Applications of Nonwovens in Technical Textiles (Woodhead Publishing Series in Textiles)

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Applications of nonwovens in technical textiles

© Woodhead Publishing Limited, 2010

The Textile Institute and Woodhead Publishing The Textile Institute is a unique organisation in textiles, clothing and footwear. Incorporated in England by a Royal Charter granted in 1925, the Institute has individual and corporate members in over 90 countries. The aim of the Institute is to facilitate learning, recognise achievement, reward excellence and disseminate information within the global textiles, clothing and footwear industries. Historically, The Textile Institute has published books of interest to its members and the textile industry. To maintain this policy, the Institute has entered into partnership with Woodhead Publishing Limited to ensure that Institute members and the textile industry continue to have access to high calibre titles on textile science and technology. Most Woodhead titles on textiles are now published in collaboration with The Textile Institute. Through this arrangement, the Institute provides an Editorial Board that advises Woodhead on appropriate titles for future publication and suggests possible editors and authors for these books. Each book published under this arrangement carries the Institute’s logo. Woodhead books published in collaboration with The Textile Institute are offered to Textile Institute members at a substantial discount. These books, together with those published by The Textile Institute that are still in print, are offered on the Woodhead web site at: www.woodheadpublishing.com. Textile Institute books still in print are also available directly from the Institute’s website at: www.textileinstitutebooks.com. A list of Woodhead books on textile science and technology, most of which have been published in collaboration with The Textile Institute, can be found towards the end of the contents pages.


Woodhead Publishing Series in Textiles: Number 102

Applications of nonwovens in technical textiles Edited by R. A. Chapman

CRC Press Boca Raton Boston New York Washington, DC

Oxford

Cambridge


New Delhi

Published by Woodhead Publishing Limited in association with The Textile Institute Woodhead Publishing Limited, Abington Hall, Granta Park, Great Abington Cambridge CB21 6AH, UK www.woodheadpublishing.com Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India www.woodheadpublishingindia.com Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW, Suite 300, Boca Raton, FL 33487, USA First published 2010, Woodhead Publishing Limited and CRC Press LLC © Woodhead Publishing Limited, 2010 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 978-1-84569-437-1 (book) Woodhead Publishing ISBN 978-1-84569-974-1 (e-book) CRC Press ISBN 978-1-4398-3057-4 CRC Press order number N10179 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 acid-free and elemental chlorine-free practices. Furthermore, the publishers ensure that the text paper and cover board used have met acceptable environmental accreditation standards. Typeset by Ann Buchan (Typesetters), Middlesex, UK Printed by TJ International Limited, Padstow, Cornwall, UK


Contents

Contributor contact details

ix

Woodhead Publishing Series in Textiles

xi

Preface

xvii

Part I Fundamental principles of nonwovens 1

The formation of dry, wet, spunlaid and other types of nonwovens

3

A. WILSON, Nonwovens Report International, UK

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

Introduction Formation of drylaid nonwovens Wetlaid nonwovens Formation of spunlaid nonwovens Meltblowing of nonwoven fabrics Formation of web bonding techniques Formation of nanofibre nonwovens Bibliography

3 5 6 8 9 11 11 16

2

The influence of fiber and fabric properties on nonwoven performance

18

P. P. TSAI, The University of Tennessee, USA; and Y. YAN, South China University of Technology, P. R. China

2.1 2.2 2.3 2.4

Background Influence of solidity or packing density (α), and porosity (ε) on nonwoven performance Experimentally calculated pore size of nonwovens Pore size distribution

18 20 21 24 v


vi

Contents

2.5 2.6

2.10 2.11

Experimentally calculated fiber size of nonwovens Theoretically calculated pore size, air permeability, pressure drop and filtration efficiency Influence of thermal insulating properties on nonwoven performance Influence of filtration efficiency (FE) on nonwoven performance Influence of mechanical properties on nonwoven performance Computer programs for measuring nonwoven performance References

3

Biodegradable materials for nonwovens

2.7 2.8 2.9

27 31 33 37 40 42 44 46

G. BHAT, The University of Tennessee, USA; and D. V. PARIKH, Southern Regional Research Center, USDA, USA

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9

Introduction Reasons for using biodegradable nonwovens Cotton, hemp and other natural fibres Cotton and flax-based nonwovens Nonwovens from animal fibres Technologies for biodegradable nonwovens Applications of biodegradable nonwovens Sources of further information and advice References

46 47 48 50 54 56 58 60 61

Part II Nonwoven applications 4

Flame retardant nonwovens

65

S. DUQUESNE and S. BOURBIGOT, Ecole Nationale Supérieure de Chimie de Lille (ENSCL), France

4.1 4.2 4.3 4.4 4.5 4.6

Introduction Basics of flame retardancy Different approaches for flame retardant nonwovens Applications of flame retardant nonwovens Conclusion and future trends References


65 67 69 79 82 82

Contents

5

Nonwoven personal hygiene materials and products

vii

85

J. R. AJMERI and C. J. AJMERI, Sarvajanik College of Engineering and Technology, India

5.1 5.2 5.3 5.4 5.5 5.6 5.7

Introduction Types of nonwoven materials used for hygiene products Properties of nonwoven hygiene materials Applications of nonwoven hygiene materials Future trends Sources of further information and advice References

6

Nonwovens for consumer and industrial wipes

85 87 89 90 96 97 97 103

D. ZHANG, Textile Research Associates, USA

6.1 6.2 6.3 6.4 6.5 6.6 6.7

Introduction Key drivers and trends Nonwoven wipes technology End-user applications of nonwoven wipes Regional development of nonwoven wipes Definitions References

103 104 108 110 115 118 119

7

Nonwovens in specialist and consumer apparel

120

B. J. COLLIER, The Florida State University, USA

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9

Introduction: key issues and properties required for apparel Comfort of nonwovens in specialist and consumer apparel Protection given by nonwovens in specialist and consumer apparel Life cycle of nonwovens in specialist and consumer apparel Types of nonwovens for apparel use Applications of nonwovens in specialist and consumer apparel Future trends Sources of further information and advice References


120 121 125 127 127 128 132 134 134

viii

Contents

8

Nonwoven textiles for residential and commercial interiors

136

F. KANE, Loughborough University, UK

8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9

Introduction The interior textiles industry Nonwovens within interiors Nonwoven textiles in bedding Nonwoven textiles in upholstery and furnishing Nonwoven textiles in wallcoverings Nonwoven textiles for floor coverings Summary References

136 136 140 142 147 150 154 157 158

9

The use of nonwovens as filtration materials

160

S. ZOBEL and T. GRIES, RWTH Aachen University, Germany

9.1 9.2 9.3 9.4 9.5 9.6 9.7

Introduction Classification of filters Filtering mechanisms, technical requirements and standards for nonwoven filtration Design of nonwoven filters Common filter designs and applications Future trends References

160 162 166 171 178 181 182

10

Nonwoven textiles in automotive interiors

184

J. Y. CHEN, The University of Texas at Austin, USA

10.1 10.2 10.3 10.4 10.5

Introduction Properties required for automotive textiles Applications Future trends References

184 190 192 200 201

Index

203



(* = main contact)

Y. Yan South China University of Technology Wushan, Guangzhou P. R. China, 510640

Editor R. A. Chapman 3 The Wardens Kenilworth Warwickshire CV8 2UH UK

E-mail: [email protected]

Chapter 3

[email protected]

G. Bhat* The University of Tennessee, Knoxville Knoxville, TN 37996 USA

Chapter 1


A. Wilson Nonwovens Report International World Textile Publications Limited Perkin House 1 Longlands Street Bradford BD1 2TP UK

D. V. Parikh USDA-SRRC New Orleans, LA 70124 USA


Chapter 4

Chapter 2 P. Tsai* TANDEC The University of Tennessee, Knoxville 1321 White Avenue Knoxville, TN 37996-1950 USA E-mail: [email protected]

E-mail: [email protected]. GOV

S. Duquesne* and S. Bourbigot Unité Matériaux et Transformations (UMET) – CNRS UMR 8207 Equipe Ingénierie des Systèmes Polymères Ecole Nationale Supérieure de Chimie de Lille (ENSCL) BP 90108 59652 Villeneuve d’Ascq Cedex France ix


x


E-mail: [email protected]; [email protected]

Chapter 5 J. R. Ajmeri* and C. Joshi Ajmeri Department of Textile Technology Sarvajanik College of Engineering and Technology Athwalines Surat – 395001 Gujurat India E-mail: [email protected]; [email protected]

Chapter 6 D. Zhang Textile Research Institute 105 Shenandoah Street Clarkesville, TN 37043 USA E-mail: [email protected] [email protected]

Chapter 8 F. E. Kane Loughborough University School of Art & Design Epinal Way Loughborough Leicestershire LE11 3TU UK E-mail: [email protected]

Chapter 9 S. Zobel* and T. Gries Institut für Textiltechnik of RWTH Aachen University RWTH Aachen University Otto-Blumenthalstr. 1 52074 Aachen Germany E-mail: [email protected]; [email protected]

Chapter 10

Chapter 7 B. J. Collier College of Human Sciences 120 Convocation Way The Florida State University Tallahassee, FL 32306 USA

J. Y. Chen School of Human Ecology Texas Materials Institute Material Science and Engineering Program The University of Texas at Austin Austin, TX 78712 USA





1 Watson’s textile design and colour Seventh edition Edited by Z. Grosicki 2 Watson’s advanced textile design Edited by Z. Grosicki 3 Weaving Second edition P. R. Lord and M. H. Mohamed 4 Handbook of textile fibres Vol 1: Natural fibres J. Gordon Cook 5 Handbook of textile fibres Vol 2: Man-made fibres J. Gordon Cook 6 Recycling textile and plastic waste Edited by A. R. Horrocks 7 New fibers Second edition T. Hongu and G. O. Phillips 8 Atlas of fibre fracture and damage to textiles Second edition J. W. S. Hearle, B. Lomas and W. D. Cooke 9 Ecotextile ’98 Edited by A. R. Horrocks 10 Physical testing of textiles B. P. Saville 11 Geometric symmetry in patterns and tilings C. E. Horne 12 Handbook of technical textiles Edited by A. R. Horrocks and S. C. Anand 13 Textiles in automotive engineering W. Fung and J. M. Hardcastle 14 Handbook of textile design J. Wilson 15 High-performance fibres Edited by J. W. S. Hearle xi © Woodhead Publishing Limited, 2010

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16 Knitting technology Third edition D. J. Spencer 17 Medical textiles Edited by S. C. Anand 18 Regenerated cellulose fibres Edited by C. Woodings 19 Silk, mohair, cashmere and other luxury fibres Edited by R. R. Franck 20 Smart fibres, fabrics and clothing Edited by X. M. Tao 21 Yarn texturing technology J. W. S. Hearle, L. Hollick and D. K. Wilson 22 Encyclopedia of textile finishing H-K. Rouette 23 Coated and laminated textiles W. Fung 24 Fancy yarns R. H. Gong and R. M. Wright 25 Wool: Science and technology Edited by W. S. Simpson and G. Crawshaw 26 Dictionary of textile finishing H-K. Rouette 27 Environmental impact of textiles K. Slater 28 Handbook of yarn production P. R. Lord 29 Textile processing with enzymes Edited by A. Cavaco-Paulo and G. Gübitz 30 The China and Hong Kong denim industry Y. Li, L. Yao and K. W. Yeung 31 The World Trade Organization and international denim trading Y. Li, Y. Shen, L. Yao and E. Newton 32 Chemical finishing of textiles W. D. Schindler and P. J. Hauser 33 Clothing appearance and fit J. Fan, W. Yu and L. Hunter 34 Handbook of fibre rope technology H. A. McKenna, J. W. S. Hearle and N. O’Hear 35 Structure and mechanics of woven fabrics J. Hu 36 Synthetic fibres: nylon, polyester, acrylic, polyolefin Edited by J. E. McIntyre


Woodhead Publishing Series in Textiles 37 Woollen and worsted woven fabric design E. G. Gilligan 38 Analytical electrochemistry in textiles P. Westbroek, G. Priniotakis and P. Kiekens 39 Bast and other plant fibres R. R. Franck 40 Chemical testing of textiles Edited by Q. Fan 41 Design and manufacture of textile composites Edited by A. C. Long 42 Effect of mechanical and physical properties on fabric hand Edited by Hassan M. Behery 43 New millennium fibers T. Hongu, M. Takigami and G. O. Phillips 44 Textiles for protection Edited by R. A. Scott 45 Textiles in sport Edited by R. Shishoo 46 Wearable electronics and photonics Edited by X. M. Tao 47 Biodegradable and sustainable fibres Edited by R. S. Blackburn 48 Medical textiles and biomaterials for healthcare Edited by S. C. Anand, M. Miraftab, S. Rajendran and J. F. Kennedy 49 Total colour management in textiles Edited by J. Xin 50 Recycling in textiles Edited by Y. Wang 51 Clothing biosensory engineering Y. Li and A. S. W. Wong 52 Biomechanical engineering of textiles and clothing Edited by Y. Li and D. X-Q. Dai 53 Digital printing of textiles Edited by H. Ujiie 54 Intelligent textiles and clothing Edited by H. R. Mattila 55 Innovation and technology of women’s intimate apparel W. Yu, J. Fan, S. C. Harlock and S. P. Ng 56 Thermal and moisture transport in fibrous materials Edited by N. Pan and P. Gibson 57 Geosynthetics in civil engineering Edited by R. W. Sarsby


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58 Handbook of nonwovens Edited by S. Russell 59 Cotton: Science and technology Edited by S. Gordon and Y-L. Hsieh 60 Ecotextiles Edited by M. Miraftab and A. R. Horrocks 61 Composite forming technologies Edited by A. C. Long 62 Plasma technology for textiles Edited by R. Shishoo 63 Smart textiles for medicine and healthcare Edited by L. Van Langenhove 64 Sizing in clothing Edited by S. Ashdown 65 Shape memory polymers and textiles J. Hu 66 Environmental aspects of textile dyeing Edited by R. Christie 67 Nanofibers and nanotechnology in textiles Edited by P. Brown and K. Stevens 68 Physical properties of textile fibres Fourth edition W. E. Morton and J. W. S. Hearle 69 Advances in apparel production Edited by C. Fairhurst 70 Advances in fire retardant materials Edited by A. R. Horrocks and D. Price 71 Polyesters and polyamides Edited by B. L. Deopura, R. Alagirusamy, M. Joshi and B. S. Gupta 72 Advances in wool technology Edited by N. A. G. Johnson and I. Russell 73 Military textiles Edited by E. Wilusz 74 3D fibrous assemblies: Properties, applications and modelling of threedimensional textile structures J. Hu 75 Medical and healthcare textiles Edited by S. C. Anand, J. F. Kennedy, M. Miraftab and S. Rajendran 76 Fabric testing Edited by J. Hu 77 Biologically inspired textiles Edited by A. Abbott and M. Ellison 78 Friction in textile materials Edited by B. S. Gupta



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79 Textile advances in the automotive industry Edited by R. Shishoo 80 Structure and mechanics of textile fibre assemblies Edited by P. Schwartz 81 Engineering textiles: Integrating the design and manufacture of textile products Edited by Y. E. El-Mogahzy 82 Polyolefin fibres: industrial and medical applications Edited by S. C. O. Ugbolue 83 Smart clothes and wearable technology Edited by J. McCann and D. Bryson 84 Identification of textile fibres Edited by M. Houck 85 Advanced textiles for wound care Edited by S. Rajendran 86 Fatigue failure of textile fibres Edited by M. Miraftab 87 Advances in carpet technology Edited by K. Goswami 88 Handbook of textile fibre structure Volume 1 and Volume 2 Edited by S. J. Eichhorn, J. W. S. Hearle, M. Jaffe and T. Kikutani 89 Advances in knitting technology Edited by K-F. Au 90 Smart textile coatings and laminates Edited by W. C. Smith 91 Handbook of tensile properties of textile and technical fibres Edited by A. R. Bunsell 92 Interior textiles: Design and developments Edited by T. Rowe 93 Textiles for cold weather apparel Edited by J. T. Williams 94 Modelling and predicting textile behaviour Edited by X. Chen 95 Textiles, polymers and composites for buildings Edited by G. Pohl 96 Engineering apparel fabrics and garments J. Fan and L. Hunter 97 Surface modification of textiles Edited by Q. Wei 98 Sustainable textiles Edited by R. S. Blackburn 99 Advances in textile fibre spinning technology Edited by C. A. Lawrence


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100 Handbook of medical textiles Edited by V. T. Bartels 101 Technical textile yarns Edited by R. Alagirusamy and A. Das 102 Applications of nonwovens in technical textiles Edited by R. A. Chapman 103 Colour measurement: Principles, advances and industrial applications Edited by M. L. Gulrajani 104 Textiles for civil engineering Edited by R. Fangueiro 105 New product development in textiles Edited by B. Mills 106 Improving comfort in clothing Edited by G. Song 107 Advances in textile biotechnology Edited by V. A. Nierstrasz and A. Cavaco-Paulo 108 Textiles for hygiene Edited by B. McCarthy 109 Nanofunctional textiles Edited by Y. Li 110 Joining textiles Edited by I. Jones and G. Stylios 111 Soft computing in textile engineering Edited by A. Majumdar 112 Textile design Edited by A. Briggs-Goode and K. Townsend 113 Biotextiles as medical implants Edited by M. King and B. Gupta 114 Textile thermal bioengineering Edited by Y. Li 115 Woven textile structure B. K. Behera and P. K. Hari


Preface

Technical textiles are differentiated from other textiles in that they are designed and made to have particular functional properties and technical performance, rather than having aesthetic or decorative properties. The term ‘nonwoven’ is unfortunate in that it is an attempt to describe a structure by what it is not. It is not woven, knitted, tufted, stitchbonded or felted. It is not a paper but some nonwovens are paperlike. ‘Textile terms and definitions’ (The Textile Institute) says that opinions vary as to the range of fabrics that are classified as nonwovens. In general a nonwoven is a sheet material made from fibres or filaments that is strengthened by bonding using one or more of several techniques. These include entanglement using barbed needles or fluids, and chemical and thermal bonding. With regard to the definition, there are problems in deciding whether or not wetlaid fabrics containing wood pulp and stitchbonded fabrics should be included. Wetlaid fabrics are distinguished from wetlaid papers by having a higher proportion of fibres with a length to diameter ratio more than 300. Early nonwovens were made using conventional carding machines designed for carding fibres to make yarns. The carded webs were consolidated or bonded (to provide strength) by one or more methods that included mechanical means (barbed needles, water jets), chemical means (using polymer lattices) and thermal means (for example using fibres that become adhesive when heated). Developments in papermaking and polymer extrusion, especially the extrusion of molten polymers, have extended the range of ways of making nonwovens. Of the latter the development of spunbonding technology was the major leap forward followed by meltblowing, which enabled finer fibres to be made. Recently the introduction of electrospinning has provided a route to even finer fibre nonwovens. Composite structures made from layers of nonwovens that have been made by different routes or from different fibres are now common. For example combinations of spunbonded and melt fabrics or combinations with nanospun webs. The wide range of fibre types from natural to ‘manmade’ combined with the availability of so many manufacturing routes provides a wide range of options for xvii © Woodhead Publishing Limited, 2010

xviii

Preface

the fabric developer who seeks to optimize function, durability and cost. The current interest in green issues has led to a renewed interest in biodegradable fibres and fabrics. Nanotechnology has opened up the possibility of very fine fibre webs being made of both conventional and new fibre types. Smart textiles is leading developments in nonwoven structures that have built-in batteries and energy storage – at the fibre level. The development of new applications for nonwovens and new fabrics for established applications in particular are seen in nonwoven products for hygiene, building, personal care wipes, household products, filters and automobiles. Of these, hygiene is by far the largest end-use, followed by building applications and personal care wipes. This book covers the basics of nonwovens – the fibres used, the principal manufacturing routes and the influence of fibre and fabric properties on nonwoven performance, are addressed in Part I. Part II describes many of the main application areas including hygiene, wipes, apparel, building and automotive interiors and filtration. R. A. Chapman


1 The formation of dry, wet, spunlaid and other types of nonwovens A. W I L S O N, Nonwovens Report International, UK

Abstract: The term ‘nonwoven’ arises from at least half a century ago when these materials were often regarded as low-price substitutes for traditional textiles and were generally made from carded, ‘dry’ fibres on converted textile processing machinery. The nonwovens industry, however, has drawn on the practices and know-how of many other fields of materials manufacturing, with a piratical disregard and an eye to the most diverse range of end-use products. Today, it would be reluctant to be associated with the conventional textile industry and its commodity associations. The nonwoven technologies originating from the textile industry manipulate fibres in the dry state. Paperbased nonwoven fabrics, meanwhile, are manufactured with machinery designed to manipulate short fibres suspended in fluid and referred to as ‘wetlaid’. ‘Spunlaid’ nonwovens – spunbond, meltblown, apertured films and the many layered combinations of these products – are manufactured with machinery developed from polymer extrusion, with the fibre structures simultaneously formed from molten filaments and manipulated like plastics. This chapter examines the various bonding processes for producing nonwovens. Key words: drylaid, wetlaid, spunlaid, carding, plastics, paper, extrusion, airlaid, meltblown, nanofibres.

1.1

Introduction

The term ‘nonwovens’ arises from at least half a century ago, when the materials were often regarded as low-price substitutes for traditional textiles and generally made from carded, staple fibres on converted textile processing machinery. The yarn spinning stage is omitted in the nonwoven processing of staple fibres, with bonding of the web by various methods – chemical, mechanical or thermal – replacing the weaving or knitting together of the yarns in traditional textiles. In dividing today’s nonwoven products into three major areas – drylaid, wetlaid, airlaid or spun – it can generally be said that drylaid materials have their origins in textiles, wetlaid materials in papermaking, and spunlaid products in polymer extrusion and plastics. However, in defining what a nonwoven is, there is always at least one exception that breaks the rule. The process of stitchbonding – which originated in Eastern 3 © Woodhead Publishing Limited, 2010

4


Europe in the 1950s and is still used for some industrial applications – employs both layered and consolidating yarns, just to prove this point. This is perhaps fitting, since while being now recognised in its own right, the nonwovens industry has drawn on the practices and know-how of many other fields of materials manufacturing with a piratical disregard and an eye to the most diverse range of end-use products. For this reason, it is possible for companies with almost nothing in common – with vastly different structures, raw materials and technologies, areas of research and development and, finally, customers – to be grouped together under the nonwovens ‘umbrella’. Many would define themselves by the customers they serve, as being in the consumer products, medical, automotive or civil engineering industries, for example. And now, certainly, the nonwovens industry would be reluctant to be associated with the conventional textile industry and its commodity associations. But nor would it want its products to be called nonpapers or nonplastics. The term ‘nonwoven’, then – describing something that a product is not, as opposed to what it actually is – has never accurately represented its industry, but any attempts to replace it over the years have floundered. The illusion created by this misnomer has certainly been of some kind of bulk commodities, when the opposite is often true. The nonwovens industry is highly profitable and very sophisticated, with healthy annual growth rates – often in double digits in certain sectors and parts of the world. It is perhaps one of the most intensive in investing in new technology, and also in research and development. In nonwoven manufacturing systems, the fibre material or extruded thermoplastic is deposited or laid on a forming or conveying surface, and the physical environment at this phase can be dry, quenched in air, wet or molten – drylaid, wetlaid or spun. The web formation phase of nonwoven manufacturing processes transforms previously prepared/formed fibres, filaments or thermoplastic resins or films into layers of loosely arranged networks – webs, batts, mats or sheets. Mechanical and fluid means are employed to achieve the preferred fibre or plastic orientation in the web, through the use of machinery adapted from the textile, paper or extrusion industries. Other critical fabric parameters established at the web formation stage are the unfinished product weight and the manufactured width. Each web-forming system is used for specific fibres or products, although the exception here is with highloft nonwoven production, which employs both cards and crosslappers and air-forming systems. A key trend observed over the past twenty years has been a tremendous shift – especially for the hygiene and medical markets – away from drylaid techniques to the spunlaid route, to the extent that the latter now account for well over 40% of nonwovens manufactured worldwide. Another trend currently having a significant impact is that of incorporating nanofibre nonwoven layers into products – most notably, to date, in the area of filtration fabrics. The next major change is


Formation of dry, wet, spunlaid and other nonwovens

5

likely to be a shift away from petrochemical-based polymers and fibres towards biobased alternatives such as polylactic acid (PLA), for some, if not all, technologies. At the time of writing it is difficult to predict how significant this will be, since it is dependent on a number of factors outside the control of the industry. It could even be driven by legislation as the drive towards less reliance on petrochemicals increasingly becomes a political tool. It can safely be said that it has the industry’s attention, and is currently the subject of expansive research and development (R&D) on the part of both technology suppliers and nonwovens manufacturers.

1.2

Formation of drylaid nonwovens

The nonwoven technologies originating from the textile industry manipulate fibres in the dry state. The fibres are carded or aerodynamically formed and then bonded by a number of methods – needlepunching, thermobonding, chemical bonding, hydroentanglement, etc. The first drylaid systems owed much to the basic wool felting process known since medieval times.

1.2.1

Carding

The main objective of carding is to separate entangled tufts of fibres from bales and to deliver the individual fibres in the form of a web. The principle of carding is mechanical action, in which the fibres are held by one surface while another combs them out. At the centre of the card is a large rotating metallic cylinder covered with needles, wire or fine metallic teeth, generally referred to as the ‘card clothing’. The cylinder is partly surrounded by an endless belt of a large number of narrow, cast iron flats positioned along the top of the cylinder. The fibres are fed by a chute or hopper and condensed into a lap or batting. This is initially opened into small tufts by a licker-in, which feeds the fibres to the cylinder. The teeth of the two opposing surfaces of the cylinder and flats, or the rollers, are inclined in opposite directions and move at different speeds. The main cylinder moves faster than the flats, and due to the opposing barbs and difference in speeds, the fibre clumps are pulled and teased apart. In the roller-top card the separation occurs between the worker roller and the cylinder. The stripping roller strips the larger tufts and deposits them back on the cylinder. The fibres are aligned in the machine direction and form a coherent web below the surface of the needles of the main cylinder.

1.2.2

Airlaid

The fibres in the airlaid process are also manipulated in their dry state – although the origins of the process are from the papermaking industry and air is the key factor. The invention of the airlaid process is attributed to Karl Krøyer in Denmark


6


during the 1960s, who sold the technology to the company M&J Fibertech at the beginning of the 1980s. For over twenty years, virtually all commercial airlaid technology was manufactured in Denmark by the companies Dan-Web and M&J, until the latter was acquired by Oerlikon Neumag in 2004. At present the leading manufacturers of airlaid nonwovens include Buckeye Technologies, Concert Industries and Georgia-Pacific. Other key nonwovens manufacturers with airlaid manufacturing capacities include Kimberly-Clark, Fiberweb and Johns Manville. Airlaying involves three key steps: fibre defibration, web formation and web bonding. In the defibration process, fluff pulp is delivered in a highly compressed roll that has a cardboard-like feel. The rolls are fed into hammermills that have a series of small hammers that rotate at high speed, separating the pulp into individual loose fibres. The fibres are then transported to the web forming system and at the same time staple fibres are fed from bales into opening systems that loosen and separate the individual fibres. There are two main forming technologies used to produce airlaid webs. With the first, the fluff pulp and staple fibres are sifted through a coarse screen and deposited with the aid of a vacuum onto a forming wire below it. The second system employs formers – the fibres pass through a series of holes or slots in a large cylinder that spans the width of the forming wire. With both technologies, the pulp sheet is kept in place by a vacuum system located below the forming wire, and additives, such as superabsorbent polymers or odour control powders, can be incorporated. Production lines generally have more than one web former to allow for flexibility in the web formation and increase line throughput. The technology often allows for the web composition and structure to be controlled to achieve various required functions. Prior to bonding, the web is compacted by large rollers to provide some integrity and cohesiveness. It can also be embossed with a design or logo. There are three primary airlaid bonding technologies – latex, thermal and hydrogen bonding. The term multi-bonding is used when more than one of the technologies are used in combination – generally latex and thermal bonding. With thermal bonding the web must contain synthetic bonding fibres – generally bicomponents of polyethylene and polypropylene. Hydrogen bonding exploits the ability of cellulose fibres to bond together when naturally occurring moisture contained in them is removed while the fibres are in close contact. The bonding is usually accomplished under conditions of high temperature and pressure. This process eliminates the need for synthetic binders to be added to the airlaid web.

1.3

Wetlaid nonwovens

Paper-based nonwoven fabrics are manufactured with machinery designed to manipulate fibres suspended in fluid and are referred to as ‘wetlaid’. To distinguish wetlaid nonwovens from wetlaid papers, a material is regarded by EDANA (the European Nonwovens and Disposables Association) as a nonwoven if more than 50% by mass of its fibrous content is made up of fibres (excluding chemically



7

digested vegetable fibres) with a length to diameter ratio greater than 300, or more than 30% fibre content for materials with a density less than 0.40 g/cm3. This definition excludes most wetlaid glass fibre constructions that others would class as nonwovens. The wetlaid process was initially developed in the 1930s by Dexter, a company that was purchased by Ahlstrom in 2000. Ahlstrom is one of the leading manufacturers of wetlaid products today. Dexter’s patented technology followed attempts to reproduce special papers made in Japan from long fibres that could not be processed at the dilution ratios normally employed in papermaking. The solution was to lower the dispersion concentration from a normal 0.5% to a 0.0025% fibreto-water ratio and at the same time to modify the forming machine by inclining the forming wire at an angle – the inclined wire system. There are three characteristic stages in the manufacture of nonwovens by the wetlaid method: • swelling and dispersion of the fibre in water and transport of the suspension on a continuous travelling screen; • continuous web formation on the screen by filtration; • drying and bonding of the web. An example of the most recent wetlaid nonwovens technology is the Hydroformer developed by Voith in Germany. The Hydroformer belongs to the group of inclined-wire formers where the headbox and sheet-forming zone are a single unit. The converging nozzle consists of an upper front wall and a lower dewatering box through which the forming wire passes. The nonwoven web is formed continuously on the wire above the dewatering box from a suspension of uniform stock consistency. A 5.2-metre-wide Hydroformer system has a maximum production speed of 400 m/min and the throughput of the white-water (clean water) circuit is a staggering 300,000 litres per minute. Inclining the forming wire and suction boxes to an angle of 5° to 30° effectively expands the forming area, which in turn decreases the flow requirements for web formation and increases drainage. The web formation phase of the wetlaid process occurs between the headbox and the forming wire. In this area, the fibres are suspended in a diluted water slurry and deposited on a moving screen that permits the water to pass through the screen, and the fibres to collect. The machine direction:cross direction (MD:CD) ratio of the fabric being formed can also be influenced by the velocity of the water and the angle of the former. One of the key advantages is the ability to process many diverse types of fibre – every staple fibre that can disperse in water can be formed on the system, including Kevlar, leather and even stainless steel. The use of the wetlaid process is confined to a very small number of companies, as it is extremely capital intensive and involving substantial volumes of water. In the production of ‘textile-like’ nonwovens, end-use applications are in surgical products, bedlinen, napkins, towels and hospital supplies, while glass-


8


based products include roofing, flooring and circuit print mats, batteries, filters and decorative materials. Speciality papers are employed in dust, air and liquid filtration, and as overlay papers in laminate and wood flooring, teabag papers, plug wrap, sausage skin papers, etc.

1.4

Formation of spunlaid nonwovens

Spunlaid nonwovens – spunbond, meltblown, apertured films and the many layered combinations of these products – are manufactured with machinery developed from polymer extrusion, with the fibre structures simultaneously formed from molten filaments and manipulated. In a basic spunbonding system, sheets of synthetic filaments are extruded from polymer onto a conveyor as a randomly oriented web in the closest approximation to a continuous polymer-to-fabric operation. Most of the first proprietary spunbonding systems were developed by synthetic fibre producers such as DuPont in the USA and Rhone-Poulenc in France. DuPont is regarded as the first to successfully commercialise spunbonding with its Typar product, launched as a tufted, carpet-backing system in the mid-1960s. The first commercial spunbonding system to be offered was the Docan system developed by the Lurgi engineering group in the 1960s and licensed to Corovin (now part of Fiberweb) in Germany, Sodoca in France (also Fiberweb), Chemie Linz in Austria, and Crown Zellerbach and Kimberly-Clark in the USA. The next major step towards the global commercialisation of the spunbond process was with the introduction of Reifenhäuser’s Reicofil system in 1984. The development of this technology was not rapid – the German company spent more than a decade in developing it after patents from the original inventors lapsed. The first Reifenhäuser Reicofil spunbonding line was installed in China in 1986 and by 2009 around 180 lines of varying sizes and outputs had been sold. This gives Reicofil technology an estimated share of as much as 87% of commercial machines serving the huge hygiene market. Reicofil became an independent subsidiary of Reifenhäuser solely dedicated to this technology, in 2005. Today, the latest Reicofil 4 technology is capable of producing an annual 800,000 square metres of lightweight materials for hygiene applications – an increase of twenty times what was possible on the first line. The technology has also allowed consumer products companies to demonstrate a considerable reduction in the weights of items such as diapers – with like-for-like performance – over the past twenty years. These factors go some way to explaining Reicofil’s dominant position on the market. Reicofil does have some established competitors, however, such as STP Impianti, which has many spunbond machines in the field, Kimberly-Clark, which has developed its own in-house technologies, and newer challengers to its crown, such as Oerlikon Neumag, Rieter Perfojet and Italy’s Faré.



9

In 2008, Reicofil officially opened its new pilot plant in Troisdorf, Germany, at a cost of €16 million (US$25 million). This accommodates a flexible production line specifically designed for technical nonwovens, as well as a six-beam line for hygienic and medical products. The six-beam, 55-tonne hygiene line is comprised of three beams for spunbond and three for meltblown, one of which can be moved out for stand-alone testing when three meltblown beams are not necessary. As the company continues to develop its technology, with the first line now twenty-two years old and many other Reicofil 1 lines still in operation, upgrading is also a big part of the company’s business. The huge capacity of the latest Reicofil lines means that when a new one comes on stream it has a significant impact on the global supply situation, which is already very price sensitive. The cost of such lines is put at between €15–30 million, depending on the number of beams.

1.5

Meltblowing of nonwoven fabrics

The concept of the meltblowing of thermoplastics to form microfibres of less than ten microns was first demonstrated back in the early 1950s by the US Naval Research Laboratories, which was interested in developing such fibres to collect radioactive particles in the upper atmosphere to monitor the worldwide testing of nuclear weapons. The process developed at that time – using an adjustable extruder to force a molten polymer through a row of fine orifices directly into two high velocity streams of heated air and forming fibres within the gas stream when cooler, ambient air solidified with the fibres – was able to make very fine fibres of around 0.3 microns by operating at very high temperatures of over 450 ºC. Conceptually it was quite similar to the manufacture of mineral or slag wool, which was practised as early as 1840. In the mid-1940s Owens Corning Fibreglass developed the flame attenuation process for making microdenier glass fibres in which the drawn 1 mm diameter fibres were aligned and then attenuated by the jet flame blast from an external combustion burner. Glass fibres as fine as 0.5 microns could be made by this process. In the late 1930s and early 1940s, The American Viscose Company also investigated spray spinning of acrylonitrile and copolymers, to make microfibres, and Dow Chemical made laboratory quantities of microfibre polystyrene, while Chemstrand tried spray spinning from solvent solutions of acrylonitrile polymers, but never commercialised the process. In the late 1960s and early 1970s, Exxon Research, in looking for uses for its newly commercialised polyolefin – polypropylene – tried to use a polypropylene reactor slurry to produce synthetic paper. Dr Robert Buntin became aware of the Naval Research Laboratories publications and these served as a starting point for a multi-year, multi-million dollar project. Exxon opted to license the resulting meltblowing technology, rather than commercialise it. Early successful licensees included 3M, Kimberly-Clark, Johnson & Johnson, James River, Web Dynamics and Ergon Nonwovens, followed by many others. Although the process was conceptually quite simple, successful production of


10


acceptable quality webs could only be achieved with precisely engineered equipment operated under a rather narrow window for each different product. To assist licensees, Exxon entered into agreements with two equipment manufacturers – Accurate Products and Reifenhäuser – to supply equipment to licensees. The most commonly accepted and current definition for the meltblowing process is ‘a one step process in which high velocity fluid – normally air – blows molten thermoplastic resin from an extruder die tip onto a conveyor, take-up screen, or substrate to form a fine fibred self bonded web’. This very broad definition covers the extremely versatile meltblowing process. The extremely fine fibres of the conventional meltblowing process result in a soft, self bonded fabric with excellent covering power and opacity. Because of the fineness and tremendous number of fibres, meltblown webs can develop significant bonding strength through fibre entanglement. The many small pores and oleophilic and hydrophobic nature of polypropylene (PP) webs made it a natural candidate for oil sorbents and wipes. Hydrophilic additives and/or topical treatments provided hydrophilicity, which enabled companies such as Ergon Nonwovens, Sorbent Products and Kimberly-Clark to produce and market meltblown webs starting in the early 1970s. This market is continuing to grow at 7–8% per annum. The replacement of glass fibres with meltblown fibres in face masks and respirators was initiated by such companies as Johnson & Johnson, again in the early 1970s. Kimberly-Clark, the most prominent practitioner of the meltblowing process, has made many important innovations. Its Spunbond–Meltblown–Spunbond (SMS) patents opened up large outlets in medical fabric and surgical wrap applications. The company’s patented CoForm technology has been widely used in wipes. Today, meltblown layers are a critical layer in composite spunmelt fabrics for personal hygiene products and vital to a large number of filtration processes. In recent developments, Florida-based extrusion equipment manufacturer Hills Inc. announced the production of submicron meltblown technology in 2004, and several production lines have subsequently been installed. Hills has now developed the technology to produce meltblown fibres with an average size of 250 nanometres (nm) and a range between 25 and 400 nm. The development of meltblown nanofibres grew out of the company’s development of bicomponent meltblown extrusion equipment and it has used its patented printed-circuit style extrusion dies to produce the fibres from high-melt-flowindex polypropylene. According to Hills, a hole count of 100 holes per inch and up and extremely high length-to-diameter ratios enable the production of these nanofibres at reasonable rates, and put meltblown production in the same size range that was previously the exclusive domain of multicomponent spinning or electrospinning technology. Reicofil meanwhile, has announced a new co-operation with Biax Fiberfilm, of Greenville, Wisconsin, USA, with a view to jointly developing turnkey systems



11

specifically for meltblown Lyocell. In the light of the current drive towards a nondependency on petrochemically derived polymers, this development is especially significant.

1.6

Formation of web bonding techniques

As has been noted, nonwoven bonding processes can be mechanical, chemical (including latent bonding using solvents) or thermal. Hydrogen bonding is also important in bonding cellulosic webs. The degree of bonding is a primary factor in determining fabric mechanical properties including strength, porosity, flexibility, softness and density. Bonding may be carried out as a separate operation but is generally carried out in line with web formation. More than one bonding process can be used for some fabric constructions. Mechanical bonding processes include needlepunching, stitchbonding and hydroentanglement. In the needlepunching process, also known as needle felting, a batt of fibres is drawn through a needleloom. Fibres are mechanically entangled by reciprocating barbed needles (felting needles). In stitchbonding warp and filling yarns are laid loosely over each other whilst a third set of yarns stitches the warp and weft yarns together to produce the completed fabric. Hydroentanglement, which has grown considerably in popularity in recent years, involves bonding fibres in a web by means of high-velocity water jets. Fibre entanglement is introduced by the combined effects of the water jets and the turbulent water flow created in the web which intertwines neighbouring fibres. Thermal bonding uses heat often combined with pressure to soften and then fuse or weld fibres together without inducing melting. Chemical bonding methods involve applying adhesive binders to webs by saturating, spraying, printing or foaming techniques. In solvent bonding fibre surfaces are softened or partially solvated with chemicals to provide self- or autogeneously-bonded fibres at the crossover points. Latex emulsions can also be used to bond wetlaid webs in particular. The water-based latex emulsion is added to the dilute fibre suspension prior to feeding into the forming wire. When the web is subsequently dried, the latex binder particles form cross-links and stable bonds between the fibres. Hydrogen bonding uses the properties of cellulose fibre to produce hydrogen bonds between the hydroxyl groups on the molecular surface of the fibres to bind the fibres together.

