly(vinyl alcohol) is used in textiles, paper, and packaging industries as paper coatings, adhesives, and films. Furthermore, PLA is currently used in packaging (film, thermoformed containers, and short shelf-life bottles) (Gross & Kalra, 2002). In a survey, 1000 Americans were questioned about solid waste management problems. The results showed that 88% of those surveyed felt that solid waste disposal was an important issue, 99% felt that recycling and biodegradability will help to alleviate the problem of solid waste, 91% would pay a few cents more for product packages that were recyclable and biodegradable, and 87% felt that the government should provide incentives for manufacturers to use recyclable and biodegradable packaging (Kashmanian, 1989). The desire for biodegradable packaging is not based on an understanding of the relative merits of degradable packaging, but rather the consumer’s desire for a ‘panacea’ to the waste disposal problem (Kashmanian, 1989).

7.9

Conclusions

Although environmental pollution seems to be one of the most important issues that the consumer is worried about, the latter seems neither to realize



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nor to be aware of the importance of recycling and/or biodegradable packaging. The main reasons for this have to be attributed to a low level of awareness because of inadequate information. Furthermore, most consumers believe that it is the government’s task to provide incentives to manufacturers (Germany is a representative example) to use recyclable and biodegradable packaging. A more ‘aggressive’ and intensive campaign towards consumers’ education vis-à-vis recycled and biodegradable packaging must be undertaken by consumer organizations worldwide in conjunction with incentives from governments.

7.10

References

alba, j.w. & hutchinson, j.w. (1987). Dimensions of consumer expertise. Journal of Consumer Research, 13, 411–454. armistead, c.r. (1994). Recycling technology for biodegradable plastics. In Chemistry and Technology of Biodegradable Polymers, 1st edn (ed. Griffin, G.J.L), Springer, Berlin, pp. 97–115. arvanitoyannis, i.s. & bosnea, l.a. (2001). Recycling of polymeric materials used for food packaging: current status and perspectives. Food Reviews International, 17(3), 291–346. arvanitoyannis, i.s., choreftaki, s., & tserkezou, p. (2005). An update of EU legislation (Directives and Regulations) on food-related issues (Safety, Hygiene, Packaging, Technology, GMOs, Additives, Radiation, Labelling): presentation and comments. International Journal of Food Science and Technology, 40, 1021–1112. auras, r., harte, b., & selke, s. (2004). An overview of polylactides as packaging materials. Macromolecular Bioscience, 4, 835–864. bech-larsen, t. (1996). Danish consumers’ attitudes to the functional and environmental characteristics of food packaging. Journal of Consumer Policy, 19, 339–363. boudouropoulos, i.d. & arvanitoyannis, i.s. (2000). Potential and perspectives for application of environmental management system (EMS) and ISO 14000 to food industries. Food Reviews International, 16(2), 177–237. bui, h. (2005). Environmental marketing: a model of consumer behavior. In Proceedings of the Annual Meeting of the Association of Collegiate Marketing Educators (ed. Johnston, T.C.), 1–5 March, Dallas, TX, pp. 20–28. cagri, a., ustunol, z., & ryser, e.t. (2004). Antimicrobial edible films and coatings. Journal of Food Protection, 67(4), 833–848. carmichael, h. (2006). Compost-ready packaging. Chemistry and Industry, 16 October. chan, k. (1999). Market segmentation of green consumers in Hong Kong. Journal of International Consumer Marketing, 12(2), 7–24. commission for environmental cooperation (1999). Supporting green markets environmental labelling, certification and procurement schemes in Canada, Mexico and the United States. Available online at (accessed 15 February, 2007). commission of the european communities (2003). Proposal for a regulation of the European parliament and of the Council on materials and articles intended to come into contact with food. Brussels, 17/11/2003, COM(2003) 689 final, 2003/0272 (COD) (On line: http://eur-lex.europa.eu/LexUriServ/LexUriServ. do?uri=COM:2003:0689:FIN:EN:PDF).


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davis, g. & song, j.h. (2006). Biodegradable packaging based on raw materials from crops and their impact on waste management. Industrial Crops and Products, 23, 147–161. dichter institut (1987). PACK12, Das Image der Verpackung. Pack 12 Sekretariat, c/o Ritter Marketing AG, Bolligen, Switzerland. doi, y. & fukuda, k. (1994). In Biodegradable Plastics and Polymers: Proceedings of the Third International Scientific Workshop on Biodegradable Plastics and Polymers, Osaka, Japan (Studies in Polymer Science, 12), (eds Doi, Y. and Fukuda, K.), Elsevier Science, New York, pp. 464–469. doyle, m. (1996a). Introduction. In Packaging Strategy. Winning the Consumer (ed. Doyle, M.), Technomic Publishing, Lancaster, PA, pp. 1–12. doyle, m. (1996b). The consumer side of packaging power. In Packaging Strategy. Winning the Consumer (ed. Doyle, M.), Technomic Publishing, Lancaster, PA, pp. 153–176. eilert, s.j. (2005). New packaging technologies for the 21st century. Meat Science, 71, 122–127. ellen, p.s., wiener, j.l., & cobb-walgren, c. (1991). The role of perceived consumer effectiveness in motivating environmentally conscious behaviours. Journal of Public Policy and Marketing, 2, 102–117. faller (1990). Arzneimittel Verpackungen aus der Sicht iilterer Menschen, August Failer KG, Waldkirch. garber jr, l.l., hyatt, e.m., & starr jr, r.g. (2003). Measuring consumer response to food products. Food Quality and Preference, 14, 3–15. garforth, a.a., ali, s., hernandez-martinez, j., & akah, a. (2004). Feedstock recycling of polymer wastes. Current Opinion in Solid State and Materials Science, 8, 419–425. goetzinger, l., park, j.k., & widdows, r. (2006). E-customers’ third party complaining and complimenting behaviour. International Journal of Service Industry Management, 17(2), 193–206. gross, r.a. & kalra, b. (2002). Biodegradable polymers for the environment. Science, 297, 803–807. guilbert, s., gontard, n., & gorris, l.g.m. (1996). Prolongation of the shelf-life of perishable food products using biodegradable films and coatings. LebensmittelWissenschaft und Technologie, 29, 10–17. hanssen, o.j., olsen, a., moller, h., & rubach, s. (2003). National indicators for material efficiency and waste minimization for the Norwegian packaging sector 1995–2001. Resources, Conservation and Recycling, 38, 123–137. harte, b.r. & gray, j.i. (1987). The influence of packaging on product quality in food product package compatability. In Proceedings of a Seminar at the School of Packaging (eds Gray, J.I., Harte, B.R., and Miltz, J.), Michigan State University, East Lansing, MI, pp. 17–29. heckman, j.h. (2005). Food packaging regulation in the United States and the European Union. Regulatory Toxicology and Pharmacology, 42, 96–122. hisrich, r.d. (2000). Marketing, 2nd edn, Barron’s Educational Series, Inc., Hauppauge, NY. holland, h., pfirrmann, a., & jakobs, p. (1989). Verpackungsvermeidung und Wiederverwertung. Wo steht der Endverbraucher? Arbeitsgemeinschaft Verpackung und Umwelt, Bonn. ingram, b. (2006). A new lease on shelf life. Innovative packaging for perishable products is becoming more crucial to brand loyalty. Progressive Grocer, 1 July. jenkins, r.r., martinez, s.a., palmer, k., & podolsky, m.j. (2003). The determinants of household recycling: a material-specific analysis of recycling program features and unit pricing. Journal of Environmental Economics and Management, 45, 294–318.



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jimenez, m., garcia, h.s., & beristain, c.i. (2004). Spray-drying microencapsulation and oxidative stability of conjugated linoleic acid. European Food Research and Technology, 219, 588–592. kangun, n. & polonsky, m.j. (1995). Regulation of environmental marketing claims: a comparative perspective. International Journal of Advertising, 14, 1–24. kashmanian, r.m. (1989). Promoting Source Reduction and Recyclability in the Marketplace: A Study of Consumer and Industry Response to Promotion of Source Reduced, Recycled, and Recyclable Products and Packaging. US Environmental Protection Agency, Washington, DC. krystallis, a., arvanitoyannis, i., & chryssohoidis, g. (2006). Is there a real difference between conventional and organic meat? Investigating consumers’ attitudes towards both meat types as an indicator of organic meat’s market potential. Journal of Food Products Marketing, 12(2), 47–78. lillford, p.j. & edwards, m.f. (1997). Clean technology in food processing. Philosophical Transactions of the Royal Society of London A, 355, 1363–1371. lingle, r. (2005). BIOTA’s high-water mark in sustainable packaging. Packaging World, 8, 62–64. lopez-rubio, a., gavara, r., & lagaron, j.m. (2006). Bioactive packaging: turning foods into healthier foods through biomaterials. Trends in Food Science and Technology, 17, 567–575. lord, a.w.w. (2005). Packaging materials. Food and Nutritional Analysis, 12, 341–352. mainieri, t. & barnett, e.g. (1997). Green buying: the influence of environmental concern on consumer behaviour. Journal of Social Psychology, 137(2), 189–205. morris, l.a., hastak, m., & mazis, m.b. (1995). Consumer comprehension of environmental advertising and labelling claims. Journal of Consumer Affairs, 29, 328–350. onusseit, h. (2006). The influence of adhesives on recycling. Resources, Conservation and Recycling, 46, 168–181. petersen, k., nielsen, p.v., bertelsen, g., lawther, m., olsen, m.b., nilsson, n.h., & mortensen, g. (1999). Potential of biobased materials for food packaging. Trends in Food Science and Technology, 10, 52–68. saphores, j.-d.m., nixon, h., ogunseitan, o.a., & shapiro, a.a. (2006). Household willingness to recycle electronic waste: an application to California. Environment and Behavior, 38, 183–208. scarlett, l. (1996). Packaging, solid waste, and environmental trade-offs. In Packaging Strategy. Winning the Consumer (ed. Doyle, M.), Technomic Publishing, Lancaster, PA, pp. 23–34. stauffer, j.e. (1997). ISO 14000 standards. Cereal Foods World, 42(4), 228–230. vining, j. & ebreo, a. (1990). What makes a recycler? A comparison of recyclers and nonrecyclers. Environmental Behavior, 22, 55–73. wangcharoen, w., ngarmsak, t., & wilkinson, b.h. (2005). Snack product consumer surveys: large versus small samples. Food Quality and Preference, 16, 511–516. wasteonline (2002). Information sheet on packaging. Waste Watch, January 2002, UK. Available online at . winder, b., ridgway, k., nelson, a., & baldwin, j. (2002). Food and drink packaging: who is complaining and who should be complaining. Applied Ergonomics, 33, 433–438.


8 Environmental assessment of food packaging and advanced methods for choosing the correct materials K. Verghese, RMIT University, Australia

8.1

Introduction

As consumers increasingly demand food that is healthy, convenient and quick to prepare, the selection of appropriate packaging materials to ensure that the food’s nutritional value and shelf-life are maintained will become more complex. Not only does the packaging development team need to ensure compatibility between product and packaging materials, required shelf-life, production line efficiency and cost, but they also need to consider the environmental impacts associated with the selection, use and postconsumer waste management of the discarded packaging system. This is compounded by the pressures and demands from retailers to use shelfready packaging and the array of different waste management regulatory and policy approaches that governments throughout the world are using to manage the waste management issues associated with the use and disposal of used packaging materials. These approaches range from bans or taxes on particular materials through to voluntary programmes, so decisions about which packaging materials to select will be influenced to some degree by the policy approach in a particular country. In response to these increasing concerns and the needs of industry to balance the functional requirements of packaging materials with the environmental burdens of their production, use and post-consumer waste management, several international collaborative partnerships are leading the way in the debate on what constitutes sustainable packaging. These partnerships are involved in engaging with stakeholders, defining what constitutes sustainable packaging and developing decision support tools to assist industry in finding a balance.


Environmental assessment of food packaging and advanced methods

183

This chapter will explore the drivers behind the need to select and develop sustainable packaging systems in the context of balancing this with trends being observed in food packaging systems. An exploration of the environmental issues associated with packaging materials will then be presented. This will be followed by a discussion of available, or currently being developed, decision support tools that will assist industry in finding the balance between commercial demands, consumer expectations, government policy and environmental impacts. The context and development of the notion of sustainable packaging will then be explored, followed by a guide to implementing environmental assessment approaches in an organisation. The chapter concludes with a discussion of future directions for environmental assessment decision support tools for the global packaging industry.

8.2

Modern day lifestyle conflicts and demands from the retail sector

With less time to prepare meals, eating on the go, the number of persons per household declining and an ageing population, our modern Western lifestyle is becoming more hectic and is placing new and challenging demands upon the way food is packaged and purchased (Erlov et al., 2000; Pira and University of Brighton, 2005; ABS, 2006) (Table 8.1). For instance, new multi-layer polymer materials are highly material resource efficient compared with the traditional steel can or glass jar, though the recovery and reprocessing of these multi-layer materials post-consumer does not occur with currently available technologies. The material is either sent to landfill or to waste-to-energy facilities. Food products are being packaged in smaller unit sizes, instead of bulk, to accommodate for the changes occurring in household structures which results in more packaging being used per unit of product. The design of packaging systems for food to be reheated in microwaves for instance, can introduce several different types of packaging materials which may not be easily separable, thereby hindering the ability to source separate for recycling. In addition, the introduction of degradable polymers, while resulting in environmental benefits in certain stages of the life cycle compared with traditional polymers, can, if mixed with polymers such as polyethylene terephthalate and high-density polyethylene, contaminate and hinder the recyclability of these polymers (ExcelPlas Australia 2004). There are also pressures being imposed upon the packaging supply chain from retailers (WalMart, 2006; Marks & Spencer, 2007; Sainsbury, 2007; Tesco, 2007). Retailers are in a unique and critical position in the supply chain as they are the only sector that interfaces directly with consumers and their business strategies have flow-on effects throughout the supply chain (SPA, 2006). Retailers determine which products will be sold and are


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Table 8.1 Examples of packaging trends, drivers and environmental impacts Packaging trend

Driver

Environmental impacts

Sale of products in smaller portions

More packaging material per unit of product

Products with longer shelf-life

Increased number of two- and single-person households; popularity of small portions for children’s lunch boxes More women working; longer working hours for those employed; increasing popularity of convenience foods; changing lifestyle priorities; reduced interest and skills in food preparation Increased popularity of convenience foods, e.g. bags of salad, stir fry mixes; trend to centrally, pre-packed meat to meet supermarket demands for efficiency and tighter health standards; increased demand for fresh and healthy foods Trend to increased consumer convenience, e.g. shopping less frequently for staples

Tamper evidence

Contamination cases

Premium packed products versus budget packed products

Lifestyle enhancement

Increasing range of complete meal replacements

Pre-packed meat and vegetables in modified atmosphere packaging (MAP)

More packaging material per unit of product, mostly not currently recyclable

More material per unit product, not currently recyclable

MAP films not currently recyclable; multi-layer barrier bottles not recyclable and may contaminate recycling streams Additional packaging, mostly non-recyclable More packaging variety for same type of products

Source: James et al. (2005; p. 373).

increasingly specifying how products will be packaged. Many are working to reduce supply chain costs; for example, with the introduction of shelfready packaging (i.e. a shipper, carton, tray or other packaging that easily converts into a retail unit for placement directly on shelf) (Wardrop-Brown, 2006), designed to save time and money in the last 50 metres of the supply chain (i.e. from the supermarket back dock to the shelf). In addition, they are targeting a reduction in the amount of packaging used on particular products, using recyclable or compostable packaging materials, and sourcing paper materials from Forest Stewardship Council certified board manufacturers (Marks & Spencer, 2007; Sainsbury, 2007; Tesco, 2007). Different packaging combinations are being explored by brand-owners to ensure that



185

retailers will accept their packaged products, including the replacement of cardboard cartons with cardboard trays and shrink film, and the introduction of roll cages and reusable produce crates. These are having major impacts upon the way brand-owners package and deliver their packed product into the retail environment such as planogram and case count requirements (i.e. diagram that illustrates how and where products are to be displayed on a retail shelf) (Randall 2006); compatibilities with current packaging equipment; pallet efficiencies and stability; integrity of packaging in the distribution environment and retail shelf presentation. There are potentially unknown and non-quantitifed environmental impacts behind shelf-ready packaging and these need to be calculated.

8.3

Recognition of the environmental impacts of packaging in the food industry

Packaging performs a multitude of functions including the protection, containment, distribution and marketing of products across the globe. The availability of packaging materials and technology allows products to be manufactured and distributed throughout the economy and across the globe; it provides for the efficient distribution and marketing of products; and prevents product spoilage and waste, thereby reducing environmental impacts (Verghese et al., 2006). There are typically three levels of packaging: • primary (or retail) packaging – its role is to contain and protect the product in addition to contributing to the promotion of the product (e.g. glass bottle); • secondary (or merchandising) packaging – holds and contains the primary packaging (e.g. cardboard carton); • tertiary (or transport, industrial or traded) packaging – facilitates the movement of the primary and secondary packaging (e.g. wooden pallet, stretch wrap film). Like any other manufactured product, packaging materials have environmental impacts that are not sustainable in the long term. These, according to James et al. (2005, p. 374) include: • ‘consumption of non-renewable resources (e.g. materials and energy); • generation of air emissions in production, transport and use that contribute to air pollution, ozone layer depletion and global warming; • generation of waterborne emissions that contribute to pollution of waterways; • production of solid waste requiring disposal in landfill.’ Each packaging material has an impact upon the environment. Challenges are experienced by those with the responsibility of trying to


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Environmentally compatible food packaging Inputs (at each stage) Energy

Water

Raw materials

Raw Processing Design material sourcing

Labour

Transportation

Manufacture

Airborne and waterborne emissions Solid waste

Distribution

Infrastructure

Use

Habitat impacts

Postconsumption

Climate impacts

Outputs (at each stage) Functions of packaging Product protection Convenience Theft deterrence Storage Information Branding and marketing Preservation

Fig. 8.1

Simplified packaging chain. Amended from Imhoff (2005; p. 14).

determine which material has a lower environmental impact, when the impacts occur at different stages of the life cycle and the severity of the impact will also vary over the life cycle. As illustrated in Fig. 8.1, there are different life cycle stages (processes) that are undertaken from extraction of raw materials through to production, conversion, transport, filling, use and waste management. At each of these stages resources and energy are consumed and emissions and wastes are generated. For the product–packaging development team, decisions typically come down to trade-offs associated with packaging materials sourced from renewable and non-renewable resources. Materials sourced from non-renewable resources (e.g. crude oil) have impacts, for example, upon the depletion of finite resources; whereas, materials sourced from renewable resources (e.g. crops, timber) have impacts, for example, upon land and water use. In the case of renewable resources, questions should also be posed as to whether the practices of growing and harvesting are performed using sustainable processes. Making decisions as to which material is preferable needs to take into consideration where the resources are extracted but also their applications in converting and use, pallet and transport efficiencies, and the availability of post-consumer waste management processes for their recovery. Table 8.2 shows examples of typical questions that should be posed when



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Table 8.2 Examples of typical questions to pose during material selection and examples of their related environmental impacts Question

Environmental impacts (examples)

Is the material from a nonrenewable resource?

Depletion on finite resources; land use transformation; air and water emissions and solid waste generation Land use and transformation, water use and run-off, chemical and fertiliser use Coal: depletion of finite resources, high greenhouse emissions generated Hydro: damming of rivers and disruptions to water flows Nuclear: depletion of finite resource, radioactive waste requiring secure disposal Fuel consumption and air emissions, e.g. • articulated truck (30 tonne of product): generates 0.114 kg CO2 per tonne kilometre of product moved • rail freight: generates 0.012 kg CO2 per tonne kilometre of product moved • international ship: generates 0.005 kg CO2 per tonne kilometre of product moved Influences transport efficiencies and fuel consumption

Is the material from a renewable resource? What energy sources are used in the manufacture of the packaging materials (e.g. coal, hydro, nuclear)? What transport mode will be required to deliver packaging materials to your operation?

What is the pallet efficiency for packaging materials being sent to your operations? What packaging is used to deliver your packaging systems? Are they single-trip packaging, reusable or returnable?

Material consumption; generation of solid waste (for single-trip packaging); transport required for reusable and returnable packaging

making decisions on which packaging material to select, as they each result in particular environmental issues. By posing these questions against each packaging material option, information can be gathered that can be used in the decision making process. Packaging systems that have been designed to use materials efficiently and effectively can also reduce environmental impacts through the protection and safe delivery of the food contained within. According to Erlov et al. (2000), by reducing the weight and volume of packaging and its role in protecting the packed product becoming wasted are the two most significant features of packaging for the prevention of environmental impacts. Erlov et al. (2000) also found that when the life cycle impacts of producing packaging materials are compared with those of sourcing and producing food products, the energy required for the product was greater than 68% of the total product–packaging system combination (Table 8.3).


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Table 8.3 Examples of total energy used for different food packaging systems Energy content (%) Product

700 g loaf of bread with PP bag and PS clip 1 kg of tomato sauce in PP bottle 1 litre of milk in aseptic carton 1 kg yoghurt in gable top carton

Consumed product

Packaging system

Product waste

79 68 75 71

3 23 18 18

18 9 7 11

Notes: the energy was calculated using publicly available life cycle assessment (LCA) data. It included all the energy needed for the production, distribution and storage (from the growing of corn to its consumption by the consumer) and for packaging. Product waste included losses during distribution, storage and at the consumer level (Erlov et al., 2000). PP, polypropylene; PS, polystyrene.

Table 8.3 demonstrates the importance of ensuring that packaging materials have been selected appropriately so that they are effective in their protection and containment of the food product and also use materials efficiently. It additionally illustrates that as a system the life cycle of the product is significant in comparison with the packaging materials, and that the product and packaging materials should be considered as a system.

8.4

Environmental assessment of food packaging systems

The product–packaging development team normally includes individuals with expertise in packaging technology, process engineering, marketing and design. Increasingly the team will also need to have expertise in environmental management to help them to consider the environmental implications of their decisions within the business context. This knowledge could be provided by an environmental manager or external consultant, or by ensuring that all staff have a basic understanding of environmental issues and access to specialist tools to assist in the design process. It is important to embed environmental considerations early in the design process because as decisions are made with respect to selection of packaging materials, graphics and inks, equipment, etc., the environmental impacts associated with these choices are being ‘locked-in’ to the product– packaging system design. It is more difficult to try and reduce or eliminate these environmental impacts when the design has been finalised and the product is to be launched into the marketplace, than in the early stages of design. The environmental impacts of packaging materials need to be considered in the context of other issues, including final product costs, maintaining product shelf-life, transport and distribution costs, compatability with captial infrastructure such as packaging machines, graphic design and retail



Raw materials

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Recyclability Recycled content Process requirements Material properties

Filling line performance Packaging Stackability Closed loop recycling conversion Product Shelf-life requirements Open loop recycling manufacture Essential Requirements and filling Identifying material legislation components Recycling Separability of components Removability of contaminants Distribution Emptying Recovery Degradability (composting) Energy content (incineration)

Use Openability, reclosability Dispensing, dosing Product preservation Information

Retail

Supply chain hazards − shock, vibration, compression Safe handling Product preservation

Handling Display Sales impact − shelf presence, brand awareness Tamper evidence, anti-counterfeiting Product preservation

Fig. 8.2 Supply chain stages for fast-moving consumer goods (FMCGs) packaging and considerations for packaging designers. Source: Pira and University of Brighton (2005; p. 18).

shelf appearance (Verghese et al., 2006). Figure 8.2 illustrates some of the issues that need to be considered early in the product–packaging system development process. As illustrated in Fig. 8.2, there are a wide array of issues that need to be considered and within most companies there is a gap in the access to available environmental decision support tools that can be used by the product– packaging system development team to select the appropriate packaging material system. Within this process, environmental assessment methods and tools can be used to facilitate communication (Lindahl, 2006) between the packaging technologists, engineers, designers, marketers and environmental managers. According to Lindahl (2006), the following requirements are important when selecting a method or tool to use: • it must facilitate and simplify the work of the user, be intuitive, logical and easy to communicate; • it must be easy to understand how all the different parts of the tool fit together; • it must be able to fit into a company culture; • the set-up time to use the tool must be low; • in the early design phase in particular, the method or tool should not require too much up-front inputting of data (as it may not be collected yet);


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• results must be presented in a visually appropriate format; • it must cover the relevant issues that are handled on a daily basis; • it must give relevant and reliable results that are easy to adopt. In order to be effective, the decision support tool should be used in the right context and be embedded early within the product–packaging system development process. The following section describes different tools that can be used.

8.5

Environmental assessment tools for food packaging systems

Table 8.4 categorises, with examples, a range of environmental assessment tools for product–packaging system development – frameworks, checklists and guidelines, matrices, rating and ranking tools, and analytical tools. Each example is discussed in subsequent sub-sections. 8.5.1 Frameworks The fundamental objective of design for environment, according to Lewis et al. (2001; p. 16), ‘is to design products with the environment in mind and to assume some responsibility for the product’s environmental consequences as they relate to specific decisions and actions executed during the design process’. This requires procedures and tools to be implemented in the product–packaging system development process that enable employees to consider the environmental aspects and impacts associated with the choices they make – such as material selection, packaging machinery selection, pallet efficiency and transport modes. The basic principles behind design for environment is a systems or life cycle thinking approach where all of the processes and interactions that occur in sourcing, producing and using products and their associated packaging systems are taken into consideration. Different tools and approaches can be used to incorporate design for environment into the business. In this section the idea of a life cycle map is introduced and in subsequent sections details of strategies and tools (Sections 8.5.2 to 8.5.5) will be presented. To begin with, a life cycle map of the product and packaging system can be composed (see Fig. 8.3) which will provide the product–packaging system development team with an overview of the processes that are undertaken to manufacture the product and packaging system. From here, environmental impacts and issues can be identified from the collective knowledge of the development team and from other resources. The objective of putting together the life cycle map is to increase the understanding among the development team of the processes that are undertaken to source, produce, use and dispose of materials and wastes and to compare this with alternative product–packaging system



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Table 8.4 Categories of environmental assessment tools to use in the product– packaging system development process Type of tool Frameworks Provide general guidance and ideas on how environmental issues should be taken into consideration in the product– packaging development process; accompanied by guidelines and technical strategies Checklists and guidelines Generally qualitative though some are semi-quantitative; typically include a list of issues to consider in the product– packaging development process

Examples of tools • •

Design for environment Life cycle map

• •

Eco-design strategies Environmental Code of Practice for Packaging (ECoPP) (Schedule 5 of Australian National Packaging Covenant NPC) Code of Practice for the Packaging of Consumer Goods (New Zealand Packaging Accord) European Committee for Standardisation (CEN) Standards

• •

Matrices Simple tool where major issues are identified on key life cycle stages Rating and ranking tools and indicators Are generally simple quantitative tools which provide a prespecified scale for the assessment, e.g. 0–10 (negligible to extreme impact) Analytical tools Are generally comprehensive quantitative tools that evaluate and measure the environmental impact of products and of materials

•

Sustainable Packaging Alliance (SPA) Packaging Material Selector

• Litter indicators • SC Johnson Greenlist (not food but good illustration of what a company can do)

• • •

LCA Online tool for environmental optimisation of packaging design (TOP) Packaging Impact Quick Evaluation Tool (PIQET)

Source: the categories of tools are adapted from Baumann et al. (2002; pp. 416–417).

formats. The life cycle map also provides the mechanism to engage with suppliers and customers about their operations and with government agencies and waste management companies regarding post-consumer waste management technologies and processes. Another way of looking at the life cycle of a product–packaging system is the case of the humble packet of crisps! One case study (http://www.


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Environmentally compatible food packaging Non-renewable resource

Raw material

Raw material

Manufacturing process

Packaging



Component

Component

Product

Distribution/ retail

Energy use and emissions from transport

Use

Disposal/ recycling

Fig. 8.3

Packaging is not recycled

Example of a life cycle map of a product–packaging system.

powerhousemuseum.com/education/ecologic/cycles.htm) undertaken in Australia revealed the following: • potatoes are grown along the eastern coast of Australia and trucked to Shepparton for processing; • the salt is trucked from South Australia; • the sunflower seed oil is extracted in Newcastle (New South Wales), refined in Sydney and trucked to Shepparton (Victoria); • the packaging is made from polypropylene film sandwiched between a layer of aluminium and ink – the film is manufactured in Wodonga (Victoria), one layer of the film is printed in Melbourne, the other metallised in Sydney and then both are fused by a printer in Melbourne;



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– the different ink components are sourced from India, China, Europe and the United States; – the cardboard cartons (100% recycled content) used to distribute the packets of crisps to the retailer are made in Melbourne. So many processes occurring throughout Australia and across the world to produce the humble packet of crisps!

8.5.2 Checklists and guidelines Government agencies and industry associations have developed checklists and guidelines to assist companies in implementing environmental considerations in their product–packaging system development process. Individual companies have also developed in-house lists to assist them in procurement and design. Such tools provide overarching guidance and questions to be considered in the design and development process. They generally include a range of eco-design strategies under headings such as: use materials efficiently, design for recovery, design for litter reduction, and educate and inform consumers. The product–packaging development team should also identify upfront which strategies they wish to pursue for the chosen product–packaging system. Table 8.5 provides examples of eco-design strategies that can be used, with more details given in Chapter 10 of this book. Environmental Code of Practice for Packaging (Australia) The ECoPP in Australia and accompanying environmental guidelines for packaging is an industry1-developed code that has been incorporated as Schedule 5 into the Australian NPC.2 The ECoPP has been ‘designed to provide companies with guidelines to help evaluate the environmental impact of new and existing packaging’ (NPCC, 2005; p. 33) and applies to all packaging of products manufactured or purchased in Australia (including imported packed product). The seven overall strategies incorporated into the code to address the environmental impacts of packaging and packaged products across their life cycles (including example questions from guidelines) are presented below. 1

Australian Council of Recyclers, Australian Food and Grocery Council, Australian Industry Group, Australian Retailers Association, Beverage Industry Environment Council, Packaging Council of Australia and the Plastics and Chemical Industries Association. 2 The NPC is the voluntary component of a co-regulatory arrangement based on the principles of shared responsibility through product stewardship, between key stakeholders in the packaging supply chain and all spheres of government – Australian, State, Territory and Local. More details can be found at http://www.packagingcovenant. org.au/.


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Table 8.5 Examples of eco-design strategies for product–packaging system development Eco-design strategy

Examples of actions to take

Use materials efficiently

Eliminate unnecessary layers or components

Design for recovery

Identify the best recovery system for your packaging: reuse, recycling, composting or energy recovery: • •

•

•

Design for litter reduction Educate and inform consumers

Reuse – design packaging to be collapsible and/or nested during return transport Recycling – design labels, caps and other components so that they can be easily separated by consumers or during the recycling process, or that are compatible with the recycling process Composting – specify a material that is truly compostable, i.e. which meets relevant standards and for which a collection and recycling system can be accessed by most people in the designated country Energy recovery – eliminate or reduce any substances that may contribute to toxic waste or emissions (e.g. heavy metals)

For products likely to be consumed away from home, minimise the number of separable components that could be littered (e.g. straws, tamper-evident seals) Use recognisable symbols for recyclability, e.g. the Mobius loop or other material-specific symbol

Source: Lewis and Verghese (2005).

• Source reduction, e.g. for the default and alternative packaging options, what quantity of material will be used per unit of delivered product? • Potential for packaging reuse, e.g. what is the average number of return trips expected under normal use in the designated system? • Recovery and recycling, e.g. what is the ability of different materials to be separated during the recovery process, e.g. caps, labels, etc.? • Ability to incorporate recycled content, e.g. what is the amount and percentage of recycled material in the retail packaging unit? • Minimising impacts of packaging, e.g. elimination of toxic and hazardous substances or minimisation of such substances where their use is necessary. • Propensity to become litter, e.g. how many separate or easily separable components does the packaging item have, e.g. screw cap lids, peel of seals? • Consumer information, e.g. has anti-litter information been included on packaging of products that are likely to be consumed away from home?



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All signatories to the NPC need to implement the ECoPP into their product–packaging development process and the ECoPP needs to be completed for all new and reformatted packaging systems introduced onto the Australian marketplace since August 2005. The ECoPP is an easily accessible document containing good reference questions to be considered when designing or redesigning your product–packaging systems. Code of Practice for the Packaging of Consumer Goods (New Zealand) The New Zealand Code of Practice for the Packaging of Consumer Goods consists of a generic set of guidelines that have been designed to assist companies when they evaluate the environmental impact of their packaging materials and products (PC NZ, 2002). It is a self-regulating Code and applies to all packaging of consumer foods, both domestic and imported, in New Zealand. The Code consists of the following sections (including an example): • General packaging requirements, i.e. legal requirements, function of packaging, convenience in use. • General principles, i.e. waste management options should be considered in the following order – reduction, reuse, recycling, recovery and disposal. • Reduction, i.e. packaging that is not essential to the distribution, retail sale, storage, use or safety of the product should be avoided. • Reuse, i.e. the preferred reuse option is to reuse for the purpose for which it was originally intended. • Recycling, i.e. the effect that any additives, coatings or inks, etc. may have on the recycling process. • Energy recovery, i.e. if the package cannot be reused or recycled it should be determined whether its energy content can be recovered by incineration while complying with the appropriate environmental regulations. • Bio/photodegradability, i.e. the issues of proper exposure conditions, time frames required and levels of breakdown will need to be considered to ensure that this is an appropriate option. • Disposal, i.e. the package should be designed where possible, to be easily compressed prior to disposal to minimise its volume in landfill. The New Zealand Code of Practice for the Packaging of Consumer Goods, like the Australian ECoPP, contains easy to understand guidelines and questions that can be implemented into company procedures to ensure that consideration is given to the environmental issues associated with packaging system selection and design. European Committee for Standardisation Standards The CEN standards were written to support the essential requirements of the EU Packaging and Packaging Waste Directive 94/62/EC and are


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mandated by the European Commission. There are six standards (CEN, 2005) as listed below. • EN 13427:2004, Packaging – Requirements for the use of European Standards in the field of packaging and packaging waste. • EN 13428:2004, Packaging – Requirements specific to manufacturing and composition – Prevention by source reduction. • EN 13429:2004, Packaging – Reuse. • EN 13430:2004, Packaging – Requirements for packaging recoverable by material recycling. • EN 13431:2004, Packaging – Requirements for packaging recoverable in the form of energy recovery, including specification of minimum inferior calorific value. • EN 13432:2000, Requirements for packaging recoverable through composting and biodegradation. These standards provide important information and guidance when designing and reviewing packaging formats. The above three examples of checklists and guidelines provide comprehensive information on the issues and questions that should be posed during the product–packaging system development process. 8.5.3 Matrices An example of a matrix is the Packaging Material Selector developed by the SPA. The Packaging Material Selector is an A3 poster-sized matrix that contains relevant information on commonly used packaging materials including polymers, metals and paper-based packaging. It features information on the material characteristics, packaging applications and recycling and other environmental considerations. Table 8.6 contains the information included in the Packaging Material Selector, using PP as an example. The selector can be used by packaging technologists, environmental managers, marketers and designers providing them with key environmental information relating to commonly used packaging materials. 8.5.4 Rating and ranking tools and indicators The two rating/ranking tools to be presented are the litter indicators (developed by Nolan ITU for Nestlé Australia) and the SC Johnson GreenlistTM (while not a food manufacturer this list provides an example of how a rating tool could be developed for food packaging). Litter indicators Two litter indicators were developed in 2004 by Nolan ITU for Nestlé Australia. As part of Nestlé Australia’s involvement in the NPC they were



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Table 8.6 Example of information included in the SPA Packaging Material Selector for PP (data reported for Australia) Packaging material

PP

Material characteristics

Rigid and flexible, tough, heat resistant up to 165 ºC, excellent chemical resistance, moderate barrier, oriented films Potato crisp bags, tubs, hinged caps, clear punnets, microwave ware, bottles, lolly wraps Crude oil; non-renewable 0.9 70.6

Packaging applications Raw materials Density (g/cc) Embodied energy (low heat value) (MJ/kg) Recyclability

Recycling rate Recycled content Landfill impacts Comments

Technically recyclable, post-industrial waste widely recycled, some councils starting to collect rigid post-consumer waste PP at kerbside but limited due to low volumes, food residue contamination and limited capacity 6% Recycled content possible in non-food applications Value of material lost Properties can be modified to meet requirements

Source: http://www.sustainablepack.org/resources/page.aspx?id=29.

broadening their environmental management programme from an internal operations focus to product life cycles, and wanted to better understand the scope and nature of the littering of FMCGs packaging. As part of this research two litter indicators were developed (Carroll and Shmigel, 2004; pp. 15 and 17). • The direct litter indicator – indicates the immediate, objective and quantifiable aspects associated with litter from a packaging type: – area (m2), maximum area of ground covered by FMCGs-littered items; – persistence (years), estimated amount of time that the litter remains in the environment. Number of littered items × area × persistence = direct litter indicator • The cumulative litter indicator – adds the following two dimensions: – environmental impact, in terms of ecosystem impact (primarily impacts on wildlife) and human toxicology (through emissions to water, air and soil);


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Environmentally compatible food packaging – risk level, in terms of the likelihood and severity of regulatory intervention and brand reputation damage.

Direct litter indicator × environmental impact × risk level = cumulative litter indicator The litter indicators can be calculated for different packaging formats and product categories, thereby highlighting the areas where attention and improvements should be focused. SC Johnson Greenlist The Greenlist was developed by SC Johnson in 2001 as a corporate policy to improve the environmental sustainability of their products and to minimise their environmental footprint (Saville, 2005). It is a programme for selecting the most environmentally sustainable raw materials and not an actual list of preferred raw materials. The Greenlist programme is used by all SC Johnson companies worldwide and each division has goals related to the environmental classification (EC) improvements through their key performance indicators. It covers 15 categories of materials, including: packaging, chelants and sequestering agents, antimicrobials/preservatives, fragrances, candle waxes/fuel, non-woven/fabrics and organic/inorganic acids and bases. The categories are classified on their environmental and biological impact with the following classifications: • • • •

0 1 2 3

for a restricted use material or where there is insufficient data; – acceptable; – better; – best.

The EC scores are combined with the kg/volumes of the materials to provide an index for a material and these are summed to provide an average for a particular formulation (see Table 8.7). The raw materials are classified against criteria including biodegradability, human and aquatic toxicity and vapour pressure. The EC score for new product formulae must be equal to or greater than the average formula EC score for other SC Johnson products in the segment and in the region. The EC score for a reformulation will be equal to or greater than the EC score of the formula it replaces. The Greenlist permits those working at SC Johnson to analyse their raw materials and allocate ratings to them relative to their impact on the environment. This allows for a consistent structure for decision making and raising awareness of issues through the organisation. The sharing of results with suppliers also provides an opportunity for improvements to be



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Table 8.7 Example of calculating the Greenlist environmental classification Content (%) A 0.2 B 0.70 C 10.39 D 0.41 E 38.3 F 49.8 Weighted average EC

EC

EC × content (%)

3 2 2 2 1 3

0.6 1.8 20.78 0.82 38.3 149.4 2.12

Source: Saville (2005).

made through the supply chain. The focus of the Greenlist is on upstream sourcing of raw materials. This is an in-house company tool, although according to their website they have shared the Greenlist process with the US Environmental Protection Agency, Environment Canada, the Chinese Environmental Protection Agency, industry associations, universities and corporations.

8.5.5 Analytical tools The three examples of analytical tools presented below are: (a) LCA; (b) TOP; and (c) the PIQET. Life cycle assessment LCA is a scientific and internationally accepted (ISO 14040 series) methodology that evaluates the potential environmental impacts of materials, products and services across the life cycle (i.e. raw material extraction, through processing, converting, manufacturing, distribution, use and waste management) (Fig. 8.4). The resources and energy consumed, the emissions to air and water, and the solid wastes generated are quantified at each stage of the life cycle to compile a data inventory list. This data inventory list is then assigned to environmental impacts (e.g. global warming, eutrophication, photochemical oxidation) through the next stage of LCA known as impact assessment. The final stage of LCA is interpretation where sensitivity analysis, for instance, may be undertaken to test the quality and validity of the inventory list and the impact assessment values (Fig. 8.5). The outputs of an LCA are a range of environmental impact categories which provide the means to identify the major environmental impacts that occur throughout the life cycle of the product–packaging system. It can also assist in determining the environmental priorities which should


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Environmentally compatible food packaging Renewable material resources

Extraction of raw materials

Pre-products

Non-renewable material resources

Production

Distribution

Energy

Use

Disposal

Recycling

Solid waste

Fig. 8.4

Air emissions

Water emissions

Life cycle stages and inputs and outputs.

Identify relevant environmental impact categories

Identify significant issues

Assign inventory to impact categories

Evaluate completeness, sensitivity and consistency of data

Evaluate

Perform impact assessment modelling

Draw conclusions and recommendations

Inventory analysis

Impact assessment

Interpretation

Develop flow chart of life cycle

Define goal

Define system boundaries (what is included)

Collect data

Do calculations Define data requirements

Goal and scope

Fig. 8.5

Stages of undertaking an LCA.

be addressed with respect to material selection, converting, transport, use and waste management. Table 8.8 presents the results from an LCA of ketchup in Europe and identifies the contribution, as a percentage, of five key life cycle stages – agriculture, food processing, packaging, transportation and the consumer phase – for five impact categories. The manufacture of the packaging contributed 36% and 24% to primary energy and global warming, respectively, although it was the agriculture and food processing stages of the life cycle of the product that had more of an impact. The information presented in Table 8.8 can be used to prioritise the areas of the life cycle where environmental impacts need to be minimised. Online tool for environmental optimisation of packaging design The TOP tool was developed in 2003 by Kiem Sustainable Innovations and CREM in The Netherlands. Commissioned by the Netherlands Packaging Centre (NVC) and funded by NOVEM (government) with input from


Table 8.8 Relative contribution of sub-systems in the LCA of ketchup Life cycle stages Impact category

Primary energy Global warming Acidification Eutrophication Photo-oxidant formation NOx VOCs

Total (per functional unit)

Agriculture (%)

Food processing (%)

Packaging (%)

Transportation (%)

Consumer phase (%)

7 14 17 69

39 41 53 12

36 24 6 5

5 9 20 12

13 12 4 3

18 GJ 1100 kg CO2 equivalent 220 mol H+ 71 kg O2

25 16

24 19

11 33

32 4

8 29

4.4 kg 1010 g ethene equivalent

Source: Anderssen (2000; p. 242). Note: a functional unit is defined as 1 tonne of ketchup consumed. The consumer phase includes storage of the ketchup bottle for 1 month in a refrigerator. VOC, volatile organic compound.


WPTF3007

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30 major packaging supply chain companies, the tool aims to assist users in optimising their packaging so that it will be in accordance with EU packaging legislation (Essential Requirements). The tool also evaluates packaging in conjunction with the product. The tool comprises Excel work sheets via CD or it can be completed online. There are seven indicators considered. 1

2 3 4

5 6 7

Product–packaging combination: compares the packaging of a product on the basis of the weight of product, volume of product, consumption volume or product yield. The outcome is the number of comparison units per packaging unit. Added value: looks at packaging costs (e.g. material procurement) versus commercial value (retail price). The outcome is packaging cost relative to the commercial value of the product per comparison unit. Logistics efficiency: determines the ratio of product volume to total packaged volume and includes transport packaging. The outcome is the number of comparison units per volume of packaging. Heavy metals: determines the amount of compounds of lead, cadmium, mercury and chromium 6 per consumer packaging and transport packaging. To be able to enter the EU market the amount needs to be less than 100 ppm per metal. Reuse and recovery: determines whether the packaging material (component) can be reused or recovered (material and/or energy) or needs to be landfilled. Material consumption: determines the amount of material used and takes reuse (trip rate) into account. Provides the weight of material (consumer and transport packaging) per comparison unit. Environmental impact: determines the environmental impact of the material (material product and converting) using the Eco-indicator 99 methods (eco-indicator points per kg of material). The outcome is the number of eco-indicator points per comparison unit.

Packaging Impact Quick Evaluation Tool The PIQET, which is based on scientific and internationally recognised LCA methodology, has been developed by the SPA;3 PIQET4 is a webbased tool which enables users from a wide range of organisations to assess 3

An initiative formed in 2002 by the Centre for Design at RMIT University, the Packaging and Polymer Research Unit at Victoria University and Birubi Innovation (www.sustainablepack.org.au). 4 PIQET© has been funded by Sustainability Victoria, the Australian Government’s Department of Environment and Heritage and the Department for Communication, Information Technology and the Arts, and five food and beverage brand-owner companies (Cadbury Schweppes, Lion Nathan, Masterfoods Australia New Zealand, Nestle Australia and Simplot Australia). The online PIQET web programming was undertaken by WSP Environmental.



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or inform packaging designs/specifications without the need for investment in the knowledge, time and resources otherwise needed, when using LCA software, to make complex environmental impact evaluations. PIQET enables packaging specifications to be quickly assessed against current LCA and environmental data, and Australian packaging recycling and waste management data. Users of PIQET are able to re-run evaluations by making changes to the packaging specification input data and thereby continuously improve the sustainability of their packaging systems. PIQET evaluates the environmental impacts of packaging systems throughout their life cycle – i.e. from raw material extraction, packaging manufacture, filling and product/packaging distribution through to packaging disposal and material recovery. Users are required to enter data on the packaging material specifications (e.g. type of material, component and level of packaging – retail unit, merchandising unit and traded unit), converting processes, transport requirements and filling operations. PIQET then calculates the environmental impact using LCA data, environmental default values and environmental impact data (e.g. recycling and landfill rates). Reports are easily generated with LCA data (Fig. 8.6) presented along with packaging-specific indicators such as product/packaging ratio, number of separable components in the retail unit level and percentage of Global warming 8.43e – 1 kg CO2 eq.

Solid waste 3.02e – 1kg

Cumulative energy demand 1.14e + 1 MJ LHV

Water use 6.37e – 3 Kl H2O

Format 1

Fig. 8.6

Photochemical oxidation 7.45e – 4 kg C2H2 eq.

Format 2

Format 3

Comparison graph from PIQET. LVH, low heat value.


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post-consumer recycled content in the packaging system. Users of PIQET are able to run simulations, identify priority areas, set goals and targets, track progress, benchmark packaging designs over time and use it as an awareness building/training tool to inform and challenge key packaging decisions.

8.6

Sustainable packaging developments

In order to develop environmentally compatible food packaging systems there needs to be general agreement among stakeholders of what constitutes sustainable packaging. In recent years there has been progress in defining sustainable packaging – by the Australian-based SPA and the United States-based Sustainable Packaging Coalition (SPC).5 Both of these organisations have drafted definitions of sustainable packaging for broader discussion and debate (Table 8.9). The definitions of sustainable packaging by SPA and SPC follow similar principles, i.e. that packaging systems need to be efficient, effective, safe, cyclic and meet market requirements. Broad acceptance of these definitions, and hopefully a common agreed definition, will pave the way for the development of packaging systems where commercial, functional, environmental and social parameters have been considered. Until consensus is gained there is no direction, or overarching framework in the industry. Consensus would provide a foundation that companies could work towards in the selection, design and use of packaging materials, that governments could use to develop appropriate policies, regulations and voluntary agreements, and that would allow consumers to be adequately informed.

8.7

Implementing environmental assessment approaches into the product–packaging system development process

Table 8.10 presents a process for implementing environmental assessment approaches into the product–packaging system development process. The key activities are given along with examples of outcomes or learning that can be gained.

8.8

Future trends

Companies need to ensure that they have clearly identified the strategies and approaches they will pursue in developing sustainable packaging. This 5

The SPC (a project of GreenBlue) is an industry working group inspired by cradle to cradle principles and dedicated to creating a more robust environmental vision for packaging (www.sustainablepackaging.org/).


Environmental assessment of food packaging and advanced methods Table 8.9

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Definitions of sustainable packaging

SPA 2004 (Australia) 1 It adds real value to society by effectively containing and protecting products as they move through the supply chain and by supporting informed and responsible consumption. 2 Packaging systems are designed to use materials and energy as efficiently as possible throughout the packaged product life cycle including its interactions with associated support systems. 3 Packaging materials are cycled continuously through natural or industrial systems. 4 Packaging components do not pose any health or environmental risks to humans or ecosystems. When in doubt the precautionary principle applies. The four principles are effective, efficient, cyclic and safe. SPC (2005) United States The packaging material: A Is beneficial, safe and healthy for individuals and communities throughout its life cycle. B Meets market criteria for performance and cost. C Is sourced, manufactured, transported, and recycled using renewable energy. D Maximizes the use of renewable or recycled source materials. E Is manufactured using clean production technologies and best practices. F Is made from materials healthy in all probable end-of-life scenarios. G Is physically designed to optimize materials and energy. H Is effectively recovered and utilized in biological and/or industrial cradle to cradle cycles. Source: SPA (2004) and SPC (2005).

should be widely communicated among the business and staff supported to ensure the right decisions and trade-offs are made. Environmental assessment tools should be embedded into the product–packaging system development process and staff trained in their need and use. For the foreseeable future, packaging will continue to have important functional and economic roles. However, its development and application must change to embrace more holistic considerations of its environmental impact and longer term fit with sustainability principles. Collectively, industry, government and society need to have a shared understanding of what constitutes sustainable packaging and how packaging systems can be designed, implemented, managed and developed in order to provide a sustainable future.

8.9


• Centre for Design at RMIT University (www.cfd.rmit.edu.au). • Envirowise (http://www.envirowise.gov.uk/home.aspx?o=home).


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Table 8.10 Implementing environmental assessment approaches into the product–packaging system development process Activity/by whom

Outcome/Learning

1

Board endorsement

• Top management support and endorsement is critical to provide leadership, to ensure that internal policies and directions are co-ordinated and to demonstrate a strong commitment to the sustainable management of packaging

2

Establish a working group consisting of representatives from across the organisation including: packaging, environment, marketing, logistics, purchasing and management

• Ideal opportunity and environment for representatives from across the organisation to be involved in the development, integration and implementation of activities, programmes and initiatives • Ensures that everyone is aware of the company direction, provides a platform for communication between different work areas, facilitates multi-disciplinary thinking and promotes team work

3

Review relevant environmental regulations, policies and voluntary programmes applicable to the countries in which product-packaging system will be marketed

• Provides important information relating to any material bans or restrictions, labelling requirements, etc. applicable to the specific country

4

Establish a packaging database to capture data relating to the types and tonnages of packaging materials used, the proportion of recycled content of packaging materials and to amend packaging specifications where appropriate

• Provides an overview of the materials used per product category • Identifies tonnages of primary, secondary and tertiary packaging used. For instance the quantity of glass, aluminium and paperboard used per year, including details on how each material is used, e.g. glass primary packaging and paperboard as secondary packaging, can give powerful insight into where particular packaging materials are being used • Provides the opportunity to review packaging specifications and determine if appropriate information is being captured with respect to the production, manufacture and use of materials and to identify opportunities for improvement

5

Review and understand the environmental impacts of the packaging materials that are used by the organisation

• Increases knowledge among the organisation of the impacts of sourcing, producing, manufacturing, use and end-of-life waste management of materials • Sources of information on the environmental impact of materials can be found through published information, e.g. LCA reports, LCA software programs, packaging tools and packaging material guidelines


Environmental assessment of food packaging and advanced methods Table 8.10

Cont’d

Activity/by whom

Outcome/Learning

Identify relevant frameworks, checklists, guidelines, matrices, rating tools and analytical tools to be used by the organisation. Implement the selected approaches in the new product development process and ensure that the packaging and marketing departments are appropriately trained in the need and use

•

7

Based on the outcomes of points 4 and 5 (above), identify activities and programmes to minimise the environmental impact of packaging systems manufactured or used

•

8

Seek input from engineering, production and accounting staff in obtaining and collating data relating to the resources consumed and wastes generated through the use of packaging materials

•

6

207

9 Define and publish the company’s packaging policy and strategic direction


•

Provides a systematic approach and questions to consider when producing a new packaging system or doing a format change Ensures that issues surrounding packaging design and material selection are considered early in the design process and that a life cycle perspective is adopted

Prioritise environmental issues that need to be addressed by the organisation or that are to be avoided. For instance avoiding a particular material through a phase-out • Allows for projects to be prioritised and implemented within the constraints of the organisation

Data relating to materials and energy consumed in the procurement and use of packaging materials and the waste and emissions generated which can then be used to optimise efficiencies, to minimise resource and energy consumption and to avoid, reduce and reuse wastes

• Provides overarching direction for the working group within the organisation so that programmes can be prioritised • Clearly communicates the organisation’s position on packaging to all internal and external stakeholders • Should be developed once the packaging database has been established and environmental issues have been prioritised • Should be stated in the organisation’s public reports (e.g. annual report, website)

208


Table 8.10 Cont’d Activity/by whom

Outcome/Learning

10

•

Establish and maintain open communication with suppliers and customers regarding packaging decisions and consult with them when making significant changes that could have an impact on their operations and processes

•

Ensures that communication channels are established and maintained across the packaging supply chain at an early stage in a project. Involves key stakeholders in the decision making process, maximising opportunities for improved environmental outcomes across the supply chain Provides opportunities for any barriers or problems to be identified early and time for it to be rectified. For example, considering capital expenditure barriers to the adoption of new technologies, looking outside existing supply chains for new partners in innovation and understanding the full cost of packaging and distribution

Adapted from Slatter and Verghese (2006).

• The Industry Council for Packaging and the Environment (INCPEN) (http://www.incpen.org/pages/pv.asp?p=incp60). • INCPEN Code of Practice for Optimising Packaging and Minimising Waste (http://www.incpen.org/pages/userdata/incp/CodeofPractice.pdf# search=′Code%20of%20Practice%20for%20the%20Packaging%20of %20Consumer%20Goods). • SPA (www.sustainablepack.org). • SPC (www.sustainablepackaging.org). • UNEP/SETAC Life Cycle Initiative (http://lcinitiative.unep.fr/). Life cycle assessment tools: these tools come with detailed databases from many sources and also allow the user to input their own unit process data. They are excellent analytical tools and generally have a range of impact assessment models. The data, however, are mostly of European origin. The cost ranges from around $2000 to $25 000. • SimaPro, Pre Consultants (http://www.pre.nl/simapro/default.htm). • TEAM, Ecobilan (http://www.ecobalance.com/uk_team.php). • Boustead, Boustead Consulting (http://www.boustead-consulting. co.uk/). • GaBi, Five Winds International and University of Stuttgart (IKP)/PE Product Engineering (http://www.gabi-software.com/). • Umberto, Institute for Environmental Informatics at Hamburg Ltd (ifu) (http://www.umberto.de/english/).



8.10

209

References

abs (australian bureau of statistics) (2006) ABS 3236.0 – Household and Family Projections, Australia, 2001 to 2026, Australian Bureau of Statistics. Retrieved 9 October 2006 from http://www.abs.gov.au/AUSSTATS/[email protected]/Lookup/ 3236.0Main+Features12001%20to%202026?OpenDocument; last updated 20 June 2006. anderssen, k (2000) LCA of food products and production systems. International Journal of Life Cycle Assessment, 5(4), 239–248. baumann, h, boons, f, and bragd, a (2002) Mapping the green product development field: engineering, policy and business perspectives. Journal of Cleaner Production, 10, 409–425. carroll, b and shmigel, p (2004) Understanding fast moving consumer goods (FMCG) litter. Presentation made at the Leading on Litter Conference, Melbourne, Victoria, May 2004. Retrieved 20 October 2006 from http://www. ecorecycle.sustainability.vic.gov.au/resources/documents/Shmigel_&_Carroll1. pdf. cen (european committee for standardization) (2005) Packaging – new Packaging Standards Published. Retrieved 9 October 2005 from http://www.cenorm.be/ cenorm/businessdomains/businessdomains/transportandpackaging/packaging/ packaging.asp. erlov, l, lofgren, c, and soras, a (2000) PACKAGING – a tool for the prevention of environmental impact. Packforsk: Kista, Sweden. excelplas australia, centre for design at rmit and nolan-itu (2004) The Impacts of Degradable Plastic Bags in Australia. Final Report to the Department of the Environment and Heritage, Commonwealth of Australia, Canberra. imhoff, d (2005) Paper or Plastic – Searching for Solutions to an Overpackaged World. Sierra Club Books: San Francisco, California. james, k, fitzpatrick, l, lewis, h, and sonneveld, k (2005) Sustainable packaging system development, in Handbook of Sustainability Research, W. Leal Filho (editor). Peter Lang Scientific Publishing: Frankfurt, Germany. lewis, h and verghese, k (2005) Sustainable Packaging Course, Centre for Design at RMIT University and Sustainable Packaging Alliance, Auckland, New Zealand, 24–25 November 2005. lewis, h, gertsakis, j, grant, t, morelli, n, and sweatman, a (2001) Design + Environment – A Global Guide to Designing Greener Products. Greenleaf Publishing: Sheffield, UK. lindahl, m (2006) Engineering designers’ experience of design for environment methods and tools – requirement definitions from an interview study. Journal of Cleaner Production, 14, 487–496. marks & spencer (2007) Plan A – Reducing Waste. Retrieved 19 October 2007 from http://www.marksandspencer.com/gp/browse.html/ref=sc_fe_c_2_50890031/2020219918-2392636?ie=UTF8&node=51445031&no=50890031&mnSBrand= core&me=A2BO0OYVBKIQJM. npcc (national packaging covenant council) (2005) Schedule 5 – The Environmental Code of Practice for Packaging. The National Packaging Covenant. A Commitment to the Sustainable Manufacture, Use and Recovery of Packaging, 15 July 2005 to 30 June 2010. National Packaging Covenant Council: Canberra, Australia. Retrieved 19 October 2007 from http://www.packagingcovenant.org.au /documents/File/National_Packaging_Covenant.pdf. pc nz (packaging council of new zealand) (2002) Code of Practice for the Packaging of Consumer Goods – A Self-Regulatory Code of Practice, Packaging Council of New Zealand. Retrieved 5 October 2006 from http://www.packaging. org.nz/packaging_info/packaging_code.php.


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pira and university of brighton (2005) Packaging’s place in society – Resource efficiency of packaging in the supply chain for fast moving consumer goods. Available at http://www.incpen.org/pages/userdata/incp/PackagingsPlace.pdf. randall, a (2006) Cadbury Schweppes case study. Presentation at the 11th Sustainable Packaging Alliance Roundtable – The Challenges of Retailing: Implications for Sustainable Packaging Design, Melbourne, Australia, 19 October 2006. sainsbury (2007) Respect for our environment. Retrieved 19 October 2007 from http://www.sainsburys.co.uk/aboutus/csr07/principle3/principle3.htm. saville, l (2005) Sustainable packaging. SC Johnson’s GREENLIST. Presentation to the Sustainable Packaging Alliance Roundtable 6 – Sustainable Packaging Indicators – Measuring and Reporting Progress, Sustainable Packaging Alliance, Melbourne, Australia, 18 February 2005. slatter, j and verghese, k (2006) Using Life Cycle Assessment to meet your obligations under the National Packaging Covenant. Peer reviewed paper, 5th Australian Conference on Life Cycle Assessment – Achieving Business Benefits from Managing Life Cycle Impacts, Australian Life Cycle Assessment Society (ALCAS), Melbourne, Australia, 22–24 November 2006. spa (sustainable packaging alliance) (2004) Draft Definition – Sustainable Packaging. Retrieved 9 October 2006 from http://www.sustainablepack.org/database/ files/Definition.pdf. spa (2006) The Challenges of Retailing: Implications for Sustainable Packaging Design. 11th Roundtable Report, Sustainable Packaging Alliance, Melbourne, Australia, 19 October 2006. spc (sustainable packaging coalition) (2005) Definition of Sustainable Packaging, Version 1.0. Retrieved 13 April 2006 from http://www.sustainablepackaging.org/ Definition%20of%20Sustainable%20Packaging%2010-15-05%20final.pdf. tesco (2007) Corporate Responsibility Review. Retrieved 19 October 2007 from http://www.tescocorporate.com/crreport07/06_wastepackre/ourapproach.html. verghese, k, horne, r, fitzpatrick, l, and jordan, r (2006) PIQET – a packaging decision support tool. Peer reviewed paper, 5th Australian Conference on Life Cycle Assessment – Achieving Business Benefits from Managing Life Cycle Impacts, Australian Life Cycle Assessment Society (ALCAS), Melbourne, Australia, 22–24 November 2006. walmart (2006) Wal-Mart Launches 5-Year Plan to Reduce Packaging. Retrieved 20 October 2006 from http://www.walmartfacts.com/articles/4466.aspx; last updated 22 September 2006. wardrop-brown, b (2006) Shelf ready packaging . . . a journey to remember . . . Presentation at The Challenges of Retailing: Implications for Sustainable Packaging Design. 11th Roundtable Report, Sustainable Packaging Alliance, Melbourne, Australia, 19 October 2006.


9 Measuring the environmental performance of food packaging: life cycle assessment G. Parker, Ciba Expert Services, UK

9.1

Introduction

Interest in the environmental performance of food packaging has never been greater. In Europe, societal pressures and legislation such as the Packaging and Packaging Waste Directive have caused packaging manufacturers and brand owners to take account of packaging environmental performance for over a decade. However, until recently environmental issues were often regarded as a ‘nice to have’ aspect rather than a business imperative, particularly in the US and Asia, where legislative drivers have often been less in evidence. One of the leading reasons for the rise up the corporate agenda of the environmental packaging issue is the growth of pressure from major retailers on their suppliers to minimise packaging, improve its recyclability and reduce its carbon footprint. The UK retailers Tesco and Marks & Spencer, and the US retailers Target and Wal-Mart, have featured prominently in this development. Undoubtedly the greatest impact has been caused by Wal-Mart. Over 60 000 Wal-Mart suppliers, including virtually all of the world’s major processed food producers, are being strongly encouraged by Wal-Mart to minimise packaging and improve packaging environmental performance. Those suppliers who perform poorly in this respect will be helped to improve. Some problematic lines could eventually be at risk of de-listing. Thus, packaging environmental performance is now critical for these companies; a key business imperative rather than a low-priority option. This increasing financial relevance of packaging environmental issues has in turn affected hundreds of thousands of packaging producers.


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Such pressures have helped to foster keen interest in potential solutions such as new materials. In particular, biopolymers – plastics made from plant material – are the subject of intense interest. Accordingly, this chapter focuses on life cycle assessment (LCA) with a particular focus on biopolymers. The biopolymer market is currently growing at more than 30% per annum, a rate far in excess of the growth rate of the traditional polymer market. Many brand owners and packaging designers are enthusiastic about the potential for more environmentally responsible packaging options. In the US, where some leading types of biopolymers such as NatureWorks, polylactic acid (PLA) were first produced and made available at feasible cost, retailers perceive biopolymers to have an additional advantage: ‘biopolymers are patriotic since they are made from US corn instead of foreign oil’.1

9.2

Environmental performance of biopolymers

As has been covered in other chapters, a biopolymer is made from a crop, which is a renewable resource, whereas a traditional polymer is, of course, made from oil, a non-renewable resource. (It is claimed by some, only partly in jest, that oil is renewable as long as we take into consideration a cycle of several hundred million years, but this is false since the geological conditions that led to oil formation are unlikely ever to be repeated.) When a biopolymer biodegrades or is incinerated, the carbon dioxide released can be considered to be reabsorbed by the next crop that is farmed to produce more biopolymer. This fact is used to support claims that biopolymers are carbon neutral and do not contribute to global warming. A selection of the main biopolymers is shown in Table 9.1, along with the claimed fossil energy and greenhouse gas emissions savings achieved by these biopolymers compared with traditional polymers.2 The savings shown are based on the claims of biopolymer producers and are generally not independently verified. 9.2.1 Renewability, biodegradation and recycling Biopolymers are usually biodegradable. (Although a biopolymer could be designed to be non-biodegradable as explained elsewhere, most biopolymers currently on the market are biodegradable.) In reality, the biodegradation of many biopolymers takes considerable heat and so biodegradation may only be successful in a commercial bio-reactor composter rather than in a home composting situation. There are few commercial composting operations in many parts of the world, with the result that in practice biopolymers are not likely to biodegrade in the short term. Nevertheless, the biodegradation potential of biopolymers is clear. Schemes exist that prove the concept. For example, in the US, the supermarket chain Wild


Table 9.1 The main biopolymers and claimed fossil energy and greenhouse gas (GHG) savings

Biopolymer type

Applications

Impact compared with petrochemical-based polymers Fossil energy

GHG emissions

Petroleum-based polymer counterpart

Biopolymer supplier and trade name

PLA

Polymer bottles, disposables, rigid containers Film: non-woven, home and office textiles, clothing

−20% to −30%

−15% to −25%

PET, PS

NatureWorks: NatureWorks polymer and Ingeo fibres Tate & Lyle: HM and XM series

Starch based

Films and bags

−50%

−60%

PE

Novamont: Mater-Bi and ORIGO-BI Rodenburg Biopolymers: Solanyl

Bio 1,3-propane diol (Bio-PDO)

Automotive parts, electrical and electronic systems, industrial and consumer products

−40%

−20%

Shell: Corterra, Nylon 6

DuPont: Bio PDO

Soy based

Construction, transportation, polyurethane, carpets, furniture and bedding, coatings, adhesives, sealants and binders

−20% to −60%

n/a

From polyol + isocyanate

Cargill: polyols-BiOH Dow polyurethanes: Biobalance Ford/Urethane Soy Systems Company: Soyol

Source: Pira International Ltd. PET, polyethylene terephthalate; PS, polystyrene; PE, polyethylene. From a market research report produced in 2006 by Pira International Ltd, Leatherhead, Surrey, UK. © 2008, Woodhead Publishing Limited

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Oats collects customers’ used PLA biopolymer packaging, mixes it with in-store organic waste, and sends it to commercial composters, where the biopolymer content biodegrades adequately within 2 months to produce commercially viable compost. In addition to composting, biopolymers could be recycled, although in practice there are few recycling routes available currently. There are unlikely to be many recycling schemes until such time as biopolymers have a sufficient market share to make separation for recycling economically viable. The fact that biopolymers are renewable, biodegradable and recyclable leads many observers to assume that biopolymers must be environmentally preferable to traditional polymers. However, the reality is not quite that simple. In themselves, crops are renewable, but they exist within a production framework that is reliant on fossil fuels. Fossil feedstock is used to produce chemical fertilisers, fossil fuel is used to power farm machinery and to transport and process crops. Coal, oil and gas are used to generate the electricity used by biopolymer production facilities. Similarly, biopolymers are recyclable, but recycling involves shipping waste and powering recycling facilities, which requires fossil fuels. It is theoretically possible that long transport distances and extensive processing of waste to produce recyclate could result in more non-renewable resources being consumed than are saved by recycling. Biopolymers biodegrade, but biodegradation can result in emissions of carbon dioxide and, in certain situations, methane, which contribute to global warming. All these factors demonstrate that environmental benefit cannot necessarily be assumed. 9.2.2 Measuring environmental impact: a retailer view LCA is the most widely accepted method used to measure the environmental performance of packaging. LCA is discussed in greater detail further on in this chapter. LCA is a detailed scientific approach, and this means that for many it is tempting to try to simplify LCA to produce faster, easier answers. As a prelude to a discussion of LCA, a simplified LCA approach used by a major retailer is presented here. Any simplification is bound to involve risks: the simplification might result in an incorrect answer, or may fail to reveal the very facts that are most useful for product improvement. However, companies may feel that the risks are worthwhile in order to take action to develop the business and to produce clear measures that can form part of corporate improvement metrics. Streamlined approaches are particularly relevant to retailers, who cannot hope to analyse every product they stock in great detail, but who are under consumer and stockholder pressure to take environmental action on packaging. Such a streamlined, business metricfocused approach was launched in late 2006 by Wal-Mart, the world’s largest retailer.3 A web-based resource for the Wal-Mart system is available at www.packagemodeling.com.


Measuring the environmental performance of food packaging

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The Wal-Mart Scorecard is a tool within Wal-Mart’s packaging sustainability value network, which is one of 13 sustainability value networks initiated by Wal-Mart to address sustainability across its business, based on three overall aims: • to be supplied by 100% renewable energy; • to create zero waste; • to sell products that sustain resources and environment. The scorecard was launched to 2000 private label suppliers in November 2006 and to over 60 000 global suppliers in February 2007. It is undergoing a process of continual development based on feedback from suppliers and other stakeholders. The scorecard is a web browser-based software tool that measures the environmental performance of packaging based on WalMart’s criteria. Wal-Mart has defined nine metrics or criteria for evaluating a package and obtaining a score. The metrics align with Wal-Mart’s internal business drivers and are only partly aligned with current LCA thinking. The nine metrics are outlined below. 1

2

3

4 5

6

Greenhouse gas emissions from packaging production. This metric is the total number of US short tons of greenhouse gas emissions that result from the packaging. The scorecard calculates emissions by taking the weights of materials input by the supplier and using its internal database to calculate a greenhouse gas tonnage figure based on LCA data. Evaluation of material types. The scorecard is designed to rank each packaging material as 1, 2 or 3; with 3 being considered the best and 1 the worst. The scores are in development. The intention is to base them on Occupational Safety and Health Administration safety figures (the US industrial worker safety record achieved during the production of each material) and the Toxics Release Inventory (the US official list of substances regarded as toxic). Distance to transport materials. This is the average distance, in miles, that the packaging had to travel before it was filled. This metric focuses on the transport of the empty packaging to the brand owner or filler and does not consider the distance the product travels to get to WalMart’s stores. Product to package ratio. This is the ratio of the weight of the package to the weight of the product. The lower the weight of packaging, the better the package fares. Cube utilisation. This metric is a measure of space efficiency; the ratio of the volume of the product to the notional cubic space it occupies. Cubic or square packs fare better than more complex shapes such as long-necked bottles. Recycled content. This is the post-consumer recycled material content in the packaging. The scorecard contains a typical recycled content figure for each material in its database.


216


7

Recovery value. Each material receives a rating of 1, 2 or 3 relating to the proportion of the material that can be reused or recycled within Wal-Mart stores. 8 Renewable energy. This is the proportion of the packaging production facility that is powered by renewable energy. Renewable energy used by the product brand owner is not counted, only the energy used by the packaging producer. 9 Innovation different from energy standard. This is the most qualitative metric. A supplier can provide Wal-Mart with an essay written by the packaging producer on special energy saving initiatives at its production site. If Wal-Mart deems the initiative appropriate, credit is given for it in this metric. Metrics 1, 3 and 8 are related to LCA, while metrics 2, 4, 5, 6, 7 and 9 are more akin to internal business metrics. All Wal-Mart suppliers input all their packaging into the scorecard. Once a supplier has input data on a packaged item, the scorecard provides the individual metrics’ scores and rankings, plus the total score and ranking. All scores are maintained in a database, enabling Wal-Mart to see how suppliers’ packaging ranks. Wal-Mart aims to approach low-scoring suppliers with a view to helping them reduce the environmental impact of their packaging. Thus all suppliers’ packaging will gradually move towards the ‘best in class’ packaging revealed by the database. In this way the overall environmental performance of packaging stocked by Wal-Mart will improve. The system’s strength is that it is a relatively simple metric that enables certain aspects of Wal-Mart’s business performance to be measured so that Wal-Mart buyers and managers can achieve change. As such it is a well designed and no doubt effective business metric. It seems likely that the scorecard will successfully aid Wal-Mart in identifying packaging improvement opportunities and will help lead to an improvement in the overall environmental performance of packaging passing through Wal-Mart’s operations. The system’s weakness is that it is, by necessity, a simplified system. LCA would produce more accurate results, but it would be impossible to apply LCA to all the tens of thousands of packaging items passing through Wal-Mart’s stores. A simplified system might produce answers similar to those produced by more detailed LCA studies perhaps 80% of the time, and perhaps 20% of the time might produce answers that a more detailed LCA study would find to be incorrect. This means that there is a risk that individual suppliers might feel unfairly treated. However, overall, the answers are likely to be correct on the majority of occasions, which means that in total, if the scorecard’s findings are applied, environmental benefit will be achieved. In other words, the Wal-Mart scorecard is more defensible as a business management tool than as a scientific method.



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Some suppliers might find grounds on which to criticise the Wal-Mart scorecard, but it is undeniable that Wal-Mart, through the use of this LCA-based method, is likely to achieve a greater improvement in packaging environmental performance than has been achieved by any other single business in history. Wal-Mart’s Chief Executive Officer (CEO) is of the opinion that the business has already gained benefit from environmental initiatives such as the scorecard: ‘Environmental and social initiatives by Wal-Mart are bearing fruit. People are starting to notice, and they like what they see. In spite of aggressive attacks by special interest opponents, our image is improving in the US’ (Lee Scott, WalMart CEO, speaking at the Wal-Mart Annual Meeting, Arkansas, 1 June 2007).

9.3

Measuring environmental impacts: the science of life cycle assessment

One of the leading scientific methods used to determine environmental performance is LCA. This involves measuring clearly quantifiable inputs and outputs throughout the life cycle of a product. 1

The entire life cycle of a product (which might be a material, a package or any other item) is investigated: extraction of raw materials, shipping, processing, material manufacture, transport, packaging manufacture, filling, distribution, sales, consumer use and waste management. 2 At each of these stages, environmental impacts are measured: materials and energy consumed, emissions and wastes produced. 3 These impacts are summed up and assessed to give a picture of the total environmental performance of the item in question. Doing this for several items enables items to be compared in order to identify environmentally preferable options.

9.3.1 Structure of the life cycle assessment method LCA is defined by the International Organization for Standardization (ISO) as ‘the compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product system throughout its life cycle’ (ISO standard 14040). An LCA includes several inter-related stages as shown in Fig. 9.1: definition of goal and scope, inventory analysis, impact assessment and interpretation of results. • Goal and scope definition involves defining the intended purpose of the study, the system to be studied, the functional unit and issues relating to data quality.


218


Life cycle assessment methodology

Goal and scope definition

Interpretation

Inventory analysis

Applications: • Identification of product improvement opportunities • Support decision making • Selection of performance indicators • Marketing • Other

Impact assessment

Fig. 9.1

Life cycle assessment methodology.

• Inventory analysis involves quantifying the resources used and the releases to air, water and land associated with a product, process or activity. • Impact assessment aims to assess the effect that the impacts identified in the inventory analysis will have on the environment. • Interpretation assesses the results of the inventory analysis and impact assessment stages. 9.3.2 Goal and scope definition The first step when initiating an LCA study is to define clearly the intended purpose or goal of the study. Types of goals may include: • product and process development, such as identifying opportunities to improve environmental performance; • setting of environmental targets for corporate management systems; • selection of environmentally preferred materials or products; • improvement in handling and distribution systems; • backing up marketing claims with scientific facts; • guidance for legislation, standards or policy.



219

The objective of the scope definition is to identify and to define the object of the assessment and perhaps to limit it to include only the aspects that are significant for the goal of the study. In specifying the scope, the following critical parameters should be defined. 1

2 3

4

5

The scenarios to be studied. The scenarios to be addressed must be consistent and capable of fulfilling the stated goal of the study. They should also be continually revisited to ensure that the goal of the study is being met. The environmental problem areas to be studied. It is important to decide early on which problem areas are of interest as this will reflect the data to be collected and the impacts to be studied. The functional unit. This defines the object of the study and expresses it as the service it provides. For beverage packaging, for example, the functional unit would typically be an agreed number of litres of beverage delivered to the end user. The system and system boundaries. A system is a collection of connected operations which together perform a defined function. A system is normally illustrated in the form of a flow diagram. All inputs and outputs defined within the system will enter or leave at the system boundary. Defining the system boundary addresses what is to be included and excluded from the system. The quality of the data. The validity and credibility of the results of any LCA study are dependent on the amount of data and its quality. There are various issues that may need to be addressed under the heading of data quality: the age of the data, the geographic area, the technology used, data variability, representativeness and reproducibility. The level of detail required depends on the goal of the study.

9.3.3 Inventory analysis There are a great many inputs and outputs, and resultant environmental impacts, that can be measured,2 as shown in Table 9.2. The inventory analysis quantifies the environmental impacts of all the quantified inputs and outputs associated with each stage or process within the system or scenario studied. The production of the inventory table itself requires that several issues be considered, such as allocation and validation of data. Allocation is the process of assigning impacts between products or functions. Frequently, when compiling the inventory, it is discovered that more than one useful product is produced from individual processes and that these additional products are not required by the system being assessed. For example, PET bottles might be recycled into carpet fibres, or PLA bottles might be composted into compost that is then bagged and sold as a product in its own right. The key allocation issue concerns the allocation of impacts between the primary system (the one delivering the functional unit, such


220


Table 9.2 LCA inventory data and impact categories Resources Oil Gas Coal Lignite Bauxite Iron ore Sodium chloride Sand Sulphur Water Others Airborne emissions Global warming potential: Nitrogen dioxide Carbon dioxide Methane Hydrofluorocarbons Perfluorocarbons Sulphur hexafluoride Formation of photo-oxidants: Non-metal volatile organic contaminants Methane Waterborne emissions Chemical oxygen demand Biological oxygen demand Nitrogenous compounds Ammonia Phosphates Absorbable organochlorine

Energy consumption Coal Oil Gas Hydro Nuclear Lignite Biomass Wind Other

Acidification potential: Ammonia Hydrochloric acid Hydrogen fluoride Sulphur dioxide Oxides of nitrogen Hydrogen sulphide Catalytic stratospheric ozone depletion: Hydrochlorofluorocarbons Chlorofluorocarbons Wastes Municipal waste Hazardous waste Industrial waste Construction waste Overburden

From ISO LCA standards 14040–14043.

as the PET or PLA bottle) and any supplementary systems (such as carpet or compost). As defined in the ISO 14041 LCA standard, allocation should be avoided wherever possible. This may be achieved by considering the process in more detail. It may then be possible to split and exclude the parts of the process that are connected to the other function. Materials of low value can be assessed as open loop outputs that leave the system boundaries without contributing to the environmental impacts of the system in question. For systems where splitting is not possible, allocation can be avoided by expanding the system boundaries so that the additional inputs or outputs remain within the system boundary. However, this adds complexity to the LCA; for example a PET bottle manufacturer is unlikely to want to carry out an LCA of carpet. © 2008, Woodhead Publishing Limited


221

Where allocation cannot be avoided, ISO 14041 suggests that the system inputs and outputs are partitioned between the product’s different functions in such a way that the underlying physical relationships (allocation by weight, energy or chemistry) between them are reflected. Where physical relationships cannot be established or used as a basis for allocation, the inputs should be allocated between the products and functions in such a way that the economic relationships between them are reflected. So, for example, if a biopolymer had a relatively high price and compost made from that biopolymer a low price, more impacts would be allocated to the biopolymer than to the compost. This reflects the commercial reality that compost is to some extent an incidental product. Where there is uncertainty regarding data values or where there are data gaps, sensitivity analysis can be used to determine the significance of decisions made. 9.3.4 Impact assessment In the impact assessment the environmental impacts quantified in the inventory analysis are related to measures of environmental concerns. Impact assessment as defined by ISO consists of classification, characterisation and optional elements such as normalisation, grouping and weighting (ISO 14042). Classification groups the data listed in the inventory into a number of relevant impact categories such as global warming, ozone depletion and acidification. Characterisation assesses the relative contribution of the individual environmental impacts to each impact category. Normalisation can be used to relate the results to the total emissions in a certain area over a given period. The idea behind this is to increase the comparability of data from the different impact categories and to provide a better basis for interpretation. Grouping is the sorting and possible ranking of the impact categories. If an organisation defined one impact category as having a higher priority than another (for example in its corporate environmental policy) this can be reflected in its LCA studies. Weighting converts the indicator results of different impact categories using numerical factors based on value choices. For example, a group of experts may reach agreement that global warming should be assigned three times the weighting of acid rain and so on. Weighting may include aggregation of the weighted indicator results. This step is commonly called valuation. 9.3.5 Interpretation In the interpretation stage of an LCA study the results are analysed, conclusions are reached, limitations are explained and recommendations are made based on the findings. The life cycle interpretation phase comprises three elements (ISO 14043): • identification of the significant issues based on the results of the previous phases of the LCA; © 2008, Woodhead Publishing Limited

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• evaluation, which considers completeness, sensitivity and consistency checks; • conclusions, recommendations and reporting. 9.3.6 Life cycle assessment software LCA can be undertaken by hand, for example using Excel spreadsheets, but by far the best approach is to use dedicated LCA software. Such software provides guidance on system design and data input, takes care of the calculations, helps undertake the ISO-defined stages discussed above, and produces results in a range of formats such as various types of graphs, charts and tables. Not least, LCA software contains invaluable databases of previously collected data. The world’s leading LCA software is SimaPro, produced in The Netherlands by PRe Consultants and sold worldwide by national LCA experts such as Ciba Expert Services in the UK (www.simapro.co.uk) and Earthshift in the US (www.earthshift.com). Other LCA software tools on the market include GaBi and Umberto. In most cases software can be downloaded and trialled for free. LCAs demand data, and while data can be collected as the need arises, it is usually more feasible to rely at least partly on existing data. The world’s largest database of LCA data is EcoInvent (www.ecoinvent.ch). The latest EcoInvent data (version 2, launched at the end of 2007) are available in SimaPro or can be purchased separately. Data without software are difficult to utilise so it is usually preferable to buy LCA software that comes with the EcoInvent database built in. 9.3.7 Energy and global warming potential as key indicators Packaging production is a relatively clean industry, which means that esoteric or highly toxic pollutants are seldom produced. For example (imagining a product very different from packaging), the manufacture of an anti-cancer drug might result in emissions with the potential to be extremely toxic. This potential human toxicological impact might be even more important than the environmental impact of the energy used to manufacture the drug. In contrast, packaging is based, in the main, on food safe materials. The production processes, and inputs and outputs of those processes, are well known and comparatively benign. Therefore the main emissions that arise during the life cycle of packaging are often those that are caused by the combustion of fossil fuels to generate electricity and to power vehicles. Figure 9.2 shows the energy used to produce 1 kg of common packaging materials.4 The data shown are adapted from data contained in several LCA databases, which in turn are based on average data from various producers investigated in the 1990s. Therefore the data are intended to be



223

250

Energy (MJ)

200 150 100 50

r Pa pe

s G la s

PP

PV C

PS

T PE

LD PE

H D PE

el St e

Al

um in iu

m

0

Feedstock energy

Process energy

Fig. 9.2 Energy requirement per kilogramme of material. Abbreviations: HDPE/LDPE, high-/low-density polyethylene; PVC, polyvinyl chloride; PP, polypropylene.

indicative of general trends and should not be relied upon for specific cases. The energy figures shown include all life cycle stages up to and including manufacture of the material. Raw material extraction and harvesting, shipping, refining, production of the material and so on are included. The later parts of the life cycle (package manufacture from the material, consumer use and disposal or recycling) are not included. Two types of energy are shown: 1 2

Feedstock energy: the calorific energy contained in the material, some of which could be regained if the material were to be incinerated with energy recovery. Process energy: the energy used in producing and shipping the material, which cannot be recovered.

In general, published LCAs show the sum of both types of energy, but since feedstock energy is quite different from process energy and is potentially recoverable, LCA results often focus on the process energy alone. It can be seen that materials vary considerably in terms of their energy requirement per kilogramme. For example, aluminium can be seen to have a high energy requirement per kilogramme while glass has a low energy requirement per kilogramme. Yet this should not be taken as indicative of the environmental performance of these materials when used in packaging. To form functional packaging, very different amounts of materials are required. For example between eight and ten times as much glass might be


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Energy (MJ)

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required to make a bottle as the amount of aluminium required to make a comparable can. (The weight of a package is not the only aspect taken into account when brand owners select packaging, of course. The packages in question have other distinctive features: the glass bottle enables the product to be seen, is resealable and conveys a premium image, while the can is convenient, light in weight and unbreakable.) Figure 9.3 shows the energy requirement of hypothetical 300 ml beverage packages.4 The graph takes the energy figures per kilogramme from Fig. 9.2 and multiplies them by weights of packages that are approximately functionally equivalent. The package weights are based on the amount of each material used in actual samples of packaging purchased from US supermarkets. The package weights are not averages of large samples of packaging and so should not be taken as representative of every packaging situation. Viewed per package rather than per kilogramme, the material energy figures look rather different. For example the glass bottle suddenly becomes one of the most energy-intensive packages. The graphs do not include the life cycle stages following packaging production. A more accurate LCA would need to include these to provide a fair picture. In general, if impacts such as the transport of the filled packages are taken into account, minimal packages such as beverage cartons or pouches begin to look increasingly impressive in environmental terms. They may contain non-renewable materials (aluminium and plastic) but they use very little of these materials, they transport efficiently and they leave very little waste. An LCA study undertaken for a UK wine importer in 20075 showed that if wine were to be shipped from Australia to the UK in laminate pouches



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instead of glass bottles, one-third of the ships used to transport the wine across the globe would no longer be required. A plastic pouch may be made from oil-based material while a glass bottle is not, yet over the life cycle the glass bottle was shown to use far more oil in this scenario. 9.3.8 Case-specific life cycle assessments Generic graphs have been shown here for the purposes of demonstration, but in the real world generic findings are seldom reliable. A case-specific LCA is usually required if a robust answer is required on which to base decision making. For example, in the 1990s European legislators investigated the potential usefulness of a ‘packaging environmental indicator’ or PEI, a tool based on streamlined LCA methodology, to guide policy decision making. The PEI would, it was hoped, reveal which types of packaging were environmentally preferable, so that the use of environmentally preferable packaging could be encouraged via legislation. However, the feasibility study found that the reality was more complicated than this, with various types of packaging performing best in various situations. For example, a heavy but refillable and recyclable glass bottle might perform well in environmental terms in an exceptionally localised market, such as the highly context-specific case of small, traditional German mineral water producers who only ship within 20 km of their well and who serve consumers that reliably return bottles for refilling. However, in the US, where mineral water might be shipped 2000 miles, and consumers are not used to returning refillable bottles, a single-trip PET packaging system usually results in lower environmental impact over the life cycle than any glass system. So a detailed, case-specific LCA is usually required to produce an accurate result. In practice, undertaking such an LCA is not easy. Simply identifying the life cycle can be difficult. For example, commodity packaging materials may come from a huge variety of sources. Even when a supplier is identified, obtaining production input and output data from a PET producer in China, for instance, may be no easy task. Businesses in the supply chain may be wary of parting with energy and material flow data because they fear that the information could be used to calculate their costs for the purposes of negotiating down the price. Once the data are collected, LCA methodology can present challenges. For example, system boundaries can be difficult to define, as in the case of PET bottles that are recycled into carpet fibres, a situation that necessitates the consideration of a whole separate life cycle, that of carpet production. Once LCA results are achieved, a clear answer may nevertheless prove elusive. Often one package will be responsible for the least water pollution, another for the least human toxicity, another for the least acid rain, and another for the least global warming. Who is to say which is preferable? There is no completely scientifically valid answer in such a situation. It is, in effect, a societal decision rather than a scientific decision.


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Different stakeholders may have different opinions about which environmental impacts are most important. However, in practice, there is increasing consensus that global warming is the most important environmental issue, which means than global warming potential or carbon footprint is the most important measure of packaging environmental performance. Since most of the global warming potential of packaging arises from the energy used during production and other stages of the life cycle, energy use and carbon footprint are closely aligned. LCA may be simplified – streamlined – as appropriate. This usually involves: • relying to a greater extent on generic, existing data rather than collecting case-specific data; • leaving out less significant aspects of the life cycle; • making data approximations, such as substituting a material for another closely related material; • limiting the number of environmental impact categories measured; • otherwise streamlining the approach. The challenge is to know what can be approximated and what must be accurate to achieve a meaningful result. That takes experience. To some extent the latest LCA software such as SimaPro can help, because it enables sensitivity analyses to be carried out to check what aspects make a significant difference to the final result. Streamlined LCAs involve a certain risk, but they are probably the most common LCAs undertaken, since they are quicker to complete and more cost effective than full LCAs. 9.3.9 Renewable energy credits and life cycle assessment The way in which energy is treated in LCAs, and in particular how credit is given for renewable energy, is critical to how well biopolymers fare in LCA studies. In the case of a package that has been made using predominantly renewable energy (such as wind, solar or hydroelectric power) the carbon footprint might be significantly lower than the energy use suggests. This is why some LCA studies adopt a methodology of crediting packages with their renewable energy, so that only the non-renewable energy is shown on comparative graphs. Since renewable energy is just that – renewable – it is by definition carbon neutral. In practice it might not be quite carbon neutral, since the electricity distribution grid inevitably consumes some fossil fuels during maintenance operations and so on, but usually in LCAs these minor impacts are ignored and renewable energy generation is considered to be 100% renewable. Therefore the carbon footprint of a renewable material, such as a biopolymer manufactured using renewable energy, can appear very low compared with that of a non-renewable material manufactured using non-renewable energy. (However this benefit is not solely available



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to producers of biopolymers: any material producer can greatly improve its carbon footprint by using renewable energy to power its production facility.) When a production facility utilises renewable energy, it may do so directly – by having a wind turbine on its roof or a small scale hydroelectric plant next door – or, more commonly, it will contract to buy renewable energy from a remote supplier (such as a wind farm) that supplies the energy via the traditional electrical distribution grid. In such a case, the electrons reaching the production facility will not necessarily be the ones fed into the grid by the renewable energy supplier. This is not a matter of concern, however, since the overall result is clear: renewable energy has been generated and used, and there is a distribution connection between the two. The situation can be considered akin to the banking system: if a person banks $1000 in cash into his local bank branch, and then the next day returns to withdraw his $1000, he is not concerned whether he receives the same actual banknotes he deposited, as long as he gets back $1000 worth of banknotes! Giving credit in LCAs for renewable energy purchased in this way is commonplace and widely considered acceptable by LCA experts. However, there is a related situation that is more contentious in LCA terms. Where there is no renewable energy available on a grid, a company may choose to buy ‘renewable energy credits’ or RECs. These are credits for renewable energy produced in another area and on another grid. RECs can be thought of as paying for the extra cost of generating renewable energy over the cost of generating conventional energy. According to the US REC certifying body Green-e (www.green-e.org): Renewable Energy Certificates (RECs) are created when a renewable energy facility generates electricity. Each unique certificate represents all of the environmental attributes or benefits of a specific quantity of renewable generation, namely the benefits that everyone receives when conventional fuels, such as coal, nuclear, oil, or gas, are displaced. What you pay for when you buy renewable energy certificates is the benefit of displacing other non-renewable sources from the electric grid.

The REC system is often used to fund the building of new renewable generation capacity such as wind farms. A wind farm developer sells the credits for a farm that is not yet built, so that the purchaser of the credits is aiding the development of renewable energy. In theory the credits can only be sold if the renewable energy capacity would not have been built if it were not for the credits. In other words, the credits should be genuinely supporting the development of renewable energy. Typically a wind farm developer (who could be on another continent from the purchaser) might sell the rights to the first 20 years of production of renewable energy from the wind farm. Then once the wind farm is producing energy, in theory the developer cannot market the energy as


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renewable for 20 years and the purchasers of the energy cannot be considered to be buying renewable energy, since the rights to that claim have been previously sold in the form of RECs. On occasion this has been found to be problematic in practice. Renewable energy developers have claimed that they have not always been fully aware when raising funds that they are selling the right to consider their development renewable, and find it illogical to be unable to claim to consumers that their energy is beneficial once the renewable energy generation facility is in operation. Consumers of the energy find it difficult to comprehend why the energy they have bought cannot be considered renewable despite the fact that it came from a renewable energy generator. However, despite these challenges, REC certification schemes such as Green-e aim to guarantee that the REC process is operating correctly and no ‘double counting’ is taking place. One example of a Green-e-certified organisation that sells RECs is Colorado-based Renewable Choice Energy. The organisation sells RECs to businesses and also direct to consumers, who can easily purchase the RECs simply by buying a ‘Wind Power Card’ available in selected US supermarkets (see Fig. 9.4). The card explains: ‘The Wind Power Card buys these credits, which represent the additional cost and value of wind energy. It ensures that the electricity you use is replaced onto the national power grid with wind energy. It does not replace or reduce your conventional power bill’.

Fig. 9.4 Wind Power Card available in selected US supermarkets.



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9.3.10 Renewable energy credits in a life cycle assessment context The REC system is problematic in LCA terms. LCA practitioners find it difficult to agree how to treat RECs. When showing energy usage in LCA results graphs, should the purchase of RECs cause energy to be credited so that the product appears to have lower energy use? Should the carbon footprint be credited so that the product appears to have a commendably low carbon footprint? The question is particularly pertinent to biopolymers, since biopolymer producers have bought RECs with the aim of achieving a lower carbon footprint. Indeed, a biopolymer that is credited with both the carbon absorbed by the crop and the carbon saved through purchasing RECs can appear to have a negative carbon footprint. This result has caused scepticism in some industry observers. As one commented dryly, ‘When it comes to solving global warming, it seems we can feel free to drive our gas guzzlers as long as we buy lots of biopolymer packaging’ (US retailer Wild Oats, personal communication, 2006). Since LCA is concerned with physical and energetic inputs and outputs, and since there is no such relationship between RECs and the product being produced by the purchaser of the RECs, it seems a defensible approach in LCA methodological terms not to credit carbon associated with RECs in LCA studies. In this case, the users of the energy would be credited with the renewability of that energy. After all, they will have paid for the energy, even if they have not paid for the notional renewability benefit of that energy. It seems that the most logical approach in LCA is to follow the actual energy flow rather than giving credit for notional purchases of renewable benefit. LCA practitioners appear to be starting to reach consensus on this point, although debate continues. Where RECs are credited in LCA studies, that fact needs to be made clear, and graphs should also be given showing the results without the credits. Where RECs are not credited in LCA studies, the buyers of RECs certainly deserve to be commended for buying RECs. They are helping to develop renewable energy, and that is admirable.

9.4

Results of existing life cycle assessment studies of biopolymers

Biopolymers are relatively new and not a great number of LCAs have been carried out to date, particularly transparent, unbiased LCAs produced by independent researchers rather than commissioned by biopolymer manufacturers. A summary of a selection of LCAs carried out to date is included here. These are LCAs based on the life cycle energy use and material inputs and outputs associated with biopolymers produced in the recent past, which means that they reflect early biopolymer production methods. Biopolymer production can be expected to become more efficient


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Table 9.3 Life cycle energy requirements of traditional polymers and biopolymers Life cycle energy requirements of traditional polymers and biopolymers (in order from highest to lowest process energy) PHA (grown in corn plants) PHA (bacterial fermentation) PLA (from starch) PS (polystyrene, general purpose) PET (bottle grade) Plastic starch + 50% polyester HDPE Thermoplastic starch pellets Plastic starch + 15% PVOH

Cradle to factory gate fossil energy requirements (GJ per US short ton of plastic) Process energy

Feedstock energy

Total energy

90 80 53 39 38 32 31 25 24

0 0 0 48 39 20 49 0 6

90 80 53 87 77 52 80 25 30

PHA, polyhydroxy alkanoate; HDPE, high-density polyethylene; PVOH, polyvinyl alcohol. Source: Narayan (2004).6

as economies of scale are realised and production processes are optimised through experience. R. Narayan of Michigan State University is one of the leading researchers involved in the assessment of biopolymers using LCA. In 2004, he published a list of biopolymer life cycle energy requirements, as presented in Table 9.3.6 The table shows that the biopolymers tended to have higher process fossil energy requirements: the factories used more fossil energy in producing the biopolymers than did fossil polymer factories. However, since the biopolymers had no feedstock fossil energy, the total energy was broadly competitive with fossil polymers. A review of LCA studies (unpublished) carried out by Jonna Meyhoff Fry at Ciba Expert Services reviewed published LCAs of biopolymer carrier bags versus traditional carrier bags. The findings were as follows: Degradable bags have similar global warming potential to conventional HDPE bags, and depending on the source of the raw material may have higher eutrophication potential from farming activities. Conversely, the conventional polymers have higher abiotic resource depletion potential. Where the compostable materials are composted and thereby kept out of landfill, the impact potentials are somewhat reduced. The global warming potential for degradable bags is due to their starch content resulting in higher methane emissions during landfill degradation as well as oxides of nitrogen emissions from the fertilising of crops. The eutrophication potential (emissions of nitrates and phosphates into waterways) for degradable polymers is due to the application of fertilisers to farmland on which the crops are grown.



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The French supermarket chain Carrefour commissioned a carrier bag study in 2004.7 One of the options studied was a biopolymer bag based on maize starch. The study found that the biopolymer bag emitted 60% more acid gases than a disposable PE bag, but 60% lower levels of photochemical oxidants. The biopolymer bag contributed 11 times more eutrophication, mainly due to the agricultural impacts of maize production. The biopolymer bag emitted 40% more greenhouse gases than a disposable PE bag, partly because it was heavier (to achieve comparable strength) and partly because the bag was manufactured in Italy, where emissions due to electricity generation are higher than in France. (French electricity generation produces lower greenhouse gas emissions than many other countries because France has a higher proportion of nuclear energy generation. The environmental impacts of building nuclear generators and the impacts of processing and storing nuclear wastes are not included in LCA, with the result that packaging manufactured in France can be at an advantage in LCA studies.) An Australian study investigating biopolymer bags8 produced mixed results, finding that certain biopolymer bags such as those made from Mater-Bi had lower overall environmental impacts than conventional PE bags, while other biopolymer bags such as those made from PLA had higher impacts. However, the Mater-Bi bags had higher global warming potential than conventional bags. Another Australian study9 found that biopolymer bags had the highest greenhouse gas emissions. The researchers felt that biodegradable bags would offer benefits in terms of achieving lower litter persistence but would not deliver significant resource use gains. A study carried out at Imperial College London in 200610 used the EcoIndicator 99 methodology (a method for weighting various environmental impacts that is found in LCA software such as SimaPro) and found that PLA bags appeared to have the highest environmental impact and highly recycled conventional PE bags the lowest. However the PLA bag considered in the study was particularly heavy and a lighter PLA bag would achieve better results. A Mater-Bi bag performed better than a conventional bag if the Mater-Bi bag achieved a 50% recycling rate while the conventional bag was not recycled. A streamlined LCA (unpublished) of two types of produce trays was carried out in 2003 for the UK retailer Marks & Spencer. The trays consisted of a PS tray and a biopolymer tray. The study found no significant difference between the trays. A German study11 compared Mater-Bi bags with paper bags and PE bags and found that the Mater-Bi bag caused lower impacts in LCA terms than paper bags and was equivalent to PE bags in 11 out of 13 environmental impact categories investigated. A study currently being conducted by Ciba Expert Services (as yet unpublished) investigated various supermarket carrier bag options including a bag made from a new biopolymer material produced by


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Novamont. This particular biopolymer was chosen because it was considered particularly suitable for bags. The interim results suggested that the biopolymer bag had slightly higher global warming potential than a conventional HDPE bag. However, this was partly due to the higher weight of the sample bag. If the bag was the same weight as the conventional bag it was approximately equivalent in terms of LCA impacts. If credit was given for the purchase of RECs, the biopolymer bag could be seen to have slightly lower global warming potential than the conventional bag. So the LCA methodology applied had the potential to change the results. The overall interim finding was that consumer behaviour was the biggest factor affecting the environmental performance of carrier bags. For example, if a consumer consistently used a strong reusable carrier bag, this was the best environmental result. However, a consumer who bought a reusable bag and then failed to use it more than once or twice would achieve the worst environmental result. A consumer who used a biopolymer bag and then gave it a secondary use in the home as a rubbish bin liner would achieve a better environmental result than a consumer who used a conventional bag and then threw it away, and vice versa. Another study carried out by the same team for a private client (unpublished) concluded that the existing LCA evidence pointed to the fact that in future biopolymer bags are likely to become the best environmental solution as production efficiencies increase and recycling and composting schemes become more common. This assumed that one-trip bags are required by supermarkets. The study concluded that if consumers can be educated to use reusable bags many times reliably, then reusable bags are the best environmental option of all. Overall, then, the existing LCA evidence concerning biopolymers is mixed. Certainly, there is no magnitude of difference between conventional polymers and biopolymers. Biopolymers appear to have been found to have slightly worse environmental impacts in some LCA studies, although they also have greater potential to improve. As more detailed LCA studies appear, the picture will become clearer.

9.4.1

Lessons from life cycle assessment: how to improve the environmental performance of packaging General trends can be perceived from the many LCAs of packaging that have been undertaken around the world, trends that help to reveal what should be done to improve an item of packaging’s success in an LCA. The three most effective actions that can be taken are outlined below. 1

Minimise packaging. Reducing the weight of a package – minimising the amount of material used to make it – directly reduces environmental impact. So if a 20% reduction in material is achieved, an approximately



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20% reduction in environmental impact is achieved (the word ‘approximately’ applies simply because certain aspects such as transport might not achieve a directly proportional reduction depending on vehicle load capacity and so on, but the main impacts will be reduced in direct proportion to any material reduction). 2 Power facilities with renewable energy. Often the easiest way to gain a significant advantage in LCA terms is to buy renewable energy. Yet many companies have not done so. This apparent apathy or distrust of renewable energy is puzzling, because using 100% renewable energy at a packaging production facility will usually achieve a zero global warming impact score in an LCA for the production stage of that package’s life cycle. In other words, using renewable energy instead of fossil energy is perhaps the most effective way that exists of gaining a significant competitive advantage in a comparative LCA of packaging. Those companies that have contracted renewable energy have found the process remarkably easy. In addition, many companies have saved money by doing so, due to the fact that the price of fossil energy has risen considerably while the companies have been on fixed price renewable energy contracts. One US sports and outdoor activity retailer12 signed a 2-year fixed price wind and solar electricity contract to supply electricity through the usual grid to all its 100 stores. Although there was initially a slight price premium involved, within a few months of signing the contract the price of standard electricity rose above the contracted price. By the time the 2-year fixed price renewable electricity contract was completed, the retailer had saved over US$100 000 compared with the cost if it had continued to use standard electricity. 3 Maximise supply chain efficiency. Continual efforts should be made to minimise energy use, material use and waste. To give one small example, energy-efficient lighting should be used and it should be automated to turn off when areas are not in use. Production waste should be reprocessed internally and production continually monitored and improved so that waste does not arise in the first place. Transport logistical efficiency should be maximised at every opportunity. Obviously companies routinely do this for cost reasons, but sometimes due to time pressures or the existence of certain areas of operations where cost pressures are less apparent, inefficiencies are allowed to creep in. For example, a pharmaceuticals company used an inefficient production process, airfreighting the product around the world for various production and packaging steps, in order to meet critical product launch deadlines. This inefficiency was recognised, but it was financially bearable because the product was innovative and commanded a premium price. However, in environmental terms such inefficiency must be eradicated irrespective of whether the inefficiency is financially viable or is justified by business pressures. Adopting the mindset that efficiency is a valid goal in its own right will improve LCA results.


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An interesting feature of these three priority actions is that some of the environmental aspects most valued by consumers – particularly recycling – hardly feature. This is because in LCA terms minimising material use, using renewable energy and maximising efficiency tend to achieve greater environmental benefit than recycling. Aspects such as recycling are worthwhile, but they are lower down the LCA priority list. This is due to the fact that it takes energy to collect used packaging for recycling (such as fuel used by kerbside collection vehicles), it takes energy to ship used packaging to recycling plants (mainly trucking, which can involve remarkably long distances due to the fact that there are often not many recycling plants for any particular material), it takes energy to power a recycling plant, and waste inevitably arises during the production of the recyclate. LCA studies reveal that once all these environmental impacts are taken into account, recycling generally achieves environmental benefit, but the net benefit is often rather less than might be assumed by some stakeholders. Therefore recycling, while commendable, is not at the top of the priority list as defined by LCA.

9.5

Measuring the environmental performance of packaging: future trends

The science of LCA will continue to develop. Data quality will continue to improve, with more accurate and transparent data available for more packaging processes from more regions of the world. For example, although many goods and packaging items are produced in China, only recently have data on Chinese production started to become available. LCA software will continue to improve, making it easier to carry out LCAs and interpret meaningful results. For instance the latest version of the LCA software SimaPro contains sensitivity analysis tools that could only be dreamed of by LCA practitioners a decade ago. However, despite all these developments, carrying out a fully detailed LCA will always be a substantial task that simply will not be financially viable in every situation. Therefore if environmental performance measurement of packaging is to become more widespread, quicker, cheaper, streamlined systems will need to be developed and improved so that they are both feasible within a fast-paced business context as well as scientifically valid and accurate enough to form a sound basis for business decision making. 9.5.1 Carbon footprinting Currently, interest in carbon footprinting is growing rapidly, and it seems likely that this subset of LCA will continue to grow in prominence. Carbon footprinting is, in effect, LCA with only one environmental impact – global



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warming potential – taken into account. Eutrophication, smog, human toxicity, resource depletion, acid rain and the various other impacts usually covered by LCA are excluded. In the case of packaging, this approach has considerable validity, as previously explained: for a relatively clean, simple product such as packaging, carbon footprinting covers most of the environmental impacts of packaging, and the impacts ignored by carbon footprinting tend to be fairly insignificant in practice. In the case of biopolymers, carbon footprinting successfully captures their main environmental benefits, and so carbon footprinting is a useful tool for assessing biopolymers. All things considered, carbon footprinting may be one of the better simplifications, not only for its methodological validity but also for its growing acceptance among the full range of stakeholders. 9.5.2 Streamlined methods Even carbon footprinting can be too time consuming to apply to many thousands of products. Several retailers, such as Marks & Spencer in the UK, aim to measure and reduce their overall carbon footprint, and they need extremely streamlined methods to do so. A variety of such methods are in development. An organisation that acts as a repository of information on carbon footprinting is the Carbon Trust (www.carbontrust.com). There will come a point where a highly simplified system is no more accurate than an extremely simple and controversial approach: that of using cost as an approximate measure of environmental impact. Packaging cost is approximately proportional to its environmental impact due to the fact that the cost of packaging is derived largely from the energy and materials used in the packaging. These are precisely the same factors that dominate packaging environmental impact results as measured by LCA. Of course, this approach would not work well with many other products where product cost is not as closely aligned with the environmental impact of the physical materials used in the product. For example, an electronic device such as an Apple iPod has less than US$5 worth of materials in it, yet the retail price of the iPod is far higher than this due to research and development costs, the specialised nature of electronic components, software development costs, advertising costs, the value of intellectual property rights and profit margins. Packaging, however, is an extremely competitive, low-profit industry without large development and intellectual property costs, and so the price of an item of packaging tends to be closely related to the materials and energy used to make it, which is reasonably proportional to its environmental impact. Therefore, if an extremely quick and approximate measure of environmental impact is desired, cost might be as good a measure as any other. Naturally this is a controversial approach. For some reason environmental pressure groups seem particularly resistant to the idea – perhaps this is simply an innate reaction against any association between


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‘virtuous green’ and ‘dirty money’? – while many packaging manufacturers can see the validity of it. 9.5.3 Biopolymers and future measurement options Regarding biopolymers, the ‘cost as an approximate measure of environmental impact’ approach may be slightly disadvantageous to them. Biopolymers tend to cost more than traditional polymers, largely because production economies of scale do not yet exist and biopolymer production has not yet enjoyed half a century of continuous improvement in the way that fossil polymer production has. In the longer term, it is inevitable that biopolymers will gain the upper hand. The price of oil will keep rising. Various projections exist concerning when oil supplies will run out, and in broad terms these projections range from around 40 years to 140 years. However, oil will become economically unviable for packaging applications well before oil actually runs out. Events such as Hurricane Katrina and unrest in the Middle East have demonstrated that financial markets overreact to any threat of curtailment in oil supplies. This means that the cost of a barrel of oil rises out of proportion to the actual dwindling in supplies. As a result, it is likely that oil-based polymers will be financially out of reach to packaging manufacturers sooner than many observers realise. Biopolymers, being less sensitive to oil price rises, may become competitively advantaged unexpectedly rapidly. LCA reveals that currently biopolymers face certain challenges in environmental terms. It cannot be assumed that present day biopolymers automatically achieve better environmental performance than traditional polymers simply because their perceived benefits of renewability and biodegradability are inherently appealing. Nevertheless, the future of biopolymers is bright. Production methods will continue to become more efficient. The use of renewable energy in production will become more common. Over the longer term, biopolymers have the potential to score better in LCA terms than any traditional polymer. Biopolymers have the ability, even if not yet fully realised, to be more renewable, more biodegradable, more cyclic and so ultimately more sustainable than traditional polymers. This is just as well, because at some point in the future they will be the only polymers we have.

9.6


• LCA software: www.simapro.co.uk; www.earthshift.com. • LCA data: www.ecoinvent.ch. • LCA consultancy services: www.cibaexpertservices.co.uk; piraconsulting.com. • US LCA organisation: www.lcacenter.org.


www.


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• Australian LCA organisation: www.lifecycles.com.au. • Carbon footprinting organisation: www.carbontrust.com. • Retailers involved in environmental retailing and sustainable building practices: www.wholefoodsmarket.com; www.wildoats.com; www.rei. com. • Wal-Mart scorecard: www.packagemodeling.com.

9.7

References

1 parker, g., 2006, personal communication with US supermarket retailer, California, July 2006. 2 drachman, p., 2007, Carbon neutrality and life cycle analysis for biodegradable plastics. Industry Insight series, IntertechPira, July 2007 edition. 3 parker, g., 2007, Wal-Mart scorecard: an analysis in the European context. Unpublished report for private client, Ciba Expert Services, Surrey, UK. 4 parker, g., 1999, Environmental considerations in beverage packaging. In Handbook of Beverage Packaging, G. A. Giles ed., Sheffield Academic Press, Sheffield, UK. 5 fernandes, v. and parker, g., 2007, LCA comparison of glass wine bottles with two types of pouches. Unpublished report for private client, Ciba Expert Services, Surrey, UK (at the time of writing a summary of the report could be downloaded from www.thecompanyofwinepeople.co.za). 6 narayan, r., 2004, Drivers and rationale for use of biobased materials based on life cycle assessment (LCA): Paper presented at Global Plastics Environmental Conference, February 2004 (paper available from www.sperecycling.org/ GPEC2004/pdffiles/papers/018.pdf). 7 ecobilan, 2004, Evaluation of the environmental impacts of Carrefour supermarket carrier bags, Carrefour, France. Price waterhouse Coopers/Ecobilan, Crystal Park, France. 8 excelplasaustralia, 2004, The Impact of Degradable Plastic Bags in Australia. RMIT Centre for Design, Australia. 9 nolan-itu and eunomia research and consulting, 2002, Plastic Shopping Bags, Analysis of Levies and Environmental Impacts. RMIT Centre for Design, Australia. 10 payne, m. a., 2006, Life Cycle Assessment of Biodegradable Carrier Bags. Research report, Imperial College London. 11 schwarzwalder, b., estermann, r. and marini, l., 2004, The Part of Life Cycle Assessment for Biodegradable Products: Bags and Loose Fill. Composto BioConsulting, Switzerland. 12 parker, g., 2007, personal communication with the US sports and outdoor activity retailer REI, Pennsylvania, September 2007.


10 Eco-design of food packaging materials H. Lewis, RMIT University, Australia

10.1

Introduction

The amount of food packaging consumed globally continues to increase, with significant impacts on the natural environment. Packaging in the European Union alone increased by 920 000 tonnes between 2000 and 2002 (ASSURE, 2005, p. 3). The environmental impacts of packaging include resource consumption, land degradation, air and water pollution and global warming, and they occur at every stage of the packaging supply chain. Climate change is now recognised as an urgent global issue, while air pollution is worsening in the rapidly growing economies such as India and China. One solution is to consider the environmental impacts of packaging during the design process so that they can be reduced at source, a process known as ‘eco-design’ (e.g. Fuad-Luke, 2002), ‘design for the environment’ (e.g. Mackenzie, 1997; Lewis et al., 2001) or ‘eco-friendly design’ (e.g. Evans, 1997). Eco-design is already being implemented by companies around the world and inspiring case studies have been documented (e.g. Denison and Ren, 2001; Imhoff, 2004), but these are isolated examples of best practice that do not reflect everyday practice in the industry. More needs to be done, and it needs to be done urgently, to support efforts by most industrialised countries to make production and consumption more sustainable. The aim of this chapter is to present a series of eco-design principles which, if followed in the product design process, would support the development of more sustainable packaging. These principles are illustrated through reference to more detailed eco-design strategies and case studies.


Eco-design of food packaging materials

10.2

239

Key drivers of eco-design of food packaging materials

The overarching goal of eco-design is sustainable development. We need to design products that meet consumer needs but do not degrade the natural environment that sustains us. A recent assessment for the United Nations Environment Program (Millennium Ecosystem Assessment, 2005) concluded that the degradation of ecosystems can be reversed while still meeting increasing demands for their services, but this will involve ‘significant changes in policies, institutions and practices that are currently not underway’ (p. 16). Many businesses already recognise this imperative and are implementing corporate social responsibility (CSR) policies and programmes which aim to minimise the social and environmental impacts of their activities and to make a positive contribution to society through philanthropic grants and projects. Eco-design is one of the many initiatives being implemented by companies in the manufacturing sector under the general banner of CSR in order to reduce their environmental impacts. The drivers of eco-design vary for each company, but in the packaging industry they include: • product stewardship or extended producer responsibility (EPR) regulations; • campaigns by non-government environment organisations to raise awareness about the environmental impacts of packaging; • consumer concerns about over-packaging and waste; • supply chain pressure, particularly from large retailers and brand owners. 10.2.1 Regulations Product stewardship is the principle that all companies in a product supply chain share responsibility for reducing the product’s environmental impacts (OECD, 1998; US EPA, 2006a). Examples of product stewardship programmes for packaging include the Australian National Packaging Covenant (NPC) (ANZECC, 1999; NPCC, 2004) and the New Zealand Packaging Accord (Ministry for the Environment, 2004), both of which rely on voluntary commitments by companies in the packaging supply chain to work with others to achieve more sustainable packaging. EPR places more responsibility on the manufacturer or importer of a product, for example the OECD (2001, p. 9) has defined it as ‘. . . an environmental policy approach in which a producer’s responsibility for a product is extended to the post-consumer stage of a product’s life cycle’. A number of European countries have implemented EPR policies for packaging, most notably Germany through its Ordinance on the Avoidance of Packaging Waste (1991). Packaging regulations are covered elsewhere in this book (Chapter 22) and so will not be covered in detail here.


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10.2.2 Environment organisations Non-government organisations have been actively campaigning for increased regulation of packaging for many years. In some cases they have negotiated directly with governments, for example the Boomerang Alliance, representing a number of different environment and local government organisations in Australia, successfully campaigned to have material recycling targets included in the revised NPC, and continue to lobby for stricter legislation (Boomerang Alliance, n.d.). Non-profit organisations that are monitoring industry activity and actively lobbying for regulation in other parts of the world include the Container Recycling Institute in the United States (CRI, 2006) and The Women’s Institute in the United Kingdom, who held a packaging ‘day of action’ on 20 June 2006 (The Women’s Institute, 2006). Greenpeace has been lobbying companies for many years to phase out the use of polyvinyl chloride (PVC) in packaging and other applications and has staged numerous protests against the industry (e.g. Greenpeace International, 2002). Despite the failure of Greenpeace to have PVC banned from use in packaging in any country, some companies have voluntarily phased out their use of the material. 10.2.3 Consumer concerns Many consumers believe that there is too much ‘excess packaging’ and are concerned about the perceived impacts of packaging on waste and litter. This was one of the conclusions of a survey of consumer attitudes to packaging that was undertaken in the United Kingdom in 1993 and repeated in 1997 (Pegram Walters Associates, 1993, 1997). The 1997 survey found that 45% of respondents believed packaging caused environmental problems (an increase from 38% in 1993), and the specific drawbacks mentioned included that it is ‘waste/wasteful’, ‘difficult to dispose of’, ‘too much rubbish’, ‘creates pollution/bad for the environment’, ‘causes litter’ and ‘nonbiodegradable’ (p. 6); 76% of respondents agreed with the statement that ‘overall there is too much packaging’, an increase from 72% in 1993 (p. 8). 10.2.4 Supply chain pressure Many large retailers and brand owners now require their suppliers to meet minimum environmental standards for packaging. One example is WalMart, which has announced plans to reduce its packaging by 5% by 2013. The responsibility for achieving this goal will be passed on to 60 000 suppliers who will be asked to come up with ways to cut packaging (ColemanLochner, 2006). Sainsbury’s is also aiming to reduce packaging by 5% relative to turnover by 2010, and is asking its suppliers to switch to recyclable or compostable packaging. They are also working with suppliers to replace the use of cardboard with returnable transport packaging (J Sainsbury plc, 2006a, p. 32).



10.3

241

Eco-design strategies for food packaging materials

10.3.1 Overview This section presents four eco-design principles for food packaging. 1 Design for efficiency, or ‘doing more with less’. 2 Design for recovery in order to eliminate waste. 3 Use of non-toxic substances which are safe for people and the natural environment. 4 Effective environmental communication. The fourth principle supports sustainable consumption, which is an essential tool for sustainable development. Unless consumers are informed and motivated to reduce the environmental impacts of packaging, the effectiveness of eco-design strategies will be limited. Consumers have two very important avenues through which they can influence packaging sustainability: their purchasing decisions at the supermarket and their waste management behaviour at home.