1.7

Formation of nanofibre nonwovens

The current annual growth of the nanofibres market is put at 30%, with the 2008 market value of US$62.5 million on course to reach $176 million by 2012, still largely dominated by the filtration sector. In the five-year period between 2012 and 2017, however, annual growth is anticipated to be 36%, to reach a value of US$825 million in 2017, as new technologies become available and new markets reach critical mass.


12


While the addition of layers of nanofibres to nonwoven webs may appear to be a recent development, the first patents in respect of the electrospinning process for textile applications were issued as far back as 1902. Electrospinning uses an electric field to draw a polymer melt or polymer solution from the tip of a capillary to a collector. A voltage is applied to the polymer, which causes a jet of the solution to be drawn towards a grounded collector. The fine jets dry to form polymeric fibres, which can be collected on a web. The nonwoven webs produced from such fibres can be given unique physical, mechanical and electrical properties associated with their very high surface area. If, for instance, a fibre is used to catalyse a chemical reaction, which has a rate of conversion of two grams per hour on a one square metre surface, then the increased surface area of a web employing 200 nm nanofibres can theoretically lead to a 100-fold increase in the reaction rate over a traditional 20 micrometre (µm) fibre. Physical property changes are also linked to the increase in specific surface area – higher fluid adsorption capacities, for example. Additionally, some materials in fibre form break under stress at critical flaws in the fibre. With a reduction in fibre diameter, these critical flaws and their overlapping becomes statistically less likely, and so a bundle of nanofibres with a certain diameter can be much tougher than a monofilament of the same diameter. Nanofibres are traditionally defined as cylindrical structures with an outer diameter below 1,000 nm and an aspect ratio – the ratio between length and width – greater than 50. Up until recently however, they have only been produced in limited quantities in a laboratories because the main stumbling block to electrospinning has been its slow production rate. On average, solution based electrospinning using needle spinnerets in a laboratory has solution throughput rates on the order of 1 ml per hour per needle. Fibres with diameters in the range of 50 to 100 nm are typically spun from solutions with relatively low concentrations, 0.5–10 wt% depending on polymer type and molecular weight. This means that – assuming a polymer density of around 1 g/ml – the typical solids throughput rate of a needle-based electrospinning process is 0.005 g to 0.01 g of fibre per hour per needle. If this calculation is extended, producing a nanofibre web with a planar density of 80 gsm at a rate of five square metres per second would require a minimum of 40,000 needles. In addition to the requirement for such a large number of needles, electrical field interference between the different needles also limits the minimum separation between them and, furthermore, continuous operation of needle-based spinnerets requires frequent cleaning of the needles, since polymer deposits block the spinnerets. So although the electrospinning process can be relatively cost effective on a lab scale, the low rates of fibre throughput on single-needle systems make production at industrial volumes almost prohibitively expensive. During the past five years, however, alternative technologies have arisen, and



13

the number of research activities resulting in patent applications and issued patents has increased rapidly, leading to the development of a range of potential massproduction fabrication methods – many still based on electrospinning. A number of the leading industrial nonwovens manufacturers and filter makers are now employing nanofibre layers in filter media, with Donaldson Company acknowledged to have been the pioneer with its UltraWeb and SpiderWeb ranges. Donaldson makes nanofibres using proprietary electrospinning processes that have been developed and enhanced since the 1970s. It claims to make tens of thousands of square metres of electrospun polyamide nanofibre filter media using several production machines every day. This may sound impressive, but they have an average weight of just 0.05 gsm and, rather than actual materials, should really be considered as another form of coating. The disadvantage is that, although improving filter efficiency considerably, the nanofibres function purely as two-dimensional surface filters and demonstrate a correspondingly short service life. The use of nanofibres as actual complete filter media, meanwhile, is limited due to a number of factors – the lack of full scale production equipment, the high costs and the previously mentioned limitations of the electrospinning manufacturing route, as well as the delicate nature of the webs that are presently used, primarily as an add-on for improved filter media. Nanocomp Technologies, based in Concord, New Hampshire, USA, however, has recently successfully produced sheets of carbon nanotube material measuring 1.8 m × 0.9 m (6 ft × 3 ft) – the largest cohesive sheets of nanotube material ever produced. At the core of the company’s process is a technology for the continuous, high-volume output of millimetre-long, highly pure carbon nanotubes that efficiently conduct both heat and electricity. By bringing this technology to practise using established industrial processes, Nanocomp can now produce sheets of material at contiguous sizes of tens of square metres. Nanocomp’s materials are said to possess a unique combination of high strengthto-weight ratio and electrical and thermal conductivity, as well as flame resistance that exceeds those of many other advanced materials by orders of magnitude. The resulting material can be a valuable addition to such applications as electromagnetic interference (EMI) shielding, electrical conductors, thermal dissipation solutions, lightning protection and advanced structural composites. In contrast to Nanocomp’s millimetre-long nanotubes, other carbon nanotubes are short – tens of microns long – and are usually delivered in powder form. Short nanotubes have limited industrial use because they are difficult to incorporate into existing manufacturing processes and do not possess the high performance properties of long carbon nanotubes. Other alternatives to electrospinning are currently the subject of much research and development. In addition to filtration, nanofibre nonwovens are being applied as sound absorption materials and in protective clothing to combat chemical and biological warfare agents, as well as in wound healing products. Nanofibres will also be


14


Table 1.1 Existing and potential applications for nanofibres Sector

Application

Electronics Biological and healthcare

Super capacitors Biosensors Tissue engineering Medical devices Wound dressings Cables for implantable devices Neural prostheses Drug-coated stents Artificial heart valves Photovoltaics Fuel cells Battery separators Printable electronics Hydrogen storage Separation membranes Affinity membranes Water filters Air filters Gas turbine filters Engine filters Personal protective masks and clothing

Energy

Biotechnology and environment

Others

Source: University of Singapore.

increasingly used in the electronics and energy sectors in the next few years, in batteries, photovoltaic cells, polymer electrolytes and membrane fuel cells, as well as in the medical world, as artificial organ components and in tissue engineering and implants. Inorganic materials, notably metal oxides, can be synthesized and electrospun for improving the conducting and ceramic properties of energy devices, while excitonic solar cells fabricated with aligned nanofibrous metal oxide electrodes can provide higher solar-electric energy conversion efficiency. Fuel cells made with nanofibrous electrodes allow the uniform dispersion of catalysts, which increases electrocatalytic activity, leading to higher chemical–electric energy conversion efficiency. It is also now believed that the reliability and durability of surgical implants such as hip and knee replacements could be greatly improved by electrospun nanofibre coatings that encourage them to bond with living bone. As a consequence of such potential end-uses the growth of the nanofibres markets is expected to be rapid after around 2012, as more and more applications reach commercial stage (see Table 1.1).



1.7.1

15

Emerging nanofibre technologies

Elmarco – Nanospider Elmarco’s Nanospider technology was developed in close co-operation with the Technical University of Liberec in the Czech Republic. The patented technology is capable of producing a consistent web of nanofibres with diameters of 50–300 nm, approximately 1,000 times smaller than a human hair. The extremely fine fibres provide enormously high surface area, approximately 150 times greater than that of commonly used spunbond or cellulose fibres. Filter media with this increased surface area collect a significantly greater number of particulates, which results in superior filter efficiency. Nanospider technology can process a wide range of polymers in diameters of 50–300 nm into nonwoven webs of 0.1–5 gsm. The fibres are formed by an electrostatic field from a thin film of an aqueous or solvent solution and a wide range of polymers, including PA6, PVA and PUR as well as more exotic types such as chitosan and gelatine, have been successfully spun. The Nanospider system employs centrifugal spinning, which is similar to electrospinning, using a high-speed rotating cylinder with nozzles to create fibres and an electrostatic field to direct them to a collector. It has high productivity but the fibres are not as fine as electrospun types. While in the electrospinning process, high voltage is used to create and electrically charge a stream of polymer solution that is electrospun by capillary action using a spinneret. Nanospider technology’s productivity is much higher since it does not use nozzles or capillaries to form fibres. The fibres are formed by an electrostatic field from a thin film of an aqueous or solvent solution and are collected in the form of a nonwoven textile on a collector. Fibre diameter is 100– 300 nm and the weight of the nonwoven web is 0.1–5 gsm. Nanospider technology enables the production of nanofibre materials on an industrial scale and is expected to bring many product advancements to the health care market including: • • • • • • • •

industrial scale nanofibre production multilayered technology delivering several therapeutics greater absorption capabilities improved efficacy of products reduced product costs bioactive availability improved physical properties customised solutions.

Integrated Nanofibre Technology Irema of Germany has developed a process for embedding nanofibres into


16


nonwoven fabrics during their actual manufacture. The company’s patented ‘Integrated Nanofibre Technology’ creates a deep, ‘three-dimensional’ filter by embedding the nanofibres down to a size of 100 nm into meltblown fabrics consisting of microfibres with a thickness of 2–20 µm. In addition to the cost benefit, the great advantage is in being able to develop and produce customer-specific products in which the gradient between coarse and fine fibres is freely selectable across a broad spectrum. In addition, of course, now post processing is required. A large proportion of Irema’s products are used in the automotive industry for interior filter systems – the company states that an Irema medium is used in about every third automotive cabin air filter. With Integrated Nanofibre Technology Irema’s media fulfil the requirements made by hepafiltration (H10 and H11 grade filters) to DIN EN 1822, even at high flow speeds. The key benefits of the technology are said to be: • • • •

much improved filter efficiency extended service life reduced manufacturing and lower costs gradients adjustable to coarse and fine fibres.

DuPont Hybrid Membrane Technology (HMT) The development of HMT involved two DuPont businesses – Nonwovens and Advanced Fiber Systems – with the role of Advanced Fiber Systems critical to developing production on a commercial basis based on the electrospinning method. The media is now made by a proprietary new process at a manufacturing plant in Korea, which started production in May 2006. HMT’s filtration efficiency is close to that of microporous membranes, but the resulting air pressure drop across the filter is lower. It offers higher flux at smaller pore sizes and its other features and benefits include a superior barrier to fine particles and allergens, exceptional breathability and moisture vapour transmission in clothing and bedding products, high uniformity, and availability in a variety of styles. With its controllable fibre diameter, pore size and sheet thickness, it can be customised for diverse applications and also combined with other materials.

1.8

Bibliography

Airlaid Pulp Nonwoven Primer, INDA, Association for the Nonwovens Fabrics Industry, January 2003. Handbook of Nonwovens, Edited by S. J. Russell, Woodhead Publishing, December 2006. Nanofibres: From Finer Filters to Advances in Electronics, Energy and Medical Applications, Technical Textile Markets, 3rd quarter 2008.



17

Nuclear Origins of Sub-micron Extrusion, W. John G. McCulloch, Nonwovens Report International, November 1999. Reicofil Opens New $25 Million Technology Centre, International Fiber Journal, June 2008. Water Worker – Voith Paper’s Hydroformer Wet-laying System, Nonwovens Report International, June 2001.


2 The influence of fiber and fabric properties on nonwoven performance P. P. T S A I, The University of Tennessee, USA; and Y. Y A N,

South China University of Technology, P. R. China

Abstract: The application of a nonwoven is determined by its performance, which is governed by its properties including fiber diameter, fiber orientation, packing density and basis weight, etc. This chapter describes the measurement and/or calculation of fiber diameter, fiber orientation, pore size, and packing density, etc. and how these parameters affect the nonwovens’ performance such as oil absorbency, air permeability, mechanical strength, thermal insulation, and filtration efficiency, etc. The nonwovens’ performance can be calculated. This chapter illustrates the correlation of the theoretical values of a nonwovens’ properties and performance with the experimental results. Key words: nonwovens, spunbonding, meltblowing, needle-punching, hydro-entangling, chemical-bonding, thermal-bonding, properties, performance, packing density, porosity, fiber size, pore size, air permeability, pressure drop, insulating, filtration.

2.1

Background

The use of nonwovens has greatly increased and there has been a steady 5–10% annual growth in the last couple of decades. Different nonwoven applications require different nonwoven properties. These properties include material type, fiber size, packing density, pore size, fiber orientation in the web, etc. and they determine the nonwoven’s physical, mechanical and chemical performance attributes, such as mechanical strength, thermal and acoustic insulating properties, barrier properties, and filtration efficiencies (FE), etc. The fiber size and other fiber properties such as the fiber shape, fiber surface roughness and surface chemical functions, the fabric porosity or the fabric packing density, and the basis weight govern the nonwoven’s properties and performance. When a nonwoven is used for oil absorbency, oleophilic materials such as polypropylene (PP) or polyethylene (PE) are selected because they have a good affinity with oil. The absorbed oil occupies the void space that is not occupied by the fibers. Therefore, the amount of oil that can be absorbed by a nonwoven is determined by its void fraction or porosity. Also, depending on the viscosity of the 18 © Woodhead Publishing Limited, 2010

Influence of fiber and fabric properties on nonwoven performance

19

oil, careful design of the fabric structure is a critical factor in order to provide enough capillary force among the fibers such that the void is capable of holding the absorbed oil. Particles are captured on the surface of the fibers in an air filtration system.1,2 Fibrous materials are more suitable for use as air filter media because they provide a large fiber surface area that contributes to high filtration efficiency, and have a high fabric porosity that reduces air resistance across the fabric. A reduction in the fiber diameter increases the fiber surface area but also proportionately increases the pressure drop. Selection of the fiber size and control of the packing density are two critical factors for meeting the requirements of the FE, the dust holding capacity (DHC), and the pressure drop of filter media.3,4,5,6 Sieving is basically the mechanism for liquid filtration.7,8 Sieving is governed by the pore size, which is determined by the fiber size and the packing density of the medium. In air filtration, the rule of thumb is to minimize the fiber size and maximize the porosity in order to achieve the desired filtration efficiency and reduce the pressure drop. In liquid filtration, it is to make the medium have a small pore size, smaller than the particle size, in order to block the particles. The packing density of a fabric can be calculated from the fabric basis weight, the fabric thickness, and the density of the polymer from which the fabric is made.9 The mean fiber size of a fabric made from a polymer-laid nonwoven process can be determined from the air permeability or the pressure drop of a fluid flow through the fabric.10 Conversely, the air permeability or the pressure drop of a fabric made from other nonwoven processes, such as needle-punched, thermally bonded, hydro-entangled, etc., can be determined from the known fiber size and the calculated packing density of the fabric.11 Pore size, which governs the liquid filtration of a fabric, can be treated as a circular channel and theoretically calculated by the modified Hagen–Poiseuille equation.10,12,13 Conduction, convection and radiation are three mechanisms of heat transfer.14 For nonwovens used as thermal insulating materials, if radiation is ignored, heat is transferred through the fibers by conduction and through the voids by convection.15 A high thermal insulating property value can be achieved by careful selection of low conduction polymer types for the fibrous material and effective control of air movement in the void, i.e. reducing the amount of polymer material used so heat transfer through conduction is minimized and reducing the pore size so the air in the void is blocked and air movement is greatly restricted. The filtration efficiency of a fabric can be simulated by single fiber efficiency theory using the fiber diameter, the fabric packing density, and the fabric basis weight. The FE and the pressure drop of a composite made from multiple plies of nonwoven fabrics can be theoretically calculated given the FE and the pressure drop of each ply of the composite.11 Mechanical properties, such as mechanical strength, are important factors for all applications since weak nonwovens are of no use. Nonwovens are composed of


20


fibers and their strength is obtained from the fiber strength and the bonding strength among the fibers. Types of bonding include thermal, chemical, hydroentangling, and needle-punching, etc. Unusually, the bonding of a meltblown fabric is obtained from self-entangling and the friction force among its microfibers. Nonwovens are anisotropic materials whose directional strength is determined by the fiber modulus and the fiber orientation distribution in the web16,17 using micromechanics.18,19

2.2

Influence of solidity or packing density (α ), and porosity (ε ) on nonwoven performance

The solidity or packing density of a web is defined as the ratio of the volume occupied by the fibers to the whole volume of the web, i.e.: Packing density, α ≡ total volume of fibers/total volume of the web Vf Wf /ρf Basis weight = —— = ——– = —————– Vweb tA tρf where: Vf = Vweb = Wf = ρf = t = A =

[2.1]

volume of fibers volume of the web weight of fibers = weight of the web fiber or polymer density thickness of the web area of the web

Porosity (ε) is the fraction of the void volume to the volume of the web, i.e.: Porosity, ε = 1 – α

[2.2]

Packing density is an indication of the web’s compactness. One of its applications is in calculating the oil absorbency capacity of a nonwoven, i.e. the ratio of the porosity to the packing density. Theoretically, a web can hold an amount of oil χ times its own weight, i.e.:

ε ρoil χ= — α —– ρweb

[2.3]

where ρoil is the oil mass density and ρweb is the web mass density. For example, a 10 gram absorbent web with a packing density of 5% can hold 190 grams of oil, assuming that the oil and the polymer have the same mass density. Additionally, as we will see in the next few sections, the packing density is a crucial factor in determining the pore size, which controls liquid filtration and fluid



21

z

2.1 Velocity profile of a fluid flow in a channel.

permeability. Packing density is also a factor in controlling air filtration efficiency, as will be described in later sections.

2.3

Experimentally calculated pore size of nonwovens

Pore size is an important factor in liquid filtration because sieving is an important liquid filtration mechanism. Sieving is the same as blocking, i.e. a particle is blocked by a pore if the pore size is smaller than the particle size. The pore size of a nonwoven fabric can be experimentally calculated if it is treated as a circular channel as shown in Fig. 2.1. The shear stress (τrz) at a radial distance r from the center of the channel in the flow direction (z) is given by Newton’s law of viscosity as: dv τrz = – µ—–z dr

[2.4]

where µ is the fluid viscosity and vz is the fluid velocity in the z direction. The shear stress of a steady laminar flow can be derived from the momentum balance as: P0 – PL τrz = ———– r 2L

[2.5]

where P0 is the fluid pressure at the upstream and PL at the downstream of the channel with a length difference (L) and a pressure difference (∆P) between P0 and PL . Combining Eqs 2.4 and 2.5 gives the following differential equation for the fluid gradient velocity: dvz ∆P — = – —— r dr 2µL

[2.6]

Integrating Eq. 2.6, one can obtain the fluid velocity at distance (r) as: ∆P vz = – —— r2 + c 4µL where c is an integration constant.


[2.7]

22


Using the boundary condition that vz = 0 at r = R gives the fluid velocity: ∆PR2 [1 – (r/R)2 ] vz = —— 4µL

[2.8]

where R is the radius of the channel. The fluid has a maximum velocity in the center of the channel, i.e. r = 0. ∆PR2 vz, max = —— 4µL

[2.9]

Summing the velocity of each differential area then dividing by the total crosssectional area gives the average velocity: 2π

R

∫ ∫ v rdrdθ = ∫ ∫ rdrdθ 0

z

0 2π

R

0

0

=

∆PR 2 8µ L

[2.10]

Total flow rate is the average velocity multiplied by the cross-sectional area (A), which is:

π∆PR4 = ——— π∆PD4 Q = A < vz > = ——— 8µL 32µL

[2.11]

where D is the diameter of the channel. Equation 2.11 is known as the Hagen– Poiseuille law. Rearranging Eq. 2.11 gives: 128µLQ ∆P = ———– πD 4

[2.12]

32µv ∆P — = —— L D2

[2.13]

or

Fluid flows along a tortuous path (l) in the medium. It travels a longer path in the pores than in a straight channel because of the path tortuosity (T), i.e.: l = LT

[2.14]

The velocity in the medium is also increased by a reduction in the available crosssectional area of the medium. The velocity in the medium becomes: v = v0/ε

[2.15]

where v0 is the face velocity, i.e. the velocity at the entrance of the medium. By correcting the fluid traveling length and velocity in the medium, using the web thickness (t) for the channel length (L), Eq. 2.13 becomes: ∆P = — tT

32µv0 —— – D2ε

[2.16]



23

Manometer tube 11 mm O.D. 9 mm I.D. Pressure regulating gauge

Needle or bleed off valve Rubber stopper

Compressed air

Zero line Drain with pressure stopcock

Heavy wall rubber tubing

2.2 An apparatus to measure the flow rate and pressure drop of a fluid flow through a medium (ASTM F902-84).

– where D is the average circular-capillary-equivalent pore size (ACCP). Substituting the tortuosity (T) by Eq. 2.17: T = 1/ε

[2.17]

the ACCP pore size becomes: – D =

32µv t ——–02 ∆Pε

1/2

[2.18]

One can calculate the ACCP from the pressure drop of a fluid flow through the medium. The porosity of a medium can be obtained from Eqs 2.1 and 2.2. Figure 2.2 shows a piece of apparatus for measuring the pressure drop of a fluid flow through the medium. A flow meter with an adjustable valve is inserted in the air line to measure the air flow rate and the pressure drop is measured by a manometer. An example calculation (Example 2.1) is shown below. Example 2.1 Pore size calculation of a meltblown fabric Using air viscosity (µ) of 1.85 × 10–5 N s/m2 at 25 °C, an entrance velocity (v0) of 5.3 cm/s, a PP web with a thickness of 0.3 mm and basis weight of 30 gsm, a pressure drop of the air across the web of 2.8 mmH2O, and a PP having a polymer density of 0.91 g/cm3, Eq. 2.2 can be used to calculate the porosity of the web as 89%. Inserting the above numbers into Eq. 2.18 and converting the pressure–drop from mmH2O to N/m2 using 1 mmH2O = 9.81 N/m2, one obtains an ACCP (D ) of 20.73 µm.

Experimentally, the value of the ACCP is close to the mean flow pore size measured with a pore size analyzer, as shown in Fig. 2.3 for a series of meltblown


24

Applications of nonwovens in technical textiles 25 ü

22.5

◊

22.85 ◊

22.23 ◊

Pore size (µm)

21.67 ü 19.85

20

MFP ACCP

◊

21.05 ◊ ü 20.8

19.5

ü 20.57

◊

ü 18.62

20.31 ◊

20.34 ◊ ü 19.64

19.2

ü ◊ ˜ 19.37 ü 19.09

ü 18.28

18.84 ◊ ü 18.45

17.5

15 1

2

3

4

5

6

7

8

9

Meltblown webs

2.3 Comparison of the mean flow pore size (MFP) from pore size analyzer and the calculated average circular-capillary-equivalent pore size (ACCP).

webs with different pore sizes from the different fiber diameters that compose the webs.10 In general, the ACCP has a higher value than the mean flow pore size (MFP) because the measurement uses a higher pressure drop. Therefore, the medium is compressed more by the applied pressure and thus the pore size is reduced by the compression during the analysis, resulting in a significant experimental error.

2.4

Pore size distribution

Pore size distribution in a medium can be obtained from a pore size analyzer, in which the pore is treated as a capillary channel. Figure 2.4 shows the meniscus of a liquid in a capillary channel. When the liquid surface force is balanced with the liquid gravity force, the following equation is true:

γ 2πr cosθ = ρπr2hg where: γ = surface tension of the liquid


[2.19]

Influence of fiber and fabric properties on nonwoven performance r θ h g ρ

= = = = =

25

radius of the capillary contact angle height of liquid gravitational acceleration constant density of liquid

When a fabric is wetted out with a liquid and an air pressure (P) is applied to force the liquid out of the medium, Eq. 2.19 becomes:

γ 2πr cosθ = πr2P

[2.20]

and the contact angle θ = 0 since the web is wetted out by the liquid. So Eq. 2.20 becomes: 4γ D = —– P

[2.21]

where D is the pore size, which is determined by the applied air pressure that forces the liquid out of the pores. When the air pressure is sufficient to force the liquid out of the first pore, a bubble is seen on the thin layer of liquid on top of the medium, known as the bubble point, and this gives the maximum pore size. Figure 2.5 illustrates the relationship between the applied air pressure and the flow rate through a meltblown nonwoven. When all the liquid filling up the pores is forced out of the fabric by the applied air, the web dries and the relationship between the applied air pressure and the air flow rate becomes linear. This is known as Darcy’s law, which will be discussed in the next section. The intersection of the wet curve and the half-dry curve is the mean flow pore size, which is the pore

P

θ

P – 2γr h P

P

P

P

2.4 Balance of surface tension force with the gravity force of a liquid in a capillary channel.


26

Applications of nonwovens in technical textiles 30 Through pore throat diameter

Flow rate (L/min)

25

20

15

Wet curve

Dry curve

Gas permeability Envelope surface area

10

Half-dry curve

5

0 0 0.2 0.4 Mean flow Bubble point pore diameter

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Pressure (PSI)

2.5 The relationship between the applied air pressure and the air flow rate (L/min) through a meltblown nonwoven (courtesy of Porous Materials, Inc.).

Distribution function, f (per micron)

60 f = –d[(fw /fd) × 100]/dD fw = flow rate through wet sample fd = flow rate through dry sample D = pore diameter

50 40 30 20 10 0 0

5

10

15

20

25

30

Average diameter (microns)

2.6 The pore size distribution of a meltblown nonwoven (courtesy of Porous Materials, Inc.).



27

size when the flow rate is half that of the flow rate immediately after the fabric becomes dry. There will be more discussion of applications for the mean flow pore size and its relationship with the ACCP in Section 2.6. Figure 2.6 shows an example of the pore size distribution of a meltblown nonwoven from a pore size analyzer. Liquid filtration is a sieving mechanism, i.e. particles are blocked or captured by the filter medium if the pore size is smaller than the particle size. Ideally, if a medium can be designed in such a way that the pore size distribution curve is similar to and smaller than that of the particle size distribution, large particles will be captured by large pores and small particles will be captured by small pores.

2.5

Experimentally calculated fiber size of nonwovens

The relationship between the pressure drop (∆P) and the velocity of a fluid (gas or liquid) flow through a porous medium in a laminar flow is described by Darcy’s law as:

κ (∇P – ρg) v0 = – — µ

[2.22]

where: v0 = superficial velocity, i.e. the flow rate divided by the face area of the medium κ = permeability of a porous medium, which will be expressed as a function of the fiber diameter and the web packing density in the derivations in Section 2.6.2 µ = viscosity of the fluid ρ = density of the fluid P = pressure on the fluid The gravity term, ρg, can be ignored for air because air has a low density, thus its body force (i.e. the weight of the air) is insignificant compared with the pressure force on the liquid. If the flow through the porous medium is not laminar, then the inertial term needs to be modified. A modified Darcy’s law has been suggested by H. C. Brinkman to include the turbulent term,13 i.e.: µ 0 = – ∇P – —v0 + µ∇2 v0 + ρg κ

[2.23]

in which the turbulent term or the inertia term, µ ∇2 v0, is included. For most of our applications, the fluid flow through the nonwoven is laminar. Therefore, we use Eq. 2.22 for further derivations. If the fluid flow is unidirectional and is perpendicular to the medium, Darcy’s law becomes a one-dimensional flow. Therefore, Eq. 2.22 is simplified to:


28


κ ∆P —– v0 = — µ ∆L

[2.24]

where ∆P is the pressure drop of the fluid across the web and ∆L is the web thickness, or

κ ∆P —– v0 = — µ t

[2.25]

where ∆L is substituted by t, the thickness of the web. Therefore, the pressure drop across the medium becomes: µtv ∆P = —––0 κ

[2.26]

Darcy’s law for a fluid flow through a porous medium is analogous to Ohm’s law for a current flow through a conductor with the following analogy: I = V — R

[2.27]

L Rα — A

[2.28]

and

where A is the cross-sectional area of the medium, or L R = ρ— A

[2.29]

L R = 1– — σA

[2.30]

or

where σ is the conductivity of the material. Substituting the resistance, R, in Eq. 2.29 for the resistance in Eq. 2.27 gives: V —I = σ — A L

[2.31]

V J = σ— L

[2.32]

or

where J is the current density, which is analogous to the velocity v0 in Darcy’s law. The conductivity (σ) is analogous to the permeability (κ). The voltage drop (V) is analogous to the pressure drop (∆P) and the length (L) of the conducting material



29

is the thickness (t) of the web. The pressure drop of a gas flow through a fibrous medium is determined by the following eight variables: Q A t µ ρ λ R α

= = = = = = = =

flow rate superficial area filter medium thickness fluid viscosity fluid density mean free path of gas molecule mean radius of the fiber packing density of the medium

These eight variables can be grouped into seven independent parameters, which satisfy the following equation: ∆P Q λ f —–, —, R, α, µ, ρ, – = 0 t A R

[2.33]

By Buckingham’s π theorem, the following function of the non-dimensional groups exists: ∆PAR2 QRρ λ f ——––, ——, α, – = 0 µQt Aµ R

[2.34]

The first term is an expression of Darcy’s law for fluid flow through a fibrous medium and is a function of the packing density of the medium, i.e.: ∆PAR2 ——— = f (α) µQT

[2.35]

According to C. N. Davies,3 the packing density function is: f(α) = 16α1.5(1 + 56α3)

for 0.006 < α < 0.3

[2.36]

Rearranging Eq. 2.35, the pressure drop can be written in terms of the fabric properties as: µv0tf(α ) ∆P = ———— df2

where f(α) = 64α1.5(1 + 56α 3)

[2.37]

where df is known as the effective fiber diameter.3 Note that the coefficient of 16 in Eq. 2.36 has been changed to 64 in Eq. 2.37 because the fiber radius (R) has been changed to diameter df . The fiber diameter can be determined in terms of air velocity, air viscosity, web thickness, web packing density, and the pressure drop across the web, i.e.: µvtf(α ) df = ———– ∆P

1/2


[2.38]

30

Applications of nonwovens in technical textiles 10 9

y = 0.561 × 100.088x r2 = 0.995

SEM fiber size (µm)

8 7 6

5 4

3

2 1 2

4

6

8

10

12

14

Effective fiber size (µm)

2.7 The master curve between the effective and the scanning electron microscope (SEM) fiber diameters of meltblown webs.

An example calculation (Example 2.2) is shown below. Example 2.2 Effective fiber diameter calculation of a meltblown fabric Using the same web and the same air flow conditions as in Example 2.1 and substituting the numbers from Example 2.1 into Eq. 2.38, one can calculate that the effective fiber diameter of the web is 5.162 µm.

The geometrical fiber diameter (dg) is equal to the effective fiber diameter (df) if the fiber is round in shape and uniform in size. For meltblown fabrics, the effective fiber diameter (df) is always greater than its geometric fiber diameter (dg) as can be observed from the experimental master curve in Fig. 2.7. Figure 2.7 is a master curve of the effective fiber diameter and the geometric fiber diameter of a meltblown web. The scanning electron microscope (SEM) average fiber diameter can be obtained from the calculated effective fiber diameter through the master curve. Table 2.1 is a comparison of the results obtained Table 2.1 Comparison of fiber diameters from calculation and from SEM measurements for three meltblown fabrics Sample no. 1 2 3

Effective fiber diameter (mm)

From calculation (mm)

5.84 7.82 10.13

1.92 3.13 5.56

SEM (mm)


1.93 2.97 5.12

Error (%) 0.5 5.3 10.8


31

for the fiber diameter measured using an SEM and those from the experimental calculation using the pressure drop measurement of the air flow through the web for three meltblown webs. For other nonwovens composed of staple fibers, such as needle-punched, hydro-entangled, thermal- and chemical-bonded fabrics, the effective fiber diameter is also the SEM-measured fiber diameter.

2.6

Theoretically calculated pore size, air permeability, pressure drop and filtration efficiency

2.6.1

Pore size

The modified Hagen–Poiseuille law was employed to obtain the average circular– capillary-equivalent pore size (D) by introducing the term tortuosity (T), and reducing the available fluid flow cross-sectional area by 1/ε, as shown in Eq. 2.18. Substituting ∆P in Eq. 2.18 using Eq. 2.37 gives: df – D = —— g(α)

[2.39]

where: 0.5 1  g(α) = 1/ ——————————  2 1.5 3  2(1 – α) α (1 + 56α ) 

[2.40]

Note that ε in Eq. 2.18 is web porosity and α in Eq. 2.39 is packing density. Their relationship is shown in Eq. 2.2. Equation 2.39 is an expression of Eq. 2.18, which is the ACCP, in terms of fiber diameter and web packing density. Equation 2.39 can be used to calculate the average circular-capillary-equivalent pore size of a fibrous medium if the fiber size and the packing density are known. Similarly, using the same equation, one can design the fiber diameter and the packing density to achieve the desired pore size of a medium. An example calculation (Example 2.3) is shown below. Example 2.3 Pore size calculation of a needle-punched fabric Assume that for a 150 gsm needle-punched fabric having fiber diameter of 25 µm with packing density of 2.63%, the calculated ACCP is 278 µm using Eq. 2.39.

As described in Section 2.1, liquid filtration is predominately a sieving or a blocking mechanism, i.e. particles are blocked when the pore size is smaller than the particle size. The nominal rating of a liquid filter refers to the percentage of particles above a particular size that are captured. For example, a typical pre-filter for drinking water will have a nominal rating of 95% for 5 µm particles. In this case, the ACCP is designed to be 5 µm using Eq. 2.39.


32


Hydrohead is the hydrostatic pressure needed to force a liquid to penetrate a medium and is the ability of a nonwoven fabric to resist liquid penetration. It is a critical factor for a nonwoven fabric that is to be used as protective clothing, such as a doctor’s surgical gown. Liquid penetrates through a medium via large pores. As indicated in Section 2.4, the ACCP is equivalent to the MFP, which is the pore size when the air flow is half that of the dry flow. The maximum pore size is typically twice that of the MFP. A finer fiber size and a larger packing density are sought to reduce the ACCP according to Eq. 2.39, and hence to increase the hydrohead. However, the ventilation rate or the moisture vapor transmission rate (MVTR) is relatively reduced by a reduction of the air permeability, according to Eqs 2.41 or 2.42. A careful design is required to take both the hydrohead and the MVTR into account by using Eqs 2.39 and 2.42 at the same time.

2.6.2

Air permeability

The pressure drop of a fluid flow across a medium is determined by the medium’s properties including fiber diameter, packing density and thickness, as well as the fluid properties such as the fluid viscosity and the fluid velocity as expressed in Eq. 2.37. Introducing Darcy’s law from Eq. 2.25 into Eq. 2.37 to replace the ∆P in Eq. 2.37 gives: df 2 κ = —–– f(α)

[2.41]

The permittivity (κ) is a function of the web packing density and the fiber diameter. One can substitute Eq. 2.41 into Eq. 2.25 to obtain the flow rate of the fluid through the fibrous medium, i.e.:

.

Q = v0 A 2

=

∆ PAd f µ tf (α )

[2.42]

· The symbol Q is a flow volume while Q is a flow rate, i.e. the flow volume per unit of time. Equation 2.42 provides the fluid flow rate through a fibrous medium with cross-sectional area (A). Similarly, one can design the independent parameters of a web, i.e. the fiber diameter and the packing density, to obtain a desired fluid permeability through the medium. Table 2.2 shows, for three meltblown fabrics that are designed to possess different diameters, the calculated data from the equations discussed in this section for obtaining the effective fiber diameter, the SEM equivalent average fiber diameter, the pore size and the air permeability. Table 2.3 shows the calculated properties for two needled felts. Needled felts have a higher porosity than meltblown webs and it is not possible to measure the



33

Table 2.2 Physical properties, theoretical (Theo.) and experimental (Exp.) results of pore size and air permeability of meltblown webs Sample

1 2 3

Basis Thickness SEM Eff. Packing weight (mm) diam. diam. density (g/m2) (µm) (µm) 34.2 55.5 35.1

0.488 0.437 0.476

2.01 2.42 2.61

5.11 6.24 6.72

0.077 0.084 0.081

Pore size (microns)

Air perm. (ft3/ft2/min)

Theo.

Exp.

Theo.

Exp.

26.5 30.3 33.6

25 31.2 33.8

50.66 73.5 82.9

51.3 74.1 83.9

Table 2.3 Physical properties, theoretical (Theo.) and experimental (Exp.) results of pore size and air permeability of needled felts Sample

1 2

Basis weight (g/m2) 70 135

Thickness (mm) 1.33 1.75

Fiber diam. (µm) 21.6 21.6

Packing density 0.058 0.085

Pore size (µm)

Air perm. (ft3/ft2/min)

Theo. Exp.

Theo.

121.7 91

515.4 416.3 215.8 166.5

– –

Exp.

large pore size in needled felts using a pore size analyzer. For a more porous medium, there is a significant difference between the measured and calculated data because the medium is compressed more by the applied test pressure. Therefore, the fabric shows a smaller pore size and a lower air permeability.

2.6.3

Pressure drop

We have learned from Section 2.5 that the pressure drop is a function of the packing density and the fiber diameter of a web, i.e.: µtv0t(α) ∆P = ———— df2

[2.37]

The pressure drop (∆P) of the fluid flow through a medium can be theoretically calculated using Eq. 2.37 if the packing density and the fiber diameter of the web are known.

2.7

Influence of thermal insulating properties on nonwoven performance

The thermal properties of nonwoven materials are governed by the type of fibrous materials used and the fiber diameter, as well as the bulkiness and the thickness of the mats. The fibrous material type can be selected while the other properties can be effectively controlled by the nonwoven process or the processing parameters.


34


Heat is transferred through the fiber by conduction and is expressed by Fourier’s law:14 →

→

q = –K∇T

[2.43]

where: q→ = heat flux K = thermal conductivity of the fiber (W/m K) → ∇T = temperature gradient Heat transferred through the air among the fibers by convection from a location that has a higher temperature T1 to another location that has a lower temperature T2, e.g. from the face side to the back of the fabric, is expressed by Newton’s law:14 q = h(T1 – T2)

[2.44]

where q is the heat flux and h is the air convection coefficient. The air convection coefficient (W/m2 K) is the heat transfer rate property of the air by convection from a higher temperature to a lower temperature. Heat is transferred from one fiber to another by the Stefan–Boltzmann radiation law:14 E(T) = σε(T 14 – T 42)

[2.45]

where: E(T) = emissive power σ = Stefan–Boltzmann constant ε = emissivity of the fibers If we can assume that still air is trapped in the nonwoven mat by the blockage of the fibers and heat transfer by radiation is negligible because of the low emissivity of the fibers, then heat is transferred through the mat by thermal conduction of the fibers and the still air, i.e., the void, in the mat. So the overall heat resistance through the mat is the sum of the heat resistance of the fibers and the air, i.e.: R = Rf + R a

[2.46]

where: R = overall heat resistance through the mat Rf = heat resistance of fibers Ra = heat resistance of the still air For example, let us consider a fiber-injected meltblown mat. This is a thermal insulating material made by injecting coarse staple fibers, usually poly(ethylene terephthalate) PET with a diameter of 15 µm or larger, into the meltblowing PP fiber stream between the die and the collector to make a more porous, thicker, and more highly resilient meltblown composite, such that the thermal insulating property of the composite is improved and the web porosity integrity is maintained.



35

4 3.5

R-value (m2 K/W)

3 Measured R-value 2.5

Theoretical R-value

2 1.5 1 0.5 0 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Sample number

2.8 Theoretical and measured R-value of carded and meltblown mats (samples are in the sequence as shown in Table 2.4 which includes both carded and meltblown mats).