10.3.2 Eco-efficiency There is general agreement in the sustainability literature that the achievement of sustainable development will require a significant improvement in the efficiency with which we use resources. We need to ‘do more with less’. This is sometimes called ‘eco-efficiency’, a term that was coined by the World Business Council for Sustainable Development (WBCSD) in its 1992 publication, Changing Course (Schmidheiny, 1992). The WBCSD argues that eco-efficiency is achieved ‘by the delivery of competitively-priced goods and services that satisfy human needs and bring quality of life, while progressively reducing ecological impacts and resource intensity throughout the life-cycle to a level at least in line with the earth’s estimated carrying capacity’ (WBCSD, 2000, p. 9). There are widely different views about the scale of efficiency improvement that is needed for sustainability, ranging from a factor four (von Weizsacker et al., 1997) up to a factor ten (Schmidt-Bleek, 2000), or even a factor 120 (Trainer, 2002). The exact number is not terribly important. As one writer noted (Schmidt-Bleek, 2000, p. 2), ‘Factor 10 is not a mathematical answer to the complex environmental crisis, nor is it an economic model. It is a valid objective. It is a flexible goal that will be refined as experience with changing life styles grows.’ The critical issue is that we have exceeded the sustainable carrying capacity of the Earth, and we need to reduce our demands on its resources. A range of possible eco-design strategies to increase efficiency are provided in Box 10.1. They include ‘source reduction’ or lightweighting of packaging, as well as improvements in the efficiency of distribution. More efficient distribution, for example by redesigning a packaging system to


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Box 10.1

Eco-efficiency strategies

• Minimise the number of packaging layers through the optimal combination of primary, secondary and transport packaging. • Eliminate unnecessary packaging, for example replace the plastic on blister packs with a simple tie. • Reduce unnecessary void space. • Use cut-out windows on corrugated shippers to reduce the weight of the pack – an added benefit is product visibility which clearly shows the pack’s contents. • Reduce the thickness of packaging. • Increase the amount of product per package to reduce the packaging/product ratio. • Use bulk packaging for distribution of industrial products. • Concentrate the product. • Eliminate the use of glues in folded cartonboard by using tab closures. For more eco-efficiency strategies, refer to the Envirowise guidelines (Envirowise, 2002).

increase pallet or container utilisation, or by using bulk packaging (e.g. the intermediate bulk container (IBC) in Fig. 10.1), can reduce the quantity of packaging material used as well as energy requirements for transport. The Waste and Resources Action Programme in the United Kingdom has undertaken research which demonstrates the environmental and cost benefits that could be achieved by wine retailers if they imported wine in bulk and bottled it locally in lightweight bottles. For example, the study has estimated that if one of Australia’s top selling branded Chardonnay wines were to be imported into the United Kingdom in bulk and the bottle was lightweighted to 300 g, the benefits could include: • transport and material savings of £1 200 000, of which 63% is attributed to savings in transport; • potential glass savings of 1300 tonnes; • possible carbon emission savings of 1220 tonnes (WRAP, 2006, p. 5). 10.3.3 Design for recovery The second eco-design principle is design for recovery at end of life. As McDonough and Braungart (2002) argued in their influential book, Cradle to Cradle, we need to follow nature’s example by eliminating waste:



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Fig. 10.1 IBCs such as this can improve the efficiency of distribution and reduce packaging waste (photo courtesy of SCHÜTZ DSL, www.schutz. dsl.com).

If humans are truly going to prosper, we will have to learn to imitate nature’s highly effective cradle-to-cradle system of nutrient flow and metabolism, in which the very concept of waste does not exist. To eliminate the concept of waste means to design things – products, packaging, and systems – from the very beginning on the understanding that waste does not exist. It means that the valuable nutrients contained in the materials shape and determine the design: form follows evolution, not just function (pp. 103–104, italics in original).

McDonough and Braungart provide a useful framework for design which makes a distinction between biological and technical ‘nutrients’. Biological nutrients are organic materials that can be easily returned to the biological cycle; literally to be consumed by microorganisms in the soil and other animals. Technical nutrients are manufactured products that can be reprocessed continuously through industrial systems. All products should be designed to become nutrients for either biological or technical cycles, in such a way that minimises contamination between the two. For example, materials that are fed into a biological cycle should not be contaminated with substances such as heavy metals which could accumulate in natural systems and damage the health of people or ecosystems (McDonough and Braungart, 2002, Chapter 4).


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This has important implications for packaging designers. The cradle to cradle framework requires packaging to be designed for either technical or biological cycles. • Recycling programmes for materials such as metals, glass, plastics and paper represent technical cycles. Packaging designed for recycling should ensure that 100% of the package can be recovered in one recycling stream (e.g. polyethylene terephthalate (PET)) without contamination from other materials that would become a waste (e.g. paper labels). If the package requires more than one material, and these materials are incompatible in the same recycling process, then they should be designed for easy separation by the consumer into different recycling streams (e.g. the separation of plastic from cartonboard in a blister pack). • Composting programmes for food and garden wastes, organic byproducts from manufacturing and biodegradable packaging represent biological cycles. Packaging designed for composting should be made from 100% biodegradable materials, and should only use inks, pigments and other additives that do not contaminate the end-product. One option for companies is to ensure that all packaging is designed for either recycling or composting, for example Cadbury Schweppes recently announced that it is committed to using 100% recoverable or biodegradable packaging by 2010 (Cadbury Schweppes, 2006, p. 41). Both options are discussed in more detail below. Design for recycling – the benefits We now have a substantial body of evidence to confirm what most of us have always instinctively believed – that recycling benefits the environment. The results of several studies have been reviewed by Denison (1996), who concluded that systems based on recycled production plus recycling offer substantial system-wide or life cycle environmental advantages over systems based on virgin material plus either incineration or landfilling. The main reason for this is that the manufacture of recycled materials produces less solid waste, uses less energy and produces lower air emissions and waterborne wastes than the manufacture of an equivalent amount of virgin material. Recycled materials have already been processed once, so reprocessing is a cleaner and more energy-efficient process. An Australian study concluded that recycling materials rather than using virgin materials and sending waste to landfill, achieves an energy saving of up to 93% (see Table 10.1). A triple bottom line analysis valued the environmental benefits of recycling at around $A 42 per household per year, or $A 266 million in total (Nolan-ITU, 2001, p. vii). The environmental impacts of landfill and incineration, while not the major concern, are also important. Modern, ‘sanitary’ landfills are built to avoid or minimise surface and groundwater contamination through careful



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Table 10.1 Embodied energy savings per kilogramme in the production of recycled product, compared to virgin product Product

Embodied energy saving (%)

Newsprint Corrugated board – unbleached Steel slab Aluminium ingot HDPE PET PVC Glass

34 22 79 93 79 76 80 57

Adapted from Grant et al. (2001, p. xi). HDPE, high-density polyethylene.

siting and use of clay and plastic liners. Leachate is recovered and treated. Nevertheless, there are no guarantees that even with the best design and management, no hazardous materials will leach out of the slowly decomposing rubbish. Many landfills, such as Fresh Kills in New York City, were not lined. To make matters worse, Fresh Kills was built on a wetland, and is watered by the ebb and flow of tides (Rathje and Murphy, 1992, p. 119). Air emissions are another problem, in particular the emission of methane, a potent greenhouse gas. At many of the newer modern landfills, this gas is recovered to generate power. It has been estimated that 123 pounds (55.8 kg) of methane are produced for every ton of municipal solid waste in landfill, but gas recovery is still the exception rather than the rule. Of an estimated 4500 landfills operating in the United States in 1993, only 127 had gas-toenergy operations (Denison, 1996, p. 215). Design for recycling – strategies Recycling systems are becoming widespread, so an important waste reduction strategy is the specification of recyclable materials for the main components of the packaging. The term ‘recyclable’ can be contentious because some companies argue that a material is recyclable because it can theoretically or technically be recycled, regardless of whether or not there is a collection and recycling programme in place. Ideally, the package should be manufactured from a material that meets the International Organization for Standardization (ISO) definition of recyclable, i.e. ‘A characteristic of a product, packaging, or associated component that can be diverted from the waste stream through available processes and programmes and can be collected, processed and returned to use in the form of raw materials or products.’ (ISO, 1999b; italics added) The most recyclable materials at present are glass, aluminium, steel, PET, HDPE, paper and cardboard, although


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Table 10.2 Packaging recycling rates (%) Country

Glass Paper

Plastics

Metals

Wood Total

Australia

30

74

21

NA

51

Austria Belgium Denmark Finland France Germany Italy Luxembourg The Netherlands New Zealand

86 93 90 49 52 86 53 83 79 49

80 78 61 61 64 88 58 60 69 72

30 29 16 15 15 49 23 28 16 21

16 55 NA NA 19 41 60 NA 29 NA

66 70 57 49 45 74 51 57 57 52

Spain Sweden United Kingdom United States

36 88 34

60 70 59

20 20 19

Steel 44 Aluminium 63 67 86 44 50 53 80 54 79 80 Steel 31 Aluminium 61 39 68 39

NA NA 55

44 65 44

25

50

Soft drinks 34 Milk bottles 29

Steel 62 NA Aluminium 45

NA

Sources: European data are for 2002 from ASSURE (2005); Australian data are for 2003 from Martin Stewardship and Management Strategies (2005); US data are for 2005 from the US EPA (2006b); New Zealand figures are for 2005 from the Packaging Council of New Zealand (2006).

collection programmes vary between countries and regions. Recycling rates for some countries are provided in Table 10.2, although the methodology used for data collection may not always be consistent between countries; they should be used as a guide only. Increasing pressure on companies to design recyclable packaging is resulting in de-selection of non-recyclable materials, particularly plastics. In food packaging, there is a preference for PET, HDPE, cardboard, paper, moulded pulp, metals and glass (although glass is being replaced with plastics in many applications for cost reasons). Coated fibre-based packaging is expanding into new applications; for example, a coated paperboard butter tub was used by Carrefour, France for its home-brand butter in 2000 (Scandinavia Now, 2000). The ‘recyclability’ of coated papers and boards will depend on the willingness of local recyclers to accept them; a decision that is likely to be based on the economics of collection and the ability of their process to separate the paper fibres from the polymer coating successfully. Recyclable packaging also needs to be designed to minimise the number of different materials and to avoid materials that could contaminate the recycling stream (see Box 10.2). More information on glass and plastics recycling is also provided below.



Box 10.2

247

Design for recycling strategies

• Choose a single recyclable material for all components of the package, e.g. bottle, lid and label. • If more than one material is required, ensure that all materials can be recycled in the same process without contaminating the endproduct, e.g. small amounts of polypropylene (PP) or low-density polyethylene (LDPE) may be acceptable in small quantities in HDPE recycling processes. • If more than one material is required and they are not compatible in the same recycling process, design them to be easily separated by the consumer. • Talk to recyclers early in the product development process to find out whether or not all components can be recycled. You may need to redesign some elements in order to improve recyclability, e.g. caps, labels or glues.

Glass recycling Glass packaging is mainly recycled by collecting and crushing it for use in the manufacture of new packaging. The containers are separated into different colours (green, brown, clear) and contaminants such as metals, ceramics and plastics are removed. The glass is crushed into ‘cullet’ and fed into the manufacturing process. There are a variety of new technologies available to sort glass and remove contaminants automatically. Some of these technologies, such as the plant developed by German company Binder+Co AG, can handle glass in sizes as small as 10 mm. This technology enables more glass to be colour-sorted to meet specifications for container manufacture. The advantages of using recycled glass in packaging are significant. The use of cullet as a raw material reduces the need for mining of sand, soda ash, limestone and felspar. Cullet also melts at a lower temperature than virgin materials and therefore saves a significant amount of energy (see Table 10.1). For manufacturers, energy savings translate into lower costs. The energy advantages of cullet may diminish as the percentage increases, although this depends on the design of the specific manufacturing plant. Glass is 100% recyclable, and can be recycled an infinite number of times with no loss of quality in container manufacturing. This requires the glass to be colour-sorted and free of contaminants. The presence of iron oxide in cullet (for example from contact with rusty metal, or from plate glass with high levels of iron for ultraviolet light protection) gives glass a distinctive green hue. This can be used to advantage, as it is in some of the rustic


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glassware imported from Mexico. In most products, however, the green colour represents a loss of quality because the desired level of clarity cannot be achieved. Clear glass is the most recyclable because it can be used in clear, green and amber glass, whereas green glass has only limited markets, such as wine bottles. The percentage of recycled cullet that can be utilised in the manufacture of containers differs between manufacturers. In the early 1990s in Australia, ACI Glass Packaging (now owned by Owens Illinois) used an average of around 40% cullet in manufacturing but up to 70% was used to manufacture the most popular bottles (ACI Glass Packaging, 1992, p. 4). The new plant built by Amcor in 1992 uses 40% cullet (Amcor, 2005). Plastics recycling There are many different plastics used in packaging (see Table 10.3) but the most recyclable are PET and HDPE. Some countries or regions also recycle PVC, PP and polystyrene (PS). Plastics recycling can be divided into two categories: • ‘closed loop’ recycling, such as recycling PET bottles back into bottles; • ‘open loop’ recycling, such as recycling HDPE milk bottles into crates or pipes. Closed loop recycling of plastics in food-contact packaging is restricted because of concerns about contamination. In the United States, the Food and Drug Administration (FDA) governs the use of recycled resins in food, drug and cosmetic packaging. In 1992, the FDA released guidelines on the use of recycled plastic resins in food packaging which have recently been updated (FDA, 2006). The FDA will provide a ‘letter of no objection’ to the use of a particular resin in a particular application, if the recycler is able to demonstrate that there is negligible risk of contaminants migrating from the container into the contents. There are stringent tests required to demonstrate compliance with the guidelines. The FDA ‘no objection’ procedure is used outside the United States, for example by recyclers in Australia involved in bottle to bottle recycling. The use of recycled plastics in packaging is becoming more widespread. It is used to manufacture containers in one of two ways: • by co-extruding the container with a layer of recycled resin sandwiched between two layers of virgin resin; • by moulding mono-layer bottles with up to 100% recycled resin. The co-extrusion process meets the requirements for food packaging by providing a functional barrier between the recycled material and the contents of the bottle. One example is the multi-layer REPETE system developed by Continental PET Technologies in the United States for Coca-Cola drink bottles. Companies are increasingly using recycled PET in mono-layer food-contact packaging, for example Visy manufactures beverage and food


Eco-design of food packaging materials Table 10.3

249

Common thermoplastics used in packaging

Type of plastic

Raw material

Characteristics

Typical applications

HDPE

Ethylene from natural gas or crude oil

Hard to semiflexible, waxy surface, opaque, melts at 135 ºC

Shopping bags, freezer bags, milk bottles, crates, household chemical bottles

LDPE

Ethylene from natural gas or crude oil

Soft, flexible, waxy surface, translucent, melts at 80 ºC, scratches easily

Garbage bags, shrink film, squeeze bottles, mulch film

PP

Propylene gas (a byproduct of oil refining)

Hard but still flexible, waxy surface, melts at 145 ºC, translucent, withstands solvents Versatile material

Potato crisp bags, ice cream tubs, take-away food containers

PS

Benzene, a byproduct of coke manufacture, and ethylene from natural gas or crude oil

Clear, glassy, rigid, brittle, opaque, semi-tough, melts at 95 ºC Affected by fats and solvents

Disposable crockery and cutlery, coffee cups, yoghurt tubs

Foamed, lightweight, energy absorbing, heat insulating

Drink cups, meat trays, fruit and vegetable boxes, protective packaging

Expanded polystyrene (EPS)

PET

Ethylene glycol and terephthalic acid (from petroleum)

Clear, tough, solvent resistant

Soft drink bottles, milk bottles, jam and peanut butter jars, fresh preprepared meals

PVC – unplasticised

Chlorine (from rock salt) and ethylene from natural gas or crude oil

Hard, rigid, can be clear, can be solvent welded

Blister packs, cordial bottles

Flexible, clear, elastic, can be solvent welded

Blood bags

PVC – plasticised Adapted from Gertsakis et al. (1991, p. 5).


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containers in Australia from FDA-compliant recycled food-contact PET (Visy Beverage, 2007). Recycled HDPE is also being used for packaging, in mono-layer and co-extruded bottles. The first FDA-compliant recycled HDPE resin was produced by Union Carbide in the United States, for use in multi-layer packages for dry food (Scheirs, 1998, p. 194). Mono-layer recycled bottles are used for detergents, bleach and other household chemical bottles. Specific guidelines for the design of PET and HDPE packaging to improve recyclability have been developed by the Australian Council of Recyclers (2006a, 2006b). Design for composting – strategies An increasing number of companies are specifying degradable or biodegradable polymers for packaging. In late 2006, Sainsbury’s announced its intention to package 500 product lines in compostable plastic packaging, including organic fruit and vegetables (see Fig. 10.2), ready meals and organic sausages and poultry. According to their media release, one in three households in the United Kingdom now have their own compost bin. They also claimed that ‘Where Sainsbury’s cannot use compostable material, it uses recyclable’ (J Sainsbury plc, 2006b). There are many types of degradable polymers that are suitable for different applications and disposal environments, so definitions are once

Fig. 10.2 Sainsbury’s is introducing compostable plastic packaging for many of its organic products (photo courtesy of Sainsbury’s plc).



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again very important. An important distinction needs to be made between (ExcelPlas Centre for Design at RMIT and Nolan-ITU, 2003, p. 5): • biodegradable polymers which are capable of undergoing decomposition into carbon dioxide, methane, water, inorganic compounds or biomass, primarily through the action of microorganisms; and • oxo-biodegradable polymers which oxidise and break down in the environment under the influence of ultraviolet light and heat. Biodegradable polymers include starch-based polymers and biodegradable polyesters. Many of these are also ‘compostable’ which means that they will biodegrade under composting conditions. The ISO defines compostable as ‘A characteristic of a product, packaging or associated component that allows it to biodegrade, generating a relatively homogenous and stable humus-like substance’ which does not ‘negatively affect the overall value of the compost as a soil amendment’ or release ‘substances in concentrations harmful to the environment at any point during decomposition or subsequent use’ (Standards Australia and Standards New Zealand, 2000, p. 9). There are a number of strategies that can help to achieve this (see Box 10.3). Starch-based polymers are biodegradable and compostable. One of the most widely used of these is Mater-BiTM, which is manufactured from corn starch by Novomont in Italy (Novamont, n.d.). One of the barriers to the use of starch-based polymers has always been its price premium compared with alternatives, although this price gap appears to be closing. Plantic’s

Box 10.3

Design for composting strategies

• Select a compostable material that complies with a relevant international standard (e.g. ISO 14855, Aerobic biodegradation under controlled conditions). If the package is going to be reprocessed in a commercial composting facility, then it must be able to biodegrade in the required time frame. • Avoid potential contaminants, such as heavy metals (lead, cadmium, mercury, chromium) in pigments or inks. • Ensure that the design of the product supports degradation. Wall thickness, pigments and coatings (particularly over-printing and lacquers) can be critical factors in the rate of degradation. • Do not use a compostable polymer for products that are similar or identical to those that already have an existing recycling programme, because there is likely to be cross-contamination. This would happen for example, if a polylactic acid (PLA) water bottle looked similar to a PET water bottle and was not labelled appropriately, e.g. ‘Please compost. Do not recycle’.


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Fig. 10.3

Plantic® is manufactured from corn starch and dissolves on contact with water (photo courtesy of Plantic).

starch-based resins in Australia are only marginally more expensive than PS. Plantic® is currently used for rigid trays (biscuits and chocolates), but research and development is underway to produce film (Plantic, n.d.). The material is compostable but it also dissolves in water (Fig. 10.3). NatureWorks® PLA is one of the most widely used of the biodegradable polyesters. It is manufactured from corn and can be used in a wide range of applications including film, trays and bottles. A recent application is beverage bottles, for example Biota Brands (US) for their spring water (Biota, n.d.) and Naturally Iowa (2007) for its natural and organic milk. Wal-Mart has also started to use PLA for fresh produce (ElAmin, 2005). Oxo-biodegradable polymers (often called ‘degradable polymers’) combine a conventional polymer such as polyethylene with a controlled degradation master-batch additive. Brands currently on the market include TDPA® manufactured by EPI (2007), and d2wTM manufactured by Symphony Environmental Technologies (n.d.). These products are often promoted as ‘degradable in landfill’ but the benefit of enhanced degradation



253

in most landfills is questionable, and the resources consumed in manufacturing are lost if the product is simply thrown away after use. They can also contaminate existing recovery systems, for example if degradable shopping bags are added to a recycling system for conventional bags. Degradable polymers may be beneficial if a product is likely to be littered and if enhanced degradation is likely to reduce the aesthetic impact or health risks to wildlife. 10.3.4 Non-toxic substances A toxic substance is ‘one that, given sufficient exposure, can cause serious health effects in humans such as poisoning, respiratory problems or cancer’ (Lewis et al., 2001, p. 76). Many companies have policies that restrict the use of hazardous or toxic substances in product development. IBM’s global packaging guidelines for example, ban the use of PVC, ozone-depleting chemicals, heavy metals, polybrominated biphenyls and polybrominated biphenyl oxides. Recent achievements attributed to the guidelines include the elimination of PVC and chemical impregnation of wooden packaging, which makes the timber unfit for recycling or energy recovery (IBM, n.d.). Heavy metals have traditionally been used in packaging inks and as pigments in plastics. The European Packaging and Packaging Waste Directive (94/62/EC) required member states to introduce regulations that would ensure that the concentration of four heavy metals (lead, cadmium, mercury and hexavalent chromium) in packaging or packaging components did not exceed a concentration of 100 ppm by 2001. A recent study (Pira International Ltd and ECOLAS N.V., 2005) evaluated the presence of heavy metals in packaging and concluded that some products still have concentrations higher than this, including glass containers, plastic crates, packaging nets, plastic bags, caps, shiny plastic/aluminium foils, steel cans and industrial steel drums (see Table 10.4). The study provides packaging designers with a guide to potential sources of heavy metals in packaging, for example in specific pigments used in plastic packaging. The European Commission has granted a derogation for undecorated glass products and for plastic crates and pallets in relation to the heavy metal requirements of Directive 94/62/EC, which allows the 100 ppm limit to be exceeded after 2001 but only if compliance problems are caused by the addition of recycled materials rather than the intentional addition of heavy metals during the manufacturing process. Heavy metals in plastic crates and pallets are assumed to be there because of the use of recycled materials, since the use of pigments with the restricted heavy metals has largely been phased out in Europe (Pira International Ltd and ECOLAS N.V., 2005). As already mentioned, Greenpeace International (n.d.) has been campaigning for many years to have the use of PVC phased out due to its perceived toxicity. They have expressed concerns about the potential release


254


Table 10.4 Heavy metals in packaging with concentrations over 100 ppm Product

Heavy metal

Source

Comment

Undecorated glass

Lead

Contamination during the recycling process, e.g. from lead capsules on old bottles, crystal glass, mirrors, ceramics, etc.

Decorated glass

Lead and cadmium

Plastic crates

Lead and chromium

Coloured nets

Lead and chromium

Plastic caps

Cadmium

Plastic bags

Lead and chromium

Plastic nonfood bottles Shiny foils with aluminium Steel cans

Cadmium, chromium and lead Chromium and lead

Enamel used in coloured decoration; lead is a basic constituent in the enamel while cadmium is used in red and yellow pigments Lead from the pigments linked to the colours red, orange and green, and chromium from pigments linked to the colours red and orange Pigments linked to the colours yellow and orange Pigments linked to the colours yellow, orange, red and green Pigments linked to the colours gold, yellow, orange, red and green Pigments linked to the colours yellow, orange and green Pigments linked to gold and silver coatings

The proposed solution is better education of householders to help them to separate contaminants at source

Lead

Solder

Steel drums

Lead and chromium

Pigments in the paint on the drums (lead and zinc chromate pigments)

Heavy metals are linked to recycled content as they have not been used in Europe since 1994 Heavy metal pigments still appear to be used

Some hexavalent chromium Some hexavalent chromium Some hexavalent chromium Largely discontinued but some lead solder still used Use of these pigments has largely been discontinued

Based on Pira International and ECOLAS N.V. (2005, pp. 163–180).



Box 10.4

255

Strategies to avoid toxic substances

• Avoid the use of PVC. • Avoid heavy metals (lead, mercury, cadmium, chromium) in inks, pigments and additives. • Avoid the use of methyl bromine, an ozone-depleting substance, as a fumigant for wooden packaging. • Avoid the chemical impregnation of wooden packaging, e.g. with preservative copper chromated arsenate, which inhibits recycling and energy recovery. • Avoid chlorine bleaching of paper. Less damaging alternatives include: – elemental chlorine-free bleaching which uses chlorine dioxide rather than chlorine gas; – oxygen pre-bleaching; – hydrogen peroxide pre-bleaching.

of dioxins during the manufacture and incineration of PVC, the viability of recycling and the release of unstable additives, such as plasticisers, during use. Their ‘pyramid’ of preferred plastics puts PVC last, as the leastpreferred polymer on environmental grounds. There have been numerous studies on the environmental effects of PVC (e.g. CEC, 2000; Thornton, 2000; Greenpeace International, 2002; PE Europe GMBH and Instituttet for Produktudvikling and Randa Group, 2004) but there is still no scientific consensus on how damaging PVC is relative to other materials on the market. One study (PE Europe GMBH and Instituttet for Produktudvikling and Randa Group, 2004, p. 13) concluded that the environmental impacts of PVC are comparable with those of PET. Use of PVC in packaging is already declining, but the application of the ‘precautionary principle’ would suggest that use of PVC should be minimised or discontinued. This appears to be the position already taken by IBM (discussed above) and some brand owners in the food industry. For example, Coca-Cola Amatil discontinued the use of PVC for cordial bottles in late 2004 and announced that in doing so it had ‘completely exited PVC packaging’ (Coca-Cola Amatil, 2005, p. 2). A list of possible strategies for the avoidance of toxic substances is provided in Box 10.4. 10.3.5 Communication The fourth eco-design strategy is effective environmental communication, which is very important for packaging designers but will only be


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covered briefly here. Other sources of information are provided below. Companies can capitalise on the environmental benefits of their products by marketing these to consumers. Some consumers are actively looking for environmentally improved products, while others may be influenced by environmental claims on a product if it is comparable with alternative products in terms of price, visual appeal and functionality. There are a number of issues that need to be taken into account by designers, in particular the need to ensure that claims do not contravene trade practices legislation. In most cases this prohibits any form of misleading advertising, including inaccurate or misleading environmental claims. Useful guidelines are provided in ISO 14021:1999, Environmental labels and declarations – Self-declared environmental claims (Type II environmental labelling). While adoption of the standard by companies is voluntary, it is an internationally recognised standard for environmental communication. The following guidelines for effective communication are taken from ISO 14021:1999 and from a government publication in the United Kingdom (DEFRA, 2003). An environmental claim needs to be relevant, accurate, verifiable, specific and unambiguous. In order to be relevant, the claim should apply to the particular product and to the particular market in which it will be sold. For example, the claim that a product is ‘chlorine free’ is only relevant if the product used to contain chlorine, for example a paper that used to be bleached using chlorine but now uses a less environmentally damaging process. The claim that a product or package is ‘recyclable’ is only relevant if there is a widely available collection system in the country where it will be consumed. Accuracy is an important requirement because inaccurate claims can result in legal action being taken against a company under trade practices legislation. Even if a claim is literally true, it should not be used if it is likely to be misleading, for example a claim that an aerosol is ‘chlorofluorocarbon free’ (CFC) might mislead consumers into thinking that this is a recent initiative or that other companies still use CFCs, whereas CFCs have been banned under the Montreal Protocol for many years. Specific claims need to be verifiable, for example if a claim is made that ‘research has shown that plastic bags use 50% less energy to make than paper bags’, then research needs to be available to back this up. Claims should also be specific, which means avoiding meaningless and misleading claims such as ‘environmentally friendly’, ‘green’ or ‘safe for the environment’. A more useful claim would relate specifically to the environmental improvement made, for example ‘made with 25% recycled post-consumer fibre’ or ‘printed with vegetable-based inks on non-chlorinebleached paper’. There are many different logos that can be used on packaging to support recycling or to discourage littering. Two of the most widely used are shown below in Figs 10.4 and 10.5.



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Fig. 10.4 The Mobius loop is used to indicate recyclability or recycled content (when a percentage, e.g. 50%, is included in the middle of the symbol). For more detail see ISO 14021:1999 (ISO, 1999).

Fig. 10.5 The internationally recognised ‘Tidyman’ symbol is used to encourage responsible disposal of packaging, often accompanied by the message ‘dispose of waste thoughtfully’.

Box 10.5

Environmental communication

Environmental communication strategies include the following: • develop an environmental marketing campaign to promote the environmental benefits of your packaging; • ensure that environmental claims are relevant, accurate, verifiable and specific; • use appropriate symbols to indicate recycling and/or recycled content; • use an appropriate symbol to encourage responsible disposal; • identify plastics packaging with the Plastics Identification Code (PACIA, 2003).


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10.4


Future trends

There is no doubt that eco-design will become more commonplace in the packaging industry, driven by increasingly stringent regulations, the demands of large customers with progressive CSR policies and the expectations of more environmentally aware consumers. Other important trends that will influence eco-design are likely to include: • The rising cost of landfill in countries such as the United States, Australia and New Zealand, as new landfills become more difficult and expensive to site. This will make recycling, energy recovery and composting technologies more economically viable, which in turn will open up new opportunities for the recovery of packaging. • If ‘peak oil’ predictions are correct, i.e. that we are close to the maximum rate of oil production, then the cost of oil will continue to rise and this will be reflected in higher polymer prices. Biodegradable polymers made from renewable resources such as corn, while currently too expensive for many packaging applications, will become more competitive. The same will apply to recycled polymers.

10.5

Conclusions

The environmental impacts of packaging are becoming unacceptable in a more environmentally conscious world. While the biggest issue has always been the amount of waste generated by packaging, the focus is increasing on its ‘life cycle impacts’ including raw material extraction, manufacturing, use and disposal. This requires a more systematic approach to design which takes into account environmental impacts through the life cycle of packaging systems, and seeks to minimise these through better design. Ecodesign is not rocket science. It is a straightforward process that should become an integral part of the design process rather than an add-on for niche green products. The four principles presented here – eco-efficiency, design for recovery, the use of non-toxic substances and effective environmental communication – provide a framework for packaging design. The most appropriate strategies will vary between companies and products, and will depend on a variety of factors including the manufacturing, functional, cost and market requirements and the availability of recovery systems for different materials. Even small environmental improvements can be significant when multiplied by the number of products sold, so the key challenge is just to get started. Start with the ‘low hanging fruit’, such as lightweighting products to help conserve resources and reduce waste while also saving the company money. Over time, start to review the environmental impacts of products in a more holistic way, and integrate eco-design into the new product development process.



10.6

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General eco-design resources: • Fuad-Luke, A. 2002. The Eco-design Handbook. London: Thames & Hudson. • Lewis, H., Gertsakis, J., Grant, T., Morelli, N. and Sweatman, A. 2001. Design + Environment: A Global Guide to Designing Greener Goods. Sheffield, UK: Greenleaf Publishing. Eco-design of packaging: • Denison, R. and Ren, G. Y. 2001. Thinking Green: Packaging Prototypes 3. Hove, East Sussex: RotoVision. • Envirowise. 2002. Packaging Design for the Environment: Reducing Costs and Quantities (Report GG360). Didcot, Oxfordshire: Envirowise, Harwel International Business Centre, . • Packaging Council of New Zealand. 2002. Code of Practice for the Packaging of Consumer Goods. Auckland: Packaging Council of New Zealand, . Environmental communication: • DEFRA. 2003. Green Claims – Practical Guidance. London: Department for Environment, Food and Rural Affairs (DEFRA), . • International Organization for Standardization (ISO). ISO 14021:1999, Environmental Labels and Declarations – Self-declared Environmental Claims (Type II environmental labelling). Geneva: 150. Websites: • Sustainable Packaging Alliance (Australia), www.sustainablepack.org. • Sustainable Packaging Coalition (United States), www. sustainablepackaging.org.

10.7

References

aci glass packaging 1992, Glass Packaging and the Environment, ACI Glass Packaging, Melbourne. acor 2006a, Recycling Guide for Fillers in PET Containers, Australian Council of Recyclers, Sydney. acor 2006b, Recycling Guide for Fillers Marketing in HDPE, Australian Council of Recyclers, Sydney. amcor 2005, Sustainability Report: Working Towards a Brighter Future, Melbourne. anzecc 1999, The National Packaging Covenant, Australian and New Zealand Environment and Conservation Council, viewed 28 January 2003, <www.packcoun. com.au/NPC.htm>.


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assure 2005, Packaging and Packaging Waste Statistics 2002, viewed 9 July 2005, . biota n.d., The Bottle, Biota, Telluride, Colorado, viewed 1 October 2007, . boomerang alliance n.d., The Campaign to Introduce Refunds on Bottles and Cans in WA, Boomerang Alliance, viewed 25 September 2007, . cadbury schweppes 2006, Corporate and Social Responsibility Report 2006, Cadbury Schweppes, London. cec 2000, Green Paper: Environmental Issues of PVC, Commission of the European Communities (CEC), Brussels. coca-cola amatil 2005, Final Report on Coca-Cola Amatil 2004-05 National Packaging Covenant Action Plan, Coca-Cola Amatil, Sydney. coleman-lochner, l. 2006, Wal-Mart to save $4.5 bn by cutting packaging, The Australian Financial Review, p. 11. cri 2006, The Container Recycling Institute (CRI), Washington DC, viewed 25 September 2007, . defra 2003, Green Claims – Practical Guidance, Department for Environment, Food and Rural Affairs (DEFRA), London, viewed 1 October 2007, . denison, r. 1996, Environmental life-cycle comparisons of recycling, landfilling and incineration. Annual Review of Energy and Environment, 21, 191–237. denison, r. and ren, g. y. 2001, Thinking Green: Packaging Prototypes 3, RotoVision, Hove, East Sussex. elamin, a. 2005, Wal-Mart Signals Move to Natural Packaging, PackWire.com, viewed 9 January 2007, . envirowise 2002, Packaging Design for the Environment: Reducing Costs and Quantities (Report GG360), Envirowise, Harwel International Business Centre, Didcot, Oxfordshire, UK. epi 2007, TDPA Additives, EPI Environmental Products, Vancouver, Canada, viewed 1 October 2007, . evans, p. 1997, The Complete Guide to Eco-Friendly Design, North Light Books, Cincinatti, Ohio. excelplas, Centre for Design at RMIT and Nolan-ITU 2003, The Impacts of Degradable Plastic Bags in Australia, Department of Environment and Heritage, Canberra, viewed 2 January 2007, . fda 2006, Use of Recycled Plastics in Food Packaging: Chemistry Considerations, US Department of Health and Human Services, Food and Drug Administration (FDA), viewed 9 January 2007, . fuad-luke, a. 2002, The Eco-design Handbook, Thames & Hudson, London. gertsakis, j., harris, c., hosken, m. and kosior, e. 1991, Design for Plastics Recycling, Centre for Design at RMIT, Melbourne. grant, t., james, k., lundie, s. and sonneveld, k. 2001, Stage 2 Report for Life Cycle Assessment for Paper and Packaging Waste Management Scenarios for Victoria, EcoRecycle Victoria, Melbourne. greenpeace international n.d., PVC Alternative Database, Greenpeace International, viewed 10 January 2007, . greenpeace international 2002, Exposing the Dirty Path of PVC, Greenpeace International, viewed 2 January 2007, .



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ibm n.d., Environmental Attributes of Products: Product Packaging, IBM, Armonk, New York, viewed 25 September 2007, . imhoff, d. 2004, Paper or Plastic: Searching for Solutions to an Overpackaged World, Sierra Club Books, San Francisco, California. iso 1999a, ISO 14021:1999, Environmental Labels and Declarations – Self-declared Environmental Claims (Type II Environmental Labelling), International Organization for Standardization (ISO), Geneva. iso 1999b, ISO 14024:1999, Environmental Labels and Declarations – Type I Environmental Labelling – Principles and Procedures, International Organization for Standardization (ISO), Geneva. j sainsbury plc 2006a, Corporate Responsibility Report 2006, J Sainsbury plc, London. j sainsbury plc 2006b, Sainsbury’s Cuts Plastic from Packaging in Environmental Revolution, viewed 8 January 2006, . lewis, h., gertsakis, j., grant, t., morelli, n. and sweatman, a. 2001, Design + Environment: A Global Guide to Designing Greener Goods, Greenleaf Publishing, Sheffield, UK. mackenzie, d. 1997, Green Design: Design for the Environment, second edition, Laurence King, London. martin stewardship & management strategies 2005, National Packaging Covenant Gap Analysis, Report to the National Packaging Covenant Industry Association, Martin Stewardship & Management Strategies Pty Ltd, Turramurra, New South Wales. mcdonough, b. and braungart, m. 2002, Cradle to Cradle: Remaking the Way we Make Things, North Point Press, New York. millennium ecosystem assessment, 2005, Ecosystems and Well-being: Synthesis, Island Press, Washington DC, viewed 1 October 2007, . ministry for the environment 2004, New Zealand Packaging Accord, Ministry for the Environment, Wellington, New Zealand. naturally iowa 2007, Sustainable Packaging, Naturally Iowa, Clarinda, Iowa, viewed 1 October 2007, . nolan-itu, s. e. a. e. 2001, Independent Assessment of Kerbside Recycling in Australia, Revised Final Report – Volume 1, National Packaging Covenant Council, Melbourne. novamont n.d., Novamont, Navara, Italy, viewed 25 September 2007, . npcc 2004, The National Packaging Covenant: A Commitment to the Sustainable Manufacture, Use and Recovery of Packaging (Draft), National Packaging Covenant Council (NPCC), Canberra. oecd, 1998, Extended and Shared Producer Responsibility, OECD, Paris. oced, 2001, Extended Producer Responsibility: A Guidance Manual for Governments, OECD, Paris. pacia 2003, Plastics Identification Code, Plastics and Chemicals Industries Association, Melbourne. packaging council of new zealand 2006, Mass Balance – Consumption/Collection, Auckland, viewed 12 January 2007, . pe europe gmbh, i. f. k. u. k. and instituttet for produktudvikling and randa group 2004, Life Cycle Assessment of PVC and of Principal Competing Materials, Report for the European Commission.


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pegram walters associates 1993, Consumer Attitudes to Packaging: Summary Report of Findings, Report prepared for INCPEN, London. pegram walters associates 1997, Project Packaging II: Report of Findings, Report prepared for INCPEN, London. pira international ltd and ecolas n.v. 2005, Study on the Implementation of Directive 94/62/EC on Packaging and Packaging Waste and Options to Strengthen Prevention and Re-use of Packaging, Final Report, Surrey, UK. plantic n.d., Plantic, Melbourne, viewed 25 September 2007, . rathje, w. and murphy, c. 1992, Rubbish! Harper Collins Publishers, New York. scandinavia now 2000, Stora Enso’s Ensocup and Ensocoat Paperboard Butter Tub – A New Packaging Concept for Europe’s Biggest Hypermarket Chain, viewed 9 January 2007, . scheirs, j. 1998, Polymer Recycling, John Wiley & Sons, New York. schmidheiny, s. 1992, Changing Course: A Global Business Perspective on Development and the Environment, MIT Press, Cambridge, Massachusetts. schmidt-bleek, b. 2000, Factor 10 Manifesto, downloadable paper, viewed 8 January 2006, . standards australia and standards new zealand 2000, AS/NZS ISO 14021:2000, Environmental Labels and Declarations – Self-declared Environmental Claims (Type II Environmental Labelling), Sydney. symphony environmental technologies n.d., Degradable Plastics, Symphony Environmental Technologies, Borehamwood, UK, viewed 1 October 2007, . the women’s institute 2006, Stop Excess Packaging Campaign, London, viewed 12 January 2007, . thornton, j. 2000, Pandora’s Poison: Chlorine, Health and a New Environmental Strategy, MIT Press, London. trainer, t. 2002, Recognising the limits to growth, Journal of Australian Political Economy, December, 165–178. us epa 2006a, What is Product Stewardship, United States Environment Protection Agency, Washington, DC, viewed 25 March 2007, . us epa 2006b, Municipal Solid Waste: Basic Facts, United States Environmental Protection Agency, Washington, DC, viewed 9 January 2007, . visy beverage 2007, PET Bottles and Preforms, Melbourne, viewed 9 January 2007, . von weizsacker, e., lovins, a. and lovins, h. 1997, Factor 4: Doubling Wealth – Halving Resource Use, Allen & Unwin, Sydney. wbcsd 2000, Eco-efficiency: Creating More Value with Less Impact, World Business Council for Sustainable Development (WBCSD), Geneva. wrap 2006, The WRAP Wine Initiative, downloadable brochure, Waste and Resources Action Programme (WRAP), Banbury, Oxon, viewed 8 January 2006, .


11 Additives for environmentally compatible active food packaging S. Irmak and O. Erbatur, Cukurova University, Turkey

11.1

Introduction

Consumers are demanding higher quality foods that are free from synthetic preservatives, low in salt, microbiologically safe and minimally processed. In addition, producers prefer to supply food to the market with an extended shelf-life. Environmental concerns necessitate the development of environmentally friendly packaging materials with biodegradable properties, preferably with components from natural sources rather than from petrochemical materials. After their useful life, the waste packaging materials should have the ability to be mineralized through biodegradation in a reasonable time period without causing environmental waste problems. Conventional food packaging focuses on the appearance, size and integrity of the package in which food safety has been maintained by incorporating synthetic preservative agents into the food. Conversely, active packaging is an integral part of food safety providing not only an inert barrier to outside influences but also some desirable functions such as high quality and microbiological safety, longer product shelf-life, etc. (Rooney, 1995). The preservatives, preferably from natural sources, can be incorporated into the packaging material, or bound on the surface either permanently or temporarily where, in the latter case, the antioxidant and/or antimicrobial agents are slowly released onto the packed food during the shelf-life. The oxygen permeability of the packaging materials can alter the headspace oxygen concentration. A reduction in oxygen concentration in a package can inhibit oxidative reactions as well as the growth of certain microorganisms. Synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are frequently used to retard lipid


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oxidation in food products. However, the toxicological aspects of using synthetic antioxidants and antimicrobials in foods on a long-term basis are being questioned, resulting in the formation of negative consumer perception which will ultimately cause their use as food additives to be restricted. Therefore, extensive research is being conducted to find some natural antioxidants and antimicrobials for use in functional packaging. The coatings and adhesive materials must meet certain functional requirements, such as moisture barrier properties, solute or gas barrier properties, water/lipid solubility, colour and appearance, mechanical and rheological characteristics, non-toxicity, etc. Food packaging films or coatings can be prepared from proteins (wheat gluten, collagen, corn zein, soy, casein, whey protein), from polysaccharides (cellulose, chitosan, alginate, starch, pectin, dextrin) and lipids (waxes, acylglycerols, fatty acids), most of which are edible and made from renewable natural resources (Cagri et al., 2004). A thin layer of biopolymer formed on a product surface as a coating, on or between food components, allows only low levels of preservative to come into contact with the food. In recent years, environmentally compatible active packaging, such as antimicrobial packaging, has attracted much attention from the food industry since it can effectively control the microbial contamination of various solid and semi-solid, preservative-free food products by inhibiting the growth of microorganisms on the surface of the food which normally comes into direct contact with the packaging material (Coma et al., 2001; Kim e t al., 2002; Miltz et al., 2004). Various antimicrobial packaging films have been developed to minimize the growth of spoilage and pathogenic microorganisms. A wide range of antimicrobial agents can be incorporated into these films to enhance the safety and shelf-life of the food products. The direct addition of antimicrobials (such as organic acids or their respective acid anhydrides, spice extracts, chelating agents, metals, enzymes, bacteriocins, etc.) into food material could result in loss of activity. This might be attributed to them being leached into the food matrix and/or cross-reaction with other food components such as lipids or proteins (Han and Floros, 1997; Davies et al., 1999; Hoffman et al., 2001). This could be solved efficiently by using packaging films containing antimicrobial agents that can release the active components in a controlled manner, and these components will then migrate into the food matrix. This type of antimicrobial action is advantageous not only for initially inhibiting undesirable microorganisms, but also for creating a residual activity over time, during storage and transport (Cutter, 2002). Alternatively, antimicrobial agents can also be covalently immobilized onto the surface of the polymer sheet and act directly from the film when it is brought in contact with the food material. In all cases, the aim of these systems is to extend the shelf-life of the packaged foodstuff, inhibiting microbial growth and preserving the foodstuff’s sensory properties while minimizing or completely eliminating the risks arising from the usage of synthetic preservatives.


Additives for environmentally compatible active food packaging

11.2

265

Antimicrobial/antioxidant agents incorporated into polymers

The use of packaging film based on antimicrobial-antioxidant-containing polymer could prove to be more efficient by maintaining controlled concentrations of the active components on the food surface with a low migration into the food matrix. There should be a controlled release of the active components from the film to the food product to provide a continuous antimicrobial/antioxidant effect. Here we will discuss the most important additives and coatings being incorporated into food packaging materials.

11.3

Chemical preservatives

A chemical preservative can be incorporated into a packaging material to add antimicrobial activity to it. Preservative-releasing films provide antimicrobial activity by releasing the preservative at a controlled rate. Common antimicrobial agents used to preserve food include organic acids and salts (sorbic, lactic, acetic, benzoic acids; potassium sorbate, sodium diacetate, etc.). Organic acids used in food preservation are mainly weak acids (pK (–log of dissociation constant) range supplying pH 3 to 5) which exhibit certain levels of buffer activity (Doores, 1993). Acetic acid, one of the commonly used food preservatives, has been shown to be a more efficient antibacterial agent than other organic acids under the same pH conditions (Cherrington et al., 1991; Abdul-Raouf et al., 1993). The World Health Organization has set the acceptable daily intake limits for sorbic and paminobenzoic acid at 25 and 30 ppm, respectively (Kabara and Eklund, 1991). When used in combination with lactic and/or acetic acid, sorbic acid can inhibit the growth of Listeria monocytogenes, Salmonella typhimurium and Escherichia coli O157 : H7 in many low-acid foods including cold-pack cheese (Ryser and Marth, 1988), bologna (Wederquist et al., 1994), beaker sausage (Hu and Shelef, 1996) and apple cider (Zhao et al., 1993; Uljas and Ingham, 1999). p-Aminobenzoic acid reportedly exhibited greater inhibitory activity against L. monocytogenes, E. coli and Salmonella enteritidis than formic, propionic, acetic, lactic or citric acids (Richards et al., 1995). The antimicrobial activity of organic acids can be enhanced by combining them with other food preservatives or heat (Greer and Dilts, 1992). Siragusa and Dickson (1993) demonstrated that calcium alginate coatings containing organic acids were marginally effective on beef muscle tissue, reducing levels of L. monocytogenes, S. typhimurium and E. coli O157 : H7. Salts of certain organic acids have also been used to control microbial growth, improve sensory attributes and extend the shelf-life of various food products. For instance, sodium salts of low molecular weight organic acids – such as acetic, lactic and citric acids – are widely used in food preservation. Organic salts such as sodium acetate, lactate and citrate were shown to


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possess antibacterial abilities against various food-borne pathogens and to have an inhibitory effect on the growth of food spoilage bacteria. Additionally, all these salts are widely available, inexpensive and considered as Generally Recognized As Safe (GRAS) substances (Salam, 2007). Potassium salts (e.g. potassium sorbate) are well-known food preservatives that have GRAS status. They are effective inhibitors of most moulds and yeasts, and some bacteria. Potassium sorbate and sodium diacetate have been used for the preservation of meat products and refrigerated packaged beef (Zamora and Zaritzky, 1987; Schlyter et al., 1993).

11.4

Peptides and proteins

Certain kinds of peptides and proteins delay lipid oxidation in food systems. They can be easily obtained as natural products from waste materials of agricultural origin. Some of the efficient peptides that have been known to delay lipid oxidation are hydrolysates of whey, soy, egg yolk, pork and fish. Some kinds of milk proteins (such as casein, bovine serum albumin and lactoferrin) also have the potential to reduce lipid oxidation in foods (Huang et al., 1999; Diaz and Decker, 2004; Viljanen et al., 2004). Bacteriocins are antibacterial proteins produced by certain bacteria that inhibit the growth of other bacteria. Many lactic acid bacteria (LAB) are known to produce a wide diversity of bacteriocins. Bacteriocins produced by LAB are peptides degradable by intestinal proteases, have specific antimicrobial activities and have potential applications in food protection. Nisin is a natural antimicrobial peptide with 34 amino acid residues produced by Lactococcus lactis subsp. lactis that effectively inhibits a broad spectrum of Gram-positive pathogenic bacteria, especially the strains of L. monocytogenes, both in laboratory media or in model food systems (Stevens et al., 1991; Hampikyan and Ugur, 2007). Nisin has widely been used in the food industry as a safe and natural biological food preservative. It has received GRAS status from the United States Food and Drug Administration and so far it is the only bacteriocin permitted for use in foods in many countries. In the United States, it is approved to be used in some processed cheese spreads to prevent the growth of clostridial spores and toxins. Nisin is commercially available and has successfully been used as a biopreservative in dairy and meat products (Reunanen and Saris, 2004; Samelis et al., 2005). The important factors that affect the antimicrobial efficacy of nisin are the pH, salt and fat content of food, the presence of curing agents and the particle size of the food material (Jung et al., 1992). A decrease in the antimicrobial capacity of nisin is caused by binding it to food components, which prevents it from inhibiting micro-organisms and reduces its solubility and dispersion throughout the foodstuff. Nisin becomes relatively insoluble because of its hydrophobic nature and it therefore loses efficacy at pH > 5 (Scannell et al., 1997; Pol and Smid, 1999).



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Gram-negative bacteria are resistant to nisin. It was reported that nisin together with certain chelators exhibited a better antimicrobial activity on Gram-negative pathogens in culture media (Cutter and Siragusa, 1995a). However, in real food systems, this combination was found to be less effective than in culture media (Cutter and Siragusa, 1995b). Pediocin is another well-researched bacteriocin that may well be the second LAB bacteriocin to be widely used in the food industry (Chikindas et al., 1993; Venema et al., 1995). Pediocin PA-1 is produced by several Pediococcus acidilactici strains of meat origin and is appealing as a food biopreservative because of its strong activity against L. monocytogenes (Muriana, 1996), a major biological hazard in the dairy industry. Pediocin PA-1 is a 44-amino acid, heatstable cationic peptide with a basic pI. Values ranging from +7 to +3 have been reported for the net charge determined on pediocin at pH 6 (Chen et al., 1997a, 1997b) and from 8.6 to 10 for the pI (Henderson et al., 1992; Lozano et al., 1992). The theoretical molecular weight of the PA-1 calculated from its amino acid sequence would be around 4624 or 4628 Da in the presence or absence of two disulphide bonds, respectively (Henderson et al., 1992; Fimland et al., 1996). Nisin A (also nisin Z) and pediocin PA-1/ AcH-producing strains were found to be effective against a wide range of Gram-positive spoilage pathogenic bacteria (Ray et al., 2001). The incorporation of such antimicrobial compounds into edible films or coatings provides a novel means for enhancing the safety and shelf-life of certain ready-to-eat foods. Padget et al. (1998) used nisin and pediocin in soy protein and corn zein films to inhibit Lactobacillus plantarum and E. coli on laboratory media. According to Ming et al. (1997), pediocin-coated cellulosic casings inhibited L. monocytogenes on ham, turkey breast meat and beef. Lactoferrin is an 80-kDa iron-binding glycoprotein, consisting of a single polypeptide chain with 689 amino acids and a pI of 9.4 (Pan et al., 2007). It is an antimicrobial peptide derived from bovine lactoferrin, present in the milk of mammals, and has an efficacy similar to many antibiotics (Wakabayashi et al., 1992). The highly positively charged peptides, which are derivatives of the N-terminus sequences of lactoferrin molecules (e.g. bovine and human lactoferricin), have a high affinity to the bacterial membrane, and are known to play an important role in its antimicrobial activity (Bellamy et al., 1992). Lactoferrin inhibits the growth of micro-organisms by binding to iron, which is an essential component for their growth (Tomita et al., 2002). The antioxidative and antimicrobial effects of a lactoferrin additive on lipid oxidation (Huang et al., 1999) and the antimicrobial properties in food systems (Naidu, 2002) have been reported. Meat samples with added lactoferrin have extended shelf-life and increased nutritional value (iron) (Chiu and Kuo, 2007). Lactoferrin is permitted at levels of 65.2 mg/kg in beef in the United States (Naidu, 2002). Lysozyme is an antimicrobial peptide and one of the most frequently used antimicrobial enzymes incorporated into packaging materials


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(Appendini and Hotchkiss, 1997; Park et al., 2004). It is of interest for use in food systems since it is a naturally occurring enzyme. This enzyme shows antimicrobial activity mainly on Gram-positive bacteria by splitting the bonds between N-acetylmuramic acid and N-acetylglucosamine of the peptidoglycan in their cell walls. Lysozyme does not show antibacterial activity against Gram-negative bacteria since Gram-negative bacterial cell walls are protected by an outer membrane; however, the addition of the chelating agent EDTA (ethylene diaminetetraacetic acid) increases the antimicrobial activity of lysozyme significantly (Branen and Davidson, 2004). Lysozyme is highly suitable for use in heat-processed films such as those prepared from corn zein and incorporation of this enzyme into zein films has been reported (Padgett et al., 1998; Gucbilmez, 2007). Lysozyme–chitosan composite films have also been developed for enhancing the antimicrobial properties of chitosan films, and their antimicrobial activity against E. coli and Streptococcus faecalis has been tested (Park et al., 2004).

11.5

Polysaccharides

Polysaccharides are most often used for edible films as support materials for antimicrobial, nutritional and antioxidant activities because their filmforming properties are derived from cellulose, starch, alginate and their mixtures. Chitosan is the polysaccharide most frequently used as a base material for forming films and coatings in food packaging due to its intrinsic antimicrobial and edible properties. It is a biodegradable and biocompatible polymer composed of glucosamine residues linked by β-1,4 glucosidic bonds. It is derived by deacetylation of chitin, a cellulose-like molecule, which is one of the most abundant natural polymers and widely available in living organisms such as crustaceans. Because of the positive charge on the C-2 of the glucosamine monomer below pH 6, chitosan is more soluble and has a better antimicrobial activity than chitin (Chen et al., 1998). The polycationic structure may be expected to interact with the predominantly anionic components of the Gram-negative surface (Nikaido, 1996). Many bioactivities of chitosan have been reported, such as antitumour activity (Suzuki et al., 1986), lowering cholesterol in humans (Kanauchi et al., 1995), and antioxidant, antimicrobial and antifungal activities (Wang, 1992; Xie et al., 2001; Liu et al., 2004). Chitosans exhibit antimicrobial and antifungal activity against various groups of micro-organisms, filamentous fungi and yeasts; therefore, they have received attention as potential preservatives and disinfectants in the food industry. In addition to chitosan’s self-activity in its original form, several chitosan derivatives have also shown antimicrobial activity; e.g. as acid-free, water-soluble chitosan (Ilyina et al., 2000), quaternary N-alkylchitosan (Jia et al., 2001), sulphonated chitosan (Chen et al., 1998) and Ncarboxybutyl chitosan (Muzzarelli et al., 1990). Chitosan has often been



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used for spraying or coating fresh fruit to extend the storage life (ElGhaouth et al., 1992; Devlieghere et al., 2004). It is also potentially important as an antimicrobial packaging for meat products because it has been found to inhibit the growth of many pathogens in various meat products (Coma et al., 2002). The bactericidal activity of chitosan has been reported against some Gram-positive and Gram-negative food-borne bacteria such as Staphylococcus aureus, E. coli, Yersinia enterocolitica, L. monocytogenes and S. typhimurium (Liu et al., 2004; Zivanovic et al., 2004). Chitosan and chitosan-laminated films containing antimicrobial agents have been used as active packaging material with the active components being released from the film and deposited on the food surface, inhibiting microbial growth (Chen et al., 1996; Du et al., 1997). Cellulose is the principal structural component of plants and the most abundant source of complex carbohydrate in the world. Its derivatives have excellent film-forming properties. Cellulose derivative-based edible films are very efficient barriers to oxygen and aroma compounds (Donhowe and Fennema, 1993; Debeaufort and Voilley, 1994). The films made from celullose ether-ester, produced by chemical modification of cellulose (Psomiadou et al., 1996), are flexible and transparent, have moderate strength, resistance to oil and fat migration and act as moderate barriers to moisture and oxygen (Kester and Fennema, 1986, 1989; Hagenmaier and Shaw, 1990). Starch is an interesting alternative for edible films and coatings for food packaging because this polymer is abundant, inexpensive and biodegradable. Starch occurs naturally as discrete particles (granules). Films based on starch have moderate gas barrier properties. Most starch granules are composed of a mixture of amylose and amylopectin polymers. Amylose is the linear fraction of starch and it is responsible for the film-forming capacity (Cha and Chinnan, 2004). Because of its inadequate mechanical properties and its hydrophilic nature, starch is often modified mechanically, physically or chemically and/or combined with plasticizer or polymeric additives to prepare packaging material (Davis and Song, 2006). The incorporation of antimicrobial peptide, dermaseptin K4K20-S4, in a corn starch-based coating has shown a greater efficiency against moulds and aerobic bacteria, even at lower surface concentrations of antimicrobial peptide (Miltz et al., 2006). Blending starch with polyester polymers exhibited good biodegradability for agricultural mulch applications, while gelatin biopolymer acted as a strength reinforcement agent for improved mechanical performance (Halley et al., 2001; Kong and Zheng, 2002). The interaction of antimicrobial agents such as sorbic and p-benzoic acid with starch produces coatings with different properties depending on the type of starch, the concentration and the chemical characteristics of the preservative used (Duckova and Mandak, 1981). Starch-based coatings formulated with potassium sorbate exhibited a significant effect on reducing the microbial count and extending the storage life of strawberries (Cha and Chinnan, 2004).


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11.6


Natural antimicrobial/antioxidant compounds from plant sources

Natural antimicrobial/antioxidant compounds from plant sources such as herbs and spices (rosemary, sage, oregano, thyme, cinnamon, clove, savory, etc.) and from cereals – such as corn, wheat, rye, oat, barley, etc. – exhibit bioactivity. The antimicrobial effects of essential oils from herbs and spices were recognized long ago, but their widespread commercial application in the food and pharmaceutical industries as natural antimicrobials has not been accomplished yet, although interest is growing quite quickly. Oregano (Origanum vulgare L.) is a herbaceous plant native to the Mediterranean regions and has been used as a medicinal plant, making use of its powerful antimicrobial, antioxidant and antifungal properties (Elgayyar et al., 2001; Puertas-Mejia et al., 2002; Sokovic et al., 2002). The primary components of oregano essential oil are carvacrol and thymol (Fig. 11.1). Carvacrol and thymol (non-crystallizable and crystallizable phenols, respectively) have been isolated from essential oils of oregano, and their antioxidative effects have been reported by Deighton et al. (1993). Several phenolic compounds from the methanolic extract of O. vulgare leaves have also been isolated. These were protocatechuic acid, caffeic acid, rosmarinic acid (Fig. 11.2), a phenyl glycoside and 2-caffeoyloxy-3-[2-(4hydroxybenzyl)-4,5-dihydroxyphenyl]propionic acid, all of which showed antioxidative activities (Kikuzaki and Nakatani, 1989).