The thermal conductivity of PET fiber (KPET) is 0.140, that of PP fiber (KPP) is 0.120 and that of still air (Ka) is 0.025 (W/m K). So the overall heat resistance through the mat in terms of the conductivities of the fibers and the air is: 1L + — 1 L R =— Kf f Ka a

[2.47]

where: Lf = total thickness of fibers La = total thickness of the still air Kf = conductivity of fiber Ka = conductivity of still air Table 2.4 gives a comparison of theoretical and measured values of R for fiberinjected meltblown mats and carded webs. The theoretical thermal resistance that is calculated based on the weight used for the R-value measurement has much higher values than those measured as shown in Table 2.4. The trend of R-values between the theoretical calculation and the experimental measurement is the same as depicted in Fig. 2.8 for the 15 samples in Table 2.4. The significant difference between the theoretical and the measured R-values illustrates that heat transfer by convection cannot be neglected for less compact and/or coarser fibers in the mat. The difference between the theoretical and the measured R-values decreases, as shown in Fig. 2.8, as the thickness of the same basis weight is reduced by compression due to the fact that convection is reduced because air is locked among the fibers. A nonwoven needs to be designed to have a small pore size using a finer fiber diameter and higher packing density in order to achieve optimal insulation by


36

Table 2.4 Thermal properties of carded and fiber-injected meltblown (MB) mats at mean temperature of 16 °C Product

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

CP1 CP2 CP3 MB 35/65 CP1 CP2 CP3 MB 35/65 MB 50/50 CP1 CP2 CP3 MB 35/65 MB 50/50 MB 65/35

Fiber diameter (µm) 30 20 17.6 17.2 30 20 17.6 17.2 13.9 30 20 17.6 17.2 13.9 10.6

Weight/area Thickness (g/m2) (mm) 776 980 842 440(4) 776 980 842 440(4) 440(2) 776 980 842 440(4) 440(2) 864(4)

70 89 75 40 55 70 58 31 31 32 41 35 18 18 36

Density (kg/m3)

K-value (W/m K)

R-value (m2 K/W)

11.09 11.01 11.23 11.00 15.11 15.00 15.52 15.19 15.19 25.25 23.90 25.06 25.44 25.44 25.00

0.0553 0.0522 0.0457 0.0416 0.0492 0.0469 0.0416 0.0385 0.0378 0.0403 0.039 0.0363 0.0343 0.0339 0.0333

1.266 1.705 1.641 0.962 1.118 1.493 1.394 0.805 0.820 0.794 1.051 0.964 0.525 0.531 1.081

CP, carded polyester. Th = 23.5 °C, Tc = 8.5 °C. The number in parentheses after the basis weight is the number of layers of the same weight. MB 35/65 means 35% PP and 65% PET. ‘Normalized’ indicates the basis weight normalized to 500 g/m2.

Theoretical R-value 2.782 3.537 2.98 1.588 2.182 2.777 2.3 1.228 1.227 1.28 1.617 1.38 0.708 0.707 1.413

Normalized R-value 0.816 0.87 0.974 1.093 0.72 0.762 0.828 0.915 0.932 0.512 0.536 0.572 0.597 0.603 0.626



No.


37

locking the air movement in the voids. In this case, Eq. 2.47 is suitable for predicting the insulating property of nonwovens. A small pore size can be achieved by increasing the packing density. However, this also increases the fabric weight for the desired thickness of the web. When the fabric weight increases, thermal conductivity increases because heat conductivity is transferred through the fibers rather than through the voids. Thus the thermal insulating property of the nonwoven is reduced and the cost also increases because of using an increased amount of material. It is suggested that the pore size is reduced by using finer fibers rather than by using more fiber mass or a higher packing density.

2.8

Influence of filtration efficiency (FE) on nonwoven performance

The filtration efficiency of a fibrous medium can be simulated by single fiber efficiency, based on mechanical mechanisms including inertia impaction, direct interception and Brownian diffusion, as well as electrostatic mechanisms such as columbic force and image force.3,4,5 In this section, we will discuss the theoretical calculation of filtration efficiency by changing the weight or the fiber surface area of the medium. From single fiber efficiency theory, the FE of a filter medium is a negative exponential function of the fiber surface area, i.e.: FE = 1 – p = 1 – e –ηsf

[2.48]

where: p = penetration of the aerosol through the filter medium η = single fiber efficiency sf = fiber surface area Single fiber efficiency is a filtration efficiency derived from capturing particles on a single fiber’s surface via mechanical mechanisms including inertia impaction, direct interception, and Brownian diffusion.3,4 The overall FE of the web is the sum of the FEs of single fiber efficiency through integration of the surface area of the fibers in the web. Given the fiber diameter, the fiber surface area is proportional to the weight of the web. Therefore, the web filtration efficiency can be expressed in terms of the total web weight, i.e.: FE = 1 – p = 1 – e –µ(wt)

[2.49]

where: µ = filtration index of unit fabric weight wt = total fabric weight If the web FE of a weight is known, the web FE of other weights can be calculated


38


Table 2.5 Comparison of the predicted and the measured filtration efficiency Sample

Description

Measured FE (%)

Filt. index (µ)

Predicted FE (%)

1 2 3 4

1 oz MB 1 oz SB MB + SB 2 plies MB

95 35 – –

2.996 0.431 – –

– – 99.75 99.75

Measured FE (%) – – 96.3 99.742

MB, meltblown; SB, spunbond.

using Eq. 2.49. Similarly, one can rewrite Eq. 2.49 to obtain the FE of multiple plies of webs if the FE of one ply is known, i.e.: FE = 1 – p = 1 – e –µn

[2.50]

where: µ = filtration index of unit ply n = number of plies The FE of a filter composite can be obtained by summing the filtration indexes of each individual component as: − µ FE = 1 − p = 1 − e ∑ i

[2.51]

where µi is the filtration index of each individual component of the composite. Given the filtration efficiency of each web, the filtration efficiency of a combination or a multiple of the webs can be calculated using Eq. 2.51, as shown in Table 2.5 as an example of the combination of meltblown and spunbond fabrics, or a multiple of the meltblowns. Conversely, given the FE of a fabric weight, the weight of fabric needed to achieve a desired FE can be calculated using Eq. 2.49. For example, if the FE is 95% for a fabric weight of 35 gsm, the weight of the fabric required to achieve a HEPA (high efficiency particulate air) filter efficiency, i.e. 99.97%, is 95 gsm. Compared with using a membrane as a filter medium, a nonwoven has a lower FE but a much lower pressure drop. In particular, the dust-holding capacity (DHC) of a nonwoven is much higher than that of a membrane. Figure 2.9 shows the slow increase in the pressure drop of a meltblown electret from loading with an NaCl aerosol, while Fig. 2.10 shows the sharp increase in the pressure drop of an expanded polytetrafluoroethylene (ePTFE) medium from the loading of NaCl. The ePTFE medium is a micro-porous membrane, in which the pores are created by expanding the extruded PTFE. The pores are quickly filled up by the loaded NaCl particles because the pore size is small and the total pore volume is small as well. The same figure shows the range of the air flow rate in liters per minute (L/min) from fluctuations in the air supply. The ePTFE medium is a thin and light-weight membrane and requires a stronger nonwoven fabric as a support. Usually, it is supported with a spunbond (W/SB) fabric as shown in Fig. 2.10.



39

Pressure drop (mmH2O)

7 MB 20 gsm 31.9–31.9 L/min MB 2 x 20 gsm 31.5–31.2 L/min

6 5 4 3 2 1 0 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Loading time (min)

2.9 Increase of pressure drop with NaCl loading on meltblown (MB) electrets.


80 70 60 50 40 30

ePTFE W/SB #1 32.1–22.9 L/min

20


10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Loading time (min)

2.10 Severe increase of pressure drop with NaCl loading on ePTFE membranes.

Note that loading theory applies without any need to take into account any electric field attraction or to use an electret. An electret is used here as an example because it has a higher filtration efficiency and thus its particle loading rate is faster. Figure 2.11 shows that the meltblown medium is a depth filter, in which the NaCl particles are deposited inside the pores. Figure 2.12 shows the large increase in the pressure drop of an ePTFE as a result of DOP (dioctyl phthalate) loading, because the micro-pores of the membrane are filled up by the DOP particles, while Fig. 2.13 shows the slight increase in the pressure drop of a meltblown fabric from the loading of DOP particles.


40


Acc.V Spot Magn 15.0 kV 2.0 2000x

Det SE

WD Exp 15.4 1

4–2

10 µm

2.11 Depth filtration of meltblown fabric by the loading of NaCl particles.


70 60


50


40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Loading time (min)

2.12 Sharp increase of pressure drop with DOP loading on ePTFE membranes. The pressure drop for ePTFE #2 went off the scale of the tester (150 mm H2O) after 3 minutes of loading.

2.9

Influence of mechanical properties on nonwoven performance

The stress–strain relationship of a material is characterized by the stiffness constant or the modulus of the material. Nonwovens are anisotropic materials in which the modulus or the stiffness tensor consists of 81 constants. The general stress–strain relationship is given by: σ = C:ε [2.52]



41

7


6 5 MB 20 gsm 31.8–31.8 L/min

4 MB 3 x 20 gsm 31.9–31.4 L/min

3 2 1 0 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Loading time (min)

2.13 Slow and steady increase of pressure drop by DOP loading on meltblown electrets.

where σ is the stress, a second-order tensor, ε is the strain, also a second-order tensor, and C is the stiffness constant, a fourth-order tensor.16 For two-dimensional nonwovens, in which the fibers are an in-plane structure, using symmetric theory, the in-plane directional stiffness of the nonwoven is given by fiber web theory.17 For some nonwovens, such as needle-punched and hydroentangled, there are fibers in the z-direction that act as the bonding strength. Their in-plane directional mechanical strength acts like a meltblown fabric and behaves in the same way as the micro-mechanical strength in Eqs 2.53 to 2.57, because the assumptions for micro-mechanical fibrous theory, as described in the next paragraph, hold true for the above two nonwovens. π

C11 = Ef ∫ cos4 f(θ)dθ 0

π

C12 = Ef ∫ cos2θ sin2θ f(θ)dθ 0

π

C22 = Ef ∫ sin4θ f(θ)dθ 0

π

C16 = Ef ∫ cos3θ sinθ f(θ)dθ 0

π

C26 = Ef ∫ sin3θ cosθ f(θ)dθ 0

[2.53] [2.54] [2.55] [2.56] [2.57]

where: C11 is the stiffness constant in the x-direction on the plane perpendicular to the xaxis C12 is the stiffness constant in the y-direction on the plane perpendicular to the xaxis, etc.


42


Ef is the fiber modulus f(θ) is the fiber orientation distribution Directional stiffness constants of a web can be obtained, given a known fiber modulus and the fiber orientation distribution in the web. Tsai and Bresee19 have shown the excellent agreement of the stiffness constants obtained from the theoretical calculations of fiber web theory and from experimental measurements of highly orientated to poorly orientated meltblown webs. It should be possible to apply this theory to other types of nonwoven such as spunbonded, needlepunched, hydro-entangled, and thermally and chemically bonded by assuming that the fibers between two bonded points are straight and that fibers are rigidly bonded, which is the case for the above-mentioned nonwovens. It is tedious and time-consuming to determine the fiber orientation distribution in a web. However, several practical methods have been developed to measure the fiber orientation including X-ray diffraction,20 tensile testing,21 laser light diffraction, 22,23 light reflection and refraction intensity,24 and electrical current measurement.18

2.10

Computer programs for measuring nonwoven performance

2.10.1 Fiber size program Two computer programs have been developed by Tsai to calculate nonwoven physical properties theoretically. One is used to calculate the packing density, the fiber diameter, the pore size, and the FE from the measurement of the pressure drop across the fabric at a certain air flow rate. Readers interested in the two computer programs can contact [email protected]. Below is a demonstration of the first program.

2.10.2 Sample ID: 30 gsm meltblown PP web Input data Input basis weight, g/m2: 30 Input thickness, mm: 0.30 Input polymer density, g/cm3: 0.91 Input pressure drop, mm of water: 2.8 Input face velocity, cm/s: 5.3 Do you want to predict filtration efficiency? Y or N: Y Particle size, µm: 0.075 Particle density, g/cm3 (e.g. NaCl = 2.165, Latex = 1.05, DOP = 0.981): 2.165



43

Calculated results: Effective fiber diameter is 5.16199 µm SEM-equivalent fiber diameter is 1.982068 µm Porosity is 0.8901099 Average circular-capillary-equivalent pore size is 20.7288 µm Frazier-equivalent air permeability is 47.625 ft3/ft2/min Predicted filtration efficiency is 37.89137% Filter quality is 0.1701018/mm of water It is difficult to measure the size of a small fiber diameter where there is a broad spectrum of fiber sizes, such as in meltblown fibers. They have a large number of fibers in the sub-micron range, which is the optical wavelength range. Therefore, the fiber boundary is not distinct under an optical microscope due to light diffraction by the micro-fibers. A SEM provides a much clearer image for measuring the fiber diameter. The coefficient of variation (CV) of a meltblown fabric is typically between 30 and 50%, therefore several hundred fibers need to be measured in order to achieve a 95% confidence in the results, according to the statistical t-distribution. The effective fiber diameter can be quickly obtained using the above computer program by measuring the pressure drop of the air flow through the nonwoven fabric. The effective fiber diameter can be instantly converted to an SEMequivalent fiber diameter. The program also calculates the pore size and the air filtration efficiency.

2.10.3 Air permeability program The second program is used to theoretically calculate the nonwoven physical properties including the packing density, the air permeability for a given pressure, the pressure drop for a given air flow rate, the pore size, and the FE, for a given fiber diameter in the web. Below is a demonstration of the second program.

2.10.4 Sample ID: 150 gsm needle-punched PET felt Input data Input basis weight, g/m2: 150 Input thickness, mm: 4.2 Input polymer density, g/cm3: 1.36 Input pressure drop, mm of water for air permeability: 12.7 Input fiber diameter, µm: 25 Do you want to predict filtration efficiency? Y or N: Y Particle size, µm: 3


44


Particle density, g/cm3 (e.g. NaCl = 2.165, Latex = 1.05, DOP = 0.981): 2.165 Filtration velocity, cm/s: 100 Calculated results Porosity is 0.9737395 Average circular-capillary-equivalent pore size is 278.1537 µm Frazier-equivalent air permeability is 728.364 ft3/ft2/min Predicted filtration efficiency is 84.83412% Pressure drop at 100 cm/s filtration velocity is 3.432343 mmH2O Filter quality is 0.5495144/mm of water The air permeability and the pore size of a nonwoven fabric can be obtained using the above computer program by measuring the nonwoven’s fabric weight and thickness. The fabric weight and processing conditions can be designed so as to achieve the desired pore size and air permeability for a nonwoven fabric. Pore size is a dominant factor that governs the nonwoven’s filtering efficiency in liquid filtration. This program also calculates the air filtration efficiency from the fiber diameter that is chosen for making nonwoven fabrics. Overall, the two computer programs are useful tools that can help engineers save a lot of time in choosing materials and designing processing conditions to achieve the desired properties and performance of a nonwoven.

2.11

References

1 Tsai, P. P. and Wadsworth, L. C., ‘Effect of Aerosol Properties on the Filtration Efficiency of Meltblown Webs and Their Electrets,’ Proceedings, 4th Annual TANDEC Conference, UT Convention Center, 1995. 2 Tsai, P. P. and Yan., Y., ‘Lifespan of Nanofiber and Microfiber Mats, and Porous Membranes Challenged with Solid and Oily-Liquid Particles,’ 5th Asian Filtration and Separation Conference, Shanghai, May 28 –30, 2008. 3 Davies, C. N., Air Filtration, Academic Press, London, 1976. 4 Hinds, W. C., Aerosol Technology, John Wiley & Sons, New York, 1982. 5 Brown, R. C., Air Filtration, Pergamon Press, Oxford, 1988. 6 Spurng, K. R., Editor, Advances in Aerosol Filtration, CRC Press, 1998. 7 Wakeman, R. J. and Tarleton, E. S., Filtration, Elsevier Advanced Technology, 1999. 8 Purchas, E. B., Handbook of Filter Media, Elsevier Advanced Technology, 1996. 9 Tsai, P. P., ‘Progress in the Development of High Efficiency Nonwoven Filter Media,’ GDNA, Nanhai, Sept. 10–12, 2007. 10 Tsai, P. P., ‘Characterization of Meltblown Web Properties Using Air Flow Technique,’ International Nonwovens Journal, 36, 36–40, Fall 1999. 11 Tsai, P. P., ‘Theoretical and Experimental Investigation on the Relationship between the Nonwoven Web structure and Web Properties,’ International Nonwovens Journal, Winter, 2002, 33–36. 12 ASTM F902, ‘Standard Practice for Calculating the Average Circular-CapillaryEquivalent Pore Diameter in Filter Media from Measurements of Porosity and



13 14 15

16 17 18 19 20

21 22 23 24

45

Permeability,’ American Society for Testing Materials, 1926, Race St., Philadelphia, PA 19103, 1985. Bird, R. B., Stewart, W. E., and Lightfoot, E. N., Transport Phenomena, John Wiley & Sons, 1960. Incropera, F. P. and DeWitt, D. P., Fundamentals of Heat and Mass Transfer, John Wiley & Sons, Inc. 1990. Tsai, P. P., Anderson, G., and Tseng, B., ‘The Effect of Polymer Types and Fibrous Structure on the Thermal Insulation Properties of Nonwovens Mats,’ INTC, Sept. 5–7, 2001, Baltimore, Maryland. Timoshenko, S. P. and Goodier, J. N., Theory of Elasticity, McGraw-Hill Book Company, 1970. Cox, H. L., ‘The Elasticity and Strength of Papers and Other Fibrous Materials,’ British Journal of Applied Physics, 3, 72–74, 1952. Tsai, P. P. and Bresee, R., ‘Fiber Orientation Distribution from Electrical Measurements, Part I: Theory,’ INDA JNR, 3(3), 36–40, 1991. Tsai, P. P. and Bresee, R., ‘Fiber Orientation Distribution from Electrical Measurements, Part II: Instrument and Experimental Measurements,’ INDA JNR, 3(4), 32–37, 1991. Prud’homme, R. E., Hien, N. Y., Noah, J. and Marchessault, R. H., ‘Determination of Fiber Orientation of Cellulosic Samples by X-ray Diffraction,’ Journal of Applied Polymer Science, 19, 2609–2620, 1975. Orchard, G. A. J., ‘The Measurement of Fiber Orientation in Card Webs,’ Journal of the Textile Institute, T380–385, 1953. Kallmes, O. J., ‘Technique for Determining the Fiber Orientation Distribution Throughout the Thickness of a Sheet,’ Tappi, 52(3), 482–485, 1969. Rudstrom, L. and Sjolin, U., ‘A Method for Determining Fiber Orientation in Paper by Using Laser Light,’ Svensk Papperstidn, 117–121, March 1970. Boulay, R., Drouin, B., Gagnon, R. and Bernard, P., ‘Paper Fiber Orientation Measurement with a Submillimeter Laser,’ Journal of Pulp and Paper Science, 12(1), J26–J29, 1986.


3 Biodegradable materials for nonwovens G. B H A T, The University of Tennessee, USA; and D. V. P A R I K H, Southern Regional Research Center, USDA, USA

Abstract: Demand for nonwovens is increasing globally, particularly in the disposable products area. As the consumption of nonwoven products with short life increases, the burden on waste disposal also rises. In this context, biodegradable nonwovens become more important today and for the future. As a result, there is increasing effort to design and develop biodegradable nonwovens, with research and development efforts from both academia and industry. Several new biodegradable polymers such as polylactic acid (PLA) and Biomax have helped the industry to produce larger amounts of biodegradable nonwovens. In addition, the use of natural fibres in nonwoven products is also increasing. There is continuing effort to develop new ways to produce biodegradable nonwoven materials by combination of natural fibres and other biodegradable resins or fibres; these research and development activities are helping these environmentally friendly fabrics to become affordable materials for many consumer products. Key words: biodegradable nonwovens, compostable materials, natural fibres, biodegradable polymers, polylactic acid (PLA), disposable nonwovens.

3.1

Introduction

Nonwovens is the fastest growing sector in textile materials. They are flat, porous sheets or web structures that are made directly from separate fibres or from molten plastics or from plastic films by entangling fibres or filaments mechanically, thermally or chemically.1 These nonwovens can be produced from both natural and synthetic fibres or directly from polymers by a variety of techniques that involve web formation and bonding. Different polymers/fibres are more suited for certain processes than others. A significantly large share of these is used as single use or short-life products, leading to disposability related problems; biodegradable or compostable nonwovens are the answer to the sustainability issues, especially in the long run. Studies done on processing, structure and properties of the nonwovens produced by different techniques from a variety of biodegradable polymers and fibres are discussed. A brief overview of the materials used in biodegradable nonwovens is provided in this chapter, followed by discussion of the processing of these materials into nonwoven webs. Structure and properties of such nonwovens from different 46 © Woodhead Publishing Limited, 2010


47

biodegradable materials, especially with reference to their processing and performance, are detailed. As the biodegradable nonwoven fabrics are becoming more and more important, recent developments as well as efforts going on are also discussed in this chapter.

3.2

Reasons for using biodegradable nonwovens

Nonwoven fabrics demonstrate specific characteristics such as strength, stretch, resilience, absorbency, liquid repellency, softness, flame-retardancy, cushioning, washability, filtering, bacterial barrier and sterility. Nonwoven fabrics can be used in a wide variety of applications, which may be limited life, single-use fabrics as disposable materials or durable fabrics for automotive and civil engineering applications.2,3 Demand for nonwoven materials in the US is expected to increase by 3.7% per year until the year 2013.4 This increasing market share will be driven by the strong growth in many key disposable markets such as adult incontinence products, filters and protective apparel, and key non-disposable markets such as geotextiles and battery separators. Disposable markets were the majority of nonwoven demand in 2002, which accounted for a 64% share.5 Disposable consumer products, which primarily include baby diapers, adult incontinence and feminine hygiene products, and wipes, were the largest market for nonwovens in 2008.4 Based on the data available, continued growth in nonwovens will be in the disposables area and the share of the short-life nonwovens is going to remain significantly large. Also, looking at the distribution of durables and disposables in terms of yardage or volume, the disposable share is four-fifths of the total nonwovens, making them much more visible in the waste stream. Considering that a large share of these materials are disposable products, it is important that issues related to their disposal be carefully addressed. Nonwovens are used almost everywhere: in agriculture, construction, military, clothing, home furnishing, travel and leisure, healthcare, personal care and household applications. Of these many applications the number of which continue to grow, more than two-thirds of them are disposables, mostly single use. The environmental impact of disposable products has become a major concern throughout the world in recent years.6,7 These disposable products are usually produced from traditional thermoplastic resins, such as polypropylene (PP), polyethylene (PE), polyester (PET), polyamide (PA) and polycarbonate (PC), which are not biodegradable. However, due to increasing environmental consciousness and demands of legislative authorities, the manufacture, use and removal of products made of traditional polymers are considered more critically. The remedy to this problem could be found in the development of substitute products based on biodegradability, and ideally from natural and renewable materials. Natural fibres, such as cotton, kenaf, coir, jute, flax, sisal, hemp and wood, etc.,


48


are the first choice due to their biodegradability. Some synthetic biodegradable fibres have also been used for nonwoven applications, including cellulosics such as cellulose acetate, rayon, lyocell, etc.; manufactured fibres such as polylactic acid (PLA), poly(caprolactone) (PCL), poly(hydroxybutyrate) (PHB), poly(hydroxybutyrate-co-valerate) (PHBV), Biomax, Biopol, polytetramethylene adipate-co-terephthalate (PTAT), etc.; and water solubles such as poly(vinyl acetate) (PVA). Thus the target for biodegradable nonwovens is to replace synthetic fibres with biodegradable fibres in the disposable nonwovens, such as the wetlaid pulp/ polyester spunlaced fabrics used mainly for industrial and professional wipe products and household and hygienic wipes, which are spunbonded or drylaid and then chemically or thermally bonded.

3.3

Cotton, hemp and other natural fibres

Natural fibres have come a long way; during the last few years, these fibres have established a positive and highly regarded name for themselves in numerous nonwovens end-use markets because of their reputation for being soft, durable, breathable and coming from renewable resources. These days, traditional natural fibres, including cotton, hemp, flax and jute have been seeing more demand internationally, while other fibres, such as milkweed, are starting to emerge in more developed nonwovens areas. Many manufacturers predict that the use of these fibres will grow as consumers become more aware of their advantages. In the meantime, manufacturers and university researchers are working on new innovations for all natural fibres. Cotton is the most used fibre due to its popularity in apparel and other fabrics. Jute, kenaf and flax come next, with the rest of the fibres having only a small share. The costs of these fibres vary and cotton is the most expensive of this group of fibres.9 Although cotton is the most attractive fibre for many applications, cost is the factor that has limited its growth. Cotton is recognized as a durable, breathable and soft fibre. Perhaps no one recognizes the benefits of cotton as well as Cotton Incorporated, a Cary, NC, USbased non-profit organization dedicated to its advancement. Its report, ‘Cotton Technical Guide,’11 sheds light on how powerful the name cotton has become. In 2000, the US apparel and home fabrics markets purchased the equivalent of 15.1 million bales of cotton, while the global nonwovens market used the equivalent of 14.7 million bales of fibres; between 1996 and 2000 global consumption of bleached cotton fibre rose by 6%. Cotton’s current global share of the nonwovens market is about 8%. In the major consumer markets of North America, Western Europe and Japan, growth of cotton usage in nonwovens is projected to be 3–6% per year for the next few years. A study, conducted by Cotton Incorporated in six cities across the US, tested consumers’ perceptions of fibre content in nonwoven products and how these



49

perceptions affected purchasing preferences. The observation was that in many cases, consumers are willing to pay more for products with the cotton seal. Although cotton in its pure, as-supplied form is widely used and accepted, cotton can also have special properties applied to it, thereby paving a path for new uses and markets. One of these properties relates to bleaching. Barnhardt Manufacturing Company, Charlotte, produces bleached cotton fibres for carded web products, chemically bonded fabrics, and spunlaced and needled fabrics, with approximately 95% of the company’s bleached fibres targeting nonwovens, due to increasing interest in bleached fibres among nonwoven manufacturers. Cotton, when bleached, is also more aesthetically pleasing to consumers who appreciate the snow-white quality of bleached cotton, and when a natural fibre such as cotton is dyed, the colours tend to be softer and pastel, unlike synthetic fibres that produce much shinier and usually glare-like effects. Cotton fibres give nonwoven fabrics unique characteristics that manufactured fibres cannot duplicate easily. Synthetic fibres are currently being used more in nonwoven fabrics than cotton because of misconceptions regarding cotton’s processability. With improved bleaching techniques and the development of new finish applications, cotton can be processed at speeds comparable to those used with synthetics while providing the superior attributes of cotton to the nonwoven. Most consumer data suggests that consumers prefer cotton fibres. Additional advantages of cotton and other natural fibres include superior wet strength as well as a quick-dry surface, notably in wipes. Bleached cotton fibres have high levels of absorbency and are soft to the touch, breathable and biodegradable. One fast-growing area, especially throughout Europe and Japan, is spunlaced cotton used for cosmetic wipes and other disposable products; these trends are likely to spread to other markets as well. Consumer demand for cotton is well documented, but because nonwovens are not required to list fibre content in products, consumers often do not know what they are purchasing. There is definitely an opportunity to increase market share by adding cotton as the fibre content, since consumers prefer to purchase cotton-containing products.11 Although cotton, with all its attributes, can tend to dominate the natural fibres market, hemp, jute, flax and milkweed are some other examples of fibres that are used not only in nonwovens, but are also growing in popularity in many other applications. As companies become more familiar with the benefits and uses of these fibres, new innovations will be developed in the future. Hemp fibres are not as well known as cotton, but they certainly have proven themselves for Hempline in Delaware, Canada. Hempline is a large supplier of hemp fibre to the nonwovens industry, primarily supplying hemp as a reinforcing fibre for substrates. With 50% of the company’s sales conducted in the nonwovens industry, Hempline is noticing a rapid increase in demand for its products, especially its reinforcement fibres.12 Aside from its high strength, hemp has been recognized for its elasticity, ease of processing and recyclability. However, there are a few setbacks, the main one being consumers’ unfamiliarity with hemp fibre.


50


Key advantages of using it are its high strength and low cost, and there are many markets still awaiting the use of this fibre as it slowly makes its way into becoming another option for manufacturers. In addition hemp fibre’s staple length and strength can be modified according to the needs of the consumer. Although the market is price-conscious, using better quality of natural fibres results in a lower reject percentage, reduces downtime on equipment, minimizes loss of fibre during processing and, overall, makes better economic sense. Another natural fibre increasing its role in the nonwovens industry is milkweed. Milkweed floss is a silky white seed with a resilient hollow tube that looks like a straw. It is similar to high quality down and is a hydrophobic, cellulose fibre with a high chemical resistance and the ability to be readily dyed. Some properties milkweed floss can provide nonwovens include super absorbency, softening, hydrophobicity, paper-strength, bulking, self-bonding and tactile change. Milkweed floss fibre from advanced agricultural production has the ability to compete in nonwoven applications, especially in filtration, absorbent products and thermal and sound insulation products. Natural Fibres has introduced a 75% recycled cotton and 25% milkweed fibre mattress pad through its subsidiary, Ogallala Comfort Company, Ogallala, US.12 Although technology is available to use many of the natural fibres in nonwovens, the industry will have to wait for a number of things to happen, including a better economic climate, which may change people’s willingness to pay for improvements. As the industry is growing internationally, it may force manufacturers and consumers alike to keep up with the competition.

3.4

Cotton and flax-based nonwovens

New nonwoven products containing cotton and lyocell, low-temperature thermalbondable bicomponent polyester/polypropylene Bico 256 binder fiber, or cotton comber noils were developed using needle punching and hydroentangling by the cooperative efforts of SRRC, UT, Fleissner and JD Hollingsworth. These lowcost hydroentangling developments were for the end use of cotton bedsheet and bleached/grey cotton bed sheets. Blends produced quality products, which cotton alone could not, and the blending improved the processability and uniformity of the webs.13,14 With the recent installment of 1 m wide needle punch and hydroentanglement pilot plant lines, scientists at the SRRC-USDA are embarking on new initiatives to study the cotton’s sustainability features in the context of nonwoven applications. Research on cotton-based nonwovens has been carried out at the University of Tennessee since 1987 by applying different kinds of binder fibres through carding and thermal calendering processes. Cellulose acetate (CA) fibre was first applied successfully as the binder fibre since it is thermoplastic, hydrophilic and biodegradable.15–18 Eastar Bio® GP copolyester unicomponent and bicomponent (Eastar/PP) fibres were further selected as the binder fibres in recent studies.19–23



51

Five different kinds of fibre were used for the study: cotton fibre as the base fibre, and four types of binder fibre, ordinary cellulose acetate (OCA), plasticized cellulose acetate (PCA), Eastar Bio® copolyester unicomponent (Eastar), and Eastar Bio® copolyester bicomponent (Eastar/PP) fibres. The chemical name of Eastar Bio® copolyester is poly(tetramethylene adipate-co-terephthalate) (PTAT). The cotton fibre used in this research as the carrier fibre was supplied by Cotton Incorporated, Cary, NC, US. The scoured and bleached commodity cotton fibre had a moisture content of 5.2%, a micronaire value of 5.4 and an upper-half-mean fibre length of 24.4 mm. Both the OCA and PCA binder fibres were provided by Celanese Corporation, Charlotte, NC, US; while the Eastar and Eastar/PP bicomponent binder fibres selected for this study were produced by Eastman Chemical Company, Kingsport, NC, US. The plasticizer used in PCA binder fibre is triethyl citrate ester (C12H20O7) with a weight concentration around 2%. The bicomponent Eastar/PP has a sheath core structure with Eastar as the sheath and PP as the core. The nonwoven fabrics in this research were produced by first carding the cotton and the binder fibre and then thermally bonding the carded webs. The fibre components were prepared by separately opening and then hand mixing the two fibre types for homogeneity. The blend of fibre was then carded to form a web using a modified Hollingsworth card with the conventional flats installed at the licker-end of the machine. The resulting carded webs had the basis weights of about 40 g m–2. After carding, acetone solvent or water dip-nip treatment was applied to some of the carded webs. Then the treated or untreated webs were fed for thermally point-bonding using a Ramisch Kleinewefers 60 cm-wide calender. The embossed roll had a diamond pattern, covering approximately 16.6% of the surface area, i.e. the bonded area was around 16.6%.

3.4.1

Cotton/cellulose acetate biodegradable nonwovens

The first studied biodegradable cotton-based nonwoven fabrics were produced by cotton and ordinary cellulose acetate (OCA) fibre. Bonding temperatures used for thermal calendering were 150 °C, 170 °C and 190 °C based on the ordinary cellulose acetate’s high softening temperature (Ts: 180–205 °C). The tensile strengths of the nonwoven fabric made with cotton/cellulose acetate nonwoven blend is quite low and is not suitable for consumer application when it is processed under the temperatures associated with cellulose acetate’s softening temperature. Solvent treatment has been introduced in order to modify the softening temperature of cellulose acetate fibre and to lower the calendering temperature, while maintaining enhanced tensile properties. Acetone, a good solvent for cellulose fibre, was chosen for the solvent pre-treatment; 20% acetone solvent pre-treatment was applied to cotton/cellulose acetate nonwovens to decrease the softening temperature and further lower the calendering temperature.17 The results showed that these solvent treatments could decrease the softening temperature of cellulose


52


acetate fibre and produce comparatively high tensile strengths. Because acetone is a flammable solvent there is a preference not to use it in commercial processes, so two alternative methods were further applied for cotton/cellulose acetate nonwovens.18 Water dip-nip treatment was used instead of acetone solvent pretreatment to make the process more environmentally friendly. It was observed that water could be used as an external plasticizer instead of 20% acetone solvent without compromising web strength and the process is environmentally friendly. A plasticized cellulose acetate fibre was developed in which an internal plasticizer was added during fibre manufacture to lower the softening temperature of ordinary cellulose acetate and further lower the bonding temperature during the thermal calendering process. The peak load was improved by using PCA instead of OCA, especially at higher bonding temperatures. Further comparison of external plasticizer (water) and internal plasticizer shows that there is no significant difference between them. Thus, an internal plasticizer (PCA) can be used in place of the external plasticizer (water) without compromising web strength, and the process is more economical. Based on the above analysis, it seems that the optimal processing conditions are either for cotton/OCA with water dip-nip treatment or cotton/PCA without treatment bonded at 190 °C for both the blend ratios. The optimal strength of the lightweight biodegradable nonwoven was around 0.8 kg, which is sufficient for many applications.

3.4.2

Cotton/Eastar biodegradable nonwovens

The desired calendering temperature of PCA bonded nonwovens was still too high to achieve good tensile properties. So, a newly introduced biodegradable copolyester unicomponent (Eastar) fibre, which has a relatively low softening temperature (~80 °C), was further selected as a binder fibre instead of cellulose acetate fibre. It has been reported that this binder fibre can be totally degraded into CO2, H2O and biomass.23 Because of the low softening temperature of the binder fibre (Ts: ~80 °C), the bonding temperatures used are 90 °C, 100 °C, 110 °C, and 120 °C. The tensile strengths of the cotton/Eastar fabrics are higher than those of cotton/ OCA nonwovens but much lower than those of cotton/PCA nonwovens. Unicomponent Eastar Bio® GP copolyester fibres are soft and somewhat difficult to crimp due to the high elasticity of the fibre. For the carding process, relatively stiffer fibres are preferred. One disadvantage of using Eastar as a binder fibre is that it is hard to get the binder fibres well distributed, which may cause the low tensile properties of the final calendered nonwoven fabrics. Thus, a bicomponent fibre with Eastar Bio® GP copolyester as a sheath on a stiffer PP core was produced by Eastman Chemical Company, Kingsport, NC, US to offer more stiffness than a 100% unicomponent Eastar Bio® GP copolyester fibre and to further improve the tensile properties of the nonwoven fabrics. This bicomponent binder fibre has higher tenacity, higher crimps and lower peak extension compared to that of the Eastar monocomponent binder fibre as listed in Table 3.1. These



53

Table 3.1 Physical properties for cotton and Eastar fibres

Filament density (g/cm3) Filament linear density (tex) Peak extension (%) Peak strength (mN/tex) Initial modulus (mN/tex) Staple length (inches) Crimps

Cotton

Eastar

Eastar/PP

1.5 0.24 5.4 152.2 360.9 0.96* †

1.2 0.44 144.0 138.0 1.0 1.0 Less

1.1 0.44 96.0 269.6 1.5 1.5 More

* Upper half mean fibre length. † Has natural convolutions.

properties are preferred for the carding process. The tensile strengths of cotton/ (Eastar/PP) nonwovens are much higher than those of cotton/Eastar nonwovens and even higher than cotton/PCA nonwovens. The optimal cotton/(Eastar/PP) web has a peak load value of 1.21 kg or 1.15 kg for the binder fibre component of 50% at a bonding temperature of 110 °C or 100 °C respectively. Therefore, using Eastar/PP bicomponent fibre as a binder fibre can improve the tensile properties of cotton/Eastar nonwoven fabrics. The optimal thermal calendering temperature is relatively lower than that for cotton/cellulose nonwovens, which means that the cost of the process can be greatly reduced by using Eastar/PP bicomponent fibre as the binder fibre for the cotton-based biodegradable nonwovens. Flexural rigidity and absorption properties of the cotton/(Eastar/PP) nonwovens were also studied. Results show that the nonwovens have good flexural rigidity and absorbency, which indicate that the nonwoven materials may be used for medical and sanitary applications. However, one has to remember that the PP component in the bicomponent fibre is not biodegradable; this puts this fabric in the category of many other cotton/binder nonwovens that may have PP or PET as binder fibres. The results obtained from these studies suggest different routes for producing high strength nonwoven webs from cotton fibres with a thermoplastic binder fibre. Newer thermoplastic polymers are good candidates for such applications. In fact, recent work in our laboratory, the University of Tennessee Nonwovens Research Laboratory, has shown that PLA can be used as a binder fibre to produce strong point bonded nonwoven webs.23 Another advantage is that PLA requires a relatively lower bonding temperature.

3.4.3

Wetlaid disposable nonwovens with flax fibre

The use of bleached elementary flax fibre in modern disposable nonwoven products was recently studied by van Roekel et al.8 Due to the long elementary fibre length and high cellulose content of flax bast fibres, they are an excellent substitution for synthetic fibres in disposable nonwovens. Wetlaid nonwoven sheets were produced and spunlaced on a pilot unit, however, further improve-


54


ments are reported to be needed for the process. Usually, wetlaid disposable nonwovens are manufactured on Fourdrinier type paper machines, stock preparation and the headbox are modified to long fibres, and surfactants are applied to help disperse the long fibres in the primary water cycle. The machine for wet-laying flax nonwovens needs to be fast rewetting, have easy dispersion in the existing stock preparation system, and homogeneous formation. Various blends of 18 mm cut flax and PET fibre, supplemented with fluff pulp fillers, were produced; no finishing was applied for the flax fibre for the process. A 1.5 m wide, 80 g m–2 web at about 100 m min–1 was formed. It was observed that the strength properties of the web disappear completely with the increase of flax content. When extrapolated to 40% flax content, strength can be fully attributed to the fluff pulp, and the strength of the web is not improved by adding more flax. Since the individual flax fibre has sufficient strength, the absence of tensile strength in the web was believed to be from the poor formation and bonding properties of the web. Therefore, further improvement of the wet-laid process is needed either by using shorter flax fibre or applying finish to flax fibre to improve its dispersion.

3.5

Nonwovens from animal fibres

Wool has been one of the most widely used animal fibres. The first nonwovens were produced from wool fibres as felts by mechanically interlocking the woollen fibres, taking advantage of their natural surface scales. Wool has excellent thermal properties and is one of the best insulating fibres. Because it is more expensive than many of the synthetic fibres used in nonwovens, it has not been one of the popular fibres. More recently, there has been an increasing effort to incorporate wool fibres in special nonwoven applications. Using nonwoven processes, it is possible to produce low-cost lightweight woollen fabrics with high stretch. Recent work24 has shown that nonwoven fabrics from wool can be produced with properties that are not possible to achieve by knitting and weaving. Some of the nonwoven products that are produced from merino wool include three-dimensional coating fabrics, stretch fabrics, windproof fabrics and footwear accessory fabrics. Thermal blankets produced from wool fibres have excellent insulation and comfort properties. They are waterproof and pack into a small volume, making them suitable for lightweight blankets used in search and rescue operations. The combination of properties such as wicking ability, moisture and sound absorption, resiliency and thermal insulation makes wool and wool-blend nonwovens suitable for many automotive uses. Thus, there is increasing effort to take advantage of wool’s properties in many emerging applications. One such example is blending 20–35% wool with rayon to produce affordable WoolFelt® nonwovens by National Nonwovens.25 These fabrics can be coloured or textured as desired, and are considered the fabrics of choice for heritage quilts, penny rugs and heirloom crafts. Silk, considered the queen of fibres, is an expensive fibre with many rich properties and is a natural protein fibre that is known to be biodegradable. Because



55

of the cost, this is not a fibre targeted for nonwovens. However, there have been efforts to produce silk nonwovens for niche applications; one advantage is that waste and poor quality silk can be used to produce many of the nonwoven products, thereby helping control the cost. Recently, spunlaced silk nonwovens with very low basis weight of 25 g m–2 have been developed using the Jetlace 2000 water jet machine from Rieter Perfojet.26 These lightweight nonwovens are targeted for sanitary materials and medical applications such as gauze and wound dressings, cosmetics and skincare products, where the property demand might be stringent. Also, by using the hydroentangling process, using any other chemical additive is avoided. These fabrics have softness, elasticity, moisture absorption, heat preservation, breathability and are not harmful to the body in any way. Some of these nonwovens can also be used in high value garments as liners for overcoats, jackets, suits or fashion fabrics. There is likely to be continuing research and development in this area as the market realizes the potential for such fabrics and with the simultaneous reduction of costs by using waste silk. Chitin is a safe natural substance found in the shells of crabs, shrimp and lobster, and in the wings of butterflies and ladybirds, etc. Chitin is one of the three most abundant polysaccharides in nature, with glucose and starch. It ranks second to cellulose as the most abundant organic compound on earth. Chitin and its derivatives, chitosan, chitin oligosaccharide and chitosan oligosaccharide, have many useful properties that make them suitable for a wide variety of health-related applications. Also, chitin products are known to be anti-bacterial, anti-fungal, antiviral, non-toxic and non-allergic. Nonwoven webs can be formed from chitin fibres for use in medical applications, such as chitin artificial skin, a newly developed patented product.27 The chitin nonwoven is produced by a special wetlaid process and has the properties of three-dimensional structures: soft handle, absorbency, breathability, non-chemical additive, compact texture, softness and smoothness. Thus it is the ideal dressing for extensive burns, scalds and other traumas. Its main features are: inhibition of bacterial growth avoiding cross-infection and control of the loss of the exudates; good biocompatibility; excellent bioactivity; stimulation of new skin cell growth; accelerated wound healing; no adverse reaction of abnormal immunity, repelling or irritation. As well as artificial skin, other chitin-based nonwoven products include wound protective bandages, wound dressings and skin beauty packs. Feather products have been used in bedding and some outerwear for cold climates. Nonwoven battings made from chicken feather fibres have been evaluated as possible insulating materials. When compared with goose and synthetic fibres, chicken feather batts show better insulating properties than those of synthetic fibres and close to that of downs. The chicken feather battings also have good resiliency, which is important for insulation battings. One disadvantage is that the properties of chicken feather, in both size and tenacity, vary depending on how they are separated from the quill.28 This introduces further non-uniformity and the process has to be very well controlled to compensate for this.


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3.6

Technologies for biodegradable nonwovens

3.6.1

Spunbond PTAT nonwovens

The Eastar Bio® GP copolyester (PTAT) can be melt spun into spunbond and meltblown fabrics. It has been reported that uniform spunbond fabrics have been produced on Ason spunbond equipment using slotted air technology and Reifenhauser Reicofil equipment at conventional spinning speeds.29 Fabrics with finer fibres, higher throughputs, higher spinning speeds (> 4500 m min–1) and basis weight ranges from 14 to 130 g m–2 have been successfully obtained. The resultant spunbonded fabrics are semi-crystalline with good drapeability, soft hand, and elastic properties. The fabrics can be gamma radiation sterilized, radio frequency bonded and ultrasonically sealed, which make the fabrics suitable for medical applications, such as hospital surgical packs, wipes, bondages, face masks, etc. The fabrics can also be used for agricultural and other absorbent disposable products such as diapers, seed mats, ground cover, etc.

3.6.2

Spunbond PLA nonwovens

Polylactic acid (PLA) first received considerable attention because of its biodegradability and biocompatibility; in recent years, researchers have been paying more attention to biodegradable nonwoven products. PLA was spunbonded and meltblown at the University of Tennessee in 1993.30 The following year, Kanebo, a Japanese company, introduced Lactron® (poly-L-Lactide) fibre and spunlaid nonwovens. Biesheim-based Fibreweb (France) developed nonwoven webs and laminates made of 100% PLA in 1997 and introduced a range of meltblown and spunlaid PLA fabrics under the brand name of Deposa™.31 The composite structures, described in US Patent 5702826.39,32 comprise one or more plies of nonwoven laminated to a film, where all the plies are totally manufactured from polymers derived from lactic acid. Each ply provides mechanical, barrier effect, absorption, filtration and thermal insulation properties that can be adapted to each application by selecting the suitable composition of the nonwovens and of the films based on polylactic acid. The spunbonded nonwoven layer is used as the support, the film provides impermeability and barrier effect, and another spunbond or meltblown nonwoven layer is added to offer filtration/absorption and thermal insulation properties. Depending on the application, a derivative of lactic acid chosen from D-lactic acid, L-lactic acid, or DL-lactic acid may be used. The PLA polymers are processed using conventional spunbond or meltblown techniques. The plies of the nonwovens can either be hot calendered, needle punched, hydroentangled, or chemically bonded. They are intended for disposable hygiene, agriculture, and medical applications such as diapers, sanitary napkins, protective clothing, surgical masks and drapes. An example of the



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three-ply nonwoven for medical application consists of the first spunbond web with a basis weight of 10–20 g m–2 and the linear density of the fibres between 1.5 and 2.5 dtex, the meltblown web with basis weight of 5–15 g m–2 and the linear density of the fibres between 0.1 and 0.3 dtex, and the second spunbond with a basis weight of 10–20 g m–2 and the linear density of the fibres between 1.5 and 3.0 dtex. The total weight is from 25–55 g m–2. The calendering temperature for the laminate is between 65 and 120 °C depending on the type of raw material and the calendering speed. The laminate has a bonded surface area of 8–15%. The strength of the composite is between 40 and 100 N and the elongation at break is from 30–60%.

3.6.3

Meltblown biodegradable nonwovens and laminates

In JP Patent 11117164,33 a kind of biodegradable nonwoven laminate of meltblown nonwoven fabrics of aliphatic polyester fibres and spunbonded nonwoven fabrics of urethane bond-containing butylene succinate copolymer fibres was described. The biodegradable laminates were prepared by sandwiching meltblown nonwoven fabrics of biodegradable aliphatic polyester fibres with a diameter of 0.5–2.0 µm between spunbonded nonwoven fabrics of long fibres consisting of polymers containing 1,4-butanediol units and succinic acid units and having urethane bonds to give laminates with meltblown nonwoven fabric content of 10-30%. The fabrics are useful for medical care materials and hygienic materials. Bionolle 1030 (butylene succinate copolymer containing urethane bonds) was melt spun at 190 °C, passed through an ejecter, and piled on a screen to give spunbonded nonwoven fabric. Bionolle 3300 (butylene succinate copolymer containing 20 mol% adipic acid units and urethane bonds) was melt spun by a meltblowing method, sandwiched between two spunbonded nonwoven layers of Bionolle 3300 fibres, and embossed at 105 °C to give a laminated nonwoven fabric with tensile strength 151 N and softness rating 98 and exhibiting weight loss of more than 50% on embedding the nonwoven fabric in soil for six months.

3.6.4

Wetlaid nonwoven fabrics with PLA fibre

In JP Patent 2003268691,34 wetlaid nonwoven fabrics comprising biodegradable fibres consisting of biodegradable polymers derived from sources other than wood and petroleum are described. The wetlaid nonwoven fabrics comprise more than 90% biodegradable fibres consisting of PLA, or more than one portion of any other biodegradable fibres consisting of fibrillated fibres. The wetlaid nonwoven fabrics are reported to be useful for packaging paper, corrugated cardboard, tissue paper, printing paper, wiping paper, toilet paper and filter paper, and for agriculture. Thus, 5:95 D-lactic acid:L-lactic acid copolymer chips were melt spun at 260 °C and wound to give undrawn fibres. The wound fibres were drawn at a hot roll


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temperature of 80 °C and a heat-setting temperature of 118 °C to give drawn fibres with elongation 40% and denier per filament 2.2 dtex. The undrawn fibres and drawn fibres were crimped and cut to give undrawn staple fibres with 5.24 crimps cm–1 and drawn staple fibres with 5.20 crimps cm–1. The drawn staple fibres were passed through an orifice at high speed and impacted against a wall at the exit of the orifice to give fibrillated fibres. A dispersion contains a 60:15:25 mixture of undrawn staple fibres:drawn staple fibres:fibrillated ultrafine staple fibres, which were made into a wetlaid nonwoven fabric using a mesh drum, dried at dryer surface temperature of 110 °C, and calendered at 140 °C to give a biodegradable nonwoven fabric showing complete fibre degradation on embedding the nonwoven fabric in a compost for fifty days.

3.7

Applications of biodegradable nonwovens

There are many companies both big and small involved in various aspects of nonwovens, from producing polymers, fibres, additives, to making machinery, producing nonwoven roll goods and converting the nonwovens into final products. Biodegradable nonwovens can be used for almost all areas of nonwoven applications. In sanitary and medical industries, a hair cap made of a poly(L-lactic acid)-based thermoplastic resin nonwoven fabric showed good hair-capturing property according to JP Patent 2002345541.35 Breathable, biodegradable/ compostable disposable personal care products were produced from Bionolle 3001 nonwovens, reported in WO Patent 2002053376 and JP Patent 2002035037.36,37 Natural coconut fibres (coir) have been applied for biodegradable erosion control mats by Landlok38 in the geotextile industry. In the automotive industry, most of the European automotive producers already use car interiors made of natural fibres. In Germany, in 1996, 3,630 tonnes of flax, sisal and jute were used for car interiors, and in 1999 this figure increased to 11,800 tonnes. The absolute figure of the production at the moment is not very high, but the average annual growth, which is about 50%, is promising.39 Nonwovens made from kenaf fibre40 offer good sound insulation properties for automobile interiors. Yachmenev et al.41 reported a variety of mouldable, cellulosic-based nonwoven composites for automotive applications with excellent thermal insulation properties, which were fabricated from kenaf, jute, flax and waste cotton using recycled polyester and substandard polypropylene. In the filtration industry, refuse bags and drain filters have been made by using fine denier biodegradable polylactic acid nonwovens for the application of sink drains;42 and biodegradable pleated filter material and filter units for air purification and liquid filtration.43

3.7.1

Flushable nonwovens

Liquid waste system disposal is quite attractive compared to solid waste disposal where the infrastructure may not be well developed. In many instances, landfill and



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solid waste disposal techniques have significant environmental problems. Considering this, the wastewater system is more convenient, hygienic and environmentally sound; there is already a massive infrastructure in place as wastes from houses go to industrial biodegraders in the form of sewage farms, or local biodegraders or septic tanks. In such situations, many disposable products can be flushed through the system rather than thrown away as solid waste.44 Flushable nonwoven diaper liners and wipes have been on the market for a while. For such products, flushability is desirable and technically it is possible to develop such products. However, lack of convenience and cost issues have driven the market towards non-degradable plastics in diapers as well as feminine hygiene products. In designing and developing flushable nonwovens, one of the challenging requirements is that the products have to be strong enough to be stored and/or used when wet, but at the same time, should be weak enough to breakdown in the sewage system. Flushability itself is not well defined and there is no accepted standard method to evaluate and certify flushability of such products. The current efforts involve comparing fabrics by agitating them in a standard volume of water for a standard time and observe the fragmentation degree or determine the time for achieving full dispersion. For a nonwoven material to be claimed flushable, the fabric must break up immediately in a toilet bowl and be small enough to be transported from the toilet bowl to the sewage system in a single flush. It should not lead to blocking of pipework and there should not be any accumulation in subsequent flushes. There have been consumer studies that have shown that many flushable wipes in the market lead to clogging of pipes. In addition to the fact that they have to break down, they should not contain any chemicals that might affect the functioning of the sewage farm or the quality of the treated water. This means that all the materials used have to be biodegradable. In these situations, the enhancement of wet strength will retard flushability. There has been more focus on development of systems where wet strength is enhanced for storage and use, but not in the sewage system. In most of the systems, there seems to be a compromise where performance has to be sacrificed to achieve flushability. Some of the approaches have been to employ water sensitive binders with salts, which enhance the solubility of the binder in the solution. For wet wipes, other alternatives suggested are to use a system where the wipes remain dry till they are ready to use, then a wet additive is incorporated just as it is being dispensed. Another suggestion is to possibly modify toilets and flushing systems to handle new materials, where the breakdown is accelerated either by additional chemical or mechanical actions.44 When one looks at all the available materials and processing technologies, air laid and wetlaid systems are more suitable. The problem with spunbond types is the difficulty in breaking down continuous fibres; using short fibres to form webs and binding them with fibres that are biodegradable or water soluble will be the best approach. There is a lot of patent activity indicating interest and inclination in the


60


industry to develop such products. One such example is the introduction of a new biodegradable polymer Nodax® (a polyhydroxyalkanoate), which may be used for flushable nonwoven products, and other biodegradable nonwoven materials as well.

3.8

Sources of further information and advice

As the nonwovens industry continues to grow, there is a lot of new information available and new materials and products are constantly being launched on the market. The reader is referred to the following resources for the latest updates. Important organizations • Association of the Nonwovens Fabrics Industry, Cary, NC, USA – INDA (http://www.inda.org). • European Disposables and Nonwovens Association – EDANA (http:// www.edana.org). • Technical Association of the Pulp, Paper and Converting Industry – TAPPI (http://www.tappi.org). • Industrial Fabrics Association International (http://www.ifai.com/). • Technical Textiles and Nonwovens Association – TTNA (www.ttna.com.au). • Cotton IncorporateD, Raleigh, NC, USA (http://www.cottoninc.com/). Prominent university centres • Nonwovens Institute, North Carolina State University, Raleigh, NC (http:// www.thenonwovensinstitute.com/). • Nonwovens Research Laboratory, The University of Tennessee, Knoxville (UTNRL) (http://utnrl.engr.utk.edu/). • Nonwovens Research Group, Department of Textiles, Leeds, UK – NRG (www.nonwovens.leeds.ac.uk). • Texas Tech University, Nonwovens and Advanced Materials laboratory (http:// www.tiehh.ttu.edu/nonwoven_advanced_materials.html). Books and other publications • Handbook of nonwovens, ed. S. Russell, Woodhead Publishing Limited, Cambridge, UK (2007). • Biodegradable and sustainable fibres, ed. R. S. Blackburn, Woodhead Publishing Limited, Cambridge, UK (2005). • Nonwovens Market International Company Profiles (http:// www.marketresearch.com/browse.asp?categoryid=1632&g=1). • Nonwovens Industry (http://www.nonwovens-industry.com). • Nonwovens World (www.marketingtechnologyservice.com/publications).



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• Nonwovens information and business network (www.nonwovens.com). • Nonwovens Report International (http://www.nonwovens-report.com/). • Other textile and polymer journals, and publications from INDA, TAPPI and EDANA.

3.9

References

1 http://www.inda.org/category/nwn_index.html. 2 Tom H., ‘What are Nonwovens – Again?’, Nonwovens Industry, March 1989. 3 Batra S. K., Cook F. L., The Nonwoven Fabrics Handbook, INDA Publications, Cary, NC, 1992. 4 http://www.freedoniagroup.com/Nonwovens.html. 5 Butler I. (Ed.), Nonwovens Fabric Handbook, INDA Publications, Cary, NC, 2004. 6 Woodings C., ‘New Developments in Biodegradable Nonwovens’, http://www.technica .net/NF/NF3/biodegradable.htm. 7 Hansen S. M., Nonwoven Engineering Principles, Nonwovens – Theory, Process, Performance & Testing, Edited by A. F. Turbak, TAPPI Press, Atlanta, GA, 1993. 8 van Roekel G. J. Jr, De Jong, E., ‘Elementary Flax Fibres for Disposable Nonwovens,’ TAPPI Pulping Conference Proceedings, Orlando, Florida, October 31–November 4, 1999, pp 677–682. 9 Robson D., Hague J., ‘A Comparison of Wood and Plant Fibre Properties’, in Wood Fibre Plastics Conference Proceedings, Madison WI, 1995, pp 41–46. 10 Bhat G. S., ‘Overview of Cotton-based Nonwovens,’ Beltwide Conference Proceedings, New Orleans, LA, January 2005. 11 Cotton Technical Guide, Cotton Incorporated, http://www.cottoninc.com/CottonNonwovens-Technical-Guide/. 12 Wubbe E., ‘Harvesting the Benefits of Natural Fibres’, http://www.nonwovensindustry.com/articles/2002/06/harvesting-the-benefits-of-natural-fibers. 13 Parikh D., Bressee R., Muenstermann U., Watzl A., Crook L., Gillespie D., ‘Spunlaced Cotton and Cotton Blend Cosmetic Pads and Bed Sheets: Study of Fiber Entanglement’, JEFF, 2, 40–49, 2007. 14 Parikh D., Bressee R., Sachinvala N., Crook L., Muenstermann U., Watzl A., Gillespie D., ‘Basis Weight Uniformity of Lightly Needled Hydroentangled Cotton and Cotton Blend Webs’, JEFF, 1, 47–61, 2006. 15 Suh H., Duckett K. E., Bhat G. S., ‘Biodegradable and Tensile Properties of Cotton/ Cellulose Acetate Nonwovens’, Textile Research Journal, 66(4), 230–237, 1996. 16 Duckett K. E., Bhat G. S., Suh H., ‘Compostable/Biodegradable Nonwovens’, US Patent 5783505 (issued July 21, 1998). 17 Duckett K. E., Bhat G. S., Giao X., Haoming R., ‘Characterization of Cotton/Cellulose Acetate Nonwovens of Untreated and Aqueous Pretreated Webs prior to Thermal Bonding,’ Proceedings of the INTC 2000. 18 Gao X., Duckett K. E., Bhat G. S., Rong H., ‘Effects of Water Treatment on Processing and Properties of Cotton/Cellulose Acetate Nonwovens’, International Nonwovens Journal, 10(2), 21–25, 2001. 19 Bhat G. S., Rong H. M., Mclean M., ‘Biodegradable/Compostable Nonwovens from Cotton-based Compositions’, INTC 2003 Proceedings, Baltimore, Maryland, September 15–18, 2003.


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20 Rong H. M., ‘Structure and Properties of Cotton-based Biodegradable/Compostable Nonwovens’, Thesis, University of Tennessee, 2004. 21 Rong H. M., Bhat G. S., ‘Preparation and Properties of Cotton-Eastar Nonwovens’, International Nonwovens Journal, 12(2), 53–57, 2003. 22 Haile W. A., Tincher M. E., Williams F. W., ‘New Biodegradable Copolyester for Fibres and Nonwovens’, Proceedings of INTC 2001 Conference, 2001. 23 Bhat G. S., Gulgunje P., Desai K., ‘Development of Structure and Properties during Thermal Calendering of Polylactic Acid (PLA) Fiber Webs’, eXPRESS Polymer Letters, 2(1), 49–56, 2008. 24 Simpson W. S., Crawshaw G. H., ‘Wool Science and Technology’, Woodhead Publishing, 2002, pp 304–312. 25 http://www.nationalnonwovens.com/pr.htm. 26 http://www.thefreelibrary.com/_/print/PrintArticles.aspx?id=65077735. 27 http://www.saccharomics.com/chitin/index.htm. 28 Ye W., Broughton R. Jr, ‘Chicken Feather as a Fibre Source for Nonwoven Insulation’, International Nonwovens Journal, 8(1), 112–120, 1999. 29 Haile W. A., Tincher M. E., Williams F. W., ‘A Biodegradable Copolyester for Binder Fibres in Nonwovens’, Proceedings of Insight 2001 International Conference, 2001. 30 Wadsworth L. et al., ‘Melt processing of PLA Resin into Nonwovens’, 3rd Annual TANDEC Conference, Knoxville, 1993. 31 Ehret P., ‘Deposa Nonwovens: Deposable Disposables’, INSIGHT 96 San Antonio. 32 US Patent 5702826, ‘Laminated nonwoven webs derived from polymers of lactic acid and process for producing’, Ehret P. et al., 1997, assigned to Fibreweb. 33 JP Patent 11117164, ‘Biodegradable nonwoven laminates of melt-blown nonwoven fabrics of aliphatic polyester fibres and spunbonded nonwoven fabrics of urethane bondcontaining butylene succinate copolymer fibres’, Kawano, Akitaka; Kin, Kasue, 1999. 34 JP Patent 2003268691, ‘Wet-laid nonwoven fabrics comprising biodegradable fibres consisting of biodegradable polymers derived from sources other than wood and petroleum’, Nakahara, Makoto, 2003. 35 JP Patent 2002345541, ‘Biodegradable, dust-capturing hair caps’, Takahashi, Masanori, 2002. 36 WO Patent 2002053376, ‘Breathable, biodegradable/compostable laminate for disposable personal care product’, Tsai, Fu-Jya Daniel; Balogh, Bridget A., 2002. 37 JP Patent 2002035037, ‘Biodegradable sanitary products containing galactomannanbased water absorbents’, Kawanaka, Satoshi; Ueda, Atsuko; Miyake, Munehiro, 2002. 38 http://www.permathene.com/htm/erosion.shtm. 39 Mueller D. H., ‘Biodegradable Nonwovens – Natural and Polymer Fibres, Technology, Properties’, INTC 2003 Proceedings, Baltimore, Maryland, September15–18, 2003. 40 Parikh D. V., Calamari T. A., ‘Performance Of Nonwoven Cellulosic Composites For Automotive Interiors’, International Nonwovens Journal, 9(2), 83–85, 2000. 41 Yachmenev V. G., Parikh D. V., Calamari T. A. Jr, ‘Thermal Insulation Properties of Biodegradable, Cellulosic-based Nonwoven Composites for Automotive Application’, Journal of Industrial Textiles, 31(4), 283–296, 2002. 42 JP Patent 2000034657, ‘Biodegradable nonwoven fabric filtering material for sink drain’, Matsunaga, Mamiko; Matsunaga, Atsushi, 2000. 43 JP Patent 2003299924, ‘Biodegradable pleated filter material and filter unit for air purification and liquid filtration’, Omori, Taira, 2003. 44 Woodings C., ‘Flushability: An update on technical options and progress’, http:// www.nonwovens.co.uk/reports/Flushability.htm.


4 Flame retardant nonwovens S. D U Q U E S N E and S. B O U R B I G O T, Ecole Nationale Supérieure de Chimie de Lille (ENSCL), France

Abstract: This chapter deals with flame retardant (FR) nonwovens. After a brief introduction, a basic review of the types of flame retardants is reported, the way they work, advantages and drawbacks as well as their potential applications in the textile industry is discussed. Then, the use of these systems for nonwoven applications is commented upon. Several approaches that can be used to flame retard nonwovens including surface treatment, the use of high performance fibers as well as the use of FR fibers are reviewed. Applications of FR nonwovens for filtration, as fire-blockers for seats and upholstery and as protective garments are illustrated. Key words: flame retardant finishing treatments, high performance fibers, fire-blockers, protective garments.

4.1

Introduction

Nonwoven products are mainly manufactured using synthetic fibers such as polyolefin, polyester or nylon (for more detail refer to Chapter 2) that represent highly flammable products. Polypropylene, in particular, burns very rapidly with a relatively low amount of smoke and without leaving a char residue because of its wholly aliphatic hydrocarbon structure (Zhang and Horrocks, 2003). Its selfignition temperature is around 570 °C and it presents a rapid decomposition rate compared with wood and other cellulosic materials. Einsele et al. (1984) reports the heat of combustion for polypropylene to be 40 kJ/g, which is higher than many other fiber-forming polymers. For comparison, the heat of combustion of polyethylene terephthalate is reported to be around 20 kJ/g (Walters et al., 2000). The use of nonwovens manufactured with synthetic fibers can thus lead to an increased fire risk in many cases. This has to be taken into account even more nowadays since there is a trend to replace high cost materials by lower cost materials, for example polypropylene. As an example, dealing with operating room fires, it is reported that their frequency has been diminished since the introduction of non-flammable anesthetic drugs but not totally eliminated because of the introduction of new potential fuels such as, for example, surgical drapes that are not designed with fire safety as a priority (Wolf et al., 2004). Nonwoven cellulose drapes combined with polyester represent a common class of surgical drape. Such products easily ignite in air after 65 © Woodhead Publishing Limited, 2010

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Applications of nonwovens in technical textiles 30

All publication types Patent

Numbner of publications

25

20

15

10

5

0 1980

1985

1990

1995 Year

2000

2005

2010

4.1 Publications regarding flame retardant (FR) nonwovens since 1980. Source: SciFinder.

a laser impact and thus represent an ignition source and potential risk products in operating rooms (Wolf et al., 2004). Another example concerns upholstery and in particular mattresses. Fire statistics show that in the US, each year, an estimated 20,800 fires are attributed to mattress/bedding fires. These fires cause 2,200 injuries, 380 fatalities, and US$104 million in property loss (USFA, 2002). This is mainly due to the fact that polyurethane foams are used to manufacture mattresses and easily burn with melting and dripping (Lefebvre et al., 2004). The molten material can flow downward with gravity leading to the formation of a pool fire. If the pool fire is close enough to nearby products, the result can be a self-propagating fire that further promotes heat release (Hirschler, 2008). The use of barriers, so called fire-blockers, can lead to furnishings complying with modern fire tests in some cases (Damant, 1994). As an example, European patent EP 1780322 describes a fireproof nonwoven cover for spring mattresses made from cellulose fibers and viscose, stitch bonded with synthetic yarns and impregnated with a fireproof agent. According to the patent, the use of such nonwoven mattress covers meet Californian standards (TB 603 regulations) (Barberis, 2006). The need to develop new flame retardant (FR) nonwovens or barrier nonwovens to protect underlying materials can be seen in the examples above. Although the development of FR nonwovens is not recent (the first patent dealing with FR



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finishing treatment for nonwoven fabrics was applied for in 1973 (Orito et al., 1973)), the literature has greatly increased in the last few years. It can be also be seen that the literature is mainly composed of patents and that there are only a few detailed studies (see Fig. 4.1). This chapter will first present a basic review of the types of flame retardants, the way they work, advantages and drawbacks as well as their potential applications in the textile industry. Then, the use of such systems for nonwoven applications will be detailed. Several approaches that can be used to flame retard nonwovens including surface treatment, the use of high performance fibers as well as the use of FR fibers, will be described. Applications of FR nonwovens as fire-blockers for seats and upholstery and as protective garments are illustrated.

4.2

Basics of flame retardancy

The process of ignition and burning can be described in short as a gas phase reaction (Bourbigot et al., 2003). Thus, a substance must become a gas for burning. As with any solid, a textile fabric exposed to a heat source undergoes a temperature rise. If the temperature of the source (either radiative or a gas flame) is high enough and the net rate of heat transfer to the fabric is high, pyrolytic decomposition of the fiber substrate will occur. The products of this decomposition include combustible gases, non-combustible gases and carbonaceous char. The combustible gases mix with the ambient air and oxygen. The mixture ignites, yielding a flame, when its composition and temperature are favorable. Part of the heat generated within the flame is transferred to the fabric to sustain the burning process and part is lost to the surroundings. The considerable fire hazards posed by textiles both in historical times and to the present day are a consequence of the large surface area of the fibers and the ease of access to atmospheric oxygen (Horrocks et al., 2005). The goal of flame retardancy is then to inhibit or even suppress the combustion process acting chemically and/or physically in the solid, liquid or gas phases (Hirschler and Piansay, 2007). It can interfere with combustion during a particular stage of this process, e.g. during heating, decomposition, ignition or flame spread. Various methods can be used to protect materials more effectively from fire (Bourbigot, 2007). The first method is to use inherently flame retarded polymers or high performance polymers but it implies the use of specific materials that might not have the required properties. The second method is to chemically modify the existing polymer to synthesize the FR polymer. The third method is to use flame retardants and/or particles (micro- or nanodispersed) directly incorporated in the materials (e.g. thermoplastics, thermosets or synthetic fibers) or in a coating covering their surface (e.g. structural steel or textiles). In this section we only focus on the mechanism of action of FR materials. Our intention is to provide the reader with the general principles of flame retardancy. The various ways in which a flame retardant can act do not occur singly but should be considered as complex processes in which many individual stages occur


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simultaneously, with one dominating (e.g. using hydroxides causes an endothermic decomposition, cooling down the substrate and diluting the ignitable gas mixture due to the formation of inert gases associated with the formation of the oxide protective barrier). Physical action. There are several ways in which the combustion process can be retarded by physical action (Lewin, 1998): • By formation of a protective layer. Under an external heat flux the additives can form a shield with a low thermal conductivity that can reduce the heat transfer from the heat source to the material. It then reduces the degradation rate of the polymer and decreases the ‘fuel flow’ (pyrolysis gases issued from the degradation of the material) able to feed the flame. This is the principle of the intumescence phenomenon (Bourbigot et al., 2004). Phosphorus additives (or phosphorus grafted on the backbone of polymeric chains or phosphorus comonomer) may act in a similar manner. Their pyrolysis leads to pyro- or polyphosphoric species that are thermally stable and which form a protective vitreous barrier. The same mechanism can be observed using boric acid-based additives, inorganic borates, silicon compounds or low melting glasses. • By cooling. The degradation reactions of the additive can play a part in the energy balance of combustion. The additive can degrade endothermally, which cools down the substrate to a temperature below that required for sustaining the combustion process. Aluminum trihydroxide (ATH) acts partially under this principle and its efficiency depends on the amount incorporated in the polymer (generally 60 (wt%) in thermoplastics). • By dilution. The incorporation of inert substances (e.g. fillers such as talc or chalk) and additives that produce inert gases on decomposition dilutes the fuel in the solid and gaseous phases so that the lower ignition limit of the gas mixture is not exceeded. Chemical action. The most significant chemical reactions interfering with the combustion process take place in the condensed and gas phases (Lewin, 1998): • Reaction in condensed phase. Here two types of reaction can take place. Firstly, breakdown of the polymer can be accelerated by the flame retardant causing a pronounced flow of the polymer and, hence, its withdrawal from the sphere of influence of the flame, which breaks away. Secondly, the flame retardant can cause a layer of carbon (charring), a ceramic-like structure and/or a glass to be formed on the polymer surface. • Reaction in gas phase. The radical mechanism of the combustion process that takes place in the gas phase is interrupted by the flame retardant or its degradation products. The exothermic processes that occur in the flame are thus stopped, the system cools down, and the supply of flammable gases is reduced and eventually completely suppressed. In particular, halogenated compounds can act as flame inhibitors.



69

The fire retardant additive systems may be used alone or in association with other systems in polymeric materials to obtain a synergistic effect, i.e. the protective effect is higher than is assumed from the addition of the separate effects of each system (Bourbigot and Duquesne, 2007). In the other sections of this chapter, we discuss how these principles can be applied and how they act in the particular case of nonwovens.

4.3

Different approaches for flame retardant nonwovens

Most fibers are highly combustible (except high performance fibers) and the flammability of derived fabrics largely depends on the construction and density of the fabric. Several approaches can be used to enhance the fire behavior of fiberbased fabrics used either alone or in blends with other fibers (Horrocks et al., 2005): • Coatings and/or finishing treatments may be applied to shield fabrics from heat sources and prevent volatilization of flammable materials. These may take the form of simple protective coatings or, more commonly, the treatment of fabrics with inorganic salts that melt and form a glassy coating when exposed to ignition sources. In more advanced forms, intumescent coatings produce a char that has sufficient plasticity to expand under the pressure of the gases to yield a thick, insulating layer. • Thermally unstable chemicals, usually inorganic carbonates or hydrates, are incorporated in the material, often as a back-coating so as to preserve the surface characteristics of the carpet or fabric. Upon exposure to an ignition source, these chemicals release CO2 and/or H2O, which, in a first step, dilute and cool the flame to the point that it is extinguished, and in a second step form a protective ceramic around the charred fibers. • Materials that are capable of dissipating significant amounts of heat are layered with the fabric or otherwise incorporated in a composite structure. These may be as simple as metal foils or other heat conductors or as complicated as a variety of phase-change materials that absorb large quantities of heat as they decompose or volatilize. If sufficient heat is removed from the point of exposure, the conditions for ignition are not reached. • Char-promoting chemical treatments that may be fiber-reactive or unreactive to yield launderable or non-durable flame retardancy, respectively. • Chemicals capable of releasing free radical trapping agents, frequently organobromine or organochlorine compounds, may be incorporated into the fabric. These release species such as Br• and Cl•, which can intervene in the oxidation reaction of the flame and break the chain reaction necessary for continued flame propagation. • In the particular case of synthetic fibers (approaches listed above are valid for


70

Applications of nonwovens in technical textiles both natural and synthetic fibers), the direct incorporation of additives (microfillers and/or nanoparticles) or the chemical grafting/copolymerization of specific groups.

4.3.1

Surface treatments

The modification of the surface of textile fabrics or of fibers is one of the easiest ways to bring flame retardancy to materials. Several processes can be used to modify the surface. It is possible to classify these processes into various categories. One can distinguish the ‘chemical processes’ including padding and back-coating, and ‘physical processes’ such as plasma treatment or flaming. In the textile industry, finishing treatments are also generally classified according to their durability (non durable, semi-durable and durable). In this chapter, the surface treatments will be classified as (i) wet processes in which an FR textile coating is applied on the fabric using different deposition processes and (ii) dry processes where either FR films are thermally bonded into the nonwoven or when plasma deposition is used. Wet processes The use of FR coating or impregnations in the textile industry is common. It was the first approach used to develop FR nonwovens (Orito et al., 1973) and is still intensively used (Weil and Levchik, 2008). FR finishing treatments can include organic phosphates (such as tri-alkyl or tri-aryl phosphates, tri-chloroalkyl phosphates, dialkyl phosphites, tetrakis-(hydroxymethyl)phosphonium chloride and related structures), halogenated compounds (such as polybrominated diphenyl ethers and chlorinated paraffins) or inorganic compounds (such as antimony trioxide, ammonum bromide, boric acid and aluminum hydrate) (Van Esch, 1997). Since some halogenated compounds have environmental impact concerns, as they are perceived to be persistent environmental hazards and produce toxic smoke when burned, their uses are becoming more restricted and halogen-free flame retardants are preferred. At present the consumption of halogenated compounds is still high in the textile industry (as an example, polybrominated diphenyl ethers was found in over 50% of treated furniture (Hofer, 1999)). The use of intumescent systems could be an answer to FR challenges in the textile industry (Horrocks and Kandola, 1997). As an example, Magniez et al. (2003) have reported that the use of textile resin binders in association with a FR additive of 15% as back-coating enabled a large improvement in the FR properties of polypropylene (PP) nonwovens. Table 4.1 shows that when a FR treatment is used as back-coating, the time to ignition increases and the peak of heat release rate obtained in the cone calorimeter test decreases. The improvement of the FR properties of the nonwoven was attributed to the quick formation of the intumescent protective layer, trapping the combustible gases released during the



71

Table 4.1 Cone calorimeter data of polypropylene nonwoven and treated polypropylene nonwoven (external heat flux of 30 kW/m²) Reference materials Polypropylene nonwoven Polypropylene bounded by treated resin

Peak of heat release rate (PHRR)(kW/m²)

Time to ignition (TTI) (s)

230 165

30 35

degradation of the textile and limiting heat and mass transfer between the flame and the material. Similarly, Duquesne et al. (2006) have compared the FR properties of PP nonwovens padded and back-coated with a polyurethane based intumescent formulation (based on ammonium polyphosphate (APP) and melamine (Mel)). When fire retardant additives are added to the polyurethane (PU), the fire retardant properties of the nonwoven materials are greatly improved whatever the formulation and the fireproofing methods (Fig. 4.2). The higher efficiency of APP obtained in the case of back-coating is explained by the fact that APP has to react with PU to develop a protective barrier. The additive in back-coating is concentrated in the resin and thus the efficiency is higher. Similar results are obtained

Back-coating

100

Padding

Burned surface (%)

80

60

40

20

0 PP

PP/PU

PP/PU-APP

PP/PU-Mel PP/PU-APP-Mel

4.2 Burned surface of the padded and back-coated PP nonwoven obtained in the vertical hybrid fire test (combination of two normalized tests: IN ISO 11925-2 and NF G07-184).