HO

OH (CH3)2CH

CH3

(CH3)2CH

Carvacrol

Fig. 11.1

CH3 Thymol

Structures of carvacrol and thymol.

OH O HO

H O

COOH

OH OH

HO O O OH

HO Rosmarinic acid

Fig. 11.2


Rosmanol

Structures of rosmarinic acid and rosmanol.


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Thyme, belonging to the Labiatae family, has been found to possess significant antifungal, insecticidal and antimicrobial activities (Cosentino et al., 1999). These properties have been mainly attributed to its carvacrol and thymol content. Essential oil of Origanum minutiflorum exhibited a very strong antibacterial activity against E. coli O157 : H7, L. monocytogenes, S. typhimurium and S. aureus bacteria (Dadalioglu and Evrendilek, 2004). Additionally, the essential oils of Origanum scabrum also exhibited extremely strong activity against S. aureus, Staphylococcus epidermidis, E. coli, Enterobacter colaceae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Candida albicans, Candida tropicalis and Torulopsis glabrata. However, the essential oil of Origanum microphyllum showed weaker antimicrobial activities against the above-tested microorganisms and no activity was observed for P. aeruginosa and K. pneumoniae (Aligiannis et al., 2001). Santoyo et al. (2006) reported that C. albicans was the micro-organism most sensitive to the oregano essential oil obtained by using a supercritical fluid extraction (SFE) system, whereas Aspergillus niger was the least susceptible one among two Gram-positive bacteria (S. aureus and Bacillus subtilis), two Gram-negative bacteria (E. coli and P. aeruginosa), a yeast (C. albicans) and a fungus (A. niger) tested for the same oregano extract. Rosemary (Rosemarinus officinalis) is an evergreen plant native to Mediterranean regions that has been recognized as one of the most important plant sources to have high antioxidant activity. The antioxidant activity of rosemary extracts has been associated with the presence of several phenolic diterpenes such as carnosic acid (Fig. 11.3), carnosol (Fig. 11.3), rosmanol (Fig. 11.2), rosmariquinone and rosmaridiphenol (Aruoma et al., 1992). Sage (Salvia officinalis L.) is widely cultivated in various parts of the world and popularly used as a culinary herb for flavouring and seasoning. The botanical name of sage is attributed to its medicinal importance. Salvia comes from salvare meaning to cure in Latin and officinalis means medicinal. It has very high antioxidant activity. The main antioxidant compounds identified in sage samples were carnosic acid, carnosol and rosmarinic acid (Cuvelier et al., 1994). Carnosol and carnosic acid have peroxyl and hydroxyl radicals scavenging activity and therefore can quench hydroxyl radicals and

OH HO HOOC

CH3

OH HO

CH3

CH3 CH3

O O H H3C CH3

H3C

Carnosic acid

Fig. 11.3


CH3

Carnosol

Structures of carnosic acid and carnosol.

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chelate metals; however, only carnosic acid can scavenge hydrogen peroxide (Aruoma et al., 1992). The antioxidant potential of carnosic acid has been reported to be almost seven times higher than that of synthetic antioxidants BHA and BHT (Richheimer et al., 1999). Clove (Eugenia caryophyllus) is a perennial tropical plant. Cinnamon (Laurus cinnamomum; synonyms are Cinnamomum verum and Cinnamomum zeylanicum) is an evergreen tropical tree, belonging to the Lauraceae family, and its dried inner bark is used as a spice or medicine. Cinnamon and clove oils are both natural preservative and flavouring substances that are not harmful when consumed in food products. There have been a number of studies reporting that cinnamon and clove oils could separately inhibit the growth of moulds, yeasts and bacteria (Azzouz and Bullerman, 1982; Conner and Beuchat, 1984; Matan et al., 2006). Eugenol (4-allyl-2methoxyphenol) (Fig. 11.4) is the major phenolic component of clove and cinnamon essential oils. This phenolic compound can denature proteins and reacts with cell membrane phospholipids, changing their permeability (Deans and Ritchie, 1987; Briozzo et al., 1989 ). Eugenol may constitute 70–90% of clove oil. Cinnamic aldehyde (Fig. 11.4) is the second important terpenoid found in cinnamon. It has shown insecticidal and fumigant activities against Mechoris ursulus (Park et al., 2000). Coriander (Coriandrum sativum L.) is widely distributed and mainly cultivated for its seeds. The seeds contain essential oil up to 1%, in which the major component is monoterpenoid linalool (Fig. 11.4), at levels between 50 and 70% (Argonosa et al., 1998; Illes et al., 2000). Coriander is highly inhibitory (minimum lethal concentration 25–50 ppm) to E. coli O157 : H7, Y. enterocolitica, P. aeruginosa, L. plantarum, A. niger, Geotrichum and Rhodotorula (Elgayyar et al., 2001). Sesame (Sesamum indicum L.) is an important oilseed crop and provides a good source of edible oil. It contains some compounds with potentially beneficial biological activities such as antioxidant and cardioprotective properties. Sesame lignans and tocopherols are well-known, naturally occurring antioxidant components present in sesame seed oil with sesamin and sesamolin being the predominant sesame lignans (Namiki, 1995). Summer

OH O

OCH3 CH CH2

CH

Eugenol

Fig. 11.4

CH

C

CH3 OH C CH H2C H2C

H

C CH3

CH2 Cinnamic aldehyde

CH2 CH CH3

Linalool

Structures of eugenol, cinnamic aldehyde and linalool.



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O OH HO O CH3 Ferulic acid

Fig. 11.5

Structure of ferulic acid.

savory (Satureja hortensis L.) also contains antioxidant and microbial compounds that are effective against various bacteria (Marinova and Yanishlieva, 1997; Sagdic and Ozcan, 2003). These are rosmarinic acid, carnosol, carnosic acid, carvacrol and thymol. Grape seed extract obtained as a byproduct of wine and grape juice processing is rich in proanthocyanidins. Grape seed proanthocyanidins are mainly composed of dimers, trimers and tetramers of catechin and epicatechin and their gallates. Grape seed proanthocyanidins make up approximately 60–70% of the polyphenol content of grape seed extract, which has been evaluated for its antioxidative effect on a few meat types and has been reported to improve the oxidative stability of cooked beef (Ahn et al., 2002) and turkey patties (Lau and King, 2003). Significant levels of antioxidants have been detected in grains and grainbased cereal products (Emmons et al., 1999; Handelman et al., 1999). The antioxidant potential and bioavailability of cereal antioxidants may depend on the species and varieties of grains, fractions of the grain (bran, flour or whole grain) and processing conditions (Zielinski and Kozlowska, 2000). Phenolic acids are known to contribute to the antioxidative potential of cereal grains. Ferulic acid (Fig. 11.5) is the primary phenolic acid in wheat; it is concentrated in the bran fractions and accounts for up to 90% of the total phenolic acids. It has many physiological functions, including antioxidant and antimicrobial activities. The phenolics of oats contain a mixture of benzoic and cinnamic acid derivatives as well as quinones, flavones, flavonols, chalcones, flavanones, anthocyanins and amino phenolics (Naczk and Shahidi, 2006).

11.7

Extraction and fractionation techniques for antimicrobial/antioxidant compounds from plant sources

11.7.1 Steam distillation Steam distillation is used for the isolation of antioxidant and antimicrobial compounds from herbs and species such as clove, rosemary, sage and thyme


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(Farag et al., 1989). It is a multistage continuous distillation process where steam is used as a stripping gas to extract the oils. Steam is directed through the plant material. The mixture of hot vapours is collected and condensed in order to produce a liquid in which the oil and water form two distinct layers. One of these layers is essential oil, which contains oil-soluble compounds, and the other is a hydrolysate or hydrosol, which contains watersoluble components. Although polar compounds of essential oil are lost in both the aqueous fraction of the distillate and the water in the still, steam distillation is still used extensively for essential oil extraction. The polar compounds lost in water can be redistilled, a process called cohobation. However, this increases the energy consumption. In addition, steam distillation is highly non-selective and may result in the extraction of undesirable components from the plant. The elevated temperature (c. 100 ºC) may speed up hydrolysis of some of the active components resulting in flavour changes (Ammann et al., 1999). 11.7.2 Solvent extraction The use of organic solvents is a common method for essential oil extraction. However, this method can induce thermal degradation of bioactive compounds or the problem of toxic residual solvents in the products (Marongiu et al., 2003). The solvent method requires several hours for complete oil extraction and more volatile compounds can be lost during removal of the solvent. Alcoholic solvents have commonly been employed to extract phenolics from natural sources by this technique. Pressurized liquid extraction, also referred to as accelerated solvent extraction (ASE) is a promising procedure that combines elevated temperature and high pressure with liquid solvents to achieve rapid and efficient extraction of analytes from various matrices. The use of pressurized liquid extraction significantly decreases the total time of extraction, the amount of solvent and the manipulation of sample and solvents compared with the Soxhlet method which is a continuous solvent extraction technique. When a solvent is heated above its boiling point in a closed system, it becomes a very potent extraction solvent. The same solvents can be used in the ASE technique as in other extraction techniques but at an increased pressure (c. 1500–2000 psi (10– 14 Mpa)) and at an elevated temperature (50–180 ºC). The analyte recoveries are equivalent to those from Soxhlet extraction but use less solvent and take significantly less time. Extraction by this technique takes only 10– 20 min. The ASE technique can be made more effective and selective by changing the solvent type, extraction temperature, pressure, time and cycles. The use of a higher temperature increases the ability of the solvent to solubilize the target components, and decreases the viscosity of liquid solvents, allowing better penetration of the solvent into the matrix. In this extraction system, the sample is placed in an extractor made of stainless steel. Following addition of the solvent, the extractor is pressurized, heated to the desired



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temperature, and the sample is extracted over a specific period of time. Next, the extract is removed from the extractor and the extractor is flushed with fresh solvent. The cycle can be repeated by extracting the solid residue. ASE has been used successfully for the extraction of components from natural plant products, food, pharmaceuticals, etc. (Alonso-Salces et al., 2001; Barbero et al., 2006; Peres et al., 2006). The disadvantage of ASE is the high cost of the equipment. 11.7.3 Supercritical fluid extraction SFE uses fluids at supercritical conditions to extract selectively the substances from materials. SFE has many advantages over classical solvent extraction methods. SFE is even efficient for materials with compact and hardly accessible structures. A wide variety of solvents are available for use as supercritical fluids including CO2 , nitrous oxide, ethane, propane, npentane, ammonia and water. CO2 has its critical point at 31.1 ºC and 72.0 bar, therefore it can easily be elevated to supercritical conditions without using excess energy. CO2 under supercritical conditions is a powerful solvent for extracting antioxidant and antibacterial compounds from plants. It has low toxicity, is inexpensive and is easy to separate from extracted products (Hawthorne, 1990; Zougagh et al., 2004). Supercritical CO2 can penetrate various matrices easily and extract high yields of active components without the risk of thermal degradation. However, supercritical CO2, because of its low polarity, can be less effective for extracting polar compounds in natural matrices. In order to overcome this limitation, appropriate cosolvents (modifiers) are commonly used. Modifiers are highly polar compounds which, when added in small amounts, can produce substantial changes in the solvation properties of supercritical CO2 and enhance the solubility of the target compounds and/or increase the extraction selectivity. The common modifiers used in supercritical CO2 extraction are methanol, ethanol, isopropanol and water. There is an advantage in using ethanol or isopropyl alcohol as the organic modifier as both solvents are classified as GRAS. The major disadvantage of SFE systems is the expensive equipment needed. Supercritical CO2 extraction has been used for extracting antioxidant and antimicrobial compounds from herbs, spices and other plant materials (Reverchon et al., 1995; Leal et al., 2003; Shan et al., 2005). It is possible to separate spice and herb extracts into several fractions by changing the extraction pressure and temperature (Nguyen et al., 1992). A sequential extraction of plant material, starting with mild conditions to extract non-desirable compounds first and then using a higher pressure and/or temperature in the second stage, may lead to the efficient release of potent antioxidant and antimicrobial compounds from plant sources. The removal of volatile compounds and waxes improves antioxidant/ antimicrobial activity. In this type of sequential extraction, volatile compounds and waxes are extracted in the first stage at low pressures, followed


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by conventional solvent extraction of the solid residue (Nakatsu and Yamasaki, 2000; Ribeiro et al., 2001). Increased levels of modifier in supercritical carbon dioxide allow the extraction of polar antioxidants (Palma et al., 2000). High yields of the phenolic antioxidants in grape seeds have been extracted by a methanol-modified supercritical CO2 system following the oil extraction (Palma et al., 1999). The separation of bioactive compounds from the solvent using classical extraction methods is tedious and time consuming. Fractionation of the bioactive components may require multiple chromatographic applications. Counter-current fractionation is a versatile technique for separating natural products from complex matrices. Many compounds with high purity have been separated and purified from various herbs using this technique (Degenhardt et al., 2000; Wei et al., 2003; Ito, 2005). Counter-current chromatography is a continuous liquid–liquid partition chromatography technique that uses no solid support matrix, eliminating the irreversible adsorption of the sample onto the solid support matrix (Ito, 1981) and allowing a high recovery and highly efficient preparative separation and purification of natural products. It relies simply on the partition of a sample between the two phases of an immiscible solvent system. The relative proportions of solute passing into each of the two phases are determined by the respective partition coefficients. A combination of SFE and counter-current chromatography, either at the liquid state or at supercritical conditions of the solvent flowing upwards in the chromatography column, is widely used to extract and separate natural products from plant sources (Aghel et al., 2004; Jiang et al., 2004; Wang et al., 2004; Eisenmenger et al., 2006).

11.8

Antimicrobial and antioxidant tests

The antioxidant and antimicrobial activity of the additives for polymers used in food packaging can be tested by several methods. Here, we will describe the most common methods (Schlesier et al., 2002) for the assessment of antioxidant and antimicrobial activity of various compounds. 11.8.1 Antioxidant assays Total phenol assay The antioxidant activity of plant extracts has been correlated to their phenolic component content. Therefore, it is important to determine the total phenolic quantity as an expression of the antioxidant activity of the extracts. The total phenol content of plant extracts can be determined by the Folin– Ciocalteu method described by Folin and Ciocalteu (1927) and Singleton and Rossi (1965). The Folin–Ciocalteu reagent is a mixture of phosphomolybdate and phosphotungstate, used for the colorimetric assay of phenolic antioxidants. Diluted Folin–Ciocalteu reagent is added to the phenolic



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extract solution and mixed thoroughly. After oxidation, saturated sodium carbonate solution is added and the mixture is left to stand at room temperature for 1 or 2 h. Absorbances of the samples and standards (gallic acid) are measured at 760 nm. The total phenolic contents are expressed as gallic acid equivalents. b-Carotene–linoleic acid assay Antioxidant capacity is determined by measuring the inhibition of the volatile organic compounds and the conjugated diene hydroperoxides that are formed from linoleic acid oxidation. A stock solution of β-carotene–linoleic acid mixture containing one of Tween 20, Tween 40 or Tween 80 is prepared in chloroform. The chloroform is completely evaporated and distilled water saturated with oxygen is added and shaken vigorously. A certain amount of this reaction mixture is added to the extracts. The emulsion system is incubated for up to 48 h at room temperature. The same procedure is repeated with a synthetic antioxidant such as BHA or BHT, α-tocopherol (as a positive control) and a blank. After the incubation period, absorbances of the mixtures are measured at 490 nm. The antioxidative capacities of the extracts are compared with those of the synthetic antioxidants and the blank. Diphenyl picryl hydrazyl assay Several methods have been developed in which the antioxidant activity is assessed by the scavenging of synthetic radicals in polar organic solvents such as methanol and ethanol at room temperature. Diphenyl picryl hydrazyl (DPPH), a stable radical and reactive hydrogen acceptor, is used as the free radical source (Blois, 1958). In its radical form, DPPH absorbs at 517 nm, but upon reduction by an antioxidant or a radical species, its absorption decreases. Briefly, in this assay an alcoholic solution of DPPH is added to test samples of different concentrations. The mixture is stirred and left in the dark at room temperature until the reaction is complete (30 min to 3 h). The absorbance of the reaction solution is measured at certain time intervals. A lower absorbance of the reaction mixture indicates higher freeradical scavenging activity. The data are commonly reported as EC50 values, which is the concentration of antioxidant required for 50% scavenging of DPPH radicals in the specified time period. Trolox equivalent antioxidant capacity assays These assays also involve spectrophotometric methods that are widely used for the assessment of antioxidant activity of various substances. Trolox (a water-soluble derivative of α-tocopherol) equivalent antioxidant capacity (TEAC) assays are based on the oxidation of ABTS (2,2′-azinobis (3ethylbenzothiazoline-6-sulphonic acid)) to the radical cation ABTS.+ (blue/ green colour), which is photometrically measured at 734 nm. In the presence of the antioxidant, the absorption of this radical cation is quenched to an extent that can be related directly to the antioxidant capacity of the


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added substance. Oxidation is delayed depending on the concentration of radical-trapping substances. The antioxidant activity of the sample is calculated by determining the decrease in absorbance at different concentrations. • TEAC assay with metmyoglobin: This test is based on the oxidation of ABTS in the presence of H2O2 and metmyoglobin to the radical cation ABTS.+. • TEAC assay with MnO2: The ABTS . + radical cation is prepared by filtering a solution of ABTS through manganese dioxide powder. The solution is pre-incubated for 2 h at room temperature prior to use. • TEAC assay with K2O8S2: The ABTS.+ radical cation is prepared by mixing ABTS solution with potassium persulphate. This mixture has to be left for 12–24 h until the reaction is complete and the absorbance is stable. 11.8.2 Antimicrobial assays Zone inhibition assay Disc-diffusion and agar-diffusion assays are the methods often used and are based on measuring zone inhibition for the screening of antimicrobial activity. The disc-diffusion test has long been the most widely applied testing method for antimicrobial susceptibility in various systems due to its ease of use, flexibility, and low cost. In this assay, a suspension of the tested bacteria is spread on nutrient agar. Filter paper discs are impregnated with the antimicrobial test solution and placed on the inoculated agar. The inoculated plates are incubated at an appropriate temperature for a certain time. Antimicrobial activity is evaluated by measuring the zone of inhibition against the tested bacteria. The agar-diffusion assay is similar to the disc-diffusion assay and is commonly used for testing antimicrobial activity. In this method, the bacteria suspension is spread uniformly on the agar surface and that surface is perforated with holes of a certain diameter. The test samples dissolved in dimethylsulphoxide (DMSO), which does not inhibit microorganism growth, are poured into these holes. Micro-well dilution assay The test sample is dissolved in DMSO and the solution with the highest concentration to be tested is prepared. This solution is subjected to a series of dilutions and placed in sterile test tubes containing nutrient broth. Each solution with a different concentration is added to a well (or a 96-well microplate) containing nutrient broth and standard inoculum. Negative controls are prepared containing the solvent that is used to dissolve the samples. The plates are covered with a sterile plate sealer, then agitated to mix the content of the wells and incubated at appropriate temperatures for 24 h. Microbial growth is determined by observing the change of colour



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(reading the respective absorbance) in the wells. The lowest concentration that shows no colour change is considered as the minimal inhibition concentration value.

11.9

Suitability of new coatings and adhesives for food packaging

Moisture resistance is the ability of a packaging material to prevent water from entering its structure and eroding its mechanical properties. As in other polymer tests, a polymer that has environmentally compatible coatings, adhesives and additives should be tested for suitability. These tests are based on the physical properties and antioxidant/antimicrobial properties of the polymer. Physical property tests involve determination of film surface colour, mechanical resistance (tensile strength, elongation and toughness), water vapour transmission and oxygen permeability tests. The water vapour transmission rate and permeability are determined to find the film’s water sensitivity. Briefly, an aluminium container containing anhydrous CaCl2 or silica gel desiccant is closed using a sample of test film. It is placed in a controlled relative humidity and temperature environment. The water vapour transmission rate is determined from the weight increase of the container over time until a steady state is reached. A similar procedure is applied for oxygen permeation properties using an oxygen transmission rate test machine. The total oxygen amount that penetrates through a tested polymer can be obtained by determining the oxygen transmission rate over time until a steady state is reached. Different kinds of polymer mixtures are tested for the effects that the addition of antioxidant or antimicrobial compounds has on physical properties such as viscosity and turbidity. Microscopic images of these polymer mixtures will give useful information about the mixing process, homogenization and the distribution of compounds on the polymer surface. The antioxidant and antimicrobial properties of the polymers can be determined by β-carotene–linoleic acid assay, radical-scavenging assays (DPPH and TEAC) and zone inhibition assays. It may also be useful to use two different methods for screening antioxidant activity since activity in foods is dependent on a variety of factors including polarity, solubility and metalchelating phenomena. In order to carry out the antioxidant activity test, release tests should be applied first. The polymer cuts are incubated for an appropriate time with continuous stirring. Antioxidant activity of the compounds released from films is monitored. The antimicrobial activity test is carried out by cutting the polymer samples into disc form and placing them on nutrient agar plates that are seeded with inoculum. The plates are incubated and the diameters of inhibitory zones surrounding the film discs and the contact area of the polymer with agar are measured. Migrant identification can be performed by high-performance liquid chromatography,


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gas chromatography, liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, nuclear magnetic resonance spectroscopy, infrared spectroscopy, etc.

11.10

Incorporation of antimicrobials/antioxidants into polymer materials

Antimicrobial or antioxidant packaging materials can be prepared in several forms. These include incorporating antimicrobial and/or antioxidant agents directly into polymers, coating or adsorbing these compounds onto the polymer surfaces, immobilizing them to polymer materials by ionic or covalent linkages or using a polymer that is itself antimicrobial such as chitosan (Appendini and Hotchkiss, 2002). Antimicrobials/antioxidants can be incorporated into polymers in the melt or by solvent compounding. Solvent compounding may be the more suitable method for the incorporation of thermolabile antimicrobials into the polymers. Heat-sensitive antimicrobials/antioxidants, such as lysozyme, which degrade during polymer processing at high temperature, are coated onto the polymer sheets prepared in advance or are added to cast films which are applied as coatings to packaging materials (Appendini and Hotchkiss, 2002). If antimicrobials are nonvolatile, there needs to be direct contact between the package and the food surface. Therefore, in the case of solid foodstuff, this technology could be applied in the form of edible coatings. The use of a multilayer film – which usually consists of four layers including a control layer, active matrix layer, barrier layer and outer layer, leads to a controlled release of active compounds onto the food surface (Floros et al., 2000). The matrix layer contains active substances and has a very fast diffusion. The release of active substances from the matrix layer to the food surface is controlled by the control layer. The control layer is placed next to the matrix layer and has appropriate thickness and diffusivity. The barrier layer reduces the rate of migration of active substances towards the outside of the package. In volatile antimicrobial-containing packaging systems such as chlorine dioxide releasing systems, precursor molecules are incorporated directly into the polymer or into carriers that may be extruded or coated onto packaging materials. In these systems, the polymer does not need to be in direct contact with the food product. The volatile antimicrobials can penetrate the bulk of the food matrix (Appendini and Hotchkiss, 2002). Active packaging technologies that employ bioactive compounds such as enzymes and peptides typically immobilize the moiety via entrapment or physical adsorption. However, covalently attaching the compound to the packaging film may have the advantage that it is unlikely that the bioactive component will migrate into the food; therefore it will probably have a longer activity duration compared with those that diffuse into the bulk of the food matrix. It should be noted that active packaging material which contains permanently bonded bioactive components can only be effective © 2008, Woodhead Publishing Limited


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in protecting the surface of the food product. On the other hand, those bioactive components that are temporarily bonded to polymer surfaces will have the ability to protect both the surface and the bulk of the food product. Therefore, the choice of permanently or temporarily bonded bioactive components will be mainly dictated by the food product type; i.e. whether it is solid or liquid and, if solid, the moisture content and the chemical nature of other components present on the surface of the food product. Immobilization of antimicrobials/antixodants by ionic or covalent linkages to a polymer requires the presence of functional groups such as hydroxyl, carboxyl, amine, epoxy, imine, etc., both in the molecular structure of the antimicrobial agent and on the polymer surface. Since most conventional polymers have no such functional groups on their surface, they should be modified so that they have reactive groups for covalent immobilization of the active substances. The immobilization may also require the use of spacer molecules that link the polymer surface to the bioactive agent. Ionic bonding of antimicrobials onto polymers allows them to be released slowly into the food. Antimicrobial moieties covalently attached to the polymer need to be active while attached to the polymer so that they can act directly from the film when they are brought in contact with the food product. Therefore, diffusion to the product is less of a concern when the antimicrobial is covalently bonded to the polymer unless the linkage is an ester or amide type, where the bioactive component may be released slowly via hydrolysis if the packed food secretes water from its bulk mass. Surface functionalization is used to modify the surface layer of a polymer such as polyethylene by inserting some functional groups onto its surface in order to improve its barrier characteristics and give it some antimicrobial properties (Ozdemir and Sadikoglu, 1998). Ultraviolet irradiation of nylon6,6 film has been reported to impart antimicrobial activity due to the formation of surface-bound amines (Shearer et al., 2000). The specific functions imparted to the inert surface must be compatible with the reactive sites on the compound to be covalently attached to that surface. Surface modification of polymers can be accomplished either by chemical or physical methods. Chitosan, inherently antimicrobial and inhibiting the growth of many pathogenic bacteria and fungi, has been widely used in films and coatings. N-Alkyl chitosan derivatives have been prepared by introducing alkyl groups into amine groups of chitosan via a Schiff’s base intermediate (Kim et al., 1997). Quaternization of the N-alkyl chitosan derivatives with methyl iodide produced water-soluble cationic polyelectrolytes. The antimicrobial activities of the chitosan quaternary ammonium salts increased with the increase in the chain length of the alkyl substituent; this increased activity has been ascribed to the contribution of the increased lipophilic properties of the derivatives (Kenawy et al., 2007). Proteins are highly suitable for chemical modification because of their numerous and diverse side chains; therefore they are important materials when tailoring the required properties of the packaging material. The peptides exhibiting antimicrobial activity can be immobilized on the surface of © 2008, Woodhead Publishing Limited

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the polymer films by modifying their surface characteristics with chemical methods based on the formation of permanent amide bonds between the polymer support and the peptide (Haynie et al., 1995). These kinds of antimicrobial films showed an antimicrobial effect without the migration of antimicrobial substances from the polymer to the food. Hayat et al. (1992) have used the surface modification procedure with ammonia plasma for derivatizing polyethylene surfaces with amine functionalities for immobilizing proteins via glutaraldehyde as a covalent binding agent. The primary amines were formed during the modification of polyethylene substrate surfaces via excitation of a low-temperature radiofrequency plasma in anhydrous ammonia at relatively low discharge powers and reaction times. In this surface modification technique, the surface morphology remained essentially unaffected during the application. It has been reported that physical methods provide more precise surface modification without needing rigorous process control. They are environmentally safe and clean processes since no chemical is involved (Ozdemir et al., 1999). Physical surface modification methods include flame, corona discharge, ultraviolet, gamma-ray, electron beam, ion beam, plasma and laser treatments.

11.11

Applications in the food industry

Food safety is becoming an increasingly important health issue for the food industry since significant increases in food-borne illnesses have been reported in many countries over the past few decades. In addition, improving the shelf life of food products has had an important economic impact by reducing losses from spoilage and allowing products to be transferred to new distant markets. The safety and effectiveness of minimally processing food products depend on the use of new preservation technologies, most notably in packaging. A higher rate of innovation and the introduction of new packaging systems are essential for the food industry. Several factors should be considered when designing an antimicrobial packaging system for food products. The concentration of antimicrobials/ antioxidants in the polymer film, the effect of film thickness on activity and the physical and mechanical properties of the polymers after conversion to the final products need to be considered. After the food has been sealed in its packaging, antimicrobial activity may be rapidly lost due to the antimicrobials not being activated by the food components or their dilution below an active concentration due to their migration into the bulk food matrix. One other possible problem is blooming, phase separation in the food matrix because of antioxidant additives, which results from poor mixing of the polymer material and the antioxidant agent during production. The development of high-quality food packaging material containing natural antioxidants and/or antimicrobials will replace the salts and syn-



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thetic chemicals used as preservatives and, therefore, more healthy food products will be supplied to the consumers. Interest in developing active packaging material is increasing and the possibility of integrating bioactive natural products as additives, coatings and adhesives for such polymeric and biofilm-type material is also under investigation. Some examples have already been given in the earlier part of this chapter and some others are as detailed below. Chitosan films prepared with oregano essential oil were applied on bologna slices and results indicated that the moisture and high lipid content of bologna helped the diffusion of the oregano essential oil from the chitosan film matrix into the product. These results support the potential use of chitosan–oregano essential oil films as antimicrobial packaging material for processed meat (Chi et al., 2006). Miltz et al. (2004) have developed an antimicrobial film containing the natural components of basil which are linalool and methyl chavicol. This film has shown a significant inhibition of E. coli and Listeria as well as other micro-organisms and extended the shelflife of cheddar cheese. Polymer coating incorporated with nisin was observed to be effective for microbial growth suppression in pasteurized milk and orange juice (Kim et al., 2002). The incorporation of lysozyme (derived from egg whites) into packaging films would allow direct contact of antimicrobials with pathogens that occur on the surface of food. Lysozyme combined with other antimicrobials may be effective when applied directly on the surface of meat products, forming a packaging film (Gill and Holley, 2000a). This combination would prevent inactivation of the enzyme during cooking. A combination of lysozyme–nisin coating (1 : 3 mixture) with 25.5 mg/ml EDTA applied onto cooked ham and bologna was bactericidal to Brocothrix themosphacta, Lactobacillus sakei, Leuconostoc mesenteroides, L. monocytogenes and S. typhimurium and inhibited the growth of organisms when stored at 8 ºC for 4 weeks (Gill and Holley, 2000b). Lysozyme incorporated into biodegradable packaging film was bactericidal to L. plantarum (Padgett et al., 1998). The inhibitory effect of edible cellulosic films, e.g. hydroxymethylpropylcellulose incorporated with nisin has been demonstrated by Coma et al. (2001) against Listeria innocua and S. aureus. Scannell et al. (2000) used L. innocua and S. aureus in cellulose-based bioactive inserts and antimicrobial polyethylene/polyamide pouches. When the bacteriocins nisin and lacticin 3147 were tested, it was reported that nisin bonded well and the bioactive film made with nisin was stable for 3 months with or without refrigeration, whereas lacticin 3147 adhered poorly to plastic film.

11.12

Future trends

The potential application of nanotechnology methods for developing natural biopolymer-based biodegradable packaging materials, creating


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additional bioactive functions, may lead to dramatic changes in active food packaging. Nanomaterials are being developed with enhanced physical properties to ensure better protection of food. The specific design of nanoscale and microscale internal structures in edible films and coatings may create powerful protection. Clay and organic polymer composites have recently evoked intense research interest in the material and polymer science areas. The dispersion of different clay particles and the bioactive components in the matrices of various polymers, forming nanocomposites with various physical and chemical properties, may create attractive materials for food packaging. Although numerous pieces of research on polymer– clay nanocomposites have been performed, the matrices of these nanocomposites have mainly been synthetic polymers. The use of this application for natural biopolymer-based nanocomposite materials is limited. Incorporation of nanosized clay minerals into natural biopolymers to this extent may lead to the formation of good-quality and biodegradable food packaging materials. Rhim et al. (2006) prepared chitosan-based nanocomposite films incorporated with unmodified montmorillonite and this film showed antimicrobial activity. The blending of synthetic polymers with natural biopolymers (protein and polysaccharides), which have a low barrier against water vapour due to their hydrophilic nature, and/or uniform dispersion of different type of clay particles in the polymer matrix may also improve the mechanical properties and stability of the food packaging material. In addition, biopolymer films developed by blending them with food-grade potent antimicrobial agents, and micro- or nanoencapsulation of these active substances in the packaging material, would have all the health and environmental benefits expected from food packaging material. New antimicrobials/antioxidants from natural sources with a wide spectrum of activities and low toxicity, and new biodegradable polymeric materials with antimicrobial/antioxidant activities will be the targets for future work in this field. Continued innovations in active packaging will lead to further improvements in food quality, safety and stability.

11.13

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12 Recycling of food packaging materials: an overview D. Dainelli, Sealed Air Corporation, Italy, and EuPC (European Plastics Converters Association), Belgium

12.1

Introduction

Throughout this chapter, the following definitions will be adopted. • Recycling: the reprocessing of the waste material in a production process either for the original purpose or for other purposes. The definition includes organic recycling but excludes energy recovery.1 • Recycling process: the physical and/or chemical process that converts collected and sorted packaging or scrap into secondary raw materials or products.2 • Secondary raw material: the material recovered as a raw material from used products and from production scrap. However, scraps arising within a primary production process are not considered to be secondary raw materials.2 • Organic recycling: aerobic or anaerobic treatment of the biodegradable part of the packaging waste to produce stabilized organic residues or methane.1 • Energy recovery: the combustion of packaging waste as a means to generate energy.1 The availability of packaging materials that are accurately sorted, washed and free from contaminants is a prerequisite for their recycling. The mere technical feasibility of the recycling is only one of the elements rendering such processes economically worth while; in fact costs associated with collection and sorting are of primary importance in the economic balance, since they may result in different qualities of the input stream, and therefore influence the quality and the value of the secondary raw materials. Costs related to logistics and transportation also play an important role


Recycling of food packaging materials: an overview

295

in the economic balance, because of the volume of the packaging to be transported. In addition, acceptance of recycled materials by consumers is also a sensitive issue: some materials have a better image than others in terms of public opinion, such as recycled paper and glass. Packaging consisting of these materials is considered more ‘environmentally friendly’, being more easily associated with the concept of ‘recyclable packaging’. On the other hand, plastics have a somewhat worse image in the consumer’s eyes, even if their recyclability is often technically feasible. Sometimes, the decision of public authorities to promote packaging recycling schemes is driven by political factors, associated with citizens’ concerns about waste incineration plants and landfilling sites, or by ‘green marketing’ operated by retailing chains or packaging manufacturing companies. Recyclability of packaging, in summary, is not always driven by environmental goals, but often economic, political and social factors play a major role. The presence of a well-established market for products containing recycled glass, paper and metals makes the recycling processes for these materials largely independent of environmental considerations, so that the development of the recycling industry for glass, paper and metals would have taken place regardless of environmental, political and social factors. The opposite situation holds for plastics, where the market for recycled products is largely undeveloped, with the exception of some specific materials, and therefore the environmental drivers are predominant. Waste minimization, best use of natural resources and limitation of the environmental impact of post-use packaging are the obvious benefits of packaging recycling. Recycling, however, is not always the best environmental option: in fact, it should be weighed against other forms of minimization of the environmental impact, such as energy recovery, which in specific ecobalances might lead to more favorable scenarios. In conclusion, three elements should be taken into consideration when dealing with recycling of packaging materials: • best environmental performance; • the economic balance of the whole processes, including collection, sorting and transportation; • consumer acceptance of the recycled materials, particularly in sensitive applications such as food packaging. All of the above elements are of utmost importance in determining the worthiness of the recycling of a given packaging material, and each of them can act as limiting factor if not properly addressed.

12.2

Regulation of recycling of food packaging materials

The legislation on recycling (as well as other forms of recovery) of packaging materials is stipulated by the body of law of the European Union,


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through Council Directive 94/62 of 31 December 1994, also referred to as the Packaging and Packaging Waste (P&PW) Directive.1 Prevention at source is the main objective of the above-mentioned Directive. In addition to prevention, recycling, recovery and reuse are indicated as means for minimizing packaging waste and, consequently, environmental impact. In this Directive, recycling is one of the options for recovery of packaging, together with energy recovery and organic recycling. The abovementioned Directive was amended in 2004 by Council Directive 2004/12/EC, through which new targets for recovery and recycling have been introduced,3 namely: • overall recovery, 60%; • overall recycling, 55% Recovery targets for specific materials are as follows: • • • • •

glass, 60%; paper/board, 60%; metals, 50%; plastic, 22.5%; wood, 15%.

These targets have to be achieved by the end of 2008 by the former Europe15 Member States. A longer deadline has been introduced through Directive 2005/20/EC4 for the ten new Member States that joined the European Community on 13 April 2003 (namely: the end of 2012 for Czech Republic, Estonia, Cyprus, Lithuania, Hungary, Slovenia and Slovakia; end of 2013 for Malta; end of 2014 for Poland; and end of 2015 for Latvia). The objective of the recovery target imposed for single materials can also be interpreted as an obligation to recycle the indicated percentage of waste for materials for which other forms of recovery, for example energy recovery, would be a more economically viable solution. Other provisions contained in the Directive that are worth noting are: • to limit combined lead, mercury, cadmium and chromium VI content of packaging materials at 100 ppm, • to ensure that packaging materials are only introduced in the marketplace if they meet the so-called ‘essential requirements’, i.e. requirements on composition and reusability, recoverability and recyclability addressed in Articles 9 and 11 and Annex II of 94/62/EC. Compliance with the essential requirements is achieved by conforming to the European Committee of Standardization (CEN) standards (version 2004), as outlined in the following paragraph. 12.2.1 The ‘essential requirements’ The ‘essential requirements’ mentioned in the above paragraph are specified in the Directive in Articles 9 and 11, and in Annex II. Requirements



297

have been set relative to the manufacturing and composition of packaging, its reusable nature and its recoverable nature. This last item is also related to recycling: it stipulates that packaging materials recoverable in the form of recycling shall be manufactured in such a way as to enable the recycling of a certain percentage by weight of the raw materials used for their production. The European Parliament gave a mandate to the CEN, with the aim of developing standard norms that would allow packaging materials to meet the ‘essential requirements’, and thereby to comply with the P&PW Directive. As a result of the mandate, in 2000 the CEN published five European standards. After scrutiny, the European Parliament decided to accept only one of these standards because, in the Parliament’s opinion, they did not correctly address the issues of reuse, materials recovery and energy recovery required by the Directive. In early 2002, the CEN was given a new mandate with the aim of reviewing the rejected standards, and new final standards that would enable users to achieve compliance with the ‘essential requirements’ were finally published in 2004 (http://catalogo.uni.com/EN/ home.html; http://www.cenorm.be/sectors/sw_res/transport/packaging.htm). These are summarized below. • EN 13427:2004 – Requirement for the use of European Standards in the field of packaging and packaging waste. This is a guidance paper that explains how the technical standards should be used. • EN 13428:2004 – Requirements specific to manufacturing and composition – Prevention by source reduction. • EN 13429:2004 – Requirements for reusable packaging. • EN 13430:2004 – Requirements for packaging recoverable by material recycling. • EN 13431:2004 – Requirements for packaging recoverable in the form of energy recovery, including specifications of minimum inferior calorific value. • EN 13432:2000 – Requirements for packaging recoverable through composting and biodegradation – Test scheme and evaluation criteria for the final acceptance of packaging. 12.2.2 Implementation in the Member States The Member States have been given the opportunity to adopt economic instruments aimed at achieving the above-mentioned objectives. The implementation of the P&PW Directive in the Community Member States gave rise to a rather complex legal framework, due to the overlap of the Directive itself with the national measures already existing in some countries such as Germany, The Netherlands, France and Austria. Germany, in particular, is the first European country that has introduced a packaging recovery scheme (Decree Toepfer, 1991),5 and has been considered for


298


many years a leading model in Europe. Its approach is based on the possibility of transferring the responsibility of recovery to a third party, authorized and controlled by the autonomous Regions constituting Germany. The most important of these third parties is called DSD-Duales System Deutschland AG, which enables its member companies to use a special logo, the Green Dot, on packaging introduced in the market. The Green Dot has gained a strong image over the years; in 1995 a consortium called Pro-Europe was founded, adopting the Green Dot logo in order to avoid the formation of commercial barriers. Pro-Europe is a pan-European organization that has been established for promoting the use of the said logo as well as promoting the convergence of the regulations in the countries that adopt it. The countries that are members of Pro-Europe are: Austria, Belgium, France, Spain, Portugal, Ireland, United Kingdom, Sweden, Luxembourg, Greece, Norway, Sweden, Czech Republic, Slovakia, Hungary, Romania, Bulgaria, Estonia, Lithuania, Latvia, Slovenia, Croatia, Turkey, Malta and Cyprus. It must be highlighted, however, that the use of the same logo in different countries does not mean that the compliance schemes are the same: as a matter of fact, each country still adopts its own scheme, and the function of the logo is limited to the mutual recognition of these schemes. In particular, the financing systems of the recovery and recycling schemes may be significantly different.6 Some countries have adopted special national schemes and are outside of the Green Dot system; notably Italy, The Netherlands, Denmark and Finland. 12.2.3 Other applicable legislation Identification system for starting materials Article 8 and Annex I of the P&PW Directive set up a packaging identification system based on numbering: it is required that the Commission shall issue a specific measure aimed at identification of packaging to facilitate collection, recovery and sorting. This provision, applicable to all packaging materials, is represented by Commission Decision 97/129/EC.7 The Decision reports the symbols that should be used for the identification of the constituent substances; these symbols (see Fig. 12.1) are often interpreted as ‘recyclability marks’ when in fact they are not and this may mislead consumers.

01

02

03

04

05

06

07

PET

PE-HD

PVC

PE-LD

PP

PS

O*

Fig. 12.1

Symbols used for the identification of constituent substances in packaging materials.



299

New regulations on post-consumer recycled plastics in contact with food Finally, we would like to mention that an important Regulation has been recently published by the European Commission8, relative to the use of post-consumer recycled plastics for use in contact with food. The Regulation lays down the basic rules of quality assurance and hygiene that should be adopted in plants that produce food-contact plastics using postconsumer plastics as starting materials. Procedures for authorization of the said plants, as well as inspection by public authorities, are established. The suitability of the final product for coming into contact with food will be determined through specific protocols of analysis aimed at assessing conformity with Regulation 1935/2004/EC9 on materials and articles intended to come in contact with food. Technical protocols already exist for polyethelene terephthalate (PET) for the production of bottles for water and soft drinks, and polypropylene (PP) crates for fruits and vegetables. This Regulation is expected to have a significant impact on the entire business of plastics recycling: one of the most important points that should be highlighted is that the process of depolymerization of post-consumer plastics, aimed at the production of new monomers or oligomers from which new food-contact plastics are obtained (a process known as ‘feedstock recycling’, used, for example, for PET, see Feedstock recycling in Section 12.4.4) will not fall under the scope of the Regulation.

12.3

Recycling paper food packaging: collection, separation and processing

12.3.1 Collection and reutilization of paper packaging Recycled paper is an important source of raw materials for the paper industry: about 42 million tonnes of waste paper were recycled in Europe in 2001, confirming a substantial growth in the last 10 years (there were 26 million tonnes recycled in 1991, which indicates a growth of 38%) (Fig. 12.2). These 42 million tonnes represent 52.1% of the total paper used in Europe. It also represents the vast majority of the total amount of paper collected, which was 44.7 million tonnes in 2001.11 Recovery of paper is mainly operated through recycling, i.e. reprocessing of waste paper into conventional pulpers, with the use of appropriate technologies for cleaning the product. Only a small fraction, equal to 2.7 tonnes or 6%, is either incinerated (with or without heat recovery) or landfilled. The biggest volume of paper collected was in Germany (11.5 million tonnes) followed by France (5.5 million tonnes) and Italy (5.1 million tonnes); offices, commercial business and households generate large quantities of paper waste, including packaging materials. The highest potential for increased collection today in Europe lies with households; however, the cheapest source of post-use paper is commercial businesses, where paper foils and cardboard boxes are available


300


50 45

Million tonnes

40 35 30 25 20 15 10 5 0

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Fig. 12.2

Recovered paper utilization in Western Europe 2004.10

in large quantities, thus decreasing the logistic costs of collection. In fact, often the paper packaging destined for recovery pulpers does not come from municipal collection and sorting schemes, but directly from commercial businesses, allowing savings because of the avoidance of trade operations, sorting costs and often volume reduction. As already mentioned, the whole recovery process in Europe has progressed significantly over recent years, making the P&PW Directive target realistic, i.e. 60% recycling of paper and board packaging to be attained by 2008.12 In theory, 70% of paper produced is recyclable, although excessive use of recycled paper would result in decreased quality in the finished products. This decrease can be compensated for by a weight increase, or a reduction in the percentage of recycled paper incorporated, which may have adverse environmental and economic consequences. Packaging materials are the largest sector where recycled paper is used: 26.2 million tonnes out of the 42.0 million tonnes of recycled paper produced in 2001 were used for manufacturing new packaging, i.e. case materials, corrugated board, wrapping and others (Fig. 12.3).11 This quantity represented 74.8% of the paper and board packaging produced in Europe in 2001. 12.3.2 Separation of contaminants The paper collected has different technical and economic value depending on its degree of purity. Sorting operations obviously have a large influence on the final purity. Conventional sorting is carried out via mechanical processes, while a more accurate level of sorting can only be achieved manually. Separation machines are commercially available and are capable of separating paper from plastics and other packaging. These machines have a feedrate of from 1.5 to 3 tonnes/hour, generating a minimum product



Newsprint 19%

301

Other graphic

paper

7%

Case materials 46%

Others

4%

Household and sanitary 8%

Wrapping, other packaging paper 9%

Carton boards 7%

Fig. 12.3

Recovered paper usage by sector in Western Europe (2004).10

purity of 90%. In a typical separation process a mixed packaging waste stream is randomly fed into the machine through an acceleration conveyor; the separation criteria are based upon infrared sensors, which are capable of classifying cartons, paper and mixed plastics. Other types of separation can also be operated, such as punched screens, slot screens and centrifugal purifiers; non-paper components that are mechanically stable, such that they remain in the form of large particles, can be removed more easily through these systems, while materials with very small dimensions cannot be removed. There are more than 60 fractions of waste paper that can be selected, as stipulated by the European List of Standard Grades of Recovered Paper and Board, EN 643.13 Sorting is carried out on the basis of the final use of the fraction, and it is strongly influenced by the demand levels and the prices for the different fractions. Both market demand and prices may vary significantly; therefore the economic worthiness of the process resides in its ability to adapt the grades produced to the actual market demand. Paper sorted into fractions according to EN 643 should no longer be considered as waste, but as a secondary raw material, since it is used in pulpers to produce new paper materials. 12.3.3 Processing of recovered paper14 The standard paper production process includes the following steps: preparation of fibers, introduction of additives, preparation of sheets, drying and coating. The production of paper from recovered fibers does not differ significantly from the process that utilizes virgin cellulose fibers. The main difference resides in the preparation of the fibers; several processes can be used to clean up the recovered material, with the aim of removing contaminants prior to further processing. Fiber preparation in the case of virgin cellulose consists of a series of treatments that aim to dissolve the natural


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wood and reconstitute the fibers with the desired consistency that will allow the production of a conventional paper sheet. When recovered fibers are introduced into the production process, the fiber preparation phase is associated with treatments capable of removing contaminants and inks. These treatments that fibers undergo when recovered material is present are described briefly in the following paragraphs. Re-pulping In the case of processing native wood, pulping is the treatment that removes the non-cellulose fraction, preparing material for paper production. It consists of a treatment to alkaline conditions at pH 8–10, operated in suitable reactors (pulpers) of different dimensions and sizes, with the aim of defiberizing and achieving a given pulp consistency. The term ‘re-pulping’ refers to recovered fibers, and consists of the water dissolution of recovered paper for further processing; re-pulping is the first step, and is associated with mechanical cleaning tools such as those used for the removal of inks. Often the desired efficiency of inks removal is a parameter used for selecting the most appropriate pulper to be used.15 In many processes virgin and recovered fibers are treated together, to obtain paper products with selected technical characteristics. Other mechanical cleaning processes Mechanical cleaning is also carried out by washing, screening and suspension, i.e. treatments using differences in size, density and surface properties. These steps have the aim of removing extraneous contaminants from the fibers, such as metals, sand, glass and other agglomerated particles derived from inks, varnishes and adhesives. Being operated after the pulping step, the control of contaminants removed during pulping is the key parameter that determines the efficiency of these mechanical cleaning techniques. Ink removal by flotation16 The most common technique for de-inking consists of flotation: the paper pulp formed is insufflated with airflow in the presence of surface-active substances. In these conditions ‘flotation bubbles’ are formed, on the surface of which inks and pigments of particle size 20–100 µm are suspended, together with fragments of fibers and other paper additives. The foam formed on the surface of the pulper is then removed. There are limitations on the ink particle size: inks containing components soluble in alkaline solutions break into particles of about 1 µm or less, which are unsuitable for flotation. In this case an option is to include an additional washing cycle to remove them. On the other hand, coarse particles resulting from crosslinked inks or inks coated with cross-linked varnishes, e.g. ultraviolet crosslinking technology, are too heavy to be floated. In this case there is still the option of dispersing these particles and then resubmitting them to a floating process. © 2008, Woodhead Publishing Limited


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Washing Washing can remove fillers, finely divided ink particles and other colloidal materials. This process can achieve high cleaning efficiency, but it involves the use of high volumes of water, with associated costs, and leads to significant loss of fibers removed by the mechanical effect exerted by the water pressure.14 Thermal treatment This treatment is also known as ‘hot-dispersion’ and is carried out on highconsistency material; it consists of submitting fibers to high mechanical forces together with vapor or steam heating at 60–100 ºC, depending on the process. Sometimes the thermal treatment is associated with chemical treatment. Hot-dispersion has the purpose of reducing chemical and microbiological contamination, especially in processes where recycled water is used in the various cleaning and de-inking steps. Chemical treatment This is also known as ‘bleaching’, and consists of treatment with biocides, slimicides, whitening agents, enzymes, ozone, hydrogen peroxide, oxygen and others. The purpose is to increase brightness and reduce contamination.14 12.3.4 Food packaging from recovered paper As already mentioned, recovered fibers represent an important source of raw materials for the paper industry, and suitable physical–mechanical characteristics are obtained by mixing virgin and recovered fibers in different proportions. The paper packaging industry is no exception: paper packaging is largely produced with the use of recovered fibers. One sensitive area where the use of recovered fibers must be carefully considered is the production of paper destined to come in contact with food. Packaging materials and articles destined for food-contact use are subject to the safety requirements of Regulation 1935/2004/EC.9 This Regulation prescribes that the said materials and articles fulfill the basic safety requirements, i.e. • should not endanger human health; • should not cause unacceptable organoleptic and nutritional modification of the food. Materials and articles made of paper and boards for food-contact applications fall within the scope of the above-mentioned Regulation. However, contrary to the case of other food-contact materials, such as plastics – which are submitted to more specific legislation – paper and board for food contact do not have further legal requirements at the European level. They are subject, however, to national provisions in some of the Community Member States, such as: © 2008, Woodhead Publishing Limited

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• the Ministerial Decree of 21 March 1973 and subsequent amendments in Italy;17 • Recommendation XXVI of BfR (Federal Institute for Risk Assessment) in Germany;18 • the ‘Materials in Contact with Food’ Ordinance in The Netherlands.19 The above legislation should also be used as reference for recycled fibers. The Council of Europe Resolution Another important text that lays down the technical specifications and safety requirements in this field is the Resolution of the Council of Europe AP (2002) 1,20 further amended in 2005. The Council of Europe, within the framework of the Partial Agreement in the Social and Public Health Field, works actively in the development of recommendations in areas not covered by Community legislation. Although these recommendations do not have a binding character, they are widely used by industry and by the Public Control Authorities of the Council of Europe Countries as reference standards. The above-mentioned Resolution consists of a text plus six Technical Documents, which are summarized below. • Text of the Resolution; • Technical Document No. 1: list of substances that may be used for the manufacturing of food-contact paper and board; • Technical Document No. 2: guidelines on conditions and methods of analysis; • Technical Document No. 3: guidelines on materials and articles made of paper and boards obtained from recycled fibers; • Technical Document No. 4: guidelines for good manufacturing practice developed by the CEPI (the Confederation of European Paper Industries); • Technical Document No. 5: practical guide on the use of the Resolution; • Technical Document No. 6: guidelines for the presentation of requests for safety evaluation of substances that may be used for manufacturing paper and board materials and articles intended to come in contact with food. The Resolution has raised discussions since it establishes, with Technical Document No. 6, an evaluation system similar to the official one carried out by the European Food Safety Authority, although on a voluntary basis (it should be highlighted that the Council of Europe Resolution is not a legally binding provision), and created by a body not officially entitled to perform the said evaluation. The evaluation system never took off, in fact, but nevertheless the Resolution is of interest both as far as paper and board purity and microbiological criteria are concerned, and in relation to recycled fibers. Particularly important and worth mentioning here is Technical Document No. 3, ‘Guidelines on materials and articles made of paper and



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board obtained from recycled fibers’; this establishes the purity criteria that should be fulfilled by recovered cellulose fibers in order to be safely used in food-contact applications. In this Technical Document three types of paper are identified, namely: • paper derived from substances reported in Technical Document No. 1 (not recycled); • unprinted recycled paper, or paper with a low print content, coming from offices or computer prints outs, including unused kraft paper; • mixed printed and unprinted paper (e.g. magazines and newspaper). Furthermore, three types of foodstuffs have been identified: • type I: aqueous and/or fatty foodstuffs; • type II: dry and frozen foodstuffs; • type III: foodstuffs that are shelled, peeled or washed before consumption. Finally, the Resolution provides a scheme indicating which type of paper should be used for the various food types and also, in the case of recycled fibers, identifying the most appropriate treatment for fiber recovery and the purifying treatments that the finished product should undergo (e.g. to remove residual solvent, whitening agents, aromatic amines and other contaminants). The European ‘Biosafe Paper’ project One of the most important initiatives that has been undertaken in recent years in the field of paper and board for food-contact applications, including products made of recovered fibers, is the Biosafe Paper project (www.uku. fi/biosafepaper/). This project lasted from December 2001 until December 2005 and had the objective of developing a procedure based on toxicological tests for the evaluation of the safety of paper and board for food contact. The project was coordinated by the University of Kuopio, in Finland; the main results were: • the development of a decisional approach to the safety of paper and board based on appropriate toxicological tests; • new ad hoc toxicological methods for the above; • new extraction procedures with solvent–absorbent systems that take into account the final use of the products; • methods for risk assessment based on the results obtained.

12.4

Recycling plastic food packaging: collection, separation and recovery

Plastic demand in the EU-25 reached 47 million tonnes in 2004. In terms of end-use applications, packaging remains the biggest single sector at 37%


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of total plastics demand followed by building and construction applications at 20%. In addition to automotive uses (7.5%) and electric and electronic applications (7.5%), other applications (29%) include agriculture, household, medical devices, toys, etc. Plastics accounted for 17% of the total packaging usage in Western Europe.21 A wide variety of polymers are used in the production of plastic packaging; the most commonly used are: • polyethylenes with different densities, i.e. high-density polyethylene (HDPE), low-density polyethylene and linear low-density polyethylene (LLDPE); • PP; • ethylene copolymers with propylene, vinyl alcohol and vinyl acetate; • polystyrene (PS) in sheets or films, or foamed; • polyesters, mainly PET; • polyamides, mainly Nylon 6 and Nylon 6/12; • polyvinyl chloride (PVC) and vinylidene chloride copolymers. Each of the above-mentioned polymers has special properties – such as barrier properties to oxygen or to water vapor, easy sealability, thermal and dimensional stability and others – that may be desired in packaging applications. In other cases, specific properties are imparted by the process technology, such as orientation, cross-linking, etc. Since packaging applications may require a combination of some of these properties, polymers can be combined in composite structures to achieve the specified performance. This leads to multimaterial products, such as multilayers either entirely made of plastics or combinations of plastics with other materials, such as paper or aluminum, that may not be suitable for mechanical recycling, but rather are recoverable in the form of energy recovery. Each year around 19 million tonnes of plastics are wasted,21 10 million tonnes of which are disposed of and 9 million tonnes recycled. In addition to industrial scraps and secondary raw plastics collected at commercial businesses, municipal solid waste (MSW) has been identified as a source of plastics suitable for recovery, since it contains about 7% plastics. As explained in the Introduction, environmental factors play a major role in the recovery of plastics from MSW; however, MSW collection schemes always result in mixed polymer fractions; these are not easy to sort and extensive labor costs are incurred in order to obtain homogeneous materials that are suitable for undergoing recycling processes. In addition, composites and multilayers cannot be separated into their components, and the fractions containing these materials can be recovered only via energy recovery. 12.4.1 The market for recycled plastic packaging Plastic recycling in the packaging industry is well established for three polymers, namely PET, HDPE and PP. PET recycling in Europe reached



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around 350 000 tonnes in 2002, and achieved the rate of 796 000 tonnes in 2005 (www.cee-foodindustry.com). The largest boost came from Germany, where more than 200 000 tonnes were collected. The main market is represented by the fiber industry but a non-negligible amount is also used for the production of soft drink bottles: for example Coca-Cola Co. uses 2.5% recycled PET in bottles for soft drinks. The use of recycled HDPE was about 100 000 tonnes in 2001, consisting of grinding and reprocessing of pallets and crates for fish and vegetables in a closed loop, i.e. in a system that envisages the recovery and reprocessing of the original pallets or crates. PP crates are also recovered in the same way. One of the main obstacles to the development of the market for these products was the lack of harmonization for their use in food-contact applications. Such use was so far based on approvals granted to specific processes by the single EC Member States, and in at least two of them – namely Italy and Spain – the use of recycled plastics for direct foodcontact applications is forbidden. Modern cleaning technologies, especially for PET (Section 12.4.4), are able to achieve a high degree of purity – as has been demonstrated by the FAIR Project 98-4318, a pan-European study carried out between 1999 and 2001.22 The new Regulation on the use of recycled plastics in food-contact applications (as mentioned in ‘Future regulations’ in Section 12.2.3) is expected to promote the plastic packaging recycling industry, as well as guaranteeing a high level of protection for consumers. 12.4.2 Economic considerations In order to make economic sense, the cost of collecting, sorting, cleaning and reprocessing plastics has to be competitive compared with the virgin material. To obtain a reasonable economic framework, a balance should be achieved between the quality of the recovered plastic fractions and the cost needed to obtain the desired degree of quality. The composition of the recovered fraction does have a major influence on the quality of the finished products obtained from the recycled plastics, while the cost that the industries are prepared to bear can only be determined as a function of the value of the secondary raw material or, in other words, of the market demand for the different fractions. The two elements are, however, strictly interconnected: for example, in the case of mixed polymer fractions, recyclers do not pay excessive attention to obtaining highly refined secondary raw materials since an established market for this fraction does not exist. In contrast, in the case of PET and, to a certain extent HDPE, for which a well-established market does exist, the quality requirements of the secondary raw material are higher, and the cost of refinement is covered by the selling price. It makes a big difference whether the plastic packaging is recovered from commercial businesses, or in closed loops or from MSW. While in the first


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two cases the recovered packaging is of homogeneous composition and needs relatively little cleaning, both sorting and cleaning heavily influence the cost of packaging fractions derived from MSW. In this latter case, since sorting is often carried out manually, the labor cost is as high as 90% of the cost of the final recyclate. For example, the cost for recycling LLDPE from MSW is around 0.7 8/kg, excluding collection costs and the price paid for the waste polymer. Since the same base virgin resin is sold at around 0.8– 1.1 8/kg, it can be clearly understood that recycling LLDPE from MSW is not economically viable. On the other hand, LLDPE industrial scraps cost 0.3–0.4 8/kg, therefore their competitiveness is extremely high, while quality, especially in terms of absence of contamination, is higher than in plastics recovered from MSW.23 PET is quite an interesting case: the recycled polymer for non-food applications is sold at 50% of the cost of the virgin resin; for this grade of resin the primary application is in the fiber industry. On the other hand, recycled PET for the soft drink bottles industry, which undergoes special purification and processing to compete with the virgin resin in terms of quality and safety, is sold at 10–20% less than the virgin resin. In this latter case the high price volatility of virgin PET can explain the strategies of investment of intensive food-contact-grade PET users in recycling technologies; i.e. companies are aiming to protect themselves against price increases by feedstock diversification. Moreover, despite the high cost of recycling, gaining access to lower priced recycled food-contact grade PET does result in an increase in the profit per bottle, so that recycling costs are exceeded. However, with the exception of PET and, to a certain extent, HDPE, for all other polymers the spread between cost and market value is such that the post-use recycling of plastics industry needs to be supported with economic measures to encourage its development. The enforcement of the P&PW Directive in the Member States led in all cases to the adoption of levies on plastic packaging; these economic measures aim to keep the price of recycled plastics at a competitive level in the market, 20–50% less than the corresponding virgin resin depending on the applications and the grade of purity. Sometimes the cost of recovery may compete with landfilling, and the lowest quality fractions that are obtained in a separation plant may be sold at negative cost. In addition, because of the general low quality of the products, the market for recycled plastic packaging can be easily reduced by factors such as variations in the cost of virgin materials and exchange rates. The above considerations lead to the conclusion that the plastics packaging recycling industry can be market driven only when sorting and cleaning costs are minimized. For this reason the treatment of MSW should be seen in the context of a political decision to reduce the environmental impact of plastics, rather than an economic opportunity.



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12.4.3 Collection and separation Collection schemes for plastic packaging Collection schemes for post-use plastic packaging, particularly PET plastic bottles, from MSW already existed in many EU Member States before the enforcement of the P&PW Directive. Post-use plastic scraps are generated at industrial, commercial or residential levels. Industrial scraps are the main source of secondary raw materials that are often reused without any treatment in the same production cycle, thus they cannot be defined as ‘secondary raw materials’. Part of this stream, however, is introduced in the recovery chain, and therefore it constitutes a source of ‘secondary raw materials’. Commercial scraps represent a great potential for high recovery and recycling rates, as well as being the main source of plastic packaging. These plastics consist of products that are generated by commercial business, such as shipping and receiving departments, warehouses, distribution centers and wholesalers’ or distributors’ bring-back programs for retail stores. The large quantities of commercial scraps available minimize the logistics and cost of transportation, maximize the efficiency of collection and ultimately result in a favorable economical balance for recovery programs. Labels, staples and tape typically contaminate these types of plastics, while microbiological contamination is unlikely; this makes them an attractive source for the production of secondary raw materials. Post-consumer plastics from MSW derive from households, and the costs of collection can be significantly different depending on whether households are dispersed over large geographic areas or concentrated in highly populated zones. The cost associated with collection and transportation to the recycling center might be prohibitive, and for this reason for dispersed households it becomes mandatory to maximize the yield of transportation by submitting the collected material to size reduction processes. These processes may consist of simple pressing and baling for materials that will undergo sorting at a later stage, or cutting, comminuting and granulating to obtain a homogeneous mixed plastic. Although business and public authorities now largely sponsor the use of separation bells and bring-back programs are increasingly in use, these plastics are rather expensive to recover and have the highest potential for contamination. Non-plastic residues such as paper, metals, earth, powders, etc., are typical contaminants, and microbiological contamination is usually high. Sorting of plastic packaging for recovery Sorting is the critical step in plastic packaging recovery; it in fact determines the purity, and ultimately the value, of the secondary raw materials. Sorting is carried out to separate high-value fractions from mixed plastics and contaminants. The plastic stream consists typically of films, foamed trays, thermoformed cups and sheets, bottles and other containers for liquid


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detergents. The large majority of bottles, as well as parts of foamed trays and thermoformed materials consist of PET which is the main material to be recovered. Containers for detergents are composed primarily of HDPE; this fraction is subjected to heavy odor contamination, and careful washing is needed prior to operating the recycling process. Films, trays and other rigid and expanded components compose the ‘mixed plastics’ fraction, consisting mainly of PP, PS and PVC, often recovered by energy recovery. The main separation is operated manually and non-plastic contaminants are removed to the highest possible extent. In some plants, pre-screened fractions are treated via automatic air classifiers and the separation is based upon infrared detection and airflow expulsion of the undesired parts (e.g. films). It must be said, however, that these processes do not achieve the same level of accuracy as manual separation, and need additional measures of purification. Light components such as films can also be ground to produce flakes, but because they contain multilayers, their properties are rather poor and they are more often recovered via energy recovery. The resulting fraction is successively washed to remove paper labels, caps and other extraneous components and finally is ground. Particular attention must be paid to removing metals, e.g. by placing magnetic separators at the entrance of grinders to avoid damage to the grinding knives. A further refinement may be made through flotation, where the recovered polymer is introduced in water together with surfactants and left to float or sediment, separating fractions with different densities; flotation can be operated in more than one step, adjusting the surfactant’s concentration to separate different components. Other practices may include stirring and gassing of the material, which improve the efficiency of the separation. 12.4.4 Recycling of plastic packaging Plastic packaging obtained from collection/separation schemes is recovered in one of two ways: either recycling or energy recovery. The choice is made based on the quality and the market demand for secondary raw materials. Despite the legislator’s tendency to raise the targets for plastics recycling, this is not always the best option from both an economic and an environmental viewpoint. Energy recovery remains the preferred option for mixed and highly contaminated plastics, often resulting as byproducts in the production of secondary raw plastics, while recycling is preferred for refined and homogeneous secondary plastics. It has been demonstrated24 that an integrated approach to plastic waste management, involving both recycling and energy recovery, results in the greatest level of environmental benefit. The majority of the industries operating plastic separation are small and medium-sized enterprises, with limited capacity for investment; not all of them produce high-purity secondary raw materials and, consequently, a residual degree of contamination may be present – consisting of metals, paper, fibers, agglomerates, polymer gels and other components. As already



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mentioned, PET is the most recycled polymer; it is used mainly by the fiber industry, which normally requires a lower molecular weight resin than the bottle manufacturing industry, and therefore finds in the secondary raw material a cheap feedstock. Recycled PET can in fact be converted into fiberfill without further treatment; another application is the production of carpets, e.g. for the automotive industry. However, when destined for the manufacture of new bottles or other types of food packaging, the recycled polymer needs specific treatments – such as more accurate removal of contaminants, purification from acetaldehyde (a typical byproduct of PET processing) by volatilization, and re-gradation, i.e. to increase molecular weight. In order to obtain foodcontact grade PET, specific processes have been developed (as described in the section on PET below); such processes have the capacity to increase greatly the quality and the value of the secondary polymer, and also have an influence on the price of the recycled PET, which becomes comparable with the virgin resin. Recycling of plastics encompasses three types of technologies applicable at industrial level, namely mechanical, feedstock and chemical recycling. Mechanical recycling is the most widely used technology due to economic reasons, while feedstock recycling and chemical recycling are not largely applied because of their unfavorable economic balance, although it is possible to produce highly refined food-contact grade secondary resins, using these processes. Mechanical recycling Mechanical recycling consists of the reprocessing of plastic packaging derived from collection and sorting systems using technologies that are normally used for virgin resins, such as extrusion, co-extrusion, injection, blow-molding, etc. These technologies offer a variety of possibilities for the use of secondary plastics, encompassing: • single-polymer recycled articles, such as polyethylene films for agricultural application or production of shopping bags; • embossing the secondary plastic into layers of virgin resin; this method is used for manufacturing, for example, PET bottles and other articles for food contact, where the secondary plastic cannot be in direct contact with the foodstuffs; • mixing the secondary raw material with virgin resin, to balance the physical and mechanical properties with cost, for a variety of products such as films, sheets, fibers. Secondary raw plastic materials normally have lower molecular weight and lower thermal stability compared with virgin resins, because of the previous exposure to the mechanical, thermal, oxidative and photochemical degradation. Conventional resins normally contain stabilizers, such as antioxidants and light absorbers. During the processing and the service life of


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the packaging materials, the stabilizers are used up to preserve the polymer matrix from degradation, therefore in the reprocessing phase it is common practice to add new stabilizers. The choice of the stabilizer is easy in the case of homogeneous recycled materials (the same stabilizers as used in the virgin resins), but is less straightforward when mixed or contaminated plastics are processed: in this case the stabilizers must be compatible with the resin mix. Some antioxidants have been specifically developed for improving the thermal resistance of plastics to recycling, such as the Recyclostab®, Recyclossorb® and Recycloblend® grades, all from Ciba Specialty Chemicals. For the same reason, in the case of mixed or contaminated plastics, compatibilizing agents might be useful to avoid melt crack during extrusion due to incompatible melt phases. Mechanical recycling rose from 1.2 to 2.2 million tonnes from 1995 to 2000, representing 11% of the total plastic waste collectable. The plastics recycling industry is quite important in countries like Italy, Spain and Sweden, where the rate of mechanical recycling has reached values of between 15 and 20%. Feedstock recycling The term ‘feedstock recycling’ includes a series of processes that consist of the pyrolysis and gasification of plastics operated at high temperatures in the absence or near-absence of oxygen. The processes lead to petroleum feedstock that is used for other purposes than producing the original material. Some specific types of feedstock recycling can generate synthesis gas (the Texaco process), a mixture of carbon monoxide and hydrogen that is used in oil refineries and in the chemical industry to upgrade commercial products. Other processes lead to heavier petrochemical fractions, consisting of liquid hydrocarbons and waxes. These products can find other applications, e.g. as fuel in the steel industry. Although several industrial processes have been developed for this type of recycling (by Texaco, BASF, Linde, SVZ, Akzo Nobel and others) the amount of plastic treated by feedstock recycling is rather small (see next subsection). This low uptake can be explained by the unfavorable overall economics of feedstock recycling compared with more conventional petroleum refining, in particular the high level of investment needed and the limited yield derived from contaminated supplies. All the above-mentioned technologies require, in fact, significant financial support from public bodies to break even, since the cost of feedstock recycling treatment has been estimated to be higher than 1 8/kg, about double the cost associated with incineration (data refer to Germany, 2000). Chemical recycling The term ‘chemical recycling’ identifies the process of de-polymerization of PET, resulting in the monomers, terephthalic acid and ethylene glycol. These monomers, after purification, can be reused to produce a new



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polymer. Chemical recycling can also be used for the de-polymerization of polyamides and polyurethane. In the case of packaging materials, the interest in chemical recycling is primarily the treatment of PET derived from soft drink bottles. The de-polymerization can be operated initially via glycolysis, consisting of the high-temperature (240 ºC) treatment of PET in excess ethylene glycol and resulting in the production of bis-hydroxyethyl terephthalate (BHET). After this step, BHET is further treated (a) by hydrolysis, where the ester is transformed in the corresponding acid; or (b) with methanol, with the consequent production of the dimethyl ester of terephthalic acid – this is a crystalline solid that can be easily purified. Another process that has found commercial interest is methanolysis. This consists of the treatment of PET in the melt state (250 ºC) with methanol in the presence of catalysts: the treatment results in ethylene glycol and di-methyl terephthalate, i.e. the constituent monomers. After purification, the monomers can be used for the production of new PET. Although this technology can originate very clean secondary raw materials, practically indistinguishable from the virgin polymer, its application in practice is extremely limited for economic reasons. In fact, both feedstock and chemical recycling in Europe represent a very small fraction of the total recovered plastics. These two technologies accounted together for 329 000 tonnes in the year 2000, less than 2% of the total plastic waste collectable.21 Recycling of polyethylene terephthalate for food contact Chemical recycling is able to provide secondary raw PET suitable for food-contact applications; another system for food-contact use of recycled PET is multilayer processing, with the recycled polymer sandwiched inside the final product. This latter system is used for manufacturing PET bottles, and has been demonstrated safe through tests involving the introduction of model contaminants into the recycled PET layer and the study of the barrier to migration of these contaminants exerted by the virgin PET layers (defined as the ‘functional barrier’).24,25 A third method for the production of food-contact grade PET is Superclean processing. This method encompasses a series of processes that are able to remove the volatile contaminants and increase the viscosity of the polymer to a grade suitable for injection-blow molding (i.e. having an intrinsic viscosity of 0.75–0.80 g/dl) and higher, for more demanding applications. Superclean processing has been also demonstrated to lead to safe PET in migration studies of model contaminants. Several proprietary Superclean processes have been developed which combine high-temperature washing, melt filtration, pressure treatment, solid-state polycondensation and other treatments to achieve high-purity/high-quality recycled PET. The main advantage of a recyclate PET produced by Superclean is that it can be used in direct food contact, without the need for a ‘functional


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barrier’. Some of the Superclean technologies available are reported below.26 • EcoclearTM, developed and used by Wellman in Holland is one of the oldest processes (1997) with a capacity of 7500 tonnes per annum; • SupercycleTM, developed by Schmalbach-Lubeca in France, operating since 1998 with a capacity of 6000 tonnes per annum; • VacuRema, a process developed by Erema and adopted by Texplast in Germany, with an output of 6000 tonnes in 2002; • Buehler AG also developed a process claimed to lead to a polymer competitive with the virgin resin in terms of quality, in use at Schmalbach-Lubeca; • PKR in Germany has adopted the process developed by OHL Stehning Gmbh, with a production capacity of 10 000 tonnes per annum; • United Resource Recovery Corporation developed a technology in collaboration with Coca-Cola Co., which has been in use at RecyPET in Switzerland since 2000 with an output of 15 000 tonnes per annum, and at Cleanway in Germany since 2002, with the same capacity. Bottles manufactured by both the multilayer and the Superclean processes, have received ‘non-objection’ letters for food-contact applications by the Health Authorities of numerous countries in Europe and by the Food and Drug Administration (FDA) in the USA. In Europe, the use of PET feedstock originating from food-contact applications is preferred as a raw material for the recycling processes. In the USA the FDA has also issued letters of ‘non-objection’ for non-food-grade PET feedstock.

12.5

Recycling of other materials

12.5.1 Recycling of aluminum Introduction Aluminum is the third most abundant element in the Earth’s crust, representing 8% of the total (oxygen is 47%, silicon 28%). It is a metal largely used for industrial and consumer goods applications. Recycling aluminum is an easy and practical way to ensure its availability to meet market requirements. The economic balance of recycling is very favorable, since the energy saving of aluminum recycling processes is as high as 75–95% compared with production from natural sources. Aluminum is 100% recyclable and can be recycled indefinitely without losing its properties: cans remain the most recyclable of all materials. In 2003, 54 billion cans were recycled in the USA: it has been estimated that in 60 days an aluminum can be recycled, turned into a new can and put back on the store shelves (www.earth911. org). The P&PW Directive does not set specific targets for aluminum recycling: it only prescribes that combined metal recycling should reach 50%



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by 2008. Aluminum, together with steel and copper, is the most recycled metal: according to the European Community27 the use of secondary raw materials in the metal industry achieved a rate of over 40% in the field of non-ferrous metals. The metal recycling industry is greatly supported by the existence of a global market and recognized quality standards shared at international levels. This allows transparent pricing and trade based on market requirements rather than being driven by governmental policies. The price of recycled aluminum may vary considerably depending on its source and quality: post-consumer washed cans are offered at 0.1–0.6 8/kg while other industrial scraps consisting of more pure metal may be offered at prices up to 1.8 8/kg. MSW collection delivers metal packaging mainly composed of aluminum cans and tin plate containers. However, while cans are normally of high quality, tin plate containers are not; therefore, unless separated, this may result in fractions that are not attractive to the market. Production of aluminum from natural mining The natural source of aluminum is bauxite ore. Bauxite is a mixed hydroxide of aluminum, silicium, iron, titanium and other metals. Bauxite is firstly transformed in alumina (pure aluminum oxide, Al2O3) via caustic soda treatment and separation from other metals, and subsequent precipitation and calcinations. Then molten aluminum is obtained from alumina through an electrolytic process (the Hall–Hèroult process) which takes place at high temperatures (950 ºC) in a fluorinated bath. The process is highly energy intensive: production of 1 kg of metal requires 14 kWh. Although the efficiency of smelters has steadily improved over the last 50 years, the overall process of aluminum production remains highly energy intensive; from a life cycle analysis (LCA) perspective such energy can be recovered thanks to the full recyclability of aluminum. Minimization of the environmental impact of the process can be ensured by the use of environmentally friendly sources of energy, such as hydro (45% in Europe) and nuclear (25%). The total process yield is about 25%: 1 tonne of aluminum is produced by 4.1 tonnes of bauxite. Bauxite extraction levels were 140 million tonnes in 2002, therefore the metal production from primary ore was about 35 million tonnes in the same year. The consumption in Europe in 2002 was 10.2 tonnes, 35% of which came from recycled aluminum. The same figures also apply at a global level, where about one-third of the total requirement is obtained from recycling. Sources of aluminum and use of recycled aluminum Three types of post-consumer scraps are available for recycling: from the automotive sector, from building and construction, and from packaging. The lifetime of most goods made from aluminum is quite high: 12 years for those used in the automotive and transport sector and 30 years for the building and construction sector. This makes the global demand higher than the


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actual availability of post-consumer scraps, and in practice, while 100% of production scraps are recycled, packaging – namely cans – constitutes the most widely available source of post-consumer metal. Western European countries produce about 3 million tonnes of primary aluminum per year and consume approximately 7 million tonnes. In Europe nowadays, 46% of the total number of cans used are recycled, 85% of the aluminum used in building and construction, and the metal derived from demolition materials is recycled and 95% of the metal used in the transport sector is recycled (www.cial.it), accounting for 1.9 million tonnes of aluminum. A considerable fraction of the metal, equal to 17%, is consumed in the packaging sector, while 36% is used in the transport sector, 25% in building and construction, 14% in engineering and the remaining 8% in other applications. Interestingly enough, it has been estimated that at least 28% of the recycled metal is sourced from old scraps, i.e. metal that has undergone more than one recycling trip. Aluminum has physical characteristics that make separation from other metals quite easy: it is lighter (density 2.7 g/cm3, compared with 7.87 g/cm3 for iron) and it is not magnetic. In addition, it can be transformed into very thin foils owing to its ductility. Because of these characteristics, after grinding of mixed metal scraps, it can easily be separated from iron and other ferrous metals through magnetic separators or though flotation. Treatment of cans is necessary to remove internal coatings and printing inks. Recycling of post-consumer scraps is normally carried out in recycling foundries, while recycling of industrial scraps occurs mainly in the so-called ‘aluminum remelters’. Recycling foundries produce bars consisting of alloys of aluminum with silicium, to which other metals may be added such as copper and magnesium. 12.5.2 Recycling of glass packaging Introduction Glass is an amorphous material produced by melting quartz sand. Quartz sand is composed almost entirely of silica (SiO2); commercial glass contains about 70% silica. The three principal raw materials used in glass manufacturing are: • sand: this is the major constituent, and it will have a minimum silica content of 99.6%. • soda ash (sodium carbonate): this is used to provide the sodium oxide in the glass, which acts as a fluxing agent. Its effect results in lowering the melting temperature from 2000 ºC (pure silica) to 1000 ºC; since soda makes glass water soluble, nowadays other metal oxides are used, such as calcium, magnesium and aluminum. • limestone: this is used to provide the calcium oxide in the glass, although calcite and dolomite are sometimes used.



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Other substances are also added to improve processability and to impart certain characteristics to the final product. These are minor constituents such as melting aids, refining aids, colorants and other materials that provide the glass with special properties. Depending upon the exact composition of the glass the total raw material cost will be in the range of 60–80 8/tonne. Ground recovered glass (cullet) can be purchased at a lower cost; however collection, transport and processing costs should be taken into account. Glass is used in a very wide range of applications, and its properties can be influenced by the use of many ingredients. In packaging materials, glass can be used in a colorless (e.g. glass jars) or colored form. In the latter case iron (II) oxide is used to obtain bluish-green glass, frequently used for beer bottles. Together with chromium, iron (II) oxide imparts a richer green color, used for wine bottles. Other metals are used to obtain a variety of colors for decorative glassware or for other industrial applications (manganese, lead, cobalt, etc.): these types of glass are not used for packaging, but may be found in kerbside glass collection and if not separated they can negatively affect the value of the recovered glass. Energy savings of glass recycling The theoretical energy requirement to produce glass from virgin raw materials is approximately 2.7 GJ/tonne while the energy needed simply to melt glass is about 1.9 GJ/tonne. Therefore, using recycled glass as a raw material represents significant energy savings and, in practice, for every 10% increase in cullet, energy consumption will fall by 2.5%. Glass manufacture is a hightemperature, energy-intensive process and the typical energy requirements range from 4 to 9 GJ/tonne. Based on energy costs of 2004 and a cullet recycling rate of 30%, it has been estimated that the UK glass container sector saves some 3 million 8/year from the use of recycled glass.28 Recycling of glass Glass is infinitely recyclable: cullet can be reprocessed to obtain a material with similar physical characteristics to the original materials. All countries in Europe recycle glass and many have achieved a recycling rate above 80%. Glass recycling data for Europe, as of 2003, are reported in Table 12.1. The most significant limitation to glass recycling is represented by the optical properties: if colored and clear glass containers are not separated into different fractions, the color imbalance is such that the final product becomes unsuitable for applications in packaging. Glass reprocessing facilities require color separation, as the different colored glasses are chemically incompatible and phase separation may occur, thus seriously impairing the optical properties of the finished product. In addition, some components used for the production of heat-resistent glass (such as borosilicates) have a strong influence, even at very low concentrations, on melt viscosity, and can totally alter the properties of the final product. Therefore, all


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Table 12.1 European glass recycling statistics 2006 (source: www.feve.org) Country Austria Belgium Bulgaria Czech Republic Denmark Estonia Finland France Germany Greece Hungary Ireland Italy The Netherlands Norway Poland Portugal Romania Slovakia Spain Sweden Switzerland Turkey United Kingdom Total

Glass collected (’000 tonnes)a 214 317b 54c 146c 119d 11 50e 1903 2550 20 25 98d 1256f 432 53 270c 181 16c 40c 840 159 308 93 1303f 10 459

Recycling rate (%) 84 91 33 76 75 32 72 60 89 10 18 81 59 77 90 28 46 9 35 51 92 96 22 50 61%

a

From the general public and from bottlers. Based on an estimate of total consumption (347 000 tonnes); considering the market represented by its members, FOST Plus records a rate of 107%; these figures relate to singletrip containers only. c Estimate. d 2005 figure. e 2004 figure. f Collected tonnage corresponds to glass actually recycled. b

contaminants must be removed before the recycled glass can be used for producing new containers for the food packaging industry. Metals, paper, plastic, organic substances, ceramics and heat-resistant glass must all be removed. This is usually done through manual inspection but also through more sophisticated technologies utilizing metal detectors, vacuums, crushers, screens, lasers, digital cameras and X-rays to detect and remove contamination. The simplest recycling plants can sort out mixed colour streams using processes that use manual inspection and digital scanning cameras to separate colour glass. They are rather labour intensive and produce relatively



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high waste levels; overall such plants remain economically inefficient due to either the low quality of the ouput or the overall low yield of high-quality outputs. Separation processes require a high level of investment and since glass recycling technology is expected to advance further, the use of more sophisticated equipment is essential in modern glass recycling plants. Glass resulting from mixed-color cullets does not have sufficient quality to be recycled in highly demanding applications, such as for food contact, and can only be used in alternative secondary markets such as: • • • • •

ceramic sanitary ware production; flux agents in brick manufacture; sports turf and related applications; water filtration media; abrasive paper.

Collection is therefore a critical point in glass recycling, and has a strong influence on the value of the resulting products. Recycling versus reuse of glass containers Refillable beverage containers may represent an economically profitable alternative to recycling, although establishing a system for reuse requires non-negligible initial investments. Specific equipment is necessary, such as a case de-packer (which removes bottles from crates and loads them onto a conveyor), washing equipment and chromatographic devices (sniffers) to inspect the washed containers for contaminants. Equipment to treat wastewater from the process is another additional expense. Adding such equipment may require expanding the plant, and entails considerable costs. Filling companies who do not want to sustain these costs may decide to consign the container-recovery operations to third parties.

12.6

Supply chain management to reduce packaging waste

Supply chains can be rather complex in the case of the production, distribution and use of packaging materials. How should a company with many distributors in different countries behave to minimizing packaging waste? What systems can be put in place to prevent excessive packaging being distributed? Continuous attention to avoid over-packaging may not be sufficient, and a combination of measures – such as adoption of reusable or recyclable packaging, longer shelf-life, etc. – may not result in a worthwhile payoff, such as to justify the effort at purchasing level. The solution lies in putting in place an integrated packaging policy, which would combine different approaches in relation to the process examined. There is not a single solution that would suit all cases, since supply chains can be very different, but there are basic concepts that may be applied and adapted in relation to the type of packaging.


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12.6.1 Example: the supply chain for plastic packaging The production of plastic packaging entails the use of many starting materials, produced by different companies and delivered with a range of packaging, for example: • polymers, in the form of pellets, that are contained in sacks – with multiple sacks stored on pallets and wrapped with a stretch film – or in cardboard containers (often referred as ‘octabins’ because of their octagonal cross-section) or in bulk, delivered by truck and stored in silos; • polymer masterbatches, produced by blending a base polymer with one or more additives (e.g. colorants, slipping agents, anti-blocking additives, etc.); these raw materials are received by the manufacturer of the final food-contact packaging in sacks or in octabins, since the quantity used is unlikely to be massive; • additives, successively used for the production of internal compounds, that, depending on their physical state, may be received in metal drums, plastic containers, sacks or cardboard boxes (often with an internal liner); • inks and solvents for printing: the former may be solid (powders) or liquid, and are normally shipped in metal drums, while the latter are delivered in trucks and stored in large tanks; • reels of materials successively used for lamination – such as plastic, aluminum and paper – always delivered on pallets and wrapped by plastic films. Reels also contain cores, often composed of thick, compressed cellulose-based material or plastics. The latter are heavy and highvolume components that may not be strictly defined as ‘packaging’ but are likely to make a significant contribution to waste in the distribution chain; • Other raw materials and chemicals used in the process – such as lamination adhesives, processing aids, water-treating substances, etc. – that are normally delivered in smaller metal, plastic or cardboard containers.

12.6.2 Strategies for minimization of packaging waste Strategies for the minimization of packaging waste begin from reduction at source: this entails use of the minimum quantity of raw materials for manufacturing packaging products that meet the required specifications. The correct choice of materials is essential: strong and lightweight materials are preferable, although the choice may often be determined by the properties that are desired, e.g. whether impact resistance or gas barrier properties are required for delivering the product. Designing products to avoid all unnecessary packaging and packaging components can also attain source reduction, by simplifying the packaging product as far as possible, for example by eliminating sleeves, labels and complex closures.



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A second step lies in designing packaging for longer use or reuse. This may be achieved by extending the shelf-life of the product, for example improving the packaging’s required properties (e.g. mechanical resitance) and eliminating potential weak points such as to allow greater distribution with minimum (or even without) secondary packaging. Design can also play an important role if it takes into account possible misuses instead of simply addressing the intended uses. This is true for single-use food packaging materials, but in particular for multiple-use goods that may not strictly be classified as packaging, but rather as ‘articles’, such as plastic household goods and containers for food-contact applications. Some food packaging goods, although not specifically designed for multiple use, may be conceived such as to encourage reuse, e.g. being easily cleanable, withstanding repeated collection, handling, washing and refilling, or simply being attractive enough to encourage consumers to retain the product for longer periods. If this might be difficult to attain with primary packaging for food, it can be easier for secondary packaging. A third strategy includes designing the packaging product for recyclability. Choosing basic materials that are easily recyclable is obviously the first step, but also selection of ancillary components – such as labels, caps, inks, etc. – that are compatible with the basic material in the recycling process or that can be easily separated from it. For example, use of water-soluble adhesives for labels would facilitate removal and improve recyclability. In general, recyclability encompasses the use of a minimum variety of materials in the packaging product, or use of materials that are compatible. This may not be easy for food packaging products, as they are often composed of more than one material, for example paper and plastic, or composed of the same material but in varieties that are not compatible with each other in a recycling process, such as multilayer plastics. Finally, waste minimization may be attained by adopting packaging composed of biodegradable raw materials. Recently, several packaging products consisting of biodegradable materials have been developed, especially in the field of plastics. Among these polylactic acid is gaining attention in the marketplace as a biodegradable resin and is becoming more and more economically interesting because of the stability of the price of maize, from which it is produced, versus petroleum. Other biodegradable polymers do exist, either derived from natural sources or from synthesis processes starting from crude oil, such as Biopol (a family of polyesters consisting of hydroxybutyric and hydroxyvaleric acids produced in nature from the fermentation of sugars by the bacterium Alcaligenes eutrophus), polyvinylalcohol, poly-beta-hydroxybutyrate and polyhydroxyalkanoate. These polymers, however, are not used today in packaging applications because of the limited production capacity, and consequently high cost, and also because of the fact that their properties often do not match the requirements for packaging materials, especially in the field of food packaging.


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The design of packaging for food-contact applications is dictated on the one hand by the strict legislation that aims to ensure the safety and hygienic quality of the packaging products (through compositional requirements and migration limits), and on the other hand by the technical properties that are needed to meet often challenging requirements, such as extended food shelf-life, the ability to withstand pasteurization and other treatments and microwaveability. In the field of primary food packaging, the most rewarding strategy is to reduce materials usage, with a ‘less and better’ approach, consisting of the development of high-performing products using thinner materials to obtain the same, or better, performances as those already on the market. A typical example is represented by multilayer plastic food packaging, where optimum food protection, shelf-life and resistance to heat treatment can be achieved with the use of new-generation polymeric materials that are capable of imparting specific properties with layers of 1–5 µm. The use of these materials results in food packaging having thicknesses as low as 15–20 µm, and being 20–40% lighter than those of the former generation. Because of the unique combinations of starting materials, these products can hardly be reprocessed, consequently they are in general not mechanically recyclable (with the exception of some limited cases). In addition, their collection may not be advisable due to contamination by food and the need for expensive and hardly efficient washing and disinfection processes before recycling. On the other hand, from the standpoint of LCA, these materials have a high energy content that can be fully or in part recovered if they are correctly treated in modern waste treatment plants.

12.7

Conclusions

Packaging materials represent a fundamental part of modern distribution chains. They are of utmost importance in the case of food, pharmaceutical products and fragile goods. Not only do they protect products from contamination and mechanical shock, extend the shelf-life of food and act as a vehicle for information, but they also provide an increasing variety of opportunities – such as the possibility of being used in microwave ovens and the capacity to increase the shelf-file of food, drugs and nutritive products through both conventional and active barrier properties. The environmental impact of packaging materials has been discussed for a long time, and a number of provisions have been issued by public authorities to minimize packaging waste. The P&PW Directive is today the framework under which national recovery schemes operate, even though such schemes are significantly different in the various countries. Large investments in research and development have been made in the last 10 years to develop new technologies for recovery and recycling of packaging; in addition, numerous studies have been undertaken in order to



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identify the best option to balance environmental needs with process economies, providing both authorities and industry with tools to maximize efficiency while minimizing the environmental impact. It is clear that there is not an option that is valid for all packaging materials in all situations, but in each case the choice of option will be influenced by the actual conditions in which the packaging material is used. For example, there will be large differences in the ecological/economic balance of a recycling operation carried out in a closed loop system compared with that of an open loop system. In addition, the closed loop could fall into competition with reuse processes, for certain types of packaging, and also vary depending on whether or not losses occured during the loop. In other words, the only correct way to decide the worthiness of a given packaging material for a defined application is to carry out an eco-balance study. In general, it is not true that one material is better than another in absolute terms, even though often the perception of environmental friendliness is linked to the material itself and overlooks all other factors. Within this framework, LCA is a powerful tool that could be of help in determining whether or not a packaging material in a defined application does represent the best option. LCA provides a systematic approach for the examination of all parameters that contribute to the environmental impact of the packaging material during its entire cycle of life, comprising energy consumption; the resource intensity of production processes; air, water and soil emissions; generation of waste; and, most importantly, economics. LCA deals with systems rather than products: the same packaging material, for example, can have a totally different environmental impact depending on its distribution system or the availability of recovery or disposal facilities at the end of its life cycle. Equally, the availability of adequate collection and sorting schemes, as well as consumer attitudes towards final disposal, can influence analysis results greatly. Therefore, LCA can be extremely useful in understanding the impact of the whole industrial system associated with packaging materials, and in identifying the critical points that need to be addressed in order to maximize the environmental yield. However, it should be used carefully, and should avoid comparing products with each other if their global industrial systems are not comparable; if not correctly used the results of LCA may be strongly misleading. For a comprehensive introductory dissertation on LCA, references 29 and 30 should be consulted. It has been demonstrated that recycling of certain packaging materials – such as aluminum, glass and paper and board packaging – is an extremely attractive option from an economic point of view, leading ultimately to the production of new packaging materials for both food and non-food applications. The industry associated with such materials is primarily market-driven, it has been developed independently of the legislation constraints introduced by the P&PW Directive, and there are reasonable expectations for further growth in the near future.


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On the other hand, recycling is more difficult in the case of plastic packaging, due to the difficulties in achieving a consistent supply, in terms of both quality and costs. The industry, public authorities and consumers all have a role to play in driving plastic recycling: • the industry needs to invest more in research and development aimed at developing alternative processes to mechanical recycling, processes that are not extensively exploited today, as well as implementing ‘design for recycling’ practices, i.e. considering recyclability as one of the key parameters that should be achieved by new packaging materials from the very beginning of their development; • public authorities should adopt further economic measures such as increased landfilling costs and economic facilitation of start-ups dealing with recycling; another important provision that would bolster plastic recycling is the harmonization and simplification of rules for the use of secondary raw plastic in manufacturing food-contact packaging materials; • consumers can help by increasing the quantity and improving the quality of the collected packaging. All of the above provisions are likely to open new markets and new applications to secondary raw plastics from packaging, with combined environmental and economic benefits.

12.8

References

1 Council Directive 94/62/EC, Official Journal of the European Communities, 20 December, 1994. 2 European Standard, EN 13437:2003 ‘Packaging and Material Recycling – Criteria for Recycling Methods – Description of Recycling Processes and Flow Chart’. 3 Council Directive 2004/12/EC, Official Journal of the European Communities, 18 February 2004. 4 Council Directive 2005/20/EC, Official Journal of the European Communities, 9 March 2005. 5 Verpackungsverordnung (Ordinance on the Avoidance of Packaging Waste), 12 June 1991. 6 s. pogutz, a. tencati, ‘Valutazione comparative dei risultati’ (Comparative evaluation of results), in: S. Pogutz, A Tencati (Eds), Dal Rifiuto al Prodotto (From Waste to Product), Ch. 13, EGEA, Milan, Italy, 2002. 7 Commission Decision 97/129/EC, Official Journal of the European Community, L 050/28 of 20 February 1997. 8 Regulation 282/2008/EC. 9 Regulation 1935/2004/EC of the Parliament and the Council, Official Journal of the European Community, L 338/4 of 13 November 2004. 10 cepi (confederation of the european paper industry), Special Recycling 2004 Statistics, October 2005, www.cpi.org. 11 cepi (confederation of the european paper industry), Special Recycling 2001 Statistics, October 2002, www.cpi.org.



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12 european recovered paper council, ‘The European Declaration on Paper Recovery’, Annual Report 2001, ERPC, Brussels. 13 European Standard EN 643:2001, available from the European national standardization bodies, e.g. http://catalogo.uni.com/EN/home.html. 14 Council of Europe Policy Statements concerning paper and board materials and articles intended to come into contact with foodstuffs. Technical Document No. 3: Guidelines on paper and board materials and articles made from recycled fibers, intended to come into contact with foodstuffs, 21 May 2002. 15 cepi (Confederation of the European Paper Industry), Guide for Good Manufacturing Practice for Paper and Board for Food Contact, CEPI, Brussels 2002. 16 cepe (European Council of the Industry of Painting, Printing Inks and Art Colors), Guide to Optimum Recyclability of Printed Graphic Paper, CEPE, Brussels, March 2002. 17 Disciplina igienica degli imballaggi, recipienti, utensili, destinati a venire in contatto con le sosanze alimentary o con sostanze d’uso personale (Hygienic discipline of packaging materials, containers and utensils intended to come in contact with foodstuffs or with substances of personal use), Gazzetta Ufficiale della Repubblica Italiana, 1973, 104, 20 April. 18 Kunststoffe im Lebensmittelverkehr, Carl Heymanns Verlag KG, January 2002. 19 Verpakingen – en Gebruiksartiklenbesluit, VGB, Koninklije Vermande/SDU Uitgevers, December 2002. 20 resolution ap (2002) 1 on ‘Paper and board materials and articles intended to come in contact with foodstuffs’, available at the Council of Europe website (http://cm.coe.int/stat/E/public/2002/adopted_texts/ResAP/2002xap1.htm). 21 Plastics Europe, Association of Plastics Manufacturers in Europe, An Analysis of Plastics Consumption and Recovery in Western Europe 2000, Plastics Europe, Brussels, 2002. 22 FAIR Project CT 98–4318 (Recyclability), available at http://www.ivv.fhg. dde/fair. 23 UK Department of Trade and Industry, Survey 2002, Plastic Recycling Report Recoup, May 2002. 24 Plastics Europe, Association of Plastics Manufacturers in Europe, ‘Assessing the Eco-efficiency of Plastics Packaging Waste Recovery, Summary Report, Plastics Europe, Brussels, 2000. 25 r. franz, m. huber, o.p. piringer, a.p. damant, s.m. jickells, l. castle, Study of functional barrier properties of multilayer recycled poly(ethylene terephthalate) bottles for soft drinks, Journal of Agricoltural and Food Chemistry, 1996, 44, 892–897. 26 r. franz, f. welle, Post-consumer poly(ethylene terephthalate) for direct food contact application – challenge text of an inline recycling process, Food Additives and Contaminants, 2002, 19(5), 502–511. 27 Recycling Forum, Final Report, 1999–2000, The European Commission, Brussels. 28 Enviros, WRAP Recycled Glass Market Study and Standards Review – 2004 Update, The Waste & Resources Action Programme, Banbury, Oxon, 2004. 29 i. boustead, ‘Theory and definitions in ecobalances’, in: J. Brandrup et al. (Eds), Recycling and Recovery of Plastics, Hanser, Muncher, Germany, 1996. 30 p. fink, ‘Methods and approaches for the evaluation of ecobalances’, in: J. Brandrup et al. (Eds), Recycling and Recovery of Plastics, Hanser, Muncher, Germany, 1996.


13 Recycled plastics for food applications: improving safety and quality V. Komolprasert and A. Bailey, Food and Drug Administration, USA

13.1

Introduction

The use of post-consumer recycled plastics for food packaging applications emerged in the 1990s and was driven by the interest of industry in mitigating the solid waste problems that were partly contributed to by plastic packaging. The use of recycled plastics for food packaging has continued in recent years and will likely increase due to the high price of crude oil, a feedstock for the petrochemicals used in the manufacture of plastics, as well as the recent advances in plastic recycling technologies that allow improved quality and safety of post-consumer recycled plastics intended for food packaging applications. Although the Food and Drug Administration (FDA) does not discourage such use, potential chemical contamination in the recycled plastics is a safety concern. In the absence of an explicit regulation that addresses the use of recycled plastics in food packaging, safety evaluation has relied on the recommendations described in the most recent version of the FDA’s recycled plastics guidance document, Use of Recycled Plastics in Food Packaging: Chemistry Considerations (FDA 2006). Since 1990, the FDA has issued more than 100 no-objection letters (NOLs) to companies that have demonstrated the capability of their recycling processes to produce recycled plastics of purity suitable for the proposed foodcontact use. This chapter will focus on recent efforts at improving the safety and quality of recycled plastics for food-contact applications in the context of the FDA’s recent recycled plastics guidance document (FDA 2006).


Recycled plastics for food applications: improving safety and quality

13.2

327

Plastic food packaging and the environment

Plastics were originally developed as synthetic substitutes for natural materials, such as rubber, wood, and metals. Over the last several decades, research in this area has made numerous advances toward development of new plastics for a variety of end-use applications. Plastics are used to manufacture an endless number of relatively inexpensive consumer products, such as household goods, toys, and food packaging. In turn, we have become so accustomed to the ubiquitous presence of plastics that it is difficult to envision our life without plastics. Advances in the development of new packaging materials and processes have shaped the way we package, deliver, and consume products (Komolprasert 2006). The emergence of fast-food outlets in the 1950s and their ever increasing popularity have created a demand for new kinds of packaging, including disposable single-serve packaging and bulk packaging for readyto-cook food portions. As thermoplastics became more readily available, the 1960s marked the growth of convenience and prepared food packages. However, as the use of plastics has increased, so has the consumer’s concern about the environmental costs and benefits associated with the use of plastics. In particular, the use of plastics has enabled the replacement of natural materials as well as the development of innumerable disposable products, such as plastic packaging, and as a consequence there are environmental impacts associated with the production and disposal of plastics. Plastics generally do not biodegrade quickly and remain in the environment for a very long time. Over the last several years, the plastics industry has adopted various approaches to plastics recycling in an effort to mitigate the solid waste concerns. The early 1990s marked the emergence of plastic recycling which has become one successful remedy to the increased generation of solid waste that would normally be disposed of in landfills. Based on the United States Environmental Protection Agency (EPA 2005) report, the United States produced more than 245 million tons (M tons) of municipal solid waste (MSW), a decrease of nearly 2 M tons from 2004. This decrease has been attributed, in part, to the decline in individual waste generation to about 4.5 pounds per person per day (lbs/p/d) and an increase in individual recycling of nearly 1.5 lbs/p/d. The EPA (2005) reported that recycling, including composting, diverted 79 M tons of material away from disposal in 2005, up from 15 M tons in 1980, when the recycle rate was just 10% and 90% of MSW was being burned with energy recovery or was disposed of by landfilling. The recycling trends across the board are generally up with container and packaging recycling increased to 40%. Among the materials recycled, paper was recycled at a rate of 50%, polyethylene terephthalate (PET) soft drink bottles at 32%, and high-density polyethylene (HDPE) milk bottles at a rate of 29%.


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13.3


The recyclability of packaging plastics

Several types of plastics are used in packaging. In order to provide a consistent national system that facilitates the collection and recycling of postconsumer plastics through the normal channels for collecting recyclable materials from household waste, the Society of the Plastics Industry (SPI) developed the resin identification code (the material container code) system for common plastics used in the manufacture of containers. The SPI code system applies to six homogeneous plastics and one heterogeneous material category as follows: 1 for PET, 2 for HDPE, 3 for polyvinyl chloride (PVC), 4 for low-density polyethylene (LDPE), 5 for polypropylene (PP), 6 for polystyrene (PS), and 7 for other (multi-layered plastics). The success and viability of recycling now largely depends on a community’s resources and structure, which include recycling programs (i.e. curbside collection, drop-off and/or buy-back centers) and the availability of markets for recovered and recycled materials. According to the 2005 National Post-Consumer Plastics Bottle Recycling Report (APR 2007), the steady growth of all recycled plastic bottles is primarily due to the adoption of ‘all plastic bottles’ curbside collection programs, where consumers put all types of plastic bottles into their recycling bins. Compared with programs that only accept bottles coded as 1 (PET) and 2 (HDPE), all plastic bottle and other co-mingle collection programs simplify the decisions of consumers, which often results in more bottles being collected for recycling. Despite such curbside collection programs, PET and HDPE comprise over 96% of the plastic bottle market. According to the 2005 report (APR 2007), the total number of pounds of all recycled post-consumer plastic bottles grew from about 400 million lbs (M lbs) in 1990 to 1500 M lbs pounds in 1999 and to about 2102 M lbs in 2005. Of the 2102 M lbs of all plastics recycled in 2005, 1170 M lbs were from PET bottles, 922 M lbs from HDPE bottles (natural and pigmented) and about 10 M lbs from PP bottles. Thus, PET and HDPE bottles comprise greater than 99% of the total plastics recycled.

13.3.1 Recycling of polyethylene terephthalate bottles The recyclabilty of PET bottles has been realized technically and economically, resulting in the continued growth of PET recycling markets according to the 2005 Post-Consumer PET Container Recycling Activity Report (APR 2006). The report shows that the use of PET resin for the production of bottles and jars continued to grow in 2005, with an overall growth rate of about 9.4%, fueled primarily by strong growth in water and isotonic beverages. About 5.1 billion pounds (B lbs) of PET bottles and jars were available in the United States for recycling in 2005, while 1.17 B lbs



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of post-consumer PET bottles were collected and sold in the United States for recycling in 2005. Thus, the gross PET recycling rate was about 23% for 2005. Of the 1.17 B lbs of PET bottles recycled in 2005, 489 M lbs (41.2%) were exported. US reclaimers imported 109 M lbs of post-consumer PET bottles, and purchased 47.2 M lbs of alternative feedstock, including preconsumer bottles, post-consumer strapping, and other unprocessed industrial scrap, a net result of about 837 M lbs of PET recycled by US recyclers in 2005. By the end of 2005, there were 12 recycling plants operating with a total capacity of 917 M lbs. Thus, the 837 M lbs recycled in 2005 was about 91% of reclamation plant capacity. The total pounds of post-consumer recycled PET (PCR PET) generated in 2005 were used for end products as follows: 54% fiber, 15% strapping, 13% food and beverage bottles, 8% sheet and film, 7% non-food bottles, and 3% other products. Clearly, PCR PET is primarily used with non-food products, with carpet and strapping applications dominating the PCR PET market. 13.3.2 Recycling of high-density polyethylene bottles and other plastics According to the 2005 National Post-Consumer Plastics Bottle Recycling Report (APR 2007), the HDPE bottle recycling rate increased slightly from 25.9% in 2004 to 27.1% in 2005. Of the 922 M lbs of HDPE bottles recycled in 2005, 162.4 M lbs (17.6%) were exported. The PP recycling rate also increased slightly from 3.2% in 2004 to 5.5% in 2005. PET and HDPE constitute more than 96% of the plastic bottle market, followed by PP with a market share of about 2%. PP bottles are commonly recycled with HDPE. PP does not have a significant impact on the properties of recycled HDPE resins when included at up to 5% of the total weight. Although PP bottles are recovered, most PP is derived from the recovery of PP closures during PET recycling. Other resins (codes 3, 4, 6 and 7) are recyclable but the production and recycling quantities of bottles manufactured from these resins are relatively small and are unavailable. Bottles coded 7 are commonly made of HDPE or PP with a barrier material layer added for protecting a sensitive product. These containers are normally recycled and counted as HDPE bottles. In 2005, the HDPE bottle recycling industry consisted of 29 companies. However, over 83% of the recycled HDPE was processed by the six largest companies. Material supply continued to be a major concern for HDPE reclaimers as the demand from export markets increased and outpaced the increase in HDPE bottles recycled. The end-use markets for domestic recycled HDPE bottles are 100% non-food applications, including: 43% non-food bottles; 22% pipe; 12% lawn and garden products; 9% lumber; 7% film and sheet; 4% automotive; 2% pallets, crates and buckets; and 1% other.


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13.4


Recycling processes

The possibility that chemical contaminants in plastics feedstock may remain in the recycled material and potentially migrate to food is one of the major considerations for the safe use of recycled plastics for food-contact applications. Any recycling process for food-contact materials must be effective in removing contaminant levels in the finished recycled plastic to sufficiently low levels that ensure that the recycled material is of purity suitable for the intended food-contact use. According to the EPA, ‘recycling’ is considered to be the processing of waste to make new articles. Recycling is a waste management practice, and so is reuse. Recycling is different from reuse. The post-consumer bottles intended for reuse will be simply reused in the original form, such as refillable bottles, which are not made to be waste for subsequent recycling. As such, the reuse of the bottles is not considered a recycling process, but rather one form of waste reduction (source reduction) that minimizes the amount of material entering the environment. Post-consumer plastics can be recycled using different recycling processes. Based on EPA’s nomenclature, there are three distinct approaches to the recycling of plastic packaging materials and these are referred to as primary recycling, secondary recycling, or tertiary recycling. These three recycling processes are further described and discussed below (FDA 2006).

13.4.1 Primary recycling (pre-consumer scrap) Primary recycling refers to the use of pre-consumer industrial scrap and salvage to form new packaging, a common practice in industry. The industrial scrap (excess or trims) produced during the manufacture of foodcontact articles is not expected to pose a hazard to the consumer. In practice, the scrap is pre-consumer, unused material. The recycling of this scrap is acceptable as long as it is handled and used according to good manufacturing practices (GMPs). Therefore, the testing protocols described below do not apply to pre-consumer scrap. However, if the scrap is collected from several different manufacturers, the recycler should determine if the level and type of adjuvants in the recycled plastic comply with the existing regulations applicable to the adjuvants.

13.4.2 Secondary recycling (physical reprocessing) Secondary recycling refers to the physical reprocessing – which typically includes grinding, remelting, and reforming – of post-consumer plastic packaging materials. The basic polymer is not chemically altered during the process, in contrast to tertiary recycling. In secondary recycling, postconsumer plastic containers are pre-sorted by polymer type, ground to flake, washed with water and surfactants to remove contaminants, and then dried



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before thermal processing. This part of a secondary recycling process is often referred to as conventional recycling. As for thermal processing, the recycled polymers may undergo different thermal remelting and reforming conditions, such as the use of vacuum stripping or other procedures, which could influence contaminant levels in a given polymer. In some cases, the reprocessed material may be blended with virgin polymer during the grinding or melting phases. Because secondary recycling processes are less effective than tertiary recycling processes, secondary recycling generally involves implementing controls of the source of post-consumer plastic containers (see Section 13.5.1). 13.4.3 Tertiary recycling (chemical reprocessing) Tertiary recycling refers to chemical reprocessing and involves subjecting post-consumer plastic packaging material to chemical treatment whereby its components are isolated, purified, and reprocessed. Tertiary recycling is primarily aimed at regenerating purified starting materials for subsequent use in manufacture of a polymer. Chemical reprocessing may involve depolymerization of the post-consumer polymer with regeneration and purification of resulting monomers or oligomers. The monomers or oligomers are then repolymerized and the regenerated or reconstituted polymer is formed into new packaging. Regenerated monomers, polymers, or both may also be blended with virgin materials. The regeneration process may involve a variety of monomer/polymer purification steps in addition to washings – such as distillation, crystallization, and additional chemical reactions. As would be expected, tertiary recycling is only applicable to condensation polymers, like PET. Based on a comprehensive review of all surrogate testing data submitted over the past decade for tertiary recycling processes for PET and polyethylene naphthalate (PEN), the FDA (2006) has concluded that tertiary recycling of PET or PEN by methanolysis or glycolysis results in the production of monomers or oligomers that are readily purified to produce a finished polymer that is suitable for food-contact use. Therefore, the FDA no longer recommends that such recyclers submit testing data for PET or PEN for agency evaluation.

13.5

Improving the recyclability of plastic packaging for food use

In order to improve the recyclability of plastic packaging for food-contact use, controls on the source of post-consumer plastics as well as limitations on the use of the specific recycled article are often needed to ensure the quality and safety of the recycled materials for the proposed food-contact application.


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These improvements are discussed below with reference to the FDA web listing (FDA 2007a) of NOLs; these NOLs represent the agency’s opinion specifically applied to a proposed recycling process (not a recycled product) which has demonstrated that it is sufficiently effective in removing contaminants from post-consumer recycled feedstock to levels that the FDA would equate to a negligible risk to public safety. As such, the agency concludes that the proposed recycling processes can produce recycled material of a purity suitable for food-contact applications (see Section 13.6.3). 13.5.1 Controls on feedstock source and limitations on use Most plastics are processed with adjuvants, which are of particular concern to the FDA when these plastics are recycled for food-contact use (FDA 2006). There are two reasons for this concern. First, adjuvants in postconsumer plastics should not react during the recycling process to form substances whose safety has not been evaluated by the FDA. Second, if additional adjuvants are added to produce a recycled polymer with the desired qualities, the type and total amount of these adjuvants must comply with the limitations as described in the existing regulations. Use of a new adjuvant in a recycled polymer, or an approved adjuvant at levels in excess of what is currently authorized for the virgin polymer, is regarded as a new food additive (new use) and would require a food-contact notification (FCN) or other submission to the FDA before it could legally be marketed for use. If a recycler has little or no control over the feedstream entering the recycling facility (e.g. commingling of food-contact and non-food-contact materials), the recycling process may be inappropriate to produce recycled polymers for food-contact articles (FDA 2006). The potential for postconsumer food-contact materials to be recycled together with other postconsumer, non-food-contact plastics may be minimized or eliminated with effective source controls or sorting procedures. On the other hand, even if the incoming feedstock were composed of food-contact materials, other limitations in addition to the use level above (i.e. such as food types and/or conditions of use) could be compromised in the finished recycled product. For example, an adjuvant approved for use only in contact with aqueous food (food-type) or only for refrigerated use (condition of use) could be incorporated into recycled packaging intended for high-temperature use with fatty foods. Thus, the resulting food-contact article made of the finished recycled material would not comply with the existing regulations. However, the FDA has found that for secondary recycling submissions, this concern is often mitigated by the development of sorting procedures that result in reprocessing of only a single characteristic container, e.g. PET beverage bottles. With specific regard to secondary recycling, the FDA (2006) recommends that secondary recyclers address the above concerns, for example, by implementing source controls and sorting procedures on the incoming feedstock,



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in addition to use limitations (such as use at room temperature or below) or food-type restrictions (such as dry or aqueous foods only) on the finished recycled packaging. By far the majority of submissions to the FDA have involved secondary recycling processes that employed one or more of these factors and these were critical to the FDA’s evaluation of the individual processes. Controls of the source of post-consumer PET containers destined for recycling for food-contact applications were the subject of studies conducted by Bayer (2002), who experimentally determined the composition of food and non-food PET containers in feedstreams collected by both deposit and curbside systems. Bayer reported that PET feedstreams from deposit systems contained 100% food containers, whereas curbside feedstreams contained 0.04–6% non-food containers. Both collection systems reportedly minimized levels of potential contaminants derived from nonfood containers. Although several substances were reportedly absorbed in the PET, Bayer (2002) reported that a proprietary decontamination process used was efficient at removing these substances to a level below the level of no safety concern. 13.5.2

Improving the recyclability of polyethylene terephthalate containers The recycling of post-consumer PET bottles emerged in the early 1990s when several studies were initially conducted to recycle post-consumer 2-L PET bottles for food-contact applications. PET is an expensive polymer and is generally used without additives for many food packaging applications, such as soft drinks and water bottles, making the recycling of post-consumer PET soda bottles an ideal candidate for food packaging applications. The original 2-L PET bottle had a round bottom supported by an HDPE base cup, and was designed to prevent damage caused by impact during shipping and handling. With the advances in blow-molding technologies, a new design for the 2-L PET bottle evolved with no HDPE base cup. The quality of regenerated PET material was improved by eliminating the HDPE that would possibly be mixed with PET during PET bottle recycling. Current PET beverage bottles in all sizes can be made to stand alone without any HDPE base support, which serves to improve both the recyclability and recycling rates of PET. Among the three recycling processes discussed, tertiary recycling initially received the most attention from the industry because it resembles the process used to produce virgin PET. PET is a condensation polymer, and is synthesized by condensation reactions that generate water as a byproduct. Its reverse reaction, called hydrolysis, in the presence of water can be used to depolymerize PET to produce starting monomers or oligomers, which are regenerated and purified before they are repolymerized by a condensation reaction to produce new PET (Novak and Oblath 1995).