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4.3 Heat release rate curve of virgin and treated hemp (a) and flax (b) obtained in the cone calorimeter (ISO 5660 at 35 kW/m²).

when APP and Mel are combined together since a condensed phase mechanism is also involved. On the other hand, the role of melamine is attributed to an endothermic effect induced by its volatilization and its decomposition in the flame. As a consequence, it is thus more active when dispersed in the system via padding since it could lead to flame retard PP as well as PU binder. In the case of natural fibers, only surface treatment can be used. Cellulosics, such as cotton and rayon, are common and well known natural fibers. They are not inherently ignition resistant and usually must be chemically treated to prevent ignition by small flames. A well known durable FR chemical for cotton is based on organophosphorus compounds, such tetrakis (hydroxymethyl) phosphonium chloride (THPC). The THPC system is effective in giving durable flame resistance to cotton fabrics, but it requires the use of special equipment in its application. Coating (or back-coating) on fabric is another way to provide flame retardancy to cotton. Horrocks’ group (Davies, 2005) used intumescent back-coatings based on ammonium polyphosphate (APP) as the main flame retardant combined with metal ions as the synergist. Metal ions promote thermal degradation of APP at lower temperatures, and this enables FR activity to commence at lower temperatures in the polymer matrix thereby enhancing FR efficiency. However, this approach was applied to woven fabrics and it is known that the structure of the textile may influence its properties. Recently, the polycondensation products of



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Table 4.2 Characteristic data obtained in a horizontal flame spread test for hemp nonwovens (NW) Material Hemp NW Hemp NW + PLA film Hemp NW + PLA/ APP/PER film Hemp NW + PLA/ APP/LIG film Hemp NW + PLA/ APP/starch film

Char length Burn (cm) time (s)

Flame spread rate (cm/min)

13 13

195 205

4 3.8

–

–

–

–

–

–

–

–

–

Observations Total burn, smoke Total burn, smoke, melted Charred, selfextinguishing Charred, selfextinguishing Charred, selfextinguishing

urea polyborates and polyphosphates were used to flame retard nonwovens made from natural raw materials (hemp and flax) (Kozlowski et al., 2007). The advantage of this treatment is its low cost and its high efficiency. Indeed, as presented in Fig. 4.3, the treatment leads to a sharp decrease of the heat release rate obtained in cone calorimeter experiments. However, it has to be noted that the treatment is not resistant to washing. Dry processes Due to environmental concerns, there is a trend to develop new processes to flame retard fabrics, in particular limiting the volatile organic compounds (VOC) and thus the use of dry processes is preferred. As a result, a new process that uses intumescent films made from renewable resources to flame retard nonwovens was developed (Réti et al., 2009). PLA (polylactic acid)-based film containing APP and a char former (lignin (LIG), starch or pentaerythritol (PER)) was extruded using a single screw melt extruder equipped with a film die. Films of about 250 µm thickness were then glued onto hemp nonwovens using a press at a temperature higher than the melting temperature of PLA. The characteristic data (Table 4.2) obtained in a horizontal flame spread test (similar to the standard FMVSS 302) show that untreated nonwovens or PLA covered nonwovens easily ignite and burn totally. In the presence of a flame, the nonwovens covered with an intumescent film are self-extinguishing. The formation of a protective structure stops the combustion of the sample. This effect was also observed in vertical configurations. This approach is very efficient, easily applied on various kinds of nonwovens (as an example, it has been validated on wool nonwovens). However, the mechanical properties of the fabrics are greatly affected and application where softness is required should be avoided. Plasma treatments are another approach to flame retard textile fabrics and in particular nonwovens. There are two approaches:


74

Applications of nonwovens in technical textiles R'

O O

O

P OR

O

DEMEP: R = Et; R' = Me DEAEP: R = Et; R' = H

O P

O

OR

DEAMP: R = Et DMAMP: R = Me O

O P

O

N H

O

OEt OEt

OR

OR

O

O

OEt P

NH

OEt

O

DEAEPN (2)

O

NH OEt P OEt

BisDEAEPN (4)

4.4 Acrylate monomers containing phosphorus that can be grafted and polymerized on cotton fabric. DEAEP, diethyl(acryloyloxyethyl)phosphate; DEMEP, diethyl-2-(methacryloyloxyethyl)phosphate; DEAMP, diethyl(acryloyloxymethyl)phosphonate; DMAMP, dimethyl(acryloyloxymethyl)phosphonate; DEAEPN, diethyl(acryloyloxyethyl) phosphoramidate (DEAEPN); BisDEAEPN, acryloyloxy-1,3-bis (diethylphosphoramidate)propan.

• the plasma induced graft polymerization (PIGP), which consists of the simultaneous grafting and polymerization of functionalized monomers, such as acrylate monomers, on the surface of a material; • and the plasma enhanced chemical vapor deposition (PECVD), consisting of the injection in the plasma of non-functionalized monomers that become excited and partially decomposed in the plasma with the subsequent formation of a highly cross-linked polymers thin film. The first approach was used to give permanent fire proofing properties to cotton textiles (Tsafack and Levalois-Grützmacher, 2006). In this study, the simultaneous grafting and polymerization of fire retardant acrylate monomers (Fig. 4.4) containing phosphorus on cotton fabric induced by argon plasma were investigated. The limiting oxygen index (LOI/ISO4589 is the minimum concentration of oxygen that will just support flaming combustion in a flowing mixture of oxygen and nitrogen) of the cotton increases from 19 vol.% for untreated fabric to 28–29 vol.% for phosphoramidate monomers. This approach was validated on PET/cotton fabrics (Vannier, 2007) but was never reported for nonwoven fabrics. Tsafack and Levalois-Grützmacher (2006) report that, for cotton fabrics, the efficiency of the treatment differs when the surface density of the fabrics vary from 120 g/m² to 210 g/m². This difference is attributed to the fact that heavier fabrics are more compact than lighter fabrics. Because of this compactness, the surface contact


Flame retardant nonwovens (a)

75

(b)

4.5 Nonwovens based on high performance fibers untreated (a) and plasma treated (b) after exposure to a heat radiator (around 35 kW/m²).

between the fabric and the solution of the monomer is weaker for heavier fabrics than that of lighter fabrics and thus grafting and polymerization are less efficient. The second approach, plasma enhanced chemical vapor deposition (PECVD), deposes an organosilicon thin film obtained from the polymerization of 1,1,3,3tetramethyldisiloxane (H(CH3)2Si-O-Si(CH3)2H) monomer using the cold remote nitrogen plasma (CRNP) process on bulk polymer (Polyamide 6, PA6) (Bourbigot et al., 1999). A similar approach was developed in our laboratory at that time in order to improve the thermal stability of high performance fibers. First results are encouraging (see Fig. 4.5). (Jimenez et al., 2009): after exposure to the heat radiator test the untreated nonwoven is greatly degraded, the treated nonwoven only presents some shrinkage.

4.3.2

High performance fibers

High performance fibers are driven by special technical functions that require specific physical properties unique to these fibers (Sikkema, 2002). They usually have very high levels of at least one of the following properties: tensile strength, operating temperature, heat resistance, flame retardancy or chemical resistance. Applications include uses in the aerospace, biomedical, civil engineering, construction, protective apparel, geotextiles and electronic areas. The resistance to heat and flame is one of the main properties of interest for determining the working conditions of these fibers. In this section we will not consider the inorganic, manmade fibers because very few of them are found in nonwoven applications. The principal classes of high performance fibers are derived from rigid-rod polymers (lyotropic liquid crystalline polymers and heterocyclic rigid-rod polymers), modified carbon fibers, synthetic vitreous fibers, phenolic fibers,


76


poly(phenylene sulphide) fibers and others. Typical high performance fibers are poly(p-phenylene-2,6-benzobisoxazole) (PBO or Zylon from Toyobo), polyp-phenylenediamine-terephtalamide (PPTA or Kevlar, DuPont), co-poly (p-phenylene-3,4-oxidiphenylene-terephthalamide) (TECH or Technora, Teijin), poly(2,6-diimidazo[4,5-b-4',5'-e]pyridinylene-1,4(2,5-dihydroxy)phenylene) (PIPD or M5, Magellan), phenolic fibers (Kynol, Kynol), melamine fibers (Basofil, Basofil Fibers LLC), oxidized polyacrylonitrile (PAN) and polyamideimide fibers (Kermel, Kermel). Three categories of fibers can be determined, rated according to their performance (Bourbigot and Flambard, 2002). The first group is PBO and PIPD. These fibers have a very low rate of heat release rate (RHR) and in the conditions of postflashover (external heat flux > 50 kW/m² in the cone calorimeter) would not be expected to fire spread; they also have a high limiting oxygen index (LOI) (> 50 vol.%), and they do not emit smoke. Kynol and recycled oxidized PAN fibers are in the second group because they have a moderate RHR (< 150 kW/m²). The recycled oxidized PAN fibers and Kynol exhibit high LOI values (> 30 vol.%), and they emit little smoke. The third group is the p-aramid fibers, which, while having comparatively high RHR values (~ 300 kW/m²), contribute to fire growth and emit smoke; they also have a high LOI (> 27 vol.%) values. According to the above ratings, the heterocyclic rigid-rod polymers (PBO and PIPD) exhibit the best performance. The two structures of the polymers are highly conjugated and are heteroaromatic. Moreover, they do not have flexible mid-chain groups that may lead to the reduction of their thermal stability. These factors provide high levels of stability to the polymer and promote high flame resistance. In contrast to PBO and PIPD, p-aramid fibers have phenylene groups linked by amide bridges. These bridges (–CONH–) lead to a reduction in the thermal stability of the fibers, which consequently yield flammable molecules upon heating. Finally, Kynol and oxidized PAN fibers are cross-linked networks with methylene (Kynol) or ether (oxidized PAN) bridges. These flexible groups lead to the reduction in thermal stability as for the p-aramids, but the stabilizing character of the cross-linked network enhances char yields. It follows that the better fire performance of Kynol and oxidized PAN fibers in comparison with p-aramids can be attributed to the formation of higher yields of char. This enhanced char can act as an insulative shield when burning and can protect the substrate.

4.3.3

Flame retardant fibers for nonwovens

To make flame retarded fibers, several approaches can be considered: (i) the incorporation of FR additive(s) in the polymer melt or in the solution prior to extrusion, (ii) the copolymerization or the grafting of FR molecules to the main polymeric chain, and (iii) the use of semi-durable or durable finishing. The third approach will not be considered here as it has been covered in Section 4.3.1. The only candidates for applying the first two approaches are synthetic fibers and our



77

discussion will focus on these. Synthetic fibers are numerous and all of them require flame retardancy, appropriate to their chemical formulation. We will then focus on the most established and used fibers. They include polylactic acid (PLA), polyester, polyamide and polypropylene. All these fibers are used for making nonwovens. PLA fibers were the first man-made (synthetic) fibers made from 100% annually renewable resources, and were publicly launched by Cargill Dow in early 2003 (Vink et al., 2004; Vink et al., 2007). Upon heating, PLA melts, drips and reaches its temperature of ignition very quickly. Very little work has been carried out on the flame retardancy of PLA textiles, but in our laboratories (Solarski et al., 2007), we have developed PLA-clay nanocomposites able to be melt spun to make multifilament yarn (and further nonwovens). Various quantities of organomodified (OM)- montmorillonite (MMT) (from 1 to 4 percent in weight (4 wt.%) have been added to PLA by melt blending via the usual procedures to produce PLA nanocomposites and then into yarn by melt spinning. It has been found that it is necessary to use a plasticizer to melt-spin a blend with 4 wt.% of OM–MMT, and the dispersion of the clay (dispersion at the nano-scale) in the yarns is quite good. The multifilaments were knitted and the flammability studied using cone calorimetry at an external heat flux of 35 kW/m². Depending on the clay loading, the peak value of RHR is decreased by up to 38 % demonstrating the improved fire performance of these PLA fibers. Formation of char is observed in the case of the nanocomposites suggesting a mechanism of condensed-phase. Polyester fibers are the main synthetic fibers used in the industrial manufacturing sector and can be found in several areas of application. As polyester fibers are easily flammable, flame retardancy is a significant issue. One of the common solutions to flame retard polyester is to incorporate a comonomeric phosphinic acid unit into the PET polymeric chain (trade name Trevira CS) (Horrocks et al., 2005). Trevira CS polyester does not promote any char formation and there is evidence that the phosphorus compound acts in the gas phase. Several flame retardants have also been designed for polyester extrusion (bisphenol-S-oligomer derivatives from Toyobo, cyclic phosphonates (Antiblaze CU and 1010) from Rhodia or phosphinate salts from Clariant). Note that the cyclic phosphonate may also be applied as textile finish as well as a melt additive. All these flame retardants were developed in the 1980s (except the phosphinate salt which was developed in the 1990s) and their modes of action have been described in the literature (Horrocks et al., 2005) but very little on this topic has been published recently. Nevertheless, a new halogen-free FR master batch for polyester has been developed in our laboratories, which at only 5 wt.% incorporation in PET allows fabrics (including nonwovens) to meet several standards such as the NF P 92 501 or NF P 92 503 (M classification), FMVSS 302 or BS 5852 (Crib 5) (Almeras et al., 2008). Like polyester, polyamides are synthetic fibers made from semicrystalline polymers and are used in a variety of applications in textiles similar to polyester. Polyamides, however, have proved difficult to render durably flame retardant by


78


incorporation of additives because of their melt reactivities. Semi-durable finishes based on thiourea derivatives are used but usually only on industrial polyamide textile where launderability is not an issue (Horrocks et al., 2005). The most recent developments for the flame retardancy of polyamides concern mainly the inclusion of nanoparticles. Nylon 6 or PA-6/clay hybrid fibers have been made by melt blending and by melt spinning (Bourbigot et al., 2002). RHR curves recorded by cone calorimetry of knitted PA-6 and PA-6/clay nanocomposite fabrics at an external heat flux of 35 kW/m² showed that the peak of RHR of the nanocomposite decreased by 40% compared to that of the pure PA-6. Visually, while a char layer can be seen on each of the two textiles, that in PA-6 seems to be crumbly and contains holes, whereas the char produced by PA-6nano is uniform and without holes. This structure could explain the better performance of PA-6nano against PA-6. Recent work by Horrocks et al. (2005) has been the investigation of the effect of adding selected flame retardants based on ammonium polyphosphate, melamine phosphate, pentaerythritol phosphate, cyclic phosphonate and similar formulations into nylon 6 and 6.6 in the presence and absence of nanoclay. They found that in nylon 6.6 all of the effective systems comprising the nanoclay demonstrated significant synergistic behavior except for melamine phosphate because of the agglomeration of the clay. They then report in the case of nylon 6 that the presence of nanoclay acts in an antagonistic manner (in terms of LOI). To explain why the nanoclay lowered the LOI value of the FR-free nylon 6 film but not that of the nylon 6.6, they proposed that the nanoclay reinforces the fiber structure both in solid and molten phases, thereby reducing its dripping capacity. Such an effect would be likely to reduce the LOI value as the melting polymer has greater difficulty in receding from the igniting flame. Polypropylene (PP) is presently one of the fastest growing fibers for technical end-uses where high tensile strength coupled with low cost are essential features. Because of its wholly aliphatic hydrocarbon structure, polypropylene by itself burns very rapidly with a relatively smoke-free flame and without leaving a char residue. While polypropylene fibers may be treated with FR finishes and backcoatings in textile form with varying and limited success (Zhang and Horrocks, 2003), the ideal FR solution for achieving fibers with good overall performance demands that the property is inherent within the fiber. An acceptable flame retardant for polypropylene, especially fiber-forming grades, should have (i) a thermal stability up to the normal PP processing temperature (< 260 °C), (ii) a good compatibility with PP and no migration of the additives, (iii) flame retardancy properties when present in the fiber and (iv) efficiency at a relatively low level (typically less than 10 wt.%) to minimize its effect on fiber/textile properties as well as cost. With such an approach, Zhang and Horrocks identified five principal types of generic FR systems for inclusion in polypropylene fibers as phosphoruscontaining, halogen-containing, silicon-containing, metal hydrate and oxide, and the more recently developed nanocomposite FR formulations. They concluded that apart from antimony–halogen or in some cases tin–halogen formulations, only



79

one single FR system, tris(tribromoneopentyl) phosphate, is presently effective in polypropylene when required for fiber end-uses. Presently, the use of phosphorusbased, halogen-free flame retardants in PP fibers is prevented by the need to have at least 15–20 wt.% additive presence. Since the latter are char-promoting while all halogen-based systems are essentially non-char-forming in polypropylene, the way forward for a halogen-free, char-forming flame retardant conferring acceptable levels of retardancy at additive levels of 10 wt.% will require either completely new FR chemistry or the development of a suitably synergistic combination based on the understanding reviewed above. The use of nanoparticles might offer this opportunity. The ‘nanocomposite approach’ (incorporation and nanodispersion of particles) alone does not provide enough flame retardancy for PP fabric. That is why Horrocks and his group combined nanoclays with conventional flame retardants as they did in the case of polyamides (Zhang et al., 2006). Flame retardants used included ammonium polyphosphate and a hindered amine stabilizer known to have flame retarding characteristics in polypropylene (Zhang and Horrocks, 2003). They reported that the flammability of polypropylene is reduced by the addition of small amounts of clay in conjunction with a conventional phosphoruscontaining and a hindered amine flame retardant. The authors also suspect a P–N synergism to exist and the LOI value for the best formulation is 22 vol.% compared to 19 vol.% for neat PP, with only 6 wt.% total loading of additives.

4.4

Applications of flame retardant nonwovens

In order to ensure the safety of the public with regard to fire, standards, regulations and requirements in this field are continually discussed and modified. It is not easy to navigate the maze of testing methods and standards. In Europe, harmonization was initiated in the 1990s and is still progressing. The new regulations present new challenges to the flame retardancy industry. Examples of applications of FR nonwovens are reported below. The application of nonwoven materials to manufacture mats for composites also require FR properties (Frechette and Bootle, 2003) but will not be considered in this chapter.

4.4.1

Protective garments

The field of protective garments is relatively large with differing requirements since it incorporates the protection of men at work and military applications, as well as clothing for firefighters. This problem is also relatively complex since a number of properties are required for a material to be used in this field of application. Indeed, heat protective performance is needed, but also heat-moisture transfer properties and comfort performance including lightness, for example, have to be taken into account, and usually a balance between the heat and moisture barrier has to be found. Usually, protective fabrics are multilayer clothing containing


80

Applications of nonwovens in technical textiles Outer shell Heat transfer

Moisture barrier

Thermal liner

Inner shell

Moisture transfer

4.6 Typical structure of protective garments for firefighters. Source: Rawas, 2008.

up to five or six layers. Fire protective clothing for firefighters consists of at least four layers: outer and inner shell, moisture barrier, and thermal liner (see Fig. 4.6). These layers are expected to provide adequate heat, flame, liquid, chemical and mechanical protection. Nonwovens composed of high performance fibers are typically used as thermal liners in protective garments. Various specialized companies have been involved in the process of developing fire protection fabrics (Anon, 2004). Among them, Consoltex introduced CRYONTM technology combining the comfort of natural cotton with the protection of modacrylic fibers and proposed some solutions for firefighters and workwear using Nomex®, Kevlar, PBI and/or Kermel® technologies. Montreal-based company Securitex has developed firefighter products that ameliorate the interaction between the firefighter and his clothing. Meanwhile, Difco Performance Fabrics have also introduced Breezeway® and Genesis® that act as safe alternatives for flame resistant fabrics. Duflot Industries, a company developing technical nonwovens, launched the first nonwoven thermal barrier (Duflot®) in 1986 using Inidex fibers from Courtaulds. This barrier was immediately adopted by the London fire brigade for their structural firefighting kit. More recently, Duflot have developed the Isomex® IsoAir® barrier for heat protection to deal with heat and moisture transfer properties. These barriers are used by the Helsinki, Berlin and London fire brigades (Rawas, 2008).

4.4.2

Fire-blockers for seat and upholstery

Fire-blockers are usually highly fire resistant materials that are placed beneath the exterior cover fabric of furnishing and the first layer of cushioning materials in seats, mattresses and upholsteries. The bulky cushioning materials represent the major fuel source and therefore the greatest hazard potential. The fire-blocker acts as a



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barrier between the heat source (flame, cigarette, etc.) and the cushioning materials limiting fire growth and development (Damant, 1996). Fabric-like fire-blockers include woven and needle punched fabrics made from highly resistant textile fibers such as glass, Nomex, Kevlar, PBI, etc. Some of the fabric-like fire-blockers available are engineered textile products that use a combination of different fibers and fabric treatments. The first modern generation of fire-blockers was introduced by Dupont under the trade name VonarTM during the 1970s. In the 1990s, Hoechst Celanese and Dupont developed products based on PBI blended with other fibers such as aramids, cotton and rayon, and based on Kevlar® and Nomex®, respectively. Kemira in Finland also introduced the use of Visil® fibers, a viscose rayon fiber with a silicic acid backbone, in the field of fire-blockers. More recently, it has been reported that Lenzing FR, an inherently flame resistant cellulose fiber, can be used for seat covers in aircraft, railway vehicles, ships and for technical applications such as fire-blockers and insulation felts (Gstettner, 2005). Even though most of the fire-blockers have been designed using high performance fibers, there has been an attempt to develop these barriers using fire protective coating, such as intumescent coating, applied to certain fabrics. F.R. Systems International, Canada, have applied this technology to introduce fire barriers for mattresses for example. The use of FR nonwovens based on natural fibers as fire barriers for upholstery has been reported (Kozlowski et al., 2004), and also that natural materials modified with safe fire retardants may be applied as valuable composites in sleeping and seating furniture with the advantages of natural materials regarding their permeability and anti-electrostatic properties.

4.4.3

Other applications

Another application of FR nonwovens is flexible insulation panels for building construction. Although traditional thermal insulation materials such as mineral wool or polystyrene are widely used, the return to ecology and nature noticed in several application fields is also observed in the building industry. Natural wool, coconut or even duck feathers are used to design thermal insulation panels. However, all these materials burn easily and thus FR treatments are required. The development of needle punched nonwovens and air-laid nonwovens based on fire retardant modified natural fibers has been reported (Kozlowski et al. 2007) and has been demonstrated that such materials meet the requirements for use in building applications. Finally, it is noteworthy that there are applications where FR properties are required in disposable nonwovens, for example for surgical drapes used in operating rooms as well as air filters used in the automotive industry. However, as only few studies have been reported these applications will not be fully developed in this chapter.


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4.5


Conclusion and future trends

The development of FR nonwovens is an important field of investigation since in a number of applications fire retardant properties or fire protection is required for the safety of people. Although this topic has been investigated for woven fabrics over a long period of time, it is relatively new for nonwovens and only a few detailed and comprehensive studies have been reported in the literature. However, we know that the structure of the materials (in particular its surface area) plays a significant role in the properties of the materials. At present, the main applications of FR nonwovens concern fire protective garments and fireblockers for seats, mattresses and upholstery applications. These barriers are mainly prepared using high performance fibers and thus the costs are relatively high. Future developments will concern the development of low cost FR nonwovens. One interesting approach consists of the development of intumescent coatings used as back-coatings that could develop a heat protective barrier in case of fire. All these developments could take into account environmental concerns and thus developments of bio-based materials and of dry process technologies will be preferred.

4.6

References

Almeras X, Vandendaele P, Vannier A, Duquesne S, Bourbigot S, Delobel R, Ortiz M, Gupta G and Pivotto E (2008), ‘New halogen free masterbatch for PET fibers’, Chemical Fibers International, 58, 178–181. Anon. (2004), ‘Firefighter and fire-resistant clothing and fabric’, Textile Journal, 121(3), 36–42. Barberis CP (2006), ‘Fireproof non-woven fabric, method of manufacturing thereof and mattress cover obtained thereby’, EP1780322. Bourbigot S, Jama C, Le Bras M, Delobel R, Dessaux O and Goudmand P (1999), ‘New approach to flame retardancy using plasma assisted surface polymerisation techniques’, Polymer Degradation and Stability, 66(1), 153–155 Bourbigot S and Flambard X (2002), ‘Heat resistance and flammability of high performance fibres: A review’, Fire and Materials, 26, 155–168. Bourbigot S, Devaux E and Flambard X (2002b), ‘Flammability of polyamide-6/clay hybrid nanocomposite textiles’, Polymer Degradation and Stability, 75, 397–402. Bourbigot S, LeBras M and Troitzsch J (2003), ‘Fundamentals – Introduction’, in Troitzsch J, Flammability Handbook, Munich, Hanser Verlag. Bourbigot S, LeBras M, Duquesne S and Rochery M (2004), ‘Recent advances for intumescent polymers’, Macromolecular Materials and Engineering, 289, 499–511. Bourbigot S and Duquesne S (2007), ‘Fire retardant polymers: Recent developments and opportunities’, Journal of Materials Chemistry, 17, 2283–2300. Damant GH (1994), ‘Recent United States developments in tests and materials for the flammability of furnishings’, Journal of the Textile Institute, 85(4), 505–525. Damant GH (1996), ‘Use of barriers and fire blocking layers to comply with full-scale fire tests for furnishings’, Journal of Fire Sciences, 14(1), 3–25. Davies PJ, Horrocks AR and Alderson A (2005), ‘The sensitisation of thermal decomposition



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of ammonium polyphosphate by selected metal ions and their potential for improved cotton fabric flame retardancy’, Polymer Degradation and Stability, 88, 114–122. Duquesne S, Drevelle C, Bourbigot S and Delobel R (2006), ‘Influence of the fireproofing method on the fire retardant performance of intumescent polypropylene non-woven’, Paper presented at the 17th Annual Conference Recent Advances in Flame Retardancy of Polymeric Materials, May 21–24, 2006, Stamford, CT. Einsele U, Koch W and Herlinger H (1984), ‘Investigations into the development of heat when textiles burn in air’, Melliand Textilberichte, 65(3), 200–206. Frechette DR and Bootle J (2003), ‘Intumescent mats in composites: Process, testing and performance criteria’, International SAMPE Symposium and Exhibition (Proceedings), 48I, 937–943. Gstettner A (2005), ‘Flame resistant and functional seating fabrics’, Textiles à Usages Techniques, 1(55), 24–25. Hirschler MM (2008), ‘Polyurethane foam and fire safety’, Polymers for Advanced Technologies, 19(6), 521–552. Hirschler MM and Piansay T (2007), ‘Survey of small-scale flame spread test results of modern fabrics’, Fire and Materials, 31, 373–386. Hofer H (1999), ‘Environmental Aspects of Flame Retardants in Textiles’, Geschäftsfeld Toxikologie – Bereich Lebenswissenschaften report for Austrian Standards Institute Consumer Council, Report N° OEFZS–L-0057. Horrocks R and Kandola BK (1997), ‘Novel intumescent applications to textiles’, Journal of Coated Fabrics, 27(7), 17–26. Horrocks AR, Kandola BK, Davies PJ, Zhang S and Padbury SA (2005), ‘Developments in flame retardant textiles – A review’, Polymer Degradation and Stability, 88, 3–12. Jimenez M, Duquesne S and Bourbigot S (2009), unpublished results. Kozlowski R, Muzyczek M and Mieleniak B (2004), ‘Upholstery fire barriers based on natural fibres’, Journal of the Balkan Tribological Association, 10(3), 422–428. Kozlowski R, Mieleniak B, Muzyczek M, Mankowski J, Magnies C, Mesnage P (2007), ‘Flammability of lightweight, flexible insulating nonwoven lade from natural fibrous raw materials’, Paper presented at the 18th Annual Conference Recent Advances in Flame Retardancy of Polymeric Materials, May 21–23, 2007, Stamford, CT. Lefebvre J, Bastin B, Le Bras M, Duquesne S, Ritter C, Paleja R and Poutch F (2004), ‘Flame spread of flexible polyurethane foam: Comprehensive study’, Polymer Testing, 23(3), 281–290. Lewin M (1998), ‘Physical and chemical mechanisms of flame retarding polymers’, in LeBras M, Camino G, Bourbigot S and Delobel R, Fire Retardancy of Polymers: The Use of Intumescence, Cambridge, Royal Society of Chemistry, 3–34. Magniez C, Dubois A, Vouters M, Delobel R and Poutch F (2003), ‘Behavior of an intumescent system for flame retardant materials coated on polypropylene textiles’, Journal of Industrial Textiles, 32(4), 253–266. Orito Z, Nakagawa O, Uzawa K, Tokuyama S and Machida M (1973), JP 48000600 19730109. Rawas C (2008), Presentation made at Club de Veille Textil’Aisne, December 17, 2008, France. Réti C, Casetta M, Duquesne S and Bourbigot S (2009), ‘Intumescent biobased-polylactide films to flame retard nonwovens’, Journal of Engineered Fibers and Fabrics, 4(2), 33–39. Sikkema DJ (2002), ‘Manmade fibers one hundred years: Polymers and polymer design’, Journal of Applied Polymer Science, 83, 484–488. Solarski S, Mahjoubi F, Ferreira M, Devaux E, Bachelet P, Bourbigot S, Delobel R, Coszach


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P, Murariu M, Da Silva Ferreira A, Elexandre M, Degeee P and Dubois P (2007), ‘(Plasticized) Polylactide/clay nanocomposite textile: Thermal, mechanical, shrinkage and fire properties’, Journal of Materials Science, 42, 5105–5117. Tsafack MJ and Levalois-Grützmacher J (2006), ‘Flame retardancy of cotton textiles by plasma-induced graft polymerization (PIGP)’, Surface and Coatings Technology, 201(6), 2599–2610. Tsafack MJ and Levalois-Grützmacher J (2007), ‘Towards multifunctional surfaces using the plasma-induced graft-polymerization (PIGP) process: Flame and waterproof cotton textiles’, Surface and Coatings Technology, 201(12), 5789–5795. USFA (2002), Mattress and Bedding Fires in Residential Structures, US Fire Administration, Topical Fire Research Series, 2(17). Van Esch GJ (1997), ‘Flame retardants: A general introduction’, Environmental Health Criteria (192), 1–56. Vannier A, Duquesne S, Bourbigot S, Delobel R, Magniez C and Vouters M (2006), ‘The use of the plasma induced polymerization technology to develop fire retardant textiles’, International Conference on Textile Coating and Laminating, November 8–129, Barcelona, Spain. Vink ETH, Rábago KR, Glassner DA, Springs B, O’Connor RP, Kolstad J and Gruber PR (2004) ‘The sustainability of NatureWorks™ polylactide polymers and Ingeo™ polylactide fibers: An update of the future’, Initiated by the 1st International Conference on Bio-based Polymers (ICBP 2003), November 12–14 2003, Saitama, Japan, Macromolecular Bioscience, 4, 551–564. Vink ETH, Glassner DA, Kolstad JJ, Wooley RJ and O’Connor RP (2007), ‘The eco-profiles for current and near-future NatureWorks® polylactide (PLA) production’, Industrial Biotechnology, 3, 58–81. Walters RN, Hackett SM and Lyon RE (2000), ‘Heats of combustion of high temperature polymers’, Fire and Materials, 24(5), 245–252. Weil ED and Levchik SV (2008), ‘Flame retardants in commercial use or development for textiles’, Journal of Fire Sciences, 26(3), 243–281. Wolf GL, Sidebotham GW, Lazard JLP and Charchaflieh JG (2004), ‘Laser ignition of surgical drape materials in air, 50% oxygen, and 95% oxygen’, Anesthesiology, 100(5), 1167–1171. Zhang S and Horrocks AR (2003), ‘A review of flame retardant polypropylene fibres’, Progress in Polymer Science, 28(11), 1517–1538. Zhang S, Horrocks AR, Hull R and Kandola BK (2006), ‘Flammability, degradation and structural characterization of fibre-forming polypropylene containing nanoclay-flame retardant combinations’, Polymer Degradation and Stability, 91, 719–725.


5 Nonwoven personal hygiene materials and products J. R. A J M E R I and C. J. A J M E R I,

Sarvajanik College of Engineering and Technology, India

Abstract: Nonwoven fabrics have traditionally been used in medical applications, but owing to their relatively low cost of production, versatility in incorporating various mechanical properties, disposability, and low lint, which reduces cross-infection and enables high levels of hygiene to be maintained, they have made major inroads in the growing field of healthcare and hygiene applications. This chapter discusses one of the emerging areas of nonwoven applications: personal hygiene. It first reviews key issues of hygiene materials and then discusses the types and properties of nonwoven materials along with applications such as diapers, feminine hygiene and adult incontinence. Key words: nonwoven hygiene materials, diaper, feminine hygiene, adult incontinence.

5.1

Introduction

Nonwovens are unique, innovative, versatile, indispensable, high-tech engineered fabrics made from fibers and are used across a wide range of applications and products. Modern life would be quite literally impossible without them. Nonwoven fabrics have traditionally been used in medical applications, but owing to their relatively low cost of production, versatility in incorporating various mechanical properties, disposability, low lint, which reduces cross-infection and enables high levels of hygiene to be maintained, they have made major inroads in the growing field of healthcare and hygiene applications.1–4 In this chapter nonwoven hygiene materials (NHMs) are discussed in detail. The definition of nonwoven supported by the European Disposable and Nonwoven Association is : A nonwoven is a manufactured sheet of directionally or randomly oriented fibers, bonded by friction, and/or cohesion, and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitchbonded incorporating binding yarns or filaments, or felt by wet-milling whether additionally needled or not. The fibers may be of natural or manmade origin. They may be staple or continuous filaments or be formed in situ.5,6 85 © Woodhead Publishing Limited, 2010

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5.1.1


Key issues of hygiene materials

Two main characteristics of nonwovens make them particularly suitable for use in an absorbent hygiene material: high bulk for imbibing and holding a large amount of fluid per unit mass of material and the low cost of converting raw material into final product. However, not-leaking is just a minimum standard. Several other properties that have significant impact on the use of nonwovens in an absorbent hygiene material are disposability, comfort, and ease of fabrication of the product. The product is usually composed of a number of components, each supporting different but important functions. These are to receive fluid, imbibe it rapidly, hold it for a period of time, keep the clothing from soiling, keep the skin of the wearer dry, mask odor, be easily worn and removed, and be conveniently disposed of.7 It is very important that the absorbing web layer with superabsorbent powder or fiber is placed inside the composite. In addition to high productivity and low cost, one of the key aims in designing hygiene materials is to reduce the size or weight without compromising the fluid holding capacity.8 Additionally, concern is now being raised about environmental consequences, longer life, biodegradability or ease of recycling.9Absorbent hygiene materials are usually highly engineered composites whose in-use performance is ultimately judged by the consumer. Each manufacturer strives to produce consistently high performing product at a low cost. The major portion of the diaper is fluff pulp: its price and availability have a significant influence on the diaper market. Because pricing of these materials is largely dictated by the market, success or failure for the suppliers is driven by economies of scale. Increases in the price of petroleum and other feedstocks have driven up pricing of polypropylene (PP) and polyethylene (PE), which have led to strongly adverse conditions for nonwovens suppliers who use these materials to make products for the hygiene market. In order to ensure that these materials will meet the exacting demands of the consumer, producers must select appropriate fibers and polymeric materials, engineer individual components with desirable characteristics and assemble them into the desired article with optimum performance. In complex structures, different layers perform different functions, some are absorbent, some transport liquid, and some are repellent.10 In recent years, the hygiene market has subscribed to a three-point holy grail that defines product success – form, fit and function. Form has been achieved through the incorporation of superabsorbents,11 which make products thinner, and textilelike back sheets, which make them softer. Fit continues to be honed through the increasing use of elastics and other stretchable materials throughout the chassis of the diaper. Once found only in the leg cuff, elasticized material is now found in the waistbands, on the side panels and is even being incorporated into closure systems. Larger sized baby diapers as well as adult incontinence products are becoming more pant-like and more discreet, meaning more comfort for the wearer. While form and fit are increasing in importance, they can never surpass function



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in performance. After all, what is the point of a disposable garment, if it does not achieve its function? For baby diapers, this means no leaking and less frequent diaper changes; for adult incontinence, this means a more active lifestyle and for feminine hygiene, this means discretion.

5.2

Types of nonwoven materials used for hygiene products

The textiles used for hygiene materials were conventionally cotton products that possessed the required level of durability, comfort, resistance to microbial contamination, and ease of washing and sterilization. Nowadays, these materials are made of tissue, reinforced with a cotton, viscose rayon, polyester or PP fiber spunlaid web.12–14 Lightweight nonwovens, i.e. less than 50 g/m2, provide a major benefit for hygiene products in that such lightweight structures give the required performance at relatively low cost.15 For adult incontinence diapers, fabrics of around 10–30 g/m2 (ref. 16) are used. Low basis weight hygiene materials are commonly spunlaid nonwovens.17,18 Cover stock for diapers and incontinence products is typically lighter spunbonded PP webs because they offer soft hand and hydrophobic properties.19–41

5.2.1

Spunbonded nonwovens

The use of spunbond fabrics in coverstock for diaper and incontinence devices has grown dramatically. This is mainly because of the favorable structural characteristics of spunbonds, which help keep the skin of the user dry and comfortable. Spunbond fabrics are seen as cost effective compared to other nonwovens. Current nonwoven materials used in topsheet applications include spunbonded PP (usually produced on a multibeam system), spunbond/meltblown/spunbond (SMS) PP composites and carded PP thermal bonds.42–45

5.2.2

Thermally bonded nonwovens46,47

Thermal bonding is an important technology for producing NHMs. It offers high production rates because bonding is accomplished at high productivity with heated calender rolls or ovens. It also offers significant energy conservation with respect to latex bonding because of more effective thermal contact and the fact that no water needs to be evaporated after bonding. It is environmentally friendly because there are no residual ingredients to be disposed of.48 Thermally bonded nonwovens have practically replaced chemically bonded nonwovens all over the world. Until recently all napkins used chemically bonded nonwovens. They had two disadvantages: firstly chemically bonded coverstock remains wet and therefore is uncomfortable and secondly chemical binders might cause skin irritation for some wearers.49


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Acquisition/distribution layers made with through-air bonded nonwovens are considered by hygiene product manufacturers to be particularly efficient in attaining improved penetration and in preventing rewetting.50 Thermally bonded airlaid nonwovens are widely used as interior absorbent core materials in feminine hygiene materials, incontinence and baby diapers.51,52 Thermally bonded technology uses PE/PP core/sheath bicomponent fibers (at a level of almost 30–40% in airlaid products) as a bonding fiber to bond pulp.53 Modern feminine hygiene materials comprise thin cores manufactured using airlaid technology and are low loaded with superabsorbent powder. The absorption of blood is another important requirement and superabsorbents such as HySorb™ provide this feature whilst retaining good integrity in airlaid cores. Superabsorbents are key to the trend towards smaller and thinner sanitary napkins, improving a woman’s sense of well-being. Most sanitary products for women on the market today contain viscose rayon, a cellulose fiber made from wood pulp.54 Some tampons are made of cotton/viscose rayon blends, while others may be completely cotton.55 Bicomponent fibers, consisting of PE sheath and PP core, are also used for tampons and incontinence products.56

5.2.3

Composites

Spunbond and meltblown webs are often combined at the production stage to achieve a variety of composite structures providing barrier properties for applications in the hygiene sector.57,58 The SMS concept was first introduced and patented by the Kimberly-Clark Corporation. SMS webs are characterized by having excellent physical properties (strength, elasticity, abrasion, secondary tearing, tear strength, etc.), uniformity, and excellent barrier qualities (preventing leakage of very fine particles and micro-organisms and aggressive liquids) while also providing controlled air permeability and softness.59–61 Cotton surfaced nonwovens (CSNs) CSNs are produced with carded cotton/PP web on one or both sides of a spunbond, calendered or thermally bonded into two or three layers. CSNs have soft but strong fabric, excellent wetting, water absorption, retention, and are ideally suited for personal hygiene. Cotton core nonwovens (CCNs) CCNs are thermally bonded laminates with a carded bleached cotton web as core. The core is encapsulated with meltblown and/or spunbonded PP after the extrusion process, prior to calendering.62 CCNs are highly suited for incontinence items due to the effective transport of liquid into the highly absorbent cotton core from the surface, their dry surface and absorbent core.



5.3

89

Properties of nonwoven hygiene materials

Absorbency is the key property of materials used in the construction of NHMs.63 A hygiene material should be very soft to the touch, maintaining high integrity while being stretched. For example, in a disposable diaper, it is highly desirable to have soft, strong, nonwoven components, such as topsheets or back sheets (also known as outer covers). The softness can be adjusted by adjusting spinning speed, polymer type and filament diameter.64 For example, by reducing the filament diameter, one achieves a fabric that is softer to the touch.65 It also must possess very good barrier properties to avoid unpleasantness caused by urine degradation. It is important to have a very uniform web as this will provide a stronger product while eliminating the need for several layers, e.g. SMS.66

5.3.1

Fibers used

Fiber extensibility/elasticity is an important criterion because this characteristic translates to better comfort and fit as the article will be able to be more body conforming in all situations. Diapers with elastic components will have less sagging in general, as body size and shape and movement vary. With improved fit, the general well-being of the user is improved through improved comfort, reduced leakage, and a closer resemblance of the article to cotton underwear.67–69 Properties of importance are: wicking, water absorption, water retention and minimal linting characteristics. The use of wood fibers is key in this type of product as they can hold 33–35% water and are relatively cheap.70 Considering the cost, cotton can certainly not replace wood fibers, but could make a contribution in products where the principle ‘thinner is better holds’. Its use provides high absorption capacity, comfort, softness, chemical resistance and biodegradability. The use of PP fiber provides the desired hydrophobic nature to the facing at a reasonable cost as this polymer is one of the lowest cost, high volume, commercial polymers. Superabsorbent fibers can be made from superabsorbent polymers (SAPs). SAPs are hydrogels that absorb water at one hundred times their own weight.71– 73 By comparison, conventional wood pulp and cotton filler absorbents absorb only six times their weight. SAPs’ granulates retain large quantities of liquid by forming a gel when in contact with it. Their free swell absorbency after only 15 seconds is equal to or greater than their retention capacity. Superabsorbent fibers such as OASIS SAF®, Aquakeep®, and Norsocryl® give a number of benefits for the hygiene industry: • low density enables the production of soft non-bulky products • almost invisible blending with other fibers to both sight and touch, giving products a pleasing natural appearance to consumers • no migration of the superabsorbent within fabric


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• fabrics are easier to slit and cut after manufacture with reduced blade wear and shedding of superabsorbent • more uniform distribution of superabsorbent particularly with low base weights • high surface area – for high absorbency rates and reduced blocking by large molecules found in blood and other body fluids.74–77 The most requested performance properties imparted by finishing treatments for NHMs are: hydrophilicity, durable hydrophilicity, softness, absorption, and appropriate combinations of these, e.g. hydrophilicity and softness.78

5.4

Applications of nonwoven hygiene materials

Modern disposable, absorbent NHMs have made an important contribution to the quality of life and skin health of millions of people. Market segments and products falling under the heading of NHMs are as given in Table 5.1.79–93 The advantages of using NHMs instead of traditional textiles are: excellent absorption, softness, smoothness, stretchability, comfort and fit, strength, double fluid barrier effect allowing moisture to be absorbed and retained, good uniformity, high strength and elasticity, good strike-through, low wet-back and run-off, cost-effectiveness, stability and tear resistance, opacity/stain hiding power, and high breathability.