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Chemical recycling by hydrolysis depolymerization of post-consumer PET can be achieved using water (Kao et al. 1998, Mancini and Zanin 2004), acids (Mishra et al. 2003a, 2003b, Mancini and Zanin 2007), or bases (Mishra and Goje 2003, Goje et al. 2004, 2005). Hydrolysis of PET may also be induced using chemicals other than water, acids, or bases to depolymerize PET to intermediates or polymer precursors instead of monomers. Methanolysis refers to the chemical recycling of post-consumer PET using methanol to initiate depolymerization of PET to yield dimethyl terephthalate and ethylene glycol at around 200ºC. Glycolysis involves depolymerization of PET using ethylene glycol to yield bis (hydroxyethyl) terephthalate and other short-chain PET polymers (oligomers). These oligomers are purified for subsequent repolymerization to produce PET for food-contact applications. Although the use of chemical recycling for post-consumer PET containers was preferred early on, such chemical recycling processes are energyintensive and costly, often making the resultant recycled PET material more expensive than virgin material. In order to make PET bottle recycling more economically viable, secondary (also known as physical) recycling processes are considered to be less costly and more economically feasible. Attempts to improve secondary recycling processes for recycling of PET bottles for food-contact applications have been the subject of studies by Franz and Welle (2002) and Franz (2002). Since 1990, the FDA has issued about 20 NOLs to companies for chemical recycling processes (i.e. methanolysis and glycolysis) and more than 60 NOLs for physical recycling processes, the majority of which were applied to PCR PET. 13.5.3

Improving the recyclability of plastic containers other than polyethylene terephthalate Besides PET, other polymers such as HDPE, LDPE, PP, PS, and PVC are also widely used and can be recycled to a certain extent. Among these plastics, HDPE is recycled the most. Unlike PET, HDPE is an addition polymer and is recycled by a secondary recycling process. The recyclability of post-consumer HDPE containers for food packaging is more difficult than for PET since HDPE tends to sorb more chemicals than PET. An attempt to recycle post-consumer HDPE milk bottles for foodcontact use was made in 1991 by the Plastics Recycling Task Force (PRTF), a coalition formed by collaboration of the National Food Processors Association and the SPI. The PRTF conducted a study to evaluate the effects of secondary recycling processes in removing chemicals from the post-consumer recycled HDPE intended for food contact (Allen and Blakistone 1995). The study applied a testing protocol developed by the PRTF using surrogates in the challenge test that were similar to those used in the FDA’s



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testing protocol (see Section 13.6.2 below). Based on the study parameters, the surrogates trimethylpentane, methyl stearate, and xylene were not sufficiently removed by the secondary recycling processes used in the study; this was attributed to the similar solubility parameters for the surrogates and HDPE. The recycled HDPE was considered not suitable for foodcontact use. Attempts to develop secondary recycling processes for HDPE for food contact have continued, and some of these have been the subject of FDA reviews for food contact under defined use conditions. Since 1990, the FDA has issued 26 NOLs to companies for secondary recycling processes for post-consumer PS, HDPE, LDPE, and PP. Of the 26 NOLs, 15 NOLs were applied to secondary recycling processes for PS, 8 NOLs were for HDPE, and 3 NOLs were for PE/PP. In comparison with the number of letters issued for PET recycling processes (about 80), it is clear that the use of recycled plastics other than PET for food contact is much lower. 13.5.4 Super clean processes As advances in new technologies evolve, secondary recycling processes have been improved with the development of so-called ‘super clean’ processes (Franz 2002). The ‘super clean’ process has primarily been developed and applied to PCR PET. The ‘super clean’ process is a specially designed thermal treatment which is capable of removing chemical contaminants (most volatiles) while it increases the intrinsic viscosity of recycled PET to a level required for bottle grade PET, i.e. an intrinsic viscosity of 0.75– 0.82 dL/g. The ‘super clean’ process conditions resemble the solid state polycondensation conditions applied during the manufacture of PET. ‘Super clean’ processes are proprietary, but are generally known to involve combinations of standard physical and mechanical recycling processes with heat treatment – such as high-temperature washing, high-temperature and -pressure treatments, and the use of pressure/catalysts and filtration – to remove residual chemical contaminants and raise the intrinsic viscosity. ‘Super clean’ processes are the subject of several secondary recycling processes for post-consumer PET recycling for food packaging, which involve a thermally deep-cleaning decontamination step applied to conventional secondary recycled flake (Welle and Franz 2007). The decontamination is carried out at high temperatures under vacuum or inert gas, such as nitrogen, to prevent oxidation that causes yellowing and deterioration of the physical properties. The ‘super clean’ process has become a preferred process for PET recycling to produce recycled material intended for food packaging applications. The process can be practically designed using combinations of physical, mechanical, and thermal treatments, depending on the type of plastic recycled and other steps that may be involved. New ‘super clean’ processes continue to emerge, some of which may be applicable to recycling of plastics


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other than PET. Welle (2005) recently reported on a ‘super clean’ process that was effective in cleaning post-consumer HDPE to produce recycled HDPE that is of suitable purity for use in making a new HDPE milk bottle. Since 1996, the FDA has issued 32 NOLs to companies for secondary recycling processes that are regarded as ‘super clean’ processes, primarily with the inclusion of solid state polycondensation steps for PCR PET.

13.6

The safety and quality of recycled plastics

The safety and quality of recycled plastics used in food-contact articles is the responsibility of the manufacturers of the food-contact articles. Any substance (called a food-contact substance) used in the manufacture of food-contact articles must be in compliance with existing regulations. However, at present there are no regulations specific to the use of recycled plastics in food-contact articles. Thus, manufacturers must ensure that the recycled plastic, like virgin material authorized for food contact, is of a purity suitable for its intended use in food contact and will meet the existing specifications and limitations with respect to both the polymer and adjuvants (as discussed above relative to source control) as described in Title 21 of the Code of Federal Regulations (denoted 21 CFR) Parts 174 through 179. In particular, recycled polymers should be identical to their virgin counterparts listed under 21 CFR 177 (Indirect Food Additives: Polymers) or that are the subject of an effective FCN. In 21 CFR 174.5 (General Provisions Applicable to Indirect Food Additives), paragraph (a) prescribes that the use of food additives should be under conditions of GMPs. In particular, subparagraph (a)(2) states ‘Any substance used as a component of articles that contact food shall be of a purity suitable for its intended use.’ Subparagraph (b) specifies that a regulation prescribing safe conditions of use for a substance for food contact should also comply with any other provision of the Federal Food, Drug, and Cosmetic Act (the Act). For example, the regulated food packaging material shall not impart odor or taste to food rendering it unfit for human consumption within the meaning of adulterated food under Section 402(a)(3) of the Act. These requirements, which are described in 21 CFR, Parts 174 through 179, serve as the framework for the safety assessment as outlined in the 2006 recycled plastics guidance document. The meaning of ‘purity suitable for the intended use’ is linked in that document to the establishment of an acceptable upper limit of dietary exposure (on the order of 0.5 ppb or less for contaminants) to chemical contaminants based on the intended use of the recycled material. Therefore, the residual concentration of a contaminant in the plastic that corresponds to this upper limit, as well as contaminant migration levels to food, should be determined.



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13.6.1

The FDA’s guidance for industry for testing the efficacy of plastic recycling processes Since there are no regulations that explicitly address the use of recycled plastic in food-contact articles, in response to industry requests for guidance and opinions on specific applications of recycled plastics, the FDA originally developed a guidance document, Points to Consider for the Use of Recycled Plastics in Food Packaging: Chemistry Considerations, in May 1992 (Kuznesof and VanDerveer 1995). The May 1992 and updated December 1992 ‘points’ reflected the agency’s opinions on issues that involve collection of feedstock and recycling processes by which the safety of finished recycled plastics can be affected. The guidance document was developed with the goal of assisting manufacturers of food packaging in evaluating processes for producing packaging from post-consumer recycled plastic. The December 1992 guidance document addressed the possibility that chemical contaminants in post-consumer plastics subjected to a recycling process may remain in the recycled material and could migrate to food. Thus, chemical contaminants were and still are a major consideration for the safe use of recycled plastics for food-contact applications. Other aspects of recycled plastics, such as microbial contamination and structural integrity of the recycled plastic, are also important, but they are not addressed in the guidance document. In order to evaluate a recycling process, the guidance document recommends a testing protocol for developing chemistry data that would be useful for determining the adequacy and efficacy of the recycling process to remove chemical contaminants from the recycled material intended for use in contact with food. The August 2006 guidance document, Use of Recycled Plastics in Food Packaging: Chemistry Considerations (FDA 2006), supersedes the December 1992 guidance. The August 2006 guidance document includes changes to the testing protocol and safety evaluation procedures that were previously recommended in the December 1992 guidance. Additional information on the August 2006 guidance document is available on the FDA website (FDA 2006). 13.6.2 Testing protocol for evaluating plastic recycling processes The August 2006 guidance document addresses two different situations by which recycled plastic could become contaminated. 1 2

Incidental chemical contamination of post-consumer food containers by consumer misuse. Inclusion of non-food containers in a recycling process.

Consumer misuse Incidental chemical contamination of post-consumer food containers by consumer misuse was originally addressed in the December 1992 guidance


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document. Consumer misuse or abuse involves secondary storage of, e.g., pesticides or automotive chemicals. For recycled plastics to be deemed suitable for food contact, the ability of a recycling process to remove contaminants from plastic that has been subjected to such consumer misuse or abuse should be demonstrated. The FDA continues to recommend that any testing protocol should simulate consumer misuse by exposing virgin polymer (either in container form or as flake) to selected surrogate contaminants and then running the exposed or ‘challenged’ polymer through the recycling process. Subsequent analysis of the processed polymer for the surrogate contaminants would provide a means of evaluating the efficacy of the recycling process. The FDA (2006) recommends that recyclers use surrogate materials that have a variety of chemical and physical properties to simulate consumer misuse. In particular, the surrogate contaminants should represent ‘common’ materials accessible to the consumer and include a volatile polar organic substance, a volatile non-polar organic substance, a non-volatile polar organic substance, a non-volatile non-polar organic substance, and a heavy metal salt (not needed for PET). The FDA’s recommended surrogates for simulating consumer misuse are shown in Table 13.1. The FDA believes that one surrogate per category is sufficient for testing the proposed recycling process. The FDA recommends that a challenge test be carried out using an actual plastic container or flaked plastic. Containers made of the virgin plastic of interest are contaminated or ‘challenged’ by filling them with the surrogate contaminants, either ‘neat’ or in ‘at use’ concentrations, using a Table 13.1 The FDA’s recommended surrogates for simulating consumer misuse (FDA 2006) Properties

Recommended surrogates

Volatile polar

Chloroform Chlorobenzene 1,1,1-Trichloroethane Diethyl ketone

Volatile non-polar

Toluene

Non-volatile polar

Benzophenone Methyl salicylate

Non-volatile non-polar

Tetracosane Lindane Methyl stearate Phenylcyclohexane 1-Phenyldecane 2,4,6-Trichloroanisole

Heavy metal

Copper (II) 2-ethylhexanoate



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solvent such as hexane as a diluent. An alternative approach that would reduce the amount of potentially hazardous wastes is to soak several kilograms of flaked virgin plastic of the type actually used in the recycling process in the selected contaminants at either ‘neat’ or ‘at use’ concentrations. A mixture, or ‘cocktail’, of the contaminants could be used so long as the components of the ‘cocktail’ do not react with each other. The recommended minimum concentrations of surrogates for a ‘cocktail’ are 1% (w/w) for non-volatiles and 10% (v/v) for volatiles in an appropriate, nonaggressive solvent to the polymer. Once the bottles are filled or after the contaminants are thoroughly mixed with the flakes, the bottles or flakes should be stored sealed for 2 weeks at 40ºC with periodic agitation. After the contaminants are drained and the bottles or flakes are rinsed, the concentration of each surrogate should be determined in the polymer. The challenged polymer should then be subjected to the proposed recycling process, and regenerated components or packaging material formed from the reprocessed polymer should be analyzed for residual contaminants. Contaminant levels in the recycled polymer can then be used to estimate contaminant levels in food using one or more of the methods described below (see Section 13.6.3) Inclusion of non-food containers as feedstock The use of PET has expanded beyond carbonated soft drinks to include other foods and beverages as well as non-food products. As a result of curbside collection programs, both food and non-food plastic containers (e.g. household cleaners, furniture polish, shampoos, soaps, pesticides, or motor oil) are being collected together for recycling. Therefore, there is interest in recycling processes that can account for the inclusion of both food and non-food plastic containers as feedstock to produce recycled material for food contact. With respect to non-food containers, the two issues of concern to the FDA include the chemical contaminants introduced by non-food-contact containers and adjuvants used in the non-food-contact containers, as well as the presence of these adjuvants in the recycled polymer. For the adjuvant issue, the FDA has determined that this would not be a concern for PET because the plastics industry has verified that all PET resin used to manufacture containers in the United States is authorized for food-contact use, i.e. food-grade PET is used to manufacture both food and non-food containers. However, the issue of chemical contaminants introduced by non-food PET containers is still present. In order to consider the inclusion of non-food PET containers as feedstock to produce recycled material for food-contact use, the FDA recommends that a challenge test be conducted and carried out with the same method as recommended when consumer misuse is investigated. Additionally, the FDA recommends that recyclers who wish to include non-food PET


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Table 13.2 Sorption of surrogate contaminants into PET after 365 days at 25 °C (FDA 2006), the FDA’s recommended initial concentrations for simulating use of non-food plastic containers as feedstock Properties

Surrogate

Sorption value (mg/kg)

Volatile polar

Chloroform Chlorobenzene 1,1,1-Trichloroethane Diethyl ketone

4860a 1080b 1050b 4860c

Volatile non-polar

Toluene

780a

Non-volatile polar

Benzophenone Methyl salicylate

49a 200a

Non-volatile non-polar

Tetracosane Lindane Methyl stearate Phenylcyclohexane 1-Phenyldecane 2,4,6-Trichloroanisole

a b c d e

154a 750a 150d 390b 170b 1100e

Begley et al. (2002). Demertzis et al. (1997). Assumed to be the same as chloroform, based on similar molecular weights. Assumed to be the same as tetracosane, based on the FDA’s experimental results. Based on the value for lindane with molecular weight correction.

containers in their feedstock establish that the concentrations of the surrogates in challenged PET flake, prior to its being run through their recycling process, are greater than or equal to the sorption values shown in Table 13.2 (FDA 2006). These minimum concentrations were derived using the FDA’s experimental sorption results (Begley et al. 2002) and data from the literature (Demertzis et al. 1997), as well as the Fickian diffusion model (Begley et al. 2002), to predict the amount of a contaminant (represented by the surrogate contaminant) that will sorb into a PET bottle during a period of 1 year at 25ºC, the shelf-life and use temperature of a typical non-food substance packaged in PET. The FDA does not recommend that the minimum concentrations be included in surrogate testing for a recycling process that uses only food containers as feedstock. If only food containers are used as feedstock, simply exposing virgin flake or intact bottles to the surrogate cocktail for 2 weeks at 40ºC is sufficient to model incidental misuse of containers by consumers. 13.6.3 Safety evaluation As discussed above, the safety of a recycled plastic for food-contact use is determined in the context of the meaning of ‘purity suitable for the intended



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use’, which is based on an acceptable upper limit of dietary exposure to chemical contaminants from the proposed use of the recycled material. Using the scientific analysis supporting the threshold of regulation approach to evaluating components of food-contact articles, the FDA has determined that the estimated daily intake (EDI) should not exceed 1.5 µg/person/day (equivalent to a 0.5 ppb dietary concentration (DC)), the level that the FDA would generally consider to be of negligible risk for a contaminant migrating from recycled plastic. Using the 0.5 ppb DC level, a maximum acceptable level for a chemical contaminant in recycled food-contact articles that can form the basis of GMPs can be determined. Based on the guidance document (FDA 2006), the maximum acceptable contaminant level in the plastic that would result in an EDI of no more than 1.5 µg/person/day can be determined using one or more approaches: the assumption of 100% migration, conducting a migration study, or using migration modeling. Each of these approaches is discussed below. Assumption of 100% migration An assumption of 100% migration to food is a conservative approach and may be regarded as the worst-case scenario in which the total amount of the residual contaminant in the plastic migrates to food. Then, the maximum acceptable level of a contaminant in the polymer that would result in an EDI equal to 1.5 µg/person/day is calculated based on the polymer’s density and thickness, the FDA’s assumptions that an individual consumes 3 kg of food per day, that 10 g of food contacts 6.45 cm2 of container, a consumption factor (CF) of 0.05 for recycled polymers (see below), and a food-type distribution factor (fT) of 1.0 for all food types. The following relationships are used in this calculation: DC = CF × <M> = CF × Σ(M)(fT) EDI = DC × 3 kg food/person/day where <M> is the weighted-average concentration of a migrant (contaminant) in food, derived by multiplying the individual migration values (M) by the individual fT values for aqueous, acidic, alcoholic, and fatty foods. In the case of 100% migration to food, the maximum M value for a migrant (contaminant) is 10 ppb (µg/kg) to food. The maximum acceptable level of a residual contaminant in a polymer (Co) that corresponds to a maximum of 10 ppb in food will depend on the polymer density, polymer thickness and CF. Using a CF of 0.05, a thickness of 0.5 mm (20 mil), and the densities of several polymers, the August 2006 recycled plastics guidance document (FDA 2006) gives the maximum acceptable levels of a contaminant in each polymer (Co). For example, the maximum acceptable level of a contaminant in PET (density of 1.4 g/cm3) is 220 µg/kg but is 300 µg/kg for PS (density of 1.05 g/cm3). The calculated


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maximum acceptable levels also depend on the thickness of the packaging. The thicker the packaging, the lower the maximum residue levels must be to meet the 1.5 µg/person/day EDI limit. In the absence of market data, the FDA conservatively assumes a CF of 0.05 for use of a recycled polymer in food packaging. However, if a specialized use for a recycled polymer can be documented, it may be possible to estimate a lower CF for use in calculating a maximum acceptable contaminant level. Using this approach, industry can quickly determine whether a proposed recycling process can be shown to remove contaminants to maximum acceptable levels. If the proposed recycling process cannot be shown to remove contaminants to maximum acceptable levels under this scenario, then additional factors or limitations on use could justify a conclusion that the recycled package will not introduce contaminants into the diet at unacceptable levels. The additional factors/limitations on use that may result in an acceptable upper limit of dietary exposure include the use of a recycled/ virgin blend, source controls (see Section 13.5.1), restricted uses, the fraction of contaminant that migrates into food or a food simulant, or the use of an effective barrier. In cases in which recycled polymer is expected to be blended with virgin polymer, and thus contaminants in the recycled polymer are diluted with virgin polymer, the maximum acceptable contaminant level is calculated using the approach described above and is then divided by the fraction of recycled polymer in the blend. Migration testing The assumption of 100% migration to food is a simple and conservative approach, yet it often presents an unrealistic scenario. As a consequence, the maximum acceptable level of a contaminant that can be present in the recycled plastic would likely be lower than those values determined by migration testing. Secondary recycling processes often produce PET that is insufficiently cleaned to withstand 100% migration calculations for the residual surrogates. Under these circumstances, additional testing is often needed to demonstrate that the finished PET meets the 0.5 ppb DC limit. Migration testing is an alternative approach to evaluate the suitability of recycled polymers for food-contact uses. Full details on migration studies with food simulants can be found in the FDA’s chemistry guidance document (FDA 2007b). Migration studies should be conducted using the appropriate food simulants under the proposed use conditions for the recycled polymer. Migration testing conducted by Komolprasert et al. (1997) demonstrated that even though the residual concentrations of surrogate contaminants in recycled PET were higher than the maximum acceptable levels under the worst-case scenario (with 100% migration calculations) these contaminants did not migrate to food simulants at a level that resulted in a DC above 0.5 ppb.



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Migration modeling As a third alternative, diffusion and migration models may be used to estimate the migration level of contaminants from a polymer to food. Since migration studies are time consuming and costly, the application of diffusion and migration models has become a common method for calculating the dietary exposures to the incidental chemicals migrating from recycled polymers. Helmroth et al. (2002) discussed several predictive models for the migration of low molecular weight compounds from packaging materials into food. These models are based on semi-empirical diffusion equations derived from the experimental data. Piringer (2007) has recently described in great detail the fundamentals of mathematical modeling of chemical migration from food-contact materials based on the Fickian diffusion equations, which support the application of migration modeling to predict migration of contaminants from recycled polymers to food. Crank (1975) has shown that sorption and desorption by a sheet in which the concentration of a migrant in the sheet is initially uniform (such as in a bottle wall for desorption) and its surface concentration is constant (such as in a well-agitated food simulant), the mass transfer equation (derived from Fick’s second law) of the substance at a fixed temperature can be expressed by equation [13.1] (Crank 1975): Mt/M∞ = (1 + a)[1 − exp(t/a 2)erfc(t/a2)1/2]

[13.1]

where t = KDt/l . In this equation, Mt and M• are, respectively, the migration level at time t and the migration level at equilibrium (or ‘infinite’ time), a is the ratio of the volume of liquid phase to the volume of the sheet, D is the diffusion coefficient of the contaminant in the plastic at a given temperature, t is the time, and l is the thickness of the plastic, and the partition coefficient (K) of the contaminant at the surface between the plastic and food is assumed to be unity. The full thickness is used for a single-sided contact (i.e. a plastic bottle filled with a liquid) while half the thickness is used for a double-sided experiment (i.e. a plastic strip soaked in a liquid solution). Mt can be calculated by solving M• from M• = aCo/(1 + a), where a is the volume of the liquid solution and Co is the starting concentration of the contaminant in the sheet. In cases when t is very small (30 20 >30 nd

>30 >30 >30 >30 >30 >30 >30 nd

>30 >30 >30 >30 >30 >30 >30 nd

>30 >30 >30 >30 >30 >30 >30 nd

a

From L. Preziosi-Belloy, A. Ben Arfa, P. Chalier and N. Gontard (unpublished observations, 2007). Adapted from Ben Arfa et al. (2006). nd, non-determined.

b


Modified atmosphere packaging

407

Table 16.2 Synergistic effect (X, synergistic effect; O, no synergistic effect) in the vapour phase of volatile antimicrobial compounds based on two criteria: lag phase and growth rate MIC

SO2 Carvacrol Cinnamaldehyde AITC Ethanol (3.8 µmol l −1) (8576 µmol l −1) (328 µmol l −1) (32.5 µmol l −1) (3.9 µmol l −1)

Ethanol SO2 Carvacrol Cinnamaldehyde AITC

— O X O O

— X X X

— X O

— X

—

MIC, against P. notatum, of the volatile compound in the vapour phase (µmol of aroma compound per litre of atmosphere). Adapted from Tunc et al. (2007).

cinnamaldehyde, AITC–cinnamaldehyde and cinnamaldehyde–carvacrol. The advantage of these combinations is the reduction in the concentration of each agent and their relative impact on organoleptic properties. The strong antimicrobial activity of carvacrol, cinnamaldehyde and AITC confirmed that these compounds could be useful preservative agents in packaged food systems in the vapour phase. In addition, aroma compounds could be introduced into the paper coating matrix to create an antimicrobial MAP system. Understanding the relationship between chemical structure and antimicrobial activity of aroma compounds The antimicrobial activity of several essential oils has been attributed to the presence of phenolic compounds, i.e. thymol, eugenol and carvacrol for the efficiency of thyme, clove and oregano essential oils, respectively (Farag et al., 1989; Moleyar and Narasimham, 1992; Kim et al., 1995a; Tsao and Zhou, 2000; Lambert et al., 2001). The inhibitory effect of phenols could be explained by interactions with the cell membrane of micro-organisms and is often correlated with the hydrophobicity of compounds (Sikkema et al., 1995; Weber and de Bont, 1996). For instance, it has been reported that oregano essential oil induces changes in the permeability of the membrane of microorganisms (Pseudomonas aeruginosa and S. aureus), with a consequent leakage of proton, phosphate and potassium (Lambert et al., 2001). Among phenolic compounds, carvacrol, an isoprenyl phenol, has been reported to have one of the strongest antimicrobial activities (Kim et al., 1995b; Roller and Sheedhar, 2002; L. Preziosi-Belloy, A. Ben Arfa, P. Chalier and N. Gontard, unpublished observations, 2007). In order to use carvacrol as an antimicrobial agent in food preservation in a rational way, a good knowledge of its mode of action is required. For example, it is well known that grafting an antimicrobial agent on to a polymer can strongly reduce its antimicrobial efficiency (Appendini and Hotchkiss, 2001). The antimicrobial properties of carvacrol and two specifically synthesized compounds


408


Table 16.3 Physicochemical characteristics and molecular structure of carvacrol and its two derivatives at 25 °C Aroma compounds Carvacrol

Molecular structure

Molecular weight (g mol−1)

Log Pa

Maximum solubility in water (g l−1)b

CH3

150.22

3.52

0.11

162

4.08

0.033

192

3.59

0.097

OH

CH3

Carvacrol methyl ether

CH3

CH3 OCH3

CH3 CH3

Carvacryl acetate

CH3 O

CH3 O

CH3

CH3

a

Octanol/water partition coefficient (log P) was estimated by modelling soft: http://esc.syrres. com/interkow/examples.htm. b Solubility (S), was calculated from the following equation: log S = −0.95 log P + 2.40.

(Table 16.3) derived from carvacrol (carvacryl acetate and carvacrol methyl ether) were evaluated in both a liquid and a vapour state on a range of different micro-organisms (Ben Arfa et al., 2006). Neither carvacrol derivative inhibited the growth of the micro-organisms (Table 16.1). This supported the hypothesis that in addition to having hydrophobic properties that allow the compound to accumulate in the membrane, free hydroxyls are essential for the antimicrobial activity of carvacrol. Moreover, the hydroxyl group must be able to exchange its proton as a result of an adequate delocalized electron system. Thanks to its appropriate hydrophobicity, carvacrol can be accumulated in the cell membrane. Its hydrogen bonding and proton release ability may induce conformational modification of the membrane resulting in cellular death. Therefore particular attention should be paid to preserving or, if possible, improving these key factors when using such phenolic aroma compounds for their antimicrobial properties. This is really important when the structure of aroma compounds has to be modified in order to make it easier to graft them onto surfaces.



409

16.3.2 Processing and characterization of antimicrobial papers Protein-based films are among the most attractive biopolymers due to their barrier properties against moisture, oils, fats and volatile compounds (Gennadios and Weller, 1991; Gontard et al., 1992, 1993; Han, 2000; Guillard et al., 2003) and interesting selective gas permeability (Gontard et al., 1996; Mujica Paz and Gontard, 1997; Mujica Paz et al., 2005). Among the proteins that have been investigated, soy proteins are known to possess good film-forming properties, and are inexpensive and widely available. They have been used traditionally in the Far East for the production of edible films called ‘yuba’ (Gennadios and Weller, 1991). Several factors are known to affect the film formation such as pH, heat treatment, ionic strength plasticizers, protein concentration and conformation (Gennadios et al., 1992, 1993; Subirade et al., 1998). Soy protein films have poor moisture barrier and mechanical properties but good oxygen barrier properties in dry conditions and proteins are effective carriers for aroma encapsulation (Brandenburg et al., 1993; Kim and Morr, 1996; Kim et al., 1996). To make the most of all these advantages, an antimicrobial paper was developed by coating a support paper with a soy protein isolate (SPI) layer acting as the inclusion matrix for the controlled release of the volatile aroma compound. Coating papers with soy protein isolate as the inclusion matrix of carvacrol Antimicrobial papers were prepared by coating paper with SPI solution as the inclusion matrix of carvacrol (Ben Arfa et al. 2007a). The addition of carvacrol (30% w/w of SPI) to an SPI solution (10% w/v) prepared at 25 ºC induced soy protein aggregates and a decrease in viscosity. Heat treatment (50, 70 or 90 ºC) of SPI solutions with added carvacrol improved homogeneity, reduced particle size and increased the viscosity of the solutions (Fig. 16.6). The aggregated structure of SPI in the presence of carvacrol at 25 ºC may have acted as a trapping device, leading to low carvacrol losses during the paper coating and drying processes (9.6% compared with 37% after heat treatment at 90 ºC) and to lower release rates, especially during the first 3 days: 0.04 g m−2 day−1 and 0.31 g m−2 day−1 when SPI coating solutions were prepared at 25 and 90 ºC, respectively. Although a better homogenization of the SPI solutions was observed, their heat treatment at 90 ºC led to high carvacrol losses during the coating and drying processes. Moreover, the high increase in viscosity and gel formation during storage would present a challenge for industrial use. Heating SPI solutions at 50 ºC appeared to be a good compromise, taking into account the SPI solutions’ homogeneity, viscosity and low carvacrol losses during the coating and drying processes. Regardless of the heat treatments received by the SPI solutions, residual carvacrol quantities in the coated papers after 50 days of storage under air flow at 30 ºC and 60% RH ranged between 0.6 and 0.7 g m−2. Coated papers prepared with an SPI–carvacrol solution at 25 ºC


410


Viscosity (Pa s)

0.1

0.08

0.06

0.04

0.02

0 25

35

45

55

75

65

85

95

Temperature treatment (°C)

Fig. 16.6 Apparent viscosity (shear stress: 109 s−1 at 25 ºC) of SPI solutions (10% w/v) as a function of heat treatment (for 30 min): () without and () with carvacrol (30% carvacrol w/w of SPI); and as a function of heat treatment (for 30 min) and ultrasonic treatment (50 watt, 50 kHz for 2 h): () without and () with carvacrol (30% carvacrol w/w of SPI). All solutions were homogenized (8000 rpm for 10 min) (from Ben Arfa et al., 2007a). Table 16.4 Antimicrobial activity of the SPI–carvacrol coated papers as a function of the carvacrol retention time duration Storage time (days)a

Residual carvacrol quantity on coated paper(g m−2) E. coli growth

0

10

25

50

2.4

1.5

1.07

0.57

−

−

−

+

a

Storage at 30 °C and 60% RH. Absence of growth, −; presence of growth, +. From Ben Arfa et al. (2007a). b

were tested at different times of the kinetic release, and therefore contained various residual carvacrol quantities (Table 16.4). Their antimicrobial activities were demonstrated on E. coli growth and were dependent on the residual carvacrol quantity of the coated papers. After 50 days of release at 30 ºC and 60% RH, the carvacrol quantity (around 0.5 g m−2) was too low to induce a growth inhibition. It should be noted that ultrasonic treatment



411

of coating solutions induced a reversible decrease of apparent viscosity (Fig. 16.6) and could thus have the potential to replace the chemical methods that are currently used to modify the flow properties of coating solutions. However, its reversible action at the power level tested (50 kHz and 50 W) should be taken into account in industrial processes. Effect of drying conditions on carvacrol losses during paper processing There are three major steps in the paper coating process: preparation of the coating solution, the coating operation itself and drying. Drying is usually done in mild conditions (i.e. at ambient temperature) on a laboratory scale, but more intense drying conditions are usually needed for an industrial-scale set-up. The optimization of drying, a key process for losses in volatile compounds and thus for antimicrobial paper with additional efficiency, is complex since the drying kinetic is controlled by several phenomena and depends not only on the operating conditions but also on the physicochemical properties of the solution. It is known that drying induces changes in protein interactions with the formation of new hydrophobic interactions or disulphide and hydrogen bonds (Krochta and de Mulder Johnston, 1997). In an encapsulation process with spray drying at high temperature, SPIs were found most effective for retaining orange oil with an encapsulation efficiency of 86% compared with whey protein isolates (73%) or sodium caseinates (81.5%) (Kim et al., 1996). The influence of drying conditions (temperature/time) on carvacrol losses was investigated for antimicrobial packaging obtained by coating paper with soy protein solutions containing 30% carvacrol (w/w of SPI) as an antimicrobial agent (Chalier et al., 2007). The lowest carvacrol losses, ranging from 25 to 30%, were obtained for three drying conditions: high temperature and short time (250 ºC for 20 s) and mild conditions (50 ºC for 210 s and 25 ºC for 3 h) (Fig. 16.7). In contrast, intermediate drying conditions (100 ºC–90 s and 150 ºC–45 s) led to carvacrol losses higher than 50%. The smaller losses observed for the drying at 250 ºC compared with the intermediate temperatures could be explained by the rapid formation of a thick, protective crust that acted as a selective membrane, letting past water and retaining carvacrol. The crust, a layer of material with a high solid content, is formed at an early stage in hightemperature drying. It was reported that the formation was dependent on a critical concentration of water at the material’s surface; as soon as the water concentration at the interface fell below the critical moisture content, the selective membrane was formed (Thijssen, 1971). Drying conditions that led to a high rate of surface water evaporation enabled high aroma retention to be achieved (Reineccius, 2004). When drying at 150 ºC, the high losses were related to water vaporization and carvacrol carrying as attested by the presence of craters observed by scanning electronic microscopy (SEM) which were due to bubble formation and bursting (Fig. 16.7).


412


70

Carvacrol losses (%)

60 50 40 30 20 10 0 25°C–3 h

50°C–210 s

100°C–90 s

150°C–45 s

250°C–20 s

Fig. 16.7 Carvacrol losses (%w/w) from soy protein-coated papers after coating and drying processes as a function of drying treatment conditions: , ambient conditions (25 ºC) for 3 h; , 50 ºC for 3 min 30 s; , 100 ºC for 90 s; , 150 ºC for 45 s; , 250 ºC for 20 s and SEM (magnification ×500) of surfaces of coated papers (from Chalier et al., 2007).

Studies were also carried out on the effect of drying conditions on the retention of carvacrol during accelerated conditions of storage at 30 ºC and 60% RH; drying conditions were found to affect the kinetic release of carvacrol. The most drastic drying treatment (250 ºC–20 s) induced the most important kinetic release in the first step. Soy proteins, having a particularly plastic behaviour, can rearrange themselves in various ways during drying, depending on the duration and temperature. These modifications, particularly at high temperature, could produce weaker interactions between the soy proteins and carvacrol that would favour its release. Moreover, the conditions of the kinetic study (30 ºC, 60% RH) may promote water uptake and induce conformational changes depending on the fixed network structure after drying. The effect of inclusion and/or coating of matrices, and nature and concentration of aroma compounds, on antimicrobial paper characteristics The functional characteristics of an effective aroma compound matrix for creating efficient antimicrobial materials include not only a good film-forming ability but also emulsion-stabilization properties, effective



413

retention properties and the ability to be released under triggered conditions. Proteins such as whey or soy possess the required physicochemical properties. Native starches and related hydrolysed products lack active surface properties and have weak retention properties. In contrast, starches that are chemically modified by grafting on hydrophobic octenyl succinate anhydrous (OSA) groups, which impart their emulsifying abilities, are highly efficient in retaining the aroma compound (Qi and Xu, 1999). The presence of hydrophobic groups contributes to the absorption of hydrophobic aroma compounds into the matrix. SPI and OSA-modified corn starch were used as paper coatings and inclusion matrices and their efficiency in retaining antimicrobial agents was compared for two aroma compounds: cinnamaldehyde and carvacrol (Ben Arfa et al., 2007b). The two agents showed similar antimicrobial activity but they had different physicochemical properties. The retention ability of the coated matrices was shown to depend on the nature of the aroma compounds and coating matrices. The losses estimated after the coating and drying processes were always higher for OSA-starch-coated papers than for SPI-coated papers and for cinnamaldehyde compared with carvacrol (Fig. 16.8). For example, carvacrol losses ranged between 17 and 40% for OSA-starch matrices compared with 12 and 30% in the case of SPI matrices, depending on the aroma compound concentration (10, 30 or 60% w/w). The cinnamaldehyde losses varied between 43 and 64% in the case of SPI matrices compared with 74–77% for OSA-starch matrices. OSA starch was shown to be an unsuitable matrix for carrying cinnamaldehyde, since the majority of this compound was lost during processing. The differences observed between the two aroma compounds could be related to

Aroma compounds loss (% w/w of the initial weight)

80 Carvacrol Cinnamaldehyde

70 60 50 40 30 20 10 0 10

30

60

Aroma compounds concentration (% w/w of SPI)

Fig. 16.8 Influence of the concentration of aroma compounds on the losses of aroma compounds during the drying step of the process of coating paper with soy proteins (from Ben Arfa et al., 2007b).


414

Environmentally compatible food packaging 100 Cinnamaldehyde retention (% w/w of the mitial weight)

90 80 70 60 50 40 30 20 10 0 0

10

20

30 Time (days)

40

50

60

Fig. 16.9 Cinnamaldehyde retention during storage at 30 ºC and 60% RH humidity from papers coated with SPI and cinnamaldehyde: ()10% (w/w); () 30% (w/w); () 60% (w/w) (from Ben Arfa et al., 2007b).

their hydrophobic nature; carvacrol, the more hydrophobic compound, was retained better than cinnamaldehyde. During storage in accelerated emission conditions (air flux at 30 ºC and 60% RH), carvacrol retention from coated papers was found to be similar, whatever the coating matrices and the carvacrol concentration. In contrast, the retention from SPI-coated papers was particularly high for cinnamaldehyde (Fig. 16.9) at a concentration of 30% (w/w) compared with the lowest (10% w/w) or highest concentration (60% w/w). In storage conditions, SPI- and OSA-starch-coated papers were able to retain carvacrol and cinnamaldehyde, used as antimicrobial agents, and to release them in conditions favourable for the development of micro-organisms. While some differences in retention and release (in the middle condition of humidity) occurred, depending on the matrices and the compound properties, both coated papers were able to create an antimicrobial modified atmosphere due to the fast active agent release by the matrices in the favourable conditions for micro-organism growth of high RH and the temperature rising to 30 ºC.

16.4

Future trends

Further studies are under development to provide better understanding, knowledge, modelling and prediction of volatile active agent release and gas transfers as a function of processing and conditions of use. This is currently leading to the study of the impact of nanocomposite structure on the



415

diffusion and sorption properties of aroma compounds in protein-based materials.

16.5

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lopez-briones g, varoquaux p, chambroy y, bouquant j, bureau g and pascat b (1992), ‘Storage of common mushroom under controlled atmospheres’, Int J Food Sci Technol, 27, 493–505. moleyar v and narasimham p (1992), ‘Antibacterial activity of essential components’, Int J Food Microbiol, 16, 337–342. mujica-paz h and gontard n (1997), ‘Oxygen and carbon dioxide permeability of wheat gluten film: effect of relative humidity and temperature’, J Agric Food Chem, 45 (10), 4101–4105. mujica-paz h, guillard v, reynes m and gontard n (2005), ‘Ethylene permeability of wheat gluten film as a function of temperature and relative humidity’, J Membr Sci, 256 (1/2), 108–115. ouattara b, simard r e, piette g, begin a and holley r a (2000), ‘Inhibition of surface spoilage bacteria in processed meats by application of antimicrobial films prepared with chitosan’, Int J Food Microbiol, 62 (1/2), 139–148. panizzi l, flamini g, cioni p l and morelli i (1993), ‘Composition and antimicrobial properties of essential oils of 4 mediterranean Lamiaceae’, J Ethnopharmacol, 39 (3), 167–170. park c m, taormina p j and beuchat l r (2000), ‘Efficacy of allyl isothiocyanate in killing enterohemorrhagic Escherichia coli O157:H7 on alfalfa seeds’, Int J Food Microbiol, 56 (1), 13–20. pranoto y, rakshit s k and salokhe v m (2005), ‘Enhancing antimicrobial activity of chitosan films by incorporating garlic oil, potassium sorbate and nisin’, LWT-Food Sci Technol, 38 (8), 859–865. qi z h and xu a (1999), ‘Starch-based ingredients for flavor encapsulation’, Cereal Foods World, 44 (7), 460–465. quintavalla s and vicini l (2002), ‘Antimicrobial food packaging in the meat industry’, Meat Sci, 62 (3), 373–380. rasooli i and mirmostafa s a (2003), ‘Bacterial susceptibility to and chemical composition of essential oils from Thymus kotschyanus and Thymus persicus’, J Agric Food Chem, 51 (8), 2200–2205. redl a, gontard n and guilbert s (1996), ‘Determination of sorbic acid diffusivity in edible wheat gluten and lipid based films’, J Food Sci, 61 (1), 116–121. reineccius g a (2004), ‘The spray drying of food flavors’, Drying Technol, 22 (6), 1289–1324. roller s and sheedhar p (2002), ‘Carvacrol and cinnamic acid inhibit microbial growth in fresh cut melon and kiwifruit at 4º and 8 ºC’, Lett Appl Microbiol, 35 (5), 390–394. sikkema j, de bont j a m and poolman b (1995), ‘Mechanisms of membrane toxicity of hydrocarbons’, Microbiol Rev, 59 (2), 201–222. sivropoulou a, papanikolaou e, nikolaou c, kokkini c, lanaras t and arsenakis m (1996), ‘Antimicrobial and cytotoxic activities of Origanum essential oils’, J Agric Food Chem, 44 (5), 1202–1205. subirade m, kelly i, gueguen j and pezolet m (1998), ‘Molecular basis of film formation from a soybean protein: comparison between the conformation of glycinin in aqueous solution and in films’, Int J Biol Macromol, 23 (4), 241–249. suresh p, ingle v k and vijayalakshmi v (1992), ‘Antibacterial activity of eugenol in comparison with other antibiotics’, J Food Sci Technol, 29 (4), 254–256. thijssen h c a (1971), ‘Flavor retention in drying pre-concentrated foods liquids’, J Appl Chem Biotechnol, 21, 372–377. tsao r and zhou t (2000), ‘Antifungal activity of monoterpenoids against postharvest pathogens Botrytis cinerea and Monilinia fructicola’, J Essent Oil Res 12 (1), 113–121.


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tunc s, chollet e, chalier p, preziosi-belloy l and gontard n (2007), ‘Combined effect of volatile antimicrobial agents on the growth of Penicillium notatum’, Int J Food Microbiol, 113, 263–270. ultee a, kets e p w and smid e j (1999), ‘Mechanisms of action of carvacrol on the food-borne pathogen Bacillus cereus’, Appl Environ Microbiol, 65 (10), 4606–4610. ultee a, bennik m h j and moezelaar r (2002), ‘The phenolic hydroxyl group of carvacrol is essential for action against the food borne pathogen Bacillus cereus’, Appl Environ Microbiol, 68 (4), 1561–1568. varoquaux p (2000), ‘Les films à perméabilité aux gaz ajustable: application aux fruits et légumes’, in Gontard N (ed.), Les Emballages Actifs, Paris, Tec&Doc, pp. 89–108. vaz c m, van doeveren p, reis r l and cunha a m (2003), ‘Soy matrix drug delivery systems obtained by melt-processing techniques’, Biomacromolecules, 4 (6), 1520–1529. vazquez b i, fente c, franco c m, vazquez m j and cepeda a (2001), ‘Inhibitory effects of eugenol and thymol on Penicillium citrinum strains in culture media and cheese’, Int J Food Microbiol, 67 (1/2), 157–163. weber f j and de bont j a m (1996), ‘Adaptation mechanisms of microorganisms to the toxic effects of organic solvents on membranes’, Biochem Biophys Acta, 1286 (3), 225–245. yam k l and lee d s (1995), ‘Design of modified atmosphere packaging for fresh produce’, in Rooney M L (ed.), Active Food Packaging, Glasgow, Chapman and Hall, pp. 55–73. zagory d and kader j (1988), ‘Modified atmosphere packaging of fresh produces’, Food Technol, 42, 70–74.


17 Active environmentally compatible food packaging R. Catalá, P. Hernández-Muñoz and R. Gavara, IATA-CSIC, Spain

17.1

Introduction

Traditionally, inertness to food has been among the most valued characteristics in food packaging. The package should have minimum impact on the product, acting purely as a container and a barrier to isolate it from the exterior. The past 20 years, however, have witnessed the rise of new food conservation technologies based precisely on using or enhancing possible interactions between the packaging and the product and/or the environment. For instance, produce stored in a modified atmosphere generates or consumes gases such as oxygen, carbon dioxide, etc. at a greater or lesser speed depending on the product characteristics. When certain substances that generate or remove these gases are placed in the package and the permeability of the packaging material is controlled, a suitable atmosphere for improved conservation of the packaged food can be maintained. This control of the package atmosphere leads to the concept of active packaging or packing in active packs. Active packaging means a food/package/environment system that works in a coordinated way to improve the quality and safety of the packaged food and increase its shelf-life (Catalá and Gavara, 2001). Generally speaking, the purpose of the packaging is to use beneficial interactions between the food and the packaging system to protect the food from the agents that cause physical, chemical, enzymatic or microbial changes. This definition broadens the concept of a pack: rather than being a mere container or ‘passive package’, it acquires an active role in maintaining or even improving the quality of the packaged food. In fact, the package corrects the deficiencies of the storage system in different ways, acting on the composition


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of the internal atmosphere – by using materials with selective permeability (permselective materials) or with substances that give off or retain gases and vapours – or on the composition and/or characteristics of the food by releasing substances that act positively on it or by absorbing/retaining undesirable components. A new European Regulation on materials and articles intended to come into contact with food (Regulation (EC) No. 1935/2004) was published in November 2004. It defines active materials and articles as those that are intended to extend the shelf-life or maintain or improve the condition of packaged food and are designed to deliberately incorporate components that would release or absorb substances into or from the packaged food or the environment surrounding the food. This same regulation distinguishes and defines intelligent food-contact materials and articles as materials and articles that monitor the condition of packaged food or the environment surrounding the food. The concept of active packaging is not really new; after all, the leaves that are traditionally used in numerous countries to cover certain products are good examples of active packaging, as they give the product the aroma compounds and enzymes that are responsible for some of the sensory characteristics for which these foods are appreciated, as well as antimicrobial agents that help to preserve them. Nowadays, the redefinition of the active packaging concept and its acceptance by the international food safety regulations makes it possible to consider designing packs and packaging technologies to meet the needs of the different products and of the consumer market, opening up new ways to store and sell foods. However, it must always be borne very much in mind that each food has a specific spoilage mechanism which must be studied and understood so that the most suitable technology for optimum product quality control can be developed or applied. Active packaging certainly responds to the steadily increasing public demand for food quality and safety.

17.2

Basic characteristics of active packaging

There are many ways of making packaging active but, essentially, only two mechanisms: placing the active material inside the package along with the product being packed or making the active element part of the packaging materials themselves. Since these technologies first started to be developed, the usual way to introduce an active substance has been to use a sachet, envelope or label containing the substance, e.g. iron to remove the residual oxygen in the pack or silica to remove moisture. The sachet is made of a polymeric material, permeable enough to allow the active principle to be released and/or to act but not, usually, to allow it into contact with the product itself. Naturally, the active substances must not endanger the food safety of the packaged product. This is how most of the systems that made


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up the first generation of active packaging work and it is still a widely used technique (Rooney, 1995). An alternative that is already being used for some products and will undoubtedly become widespread in future is to add the active principle to the packaging material itself, whether as part of the polymer or on a packaging component (Kruif et al., 2002). These active materials or components make positive use of migration and sorption mechanisms: instead of releasing undesirable substances into the food or absorbing desirable ones, substances with a beneficial effect are incorporated into the package and transferred to the food, or undesirable food components are removed by sorption. This is undoubtedly the most attractive form of active packaging for consumers, as in this way they do not find anything strange inside the package that could catch the eye and raise doubts about the safety of the food they will be eating. It also simplifies the packing technology by doing away with the step of placing the active system in the package. Active packaging has been making commercial headway and has already been put to many highly diverse uses, particularly in Japan and Australia, and to a lesser extent in the United States. In Europe, the penetration of this type of packaging has so far been minimal, but the recent passing of new European legislation should bring rapid expansion. Many different types of active packaging have been proposed for combating different food quality loss or deterioration problems. They include controlling the gases inside the package (e.g. oxygen, carbon dioxide, ethylene), regulating the moisture content, adding chemical preservatives, adding aromas, removing foreign odours and undesirable substances, and controlling microbiological contamination (Rooney, 1995; Floros et al., 1997; Vermeiren et al., 1999; Ahvenainen, 2003). The materials used as substrates are generally conventional synthetic polymers. Polyolefins are widely used when there are no particular gas or vapour barrier requirements. When a more impermeable packaging material is required, the alternatives are polyesters or polyamides and, above all, multi-layer structures that include high barrier materials such as ethylene vinyl alcohol copolymers. As an alternative to the current petroleum-based polymers, increasing interest is being shown in biopolymers derived from renewable sources. Biopolymers obtained directly from biomass (starch, chitosan, gelatine, collagen, gluten, zein, etc.), by chemical synthesis from monomers obtained from biomass (polylactic acid (PLA) and other polyesters), or produced by micro-organisms (polyhydroxyalcanoates, bacterial cellulose, etc.) (Weber et al., 2002) are already being used as packaging materials or coatings for food. These biomass-derived macromolecules generally possess excellent film-forming capacity. The films can be obtained by conventional extrusion or lamination methods or by casting after solubilising, dispersing or emulsifying the polymer. Generally, they have good oil and fat barrier properties and good gas and vapour permeability coefficients (Cha and Chinnan,


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2004). These materials can be biodegradable and many of them are edible. They make it possible to control physical, chemical and microbial processes in foods as well as or better than conventional plastics and can be a good alternative to these for active packages and coatings. When used as edible coatings, they need to be treated as a food component and therefore have to comply with a series of requirements such as good sensory properties; physical, chemical and microbiological stability; and nil toxicity (Debeaufort et al., 1998; Olivas and Barbosa-Cánovas, 2005). Whatever type of polymer is used to develop active packages, the speed of mass transfer of the active substance in the polymer is a critical parameter as the active substance can modify the properties of the polymer, desorption kinetics are variable and the active capacity can be reduced by premature reactions if there is no mechanism to control the onset of activity (López Rubio et al., 2004). This chapter presents some recent developments in active packaging based on the use of biopolymers.

17.3

Biopolymer-based active materials for food packaging

17.3.1

Active materials for controlling microbiological contamination in packaged foods Controlling microbiological contamination is one of the applications of active packaging that is generating the most interest and is increasingly used. The development of micro-organisms is one of the main causes of deterioration in food. Microbiological contamination of foods mainly occurs on their surface as a result of the handling and preparation operations they undergo up to the moment when they are consumed. Various antimicrobial substances are habitually applied directly to the surface of the product to control the micro-organisms, as complements or alternatives to physicochemical conservation methods. However, direct application of antimicrobial substances is not always sufficiently effective, as the activity of many of these substances may be reduced by their neutralisation or rapid diffusion inside the product. Incorporating the antimicrobial agent into the package is undoubtedly a possible alternative for maintaining their effectiveness.The potential applications of antimicrobial active packaging have attracted considerable attention from many research teams and various commercial systems for conserving foods such as fruit, vegetables, chicken, cheese, meat, etc. have already been developed (Vermeiren et al., 2002; Suppakul et al., 2003; Cha and Chinnan, 2004; López Rubio et al., 2004; Han, 2005). The antimicrobial action can be based on the emission of volatile substances into the headspace of the package, or migration of the active component into the packaged food, or direct contact between the product and the packaging surface that has been coated with the active compound, or the antimicrobial nature of the packaging material itself.



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Direct addition of common antimicrobial volatiles – such as SO2, Cl2O or ethanol – over the foods is a widespread practice for conserving certain products. They can be added to the packages on an adsorbent material or inside sachets made from a porous or permeable material so that they pass into the headspace of the package (López Rubio et al., 2004). SO2, incorporated as a metabisulphite into polymer structures, has proved effective for delaying the growth of moulds such as Botrytis, Penicillium, Aspergilus or Rhizopus in citrus fruit and berries (Suppakul et al., 2003). ClO2 has also been incorporated into polyolefin polymers by extrusion processes (LópezRubio et al., 2004). Some other volatile compounds that have attracted attention are found in foods. Compounds such as hexanal, 1-hexenol and methyl benzoate, among other components of certain food aromas, inhibit the growth of fungi such as Botrytis cinerea in strawberries (Fallik et al., 1998). Similarly, 2-nonanone is a characteristic volatile of strawberry aroma that displays fungicidal properties which increase the shelf-life of strawberries and apples (Almenar et al., 2002). Allyl isocyanate, a plant-derived microbicide authorised in Japan as an additive, can be released from the package in vapour form to extend the shelf-life of meat, fish or cheese (López-Rubio et al., 2004). A large number of non-volatile substances with antimicrobial effects can be combined with polymeric materials, whether as components of these materials, from which they migrate into the packaged food, or by immobilising the active substance on the packaging material so that it acts through contact with the packaged product. Many such antimicrobial substances have been studied: weak organic acids (acetic, benzoic, sorbic, citric and propionic, among others) or their salts; enzymes (lysozyme, glucose oxidase); bacteriocins (nisin, pediocin); synthetic fungicides (imazalyl, benomyl); metals (silver, copper, zirconium); and natural plant extracts (rosemary, thyme, oregano, etc.) (Cha and Chinnan, 2004; Han, 2005). The materials that have been developed are generally based on conventional synthetic polymers, mostly polyolefins. Biopolymers have not been the subject of much work, although the growing presence and excellent potential of these materials are increasing their use. Biopolymers based on polysaccharides such as cellulose and cellulose derivatives, starch, alginates, carrageenans and chitosans – as well as protein derivatives such as maize zein, wheat gluten, casein, soy isolates, collagen and gelatine, among others – have been used as a basis for developing antimicrobial active biopolymers, as the wideranging review by Cha and Chinnan (2004) has shown. As cellulose is the most abundant natural polymer, it has received the most attention as a packaging material. Cellulose and derivatives such as carboxymethylcellulose (CMC) or hydroxypropyl methylcellulose (HPMC) form flexible, water-soluble and oil- and fat-resistant films and coatings with good mechanical and barrier properties and are therefore widely used in the conservation of fruit and vegetables, meat products and fish (Cutter, 2002). The addition of antimicrobial substances such as weak acids


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or bacteriocins has given rise to the development of antimicrobial active materials, with interesting results. Vojdani and Torres (1990) and Rico-Pena and Torres (1991) obtained CMC and HPMC films with additions of sorbic acid and potassium sorbate that have antimicrobial properties. Zhuang et al. (1996) used HPMC coatings with ethanol and weak acids and found them effective for controlling Salmonella development in tomatoes. Cellulose and its derivatives have also been used as a basis for applying bacteriocins, particularly nisin, a substance that is very active against most of the Gram-positive bacteria and some types of spores. Its mode of action is associated with the phospholipids of the cytoplasmic membrane. Ming et al. (1997) studied the application of nisin and pediocin in cellulose coatings to control Listeria monocytogenes in meat and poultry. Appendini and Hotchkiss (1997) studied immobilising lysozyme in cellulose acetate, with similar results to those obtained with synthetic polymers such as polyamide and polyvinyl alcohol polymers, demonstrating the effectiveness of this combination in culture media. Scanell et al. (2000) developed an antimicrobial material with applications in the control of Listeria innocua and Staphylococcus aureus in cheeses and hams by immobilising nisin and lacticin in cellulose. Coma et al. (2001) also found an effect on those same microorganisms by using nisin in edible coatings with cellulose ethers and fatty acids. Cha et al. (2003) have studied the speed of emission of nisin added to MC and HPMC films and other biopolymers such as carrageenan or chitosan, and its effectiveness against L. monocytogenes. Similar results have been presented by Grower et al. (2004), who studied the inhibition of Listeria growth in frankfurters (hot dog sausages) using MC and HPMC films containing nisin. Other polysaccharides that have been tested as a basis for adding antimicrobial substances are starches, alginates and carrageenans, which are widely used as edible food coatings owing to their excellent properties (Nísperos-Carriedo, 1994). These coatings provide selective gas permeability, enabling modified atmospheres to be created without leading to anaerobic conditions, and are therefore used to improve the shelf-life of fruit, vegetable and meat products (Baldwin et al., 1995; Olivas and BarbosaCánovas, 2005). Baron and Sumner (1994) studied the addition of potassium sorbate and lactic acid to maize-starch-based edible coatings and observed Salmonella typhimurium and Escherichia coli inhibition in chicken. Using potassium sorbate as the antimicrobial agent, Garcia et al. (1998) also formed films with starch that can be used to improve the shelf-life of strawberries. Chen et al. (2003) studied the formation of complex films made from starch and polyvinyl alcohol with the addition of catechins and assessed their activity in culture media. Rojas de Gante (2004) made a wide-ranging study of biofilm development from sorghum starch with nisin and benzoates, obtaining good practical results. Using calcium alginate coatings containing acetic or lactic acid, Siragusa and Dickson (1993) studied lean beef protection and reduced the L. mono-



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cytogenes and E. coli populations significantly. Fang and Lin (1994) studied the combination of a modified atmosphere system with a calcium alginate coating containing nisin to control L. monocytogenes and Pseudomonas fragi in cooked pork. Cutter and Siragusa (1996, 1997) also added nisin to alginate gels applied to meat and found that the presence of Brochotrhix thermosphacta was reduced. Along the same lines, Wan et al. (1997) studied the properties and antimicrobial activity against Lactobacillus curvatus of calcium alginate films to which nisin had been added, while Natrajan and Sheldon (2000) applied these films to control Salmonella contamination of chicken. Cha et al. (2003) studied bacteria inhibition using nisin, lysozyme and ethylene diamine tetraacetic acid (EDTA) in alginate films, as well as in carrageenan- and cellulose-derived films. Antimicrobial materials have also been developed using polymers derived from proteins such as zein, wheat gluten, soy isolates or milk whey. Biopolymers derived from proteins present good barriers to oxygen and carbon dioxide but not to moisture (Baldwin et al., 1995). Owing to their nutritional characteristics and good mechanical and barrier properties, they are used as edible coatings to protect fruit, vegetable and meat products (Cutter and Sumner, 2002; Chapman, 2004). Zein is employed commercially in the formulation of coatings for fruit, vegetables and nuts. Various authors, such as Dawson et al. (1996) or Padgett et al. (1998, 2000), have tested zein with the addition of nisin and lysozyme, using hot pressing and casting methods, and assessed the properties of the material and its inhibition of bacterial growth in culture media. Cooksey et al. (2000) assessed the application of zein sachets containing nisin for reducing microbial growth in refrigerated cheese, while Hoffman et al. (2001) studied the impregnation of zein films with nisin, lauric acid and EDTA to control L. monocytogenes and Salmonella enteritidis. Teerakarn et al. (2002) and Dawson et al. (2003) studied the effect of the film-forming method and of temperature on nisin diffusion in maize zein and wheat gluten biopolymers. Similar experiments described by Dawson et al. (2003) evaluated activity against Lactobacillus plantarum, encountering better results with films obtained by casting than with hot pressed films. Soy protein derivatives have been studied by Padgett et al. (1998), adding nisin and lysozyme as active antimicrobial agents and finding an inhibiting effect on L. plantarum and E. coli in culture media, while Dawson et al. (2002) studied the application of these biopolymers with nisin to control L. monocytogenes on turkey bologna. Edible films made from whey protein with the addition of potassium sorbate have been studied and the diffusion of the antimicrobial agent has been modelled by Ozdemir and Floros (2001). Cagri et al. (2001) studied the properties of these films with the addition of sorbic acid and p-aminobenzoic acid, finding inhibition of L. monocytogenes and E. coli. The activity of most of the antimicrobial biopolymers mentioned is the result of migration into the packaged food of the active component


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incorporated into the polymer or of contact between the food and the active substance that has been coated on the packaging material. However, some other biopolymers, such as chitosan, present antimicrobial activity in their own right. Chitosan is a natural polysaccharide from the exoskeletons of crustaceans and the cell walls of certain fungi.While the physical and chemical properties of chitosan films vary according to their source and the method of obtaining the polymer, in general they present excellent mechanical properties, very low permeability to oxygen and carbon dioxide, flexibility, transparency, innocuousness and low cost (Sirinivasa et al., 2004; Suyatma et al., 2004). As a result of these properties, chitosan films have many practical uses, but above all, they are valued for their antimicrobial properties against bacteria and fungi, which are of great interest in food protection (Shahidi et al., 1999; Rhoades and Roller, 2000; Chapman, 2004). Edible chitosan coatings applied to fruit and vegetables make it possible to create a balanced modified atmosphere and reduce water loss while at the same time providing direct protection against fungal infections. Chen et al. (1996) studied different chitosan formulations and encountered inhibition of Rhodotorula rubra and Penicillium notatum growth. Similar fungal inhibition results with different chitosan formulations have been published by other teams. El-Ghaouth et al. (1991, 1992) studied the application of chitosan coatings on strawberries and tomatoes and encountered lower respiration and ethylene production rates and control of fungal contamination. Other studies include protecting salmon or cod fillets (Skonberg, 2000), pieces of apple (Nussinovich, 2000) or pizzas with edible chitosan coatings. Kume et al. (2002) studied mango conservation with irradiated chitosan films and obtained a rise in shelf-life from 7 to 15 days while maintaining the natural ripening and colour characteristics. It was considered that this was due to the antifungal properties and changes in the physical and chemical properties of irradiated chitosan. Galed et al. (2004) studied the ripening and deterioration process in citrus fruits treated with chitosan solutions and demonstrated their efficiency in reducing physiological deterioration. Hernández-Muñoz et al. (2006) studied the conservation of strawberries with chitosan coatings applied by dipping and Gentili et al. (2005) used immersion coating with different chitosan formulations for quince, pear and tomato conservation, with good results. Chitosan films can also have other antimicrobial substances added to them to reinforce their action, or other active agents such as antioxidants, vitamins, minerals, etc., forming multi-functional active biopolymers. Ouattara et al. (2000) tested the addition of antimicrobial agents such as acetic acid, propionic acid and essential oils to chitosan and encountered improved inhibition of bacterial growth in meat products. Han et al. (2004) studied chitosan coatings with added calcium and vitamin E in strawberry and raspberry storage, showing that the presence of these nutrients does not alter the antifungal and barrier properties of the polymer, so this constitutes an interesting process for improving the nutritional quality of these fruits.