5.4.1

Diapers94,95

According to a diaper market sustainability report issued by EDANA, Brussels, Belgium, the average baby diaper comprises 35% fluff pulp, 33% SAP, 17% PP, 6% PE, 4% adhesives, 4% other, and 1% elastics.96 The nonwoven PP fabric required is 20–25 gsm.97 Disposable baby diapers were first introduced in the early 1960s and since then have been marked by continuous product innovations Table 5.1 Market segments and products falling under the heading of NHMs Diapers

Feminine hygiene

Adult incontinence

Baby diapers Nappies Training pants

Sanitary napkins Feminine pads Sanitary towels Panty liners Panty shields Tampons

Adult diapers Briefs Insert pad and pant Bladder control pads Undergarments Guards Shields Panty liners Underwear Underpads Bed pads



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including the addition of SAP, resealable tapes and elasticized waistbands. Baby diaper-making machines available in the market have production speeds of around 250–750 pieces per minute.98,99 Diaper coversheet The nonwoven fabric that is positioned next to the skin of the wearer of a hygiene material has been given various names, including: (a) cover, (b) coversheet, (c) coverstock,100 (d) facing, (e) topsheet, and others. Fiber selection, processing conditions and binder considerations all are focused on the requirement for maximum absorbency of the diaper facing. Today, with the requirement of a dry surface in contact with the skin, which is supposed to be more comfortable and less irritating and toxic for the wearer, the fiber choice has shifted from the hydrophilic viscose rayon to the wholly synthetic hydrophobic fibers. In attempts to design a binder-free facing there has been a growing interest in the use of thermally bonded nonwoven technology in order to produce hydrophobic facings without chemical additives such as formaldehyde. The property of hydrophobicity in a diaper facing is necessary but not sufficient for optimum performance. The fabric must also quickly pass liquid through to the interior of the diaper. The perfect facing must function as a ‘one-way valve’, quickly passing the liquid through (rapid strike-through), restricting passage of the liquid back through in the reverse direction (wet-back), and presenting a dry and soft fibrous surface to the skin. Consequently, a technology for conveying wetting properties to the surface of the facing to ensure rapid strike-through of the voided liquid is necessary. This is most easily achieved by uniformly adding onto the surface of the facing a small amount (0.2–0.6 wt%) of an effective rewetting agent. This is generally applied by spraying. For example, Sandler sawabond® thermally bonded topsheet qualities are made from co-polymer fibers, bi-component fibers or even blended-in viscose rayon fibers, and fine PP fibers with a hydrophilic or permanently hydrophilic finish, in various softness grades and bonding patterns. Secondary facing The secondary facing is intended to facilitate rapid passage of liquid from the back of the cover into the adjacent pulp pad or ply. This takes the form of a very lightweight fiber web with little or no bonding between the primary facing and the absorbent core. In another form, the single facing is fabricated with a rough top (outer surface) and a smooth bottom (inner surface). In this system, liquid tends to move from the rough side to the smooth side, enhancing wicking toward the center.


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Acquisition/distribution layer The mechanism of enhancement of liquid movement has been further advanced by the use of an acquisition101/distribution layer (ADL) between the topsheet and the absorbent core.102 The ADL provides for more rapid liquid acquisition (minimizing flooding in the target zone), and more rapid transport and thorough distribution of the fluid into the remainder of the absorbent region. The absorbent core The absorbent core is the heart of an absorbent hygiene material. There are several properties to be considered in the design of the polymer matrix for the diaper core. The absorption rate of the diaper must not be slower than the urination rate of the baby, otherwise leakage will occur. The absorption rate of the composite is influenced by the absorption rate of the SAP. However, fast swelling of the polymer may or may not be desirable: in some diaper designs, fast swelling may cause the diaper to leak if the result of the swelling is that the porosity and permeability of the composite is reduced. The absorption rate of SAP is affected by the maximum absorption capacity of the polymer and its particle size and shape. The placement of fast or slow absorbing polymers in the composite structure therefore has important implications for the effectiveness of the composite. In addition, particle size, placement, and relative amounts play a large role in the optimization of absorption. When the superabsorbent swelling is delayed in the wetting region of some diaper designs, there is more time to distribute urine through the diaper. By distributing the liquid better throughout the diaper, there is less saturation of the core in the wetting region, so further wetness may be absorbed. With a refined understanding of the impact of SAP on the absorbent core in the early 1990s ultra-thin diapers became possible. The amount of cellulose pulp fluff used in these diapers was reduced by half, yielding a thinner diaper with a higher concentration of SAP in the absorbent core. As polymer properties become increasingly understood, diapers become thinner as the ratio of polymer to fluff increases. In modern diapers, the core consists of hydrophilic wood pulp and SAP.103–105 The fluffy pulp used is between 13 and 25 g/m2, depending upon diaper thickness. It can also consist of grafted cellulose and starch, interlinked carboximethyl cellulose derivatives and modified hydrophilic polyacrylics.106 Because the core must often withstand several insults, it must be able to absorb, transport, distribute and hold body fluid at more than 50% of its own weight. SAPs are added to baby diapers in basically two ways: layered or blended. Japanese diaper manufacturers commonly adopt the layered application. The blended application of SAP is representative of American diaper manufacturers. The back sheet Finally, the back sheet is an impermeable thin film or barrier fabric that prevents



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leakage. To improve the handle and aesthetics, it is often embossed for flexibility and to provide a cloth-like appearance. Diaper test methods Properties that are commonly tested include such special tests as ‘strike-through’ (time in seconds for liquid to penetrate the topsheet), ‘run-off’ (volume of liquid not absorbed into the porous material when the fabric is maintained at a specified angle), and ‘wet-back’ (volume of liquid squeezed out of an absorbent and back through the facing under standard conditions). Other properties of interest that relate to the performance of the diaper include ‘total absorption’ (saturation to the drip-free point), and ‘absorption under load’ (total amount absorbed and held under a standard load).107–111

5.4.2

Feminine hygiene

Feminine hygiene is a general term used to describe personal care products used by women during menstruation, vaginal discharge, and other bodily functions related to the vulva. Sanitary towels (also known as maxi-pads or napkins), panty liners, tampons, menstrual cups, and feminine wipes are the major categories of feminine hygiene products. Sanitary napkins The functions of sanitary napkins are to absorb and retain menstrual fluid, and isolate menstrual fluids from the body. Important and desired properties are: no leakage, no unaesthetic appearance or color, no odor, no noise, stay in place, comfortable to wear (thin body shape), and a high level of hygiene. The average sanitary napkin comprises 48% fluff pulp, 36% PE, PP and PET, 7% adhesives, 6% superabsorbent and 3% release paper. Options are available for napkins with fluff, airlaid or double fluff core, in combination with panty liners, additional core or materials, embossings,112 elastic cuffs, and with trifolders or single wrappers. Sanitary napkin-making machines available in the market have production speeds of around 500–1000 pieces per minute. Panty shields The function of panty shields is to protect underwear from vaginal discharge. Important and desired properties are sufficient absorption capacity, discretion, comfortable to wear (softness, body shape), and good hygiene. Pads and panty liners are mainly made of materials such as wood pulp, nonwoven fabrics made from polymers (PE, PP), SAP, and adhesives of natural and synthetic resins. These raw materials are chosen for their ability to absorb and retain fluids, to avoid


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leakage and to provide comfort.113 Panty shield-making machines available in market have production speeds of around 1500 pieces per minute. Tampons The most common type of tampon in daily use is a disposable plug that is designed to be inserted into the vagina during menstruation to absorb the flow of blood. Its function is to absorb and retain menstrual fluid inside the body. Important and desired properties are no leakage, no odor, easy to insert, easy to remove, softness, comfortable to wear (dimensionally correct), high level of hygiene; the tampon should also be discreet. Modern tampons are mainly composed of cellulosic absorbent material, either viscose rayon or a mixture of these fibers. In most instances, the absorbent core is covered by a thin, smooth layer of nonwoven or perforated film helping to reduce loss of fibers and making the tampon easy to insert and remove. The withdrawal cord that is necessary to remove the tampon is usually made of cotton or other fibers and can be colored.

5.4.3

Adult incontinence

Incontinence is the lack of voluntary control of excretory functions; the term is a contraction of a complete expression, such as ‘incontinence of urine’ or ‘incontinence of feces’. Adult incontinence products (AIPs) need to combine performance, comfort, discretion and aesthetics to fulfill all the needs of this emerging market. Comfort is a vital element for AIPs. Part of comfort is fit – the garment must fit snugly to prevent leakage, but should not bind or chafe the skin of individuals wearing them all day. Skin health can be even more important for an adult user than for babies. Pulling liquid away from the skin is a top priority for an AIP – absorption rate and wicking action are essential. Part of the comfort experience for adults is discretion. AIPs need to be ‘a silent partner in protection’. People do not want them to rustle like a baby’s diaper. Beyond sound, adults worry about odor. Odor has a function in baby diapers – it’s an alarm that signals to parents when to change their children’s diapers. For adults, however, that alarm becomes a source of embarrassment. Odor control is highly important for the adult market. Cotton is receiving renewed interest as a sustainable and eco-friendly fiber, while being good for comfort, and is hypoallergenic next to the skin. AIPs are designated according to the severity of the incontinence problem to be managed as light, moderate or heavy/double incontinence. The average incontinence product composition according to EDANA is: 62% fluff pulp, 12% SAP, 10% PE film, 10% nonwoven PP, 3% adhesives, 2% others and 1% elastics. Basic processes in the manufacture of incontinence products are: the fiberization of fluff pulp, addition of SAP and absorbent core formation; lamination with films,



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nonwoven substrates, elastic elements and tapes; printing of wetness indicator and traceability markings; shaping, cutting, folding, and packaging. Heavy incontinence The primary functional requirements of products designed to deal with heavy incontinence are to absorb and retain urine, retain feces inside the product, isolate wetness from the skin, and reduce odor. Important/desired properties are maximizing comfort, simplicity (ease of use and putting on/taking off), low noise factor (particularly for non-institutionalized persons), and hygiene.114 Odor-control SAP products such as Hysorb™, which inhibit the generation of ammonia, have been specifically developed for heavy incontinence. By enhancing absorption capabilities, SAPs improve incontinence protection and create a new level of confidence and comfort.115 Medium–low incontinence The primary functional requirements are to absorb urine during micturition and distribute the urine throughout the absorption pad, provide medium capacity absorption, retain urine effectively in the absorbent core, isolate wetness from the skin, and reduce potential odor problems caused by urine degradation. Important and desired properties are maximizing wearer comfort, good product fit, good level of discreetness with the product, and a high level of hygiene. The structure of these products is similar to feminine hygiene products like sanitary pads and panty liners, but they are specifically designed for incontinence with sophisticated leakage protection for urine. These products are sandwich-structured with an absorbent core comprising a blend of fiberized fluff pulp and SAP.116 The topsheet is a layer of PE or PP nonwovens or can be a mix of both. The back sheet is usually composed of a PE film or a nonwoven/film composite, which may be breathable. It prevents wetness transfer to the clothes. The product is fastened to the underwear by an adhesive strip on the back sheet, protected by release paper prior to use.

5.4.4

Products for adult incontinence

The absorbent product sector of the personal care industry related to adult incontinence contains the products such as adult diapers, adult pant diapers, twopiece insert items, personal/medical wipes, protective underwear, briefs, undergarments, guards, underpads and panty shields. The current product range is extensive and designed to meet the needs of people of all ages and both sexes. Additional protection can also be provided by products such as underpads. Adult diaper-making machines available in the market have production speeds of around 400–800 pieces per minute depending upon whether they are producing light or heavy incontinence products.


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Protective underwear There is a way to achieve effective adult incontinence protection without compromising dignity. Protective underwear is a stretchable, disposable low-profile undergarment that offers superior containment and fit. Less bulky and without the tapes or belts of traditional adult briefs and undergarments, it slips on and off just like ordinary underwear for easier, more dignified and discreet use. Adult brief with waistband The adult brief meets the need for the most demanding protection against urinary and fecal incontinence. Its SAPs lock in fluid for maximum absorption, aiding patient comfort and skin protection. The brief’s innovative design features a flexible waistband and six adjustable tape tabs that provide superior fit and security. The addition of a dryness strip promotes optimum skin care by keeping moisture in the brief and preventing it from coming back onto the skin. Underpads The underpad is designed in an extra-large size and offers maximum absorbency, making it ideal for overnight use. Its SAP gels fluid, pulling it away from the skin, and the strong waterproof PP backing protects against leakage. Its oversized 30 inch × 36 inch (76 cm × 91 cm) dimensions protect a larger area of the bed, reducing bedding changes and laundry costs.

5.5

Future trends

The engineering of improved levels of thermo-physical and tactile comfort in wearable hygiene materials is a further area of fundamental research. In terms of product developments, we are likely to see increased levels of absorbency performance and the use of thinner materials, resulting in higher levels of comfort as well as discretion.117 A future trend is in the use of bioactive fibers processed into nonwoven material by needlepunching or hydroentanglement. These are used in blends with synthetic fibers to prevent the cross-infection of diseases and to suppress the generation of unpleasant odors.118,119 Alloy fibers consisting of sodium carboxymethyl cellulose and regenerated cellulose may be used.120 Because of the promise of a growing market, in the future, there will be a lot more innovation in AIPs in fiber development and in nanotechnology with performance coatings such as inclusion of skin health additives and progress toward infection and bedsore control. One can foresee AIPs looking more and more like normal adult underwear. Recent developments in polymer technology including the availability of metallocene PP and alternative web-forming technologies, such as those of Ason



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Engineering, Ft Lauderdale, FL and Kobe, Tokyo, Japan that provide the capability to produce bicomponent and microdenier webs, can produce materials with better web formation, better softness and improved strength, allowing a reduction in web weight and consequently the possibility of a reduction in cost.

5.6


• M.D.VIOLA MACCHINE SRL, Via Lombardia 16/18 27010 Valle Salimbene (PV) – Italy. • DIATEC SRL, Strada Statale 151, Km. 13 – 65010 Collecorvino, Pescara, P. IVA 01813600689. • BICMA Hygiene Technologie GmbH/Basaltweg 3, D-56727 Mayen, Germany; PO Box: 1262, D-56702 Mayen, Germany • Caldiroli SRL, Via Giolitti, 19 - 21053 Castellanza (Varese) – Italy. • M/s. Fameccanica, Italy. • Rainbow Fame, Taiwan. • Sanimac Sanitary Products Machinery, Via Leonardo Da Vinci, n° 19 Zona Industriale Scopeti, 50068 Rufina (FI), Italy. Global technology and equipment suppliers for NHMs.

5.7

References

1 Arun N., ‘Technical Textiles and the challenges in India part 2: materials and method of manufacturing’, Synthetic Fibres, April/June 2001, 23–31. 2 Chakrabarty S., ‘Nonwoven textile – a good avenue for machinery development’, The Textile Magazine, May 2008, 86–92. 3 Walker I. V., ‘Nonwovens – the choice for the medical industry into the next millenium’, Asian Textile Journal, September 2001, 122–125. 4 Dharmadhikary R., ‘Application of nonwovens in medical fabrics and the Indian market potential’, Proceedings of seminar on nonwovens, 14–15 October, 2005, Department of Textile Technology, IIT New Delhi, 56. 5 Gupta B. S. and Smith D. K., ‘Nonwovens in absorbent materials’, P.K. Chatterjee and B.S. Gupta, Absorbent Technology, Elsevier Science, 2002, 349–386. 6 Hongu T., Phillips G. O. and Takigami M., New Millennium Fibers, Woodhead Publishing Limited, Cambridge, 2005. 7 Chatterjee P. K., ‘Products and technology perspective’, P. K. Chatterjee and B. S. Gupta, Absorbent Technology, Elsevier Science, 2002, 447–475. 8 Gupta B. S., ‘Fluid absorption in high bulk nonwovens’, P. K Chatterjee and B. S. Gupta, Absorbent Technology, Elsevier Science, 2002, 93–127. 9 Prescott B. A., Anand S. C., Richards A. F. and Halfpenny J. R., ‘Cotton-blend nonwoven fabrics for medical use’, Textile Asia, 2001, 45–48. 10 Gupta B. S. and Chatterjee P. K., ‘Measurement techniques for absorbent materials and products’, P. K. Chatterjee and B. S. Gupta, Absorbent Technology, Elsevier Science, 2002, 389–444.


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11 M² Polymer Technologies, Inc., Superabsorbent Polymer Fiber, Technical Absorbents Limited (TAL) Grimsby, North East Lincolnshire, UK, www.m2polymer.com. 12 Bardhan M. K., ‘Advantage and disadvantage growth of technical textiles in India’, Proceedings of 9th International and 63rd All India Textile Conference – Advantage India – Textiles and Apparels, The Textile Association (India), Ahmedabad, 5–6th January, 2008, 107–119. 13 Ghosh S., ‘Medical textiles’, The Indian Textile Journal, 2000, 10–14. 14 Watzl A. and Eisenacher J., ‘Spunlace process for cotton pads and other products’, Nonwovens Industrial Textiles, 3 August 2000, 16–18. 15 Groitzsch D., ‘Ultrafine Microfiber Spunbond for Hygiene and Medical Application’, EDANA 2000 Nonwovens Symposium. 16 Ward D. T., ‘Techtextil: World’s biggest technical textiles event’, Nonwoven Industrial Textiles, 3/2001, 37. 17 Pourdeyhimi B., ‘Nonwovens technology: implications for the nonwovens industry’, Textile World, Jan/Feb 2008, 49–55. 18 Sharma N. K., ‘Spunbonded nonwovens’, Proceedings of seminar on nonwovens, 14–15 October 2005, Department of Textile Technology, IIT New Delhi, 76. 19 Tarafder N., ‘The versatility of polypropylene fibres used in industrial textile – a review’, Man-made Textiles in India, May 2008, LI, 166–171. 20 Maggio R. and Guichon O., ‘A new spunbond technology for new products’, Nonwoven Industrial Textiles, 3/2001, 68. 21 Mahmud R. and Ramkumar S.S., ‘An update on meltblown technology’, Man-made Textiles in India, Sept. 2001, XLIV(9), 341. 22 Horrocks A. R. and Anand S. C., Handbook of Technical Textiles, Woodhead Publishing Limited; The Textile Institute, Cambridge, 2000. 23 Adanur S., Wellington Sears Handbook of Industrial Textiles, Technomic Publishing, Co. Inc., Lancaster, 1995. 24 Ward D. T., ‘Techtextil 2003: Machinery and fibre focus’, Industrial Fabrics Bulletin, 2/2003, 14. 25 Akalin M., Yuseloglu S.M., Gultekin B. C. and Agirgan A. O., ‘Novel approach to breathable non-woven hygienic products’, Proceedings of MEDTEX’03, Bolton Institute, Bolton, UK, July 7–9, 2003. 26 Bhat G., ‘Recent advances in scientific aspects of polymer laid nonwovens’, Proceedings of International Conference on High Performance Textiles and Apparels – HPTEX 2004, 7–9 July 2004, Kumaraguru College of Technology, Coimbatore – 641 006, India. 27 Kothari V. K., ‘Fibre applications in technical textiles’, Proceedings of International Conference on High Performance Textiles and Apparels – HPTEX 2004, 7–9 July 2004, Kumaraguru College of Technology, Coimbatore – 641 006, India. 28 Gulati T., ‘Polyester spunlaid nonwovens’, Proceedings of International Conference on High Performance Textiles and Apparels – HPTEX 2004, 7–9 July 2004, Kumaraguru College of Technology, Coimbatore – 641 006, India. 29 Reifeuhäuser Reicofil, ‘New nonwovens technology center online’, Chemical Fibers International, 2/2008, 78. 30 Fisher G., ‘Innovation keeps Reifeuhäuser on top in nonwovens machinery technology’, International Fiber Journal, February 2001, 42–25. 31 Teli M. D., ‘ Functional textiles and apparels’, Proceedings of 9th International and 63rd All India Textile Conference – Advantage India – Textiles and Apparels, The Textile Association (India), Ahmedabad, 5–6 January 2008, 120–135. 32 Rieter Perfojet, Z.A. Pré-Milliet-FR 38330 Montbonnot, France, rieter-perfojet.com.



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33 Anon., ‘Spunbond project: techno-economic executive digest’, Proceedings of National seminar on technical textiles an emerging business opportunity, Surat, India, 25 February 2004, 75–78. 34 Kavrie M., ‘Technical textiles: an emerging business opportunity’, Proceeding of national seminar on nonwoven fabrics: raw materials, production technologies and applications, The Institution of Engineers (India), Surat, September 2005, 25–39. 35 Naik D. V. and Shah K. C., ‘An introduction of nonwoven fabric world’, Proceedings of national seminar on nonwoven fabrics: raw materials, production technologies and applications’, The Institution of Engineers (India), Surat, September 2005, 60–66. 36 Maggio R. and Guichoni O., ‘PerfoBond: spunbond technology for new products’, Asian Textile Journal, June 2005, 25–26. 37 Leifield F., ‘Dry-lay process’, Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Process, W. Albrecht, H. Fuchs, W. Kittelmann (eds), WILEY-VCH, Weinheim, 2003, 141–236. 38 Hoffmeister R., ‘Polypropylene nonwovens – their manufacture and uses’, in Film, Woven, and Nonwoven Fabrics Made from Polypropylene, VDI-Verlay GmbH, Dusseldorf, 1979. 39 Anon., ‘Fibers fight back – fibers in nonwovens’, Nonwovens Industry, June 2005, www.non wovens-industry.com. 40 Hegde R. R., Dahiya A. and Kamath M. G., ‘Olefin fiber’, www.engr.utk.edu/use/ Textiles. 41 Kiekens P. and Zamfir M., ‘Non-wovens from cotton fibres for absorbent products obtained by the needle-punching’, Autex Research Journal, 2(4), December 2002. 42 Starr J. R., ‘Nonwovens in hygiene and medical applications’, Nonwovens Industrial Textiles, 3 August 2000, 8–9. 43 Reifenhäuser REICOFIL GmbH & Co. KGD-53850 Troisorf, Germany, www. reicofil.com. 44 Rigby A. J. and Anand S. C., ‘Medical textiles’, in Handbook of Technical Textiles, Woodhead Publishing Limited, Cambridge, 2000, 407–424. 45 Adanur S., ‘Medical textiles’, in Wellington Sears Handbook of Industrial Textiles, Technomic Publishing Company, 1995, 329–355. 46 Rakshit A., ‘New developments in polyester to meet global demands’, Proceedings of 9th International and 63rd All India Textile Conference – Advantage India – Textiles and Apparels, The Textile Association (India), Ahmedabad, 5–6 January 2008, 19– 28. 47 Pourmahammadi A., ‘Thermal bonded’, in S. J. Russell (ed.), Handbook of Nonwovens, Woodhead Publishing Limited, Cambridge, 2007, 298–329. 48 Dharmadhikary R. K., Gilmore T. F., Davis H. A., and Batra S. K., ‘Thermal bonding of nonwoven fabrics’, The Textile Institute, 1983. 49 Anon., Report of the expert committee on technical textiles, Vol. I, Office of Textile Commissioner, Government of India, Mumbai, July 2004. 50 Wubbe E., www.nonwovens-industry.com/articles/2003/05/feature2. 51 Danish Airlaid Technology A/S, Egeskowej 88700 Horsens, www.airlaidtech.com. 52 Dan-web, Bryggeryej 21, DK-8240 Risskoy, Aarhus, Denmark, www.dan-web.com. 53 Xuan J., ‘Airlaid technology and its material in China’, www.nonwovens-industry.com/ articles/2006/10. 54 Albrecht W., ‘Other raw materials’, in Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Process, W. Albrecht, H. Fuchs, W. Kittelmann (eds), WILEY-VCH, Weinheim, 2003, 87–118.


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55 Shin J. H. and Ahn Y. G., ‘Analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans in sanitary products of women’, Textile Research Journal, 77(8), 597–603. 56 Mclntyre J. E., Synthetic Fibres: Nylon, Polyester, Acrylic, Polyolefin, Woodhead Publishing Limited, Cambridge, 2005. 57 Rupp J., ‘Spunbond and meltblown nonwovens’, Textile World, May/June 2008, 38–40. 58 Bharani M. and Timble N. B., ‘Meltblown nonwovens an overview’, Asian Textile Journal, June 2005, 48–54. 59 Avgol Limited, 32 Habarzel St, PO Box.13281, Tel Aviv 61132, Israel 55, www.avgol.com. 60 Bhat G. S. and Malkan S. R., ‘Polymer-laid web formation’, S. J. Russell (ed.), Handbook of Nonwovens, Woodhead Publishing Limited, Cambridge, 2007, 143–200. 61 Pegas Nonwovens s.r.o, Prímetická 86, 669 04 Znojmo, www.pegasas.cz. 62 Anon., ‘Cotton core nonwovens’, Asian Textile Journal, June 2002, 23. 63 Thiry M. C., ‘Baby grows up’, AATCC Review, February 2008, 22–28. 64 Allgeuer T. T., Chang A. C., Claasen G.J., Doufas A. K., Knickerbocker E. N., Peng H., Pepper R. E. and Van Duan J. J., ‘Polypropylene based meltblown nonwoven layers and composite structures, Patent application title 8-21-2008, IPC8 Class:AD04H142F1, USPC Class:428219, www.faqs.org/patents. 65 Chapman R. A., ‘Chemical bonding’, S. J. Russell (ed.), Handbook of Nonwovens, Woodhead Publishing Limited, Cambridge, 2007, 330–400. 66 Synthetic fiber plants, The Neumag Catalogue, volume 4. 67 Watzl A., ‘Cost saving in production of hygiene, medical and wipes nonwovens’, Chemical Fibers International, 2 April 2006, 56, 127–129. 68 Watzl A., ‘Cost saving in production of hygiene, medical and wipes nonwovens’, Manmade Fiber Year Book, August, 2006, 105–107. 69 Leisen J., Schauss G., Stanley C. and Beckham H. W., ‘Magnetic resonance imaging applications in textile and fiber engineering: fabrics and diapers’, AATCC Review, May 2008, 32–36. 70 Watzl A. and Mayekar A. J., ‘Spunlaced and airlaid non-wovens for medical textiles’, Textile Magazine, October 2002, 73–80. 71 Adivarekar R. V., Kanoongo N. V. and Sabale A. G., ‘Super absorbent polymers in textiles’, Asian Textile Journal, June 2007, 31–38. 72 Duran K., ‘Nonwovens in hygiene applications’, Asian Dyer, June 2006, 37–39. 73 Personal Absorbent Products Council, Jack Murray, Executive Director, 1850 M Street, NW Suite 700, Washington, DC 20036–5810, www.superabsorbents.com. 74 Shanmugasundaram O. L., ‘Biopolymers in healthcare and medical applications’, Synthetic Fibres, July/September 2007, 13–17. 75 Aker P. and Heath R., ‘Superabsorbent fibres, the key to the next generation of medical products’, Proceedings of Medical Textiles 96, Bolton UK, Woodhead Publishing Limited, Cambridge, Cambridge, 1997. 76 Technical Absorbents Ltd, PO Box 24, Great Coates Grimsby DN31 2SS, UK, www.techabsorbents.com. 77 Arkema, 420, rue d’Estienne d’Orves, F-92705 Colombes Cedex, France, www.arkem.com. 78 Husmann S., ‘Functional finishing treatments for technical nonwovens’, Chemical Fibers International, 6 December 2007, 326–331. 79 Massey S. and Goel A., ‘Clothing hygiene: its effect on insulation and comfort properties’, Man-made Textiles in India, May 2008, LI, 172–175. 80 Ajmeri C. J. and Ajmeri J. R., ‘Medical textiles: extracorporeal devices’, Proceedings of International Conference on High Performance Textiles and Apparels – HPTEX 2004,



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7–9 July 2004, Kumaraguru College of Technology, Coimbatore – 641 006, India. 81 Timble N. B., ‘Nonwoven technologies and markets’, Proceedings of International Conference on High Performance Textiles and Apparels – HPTEX 2004, 7–9 July 2004, Kumaraguru College of Technology, Coimbatore – 641 006, India. 82 Marimuthu M., ‘Business opportunity for nonwovens and technical textiles in India’, Proceedings of 9th International and 63rd All India Textile Conference – Advantage India – Textiles and Apparels, The Textile Association (India), Ahmedabad, 5–6 January, 2008, 137–144. 83 Shishoo R., ‘Future developments in fibres, yarns and fabrics for technical applications’, Nonwovens Industrial Textiles, 3/2001, 24–28. 84 Jaipuria S., ‘Medical textiles: future is nonwoven’, Proceedings of national seminar on medical textiles: production technologies and applications, The Institution of Engineers (India), Surat, 14–24 October 2007. 85 Kadam S. C., ‘Nonwoven fabrics: raw materials, production processes/ technologies, product applications’, Proceedings of national seminar on nonwoven fabrics: raw materials, production technologies and applications, The Institution of Engineers (India), Surat, September 2005, 40–58. 86 Menezes E., ‘Nonwovens’, Nonwoven and Technical Textiles, January–March 2008, 33–38. 87 John R. Starr Inc., 5150 North Tamiami Trail, Newgate Tower, Suite 202, Naples, FL 34103, www.johnrstarr.com. 88 Moorthi P. M. and Shetty G. S., Nonwoven, Mahajan Publisher Private Ltd, Ahmedabad, 2005. 89 Anon., ‘Nonwovens in technical textiles’, Asian Textile Journal, April–June 2008, 31– 36. 90 Anon., ‘The Indian healthcare industry proving to be the pulse of the growing technical textile and nonwoven industry’, TechTex India, Oct–Dec. 2007, 1(1) 4–9. 91 Nadiger G. S. and Ghosh P. S., ‘An important technical textile segment medical textiles’, Asian Technical Textiles, January–March 2008, 34–35. 92 Anon., Report of the expert committee on technical textiles, Vol. II, Office of Textile Commissioner, Government of India, Mumbai, July 2004. 93 Massenaux G., ‘Introduction to nonwovens’, in Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Process, W. Albrecht, H. Fuchs, W. Kittelmann (eds), WILEY-VCH, Weinheim, 2003, 1–12. 94 Basu S. K., Naik S. R., Pancholi B. S. and Ghosh D., ‘Baby diapers: overview – marketing potential, raw material, manufacturing and properties’, Proceedings of national seminar on medical textiles: production technologies and applications, The Institution of Engineers (India), Surat, October 2007, 45–54. 95 Anon., ‘Incontinence (adult) diapers and baby diapers techno-economic executive digest’, Proceedings of national seminar on technical textiles: an emerging business opportunity, Surat, India, 25 February 2004, 67–69. 96 EDANA, European Disposables and Nonwovens Association, 157 Avenue Eugene Plasky, 1030 Brussels, Belgium, www.edana.org. 97 Pancholi B. S. and Naik S. R., ‘Baby diapers: cost economics, marketing potential’, The Indian Textile Journal, April 2008, 83–88. 98 DIATEC SRL, Strada Statale 151, Km. 13 – 65010 Collecorvino, Pescara, P. IVA 01813600689, www.diatec.it 99 BICMA Hygiene Technologie GmbH/Basaltweg 3, D-56727 Mayen, Germany, www.bhtbicma.com.


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100 Kazi G., ‘Medical textiles’, Proceedings of national seminar on medical textiles: production technologies and applications, The Institution of Engineers (India), Surat, October 2007, 37–44. 101 Cookson P., Wang X. and White B., ‘A case study in medical applications for textiles’, Textile Review, October 2007, 151–160. 102 Ajmeri C. J. and Ajmeri J. R., ‘Application of nonwovens in healthcare and hygiene sector’, in S. C. Anand, J. F. Kennedy, Dr M. Mriaftab, Dr S. Rajendra (eds), Medical Textiles and Biomaterials for Healthcare, Woodhead Publishing Limited, Cambridge, 2006, 80–89. 103 Purdy A. T., ‘Developments in nonwoven fabrics’, The Textile Institute, 1983. 104 Malik A., ‘Polymers and fibres in disposable medical product’, Asian Textile Journal, January 2001, 36–40. 105 Anon., ‘Chemical Finishing’, in Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Process, W. Albrecht, H. Fuchs, W. Kittelmann (eds), WILEY-VCH, Weinheim, 2003, 421–459. 106 Fahrbach E. et al., ‘Properties and end-uses of nonwoven bonded fabrics’, in Nonwoven Bonded Fabrics, J. Lunenschloss and W. Albrecht (eds), Ellis Horwood Limited, England, 1985. 107 INDA, Association of the Nonwoven Fabrics Industry, 1300 Crescent Green, Suite 135, PO Box 1288, Cary NC 27512 USA, www.inda.org. 108 TAPPI, Technical Association of the Pulp and Paper Industry, Technology Park, Atlanta, PO Box 105113, GA 30348, USA. 109 ANNA, All Nippon Nonwovens Association, Soto-Kanda, 6-Chome, Bldg 3F, 9-2, Chiyoda-Ku, Tokyo 101, Japan. 110 ASTM, American Society for Testing Materials, West Conshohocken, Pennsylvania, USA. 111 Cusick G. E. and Hopkins T., ‘Absorbent incontinence products’, The Textile Institute, 1990. 112 Stukenbrock K. H., ‘Mechanical finishing’, in Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Process, W. Albrecht, H. Fuchs and W. Kittelmann (eds), WILEY-VCH, Weinheim, 2003, 411–420. 113 Yokura H. and Niwa M., ‘Changes in disposable diaper properties caused by wetting’, Textile Research Journal, 70(2), 2000, 135–142. 114 Ajmeri J. R. and Ajmeri C. J., ‘Application of non-wovens in healthcare/hygiene sector’, The Textile Industry and Trade Journal, September–October, 2003, 69–72. 115 BASF Corporation Superabsorbents, www.functionalpolymers.basf.com. 116 Anon., ‘Super absorbent polymers’, Asian Textile Journal, May 2007, 72–74. 117 Attesby A., ‘Flow of incontinence products picks up as consumers warm to the idea of protection’, Nonwovens Industry, March 2007. 118 Rahbaran S., Redlinger S. and Einzmann M., ‘New bioactive cellulosic fibers’, Chemical Fibers International, 2, April 2006, 56, 98–102. 119 Rahbaran S., Redlinger S. and Einzmann M., ‘New bioactive cellulosic fibers’, Manmade Fiber Year Book, August, 2006, 25–29. 120 Stannett V. T., Fanta G. F., Doane W. M. and Chatterjee P. K., ‘Polymer grafted cellulose and starch’, P. K.Chatterjee and B. S.Gupta (eds), Absorbent Technology, Elsevier Science, 2002, 323–344.


6 Nonwovens for consumer and industrial wipes D. Z H A N G, Textile Research Associates, USA

Abstract: Nonwoven wipes are becoming a key player in the nonwovens industry; 15% of all nonwovens produced are intended for wipes. This chapter looks at technology, the end-use sector and the nonwoven wipes market by region and country from 2001, examining trends for growth and forecasting growth to 2011. It analyses the current and projected sales of nonwoven wipes and provides up-to-date details about key marketers of these products. The chapter also spotlights new products and cutting-edge technology, and highlights trends and marketing opportunities within the nonwoven wipes industry. Key words: nonwovens, consumer wipes, industrial wipes, market, technology.

6.1

Introduction

The nonwoven wipes market has changed dramatically in the last few years as seen in recent studies on the development of nonwoven wipes1 and the future of global markets for nonwoven wipes to 2011.2 The nonwoven wipes industry as a whole has experienced explosive growth for a decade, the market having increased from about US$2 billion in 1997 to about US$8.7 billion in 2007.3 It is estimated that it will be worth over US$12 billion by 2011.2 The nonwoven wipes market was about US$6.33 billion in 2001; the market has been increased with a compound annual growth rate (CAGR) of 6.66% to 2006 and will be increased with a CAGR of 6.63% to $12 billion in 2011. Innovative design, strategic product placement and continuous new product development are all keys to future profitability. The field is dominated by major producers of nonwovens, especially in well-known brands, although private label producers are taking a growing share of the market. Nonwoven wipes (excluding paper wipes) are divided into two categories: consumer wipes and industrial wipes. Consumer wipes include baby wipes, personal care wipes and household cleaning wipes. Industrial wipes include food service wipes, industrial general wipes, industrial speciality wipes and medical wipes. Baby wipes used to be the leader in the market a couple of years ago, but now household cleaning wipes have taken over. Flushable and biodegradable wipes are the main focus for the wipes industry because of their convenience, ease 103 © Woodhead Publishing Limited, 2010

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of use, and reduced impact on the environment. This requires environmentally friendly and cost-effective raw materials. Airlaid, spunlaid and the combined versions of these technologies, airlaced technology, have been the key processing techniques for nonwoven wipes. Consumer needs and emerging markets are driving product growth. North America and Western Europe have recently seen single digit growth and will probably continue to do so for the next few years, while developing regions such as China and India, Eastern Europe and countries in South America, have seen double digit growth in some categories. This is due to their fast growing economies and to the expansion of the middle class in these countries. Consumer wipes are becoming the dominant sector in nonwoven wipes and these will become more sophisticated and widely used as discussed in a recent review of the development of nonwovens for personal care products.4 As about 15% of nonwoven production is converted to wipes, manufacturers are focusing not only on reducing the cost, but also on marketing to advise consumers how to utilise the wipes effectively in their daily lives where their use is widespread: from babies to adults; from bathroom to kitchen; from supermarket to restaurant; from home to office; in the car or on the go…

6.2

Key drivers and trends

The factors driving the sale of nonwoven wipes are price and value, functionality, convenience, ease of use, disposability, time saving, safety and regulatory aspects. Nonwoven wipes are evolving in all these areas. Numerous product launches have led to a diverse and competitive marketplace throughout the full range of wipes. Cutting edge technologies such as airlacing, and product innovations such as antimicrobial and antibacterial wipes5 have made a significant impact upon the industry, maintaining the momentum of rapid growth. This consumer driven market is now an US$8.7 billion industry that is set to grow to over US$12 billion by 2011.2 Over 563,267 metric tonnes of nonwovens were used for consumer and industry wipes in 2006. Consumer wipes constituted 80% of the output, and industrial wipes 20%, as shown in Fig. 6.1. As consumers prefer a soft texture in wipes for use on the skin, spunlace and airlaid are about 73% of the total nonwovens used for wipes, of which around 43% are spunlace. These processes use natural fibres and the resultant softness of the wipes is the main reason for the rapid growth of these technologies during recent years. The new technology has enabled the industry to achieve high quality, high productivity and targeted applications at a low cost. Airlaced technology in particular has allowed the use of wood-pulp (a low cost raw material) in nonwoven wipes. Together with synthetics, it produces superior absorbency and softness and enables a one-step process for the manufacture of textile-like nonwoven wipes. This niche material is particularly suitable for baby wipes and personal care wipes. Household cleaning wipes have the highest growth rate and the largest segment among consumer wipes



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Industrial wipes 20%

Consumer wipes 80%

6.1 Market shares of consumer and industrial wipes 2007. Source: Zhang, 2006 (ref. 1). Baby 39%

Household 40%

Personal 21%

6.2 Market shares of different consumer wipes 2007. Source: Zhang, 2006 (ref. 1).

(as shown in Fig. 6.2), because they offer consumers convenience in household cleaning. Functionality such as removing dust or absorbing liquids, delivering liquids, wax, or mild abrasives are factors in consumer product selection. The use of nonwoven wipes in the multi-purpose, household cleaning and personal care sector is on the rise and clearly presents the greatest opportunities for growth. Consumers want time-saving products that offer ease of use, high performance, hygiene benefits and an improved quality of life. Manufacturers continue to seek new specialised areas where nonwovens may be used, especially flushable and biodegradable wipes for bathroom and toilet cleaning. New products are incorporating innovations in scent, ingredients, colours and sizing to meet consumer needs, especially for wet wipes that may be used during travel. New wipe products have utilised plant extracts, lotion, oils, and other moisturisers, as well as varied scents, for the baby wipe and personal care markets. Household cleaning products impregnated with soaps, waxes, deodorisers and recently, antimicrobials will continue to gather strength in the marketplace.


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Antimicrobials and medications have been incorporated into health care wipes. The need to make wipes more environmentally friendly has given increased importance to flushability and biodegradability in the personal care wipes industry. Nonwoven wipes have also become more desirable for emergency rescue teams and clean-up crews, especially in the recovery operations that follow natural disasters. Growth is also driven by these key factors: • For baby wipes: a continued increase in the number of wipes used per nappy change in the already developed markets, and their growing use in emerging markets. • For industrial wipes: continuing replacement of cloth by advanced technology nonwovens (dry and pre-moistened) in general purpose industrial, food service, clean-room and controlled environments, surface preparation, printing and other uses. • For consumer wipes: increased consumer acceptance of new personal care and household cleaning products. The mature market regions of North America and Western Europe, which account for the lion’s share of global wipes sales, are likely to see even further diversification of products. Driven by convenience, demand, increased segmentation and competition among brands, wipes will continue to appeal strongly to cash-rich, time-poor consumers in a number of developed markets. Other geographical areas, most notably Asia, Eastern Europe and South America are set to follow suit, as higher disposable incomes and an inevitable process of westernisation increasingly influence consumer lifestyles. The top five players in nonwoven wipes are Procter & Gamble Co. (P&G), Kimberly-Clark Corp., Kao Corp. (Kao), Johnson & Johnson Inc. (J&J) and SC Johnson & Son Inc. (SCJS). As shown in Fig. 6.3, these top five companies took about 46% of the market in nonwoven wipes sale in 2006. Private label companies took about 15%. Nonwoven wipes offer end-users greater absorbency, versatility, uniformity and durability when compared with traditional wiping materials. Any type of nonwoven roll goods, regardless of the manufacturing technology, could be perceived and used as a wipe if cut into a small square. This has been a blessing for the nonwoven wipes industry. Because nonwovens may easily enter the wipes market in this way, nonwoven wipes of carded, airlaid, thermally bonded, chemical bonded, especially spunlaced and spunlaid material, have become a multi-billion dollar market at the end product level in the world today. Any company with cutting capabilities and access to excess capacity believes it can create a product. Growth in the wipes industry is strong, with many nonwoven wipe producers eyeing niches currently filled by traditional textile products or scrap materials. Nonwovens bring the key factor of consistent quality to the wipes segment. In many cases in the industrial arena, nonwoven wipes have supplanted scrap textile



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21%

.. . ... .. ...... .......... ... ........ .. ... ..... . . . . . . . .. ..... .. . . .. ......... .. . .

55%

4%

4%

11%

5%

Procter & Gamble Co.

... ..

Kimberly-Clark Corp. Kao Corp. Johnson & Johnson Inc. SC Johnson & Son Inc. Other

6.3 Market shares of top five nonwoven wipes companies in 2006. Source: Zhang, 2006 (ref. 1).

materials for cleaning purposes because of their reliability. Price is another major issue. Industrial customers are looking for the lowest cost product to perform the required job. Nonwoven wipes offer many advantages for most applications and needs in industry because they outperform scrap materials on quality and are more cost-effective than woven and knitted fabrics. Disposable wipes provide better economy, higher convenience, lower risk of cross-contamination and a consistently high level of quality. In summary, they help to save money and to increase productivity. To meet consumer demand, wipes must be low cost, disposable (to prevent cross-contamination) and convenient, but without any sacrifice of quality. This is not an easy task and some consumer goods companies are more successful than others. Task-specific wipes have provided great opportunities for brand owners and large retailers, such as supermarkets, to develop their own low cost range. Future trends include user-friendly and convenient packaging, new fragrances, varied wet wipe lotions and products designed to meet specific needs (such as feminine hygiene wipes). It is predicted that wet wipes for cars, purses, backpacks and lunch boxes will benefit from an increasingly hygiene-conscious society, especially during the flu season. In terms of technologies, many companies are keeping a watchful eye on the growth of spunlace products, particularly for baby wipes, due to the softness of the webs. Flushability and biodegradability are expected to remain key issues for the nonwoven wipes industry. Antimicrobial wipes are also being developed to meet market needs. Possible ‘smart’ wipes are also being considered, into which indicator patches are incorporated, and wipes that change shape and absorbency according to the type and volume of liquid they absorb.


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Consumers are cost-conscious and are expected to become even more so as the personal care wipe market matures and usage expands throughout the population. While consumers continue to search for the right combination of quality and price, producers must respond with products that exceed these demands. Wipe products need to strike the right balance between functionality and cost if they are to be successful in the market. Price alone will not build the market or meet the consumer’s expectations of functionality and quality. For the future, one thing is sure: as quality continues to rise, producers will be able to protect their niche markets even more effectively. Wipe producers are introducing value-added products that are harder for competitors to imitate and will be more profitable. Wipes will continue to expand into segments where they were not previously used. For example, they will offer strong competition in paper towels, woven janitorial supplies and bottled lotions.

6.3

Nonwoven wipes technology

The main technologies used to produce nonwoven wipes are spunlace, airlaid and their combination (airlace). Other technologies include drylaid, wetlaid, spunbond, meltblown, CoForm and their combinations. The raw materials used include, but are not limited to, synthetic fibres such as poly(ethylene terephthalate) (PET), polypropylene (PP), and rayon; natural cellulose fibres such as wood pulp and cotton, and speciality materials such as bi-component fibres and nanofibres.

6.3.1

Spunlace

Fundamentally, spunlace is a nonwoven web bonding process. The web can be formed by drylaid (carded), wetlaid, or a combination of both with airlaid, which is called airlace. Spunlacing (hydroentanglement or hydraulic needling) is a process of entangling a nonwoven web of loose fibres on a porous belt or forming wire, producing a sheet structure by subjecting the fibres to multiple rows of fine, high-pressure water jets. Spunlace has become a leading choice for wipes manufacturers due to its costefficiency, durability and textile-like feel. The global output of spunlaced nonwovens totalled more than 400,000 metric tonnes in 2007.3 Over 60% of spunlaced webs are converted to wipes. The growth of this technology during the past decade has been in the double-digit range. Considerable capacity has been added in emerging market regions including China, South America, and Eastern Europe. These production lines are all modern systems installed to supply the nonwoven wipes markets. Major producers of spunlace are DuPont, PGI, Ahlstrom, Jacon Holm and Spuntech. The leading wipes producer P&G has switched its Pampers range of baby products from airlaid to spunlace. Most wipe producers, including private label companies, now use spunlace for baby wipes and personal care wipes.



6.3.2

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Airlaid

Airlaid is a web formation process. Airlaying (airforming) is a method of forming a web by mixing fibres with air to form a uniform air–fibre mixture that is then deposited on a moving air-permeable belt or wire. Webs produced in this way can be bonded using latex bonding (LBAL), thermally bondable fibres (TBAL), a combination of the two (MBAL) or high pressure bonding (HBAL) such as hydroentanglement. The term airlace refers to the process of hydroentangling airlaid webs. Airlaid wipes provide an efficient carrier for the effective and economical application of a variety of active ingredients. Throughout the technology’s history, it has been successfully used for a number of wiping applications. Airlaid pulp technology showed a remarkable growth during the 1990s. The technology’s worldwide growth in tonnage has averaged 12% per year during the past decade. The output of global airlaid nonwovens totalled more than 420,000 metric tonnes in 2006.3 Over 40% of the webs are converted to wipes. Dan-Web and M&J Fibretech are two major air former manufacturers. Major airlaid nonwoven producers include Buckeye Technologies, Concert Industries, Georgia-Pacific Nonwovens, Rexcell (Duni), McAirlaid, Oji and BBA. The growth of this technology will continue to be propelled by the expanding use of airlaid pulp materials in wipes and by regulation regarding flushability of the wipes. Airlaid technology generally differs from other drylaid webs in its use of very short fibres, (mainly wood pulp). As a result, most products obtained through this method offer high absorbency, are inexpensive and biodegradable. When the latex used as bonding material in airlaid webs is dissolved in water, the web becomes dispersible and flushable.

6.3.3

Drylaid

The drylaid web forming process is referred here to as carding: a web forming process that separates small tufts into individual fibres, to begin the process of parallelisation, and delivers the fibres in the form of a web. Carded nonwoven fabrics are made from a variety of fibres, including rayon and polyester, with fibre lengths ranging from 1.2 cm to 20 cm. Webs produced in this manner are bonded by thermal, mechanical, chemical and stitching methods, which do not include spunlacing. Airlaid and spunlaced webs are not included in this category.

6.3.4

Needlepunched

Needlepunching is a web bonding process that creates nonwovens by mechanically orienting and interlocking the fibres of a spunbonded or carded web. This mechanical interlocking is achieved by thousands of barbed felting needles repeatedly passing into and out of the web. The fibres may be natural or synthetic.


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The main product driving the growth of this technology are packaged wipes used for patient care in hospitals and long term care facilities.

6.3.5

Spunlaid

Here spunlaid refers to meltblown, spunbond and their combinations. It is a web forming process in which molten polymers are extruded and laid down to form webs. Normally, meltblown webs are self bonded due to the hot quenching air and the short distance between die and collecting device. Spunbond webs are thermally bonded, although they may also be chemically or mechanically bonded.

6.3.6

Other processes

Other web forming processes include wetlaid and CoForm. In the wetlaid process, the formation of the precursor web for entanglement is best achieved by using wetformed nonwoven systems. Fibres are dispersed in water at very high dilution and then deposited on a screen to separate water from the fibres. Hence, uniform, almost perfectly isotropic sheet structures for hydroentangling, can be produced by wet-forming systems. These systems are fast and efficient compared with other web forming technologies. Several bonding technologies may be applied to wetlaid webs. For flushable wipes, hydrogen bonding produces minimal wet strength so the webs are dispersible in water. However, the stiff structure produced by hydrogen bonded webs is not ideal for personal wipes. For latex bonded wetlaid webs, wipes will be dispersible and flushable if the latex binder can be dissolved in water. Wetlaid nonwoven wipes are used for a wide variety of different applications, especially in the hygiene market and in disposable nonwovens for medical and surgical purposes. They can be used for wet wipes for spectacles, wet toilet wipes, dental wipes, disinfection wipes, perfumed wipes, cleaning wipes and many more. CoForm is a proprietary technology from Kimberly-Clark in which fluffed wood pulp is introduced into a meltblown stream of polypropylene fibres. The result is a soft, moderately strong entanglement of the two fibres. Most of this CoForm nonwoven material is used in the production of wipes. The product is also used in feminine hygiene and medical products. About 80–85% of KimberlyClark wipes material is used to make Huggies baby wipes and some of the output is used in their Splash ‘n Go personal wipes. Their product is also used by SC Johnson’s Pledge wet floor wipe product.

6.4

End-user applications of nonwoven wipes

Nonwoven wipes are divided into two categories: consumer wipes and industrial wipes. Consumer wipes include baby wipes, personal care wipes, and household cleaning wipes. Industrial wipes are disposable nonwoven products used for a



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variety of applications in industry and commercial institutions, including food service wipes, industrial general wipes, industrial speciality wipes and medical wipes. Baby wipes were the dominant product in the consumer market in the 1980s. Innovative producers were creative in expanding the concept of baby wipes to include other uses, for example impregnated wipes for areas such as cleaning surfaces, cleansing hands, cosmetics, and other personal care uses. With the rapid growth of new wipes available to the consumer, there is no longer a need to use one (baby) wipe for many applications. Baby wipes do not clean stains or surfaces as effectively as wipes made and designed specifically for those purposes. The increasing popularity of speciality wipes for specific applications has brought about a decline in baby wipes, which at one time were used for everything from adult hygiene to cleaning leather car seats. The addition of new products such as household cleaning wipes and feminine hygiene wipes has given consumers a choice of products specifically designed for their needs. Personal care wipes encompass anything that touches human skin, including antibacterial wipes, acne medication pads, alcohol prep pads, deodorant and refreshment wipes, eye pads, feminine hygiene wipes, general clean-up wipes, haemorrhoid wipes, incontinence wipes, make-up remover wipes, wet and dry wipes, moist flushable wipes, wound wipes and more. Household cleaning wipes may be wet or dry and are used for surface cleaning including automotive care wipes, computer wipes, disinfectants wipes, dry cleaning wipes, furniture polish wipes, glass cleaners, household cleaners, jewellery wipes, paint removal wipes, pet wipes, silver and brass cleaners, dish-washing wipes, stain remover wipes, and tough task wipes for the removal of soiling. These nonwoven wipes are easy to use, disposable, convenient, cost-effective and customised for specific applications. The most important use for disposable wipes is the prevention of cross-contamination.

6.4.1 Baby wipes These are products that make contact with babies’ skin for care purposes such as cleaning and applying lotions. In this chapter, baby wipes include those for toddlers and children and are listed as one category in the consumer wipes sector. The overall demand for this category has been driven by parents who appreciate the portability of the product and the convenience of being able to clean their children where conventional facilities may not be available. Baby wipes are versatile and may be used in a variety of locations, for example, in the car or at day care, so minimising the nuisance of cleaning up after meals and snacks.

6.4.2

Personal care wipes

Personal care wipes are those that touch human skin for cleaning, cosmetic and


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personal care purposes including adult care wipes, facial cleaning and make-up wipes, feminine care wipes and some wet wipes. In this chapter, personal care wipes excludes baby wipes, toddler wipes and wipes for children. This category is too large to be included in personal care wipes and is discussed above as one category in consumer wipes. Innovative producers have become quite creative in expanding the concept of baby wipes to include other applications, such as impregnated wipes for cleaning surfaces, cleansing hands, cosmetics, and other personal care uses. Adult care wipes Adult care wipes are designed to be used by those suffering from incontinence. A typical product in this segment are CVS’s Incontinence Wipes. They are produced from spunlaced or airlaid pulp nonwovens, with the exception of KimberlyClark’s product, which is made by their proprietary CoForm technology. In 2002, Codi International in Veenendaal, The Netherlands, invested in higher speed machinery with the capability to produce larger sized wet wipes for use in the incontinence market. The company produces private-label adult incontinence products. Facial cleaning/makeup wipes Facial cleaning wipes are specifically designed to carry cleansing creams for the face with specific ingredients to help in the removal of make-up, exfoliation of dead skin and improvement in the health, look and feel of facial skin. This is a fast growing sector in personal care wipes. These wipes are available in either a premoistened form or as a dry wipe that is activated by immersion in water. The pre-moistened product is the more popular format and outsells the dry format by a ratio of three to two. Personal care and cosmetics wipes mainly utilise cotton, rayon, wood pulp, cotton linters, synthetic fibres and blends of fibres. Feminine care wipes Feminine care wipes are designed to be used mainly by women during their menstrual periods as well as by women with mild incontinence that can be caused by pregnancy, menstruation or increasing age. (They are not for adult incontinence, which is discussed in the adult care wipes section.) As women have been slow in accepting these products, this is a relatively small sector, having only about 6% of the market share in personal care wipes. One reason for the slow acceptance of this product is advice from doctors and skincare specialists warning women about the dangers of cleaning with feminine care wipes and similar products. With age, there are fewer glands secreting oil and lubricating the skin. This is especially true in the perineal area where the skin may be affected by clothing, wiping and



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frequent washing. Menstruation and incontinence heighten skin irritation due to repeated washing and the wearing of pads or other protection. Specialists recommend washing with plain water to remove urine, as washing with a warm soapy solution will remove the natural oils that provide protection for the skin. Wipes designed for feminine care should therefore have a simple, non-irritant formula and be alcohol free. The product could be medicated with some type of skin lubricant, like aloe, to provide a moisture barrier.

6.4.3

Household cleaning wipes

Household cleaning wipes include wet floor wipes, general cleaning wipes and furniture polishing wipes. Household cleaning is a broad segment including many products from kitchen and bathroom to automobile cleaning and maintenance, computer cleaning, furniture waxing and polishing. In developed regions, household cleaning is now the largest consumer segment in the wipes industry and did not exist 10 years ago. The growth of this segment was driven by the introduction of new categories of wipes, including all-purpose cleaning and disinfecting wipes, wet and dry floor cleaning products and polishing wipes. Wet floor products Wet wipes are continuing to dominate the household cleaning market with manufacturers competing to meet the latest consumer demands for a product that will take on every household chore. It has seen wide diversification in the market, particularly in floor wipes, as hard floor surfaces grow in popularity. Wet floor wipes achieved the highest market share in 2006, at 44%, for a single category in household cleaning wipes, as shown in Fig. 6.4.

8%

Furniture Wet floor Cleaning

48% 44%

6.4 Market shares of wipes in the household cleaning sector.


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Cleaning wipes General cleaning wipes include hard surface disinfecting wipes, electrostatic floor wipes and dry wipes/mop heads. The largest household cleaning sector is that of disinfecting and hard surface wipes, which are referred to as all purpose cleaning and disinfecting or hard surface products. These products, made from nonwovens, are designed for the quick cleaning of kitchen and bathroom surfaces, as well as for sink handles, toilet areas, refrigerator handles, door knobs, cupboards, telephones, the interior of microwaves, computer keys, toys, and so on. Furniture polishing wipes SC Johnson’s Pledge is the leading brand of furniture polish. The product is a wipe pre-moistened with a polishing compound similar to the conventional formulation in the spray cans. This disposable wipe product is available in a soft pack, orange or lemon scented, with 10 wipes per package. Other furniture-related wipes are available in canisters from Old English by Reckett Benckiser; Orange Glo by Orange Glo International; and Leather Wipes by Weiman. SC Johnson’s Pledge is the brand leader with at least half the market.

6.4.4

End-user applications for industrial wipes

Industrial wipes are disposable nonwoven products used for a variety of applications in industry and institutions. These include food service wipes, industrial general wipes, industrial speciality wipes and medical wipes. Different nonwoven processes and technologies are used to produce specific properties in industrial wipes, thus enabling a suitable nonwoven product for every industrial requirement. Industrial wipes overlap with other major wiping segments as some of the same wipes are used for both consumer and industrial applications. Segments include: factory and shop cleaning; maintenance repair operations; janitorial commercial cleaning; food service; automotive, military, aerospace; and spill control absorbent mats. Task applications include general and surface cleaning, skin cleansing, tough task cleaning, scrubbing, dusting and electrostatic, critical task controlled environment, polishing and glass cleaning. Wipes for food service Wipes for food service are mainly used in restaurants, including fast food outlets, from food preparation areas to dining areas, service counters and tables. This is a relatively small market, having a 12% share of the industrial wipes sector. According to the Centers for Disease Control (CDC) up to 81 million cases of food-borne diseases occur in the US each year, 6.5 million of which are serious enough to be reported to the CDC. Dirty towels or rags have been identified as a



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major factor in the spread of bacteria from food preparation areas to dining areas. This led Atlantic Mills, Lakewood, NJ to introduce Kerri Klean Microbe Guard with the AEGIS Microbe Shield to prevent the growth and transfer of microorganisms in towels, and Simple Solutions, a pretreated, water activated all-surface sanitising wipe for food preparation surfaces. Industrial general wipes Industrial general wipes include general and surface cleaning, skin cleansing, heavy-duty cleaning, scrubbing, dusting and electrostatic, controlled-environment cleaning (e.g. in clean rooms for pharmaceutical manufacture), polishing and glass cleaning. They may be used for removing corrosion on steel parts, polishing cutlery or pots and pans, cleaning steel and aluminium, imparting decorative finish on stainless steel, removing weld marks, reducing scratches and marks, removing paint from boats and the de-burring of industrial moulds. They are also used in factory and shop cleaning, maintenance repair operations, janitorial commercial cleaning, automotive, military aerospace, and spill control absorbent mats. Industrial speciality wipes The main end markets for industrial speciality wipers are: clean rooms, the photography and printing industries, and the auto and aerospace industries (also referred to as transportation), or the preparation of surfaces before applying paint. The common feature of these speciality markets is the requirement for wipes to be non-linting to prevent microscopic particles from contaminating the product. At 14%, industrial speciality wipes have a similar market share to food service wipes. Medical wipes Medical wipes, which include hard surface antibacterial, bathing and incontinence wipes, are designed for use in hospital and health care facilities. Medical wipes have a market share of 27%. The wipes need to register with the Environmental Protection Agency (EPA) as suitable for antimicrobial use in the US. There is a significant medical market in germicidal or antibacterial disposable wipes for use in hospitals and health care facilities, where controlling cross-contamination is essential. These wipes are impregnated with chemicals that destroy a variety of micro-organisms. Products such as PDI’s Super Sani-Cloth are available in a variety of sizes to clean gurneys and trolleys, counters, carts, bed rails, door handles, etc.

6.5

Regional development of nonwoven wipes

The market for nonwoven wipes is consumer driven and there is a widespread


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international need for the convenience and ease of use that they offer. However, due to unequal economic and technological developments around the world, the development of nonwoven wipes differs in terms of the amount, type and quality of wipes used, and therefore of growth in the sector. Developed regions such as Western Europe and North America show high retail sales amounting to several billion US dollars. These two regions together represent over 70% of the world’s consumption of nonwoven wipes. But growth over the next five years is likely to be in single digits for these regions. Developing regions in Eastern Europe, South America and Asia will show low retail sales but very high annual growth rates over the next few years.

6.5.1

Development of nonwoven wipes in Western Europe

Western Europe has been the leading market for nonwoven wipes since 2002 and is expected to continue to lead in this area for the next few years, although the growth rate will be low. The big five, UK, Germany, France, Italy and Spain, are about 80% of the market. Baby wipes led sales up to 2005. Over the same period, household wipes led in only 5% of markets, with baby wipes in second position, although estimated to be comparable with household wipes. Consumer wipes were about 80% of the market share and industrial wipes around 20%.

6.5.2

Development of nonwoven wipes in Eastern Europe

The accession of European countries to the European Union, coupled with rising incomes in many of these countries and their proximity to Western Europe, has created commercial opportunities in the region. On the end-user side of the wipes business, a crowded field of product manufacturers exists in Eastern Europe with small, regional players capturing some market share in most countries. However, large multinationals such as US-based Kimberly-Clark, P&G and their European counterparts, Hartmann AG, SCA Hygiene and Ontex, are working hard to gain market share. When the EU changes become effective, these markets will provide unique opportunities for increased sales as these nonwoven product companies and others like them recognise just how important Eastern Europe will be in the future, due to its highly skilled, low-cost labour base and a population with a growing desire for western consumer goods.

6.5.3

Development of nonwoven wipes in North America

North America is one of the leading markets for nonwoven wipes and is comparable with Western Europe. Baby wipes took first place in sales until 2003. Household wipes now lead consumer wipes, taking 39% more of the market than baby wipes. It is estimated that household cleaning wipes will continue to



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lead the sector. Sales of these products increased by about 90% between 2001 and 2006, personal wipes by about 67.5% and industrial wipes by around 34% over the same period. In North America, sales of nonwoven wipes increased over 47% from 2001 to 2006 with consumer wipes taking about 80% of the market and industrial wipes about 20%. Household cleaning wipes reached the US$1 billion mark in 2004. Major brands account for over 50% of the wipes market. The category is dominated by P&G with such products as Pampers, Olay, and Swiffer, and Kimberly-Clark with its Huggies brand. J&J, Kao, and The Clorox Company follow. Other major brands include Pledge (SC Johnson), Lysol (Reckitt Benckiser), and Ponds (Unilever). Private label products account for almost 15%. The North American sales of industrial wipes to end-users approached US$3.6 billion in 2006, consuming 2.7 billion square metres of nonwoven materials, almost triple the volume consumed a decade earlier. The use of spunlaced material now exceeds that of airlaid pulp. However, there are developments within the industry that could put airlaid pulp back into the top spot. Baby wipes have historically been the largest consumer segment but household wipes are now the leading product segment, accounting for 45% of the sales of consumer wipes. The top 10 brand baby wipes in 2005 were Huggies Natural Care, Pampers Natural Aloe Touch, Huggies, Pampers Sensitive, Huggies Supreme Care, Pampers Kandoo, Pampers Original Cotton Care, Huggies Pull Ups, Huggies Newborn, and Huggies Supreme.

6.5.4

Development of nonwoven wipes in South America

Among the consumer wipes sector in South America, pre-moistened baby wipes take almost 80% of the market. Pre-moistened personal, household and dry wipes make up the remaining 20%. Canister baby wipes dominate the market as they are predominantly manufactured within the region. These have a significant cost advantage over tub-packaged wipes, which are mostly imported and therefore carry substantial transport costs, duty rates, local distribution costs and markups. South American producers of baby wipes generally use carded thermally bonded polypropylene nonwoven substrate. Small quantities of spunlaced and airlaid pulp nonwovens are imported in roll goods form and converted into wipes. These wipes are sold at a premium due to the higher material costs. Currently, there are no known domestic producers of baby wipes packaged in tubs. Baby wipes in tubs are all imported, primarily from North America, Europe and Israel. There are now many companies producing pop-up canisters of baby wipes. The larger suppliers are Kimberly-Clark, J&J and P&G, all of which manufacture regionally. The production centres for baby wipes are: J&J in Argentina and Brazil, Kimberly-Clark in Brazil and P&G in Brazil.


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6.5.5


Development of nonwoven wipes in Asia

Asia is the third largest region for the consumption of nonwoven wipes. Sales increased over 20% between 2001 and 2006 with consumer wipes accounting for about 80% and industrial wipes for about 20%. This region has shown uneven development in nonwoven wipes. Japan is becoming a mature market, though with low growth predicted over the next five years. However, high growth is expected in India and particularly in China, as its national economy has been growing in recent years. China accounts for nearly half the output of nonwovens in the AsiaPacific region and it is estimated that the industry will grow 12% per year during the next few years. During the past 10 years, output in China has increased more than five-fold, from 115,000 to 650,000 metric tonnes. With a population of nearly 1.4 billion, this massive consumer market could prove the ideal location for converters of nonwoven materials, such as producers of nappies and wipes, to grow their businesses in the twenty-first century.

6.6

Definitions

Airlaid: web forming process that disperses fibres into a fast moving air stream and condenses them onto a moving screen by means of pressure or a vacuum. Biodegradability: the capacity of a consumer product to biodegrade. Biodegradable: the breakdown of the organic components of a consumer product into simple components such as carbon dioxide (CO2), methane (CH4) and water (H2O). CAGR: compound annual growth rate. Carding: a process for making fibrous webs in which the fibres are aligned either parallel or randomly in the direction in which the carding machine produces the web. CDC: Centers for Disease Control (USA). EDANA: European Disposables and Nonwovens Association. EPA: the US Environmental Protection Agency. Flushability: the capacity of a consumer product to be flushable. Flushable: for a product to be defined as flushable it must: (a) pass through toilets and properly maintained drainage pipe systems under normal conditions for usage of the product; (b) be compatible with existing waste-water conveyance, treatment, re-usage and disposal systems; and (c) break down completely within a reasonable period of time and be safe in the natural environment.6 Hydroentangling, or spunlacing: bonds a web of fibres lying on a conveyor belt using fine, high-pressure speed jets of water. After passing through the sheet, these jets rebound from the threads of the conveyor belt. This combination of direct and reflected jets creates an intense agitation inside the sheet, entangling the fibres and increasing fibre-to-fibre interaction. INDA: the Association of the Nonwovens Fabric Industry (North America).



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Latex bonding: the use of an adhesive to bond the fibres of a web together. Meltblown: molten polymer resins are heated, extruded, and drawn with high velocity air to form fine filaments. The filaments are cooled and collected as a web on a moving screen. Needlepunched: mechanically binding a web to form a fabric by penetrating the web with an array of barbed needles that carry tufts of the web’s own fibres in a vertical direction through the web. Nonwoven: a manufactured sheet, web or batt of directionally or randomly orientated fibres, bonded by friction, and/or cohesion and/or adhesion. This excludes paper and products that are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments, or felted by wet-milling, whether or not additionally needled. The fibres may be natural or of man-made origin. They may be staple or continuous filaments or may be formed in situ. Rayon: man-made textile fibres and filaments composed of regenerated cellulose. Also called viscose or viscose rayon. Spunbond: filaments are extruded, drawn, laid on a moving screen and bonded to form a web. Spunbond/meltblown/spunbond (SMS): a web formed by layered webs of spunbond, meltblown, and spunbond processing. Spunlace: see hydroentangling. Thermal bonding: the bonding of a web of loose fibres by passing them through a pair of calender rolls, of which one or both are heated. Plain or patterned rollers may be used. Wetlaid: the web is produced by filtering an aqueous suspension of fibres onto a screen, conveyor belt or perforated drum. Wipe: a piece of disposable absorbent cloth or paper, especially one treated with a cleansing agent. (Nonwoven wipe: a wipe made from nonwoven material.)

6.7

References

1 Zhang, D. Developments in Nonwovens for Wipes, ISBN 1-85802-550-8, Pira International, 2006. 2 Zhang, D. The Future of Global Markets for Nonwoven Wipes to 2011, Pira International, 2006. 3 Zhang, D. The Future of Global Nonwoven Markets: strategic five-year forecasts, Pira International, 2007. 4 Zhang, D. Developments in Nonwovens for Personal Care, ISBN 1-85802-550-9, Pira International, 2006. 5 Zhang, D. The Future of Antimicrobial and Antibacterial Wipes, Pira International, 2007. 6 INDA and EDANA. Guidance Document for Assessing the Flushability of Nonwoven Consumer Products, June 2008.


7 Nonwovens in specialist and consumer apparel B. J. C O L L I E R, The Florida State University, USA

Abstract: Protective clothing is the primary application for nonwovens in specialist and consumer apparel. These applications fall into the general areas of personal protective equipment (PPE) and medical apparel and accessories, both of which are highly end-use and task specific. The type of hazard determines the level of protection needed against permeation or penetration of hazardous substances. An emerging area of interest for nonwovens is wearing apparel. For protective and medical garments, a key challenge is balancing protective barrier properties with the desire for comfort. For more traditional apparel, the ability of the nonwoven to drape and conform to the body has been a challenge for designers. The issue of disposability or durability is a consideration for all materials used in apparel. This chapter addresses these issues and applications for nonwovens in apparel. Key words: nonwovens, apparel, personal protective equipment (PPE), medical nonwovens.

7.1

Introduction: key issues and properties required for apparel

7.1.1

Historical context

Felt nonwovens were one of the oldest textile structures to be used for apparel. As they were constructed of wool, and fairly thick, they were important protective garments throughout history, providing much needed warmth in many climates. Modern-era use might be said to begin with the nonwoven interfacings and interlinings for garments in the 1950s, followed by protective garments produced for industrial and farm workers in the 1960s. It is this latter category of protective apparel, whether for health care personnel, industrial workers, or first responders, that is the focus of much of the material in this chapter. Nonwovens – cheaply produced and engineered for specific applications – have transformed and greatly enlarged the area of protective clothing. We do not neglect, though, the intriguing area of wearing apparel as a market for some new nonwoven materials, such as those with elastic properties. 120 © Woodhead Publishing Limited, 2010


7.1.2

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Key issues

Comfort vs protection As technical nonwovens increasingly dominate the market for protective and medical garments, the challenge is balancing protective barrier properties with the desire for comfort. There are several factors contributing to the comfort, or discomfort, of apparel. One is thermal comfort, which depends in part on the properties of the garment fabric that promote the passage of heat, air, moisture vapor, or liquid perspiration.1 Yet, nonwovens are frequently used in protective apparel to prevent the passage of gases and liquids. Their structure of fine fibers randomly assembled provides a high surface area to entrap particles, gases, and liquids. As we shall see, manufacturers engineer nonwoven or composite structures to maximize barrier properties while making adjustments to keep the wearer comfortable. Comfort is also affected by the tactile sensation of fabric next to skin and, in particular, how soft the fabric feels. Many of the early manufactured nonwoven fabrics felt stiff and therefore were not considered suitable for apparel. With softness now a primary consideration for nonwovens in many technical apparel applications, processes are continually being developed and refined to enhance softness. A further factor is how a fabric makes up into a garment, forming around the contours of the body or draping from the body. The stiffness of many nonwovens inhibits such conformability and drape, which can affect the perceived comfort of a garment. More often than not therefore nonwoven garments are simple in design and loose fitting, which may or may not be comfortable to the wearer. Disposable vs durable Many of the apparel applications in which nonwovens have made significant inroads, mainly in the area of protective clothing, were dominated for many years by woven or other fabric structures. The garments were produced for multiple uses, launderability was a factor, and the product life cycle was longer. Today, however, protective apparel must act as a barrier to a wide variety of liquids, organisms, gases, or other matter, some of which may be retained in the fabric. Disposal after a single use is the safest course and this necessity has been the impetus for the growth of the lower cost nonwovens in so many areas of protective clothing. If nonwovens are to penetrate the non-protective apparel market, however, their durability will need to be improved.

7.2

Comfort of nonwovens in specialist and consumer apparel

7.2.1

Formability and drape

Making apparel from a flat fabric involves the manipulation of what is essentially


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Applications of nonwovens in technical textiles (a)

(b)

(c)

7.1 (a) Woven fabric shearing. (b) Nonwoven fabric resisting shearing. (c) Elastic nonwoven fabric shearing.

a two-dimensional structure into complex three-dimensional shapes to accommodate the human form. As the fabric conforms to the body shape and the design features of a garment, it may bend in one direction or be made to bend in two directions, forming double curvature in the latter case.2 This requires that the fabric be able to shear without buckling, which many woven and knitted fabrics easily do (Fig. 7.1a). Nonwovens however, with their fiber-to-fiber bonding, cannot accommodate a shearing force and will resist shearing, remaining stiff, or may buckle when the shearing force is large (Fig. 7.1b). This has limited their application in apparel for normal use. Drape is an important consideration in the aesthetics and appearance of apparel.



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(a)

(b)

(c) 7.2 Simple sleeve styles: (a) drop shoulder sleeve, (b) kimono sleeve, (c) raglan sleeve. Diagrams by Wanda Brown and Silkia Cuchi-Brock.

It is generally defined as the ability of a fabric to form pleasing folds when bent under its own weight. In most garments, these folds are formed by fabric curvature in more than one direction. Again, the inability of nonwovens generally to bend other than unidirectionally, and therefore to resist shearing, is a disadvantage. A study of the mechanical properties of woven, knitted, and nonwoven fabrics showed that shear and bending stiffness of nonwovens was high compared to other fabric structures.3 With these disadvantages, that nonwovens are currently used in any volume in apparel is due predominantly to their low cost, the limited range of applications, and also to new innovations such as nonwovens with elastic properties. For traditional cut-and-sewn garments made with woven or knitted fabrics, different shapes or curvature at the seam lines have not been a problem. Shaping a shoulder seam or sleeve inset into a three-dimensional form is a routine operation. Not so with nonwoven fabrics, which do not stretch, compress or shear to accommodate such actions. The solution has been to design around these difficulties, and this of course limits the types of apparel in which nonwovens are used. Protective and medical apparel are discussed below as primary applications for


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nonwovens. These garments are usually very simple in design, requiring a minimum of seaming and limiting design features to those that are functional for the purpose, such as pockets or cuffs. A surgical gown does not have to fit the wearer as carefully as does the shoulder of a finely tailored suit jacket. A minimum of seaming is desirable and seam edges are kept as straight as possible. For example, sleeves are cut in one piece with the body of the garment, or they are drop shoulder or raglan sleeves (Fig. 7.2). The important property is not appearance, but protection by covering the wearer. The advent of elastic melt spun nonwovens has spurred new interest in apparel end uses for these materials.4 The elastic nonwoven materials can better accommodate shearing forces by fiber stretching and thus can be formed into more complex shapes than can nonelastic fabrics (Fig. 7.1c).

7.2.2

Softness

For comfort, wearers of all types usually prefer fabrics with a soft ‘hand’ or ‘handle’, described as the tactile sensations when fabrics are touched or held in the hand. Many of the first nonwovens used in apparel were considered stiff and/or slippery and were not appealing to wearers. As with drape described above, the ability of a fabric to shear and bend when it is manipulated contributes to a soft hand. Other factors such as how easily a fabric can be compressed or stretched also play a part, and there are tradeoffs where nonwovens are concerned. A low basis weight fabric may bend easily, providing some features of softness, but also resist compression and not feel as soft as a thicker fabric that is also lightweight. Some types of nonwovens, such as spunlaced, are preferred for their softness.

7.2.3

Thermal comfort

Because of their structure of fibers in random entanglement, presenting a high surface area, nonwovens have long been used as barriers to heat transfer. Wool felt as thermal protection is well known and nonwoven interlinings are still used between the lining and face fabrics in outerwear. In most current and potential apparel applications, however, promoting heat transfer, rather than inhibiting it, is the objective. So thinner, more porous materials are employed to allow heat generated by the body to escape. Not only heat, but perspiration must be carried away to keep the wearer comfortable. Absorbent fibers, such as cotton and linen, can take up moisture, either as vapor or liquid. Thus the wearer feels cooler. Fabrics that ‘breathe’ absorb moisture vapor from the body and then desorb it into the atmosphere. For this to occur, however, there must be a fairly significant temperature, and thus humidity, gradient between the body surface and the outside air.5 Important too in enhancing breathability is the convective heat transfer away from the body, reducing humid-



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ity inside the garment. Many nonwovens are used as breathable barrier fabrics in apparel, with porous structures that allow air and heat to escape. Blends of cotton or wood pulp with synthetic, predominantly nonabsorbent, fibers have been used in fabrics for hospital and surgical gowns. Melt spun nonwovens, on the other hand, are manufactured almost exclusively from synthetic materials and do not absorb perspiration from the body. The randomized fiber configurations in nonwovens inhibit somewhat the ‘wicking’ action that is operative in woven and knitted fabrics made with yarns. In these fabrics liquid water is transferred through the capillary channels within the yarns and carried away. These aspects of thermal comfort argue against the use of nonwovens in closefitting apparel worn next to the skin. Garments designed to be worn over other clothing for protective purposes are more common.