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Other biopolymers manufactured by synthesising monomers obtained from biomass, such as PLA and other aliphatic polyesters, have also been tried for antimicrobial active material preparations. PLA is made by polymerising lactic acid obtained from the fermentation of crops such as maize or sugar cane. While its properties depend on the polymer composition, in general the films possess similar properties to those of conventional polymers such as polypropylene and polyethylene terephthalate (Petersen et al., 1999; Perepelkin, 2005). Studies have been published that show the potential of PLA in combination with active agents to control microbial growth in meat and vegetables. Musthapha et al. (2002) studied the use of low molecular weight PLA films with added lactic acid and nisin against. E. coli in beef. Almenar et al. (2006) have developed antifungal films with volatile antifungal compounds immobilised into cyclodextrins. Biopolymer materials undoubtedly constitute a good basis for developing antimicrobial active packaging and coatings that slowly release fungicides and bactericides which migrate onto the food to control microbial contamination of packaged foods and lengthen their shelf-life, providing the best guarantees of quality and safety. 17.3.2 Active materials for controlling oxidation in packaged foods The presence of oxygen is a concurrent cause in many of the ways in which packaged foods deteriorate, such as fatty components turning rancid, enzymatic deterioration, oxidation of vitamins and changes in aroma, or microbiological alteration by aerobic micro-organisms. Although foods that are sensitive to oxygen can be suitably packed with technologies that limit the presence of this gas – such as vacuum or modified atmosphere packaging combined with high barrier packaging materials – the oxygen is not always completely and effectively eliminated, whether because of a residual presence at the time of packing or because it permeates in from the exterior through the package wall (Kerry et al., 2006). As well as oxygen, reactive species such as free radicals, superoxide, hydroxyl and singlet oxygen are generated in food or in the surrounding atmosphere by different mechanisms (Kruk, 1998) and can be involved in oxidation reactions in lipids and other food components, contributing to their deterioration. Active packaging systems that absorb residual oxygen or reactive species can be a good choice for many products and currently constitute one of the most widespread uses of active packaging (Ozdmeir and Floros, 2004). In general, current technologies for removing oxygen are based on one or more of the following concepts: oxidation of metals or metal oxides, oxidation of ascorbic acid, unsaturated fatty acids such as oleic or linoleic acid, enzymatic oxidation (glucose oxidase/catalase), yeasts immobilised on a solid medium or photosensitive oxidation of compounds (Floros et al.,


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1997). The formation of free radicals and reactive species that cause oxidation problems in foods is controlled by adding antioxidants such as butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate or essential oils from plants to the foods (Park et al., 2004; Shan et al., 2005). Oxygen absorption or sequestration systems (oxygen scavengers) manage to reduce the presence of this gas inside the packs to below 0.01% when combined with high barrier packaging materials that prevent it from entering the package. Some of these systems have been used successfully for oxygen control in bakery products, pasta, cheese, nuts, cured or smoked meat or fish and drinks (Rooney, 2005). Most commercial applications nowadays enclose the oxygen-scavenging substances in sachets made from permeable materials or in labels, placed inside the pack or adhering to its side. As previously mentioned, the drawbacks of these methods are leading to the active agent being added to the container itself, whether incorporated into the material or immobilised in some way on its surface. Oxygen scavengers can be incorporated into polymers by solution or dispersion, adding them to the masterbatch, or they can be included in an inner layer in the case of multi-layer materials. Designing materials with oxygen scavengers requires the active polymer to be capable of being processed into packaging materials by conventional methods and being able to maintain its properties as a container after the active agent has been exhausted by its oxygen-absorption function (Speer and Gauthier, 2001). In addition, since oxygen-scavenging systems are based on the use of reducing agents that react with oxygen, the system must contain a barrier material to prevent reactions with oxygen on the exterior and, above all, some mechanism to activate the scavenging activity so that it is not exhausted before the package is used. The most widespread active systems for absorbing oxygen use iron powder in permeable plastic sachets. On the same principle, active films in which iron or similar reducing agents are dispersed in the polymer structure have been developed (Suppakul et al., 2003). These systems require moisture to trigger the oxygen sequestration reaction. The presence of iron and similar agents can affect the transparency and mechanical properties of the polymer. In addition, the active substance and its reaction products can migrate into the packaged product and affect its sensory acceptability and its ability to meet statutory standards. Despite the drawbacks, various materials that use this technology have been patented (López-Rubio et al., 2004). A number of patents describe active plastics for oxygen control which make use of a catalyser, Pd or Co for instance, to excite oxygen to singlet oxygen which is highly reactive and quickly binds to unsaturated hydrocarbons such as squalene, fatty acids or 1,2-polybutadiene. These must therefore be present in the active plastic formulation; they are added to thermoplastics such as polyethylene, polystyrene or polyester, which are processed into containers by conventional methods. In these materials the



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oxygen removal mechanism is usually triggered by photoinitiators that have also been added to the plastic material (Kulzick et al., 2000; Barski et al., 2002; Goodrich et al., 2003). Other oxygen absorbers have been developed by adding enzymes to the packaging materials, the most widely used being the glucose oxidase/ catalase enzyme combination. The enzyme system can be immobilised as a coating on substrates such as waxed paper or polymers, or trapped in liquid form between two films: an outer one that is a good gas barrier and an inner one that is highly permeable. One essential requisite when the substance is immobilised is that the surface containing the enzyme must be in direct contact with the food for the redox reaction to take place, thus limiting the use of this type of material (Brody et al., 2001a) Sulphites are other compounds that can be added to polymer structures to act as oxygen scavengers. For instance, one proposal is to use potassium sulphite dispersed in a high-density polyethylene substrate as the internal layer of a polymer structure which would be activated by the moist warmth produced by the processes used to sterilise the packaged food (Brody et al., 2001a). Based on the different mechanisms discussed, some oxygen-scavenging plastics have been developed commercially, such as Amosorb, Cryovac OSP, OS 2000, OxBar, Oxygard, Shelplus O2, Zero2, etc. (López-Rubio et al., 2004; Rooney, 2005), and are being used for oxygen removal in packaged foods. Active systems for controlling food oxidation by reactive oxygen species have also been developed by adding antioxidants such as butylated hydroxyanisole or butylated hydroxytoluene to the packaging material instead of the normal practice of adding them to the food (Wessling et al., 1998). However, the presence of these synthetic antioxidants in foods is questioned, owing to the potential risks, and strict statutory controls are required. The alternative that is being studied widely is to use natural antioxidants, particularly those from herbs such as rosemary, oregano, thyme, etc. (Park et al., 2004; Nerín et al., 2006). All these active systems to control oxidation, like those mentioned earlier, are based on conventional polymers, with most of those developed commercially being composed of polyolefins (Wessling et al., 1998; Gavara et al., 2004). Only recently has work begun with biopolymers and although the prospects are excellent, the results are still very scarce. Lee et al. (2003) reduced browning in pieces of minimally processed apples by applying carragheenate or whey protein concentrate coatings with the addition of antibrowning agents and managed to extend the shelflife in good sensory condition for up to 2 weeks. Perez-Gago et al. (2006) also studied colour changes in apples using whey protein concentrate and beeswax coatings with the addition of antioxidants. Ou et al. (2005) have developed edible films from soy protein isolates with the addition of ferulic acid and obtained good oxidation control results in butter. Oussalah et al.


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(2004), for their part, have worked on developing milk protein films with the addition of oregano essential oil as an active agent and found antioxidant and antimicrobial activity for preserving beef. Park et al. (2004) observed that deacetylated chitosan has free radical absorption capacity and could therefore be used as an active antioxidant material as well as being antimicrobial, as mentioned previously. Güçbilmez et al. (2007) also encountered antioxidant and antimicrobial activity in zein films with lysozyme and albumen extract incorporated. Biopolymers can undoubtedly be a good option for developing active materials to control oxidation problems in packaged foods. 17.3.3

Active materials for retaining food components or releasing beneficial compounds Active packages to control microbiological contamination and oxidation problems in packaged foods, as discussed above, are currently the types of active packaging with the greatest degree of development and commercial introduction. Other active systems are also receiving attention, including those that try to retain or add components that may be beneficial for maintaining the quality or safety of the packaged foods, such as ethylene control, moisture regulation, the addition of aromas or the removal of foreign odours and undesirable substances. Ethylene (C2H4) is considered a plant hormone owing to its physiological effects on fresh fruit and vegetables. Although its effect can be beneficial in some cases (degreening citrus fruits), its presence is often detrimental to produce quality and shelf-life. One of its effects is to accelerate respiration, ripening the fruit and softening its tissues, and so it hastens senescence. Other effects are that ethylene accumulating in the pack causes yellowing in green vegetables and seems to be responsible for various post-harvest disorders in fresh fruit and vegetables (Zagory, 1995). These are good reasons to use substances that can eliminate or inhibit ethylene production in packages of this type of food. Different ways to remove ethylene have been applied with greater or lesser degrees of success, using substances such as active carbon, silica gel, silver nitrate and other minerals to absorb it, but the most frequently used absorber is potassium permanganate, on substrates such as aluminium oxide, zeolite, sepiolite and vermiculite. Different commercial systems are available, both as permeable sachets containing the absorber and as flexible plastic films, generally polyethylene, impregnated with the active substance (Soto-Valdez et al., 2005). Moisture control is another practical application of active packaging. For meat or fresh vegetable products, active packs are widely used to control vapour condensation inside the package, which detracts from the presentation of the product. Antifogging additives, generally monoglycerides, are added to the plastic to reduce the surface tension of the condensed droplets



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so that they form a continuous fine film that is barely perceptible (Vermeiren et al., 1999). Absorbing the liquids exuded by packaged fresh meat and fish is another interesting application. Different systems have been developed, based on absorbent polymers with starch copolymers or with polyacrylates, which can be placed under the food in the trays in which it is sold, protected by a sheet of polyethylene or polypropylene (López-Rubio et al., 2004). Sorption of the compounds responsible for the characteristic aroma profile of the food by the packaging material or permeation or migration of foreign aroma components into the food generally has a very negative impact on the quality of the packaged product. For instance, during processing, some polyolefin plastics can form short-chain hydrocarbons which in many cases give undesirable odours to the food. The presence of these compounds can be controlled by adding an absorbent substance such as zeolite to the packaging material to trap the aromatic compound within its structure (Brody, 2002). Compounds such as hexanal or heptanal that can be formed by oxidation in some foods with a high fat content – such as snacks, bakery products, etc. – can be removed by absorption by an ethylene/acrylic acid copolymer incorporated into the packaging, thus preserving the aroma quality of these products (Rooney, 1995). Equally, different patents have been registered for eliminating substances such as mercaptans, hydrogen sulphide or amines that can develop from protein components in some packaged meats or fish, causing odours that may lead to rejection by the consumer (Brody et al., 2001b). Along the same lines, the proposal to incorporate aroma compounds into the packaging material attempts to minimise aroma loss or to improve the aroma profile of the packaged foods. Dimensioning this technology correctly is a key factor, as it could accidentally present a risk to consumers by masking off odours from poor quality products (López-Rubio et al., 2004). Immobilising enzymes in polymers has also been proposed for very specific uses that could be of considerable practical interest. Soares and Hotchkiss (1998), for instance, studied immobilising naringinase, an enzyme that breaks down the flavonones responsible for the bitter taste in citrus fruits, in a cellulose acetate film that can be added to the interior of a complex cardboard container such as those habitually used for fruit juices, so that when the juice comes into contact with the polymer the enzyme hydrolyses the bitter compounds and the drink becomes sweeter over time. With the same idea, Del Nobile et al. (2003) studied naringinase immobilisation on PVA films to reduce the naringin content of grapefruit juice. The immobilisation of enzymes in the container has also been tested for eliminating lactose and cholesterol in milk, which would make it possible for those with a lactose intolerance to consume this product (Brody and Budney, 1995). An interesting development, although it cannot be considered active packaging in the same sense, is to add substances to the package that detect


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the presence of certain pathogens in the food and advise the consumer of its safety before consuming the product. The idea is attractive but has not yet been developed sufficiently.

17.4

Future trends

Active packaging already constitutes a fully accepted technological means of conserving foods and presents excellent future prospects for improving the safety and extending the shelf-life of industrialised foods. Abundant information has been published on active packaging systems, with a great diversity of possible substrate/active agent combinations. Generally speaking, these works have concentrated on the technological aspects of the active systems that have been developed but there is little information on interactions and physico-chemical changes with or in the packaging, or on the health, nutritional and cost implications, particularly in comparison with conventional technologies. More attention needs to be paid to these aspects. Active systems where the active agent is contained in a permeable sachet and placed in the package together with the food, which were the most used in the initial stages of these technologies, are gradually being replaced by systems that add the active agents to the packaging material itself. Many active materials have already been developed and it is to be expected that this method will become widespread in future. Although all kinds of conventional polymers have been used to develop active systems, the majority of those in greatest use are polyolefin polymers. To date, not many active systems have been based on biopolymers. Nonetheless, a fair amount of work has been done on developing antimicrobial active systems using various polysaccharide and protein-based biopolymers, which in some cases (chitosan, for example) themselves possess antimicrobial activity. This is unquestionably a field in which biopolymers can confer advantages over conventional plastics for many uses. They constitute a good basis for developing antimicrobial active packaging and coatings that slowly release fungicides and bactericides which migrate onto the packaged foods and combat contamination, so further development should be expected in future. Although to a far lesser extent, work is also being done to develop active packaging with biopolymer materials to control oxidation problems in foods and some interesting studies have been published. One possibility with good prospects is to develop active biopolymers that incorporate natural antioxidants such as vitamins or herb extracts. In the many other different forms of active packaging that are intended to retain or add components which may be beneficial for maintaining the quality or safety of packaged foods, the use of biopolymers has to date been anecdotal in practice.



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With active packing technologies, solutions to the possible sensory or even toxicity problems caused by a number of substances that may be present in foods as a result of food–package system interactions can certainly be found. Biopolymers are an excellent option for this purpose. They open up possibilities that conventional polymers do not offer and also help to limit the problems of using non-renewable raw materials and polluting the environment.

17.5

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18 Biobased intelligent food packaging P. Taoukis, National Technical University of Athens, Greece; M. Smolander, VTT Technical Research Centre of Finland, Finland

18.1

Introduction

The current attitude of the global society regarding the direction in which food packaging technology should evolve comprises two main concepts.The first focuses on maximum efficiency with minimum burden to the environment by use of the most environmentally friendly solutions that can provide the protective functionality required for food safety and integrity. Costefficient biodegradable materials and even edible packaging with improved technical characteristics are being intensively researched. The second concept aims to achieve additional functionality from the food packaging. Active, intelligent packaging allows for more than passive protection, potentially providing valuable information about the quality and safety status of the food product and contributes to better management of the food chain, reduction of food waste and increased protection of the consumer. The communicative ‘intelligence’ of a package refers to its ability to give information about the requirements of the product quality, such as package integrity (leak indicators) and time–temperature history of the product (time–temperature integrators (TTIs)). Intelligent packaging can also give information on product quality directly. Freshness indicators indicate directly the quality of the product (Smolander, 2003). Thus a signal of microbiological quality could be a result of a reaction between the indicator and the metabolites produced during the growth of the microflora of the product. Such direct or indirect indicators of quality or safety of the products are based on the recognition and thorough kinetic study of the deteriorative phenomena that define the spoilage process of the food through its


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shelf-life. Smart systems, usually biobased, are then designed, capable of responding or correlating to selected spoilage indices and communicating through an easily recognisable signal, such as the development or change of a colour, the quality or safety status of the product. Such systems have been sought for many years, with the first patents being recorded several decades ago (Clark, 1949; Lawdermilt, 1962). Various biomolecules – particularly enzymes, antibodies and nucleic acids – have been widely harnessed for such functional purposes. These biomolecules can be incorporated into paper, paper-like or other environmentally compatible materials, enabling the mass production of functional materials for various purposes. In this chapter the different types of biomolecules, as well as examples of their potential utilisation for functional purposes, are reviewed.

18.2

Biobased tools for the detection of quality-indicating metabolites

Enzymes have been widely utilised for analytical purposes, often in the form of spectrophotometrical assays, diagnostic test strips or different types of biosensors. On the other hand, the detection of quality-indicating metabolites of food products has been actively studied, work being motivated by the possibility of replacing time-consuming sensory and microbiological analyses used in the quality evaluation of food products. Several potential quality-indicating metabolites have been proposed as target molecules of the package-integrated communicative devices, i.e. freshness indicators. However, it should be stressed that the formation of the different metabolites always depends on the nature of the packaged food product, spoilage flora and the type of packaging, hence the correlation of the potential quality-indicating metabolite and the product quality should always be validated case by case (Dainty, 1996). A wide variety of freshness indicators reacting to the presence of mainly volatile quality-indicating metabolites by a colour change or by change in the electrical properties of the indicator material have been presented in the scientific literature (e.g. Honeybourne, 1993; Wolfbeis & List, 1995; Namiki, 1996; Wallach & Novikov, 1998; Miller et al., 1999; Byrne et al., 2002; Smolander et al., 2002, 2003, 2004b; Van Veen 2004; Pacquit et al., 2006a, 2006b; Williams et al., 2006). Many of these concepts, reviewed recently by Smolander (2003, 2008) and Kerry et al. (2006), are so far based on purely chemical reactions, but in the future the utilisation of biomolecules as the metabolite-recognising elements can be expected to expand due to the specificity and sensitivity offered by the biocatalysts. It has been proposed that considerable growth potential for biosensors is offered by pathogen detection and safety systems in the food packaging area (Aloncilja & Radke, 2003). Enzyme-based assays and sensors have already been established for several analytes potentially useful


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in the shelf-life assessment of food products; among the target metabolites for enzymatic detection methods are glucose, acetate, gluconate, d-lactate, ethanol, ammonia, biogenic amines, diamines and l-lactic acid (DeLuca et al., 2005; Nychas et al., 2008). The potential utilisation of different types of biomolecules for functional purposes, e.g. in diagnostics and packaging, were recently reviewed by Aikio et al. (2006). In this chapter the potential of biobased tools in the detection of deterioration taking place in the packaged food product via the use of quality-indicating metabolites is discussed. Where the target molecules for enzyme-based analytical devices are concerned generally, glucose is by far the most important analyte of enzymatic analysis due to the importance of evaluation of the blood glucose level in diabetes control. In the food sector, for instance, fruit quality has been proposed to be analysed with a biosensor array containing a glucose sensor (Jawaheer et al., 2003). In addition, glucose is also an initial substrate for many spoilage bacteria in air, vacuum packages and modified atmosphere (MA) packages. Glucose is consumed from the meat surface as the microbial growth takes place (Dainty, 1996) and it has been proposed by Kress-Rogers et al. (1993) that the measurement of the glucose gradient with a knife-type biosensor array probe could be utilised to evaluate the freshness of meat. However, instead of the glucose-type metabolite, which is consumed as the deterioration proceeds, metabolites with low or nonexistent initial concentrations are preferred in freshness evaluation with the aid of package-integrated, biobased indicators and sensors. Ethanol, in addition to lactic and acetic acid, is an important indicator of fermentative metabolism of lactic acid bacteria. The concentration of ethanol has been found to increase as a function of total viable count of the product and storage time (e.g. Rehbein, 1993; Randell et al., 1995). Ethanol together with acetaldehyde has a remarkable role also in fruit ripening, as reviewed by Pesis (2005). The accumulation of ethanol from fresh produce due to low oxygen concentration and elevated carbon dioxide concentration is generally considered as an indicator as well as a cause of quality deterioration (Gonzalez-Aguilar et al., 2004; Imahori et al., 2007). Enzymatic biosensors based on alcohol oxidase have been widely studied and are reviewed by Azevedo et al. (2005). The bi-enzymatic (alcohol oxidase and horseradish peroxidase) system together with a redox dye or pH indicator has been utilised in ethanol-detecting colour indicators by Barzana et al. (1986) and Adams (1988), the main application being in human diagnostics. Reports on the utilisation of ethanol for quality indication of packaged fresh produce have also been published, e.g. by Cameron and Talasila (1995) who studied the potential of detecting the unacceptability of packaged, respiring products by measuring ethanol in the package headspace with the aid of alcohol oxidase, peroxidase and a chromogenic substrate. Smyth et al. (1999) reported also that enzymatic test strips for ethanol could be used to measure ethanol in the gas phase and were


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suitable for detecting low-oxygen injury in MA packages containing lightly processed vegetables (lettuce, cauliflower, broccoli and cabbage). The extent of adenosine triphosphate (ATP) degradation, expressed as the K-value (ratio of the sum of hypoxanthine and inosine, and the total concentration of ATP-related compounds, as defined by Henehan et al., 1997) has been reported to correlate with the sensory quality of fish and also other types of meat, and has been used as a freshness-indicating parameter (Watanabe et al., 1989; Yano et al., 1995a; Hattula, 1997; Sallam, 2007). ATP degradation products indicating the quality deterioration of fish can be analysed by enzymatic test strips manufactured by Transia, and ATP degradation products have also been frequently measured with biosensors. For instance, Cubukcu et al. (2007) measured hypoxanthine from canned tuna with a xanthine oxidase-based sensor and Yano et al. (1995a) and Mulchandani et al. (1990) developed enzymatic, electrochemical sensors for the quality control of beef. Package-integrated, freshness-indicating concepts reacting to ATP degradation products have not been presented, but a non-destructive colorimetric test for the evaluation of the remaining shelflife of a Japanese raw fish dish, sashimi, was presented by Watanabe et al. (2005). In this system a test solution containing hypoxanthine, thiazole blue redox dye and xanthine oxidase is kept with a fish product and reacts analogously with it to the storage time and conditions. The concentration of endogenous biogenic amines (tyramine, histamine, tryptamine, phenylethylamine, serotonin, putrescine, cadaverine, spermine and spermidine) is low in non-fermented, fresh food and the quantity of biogenic amines is considered as a marker of the level of microbiological contamination in food (Önal, 2007). For instance, the accumulation of tyramine at bacterial numbers above 106/g has been reported in many studies of different types of stored meat, and tyramine has been proposed as a quality indicator for beef, pork and poultry (Edwards et al., 1987; Ordonez et al., 1991; Schmitt & Schmidt-Lorenz, 1992; Smith et al., 1993; Yano et al., 1995b). In our own studies the effect of storage temperature in various constant and variable temperature schemes on the formation of biogenic amines in MA-packed broiler chicken cuts, as well as the applicability of biogenic amines as quality-indicating metabolites of MA-packaged broiler chicken cuts, have been studied (Rokka et al., 2004). It was found that the formation of tyramine seemed to be highly consistent with the increase in the aerobic mesophilic viable count. It was also found out that in conditions without putrescine and cadaverine formation the growth of Enterobacteriaceae, proteolytic bacteria, hydrogen sulphide-producing bacteria and clostridia was also clearly retarded. Thus the three amines tyramine, cadaverine and putrescine seemed to be promising indicators for both storage time and temperature as well as for the microbiological quality of MA-packed broiler chicken cuts. In addition to their quality-indicative nature, biogenic amines can have toxic effects. Histamine is associated with scombroid poisoning and a



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tolerance level of 100 mg/kg of fish has been established for it by the Food and Drug Administration (Kaniou, 2001). A specific colorimetric enzymebased determination of histamine by recombinant histamine dehydrogenase was recently presented by Bakke et al. (2005). Another simple and rapid histamine-specific detection method was recently developed by Patange et al. (2005). This method is, however, not based on biomolecules but on p-phenyldiazonium sulphonate. Enzymatic biosensors based on amine oxidases have been developed for the detection of biogenic amines from, for example, cheese, poultry, fish and beef (Yano et al., 1995b; Frébort et al., 2000; Niculescu et al., 2000; Okuma et al., 2000; Carelli et al., 2007). An enzymatic determination of the total amount of biogenic amines using transglutaminase was suggested by Punakivi et al. (2006). Volatile amines trimethylamine (TMA), ammonia (NH3) and dimethylamine constitute total volatile basic nitrogen compounds, the levels of which have been recognised as an indicator of seafood spoilage under EU Directive 95/149/EEC. TMA, formed by microbial action in the fish muscle, is generally considered as a major metabolite responsible for the spoilage odour of seafood; however, the variation in the concentration of its precursor TMA N-oxide according to the species and season restricts the applicability of TMA as a general fish quality indicator (Dainty, 1996; Rodríguez et al., 1999). In addition to seafood quality indicators, volatile amines have also been preliminary suggested as an indicator for the quality of poultry meat (Balamatsia et al., 2007). Numerous freshness-indicator concepts targeted to volatile amines, although mainly based on chemical reactions, have been presented (Miller et al., 1999; Loughran & Diamond, 2000; Khalil et al., 2003; Oberg et al., 2006; Pacquit et al., 2006a, 2006b). In addition to the purely chemical reagents, betalain- or flavonoid-based molecules have been used as pHsensitive dyes for detecting amines from packaged foodstuff by Williams and Myers (2005) and Williams et al. (2006), who describe a colour-changing indicator, the sensitivity of which can be adjusted by tuning the original pH of the indicator. This concept by Williams et al. is currently being marketed as freshQTM. An enzymatic monooxygenase-based biosensor system in the form of a microconductometric biosniffer for the detection of TMA was proposed by Fillit et al. (2007). Sulphuric compounds have a remarkable effect on the sensory quality of meat products due to their typical odour and low odour threshold, and they have been found to be produced during the spoilage of poultry by many bacteria (Lea et al., 1969; Freeman et al., 1976; Vieshweg et al., 1989; Russell et al., 1997; Arnaut-Rollier et al., 1999; Kalinowski & Tompkin, 1999). H2S has been proposed to indicate quality problems in meat (Nicol et al., 1970; Gill & Newton, 1979; Egan et al., 1989; Dainty, 1996) and also cause putrid spoilage aromas in fish (Olafsdóttir & Fleurence, 1997). In our studies we have reported a clear effect of the storage time and temperature on the accumulation of hydrogen sulphide and dimethyl sulphide


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in MA-packaged broiler chicken cuts (Rajamäki et al., 2006) and on the sulphuric odour of the product (Smolander et al., 2004a). We have utilised a reaction between hydrogen sulphide and biomolecule myoglobin in a freshness indicator for the quality control of MA-packed poultry meat (Ahvenainen et al., 1997; Smolander et al., 2002). Freshness indication is based on the colour change of myoglobin by hydrogen sulphide (H2S). Another, non-biobased system by UPM Raflatac based on a reaction between hydrogen sulphide and a nano-scale layer of silver (Smolander et al., 2004b) has also been presented.

18.3

Biobased tools for the detection of pathogenic and microbial contamination

In addition to the biobased sensor and indicator systems described above, which react to the presence of metabolites produced in the normal microbiological spoilage of food products, the direct determination of the contaminating microbes, especially pathogenic contaminations, would be advantageous. Immunochemical methods rely on specific binding of an antibody to the target compound or class of compounds. Immunochemical detection methods have been utilised in clinical chemistry, environmental analysis and evaluation of food safety. Immunochemical test kits have been developed for the specific detection of several pathogenic bacteria such as Escherichia coli O157, Listeria monocytogenes, Campylobacter jejuni, Clostridium botulinum and Salmonella (Arora et al., 2006). Typically, for pathogen-detecting immunoassays, the enrichment of bacteria is often recommended prior to analysis, hence complicating the direct adaptation of this system to package-integrated functionality. On the other hand, rapid pathogen detection would offer advantages not only in package-integrated applications, but also in quality assurance where the Hazard Analysis and Critical Control Point concept, with strong emphasis on the rapid screening of raw material quality, is applied. New methods potentially enabling on-site testing are continuously being developed and have been recently reviewed by Arora et al. (2006). Some examples of immunochemical, material-integrated, pathogendetecting systems based on immunochemical reactions have been presented. The commercially marketed Toxin GuardTM by Toxin Alert Inc. (Ontario, Canada, http://www.toxinalert.com/) is a system of building polyethylenebased packaging material that is able to detect the presence of pathogenic bacteria (Salmonella, Campylobacter, E. O157 and Listeria) with the aid of immobilised antibodies. As the analyte, i.e. toxin or micro-organism, is in contact with the material, it will first be bound to a specific, labelled antibody and then to a capturing antibody printed in a certain pattern, resulting hence in a visually readable signal (Bodenhamer, 2000). Another commercial system for the detection of specific micro-organisms like Salmonella sp.,



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Listeria sp. and E. coli is the Food Sentinel SystemTM by Sira Technologies Inc. (USA). This system is also based on an immunochemical reaction and the reaction takes place in a bar code (Goldsmith, 1994; Woodaman, 2002). If the particular micro-organism is present, the bar code becomes unreadable. The harnessing of nucleic acids for diagnostic purposes has been widely studied in recent years. The principles and recent developments of nucleic acid-based biosensors generally and the detection of food pathogens have been reviewed, for example by Junhui et al. (1997) and Arora et al. (2006) respectively. The basic principle common to nucleic acid biosensors relies on nucleic acid hybridisation of the single-stranded deoxyribonucleic acid (DNA) on the sensor surface and a complementary DNA molecule. Hybridisation can be detected with different detection methods, such as optical, electrochemical and piezoelectric methods. Nucleic acids have also been widely utilised in microarray-based systems emerging from traditional biochemical assays. For instance, Affymetrix (USA), in collaboration with the Institut Pasteur (France), has been developing a microarray-based pathogen-detection method that could be used to type multiple pathogens in a single experiment, with high sensitivity and specificity. In addition to the diagnostic functionalities that can be built into intelligent packaging, the specific hybridisation of DNA can also be utilised in concepts protecting packaged goods from counterfeiting and tampering. SigNature™ DNA Markers offered by Applied DNA Sciences (USA) are based on DNA segments from one or more botanical sources, which are rearranged into unique encrypted sequences and act as an anti-counterfeit technique, potentially integrated with existing security solutions such as barcodes, radio-frequency identification (RFID), holograms and microchips. On-site verification is carried out using an encryption detector pen, which in contact with the DNA label triggers a reversible colour change: for forensic level authentication polymerase chain reaction testing kits can be used. Not only pathogenic contamination, but also microbial contamination of any sterile product can be detected with a package-integrated intelligent system. Van Veen (2004) patented a method for non-invasive detection of contamination with a micro-organism in a closed, sterile container, which is based on detecting the extracellular enzymatic activities of the contaminating micro-organism. An indicator substrate is provided in a coating of the inner side of a package, and the conversion of this substrate by the enzyme is detected either visually or by optical measurement. DeCicco and Keeven (1995) described an indicator based on the colour change in the chromogenic substrates of enzymes produced by contaminating microbes. The indicator can be applied to contamination detection in liquid health care products. Hydrolytic enzymes were also reported to indicate fungal spoilage in bakery products (Marin et al., 2003). Colorimetric detection of


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the enzymatic activity of peroxidase has been proposed for use as a tool for the evaluation of the freshness of rice grains (Chen & Chen, 2003). An indicator for the detection of micro-organisms was proposed by Namiki (1996). The principle of the indicator is the degradation of the lipid membrane by micro-organisms and the subsequent diffusion of a coloured compound. In addition to purely informative intelligent packaging systems, the materials can not only signal but respond to the presence of contaminating microbes.Antimicrobial packaging systems combine food packaging materials with antimicrobial substances to control undesirable microbial surface contamination of foods. For instance, hydrogen peroxide, a substance with antimicrobial activity, can be introduced into the package in the reaction catalysed by glucose oxidase, which has been covalently immobilised onto amino or carboxyl plasma-activated bi-oriented polypropylene films via suitable coupling agents (Vartiainen et al., 2005). In the work by Vartiainen et al. the biomolecules attached to the packaging surface retained the necessary enzymatic activity level for complete inhibition of food spoiling bacteria in various conditions for a storage period of 1 month. Another type of ‘release-on-demand’ approach to the use of antimicrobial substances is presented by Thijssen et al. (2003), who patented a preservative-releasing packaging system that only releases its preservative when bacterial growth occurs. An antimicrobial substance is provided in or on the packaging material in a capsule of carbohydrates and/or proteins, which can be decomposed by a micro-organism. Thus, the antimicrobial substance only comes into contact with the packaged goods at the moment when there is microbial activity.

18.4

Biobased indicators for monitoring the time–temperature history

Perishable food products, even when they are optimally processed and packaged, have a limited shelf life which can be considerably shortened if they are not distributed and stored appropriately through the entire product life cycle, including the post-processing phase and ideally extending to the consumer’s table. In practice, temperature conditions in chilled or frozen distribution and handling very often deviate from those recommended (Taoukis et al., 1998; Giannakourou and Taoukis, 2003; Giannakourou et al., 2005). Since temperature is the main shelf-life-determining, post-processing parameter, monitoring it constitutes an essential prerequisite for effective shelf-life management. The complexity of such a task is emphasised when the variation in temperature exposure of single products within batches or transportation subunits is considered. A cost-efficient way to monitor the temperature conditions of food products individually throughout distribution would be required in order to indirectly indicate their real quality state. TTIs could be effective tools to fulfil this requirement. Based on reliable



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models of food product shelf-life and the kinetics of TTI response the effect of temperature can be monitored, recorded and translated, from production to the consumer’s table. A TTI-based system could lead to realistic control of the chill chain, optimisation of stock rotation and reduction of waste, and efficient shelf-life management. TTIs are inexpensive, active ‘smart labels’ that can show an easily measurable, time–temperature-dependent change that reflects the full or partial temperature history of a food product to which it is attached (Taoukis & Labuza, 1989). The principle of TTI operation is a mechanical, chemical, enzymatic or microbiological irreversible change usually expressed as a visible response, in the form of a mechanical deformation, colour development or colour movement. The rate of change is temperature dependent, increasing at higher temperatures similarly to the deteriorative reactions responsible for the food spoilage. The visible response of the TTI thus cumulatively reflects the time–temperature history of the food product it accompanies. TTIs as an integral part of an intelligent package can serve as an active shelf-life signal in conjunction with the ‘use by date’ on the label. Over the last three decades numerous TTI systems have been proposed, of which only few reached the industrial prototype and even less the commercial application stage (Taoukis, 2001; Taoukis and Labuza, 2003). Biological TTIs have been developed based either on enzymatic reactions (Tsoka et al., 1998; Reichert et al., 2006; Sun et al., 2008) or on microbiological principles (Ellouze et al., 2007; Vaikousi et al., 2007). Systems that are currently available for application at least as prototypes and are based on biological principles are described below. The CheckPoint® TTI (VITSAB A.B., Malmö, Sweden) is an enzymatic system. The TTI is based on a colour change caused by a pH decrease which is the result of a controlled enzymatic hydrolysis of a lipid substrate (Blixt et al., 1977; Angerhem and Nielsson, 1981). Before activation the indicator consists of two separate compartments, in the form of plastic mini-pouches. One compartment contains an aqueous solution of a lipolytic enzyme, such as pancreatic lipase. The other contains the lipid substrate absorbed in a pulverised polyvinyl chloride carrier and suspended in an aqueous phase and a pH indicator mix. As substrates, glycerine tricapronate (tricaproin), tripelargonin, tributyrin and mixed esters of polyvalent alcohols and organic acids are mentioned. Different combinations of enzyme–substrate types and concentrations can be used to give a variety of response lives and temperature dependencies. At activation, enzyme and substrate are mixed by mechanically breaking a separating barrier inside the TTI. Hydrolysis of the substrate (e.g. tricaproin) causes acid release (e.g. caproic acid) and the pH drop is translated as a colour change of a pH indicator from deep green to bright yellow or orange red (Fig. 18.1).A visual scale of the colour change can facilitate visual recognition and evaluation of the colour change. The continuous colour change can also be measured instrumentally and be used in a shelf-life management scheme.


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Expiration

Production Food product shelf life

Fig. 18.1

Response scale of enzymatic CheckPoint® TTI.

(a)

(b)

(c)

Fig. 18.2

Response scale of Microbial TTI (eO)®.

The (eO)® TTI (CRYOLOG, Gentilly, France) is based on a time– temperature-dependent pH change that is expressed as a colour change through suitable pH indicators. The pH change is caused by controlled microbial growth occurring in the gel containing the TTI (Louvet et al., 2005; Ellouze et al., 2007). The parameters of the TTI can be adjusted in relation to the selected micro-organisms and the composition of the gel. The response of the TTI is claimed to mimic the spoilage of the monitored food products as it is based on similar micro-organisms, such as selected patented strains of micro-organisms, e.g. Carbonbacterium piscicola, Lactobacillus fuchuensis and Leuconostoc mesenteroides. The pH drop is translated into a gradual colour change of a pH indicator from green to red (Fig. 18.2). A visual scale of the colour change can facilitate visual recognition and evaluation of the colour change. The continuous colour change can also be measured instrumentally and can be used in a shelf-life management scheme. A kinetic modelling approach allows the potential user to develop an application scheme specific to a product and to select the most appropriate TTI without the need for extensive testing of the product and the indicator (Taoukis et al., 1999; Taoukis, 2001). This approach emphasises the importance of reliable shelf-life modelling of the food to be monitored. Shelf-life



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models must be obtained with an appropriate selection and measurement of effective quality indices and based on efficient experimental design at isothermal conditions covering the range of interest. The applicability of these models should be further validated under fluctuating, non-isothermal conditions representative of the real conditions in the distribution chain. Similar kinetic models must be developed and validated for the response of the suitable TTI. Such a TTI should have a response rate with temperature dependence, i.e. activation energy EA1, in the range of the EA of the quality deterioration rate of the food. The total response time of the TTI should be at least as long as the shelf-life of the food at a chosen reference temperature. TTI response kinetics should be provided and guaranteed by the TTI developer as specifications of each TTI system they supply. The information provided by the TTI bearing intelligent packaging, signalling the remaining shelf-life at any point of the cold chain, can be used to improve distribution control and stock rotation practices. The conventional approach, the first in, first out (FIFO) system, aims to establish a ‘steady state’ with all products being sold at the same quality level. FIFO assumes that all products have gone through uniform handling, thus quality is solely a function of time. The use of the indicators can help to establish a system that does not depend on this unrealistic assumption. This system would ensure that products with the shortest remaining shelf-life would be sold faster. This approach was coded LSFO (least shelf-life, first out). The LSFO reduces the number of rejected products and the consumer dissatisfaction since the fraction of product with unacceptable quality at the time of use or consumption is minimised. LSFO succeeds in reducing wasted products, by accelerating, at selected decision making points of the product life cycle, those product units with the shorter shelf-life, according to the response of the TTI intelligent packaging (Taoukis et al., 1998; Giannakourou et al., 2001; Giannakourou and Taoukis, 2003). The state of the TTI technology and of the scientific approach with regards the quantitative safety risk assessment in foods allowed further development of a TTI-based management system that could assure both safety and quality in the food chill chain (Koutsoumanis et al., 2005). The development and application of such a system with the acronym SMAS was the target of the multinational European research project ‘Development and Modeling of a TTI based Safety Monitoring and Assurance System (SMAS) for chilled Meat Products’ (project QLK1-CT2002–02545, 2003– 2006; http://smas.chemeng.ntua.gr). SMAS uses the information from the TTI response at designated points of the chill chain, ensuring that the temperature-burdened products reach consumption at acceptable quality and with a reduced risk level. Although SMAS is developed for meat products, the same principles can be effectively applied to the management of the chill chain of all chilled food products (Tsironi et al., 2007).


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18.5

Other intelligent packaging systems utilising biomolecules

The main applications of biobased intelligent packaging lie naturally in the detection of microbiologial quality of the packaged product either directly or through metabolites produced by the bacteria or through the time– temperature history of the product. However, some other application areas, such as indicators for humidity and package-integrated power sources – can also be identified for biobased communicative devices. Humidity has an important role in the quality maintenance of many food products. Excess moisture can deteriorate the food quality principally in two different ways. Microbiological quality can be affected by condensed moisture which enables microbial growth. Moisture absorbed to the product can also cause physical changes in the product. On the other hand, the quality maintenance of many fresh products like fruits and vegetables requires certain relative humidity levels in order to prevent the drying and weight loss of the product. Enzymatic reactions have been utilised in humidity and moisture indicators in two basic ways: the water molecules present can participate in the enzymatic reaction itself, or the presence of moisture can be followed by dissolution of other reagents participating in the reaction. In the system described by Sahlberg et al. (2003) water participates as a reagent in the enzymatic hydrolysis reaction catalysed by urease. The accumulation of the reaction products is followed by an increase in conductivity, which can be read electrically. This label-type moisture-sensitive system could be applicable to the evaluation of the moisture exposure of fibre materials and transported goods. In another enzymatic indicator system described by Powell (1982) the enzymatic reaction catalysed by glucose oxidase is activated by the dissolution of the substrate (glucose) in the presence of moisture. In the enzymatic reaction the colour-forming reagent added to the system undergoes a visual colour change due to the hydrogen peroxide produced. Eakin (2003) also described the use of enzymes in a moisture indicator for a wound dressing. The indicator is based on a colour change taking place as moisture enables the mixing of the indicator compounds. An enzyme, e.g. glucose oxidase, forms part of the colour-changing reaction mixture. Biofuel cells are devices capable of directly transforming chemical energy to electric energy via electrochemical reactions involving enzymatic catalysis. Various oxidoreductases can be potentially applied as biocatalysts for the anodic or cathodic half-cell reactions in biofuel cells, as recently reviewed by Minteer et al. (2007) and Davis and Higson (2007). The introduction of enzymes enables the operation of the cell under mild conditions and the utilisation of various renewable chemicals as fuels. Biofuel cells can be utilised in various applications, including miniaturised electronic devices, self-powered sensors and portable electronics. It is also anticipated that



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implanted biofuel cells could utilise body fluids, particularly blood, as the fuel source for the generation of electrical power, which may then be used to activate pacemakers, insulin pumps, prosthetic elements or biosensing systems. Biofuel cells have also been suggested for use in military or security fields for the detection of explosives. If realised using roll-to-roll manufacturing methods, these biobased devices could also be applicable in intelligent packaging applications as disposable power sources for, for example, active RFID tags, where a local power source enables longer reading distance than presently and more functions, such as memory and sensors. Printed bio-electronic devices have been realized, for example by Setti et al. (2005, 2006), who have studied thermal inkjet printing as a tool to deposit enzymes in biosensor applications as a separate layer on top of the conductive surface. Incorporation of the biocatalyst directly into the conducting layer, as well as the improvement of the biocatalyst stability by ink additives, has also been presented by Hart and Collier (1998), Schumacher et al. (1999), Mersal et al. (2004) and Tymecki and Koncki (2006). In our own studies we have aimed at the realisation of a cheap, disposable enzymebased power source: a Tekes (Finnish Funding Agency for Technology and Innovation)-funded project ‘Printable miniature power source’ was recently carried out in collaboration with Helsinki University of Technology and Åbo Akademi University. The work focused on the construction of printable enzyme electrodes, which is a challenging area since most conductive inks are based on various solvents, which runs contradictory to the fact that most enzymes need aqueous solutions for their stability and catalytic activity (Boer et al., 2005; Smolander et al. 2008). The results showed that the enzymatic activity can be retained and maintained for months in different conductive inks, depending on the storage conditions. Under optimised conditions, a fuel cell containing a laccase-based cathode maintained its capacity to generate power for several days.

18.6

Future trends

The main research on biological indicators focuses on the detection of the microbiologial quality of the packaged product, whether directly, through metabolites produced by the bacteria or through the time–temperature history of the product. The results of research in this exciting area will gradually be translated to the wider application of biobased intelligent packaging. An example of the various possibilities enabled by the introduction of biomolecules into materials in the area of food packaging is illustrated by Hamilton et al. (2004). A multifunctional food wrap comprising a material web, an adhesive and at least one secondary function is described. The material web is selected from the group consisting of paper, polymeric films, plastic films, cloths, fabrics, wovens, non-wovens, laminates, metal foils and coated papers. The secondary function can be antimicrobial protection


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(by using bacteriocins, enzymes), food preservation, atmosphere modification (by using oxygen-absorbing enzymes), odour elimination (by using surfactant-treated chitosan), product spoilage indication (by using detector antibodies), temperature indication, flavour enhancement and moisture absorption. Active, intelligent packaging will provide more than passive protection, making readily and practically available valuable information about the quality and safety status of the food products and will contribute to better management of the food chain, reduction of the food waste and increased protection of the consumer.

18.7

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19 Environmentally compatible packaging of fresh agricultural and horticultural produce C. Bishop and S. Hanney, Writtle College, UK

19.1

Introduction

Traditionally many fresh products are already packaged by nature – for example the skin of an apple, mango or banana – this outside layer acts as a protective coating against damage, disease, water loss and insects. However, in all three cases they can only be stored in ambient conditions in their natural state for a short period of time without losing quality, such that they become unsaleable. Postharvest principles and packaging tries to extend this period for one or a combination of the following requirements: (a)

to extend marketability, to store until prices rise after the initial harvest or to gain access to other markets locally or worldwide; (b) to give additional consumer benefits by extending the ‘at home’ life; (c) to reduce in-store wastage by giving longer display periods while still allowing the customer sufficient eating opportunities. The presence of food packaging in many domestic waste bins worldwide is a reflection of the increasing benefit of postharvest practices such as packaging innovation. It must be stressed that the challenges of food packaging are very varied depending on the fresh product and Table 19.1 summarises the issues for a range of fresh products. The maintenance of the correct temperature with fresh produce is of paramount importance, as this will affect its life after harvest and the length of time that it is saleable or eatable. Any form of packaging that compromises the ability to maintain the desired temperature will certainly result in higher wastage and so will be counter-productive from an environmental standpoint. All fresh produce is respiring so it is consuming oxygen, using


Table 19.1 Common storage requirements for a selection of fruits and vegetables (UC Davis Postharvest Center, 2007) Storage temperature (°C)

Storage relative humidity (%)

Highest freezing temperature (°C)

Ethylene production

Ethylene sensitivity

Approximate storage life

Common name

Scientific name

Apricot

Prunus armeniaca Asparagus officinalis Persea americana Musa paradisiaca var. sapientum Brassica oleracea var. Italica Brassica oleracea var. Gemnifera Daucus carota

−0.5–0

90–95

−1.1

M

M

1–3 weeks

2.5

95–100

−0.6

VL

M

2–3 weeks

3–7

85–90

−1.6

H

H

2–4 weeks

13–15

90–95

−0.8

M

H

1–4 weeks

0

95–100

−0.6

VL

H

10–14 days

0

95–100

−0.8

VL

H

3–5 weeks

0

98–100

−1.4

VL

H

3–6 months

Apium graveolens var. Dulce Prunus avium

0

98–100

−0.5

VL

M

1–2 months

−1 to 0

90–95

−2.1

VL

L

2–3 weeks

Solanum melongena Vitis vinifera a = fruit b = stem

10–12

90–95

−0.8

L

M

1–2 weeks

−0.5–0

90–95

−2.7 a −2.0 b

VL

L

1–6 months

Asparagus, green, white Avocado cv Fuerte, Hass Banana Broccoli Brussel sprouts Carrots, topped

Celery Cherries, sweet Eggplant Grape


Observations and beneficial CA conditions 2–3% O2 + 2–3% CO2 5–12% CO2 in air 2–5% O2 + 3–10% CO2 2–5% O2 + 2–5% CO2 1–2% O2 + 5–10% CO2 1–2% O2 + 5–7% CO2 no CA benefit; ethylene causes bitterness 1–4%O2 + 3–5% CO2 10–20% O2 + 20–25% CO2 3–5% O2 + 0% CO2 2–5% O2 + 1–3% CO2; to 4 weeks 5–10% O2 + 10–15 CO2

Kiwifruit; Chinese gooseberry Lemon

Actinidia chinensis

0

90–95

−0.9

Citrus limon

10–13

85–90

−1.4

Lettuce

Lactuca sativa

0

98–100

−0.2

VL

H

2–3 weeks

Mango

Mangifera indica

13

85–90

−1.4

M

M

2–3 weeks

Melons – cantaloupes and other netted melons Mint

Cucurbita melo var. reticulatus

2–5

95

−1.2

H

M

2–3 weeks

Mentha spp.

0

95–100

VL

H

2–3 weeks

Mushrooms

Agaricus, other genera Prunus persica

0

90

−0.9

VL

M

7–14 days

−0.5–0

90–95

−0.9

M

M

2–4 weeks

Allium cepa

0

65–70

−0.8

VL

L

1–8 months

0

95–100

−1.1

VL

H

1–2 months

Parsnips

Petroselinum crispum Pastinaca sativa

0

95–100

−0.9

VL

H

4–6 months

Pineapple

Ananas comosus

7–13

85–90

−1.1

L

L

2–4 weeks

Nectarine

Onions – mature bulbs, dry Parsley

L

H

3–5 months

1–2% O2 + 3–5% CO2

1–6 months

5–10%O2 + 0–10% CO2 2–5% O2 + 0% CO2 3–5% O2 + 5–10% CO2 3–5% O2 + 10–15% CO2 5–10% O2 + 5–10% CO2 3–21% O2 + 5–15% CO2 1–2% O2 + 3–5% CO2; internal breakdown 3–10 °C 1–3% O2 + 5–10% CO2 5–10% O2 + 5–10% CO2 Ethylene causes bitterness 2–5% O2 + 5–10% CO2 (Continued)


Table 19.1 Cont’d Storage temperature (°C)

Storage relative humidity (%)

Highest freezing temperature (°C)

Ethylene production

Ethylene sensitivity

Approximate storage life

−0.5–0

90–95

−0.8

M

M

2–5 weeks

10–15

90–95

−0.8

VL

M

10–14 days

4–8 −0.5–0

95–98 90–95

−0.8 −0.9

VL L

M L

5–10 months 3–6 days

Common name

Scientific name

Plums and prunes Potato, early crop Potato, late crop Raspberries

Prunus domestica Solanum tuberosum

Rhubarb

0

95–100

−0.9

VL

L

2–4 weeks

Spinach

Rheum rhaponticum Spinacia oleracea

0

95–100

−0.3

VL

H

10–14 days

Strawberry

Fragaria spp.

0

90–95

−0.8

L

L

7–10 days

8–10

85–90

−0.5

H

L

1–3 weeks

10–13

90–95

−0.5

VL

H

2–5 weeks

0

95–100

−0.3

VL

H

2–3 weeks

10–15

90

−0.4

VL

H

2–3 weeks

Tomato, firm-ripe Tomato, mature-green Watercress; garden cress Watermelon

Rubus idaeus

Lycopersicon esculentum Lepidium sativum; Nasturtium officinales Citrullus vulgaris

CA, controlled atmosphere; L, low; H, high; M, moderate; VL, very low. © 2008, Woodhead Publishing Limited

Observations and beneficial CA conditions 1–2% O2 + 0–5% CO2 No CA benefit No CA benefit 5–10% O2 + 15–20%CO2 5–10% O2 + 5–10% CO2 5–10% O2 + 15–20%CO2 3–5% O2 + 3–5% CO2 3–5% O2 + 2–3% CO2

No CA benefit

Environmentally compatible packaging of produce

463

up the carbohydrate and releasing water vapour and carbon dioxide: this reaction like any chemical reaction increases with temperature, sometimes exponentially. Almost all diseases and fungi will develop faster at higher temperatures. Moisture loss through the skin of fresh produce is directly proportional to the vapour pressure deficit which is a combination of relative humidity and temperature with temperature predominating. One of the largest users of packaging within the food sector is the fresh horticultural and agricultural produce sector. Many people remember the days gone by when the total packaging of all their fresh produce was a few brown paper bags (the same people seem to have less clear memories of the smaller range of fresh produce, the time taken in food preparation or even how much of the bought produce was thrown away because it was damaged or became diseased). Today the situation is very different and although there are challenges facing the whole packaging industry there are a number of specific challenges facing fresh produce.

19.2

Specific challenges for fresh produce packaging

The specific challenges for fresh produce packaging can be summarised as: (a) seasonal variation of demand – which may change by the day depending on the weather; (b) differences in supply location depending on the time of year and the weather. The packaging can influence the shelf-life of fresh produce (Jacomino et al., 2005). Figure 19.1 shows the difference in supply of three products in the UK, but only shows a very simplistic situation which warrants some further explanation. The supply of cherries is mainly from the UK, Italy and Turkey in the summer where the fruit is seen as a pleasant addition to summer fruits with ‘medium cost’ packaging; in contract, in the winter the supply is from the southern hemisphere and cherries are then seen as a luxury item and are packaged and marketed as such. The lettuce supply is mainly from the UK in the summer and from Spain in the winter (although supply can be introduced from California if there is bad weather in Europe). The majority of whole-head lettuce is marketed in a bag or configured sheet wrap throughout the year. There is increasing demand for minimally processed lettuce both from the food service and the domestic sectors either as single or mixed varieties; the packaging of this is commonly in modified atmosphere bags with 90% nitrogen, 5% carbon dioxide and 5% oxygen or atmospheres similar to this. The packaging type is very different to that used for whole-head lettuce. Reduction of oxygen levels will reduce the rate of respiration of most fresh produce and increased levels of carbon dioxide can have a fungistatic effect (Kader, 1986).


464

Environmentally compatible food packaging Apples

Cherries

Lettuce

Percentage of annual total

35 30 25 20 15 10 5 0 Jan Feb Mar Apr May Jun

Jul Aug Sep Oct Nov Dec

Month

Fig. 19.1

Graph showing the UK monthly demand of three different produce types (as a percentage of annual total) (Mason et al., 2002).

Apples come in a large variety of packaging forms of which the following are some examples: (a) supplied loose to the customer but having arrived at the retail outlet in cartons with the apples being kept in layers on dimple trays (one supermarket store visited in February 2007 had apples being supplied in seven different types of dimple tray); (b) supplied in plastic bags packed at source or taken from a carton and repacked with either a specific weight or number of fruit of a specific size; (c) supplied in a tray with an over-wrap; (d) supplied in a punnet. A further example of the variety of packaging that exists is one UK potato packer who supplies potatoes in over 30 different forms of packaging (some just different bag sizes) to one supermarket alone.

19.3

Industry response

There has been considerable publicity, particularly in the trade press, on initiatives by the supermarkets to introduce more environmentally compatible packaging. It is commonly recognised that the first supermarket to introduce this was the UK retailer Sainsbury’s (European Bioplastics, 2007). Global consumption of biodegradable packaging during 2005–6 was nearly 43 000 tonnes, and this is expected to grow to 116 000 by 2011, an average annual growth rate of 22% (Pira report, as reported by plastemart.com, 2007). The Fresh Produce Journal frequently has articles headlined ‘Degradable produce packaging in the Co-op’ (FPJ, 2005b) or ‘Belgium goes biodegradable’ (FPJ, 2003) or ‘Bio-degradable packs on show’ (FPJ, 2005a) and many



465

more, often featuring specific supermarkets. Common examples of these supermarkets include Delhaize (Belgium), Iper (Italy), Albert Heijn (The Netherlands) and Migros (Switzerland), and during 2006 WalMart introduced its first range of fresh produce in poly-lactic acid (PLA) (European Bioplastics, 2007). The European Bioplastics organisation announced a rise in demand of up to 100% for biodegradable products during 2006, but they still have some way to go as currently less than 1% of packaging used in the EU is biodegradable (European Bioplastics, 2007). It is estimated that half of the 6 million tonnes of plastic packaging used annually in the European Union could be substituted by bioplastics, with vegetable packaging alone potentially accounting for 400 000 tonnes (Bioplastics24, 2007). Currently fresh produce dominates biodegradable materials usage, with a 41% share of the bioplastic market (Pira report, as reported by Merrett, 2007), due in part to the short shelf-life and low unit weight of many fresh produce items. The EU bioplastic substitution programmes may feature the introduction of biodegradable packaging for a specific range of products, such as organic salads or replacing potato packaging with a recyclable co-extrusion film. This is slightly ironic though, as in many cases the co-extruded or laminated film cannot be re-pulped, adding cost from the skeletal waste and also hindering further recycling, and so making the packaging less environmentally sound. All the programmes that have been introduced to date are for specific parts of the range and although there is much discussion over using only biodegradable packaging, this may still be some way into the future. Retailers such as The Greenery and Eosta in The Netherlands are looking at ways to convert their whole packaging range to biodegradable materials (European Bioplastics, 2007). Current usage of biodegradable materials is centred around the US (16 047 tonnes p.a.) and Europe (19 350 tonnes p.a.), but demand is expected to rise most, at 24.6%, in Eastern Europe, increasing consumption by 2463 tonnes p.a. (Pira report, as reported by Merrett, 2007). One further concern, particularly with the packaging of organic products, has been the use of source material based upon GM bred corn being used to produce the starch (such as PLA) that is then used to produce the packaging material. This is an issue yet to be resolved, and remains a challenge as currently the main worldwide supplier of this material is located in the US, and segregation of raw input materials here would be difficult; it is possible that this issue may lead to opportunities for producing the raw materials on another site or even in another part of the globe. It highlights the need for foresight and expensive investment in specialist production facilities, especially at this time when these higher priced products are finding it difficult to enter a highly competitive marketplace and gain both product recognition and brand/material reputation. This also highlights the need to transport the material, adding further carbon emissions and reducing the sustainability index of these products. Despite these disadvantages,


466


it is widely recognised that biodegradable materials offer a significant improvement in energy usage and carbon dioxide emissions over conventional plastics (Pira report, as reported by Merrett, 2007). PLA alone accounts for 43% of the market (18 000 tonnes p.a.) and it is estimated that there will be a rise in consumption to 50 000 tonnes by 2011 (Pira report, as reported by plastemart.com, 2007). 19.3.1 Strength of packaging under different environmental conditions When looking at the suitability of any material, there is a need to consider its strength and performance in order to asses whether the material will be able to deliver the necessary properties that are required of the packaging. For example, if the primary objectives are protection, containment/unitisation, stack-ability/handling, visual appearance or permeability, any material that cannot consistently deliver these specified properties will not be suitable for use. Mistakes in the choice or use of a material or package can be costly, leading to reduced shelf life, customer or retailer complaints, product recalls, loss of confidence in a supplier and could even be a contributory factor to a packaging supplier being unsustainable and going bankrupt. There is often a lack of suitable testing to reinforce packaging decisions, particularly where there is only going to be a short run with a specific fresh product. Commonly, tests such as plain film tensile testing are carried out by the resin or packaging supplier, but materials can fail for more complex reasons. These include the interaction at a heat-seal produced under factory conditions, the seal settings (heat, pressure, heat and dwell time), failure to accurately determine and model the demands of the supply chain and undertake full product life cycle tests. Heat-seal settings commonly lead to product packaging problems when heat-seals are formed under less than ideal conditions. For example, machines may not have been calibrated since being built, and the settings may not reflect the actual conditions. A second example is the creation of a vertical form-fill and seal bag for a bagged leaf salad or processed carrots: this relies on three seals in order to produce a finished bag. These three seals can be produced under different conditions: single impulse sealers, continuous sealers and/or crimped seals with perforations. These will each be exposed to differing amounts of water or contamination from the product being packed – prior, during and throughout the supply chain – but each must maintain at least a minimum seal strength in order for the packaging to work. As highlighted earlier, bagged lettuce relies on a modified atmosphere and if the seals are not satisfactorily gas tight, or if they subsequently leak, this can result in loss of the atmosphere. This in turn may lead to deterioration of the product, and possibly may present a public health hazard through the growth and multiplication of dangerous microbes such as Listeria spp. and Escherichia coli. Some types of biodegradable tray are based on similar polymers to those used in water-soluble applications, and hence they are sensitive to both



467

increases and decreases in water content and humidity. Even if certified for food contact in this market segment, these products would obviously be unsuitable for the vast majority of fresh produce applications. When trying to produce a ‘cleanly peeling’ seal, for example in a mixed salad with several compartments for a convenience food product, it is desirable for the two materials to part easily when pulled. However, it is critical that the package holds together through the packing process, handling chain and retailer display, including consumer inspection of the product and transport to the home environment and any subsequent storage. Therefore it is essential that the settings of the machinery (both the production machinery and packaging/sealing machinery) are optimised to allow the greatest strength from the seal, but also still ensure that it can be peeled cleanly. This can present a problem with many clear lidding films being prone to being particularly brittle or having a low Elmendorf tear value, but some manufacturers of biodegradable materials appear to be making progress in overcoming these problems (e.g. Treofan; European Bioplastics, 2006). Additional attention must be given to the possible use by consumers who are elderly, disabled or infirm, who may be likely to benefit from the convenience of packaged food and should be able to gain access (and undertake any cooking process) without any additional hazard (Yoxall et al., 2006). The hydrophilic nature of many starch and starch-based polymers means that the resulting films often have high permeabilities and for fresh produce the water vapour transfer rate is of particular importance. This can be beneficial for some product groups, where the removal or easy dispersal of additional moisture prevents the onset of disease in the fresh produce. Conversely, it can become an issue if the package is placed in a high-humidity environment, where moisture could be transferred into the package. Take, for instance, the case of unwashed potatoes being transported and exposed to different humilities (either natural or artificially created); this could result in weight changes, which would not only affect the quality of the product, but could also increase disease and microbial populations, reduce skin condition and affect the pack weight. This latter point is very important in many retail environments, where the weight is stated on the pack and excessive or unpredicted weight loss can result in the product being ‘underweight’, and so illegally labelled in many trading environments. There are manufacturers of biodegradable packaging that are working on improving the barrier properties of their materials and even metalising films (e.g. Innovia Films and Treofan; European Bioplastics, 2006),The authors are not currently aware of any reports of the ‘holy grail’ of a cost-conscious, clear material with suitable barrier and working/strength properties that would be direct replacement for crystal clear, transparent polyethylene for many applications, but many companies in this sector are making progress. Consideration also has to be given to some of the secondary functions of a package within the retail environment. For example, how the products stack within returnable plastic crates (RPCs). Will the product stack safely


468


and correctly, or even number in a crate? Will the lower products withstand the compressive forces? Does the package rely on a specific airflow around the outside, for cooling, for avoidance of condensation or for sustaining a more complex modified atmosphere environment within the package? It is therefore important for all environmentally sound packaging manufacturers to ensure that they have tested their products thoroughly, not only at extrusion and manufacture, but also after likely periods of storage and in-use service, particularly in contact with the food environment as in many cases this will be similar to some of the conditions surrounding biodegrading/composting.

19.4

Storage of packaging material

The requirements for packaging are at their most erratic in the fresh produce sector as from one year to the next there cannot be confidence in exactly when the produce will be harvested and therefore is ready to pack; also there can be big variations in demand depending on the weather from one year to the next. These factors can mean that packaging may have to be stored for longer periods than is ideal and on occasions from one year to the next.The next year the size, style or presentation of the package required may have changed and so the previous year’s packaging has to be disposed of or re-transported, stored and reground. This can present cash-flow challenges with synthetic plastic packaging but can give more serious problems with some types of degradable packaging that may not last from one year to the next; it has been known for the packaging to be stored in a cold store to slow down the degradation process. These issues increase the cash-flow risk as environmentally sound packaging is commonly more expensive per unit weight, and so there is more capital tied up in stock held in the packaging store. This stock can of course instantly become useless if the retailer decides to change its packaging format, or even a small detail in the artwork. This can result in great quantities of packaging material (conventional plastic, degradable or biodegradable) being condemned, and in many cases this packaging cannot be reground for reuse. Certain starch-based packaging can also be edible by rodents and so hygiene and protection, which are always important, become even more so. The starch-based packaging may be stored in a non-starch-based outer as further protection; therefore there can be additional costs in storage as well Hazard Analysis Critical Control Point and British Retail Consortium considerations. 19.4.1 Appearance versus utility In retail, the contrasting requirements of appearance and ensuring that the packaging completes its task regularly come into conflict, as summarised in



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Table 19.2 Summarising the different requirements of packaging and fresh produce Packaging needs

Fresh produce requirements

A low relative humidity is often preferable so materials like cardboard retain their strength Temperature not important, providing there are no extremes Temperature fluctuations acceptable Solid materials for ease of manufacture and strength Heat transfer not a consideration Proximity to other packaged material is rarely an issue

High relative humidity all the time (but no free water)

Vibration unlikely to affect the packaging

Temperature critical at or close to a specific figure, e.g. 4 °C Temperatures fluctuations not acceptable The potential to have perforations for even/uniform airflow is important Heat transfer important Proximity to other packaged material is often an issue (disease, taint, ethylene gas which can cause accelerated ripening) Vibration can damage the fresh produce

Table 19.2. This is the case for environmentally sound packaging, when the partners in the supply chain also have to consider the environmental and social functions of the packaging, both during and after its utilisation. Ensuring that a lidded mixed salad product has sufficient visual attractiveness is very important to how successful the product is in terms of sales. Factors such as gloss, feel (coefficient of friction), anti-static properties (or ability to become charged) and other characteristics should all meet the expectations of consumers and the existing supply for the fresh produce, while still producing environmentally sound packaging. Factors such as ink printing, bleed characteristics and colour fastness can be a challenge with starch materials and when combined with the high water vapour contents commonly found in environments containing fresh produce. The environmentally sound packaging has to continue to look ‘fresh’, clean and suitable for food packaging throughout its life. The printing can also be an issue when being handled in the waste stream, as environmentally sound packaging such as biodegradable packaging, needs to be clearly labelled, with a recognisable logo/symbol, in order for it to be correctly identified, despite any fruit or vegetable waste left on it. This allows the packaging to be included within garden waste/compostable channels, rather than being ‘rejected’ or ‘picked out’ by workers confusing the packaging for nonenvironmentally sound materials. The widespread acceptance of the DIN CERTCO biodegradable ‘b’ logo throughout Europe (European Bioplastics, 2006) will assist the situation; the logo is already in common use and is recognised in the UK, The Netherlands, Denmark and Switzerland. There


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are also similar themed symbols in use in Japan and the US. This will help to inform the consumer under one banner, as well as ensuring that development costs are kept to a minimum by only needing to comply with one universal standard (with associated secondary acceptance by US and Japanese systems working to similar targets).

19.5

Supply chain

Within the supply chain a number of important factors are involved in ensuring that the whole picture is taken into consideration and these include the selection of packaging outer, maintaining temperature and the mode of transport (Bishop et al., 2002). It may be that in the case of a loose product, such as oranges, there is only one layer of packaging, i.e. the outer carton or crate, but in many situations there will be two layers of packaging – such as apples in a bag and then so many bags per carton or crate. Increasingly the cardboard cartons that are used can be reused or can be recycled, with the cardboard often baled at the place where it is stripped off. However, there can be disease transference issues if a cardboard carton is used for a second time with fresh produce and that is why this does not commonly occur. It should also be remembered that during paper recycling, each time the paper is re-pulped, it will lose a ‘grade’, which makes it economically lower in value, and may also restrict the types of products it can be utilised in. Consideration should also be given to how much carbon is released into the atmosphere as the ‘waste’ is transported to collection facilities, baled, transported, during the re-pulping process and then also transported to the paper mill/production unit. In addition, with the increasing focus on carbon emissions as a result of our actions, the fresh produce industry is being put under increasing pressure to change transportation modes to more environmentally sound substitutes, for example from air to sea transportation. The UK’s largest retailer, Tesco, has recently announced an investment of £500 million to carbon rate all their products (Food & Drink Europe, 2007), in response to consumer demands. This will impact upon the fresh produce industry in particular, given the necessary refrigeration and transportation needed. Transport changes will require additional ‘storage life’, while providing the retailer and consumer with sufficient ‘shelf-life’ for display and consumption. Air freight is under additional focus at the moment, with the UK organic movement, the Soil Association, proposing to remove ‘organic’ status from fresh produce imported by air (Food & Drink Europe, 2007). The UK government Department of the Environment, Food and Rural Affairs calculates that air freight of food accounts for 1% of food tonne kilometres and 0.1% of vehicle kilometres, but yet it produces 11% of the food transport carbon dioxide equilivant emissions (DEFRA, 2005).



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Environmental focus is also being placed upon the packaging used and the amount of packaging, for what in many cases is an already wrapped product (bananas, apples, oranges, etc.). This packaging should provide sufficient protection (or extension of storage life), but should not produce too great a carbon footprint such that the benefits of the packaging are outweighed by the environmental cost. As mentioned previously, the maintenance of the correct temperature with fresh produce is of paramount importance, as this will affect its life after harvest and the length of time that it is saleable or eatable. The maintenance of temperature during transport and storage depends primarily on the modes of heat transfer conductance and convection with the latter predominating. The main way in which convective heat transfer works is through airflow into the outer packaging and around the product. This normally depends on the number of vents in the packaging and their total size, often referred to as the percentage free area. There have been countless occasions when a change of packaging has meant poor temperature control through altering the direction, or the restriction/prevention, of the airflow used to maintain constant conditions. Research work is being carried out on the percentage of free area in relation to the compressive strength (Jongkoo and Park, 2007). It is important to be aware that fresh produce respires and so produces water vapour and also requires high relative humidity to reduce wilting. Therefore changes in temperature can produce condensation which increases the potential for disease and also makes sealing more difficult through the production of steam and hence bubbles in the sealed area and leading to structural weakening in many materials.

19.6

Reducing the environmental impact of secondary packaging – returnable plastic crates

There is an increasing use of plastic crates for transporting fresh produce from the packhouse to the retail market, and also to a lesser extent between the farm and the packhouse. In most cases these plastic crates are returnable and can be used many times with the figure of 80 trips in the lifetime of the crate often being used, although no published documentation has been found to support this figure. The RPCs follow a path from grower/ packhouse to retail outlet to washing unit and back to the grower or packhouse. The same trucks that are delivering fresh produce are also used to take the RPCs to the next stage, during the (normally empty) ‘back-haul’ journey, which may presently only contain a few Chep pallets. This use of RPCs greatly reduces the quantity of packaging that has to be disposed of whether it is degradable or not. A study carried out by Michigan State University compared ten different produce items – such as apples, carrots, grapes, oranges, onions, tomatoes and strawberries – and showed that the


472


Temperature increase per hour (°C)

reusable plastic containers require 39% less total energy, produce 95% less total solid waste and generate 29% less total greenhouse gas emissions compared with single-use cardboard packaging. This study focused on the North American market (Singh et al., 2006b). The percentage free area is greater with the RPCs than with traditional cardboard cartons and this can allow for faster cooling as the air is less restricted in its contact with the contents of the crate. However, there have been concerns that the RPC will also allow the produce to warm up faster if left outside a cold store. There may be times in the supply chain, such as in the supermarket distribution centre, when crates may be in ambient conditions for a short time. These short events have previously not meant a break in the temperature in the cool chain as the insulation or protection provided by the cardboard has minimised temperature change. An example of a trial carried out by the authors is given in Fig. 19.2 and shows the typical increases in flesh temperature in pallets of netted oranges that were initially at 6ºC and were then placed in a room of still air at 20ºC; it can be seen that the temperature increase is 3–4 times as fast with the RPCs compared with the cardboard cartons (mean of nine temperature loggers at various locations for each pallet). The carbon dioxide emissions per kilogramme of produce transported are a very important issue. The emissions are much higher with air freight than with sea transportation (Fig. 19.3) and so there is pressure to reduce air-freighted fresh produce. In some cases, the use of modified atmosphere packaging (MAP) or similar may mean that sea transport is an option even though the packaging that is used may be non-recyclable or bio-degradable. One example of this is where developments in the use of MAP have meant that spring onions can be sea freighted from Egypt to Northern Europe rather than being air freighted. This packaging, which is normally in 8 kg bags within a carton, is non-recyclable and non-degradable at present but there are commercial trials being undertaken to try and find a biode gradable option. One of the challenges in supply chains such as these, is that the material can operate satisfactorily, but the product is rejected on 1.2 1 0.8

Cardboard Reusable

0.6 0.4 0.2 0 1

2

3 4 5 Hours from the start

6

7

Fig. 19.2 The effect of secondary packaging on the core temperature increase of fresh produce.


CO2 emissions (kg CO2/t km transported)

Environmentally compatible packaging of produce 0.6

0.57

0.5 0.4 0.3 0.2 0.1 0 Air

Fig. 19.3

473

0.007

0.013

Sea

Road

Chart showing the different amounts of carbon dioxide released for each tonne/km transported (Mason et al., 2002).

cost grounds, as the biodegradable properties of the material are valued differently in different countries. This can be a result of local taxation, variations in environmental and social awareness or perhaps just ignorance. Many of the materials, products and wastage in the supply chain are ‘hidden’ from the final consumer, and so avoid the typical ‘press attention’ that is focused on primary packaging. Some governments have tried to control this in several ways which have had direct impacts on the fresh produce sector. Germany, for example, has the ‘green dot’ system, with environmentally sound packaging being exempt from disposal taxes; others apply a ‘landfill tax’ which can result in businesses being set up purely to export waste streams, and leaves the fresh produce sector with heavy fines to pay since its waste streams are usually unsuitable for export. The use of RPCs with their high percentage free area can allow more cool air to circulate around the MAP bag which can mean that better temperature control is possible.With the traditional cardboard carton combined with the additional insulation provided by the MAP bag there was occasion where not enough potential for heat transfer to allow good temperature control. The physical strength of the cardboard carton is compromised by an increase in vent area.This can result in failure of the secondary packaging during the supply chain, which may hinder or delay handling operations, result in damaged fresh produce, or in severe cases result in a whole pallet or load being rejected as waste. Figure 19.4 shows avocados transported in MAP bags; the correct location of the label is also shown (and also how difficult it is to remove sticky labels that have been used incorrectly). Although almost the whole fresh produce industry is working towards the reduction or total elimination of postharvest chemicals, where they are used it is obviously important that they are used as effectively as possible. Figure 19.5 shows the locations where there may be high and low concentrations of the sulphur dioxide used on table grapes to reduce the occurrence of botrytis. There can be variations of over 100% in residue deposits even with a ventilated system and much of this variation is due to


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Fig. 19.4 Photograph showing the use of an MAP liner within an IFCO packing crate.

High residues

High decay

Fig. 19.5

Diagram showing the sulphur dioxide penetration into a pallet of grapes (Luvisi et al., 1995).

packaging. However, research on ozone, considered to be an environmentally friendly chemical, has shown that this can be used to discourage botrytis (Palou et al., 2002). One of the challenges of using ozone is that it has poor penetration and can be absorbed by the packaging; however, work



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Table 19.3 Average ozone concentration and percentage of ozone penetration for the entire storage period inside the different types of packages for oranges (Palou et al., 2003) Ozone concentration (ppm (v/v))

Ozone penetration (%)

In the atmosphere of the room Inside an RPC Inside a plastic bag inside an RPC Inside a carton

0.72

—

0.59 0.12

81.9 16.7

0.07

9.7

Inside a plastic bag inside a carton

0.07

9.7

Packaging system

Sampling point

RPC (naked) RPC (bagged) Fibreboard carton (naked) Fibreboard carton (bagged)

has also been done that shows a 9-fold difference in ozone concentrations at the fresh product surface when using RPCs with their high percentage free area, and the work also shows that they do not absorb chemicals in the same way as cardboard (fibreboard). The results of a trial with oranges are summarised in Table 19.3. As well as uniformity of temperature being important during transit, there is also the need to avoid damage to the fresh produce. The extent of any damage can be an interaction between the mode of transport and the packaging (Jarimopas et al., 2005; Singh et al., 2006a). There are also many studies on cushioning and damage protection of fresh produce through packaging but these are normally only concerned with damage and packaging (Jarimopas et al., 2007) and do not usually consider the environmental impacts.

19.7

Conclusions

The use of environmentally “sound” packaging options will continue to grow and develop from its origins in the fresh produce sector. The environmental impact of packaging options will be more closely scrutinised, and researchers and industry will continue to look at alternative materials but also at ways to reduce packaging use in the supply chain, as well as to reduce product wastage and carbon emissions during transport. Environmentally sound packaging will spread from not only the plain and simple whole fresh produce products, but also to more complex ‘fresh cut’ products. The retail sector growth, through the establishment of more convenience food and the inclusion of new taste experiences, will continue. For example, some new salads have several compartments within


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one package, and even horticultural food-on-the-go (such as cut fresh fruit salads, celery sticks, etc.) often have disposable spoons and forks, which need to have a certain amount of strength and rigidity as well as being of thick enough profile to be ergonomic, but must also be disposable (and conform with EN13432). The future for environmentally compatible packaging of fresh produce may lie in the development and introduction of multilayered biodegradable materials, offering combinations of material strength performances as well as the visual and presentation requirements for retail, and also possibly providing extensions to the shelf-lives of perishable fresh produce. Within these combinations of materials, the individual requirements of the many different fruit and vegetable products need to be harmonised, but the ultimate focus may be that once the consumer has enjoyed the taste experience, they do not have to concern themselves with the environmental implications of their enjoyment of fresh produce.

19.8

References

bioplastics24 (2007) Bioplastics 24 Overview of the Bioplastic Market, www. bioplastics24.com (accessed Spring 2007). bishop, c.f.h., wainwright, h. and pailes, p. (2002) Cool-chain – an integrated temperature management system for fresh produce. In Crop Management and Postharvest Handling of Horticultural Products, vol II, ed. Ramdane, Dris, pub Science Publishers, Enfield, NH. defra (department of the environment, food and rural affais) (2005) The validity of food miles as an indication of sustainable development, Final Report EDSO254, p. 117. european bioplastics (2006) Bioplastics show signs of a boom in 2006, Annual Review, Formally International Biodegradable Polymers Association and Working Group, www.european-bioplastics.org, (accessed Spring 2007). european bioplastics (2007) Formerly International Biodegradable Polymers Association and Working Group, www.european-bioplastics.org, (accessed February 2007). food & drink europe (2007) www.Food&Drinkeurope.com, Tesco carbon rating to force greener processing, G Reynolds (accessed Spring 2007). fpj (Fresh Produce Journal) (2003) Belgium goes biodegradable, 11 September 2003. fpj (Fresh Produce Journal) (2005a) Biodegradable packs on show, 15 March 2005. fpj (Fresh Produce Journal) (2005b) Degradable produce packaging in the Co-op, 11 June 2005. jacomino, a.p., bron, i.u., grígoli de luca sarantópoulos, c.i.g. de l. and sigrist, j.m.m. (2005) Preservation of cold-stored guavas influenced by package materials packaging. Packaging Technology and Science 18 (2) 71–76. jarimopas b., singh, s.p. and saengnil, w. (2005) Measurement and analysis of truck transport vibration levels and damage to packaged tangerines during transit. Packaging Technology and Science 18 (4) 179–188. jarimopas b, singh, s.p., sayasoonthorn, s. and singh, j. (2007) Comparison of package cushioning materials to protect post-harvest impact damage to apples. Packaging Technology and Science 20 (5) 315–324.



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jongkoo, h. and park, j.m. (2007) Finite element analysis of vent/hand hole designs for corrugated fibreboard boxes packaging. Packaging Technology and Science 20 (1) 39–47. kader, a.a. (1986) Modified atmosphere packaging of fresh produce. Outlook 18 (2) 9–10. luvisi, d.a, shorey, h.h., thompson, j.f., hinsch, t. and slaughter, d.c. (1995) Packaging California Table Grapes, UCD publication 1934, University of California, Davis. mason, r., simons, d., peckham, c. and wakeman, t. (2002) Wise Moves Modeling Report, Transport 2000 Trust, London, UK. palou, l., crisosto, c.h., smilanick, j.l., adaskaveg, j.e. and zoffoli, j.p. (2002) Effects of continuous 0.3 ppm ozone exposure on decay development and physiological responses of peaches and table grapes in cold storage postharvest. Biology and Technology 24 39–48. palou, l., smilanick, j.l., crisosto, c.h., mansour, m. and plaza, p. (2003) Ozone gas penetration and control of the sporulation of Penicillium digitatum and Penicillium italicum within commercial packages of oranges during cold storage. Journal of Crop Protection 22 1131–1134. pira report, as reported by Merrett (2007) CEE Foodindustry.com, www.ceefoodindustry.com/news (accessed February 2007). pira report, as reported by plastemart.com (2007) www.plastemart.com (accessed February 2007). Singh, j., Singh, s.p. and Joneson, e. (2006a) Measurement and analysis of US truck vibration for leaf spring and air ride suspensions, and development of tests to simulate these conditions. Packaging Technology and Science 19 (6) 309–323. singh, s.p., chonhenchob, v. and singh, j. (2006b) Life cycle inventory and analysis of re-usable plastic containers and display-ready corrugated containers used for packaging fresh fruits and vegetables. Packaging Technology and Science 19 (5) 279–293. uc davis postharvest technology center (2007) Produce Facts, Postharvest Technology Research and Information Center, University of California, Davis, http:// postharvest.ucdavis.edu/produce/Producefacts/index.shtml (accessed February 2007). yoxall, a., janson, r., bradbury, s.r., langley, j., wearn, j. and hayes, s. (2006) Openability: producing design limits for consumer packaging. Packaging Technology and Science 19 (4) 219–225.


20 Biobased packaging of dairy products M. Jakobsen, University of Copenhagen, Denmark; V. Holm, Danish Technological Institute, Denmark; G. Mortensen, Danish Dairy Board, Denmark

20.1

Introduction

The dairy packaging market is worth US$ 43.5 billion according to the Packaging Gateway (2007), and hence a switch from conventional packaging materials to biobased packaging for even a small fraction of dairy packaging poses interesting challenges. Dairy products are packaged in a wide range of materials: • cellulose-based materials for fluid milk, paper wraps for butter, etc.; • glass for milk, yoghurts, and sterilized products; • metals for milk powder, autoclaved cheeses, and condensed milk, as well as for metallized layers of laminates for cheeses; • plastics, to include biodegradable plastics and Ecolean CalymerTM, which are used for packaging of basically any dairy product category; • biobased materials derived from renewable resources (see definition in Box 20.1), which at present may be used for dairy products with limited shelf-life.

Box 20.1

Definition of biobased materials

Biobased materials are here defined as materials derived from primarily annually renewable sources. These materials may be compostable. However, compostability in itself is not a focal point at this stage, since general waste management of compostable materials leaves a lot to be desired.


Biobased packaging of dairy products

479

This chapter emphasizes only the latter category of materials, which does not necessarily mean that the cellulose- or plastics-based materials cannot be considered as environmentally compatible food packaging. This chapter provides an overview of biobased packaging materials for dairy products, ranging from scientific publications to commercially available applications. It presents the requirements that range of dairy products demand of biobased materials and suggests how to improve the materials in order to utilize fully the potential of biobased materials for dairy product packaging.

20.2

Properties required in relation to dairy products

20.2.1 General aspects Biobased packaging materials must meet the criteria that apply to conventional packaging materials. Consequently, the biobased materials must protect the dairy product from the surroundings and reduce the quality deterioration during transportation and storage. The critical aspects include mechanical and barrier properties (oxygen, carbon dioxide, water, light, and aroma). Furthermore, safety aspects (migration, microbial growth), resistance properties (temperature and chemical resistance), production requirements (welding and moulding properties), convenience, and marketing requirements (communication, print options) should be considered when selecting packaging materials for dairy products (Haugaard et al., 2001; Robertson, 2006). The following will focus on mechanical and barrier characteristics, resistance properties, and safety aspects. 20.2.2 Mechanical properties Mechanical properties are critical and should be tailored in such a way that the dairy product is protected even during extensive storage and transportation. Polymers can to some extent be tailored to meet specific mechanical properties by, for example, the choice of raw materials such as blending with other polymers or fillers, or by addition of fibres, by cross-linking, plasticizing (van Tuil et al., 2000), and by controlling the crystallinity (Södergård and Stolt, 2002). For instance, a positive correlation can be obtained between the amount of plasticizer in the polymer and the tensile strength (Parris et al., 1995). Furthermore, polymer orientation during processing may improve mechanical strength and heat stability of polylactide (PLA) polymer (Sinclair, 1996). Superior mechanical properties can be obtained by semi-crystalline PLA rather than amorphous PLA. As the crystallinity can be determined by the enantiomeric forms of PLA, its mechanical properties are controlled by the ratio between poly(l-lactic acid) (PLLA) and poly(d-lactic acid). Subsequently, there are different processing parameters that may be varied to obtain specific mechanical properties of biopolymers, which mimic the properties of conventional oil-based polymers such as stiff


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materials (i.e. polyethylene terephthalate, PET) and flexible materials (i.e. polyethylene, PE) (van Tuil et al., 2000; Södergård and Stolt, 2002). The mechanical properties of polyhydroxy butyrate (PHB) resemble those of isotactic polypropylene (PP) (van Tuil et al., 2000), and PLA has mechanical properties similar to conventional packaging materials such as PE, PP, and PET (Kharas et al., 1994; Auras et al., 2003). Other comparisons show that tensile strength, percentage elongation, and tear strength of PLA and starch–polycaprolactone (PCL) films were lower than those of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) films (Ikada and Tsuji, 2000; Petersen et al., 2001), and that compression of cups based on starch, PLA, and PHB was in the range of that of PP, polystyrene (PS), and PE cups (Krochta and De MulderJohnston, 1996; Petersen et al., 2001). Native starch alone does not meet the requirements for food packaging applications as its mechanical strength and stability are too low (Ahvenainen et al., 1997). Such results have also been reported for LDPE–starch blends, where a negative effect on the mechanical properties was pinpointed when the starch content was increased (Psomiadou et al., 1997; Arvanitoyannis et al., 1998). Studies have shown that PLA polymers are sensitive to moisture and heat, which results in loss of mechanical properties. PLA films lost mechanical properties faster when stored at high temperatures and humidities than when stored under the opposite conditions (Ho et al., 1999a, 1999b). However, another study showed that PLA was mechanically stable when packaging foods that were in the dry to moist range of moisture contents, and with storage temperatures ranging from chilled (5 ºC) to ambient and (25 ºC) (Holm et al., 2006a). 20.2.3 Thermal resistance Usage temperatures for most dairy products are within 0 to 40 ºC. However, hot-filling and sterilizing may be used for long-shelf-life fluid milk products. Furthermore,during processing of the packaging materials (forming,sealing), they are subjected to high temperatures. Consequently, the packaging materials should be able to withstand deformation at high temperatures for different lengths of time depending on the products to be packaged. The thermal application range of biobased packaging materials is expected to be relatively limited, since stability decreases with increasing temperature, as has been observed for PLA (Södergård and Stolt, 2002), especially when exposed to high humidities (Holm et al., 2006a). Thus, the first generation of PLA cups will remain stable up to a temperature of 55 ºC only (Anon., 1997, 1998). However, one supplier of PLA claims to have an oriented PLA (OPLA) film with use temperatures of up to 150 ºC (NatureWorks LLC, 2007), and Hycail also has a PLA grade available that may be used at elevated temperatures. In addition, commercial usage of PLA cups for hot drinks indicates that PLA may be used at high temperatures.



481

T. Rasmussen and M. B. Olsen (The Danish Technological Institute, Taastrup, Denmark) and P. Togeskov (Danisco Flexible, Lyngby, Denmark) found that deformation of cups and trays based on starch–PCL blends occurred between 60 and 90 ºC (unpublished observations, 2001). As is apparent from the above, only a few reports on the heat stability of biobased packaging materials exist and there is a need for further studies before a thermal application range can be defined. 20.2.4 Barrier properties Water vapour barrier requirements differ depending on the type of product. For instance, a high water vapour barrier is critical when packaging dairy products such as butter and cheese, where the key parameter is to prevent moisture loss and surface drying. On the other hand, the packaging of shortshelf-life products is less critical as the temperature is low and the shelf-life is less than 10 days. Thus, a thin PE layer is a sufficient water barrier in milk cartons. Almost the same scenario exists with respect to gas barrier properties. Here, the requirements increase with the complexity of the products. For instance, a high gas barrier is required for packaging of products in modified atmospheres such as sliced cheeses and milk powder, whereas a lower gas barrier is sufficient when packaging products with short shelf-lives, e.g. fresh milks and yoghurts. The literature provides numerous references on the barrier properties of biobased materials (Gontard et al., 1996; Sinclair, 1996; Arvanitoyannis et al., 1997, 1998; Psomiadou et al., 1997; Kittur et al., 1998; Barron et al., 2001; Lehermeier et al., 2001; Petersen et al., 2001; Auras et al. 2005; Plackett et al., 2006). However, comparisons between the different materials are complicated and often impossible due to the use of different types of processing equipment, variations in raw material parameters, and dissimilar measuring conditions.The solution remains to perform shelf-life tests on the actual product and desired packaging material. When doing so, it is important to consider the dimensions of the packaging and to avoid large surface areas relative to the total volume of the package (refer to Section 20.3.1). The reason for this is that many biobased polymers are hydrophilic and hence may not function properly if a high water vapour barrier is required. However, when comparing the water vapour transmission rates (WVTRs) of various biobased packaging materials to materials based on mineral oil, it becomes evident that it is indeed possible to produce biobased materials with acceptable WVTRs, especially for short storage of dairy products. Research and development efforts are directed at improving the water vapour barrier of biobased materials, and future materials may very well have similar water vapour barrier properties to conventional materials. The water vapour barriers of biobased materials consisting of starch, protein, and chitosan are inferior compared with those of conventional


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food packaging materials (Petersen et al., 1999; Guilbert, 2000; van Tuil et al., 2000; Kantola and Helén, 2001). The WVTRs of blends of starch and oil-based films and cups have been compared with those of LDPE and HDPE films as well as PP, PE, and PS cups of identical thickness. Results showed that the WVTRs of the starch-based films were 4–6 times greater than those of conventional films. Furthermore, the starch-based cups had WVTRs of 100–300 times greater than those of PP and PE cups, and 5–9 times greater than PS cups (Petersen et al., 2001). However, developments in the production process and compounding with other (bio)polymers may result in starch-based materials suitable for short-term storage of dairy products. Garcia et al. (2006) markedly improved the water vapour barrier of starch films by the addition of chitosan. Furthermore, an evaluation of how efficient the water vapour barrier must be in order to retain shelflife and quality of the individual products should be considered rather than simply comparing with, in some cases, over-performing conventional materials. PLA provides a better water vapour barrier than the starch-based materials, and Petersen et al. (2001) noted that the WVTR of PLA was only 4 times greater than that of the conventional films evaluated (polyvinylidenchloride and LDPE), 2 times greater than PS cups, and 40–60 times higher than PP and PE cups. PLA is moderately polar, and hence moisture was expected to affect its water vapour barrier properties. However, no effects on permeability were noted when exposing PLA to different internal and external relative humidities (Auras et al., 2003; V. K. Holm, unpublished observations 2004). Polyhydroxy alkanoates (PHAs) have low WVTRs, which resemble those of LDPE (van Tuil et al., 2000); this makes the material interesting, for example as a moisture barrier in milk cartons or butter wraps. Biobased materials mimic quite well the oxygen transmission rates (OTRs) of a wide range of conventional mineral oil-based materials. It is possible to choose from a range of barriers among the biobased materials, and it should be noted that improvements continue to take place. The OTR of PLA is high (Ikada and Tsuji, 2000). Auras et al. (2005) reported the OTR of OPLA to be approximately 10 times lower than that of oriented polystyrene (OPS), but approximately 6 times higher than that of PET. Packaging films of 20 µm based on PLA, blends of wheat starch and PCL, as well as blends of cornstarch and PCL had OTRs that were considerably lower than those of LDPE and HDPE films (Petersen et al., 2001). The OTRs of cups based on PLA and PHB were also lower than those of PP, PS, and PE (Petersen et al., 2001). It may be possible to improve the barrier properties of PLA and PHB by combining them with a layer of chitosan, protein, or modified starch film, which all have high oxygen barrier properties (Kittur et al., 1998; van Tuil et al., 2000). The materials may provide less expensive alternatives to the gas barrier materials presently applied, such as ethylene vinyl alcohol (EVOH) and polyamide. The selectivities (permeability ratios) of biobased materials to other gases are in the range of those for conventional food packaging materials. © 2008, Woodhead Publishing Limited


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As a rule of thumb, mineral oil-based polymers have a carbon dioxide: oxygen ratio of typically 4 :1 to 6 :1 (Robertson, 2006). The permeability ratios of two specific PLA films were 3 : 1 (V. K. Holm, unpublished observations, 2004) and 7 :1 (Petersen et al., 2001), which is within the range of conventional plastics. A ratio of 15 :1 for wheat gluten films has been reported in the literature (Barron et al., 2001). An increase in the ratio at higher relative humidities implies that the films gradually become more permeable to carbon dioxide as compared with oxygen (Gontard et al., 1996). This may be a desirable property for products generating large amounts of carbon dioxide during storage, e.g. Emmental cheeses. The OTRs of polar biobased and conventional packaging materials may be affected by moisture in the environment, resulting in a considerable increase in the OTR with growing moisture content. This is observed for materials such as EVOH and chitosan (Despond et al., 2001; Muramatsu et al., 2003). The gas barriers of PLA and PHA are not notably dependent on humidity (Auras et al. 2005; Robertson 2006). The OTR has been reported to decrease slightly when the relative humidity increases. However, this phenomenon was observed at 40 ºC only, whereas no major effect was noted at 5 ºC and 23 ºC (Auras et al., 2004). Consequently, the influence of humidity on OTR is not important for refrigerated storage of dairy products. Hence, PLA and PCL may protect the moisture-sensitive gas barrier provided by chitosan, polysaccharide, or protein (Martin et al. 2001; Fang et al. 2005). In addition, developments have made it possible to improve the water vapour and gas barrier properties of biobased materials substantially by plasma deposition of glass-like silicium oxide coatings or by applying nanocomposites from natural polymers and modified clays (Fischer et al., 2000; Johannson, 2000; Ray et al., 2006). The aroma barrier is an important characteristic, especially with respect to products such as butter and milk which may take up flavours from, for example, citrus fruits. Furthermore, a poor aroma barrier may lead to aroma loss from mature cheeses, thereby resulting in quality deterioration. Unfortunately, data on aroma permeability is almost non-existent. Auras et al. (2006) found that PLA demonstrated a good barrier to ethyl acetate and d-limonene, and thus is expected to be a good aroma barrier. No critical reports exist, and hence the aroma barrier does not seem to be a specific problem for biobased materials. Light barrier properties are important in order to prevent photooxidation of proteins, lipids, and nutrients. However, these properties can be modified to match the requirements of the dairy products, using biodegradable colours, which are a major focus area for the industry supplying additives and colorants. 20.2.5 Chemical resistance Exposure of packaging materials to oil as well as acids can reduce the polymer performance. As many dairy products are acidic, salty, and/or high © 2008, Woodhead Publishing Limited

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in fat content, it is relevant to evaluate the chemical resistance of the materials. Auras et al. (2005) compared OPLA to PET and OPS and found that exposure to acids (pH 6 and pH 2) and vegetable oil resulted in only minimal strength degradation, whereas OPLA with 40% regrind actually showed an improvement. In another study, the OTR of PLA bottles was not altered by 4 months of exposure to canola oil, and neither were the mechanical properties (Marboe, 2006).

20.2.6 Microbial growth Micro-organisms may utilize biobased packaging materials as sources of energy. This may induce a potential risk of growth of undesirable mould and bacteria on the packaging, and should the packaging be degraded during storage of the foods, exterior microbial migration may occur, thereby contaminating the food. Only a few reports have been made on the growth of micro-organisms on biobased packaging materials. Studies show that PLA and PHB did not support the growth of undesirable food-related fungi (Bergenholtz and Nielsen, 2002; Plackett et al., 2006), whereas packaging materials based on starch–PCL supported growth of undesirable foodrelated fungi. The authors therefore suggested a modification, i.e. incorporation of antimicrobial compounds into the starch-based packaging materials.

20.2.7 Migration In food packaging terminology, ‘migration’ is used to describe the transfer of substances from the package to the food, which is an important aspect to consider when employing packaging materials for foods. In the European Union, the overall migration must not exceed the 10 mg/dm2 limit. Migrants from biobased packaging materials may include, for example, lactic acid, the linear and cyclic dimer of lactide, various small oligomers of PLA (Conn et al., 1995), and edible and hydrolysed starch. These migrants may be naturally present in foods and may hence be considered safe for food packaging purposes. In Europe, the categories of lactide, edible and hydrolysed starch, and PHB are mentioned without any specific restrictions in the monomer list of the Plastic Directive (Commission Directive 2002/72/EC). Studies have shown that overall migration from different PLA polymers into water, acetic acid, iso-octane, olive oil, and a solid stimulant – modified phenylene oxide – is well below the 10 mg/dm2 limit (Conn et al., 1995; Selin, 1997; Plackett et al., 2006). Therefore, PLA is Generally Recognized as Safe for its intended purpose as a polymer for manufacturing articles used for containment or as food packaging material (Conn et al., 1995).



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20.2.8 Degradation Future requirements for biobased packaging materials should include full post-use compostability (Kale et al., 2007). This includes a so-called ‘biodegradation process’, where enzymes from micro-organisms hydrolytically degrade the polymers. PLA polymers are hydrolysed without any help from hydrolytic enzymes, when moisture is present (Ikada and Tsuji, 2000). In addition to moisture (water activity), parameters such as pH, available nutrients, oxygen, storage time, and temperature are important in the biodegradation process. It is thus important to control these parameters during product shelf-life in order to protect the packaging material from being degraded and to protect the packaged dairy products. With respect to the resistance of the packaging materials towards ultraviolet light, a study has shown that the resulting decrease in physical integrity and degradation of the polymer were much lower for PLA than for PE (Ho and Pometto, 1999).

20.3

Current applications of biopackaging of dairy products

20.3.1 Scientific evaluations Systematic scientific evaluations of the biopackaging of dairy products, covering both packaging material and food quality aspects, are not available in the literature. There are only a few research papers that have investigated the applicability of biobased packaging for dairy products. These include the use of PLA for packaging of plain yoghurt (Frederiksen et al., 2003) and semi-hard cheese (Holm et al., 2006b, 2006c; Plackett et al., 2006). Scientific evaluations of other biobased packaging materials include an evaluation of Canestrato Pugliese cheese (Italian semi-hard cheese made from sheep’s milk) packaged in Novamont starch-based materials (Di Marzo et al., 2006). Di Marzo et al. (2006) noted that the Novamont biodegradable films could be used for packaging of cheese although their performance proved lower than that of high-barrier, conventional films. The potential to use PLA for the packaging of plain yoghurt has been demonstrated by Frederiksen et al. (2003). Plain yoghurt (3.5% fat) was stored for 5 weeks in PLA or reference (PS) cups under fluorescent light (3500 lux) or in darkness. The study evaluated the suitability of PLA by measurements of relevant quality parameters of the product. Results showed that PLA was at least as effective in preventing colour changes and formation of primary lipid oxidation products as were the reference cups. During light exposure, the PLA material provided better protection against the formation of secondary lipid oxidation products. In addition, losses of the vitamins riboflavin and β-carotene, were lower in light-exposed yoghurts stored in PLA than in those stored in PS cups. Hence, it was concluded that, when measuring light-induced quality changes, PLA was a suitable alternative to PS when packaging yoghurt. In addition, migration of styrene from


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PS into the yoghurt increased during storage, whereas lactate from PLA was not detected in PLA-packaged yoghurts. Dark storage provided high protection of the quality of the yoghurts irrespective of the choice of packaging material. Hence, from a food-quality perspective, PLA is at least as effective as PS in preventing light-induced oxidation in yoghurt, which also reflects the similarities in the material properties of the two materials. PS is used for the packaging of a range of dairy products with short shelflife and not requiring high-barrier protection. Examples include sour cream, cottage cheese, and quark – products that are quite similar to yoghurt. As PLA has been scientifically proven to be applicable for the packaging of yoghurt, PLA may also be used for packaging of other dairy products with short shelf-life and with few requirements for the barrier properties of the packaging material. In addition, in another type of fatty food (salad dressing), both PLA and PHB have been proven to provide a similar level of protection as the conventional HDPE – with respect to colour changes, lipid oxidation, and loss of α-tocopherols (Haugaard et al., 2003). Hence, PHB may also be applicable for dairy products that are normally packaged in materials with low gas barriers. The use of PLA for the packaging of dairy products requiring high gas and water vapour barriers has also been investigated (Holm et al., 2006b, 2006c), and this study revealed the present challenges and limitations of the use of PLA as a packaging material for products with complex requirements from the packaging material. The influence of the barrier properties of a PLA, relative to a reference (amorphous PET/PE) material, on the quality of semi-hard cheese during light or dark exposure was studied (Holm et al., 2006b). Results showed that moisture loss from cheeses packaged in PLA was approximately 10 times higher than from the reference packages, but dry surface spots were observed only after 56 days of storage in the PLA packages. Secondary lipid oxidation products were primarily developed when both oxygen and light were present. During light exposure, lipid oxidation of cheeses packaged in PLA was rather limited for the first 56 days of storage, whereas lipid oxidation was almost negligible when the cheeses were protected from light during the 84 days of shelf-life. The results indicated that the PLA material could be used for packaging of the semi-hard cheese for a shelf-life maximum of 56 days in order to protect against both moisture loss and lipid oxidation. In addition, estimates of moisture loss indicated that PLA might provide adequate protection for 84 days, if the amounts of cheese and the depths of package were doubled (amount of cheese compared with the surface area of the package) (Holm et al., 2006b). Another study pinpointed the challenges of using PLA for packaging of semi-hard cheese even when oxygen scavengers were added to compensate for the low oxygen barrier of PLA (Holm et al., 2006c). The effect of a PLA package relative to a conventional polyester package was investigated,



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evaluating the quality of long-term stored (12 weeks), semi-hard cheese during light exposure and storage in the dark, and when applying oxygen scavengers to the cheese packages. The migration of volatile compounds from PLA into the cheese was minute and well below any critical levels. The development of secondary lipid oxidation products and loss of riboflavin primarily took place when both oxygen and light were present. As more oxygen was present in the PLA packages than in the reference packages due to a higher OTR of PLA, a higher degree of lipid oxidation was noted in cheeses packaged in PLA. The degree of lipid oxidation was reduced when applying oxygen scavengers but to a lesser extent than when the products were stored in the dark. Riboflavin was degraded to the same extent in the PLA- and the reference-packaged cheeses. The results indicated that dark storage or use of non-transparent materials and reduction of the WVTR are recommended when using the investigated PLA for packaging of semi-hard cheese, in order to protect the products against both lipid oxidation and moisture loss (Holm et al., 2006c). The above studies stressed that the barrier properties of PLA should be improved to fulfil the long-term storage requirements of cheese. Plackett et al. (2006) produced different films based on PLA polymers (impactmodified and unmodified PLLA) and co-polymers (PLLA–PCL), and investigated their suitability as materials for cheese packaging by means of biodegradation, transparency, moisture uptake, mechanical properties, etc. In some cases, the polymers were compounded with nanoclay as a possible route to enhance barrier properties. The materials demonstrated complete biodegradation under controlled composting conditions, and the extruded films had acceptable transparency. Moisture uptake by films and a decrease in polymer molecular weight with time of exposure to high humidity were identified as areas of concern, although the polymer stability experiments were undertaken at 25 ºC, and stability at normal cheese storage temperatures (∼4 ºC) is expected to be better (Plackett et al., 2006); as shown in another study, where a PLA film was found rather stable at most conditions simulated by different relative humidities (11–98%) and two temperatures (5 and 25 ºC). In this study, moisture sorption and decrease in molecular weight were pronounced at 25 ºC, but hydrolytical degradation was reflected only in the loss of tensile strength at 98% relative humidity after more than 60 days. Hence, PLA was expected to be stable when packaging dry to moist foods at both chill and ambient temperatures (Holm et al., 2006a). Nanoclay addition enhanced the thermal stability of the polymer, but a reduction of OTR and WVTR to target levels was not achieved. However, a novel, impact-modified PLA was developed, which overcame the problems with brittleness in unmodified PLLA and PLLA–PCL copolymer films. Based on this study, the most significant challenge facing the adoption of PLLA or PLLA–PCL films in cheese packaging is the film permeability issue. The use of nanoclays was not fully effective in the study due to improper nanoclay dispersion. However, further process


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optimization could probably deliver additional reductions in OTR and WVTR. Hence, before PLA can become widely used for the packaging of semi-hard cheese and other similar foods, methods to reduce film permeability are needed to meet the performance of existing packaging materials (Plackett et al., 2006). 20.3.2

Commercial and suggested applications for packaging of dairy products So far, most biopolymer-based plastics on the market are used for non-food purposes; however, applications in the dairy sector and related food sectors are picking up speed. In addition, the performance of environmentally compatible packaging is undergoing progressive improvements as a result of extensive research and development at industry and academic levels. At present, fresh food products have a 41% market share of all biodegradable packaging, in part due to the relatively limited requirements posed by short shelf-life products (Merrett, 2007). Commercial dairy applications are also characterized by being short-shelf-life products. Commercial examples include: • Danone yoghurt, which was test launched in a PLA cup in Germany back in 1997; • Naturally Iowa milk, packaged in PLA bottles produced by NatureWorks LLC. • Coeur de Lion Brie cheese, which was packaged in a laminate consisting of PLA, wax, and craft paper. The product is, however, no longer available in the biobased material. As can be seen from the list of commercial products, PLA has been the polymer of choice when it comes to the packaging of dairy products. It is now produced on a comparatively large scale, the primary developer and commercializer being NatureWorks LLC (Datta and Henry, 2006; Robertson, 2006). PLA’s optical, physical, and mechanical properties approach those of PS and PET (Auras et al., 2005). Furthermore, PLA can be plasticized in many ways resulting in properties that will match those of polymers such as LDPE and linear low-density polyethylene (LLDPE) (Sinclair, 1996).Therefore, it is expected that PLA will be suitable for short-shelf-life dairy products such as yoghurt, milk, cottage cheese, and sour cream, as these products do not require any specific gas barrier. Unfortunately, very few food storage experiments have been published despite the fact that OPLA films, PLA extrusion sheets, and PLA injection stretch blow-moulded bottles are available for tests (NatureWorks LLC, 2007). On a long-term basis, where the barrier properties of PLA have been improved, PLA may also be used for packaging of fresh and ripened cheeses (Holm, 2004). PHB and paperboard cartons coated with PLA or PHB have



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been suggested for dairy products with short shelf-life (Haugaard et al., 2001). NatureWorks LLC recommends the use of PLA for dairy containers and bottles.

20.4

Future trends

Extensive research and development on biopolymers has been carried out recently, and large capital investments are taking place. However, few packaging materials on the market today have been used for direct food contact, and assessment of package–product compatibility during realistic food storage experiments is called for. One of the primary issues of development is the improvement of barrier properties. As mentioned in Section 20.2.4, this can be achieved through modification of the polymers with silicium oxide coatings or incorporation of nanocomposites produced from natural polymers and modified clay. In many cases, it will be necessary to laminate biomaterials in order to improve the overall performance with respect to food packaging. This is already done with respect to conventional food packaging materials, which often comprise three to nine layers of different polymers to meet the multiple demands of food packaging; namely, the outer layers normally consist of water barrier polymers with good mechanical properties, the middle layers consist of good gas barrier polymers, and the inner layer should possess good sealing properties. The use of modified atmosphere packaging (MAP) is ever increasing; however, biobased materials do not yet possess the necessary oxygen barrier properties. Thus, laminated materials based on good oxygen barriers such as modified starch, proteins, xylophane, and chitosan may prove successful for MAP of dairy products, if they become less susceptible to water uptake. Standa Industries has developed a biodegradable oxygen absorber, which may reduce the problem of the insufficient barrier characteristics of many biobased materials (Anon, 2006). Development of a feasible PHA production may be an interesting alternative to PLA due to PHA’s superior barrier characteristics. According to Metabolix, the company will join forces with Archer David Midland and will start producing PHA (Mirel) in 2008 with an initial capacity of approximately 50 000 tonnes a year (http://www.metabolix.com). Grades for extrusion coating may be suitable for coating of paperboard for milk containers and yoghurt cups. Other PHA developers are also considering increasing their production. Finally, Novamont is investing substantial research and development efforts in the development of starch-based polymer grades, which may be compared with those of PE. Combining biobased materials with other conventional, highperformance materials may also be a feasible route, as such hybrid materials may possess slightly different characteristics than those of both the biobased and the petrochemical-derived materials. Developments in the


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converting technology will surely pave the way for improved and more multi-faceted packaging characteristics. At present, PLA shrink sleeves and resealable lids are being developed, which could be used for fresh milk and cheese products. An increased focus on sustainability may also lead to hybrid materials, where the sustainability issue is more in focus than whether the entire material is biobased or not (Bird, 2007). Martin et al. (2001) successfully prepared multilayer films based on plasticized wheat starch and various biodegradable aliphatic polyesters in order to improve the properties of the starch in terms of mechanical performance and moisture resistance. No specific tie layer was added, and the properties of the laminates therefore rely on the compatibility of the respective materials. Fang et al. (2005) suggested new laminate films based on starch and PLA. However, additional research is needed within this area. Development of additives that make the materials less brittle and more durable is required. Undoubtedly well-performing biodegradable plasticizers, colourants, inks, adhesives, and additives will surface in the coming years, as many suppliers are working on these aspects. One example of the continued developments is Rohm and Haas, who have developed a PLA impact modifier based on nanoparticles (Paraloid BPM-500). The impact modifier apparently improves the strength of PLA without sacrificing transparency (Rohm and Hass, 2007). Testing is most often retailer driven, e.g. by Sainsbury’s and Marks and Spencer in The United Kingdom, Delhaize in Belgium, Auchain in France, Albert Heijn in The Netherlands, Migros in Switzerland, Iper in Italy, and Walmart in the United States. The biodegradability of most biobased packaging materials represents a challenge to the retailers, since the packages should remain stable during shelf-life and subsequently biodegrade efficiently at the time of disposal. Therefore, it is important to identify the shelf-life stability of biobased packaging materials. Disposal options must also be addressed at an international level. Without the infrastructure to dispose of, collect, and properly compost PLA and other bioplastics, these emerging classes of sustainable packaging materials lose their green appeal. Temperature stability is another important aspect in order to ensure stability and high quality during processing and storage. As discussed previously, many of the biobased materials degrade at relatively low temperatures, and it is important to use these new materials for products not requiring, for example, hot-filling, or for products to be heated directly in the package. However, new developments may result in increased temperature resistance, and thus, a broad spectrum of use will manifest itself. It appears that both Hycail and NatureWorks LLC have developed heatresistant PLA grades. Increased crude oil prices and a growing demand for oil in the developing countries constitute major reasons why a significant market growth in



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biobased packaging is expected within the next few years. Reduced costs of the biobased packaging materials are very important if the materials are to find applications other than niche products, and lower costs are anticipated for large-scale production. Thus, when PLA is produced on an even larger scale, the costs are expected to drop further, thereby approaching the costs of PE and PS. Another important issue when discussing the future of biobased packaging materials is the raw materials used in the products. One aspect is the use of genetically modified crops for the production of PLA. Recently, Sainsbury’s announced that it will not be using packaging materials derived from genetically modified crops (Hutson, 2006). Another aspect is the discussion of whether agricultural resources should be used for the production of packaging materials, as long as there is a shortage of food supply in the third world. Finally, the supply for packaging production will be competing with the production of bioethanol etc., which may challenge the producers in their wish to scale up production to meet market demands. Currently, bioplastics account for less than 1% of the European market for plastics. Experts claim that the bioplastics may capture 10% of the plastics market – part of that market share may very well be the introduction of dairy products in biobased materials (ElAmin, 2006). Just consider a future scenario – eating yoghurt out of a yoghurt cup produced from whey derived from cheese production. A truly fascinating thought!

20.5


• European Bioplastics focuses on catalysing the development of the biopolymer market (www.european-bioplastics.org). • News on bioplastics as well as reports on the processing parameters and technical characteristics of most bioplastics may be found on the bioplastics24 website (www.bioplastics24.com) • Bioplastics Magazine gives the latest on bioplastics. More information may be obtained at www.teamburg.de/bioplastics/index.php. • The biopolymer website provides information on materials, products, news, etc. in relation to biopolymers (www.biopolymer.net). • Packaging Network.com provides information for the packaging industry including products, suppliers, news, etc. (www.packagingnetwork. com). • Pira is a commercial consultancy business specializing within the packaging, paper, printing, and publishing industries. The company also provides information on biobased and biodegradable packaging material and produces electronic newsletters on biopackaging and market intelligence studies (www.intertechpira.com). • Biodegradable Products Institute (www.bpiworld.org).


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• Biobased Packaging Materials for the Food Industry, edited by C. J. Weber, is available on www.biomatnet.org/publications/f4046fin.pdf (accessed October 2007). • The chapter on ‘Biobased food packaging’ by V. K. Haugaard and G. Mortensen, Chapter 25, in Environmentally-Friendly Food Processing, edited by B. Mattsson and U. Sonesson (Woodhead Publishing, Abington, UK 2003). Selected suppliers and converters of biobased materials (accessed October 2007) include: • • • • • • • • • • • • • • • • • •

Avebe: www.avebe.com. Biocorp: www.biocorpna.com. Biomatera: www.biomatera.com. Biomer: www.biomer.de. Biotec®: www.biotec.de. Econeer: www.econeer.com. Hycail: www.hycail.com. Ibek www.apack-ag.de. Metabolix: www.metabolix.com. National Starch: www.nationalstarch.com. Natura Verpackungs GmbH: www.naturapackaging.com. NatureWorks LLC: www.natureworksllc.com. Novamont: www.materbi.com. Plantic: www.plantic.com.au. Plastiroll: www.plastiroll.fi. PSM North America: www.psmna.com. Stanelco: www.stanelco.co.uk. Trespaphan: www.trespaphan.com.

20.6

References

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21 Environmentally friendly packaging of muscle foods P. Dawson, K. Cooksey and S. Mangalassary, Clemson University, USA

21.1

Introduction

Large amounts of packaging waste are discarded into municipal waste systems each year. Each of the 16 countries in the EU listed in Table 21.1 produces over 100 kg of packaging waste per person per year. (http://www. ehsni.gov.uk/waste/regulation-and-legislation/regulations_packaging.htm) and over 29 million tons of plastic packaging waste were generated in the US in 2005 (EPA, 2007). Comstock et al. (2004) estimated that 70% of all packaging was devoted to food and that in the 1990s less than 10% of packaging material was recycled by consumers. In order to reduce the amount of synthetic polymer waste, a considerable amount of research has been devoted to source reduction, recyclable materials, and the production of biobased polymer films derived from natural sources.

21.2 Types of meat packaging materials The US Department of Agriculture–Food Safety and Inspection Service website (http://www.fsis.usda.gov/Fact_Sheets/Meat_Packaging_Materials/ index.asp) has a description of the materials used for meat packaging. Part of this description is given below: What are some materials used in meat packaging? • Plastic wraps and storage bags: consumer plastic wraps and bags are made from three major categories of plastics: polyethylene (PE), polyvinylidene dichloride (PVDC), and polyvinyl chloride (PVC). The


Environmentally friendly packaging of muscle foods Table 21.1 Europe.

Packaging waste per person per year in

Country Ireland France

Packaging waste (kg per capita per year) >200

Germany Italy The Netherlands Luxembourg

176–200

United Kingdom Spain Denmark

150–176

Sweden Austria Portugal Belgium

100–150

Finland Greece

497

Environment > Waste > Packaging Waste), http://ec.europa.eu/environment/waste/packaging_index.htm (consulted February 2007). 4 studies. European Packaging Waste Management Systems, European Commission, DG Environment. (EUROPA > European Commision > Environment > Waste > Studies), http://ec.europa.eu/environment/waste/studies/packaging/epwms.htm (consulted February 2007). 5 European Parliament and Council Directive 94/62/EC of 20 December 1994 on Packaging and Packaging Waste (OJ L 365, 31.12.1994, p. 10). Amended by: •

M1 Regulation (EC) No. 1882/2003 of the European Parliament and of the Council of 29 September 2003 (L 284 1 31.10.2003); • M2 Directive 2004/12/EC of the European Parliament and of the Council of 11 February 2004 (L 47 26 18.2.2004). • M3 Directive 2005/20/EC of the European Parliament and of the Council of 9 March 2005 (L 70 17 16.3.2005) http://eur-lex.europa.eu/LexUriServ/site/ en/consleg/1994/L /01994L0062–20050405-en.pdf). 6 generation and recycling of packaging waste (CSI 017). Assessment published November 2005. Copyright European Environmental Agency EEA, Copenhagen, 2005. Data source: DG Environment, http://themes.eea.europa.eu/IMS/ISpecs/ ISpecification20041007131825/IAssessment1116508857878/view_content/ (consulted March 2007). 7 packaging waste generation per capita and by country. Copyright European Environment Agency EEA, Copenhagen, 2005. Data source: DG Environment and the World Bank, http://dataservice.eea.europa.eu/atlas/viewdata/viewpub. asp?id=1740, (consulted March 2007). 8 Waste, European Commission, DG Environment (EUROPA > European Commision > Environment > Waste), http://ec.europa.eu/environment/waste (consulted February 2007). 9 weber, m. Global review of biodegradable plastics testing and standards, DIN CERTCO Gesellschaft für Konformitätsbewertung mb, Berlin, http://www.co2sachverstaendiger.de/pdf/Lecture%20Biodegradable%20Plastics%20Conferenc e%2026.10.2001.pdf (consulted February 2007).


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