7.2.4

Fit and ease of movement

For most clothing the fit of the garment is of primary importance. Garments are sized for different individuals and style features are often designed to enhance fit. Nonwoven fabrics, because of their resistance to shearing, bending, and stretch do not easily adapt to the many conformations needed to fit the body. In addition, as mentioned above, nonwovens are difficult to sew into complex shapes that require other than simple straight seams. For more loosely fitting garments to be worn over other clothing and to provide ease of movement for a variety of tasks, nonwovens are a good choice, with the added advantage of low cost. A caution though is the limited number of sizes available for many protective garments. Since these are worn in work-related settings, individuals must be able to perform a variety of movements without constriction. If a garment is large enough to provide that ease of movement, there may be excess fabric creating bulk in either the width or length. A study of surgical gowns found that bulkiness was indeed a concern among wearers as the fabric bunched up under the arms or in the front of the gown, making the wearer uncomfortable.6

7.3

Protection given by nonwovens in specialist and consumer apparel

7.3.1

Barrier properties

Nonwoven structures are ideal for providing barrier properties in apparel where such properties are desired. Individual randomly entangled fibers within the structure afford a high surface area for entrapping any number of substances that could be harmful to the wearer. For optimal barrier protection nonwovens are often layered with an impenetrable film as the outer surface. The inner nonwoven layer(s) can provide a substrate for the film coating. Depending on its thickness the


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outer layer also contributes to the strength of the structure, allowing the fabric to maintain its integrity through construction processes and wear. Depending on the application, the barrier should be impenetrable to chemicals, body fluids, infectious agents, gases, or other materials. Barrier fabrics are selected for protection against exposure in a variety of environments and tested for their ability to withstand penetration.1 Some tests determine resistance of the fabric to penetration by water, either by measuring the weight of blotter paper placed between a fabric specimen on which the water is poured, or by measuring the hydrostatic pressure required to force drops of water through the tautly held fabric. More severe tests involve mounting a fabric specimen in a holder and subjecting it to a challenge liquid such as synthetic blood or a liquid suspension of a bacteriophage, a type of virus that infects bacteria and is similar in size to the hepatitis and HIV viruses. If the challenge liquid penetrates, or strikes through, the fabric fails.

7.3.2

Design features

The fabric barrier itself is but one element of a protective garment. If such a garment is to truly inhibit penetration of chemicals, body fluids or airborne infections, attention must be paid to seams, and neck, sleeve, and ankle closings. Ultrasonic seams, which heat seal the edges together, offer advantages over stitched seams. Another issue with stitched seams, particularly for medical apparel, is the added expense of ensuring that the thread in the seams is sterile. Neck, sleeve, and ankle openings are other avenues for breaching the barrier of protective garments. Knitted cuffs, such as those on sweatshirts and pajamas are sometimes used. In cases where hands are to be protected, tight-fitting gloves of rubber, latex, or other film/barrier material cover the cuffs. For the ultra-protection necessary for first responders, who may be exposed to biological agents, toxic gases, or radiation, more complex connections of gloves and boots to the body suits are utilized. Closures of protective garments are simple so that they can be easily put on and taken off. Types of closures range from hook and loop tape (Velcro®) in medical apparel to zippers in higher-end protective garments. Closures are often in the back of the garment to facilitate removal and also because exposure to a hazardous substance, particularly liquids, is from the front of the body.

7.3.3

Visibility

There are occasions when first responders and others working in particularly hazardous environments must also be visible to those supervising the operations and to each other. Smoke, chemical vapors, or darkness may obscure the workers and increase the hazards of the situation. Body suits of very bright colors – yellow, lime green, orange – provide further protection for the wearer. These are usually



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designated as high-visibility suits. On the other hand, the safety of workers in such situations may depend on them not being visible, for example in military operations, and protective suits are available in muted colors such as tan or gray. Another consideration here is the opacity of the fabric. Many nonwovens are fairly sheer and would not be appropriate for apparel in the light weights that are needed for other apparel properties.7,8 Adding pigments, for either high or low visibility, increases fabric opacity. Some nonwovens reflect light and do not need pigments to make them opaque.

7.4

Life cycle of nonwovens in specialist and consumer apparel

7.4.1

Disposable

Disposable items are made for one, or a very few, uses.9 By far the majority of protective nonwoven garments are intended for the disposable market. Some may be durable enough for multiple uses but, because of their intended application, are classified as disposable. The wearer may have been exposed to chemicals, infectious agents, blood-borne pathogens, or radioactive materials, contaminating the garments that then must be disposed of for safety reasons after the initial use. This puts them in the category of limited use, rather than durable, apparel. The nonwovens advantage over woven or knitted fabrics is significant here, primarily because of cost. A nonwoven gown or suit, with minimal construction details, provides cost-effective protection.

7.4.2

Durable

Durable products (may also be called reusable) are designed to be used multiple times. Protective garments, currently the largest field of use for nonwovens, can be reused if they are not damaged or contaminated. Refurbishing nonwoven apparel is another matter. In many instances, the fabric will not withstand laundering or other cleaning methods as is common with most woven and knitted fabrics. Some nonwovens are now being engineered for durability to laundering and use.4 Initial evaluation showed that these fabrics maintained most of their strength, and that softness increased with laundering. This points the way to potential use in wearing apparel.

7.5

Types of nonwovens for apparel use

7.5.1

Spunlaid

The most widely used nonwoven fabrics for current apparel uses are spunlaid, either spunbonded, meltblown, or flashspun. Spunbonded materials occupy a


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prominent position in the market because of their strength and relatively low cost. Increasingly the standard for medical gowns is spunbonded and meltblown layers. Most of these fabrics are composed of polypropylene. Also important for protective apparel are solvent flashspun nonwovens of polyethylene. The heat bonding of the fibers in these fabrics makes them tear and puncture resistant and the fine fibers trap particles conferring protective properties. Spunbonded and meltblown processing now includes bicomponent fiber structures that not only combine properties of different polymers, but also can be split into microfibers. Resulting fabrics are softer and have higher filtration efficiency for enhanced barrier properties. In addition elastomeric polymers are being melt spun into nonwovens, resulting in stretchable web structures.

7.5.2

Other

Spunlaced nonwovens have enjoyed use in medical applications for some time. Their soft hand has been noted by wearers as a distinct advantage over some of the earlier spunbonded materials. New developments in spunbonded nonwovens however, including finer fibers and polymers other than polypropylene, produce fabrics with a soft hand rivaling that of spunlaced materials.

7.5.3

Composite/laminate structures

Layering spunbonded webs with melt blown nonwovens combines strength with the filtration properties of the melt blown layer. Such structures are now commonly produced for protective fabrics. There may be one, or more than one, meltblown layer in between the outer spunbonded layers. The layers are labeled ‘S’ for spunbonded and ‘M’ for meltblown. Thus an SMMS fabric would have two layers of meltblown webs in between outer layers of spunbonded fabric. For higher barrier protection, microporous films are bonded to single or multilayer spunlaid nonwovens. The film enhances impermeability to liquids. Gases can diffuse through, but not liquids, making the laminated structure somewhat breathable. These materials are not, however, as breathable and comfortable as SM layered nonwovens. The microfilm composites are 1,000 times less porous, and consequently less comfortable.5 Balancing protection and comfort becomes a challenge.

7.6

Applications of nonwovens in specialist and consumer apparel

7.6.1

Personal protective equipment

Personal protective equipment (PPE) is used, or required, for a wide range of industrial or personal activities. Equipment can range from hard hats to fire



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extinguishers. Apparel for such activities is of great importance because it covers so much of the body and can provide the degree of protection suitable for a specific pursuit or workplace environment. Nonwoven materials have been prominent in PPE for many years. In the 1970s DuPont’s Tyvek® was used to construct coveralls and aprons for mechanics, painters, and other industrial workers. The heat bonded fabric of nonabsorbent polyethylene did not absorb liquids, thus protecting the wearer from spills and splashes. The small fibers in the nonwoven structure also trapped particulates. It had a slippery surface and somewhat stiff hand, properties that dictated the types of protective apparel in which it was used. Style features were simple, keeping the cost of garment construction low. Nonwovens have made the leap to garments with barrier properties beyond those of these first materials. Coveralls and body suits are made from nonwovens and laminates with varying levels of resistance to permeation, penetration, and degradation by hazardous substances.10 At the lower end of cost and level of protection are the flashspun polyethylene fabrics. The standard for many applications is rapidly becoming layered SMS fabrics. The nonwoven SMS can be used in different weights to provide the level of protection needed and it can also be a supporting substrate for microporous films. The film laminates have increased barrier protection. A range of garment styles and features enables those selecting protective garments to obtain the appropriate level of protection for the hazard anticipated. For some types of exposure, coveralls with detached gloves and hoods may be sufficient. For others, hard hats and respirators may be needed. The body suit can be made with attached socks, so that there is no penetration at the ankle. Two considerations in design are facilitating donning and doffing the garment and providing ease of movement without bulk. Back zippers are common as closures and can be covered by a strip of material called a ‘storm flap’. The flap is an added protection against penetration. The garments are cut large enough for the wearer to perform any necessary physical movements and also to be worn over an inner layer of clothing. This inner layer can be normal wearing apparel, regular or long underwear, or a nonwoven – usually spunlace – garment. At the high end of PPE is the totally encapsulated chemically protective suit (TECP suit), which must maintain a fixed positive pressure thereby inhibiting penetration.10 In this case, the garment style and structural details (seams and closures) become as important as the fabric itself. All parts of the body must be enclosed in the ensemble, including head, hands and feet. Gloves and boots are attached or sealed to the suit in some manner; a respirator must be worn and is enclosed in the suit. Again, construction elements are kept to a minimum. As the complexity of the suits and the level of barrier protection increases, so does the cost. It can range from less than US$5 for basic Tyvek® coveralls to over US$1,000 for a TECP suit.


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7.6.2


Medical apparel and accessories

Much of the volume of nonwovens in apparel is used in this field. Disposable nonwovens such as surgical gowns, decontamination garments, and isolation gowns have significantly penetrated this market and their use is expected to grow into dominance.11,12 It is estimated that 3.3 billion square yards of nonwovens go into medical applications in North America. Not all of that is destined for apparel because fabric for surgical drapes is included in this total. Since the properties demanded for surgical drapes are often similar to those required for gowns and other garments, similar nonwoven materials are produced for both end uses and volumes of roll goods are difficult to separate. Asian-Pacific countries should experience rapid growth in medical nonwovens as the number of surgical procedures in this region increase and become more commonplace.11 Medical nonwoven garments are intended to protect health care workers from the ‘transfer of blood, body fluids, other potentially infectious materials (OPIM), and associated microorganisms’.13 Decontamination garments protect health care workers from infections or transfer of other agents during procedures to decontaminate medical instruments and devices. Isolation gowns are used to protect both health care workers and patients from body fluids and microorganisms while patients are isolated in medical facilities. Surgical gowns for operating personnel are designed to be worn over scrub suits, which are generally woven cotton for comfort and control of static electricity. The gowns are loose fitting to cover the scrub suits and allow a range of movement; they should not gape at the neck and be gathered or cuffed at the wrist to allow surgical gloves to cover the sleeve above the wrists (Fig. 7.3). An important feature in many cases is reinforcement of the places on the gown most likely to be exposed to penetration by liquids. These are called the critical zones. The reinforcing layer may be the same material as the garment body or may be one with higher barrier properties. Areas of surgical gowns most frequently reinforced are the front of the gown and the sleeves from above the elbow down to the cuffs. For isolation gowns the critical zone is the entire garment because the position of the patient, doctor, or nurse can vary and exposure is all around. This is often the case for decontamination gowns as well. Manufacturers of medical apparel can use the system for classification and labeling of levels of barrier performance developed by the Association for the Advancement of Medical Instrumentation (AAMI) and accepted by the American National Standards Institute (ANSI). The classification system consists of four levels related to the barrier properties required for the critical zones of specific garments (Table 7.1). It can be seen that higher level designations are more stringent in terms of penetration of liquids or microorganisms. A surgical gown for instance may require level 1 resistance for the body of the gown and level 2 barrier properties for the front and sleeve critical zones. In this case, a second layer of fabric would be needed in the critical zones to meet the higher level.



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7.3 Surgical gown with raglan sleeves and knit cuffs.

Table 7.1 Classification system for barrier properties Required result1

Level Test method 1 2 3 4

AATCC 42, Water resistance: Impact penetration test AATCC 42, Water resistance: Impact penetration test AATCC 127, Water resistance: Hydrostatic pressure test AATCC 42, Water resistance: Impact penetration test AATCC 127, Water resistance: Hydrostatic pressure test ASTM F1671, Resistance of materials used in protective clothing to penetration by blood-borne pathogens using Phi-X 174 bacteriophage penetration as a test system

≤ 4.5 g ≤ 1.0 g ≥ 20 cm ≤ 1.0 g ≤ 50 cm Pass

Compiled by author from ANSI/AAMI Standard PB70: 2003. 1 For all results, the acceptable quality level (AQL) is 4%, i.e. the maximum fraction of defective specimens allowed to meet the performance level.

The European Committee for Standardization (CEN, Comité Européen de Normalisation) has published EN 13795, a comparable standard providing guidance


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in determining the barrier properties of surgical gowns, drapes, and clean air suits. More stringent than the ANSI standard, it specifies test procedures and acceptable performance levels for resistance to wet and dry microbial penetration, potential microbial contamination, resistance to liquid penetration, and wet and dry bursting and tearing strength. The last two requirements take into account the stresses garments may undergo during wear in an operating room environment. Booties and bouffant hair caps are also worn in medical settings, both by patients and by health care personnel. These are usually made of very low cost spunbonded fabric and are disposed of after one wearing. They protect individuals in hospitals and other medical facilities from infectious agents.

7.6.3

Wearing apparel

Nonwovens have not been extensively used in apparel other than protective garments. The two most significant challenges have been the lack of drape and formability of most nonwovens (as described in Section 7.2.1 above) and the durability of the fabrics to use and care.14 Attempts by apparel designers to use nonwovens have been more successful when the nonwoven fabrics have some elastic properties to allow for the fabric manipulation, stretching and compression, that are desirable in constructing garments.7,8 When regular spunbonded nonwovens were used, designers opted for various techniques to simulate some shearing or three-dimensional bending properties. The nonwovens were cut into strips and woven in an interlacing pattern or knitted with large needles (Fig. 7.4). These methods for providing some formability into garments made from nonwovens also addressed another challenge identified by designers working with the fabrics, namely the flat surface appearance of the spunbonded nonwovens. Weaving or knitting strips of the fabric presented a more appealing threedimensionality to the nonwovens in the garments. Novel painting or dyeing techniques, or even different calender patterns, can also be used to confer a more interesting texture to nonwoven fabrics. When working with stretchable melt blown fabrics, garments with more pleasing drape and greater freedom in fitting and forming were possible (Fig. 7.5).8 The lightweight fabric was able to bend and shear to some extent.

7.7

Future trends

For the near future the greatest area of growth for nonwovens in apparel will probably remain in medical protective garments. Refinements will be micro- and nanofibers to improve barrier properties in lighter weights, and other methods for producing softer fabrics. Since most medical nonwovens are disposable, cost will continue to be a driving force, with strong competition among nonwovens suppliers. Some configuration of spunbonded-meltblown composites will continue to



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7.4 Fashion garment with collar of spunbond nonwoven strips. Design by Rosetta LaFleur, reprinted by permission of INDA.

7.5 Fashion garment of elastic nonwoven. Design by Brenda Green, reprinted by permission of INDA.


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dominate both medical and PPE markets. Producers will continue to seek the best ‘balance between barrier protection, comfort, and overall value’.11 For these protective garments, improvements in design can increase comfort and fit. Sleeve and seam modifications can reduce bulk while allowing ease of movement. Further, a wider range of sizes, including smaller sizes to fit women, would be helpful. As discussed, comfort also entails adequate heat transfer from the body of the wearer through a protective garment. Enhancing this heat transfer, especially for apparel that is part of PPE, is a goal for the industry.5 With the interest in sustainability, efforts to produce biodegradable nonwovens should yield some interesting possibilities for apparel. Since many of the garments today are destined for the disposable market, biodegradable materials that can be manufactured at low cost should be appealing for a number of applications. Garments made from such materials would also be more comfortable, thus increasing the acceptance of nonwovens in apparel. The joint effort of Lenzing and Weyerhauser to produce lyocell nonwovens is promising. Although momentum has slowed somewhat, there should be further progress in developing nonwovens for wider use in apparel. The significance of drape, hand, and conformability depend on how garments are worn and used. Elastic materials can lead the way in this effort because they display properties more similar to woven and knitted fabrics. Balancing weight with the need for opacity will challenge producers. Dyeing, printing, and finishing of the nonwoven fabrics are important, as is durability. It is expected that we will see more well-known fashion designers become interested in new nonwovens materials. Up to this point, much of the work in fashion apparel has been by students in universities.

7.8


Nonwovens organizations, such as INDA and EDANA, have current web sites that highlight developments and usage worldwide. Trade magazines such as Nonwovens and Nonwovens Industry have up-to-date information on applications and production data. Producers of medical nonwovens and personal protective apparel are continually enhancing their products, and their web sites keep buyers and consumers apprised of new developments. Standards organizations (ANSI and CEN) regularly review and, when deemed appropriate, revise their standards.

7.9

References

1 Collier, B. J. and Epps, H. H. Textile Testing and Analysis, Merrill/Prentice Hall, Upper Saddle River, NJ, 1999. 2 Hearle, J. W. S., Shear and Drape of Fabrics, in J.W.S. Hearle, P. Grosberg, and S. Backer (eds), Structural Mechanics of Fibers, Yarns, and Fabrics, Wiley-Interscience, New York, 1969. 3 Collier, B. J., Chen, Y., Moore, M. A., Orzada, B. and Dahiya, A., Drape and Formability of Nonwovens, INTC 2005, St Louis, MO, September 19–22, 2005.



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4 Grisset, G. New Dimensions in Apparel Quality Nonwovens, INTC 2005, St Louis, MO, September 19–22, 2005. 5 Jim Ziegler, Personal communication, DuPont Personal Protection. 6 May-Plumlee, T. and Pittman, A., Surgical Gown Requirements Capture: A Design Analysis Case Study, Journal of Textile and Apparel Technology and Management, 2(2), Spring 2002. 7 Orzada, B., Non-Wovens Design Challenge: Fashion Application, INTC 2005, St Louis, MO, September 19–22, 2005. 8 Orzada, B., Blank Canvas: Elastomeric Nonwovens as Fashion Apparel, INTC06, Houston, TX, September 25–27, 2006. 9 Collier, B. J., Bide, M. J. and Tortora, P. G., Understanding Textiles, Pearson/Prentice Hall, Upper Saddle River, NJ, 2009. 10 US Department of Labor, Personal Protective Equipment Test Methods, US 29 CFR 1910.120 App A. 11 Wuagneux, E., Medical Market Maturation, Nonwovens Industry, 39(8), 26–33, 2008. 12 Engqvist, H., The Benefits of Using Nonwovens in Medical Products, Nonwovens Industry, 40(8), 30–34, 2009. 13 Association for the Advancement of Medical Instrumentation, Liquid Barrier Performance and Classification of Protective Apparel and Drapes Intended for Use in Health Care Facilities, ANSI/AAMI Standard PB70, AAMI, Arlington, VA, 2003. 14 Blackhouse, D. and Webster, L., Fashion: Function in Action, Nonwovens Industry, 38(12), 36–40, 2008.


8 Nonwoven textiles for residential and commercial interiors F. K A N E, Loughborough University, UK

Abstract: Nonwovens have established a key role within the interior textiles sector. This chapter gives an overview of the interior textiles industry and applications of nonwovens within it. Nonwovens that perform functional, technical and aesthetic roles will be discussed including bedding, upholstery and furnishing fabrics, wallcoverings and floor coverings. Product examples, production methods, materials, product requirements and fabric properties will be outlined in relation to each area. Key words: interior textiles, design, nonwovens.

8.1

Introduction

This chapter provides an overview of current applications of nonwovens within residential and commercial interiors including key terms, market segments, product areas and product requirements. Current interior applications of nonwovens in relation to production methods and key product areas including bedding, upholstery and furnishing fabrics, wallcoverings and floor coverings are discussed in detail and specific product examples given. Production methods, materials, product requirements and fabric properties are outlined in relation to each area. Nonwovens that perform functional, technical and aesthetic roles are also discussed.

8.2

The interior textiles industry

The interior (or home) textiles industry is part of the textiles and clothing sector (http://ec.europa.eu). As the world’s population increases and the number of residential and public buildings increases, so does the potential for interior textile products. This is reflected and confirmed in CIRFS’ (Comité International de la Rayonne et des Fibres Synthétiques) market projections which suggest that between 1990 and 2012 consumption of bedding products, table linen, blankets and curtains will continue to grow in key European countries and the United States (US) (Morris, 2008). The consumption of other furnishing articles is anticipated to remain constant in Europe and continue to grow in the US. The report also suggests, 136 © Woodhead Publishing Limited, 2010


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however, that the consumption of textile based floor coverings will decline in key European countries, with the exception of needle-punched products, but will grow in the US. These figures suggest that interior textiles form an important aspect of the textiles and clothing sector. As this chapter will show, nonwovens have a key role to play in the continued development and growth of interior textiles. Within European nonwovens production, 5.5% of roll goods were accounted for within the household textiles category in 2007 (www.edana.org). The interior textiles market therefore provides a potentially significant market area for nonwovens.

8.2.1

Key terms and product areas

Interior textiles are produced for either the ‘domestic’ (also referred to as ‘private’ or ‘residential’) or ‘contract’ (also referred to as ‘commercial’) markets. Domestic textiles are those found in the home or private interiors. Contract textiles are those found in public or commercial interiors. Interior textiles are usually discussed in relation to two key categories: ‘furnishing fabrics’ and ‘household textiles’. Furnishing fabrics include: upholstery fabrics, soft floor coverings, wallcoverings, window furnishing (curtains, drapes, blinds) and accessories such as cushions and throws. Household textiles include all textiles used in domestic interiors apart from furnishing fabrics. For example: bedding, towels, blankets, tablecloths and napkins. When designed for hospitality and care-type facilities, these products are referred to as ‘institutional textiles’ as they are required to conform to specific performance and safety criteria (Yeager and Teter-Justice, 2000, p. 5). Within these product areas there are differences in raw materials, fabric structures, aesthetics and performance requirements.

8.2.2

Industry segments

The main segments of the interior textile industry are shown in Fig. 8.1. As the diagram shows, nonwoven processes are integral to the industry.

8.2.3

Requirements of interior textiles

Consumer requirements of interior textile products vary depending on the product in question and the market for which they are sought (domestic or contract). Selection and evaluation criteria take into consideration aesthetics, performance and safety factors, maintenance, environmental concerns and costs. Performance and safety factors are often of concern to consumers when selecting interior textile products. Depending on the product several functional properties may be desirable, for example insulation, acoustic control, glare reduction and flame resistance (Yeager and Teter-Justice, 2000, p. 9). General performance specifications are often developed by design professionals in relation


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Applications of nonwovens in technical textiles Natural fibre suppliers/synthetic fibre manufacturers Harvesting and preparation/fibre manufacture and engineering Wool, silk, cotton, linen, jute, etc. Acetate, acrylic, nylon, polyester, viscose, etc.

Yarn manufacturers Colourists Opening, carding, spinning and texturing/monofilament and multifilament yarns

Greige fabric manufacturers

Textile designers

Weaving, knitting, needle-punching, spunbonding, felting, extruding, chemical and thermal bonding, tufting, braiding, etc.

Nonwoven technologies

Greige upholstery and automotive fabrics Greige window and wallcoverings Greige roll goods, flooring and cushions Greige linens, beddings and towellings, etc.

Converters Product designers Mechanical and chemical finishing

End product producers Cutting, sewing, trimming Upholstered furniture, yard goods, curtains, draperies and wallcoverings, soft floor coverings, domestic and contract goods, etc.

Distributors

8.1 Flow chart showing the main segments of the interior textiles industry (based on Yeager and Teter-Justice, 2000, p. 3).

to the product requirements. Manufacturers may be required to perform standard tests, or supply a sample for testing to ensure that their product shows an acceptable level of in-use performance.



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Within the contract interiors market, flame resistance is often mandatory. Government bodies exist that set regulations in regard to fire safety. In the UK The Furniture and Furnishings Fire Safety Regulations 1988 (amended 1989 and 1993) sets levels of fire resistance for domestic upholstered furniture, furnishings and other products containing upholstery (http://www.berr.gov.uk). These regulations refer to specific standards and test methods upheld by organizations such as British Standards (BSI). The regulations deal with the duties of manufacturers (and of importers, if the goods are manufactured abroad) in supplying safe products. Such regulations can sometimes stifle innovation but ultimately provide business opportunities. Aesthetic considerations play a leading role in a consumer’s selection of a product. These will relate to both the visual appearance and ‘touch’ of the fabric and its relevance to current fashion trends within interiors. Considerations are likely to include colour, pattern, texture, hand, drapeability and the availability of co-ordinate products. The maintenance of interior textile products relates to their serviceability and can affect how well the product retains its original appearance, the level of wear incurred through cleaning and the impact of cleaning on the durability and safety of the product. Consumers within the domestic market are likely to consider how often the product will need to be cleaned, the cleaning products/equipment required for cleaning and ease of cleaning. Within the contract market labour costs associated with cleaning and the impact of cleaning on the durability of the product may also be considered. As noted previously, consumers are becoming increasingly aware of the environmental impact of the products they buy in terms of their production, use and disposal. Concerns may relate to the origins of source materials, location of production, energy and effluents used in production, the impact of required cleaning, the durability of the product and the potential to recycle or reuse at the end of original life cycle. Cost considerations relate to the initial cost of a textile product and also its ‘life cycle’ cost. Yeager suggests that initial costs relate to the purchase of the product and its installation and life cycle costs relate to maintenance, including cleaning equipment and, within the contract market, labour, energy and insurance costs (Yeager and Teter-Justice, 2000, p. 16).

8.2.4

Design considerations

Consumer requirements need to be taken into consideration when designing and selecting nonwovens for use within interiors. The criteria for the nonwoven will vary depending on the product in question and the function that the nonwoven is to play. For example, when designing or selecting a nonwoven to provide covering and support within the core of a mattress, the tensile strength and dimensional stability of the nonwoven will be paramount. For use as a visible cover for a


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mattress, in addition to this the nonwoven will need to be aesthetically pleasing and may need to be printed upon. Construction technique, production parameters and raw materials need to be carefully considered to achieve a nonwoven with the desired properties and within the budget allocated. Each nonwoven production technology provides the opportunity to produce fabrics with specific characteristics; some enable greater strength, others greater flexibility in design. For example spunbonded technology enables high levels of strength to be achieved whilst needlepunching enables flexibility in terms of raw materials. If a new fabric, beyond the manufacturer’s current range, is required, careful discussion is needed in terms of product characteristics. Test sampling is often necessary. This can be done economically using pilot scale production lines either with the manufacturer in question or in collaboration with a specialist research and development centre (R&D) centre within industry or academia, for example the Centre for Materials Research and Innovation at Bolton University UK or the Nonwovens Research Group at Leeds University, UK. When working to develop a new product, the designer, researcher and machine operators must work closely together to achieve the desired results and to innovate new products through collaboration.

8.2.5

Environmental developments

The interior textiles industry is becoming increasingly aware of the need to develop processes and products in an environmentally conscious manner. Improvements are being made in the following key areas: the reduction of raw material consumption and the use of harmful processing agents, reuse of existing textile products and, recycling existing textile products. The ability to recycle products is often dependent on their original material content and construction. Product design can be approached in such a way to enable recycling or more effective disposal or disassembly at the end of the product’s life cycle. In the industrial design sector, design for recycling (DFR) and design for disassembly (DFD) initiatives have resulted in the production of checklists and recommendations that enable the manufacture of products that can be recycled or are easy to take apart for reuse (Fletcher, 2008, pp. 105–106). In relation to nonwovens this could focus on the use of pure, non-composite products to aid recycling, the use of biodegradable fibres to aid decomposition in landfill or the design of component fabrics that are easy to remove from the final product for reuse, specific disposal or recycling.

8.3

Nonwovens within interiors

Nonwovens are increasingly used within interiors alongside and in replacement of conventional materials (such as woven fabrics and papers). As will be discussed,



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Table 8.1 Nonwoven production methods and interior applications Nonwoven production method

Interior application

Needle-punching

Carpet underlay/backing Wallcoverings Blankets Upholstery (including synthetic leather) Wadding and padding Backings for wallcoverings Upholstery (synthetic leather) Coverings for bedding (for example mattress covers) Semi-durable bedsheets Semi-durable tablecloths and napkins Tablecloths Coverings for bedding (for example mattress covers) Carpet underlay/backing Wallcoverings Backings for wallcoverings Curtain header tapes/backing Upholstery (including synthetic leather) Furniture backings Wadding and padding/fibrefill Carpet underlay/backing Furniture and bedding components Wadding and padding Table linen, cloths and napkins (often disposable) Glass fibre matt for flooring Wallcoverings Insulation materials

Spunlacing/hydro-entanglement

Spunbonding

Chemical bonding Thermal bonding

Wet-laid

they are used to fulfil a range of functional and aesthetic roles. In some applications, for example wallcoverings, they perform better than conventional materials. In others they provide economical alternatives to traditional textile materials. Their use is expanding to innovative smart materials such as blast resistant curtains and anti-microbial bedding.

8.3.1

Key application areas and technologies

The main application areas for nonwovens within the home are: backings for textile and flexible floorcoverings, carpets and upholstery, backings and facing materials for wallcoverings, and bedding components (Nonwovens Industry, 1999). The main production technologies used to produce such nonwovens are needle-punch, spunbond and wet-laid (http://www.edana.org) and, according to Stein, the order of importance of nonwovens in relation to the US home textiles sector is firstly high-bulk, then needled nonwovens, followed by filament and


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random-web nonwovens (Stein and Slovacek, 2003, p. 515). Products are not limited, however, to these construction areas. As shown in Table 8.1, various production methods are used to make nonwovens for a range of applications evidencing the flexibility and breadth of products for this market.

8 3.2

Benefits of nonwovens

The main benefit of using nonwovens within the home sector is that they can achieve a range of technical functions more economically than traditional textile materials. The engineerable properties and performance advantages of nonwovens relevant to interior products include fire retardancy, dimensional stability at high temperatures, non-fray, colour stability, high tear strength, breaking strength and abrasion resistance, elimination of de-lamination risk, stretchability, strength, uniformity, fluid resistance and retention, anti-allergy and anti-microbial properties. As such, nonwovens can provide safety, comfort and aesthetic benefits (Engqvist, 2005). In some applications, for example mattress covers, nonwovens are perceived as a lower quality option than woven fabrics. In others, however, for example carpet backings, they perform equally well and in some cases better than wovens. The following sections will discuss in more detail the use of nonwovens within key interior product areas.

8.4

Nonwoven textiles in bedding

Bedding products are an important area of the interior textiles industry. In 1998 this area accounted for up to a third of the total fibre used in home textiles (Yeager and Teter-Justice, 2000, p. 432). Bedding products include mattresses, mattress pads and covers, pillows, sheets and pillow cases, quilts, bedspreads, throws, comforters and sleeping bags. A number of these products are multicomponent structures in which nonwovens have, in many cases, replaced traditional materials providing better or equal quality often at lower costs. They are used in the construction of mattress flanges, quilt backings, mattress insulation, spring covers, pillows, dust covers and mattress pads. Key to this application area is the ability of nonwovens to be engineered to have flame retardant and anti-microbial properties.

8.4.1

Mattresses

Nonwovens are used in the production of mattresses as support and insulation materials, as external coverings and as replacements for traditional foams. Mattresses are produced in two key constructions: ‘inner spring’ and ‘foam core’. Figure 8.2 shows a cross-section of an ‘inner’ spring mattress highlighting the areas in which nonwovens are used and Fig. 8.3 shows a foam core construction.



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Insulation layer Cushioning and padding Cover layer

Edge support Support layer Foam Nonwoven

Spring core

Nonwoven

8.2 Inner spring mattress showing use of nonwovens (based on Yeager and Teter-Justice, 2000, p. 434 and Stein, 2003, p. 516).

Nonwoven

Foam

8.3 Foam core mattress/cushion showing use of nonwoven/batting (based on Yeager and Teter-Justice, 2000, p. 200 and Stein, 2003, p. 517).


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Support, covering and insulation Nonwovens are used as internal support and covering materials in mattresses. Nonwovens used in this area include: chemically bonded polyester wadding (used in low stress applications); thermally bonded nonwovens; and nonwovens laminated with woven or knitted fabrics to provide covers with high dimensional stability. According to Stein (Stein and Slovacek, 2003, pp. 515–516) nonwovens are used in up to 90% of foam-backed mattresses (and upholstery) as support and cover materials. Polyester or polypropylene filament nonwovens are increasingly used to replace plain weave cotton fabrics as mattress covers. For this purpose they are required to have equally high tensile strength in all directions to resist tearing after sewing, to be processable in any direction, to have a high area and dimensional stability, and to not fray when cut (Stein and Slovacek, 2003, pp. 515–516). Nonwovens are also used as the backing material to which the mattress ticking and foam (or fibrefill) is quilted. The weight of nonwovens used in this application varies from 10–15 grams/metre² (g/m2) up to 50 g/m² (http://www.inda.org). The insulation layers that prevent the springs from penetrating the upper layers of the mattress are made from nonwovens. Various nonwovens can be used to cover springs, however, needle-punched materials are often used to provide both support and comfort. They are required to be strong enough to be fastened into place and to have good abrasion resistance properties. Mattress flanges, the panels that surround the edge of a mattress to join the mattress top and bottom together, are also produced using needle-punched and spunbonded materials. Mattress pads and external covers To protect mattresses from dust, moisture and wear, covers and pads are used. Yeager and Teter-Justice (2000, p. 435) describe mattress pads as ‘multi-component structures that cushion and soften while they cover and protect the mattress’. Pads are constructed from a batting of polyester that is quilted between two woven or nonwoven facing and backing materials. Spunbonded polyester is often used as a facing as it is strong and retains it shape during laundering. They are usually 42–65 g/m² in weight and backing fabrics are usually 15–20 g/m² in weight (http://www.inda.org). According to INDA nonwovens compete directly with woven cottons in this area, accounting for up to half of the total volume used (http://www.inda.org). Fabrics that are used to cover the exterior of mattresses are often referred to as ticking. Woven fabrics are usually used for this application and twill and damask fabrics are common. Printed spunbonds are, however, occasionally used in the production of cheaper mattresses. They are required to have good stability and strength and it must be possible to print on them. Anti-microbial properties An important development in use of nonwovens in bedding products is the



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ability to engineer anti-microbial properties. This is achieved through the application of anti-microbial treatments. Anti-microbial treatments, including antibacterial and antifungal treatments, control, destroy or suppress the growth of microorganisms (for example bacteria, mildew, mould and fungus). They therefore control their negative effects, which can include staining, odour and deterioration (Gopalakrishnan and Aswini, 2009). More specifically in relation to bedding, such treatments reduce the microbial growth on which dust mites feed. This reduces the risk of irritation, associated with dust mites, to asthma and allergy suffers. In terms of application the treatments can be applied as finishes or built in at the fibre construction stage. Anti-microbial agents can be applied to the nonwoven substrates by means of padding, spraying, aqueous coatings or foam applications. They can also be applied by direct addition to the fibre spinning dope (Gopalakrishnan and Aswini). Ahmed notes that proprietary compounds, metallic compounds containing silver and natural biopolymers such as chitosan are important in this area (Ahmed, 2007, pp. 376–377). He explains that aqueous dispersions of chlorinated phenoxy-compounds containing pyrithione are effective against bacteria, algae, yeast and fungi and can be applied to fabrics other than polypropylene (Ahmed, 2007, pp. 376–377). To achieve maximum benefits the anti-microbial treatments must be durable to washing; selective in their activity towards undesirable microorganisms; unharmful to the manufacturer, the user and the environment; compliant with regulatory agency requirements; unharmful to fabric quality; and resistant to bodily fluids and disinfection treatments (Gopalakrishnan and Aswini). Foam replacements Due to fire and health hazards associated with polyurethane (PU) foam, nonwovens are increasingly being used as a replacement material in the construction of mattresses. To produce suitable nonwovens, webs made from high-bulk fibrefill (of which up to 25% is thermoplastic bi-component fibre) are thermally bonded using hot-air bonding before being cooled and compressed to the required thickness between steel belts. For this application the nonwoven needs to be stable under dynamic loads, have high compressibility and a good recovery capacity. The nonwovens produced are thick and bulky and are of equal quality to conventional foams of the same thickness. They have good air permeability and comfort properties (Stein and Slovacek, 2003, p. 515).

8.4.2

Pillows, quilts, duvets and blankets

Nonwovens and fibre fillings are frequently used within the production of pillows, quilts and duvets. Further to this, needle-punch technology can be used to produce blankets at low cost.


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Fibrefill Loose fibres in wadding and fiberfill products are being increasingly used within furnishings. Hollow fibres, which have excellent insulating properties, are widely used in bedding and sleeping bags. Fibres used for this purpose are commonly bonded using self-cross-linking styrene co-polymers, which have good chemical resistance and good ageing properties. These are applied using saturation, spray or foam bonding technologies (Chapman, 2003, p. 365). Pillows The two main components of pillows are filling materials and ticking fabrics. Fibrefill, down, feathers and foam are used as filling and in most cases it is enclosed in a non-removable cover that is then protected by a removable casing to keep the filling in place. The non-removable cover is usually made from a woven fabric with a high fabric count. Outer casings must be washable. A range of wovens are usually used for this purpose but polypropylene spunbonds of around 50 g/m² can been employed (Yeager and Teter-Justice, 2000, p. 443). Quilts and duvets Quilts and duvets can be described as ‘a bedcovering assembly, consisting of insulating filler secured between two layers of fabric, primarily to reduce heat loss’ (Yeager and Teter-Justice, 2000, p. 443). Quilts are lighter in weight and thinner than duvets (Yeager and Teter-Justice, 2000, p. 443). The insulating filler can be down, feathers, fibrefill or a loose batting of polyester. The filling is encased in an outer covering that often includes a spunbonded lining to keep the filling from penetrating the surface. Nonwovens are also used as the outer covering in cheaper products. Blankets Needle-punching has been used to produce blankets for over 50 years and was one of the earliest applications of the process. High quality synthetic and natural fibres are still used but the process is usually employed to produce economical products from regenerated fibres that are often used as emergency or disposable blankets (Anand, 2007, p. 225). In the production of needle-punched blankets, modifications to the needlepunch process have been made to improve their properties. The Fibrewoven® process, developed by the Chatham Manufacturing Company in the 1950s, now owned by WestPoint Homes (http://www.hometextilestoday.com), involves the use of double sided alternating needling with diagonally penetrating needles (Kittlemann et al., 2003, p. 276). This enables more intense binding of fibres resulting in products with better compression and solidification. Thick webs are



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produced by cross-layering and incorporate a layer of woven scrim that acts as a supporting substrate.

8.5

Nonwoven textiles in upholstery and furnishing

Within the upholstery area, nonwovens are used in the production of foam backed mattresses as support and cover materials, as foam replacements and as leather replacements.

8.5.1

Support and cover materials

As discussed, bonded polyester wadding (used in low stress applications), thermally bonded nonwovens and nonwovens laminated with woven or knitted fabrics to provide covers with high dimensional stability are used in the production of foam-backed mattresses for upholstery as support and cover materials. As noted previously, needled waddings and paddings are incorporated into furniture as insulation and comfort layers. Fibres used for such applications include recycled natural and synthetic fibres obtained from waste clothing; bast fibres; cotton; and virgin synthetic fibres such as polyethylene terephthalate (PET), polypropylene (PP) and acrylic (Anand et al., 2007, p. 253).

8.5.2

Foam replacements

As well as the foam replacements described in 8.4.1 in relation to mattresses, Multiknit fabrics, based on stitch-bonding technologies, and nonwoven composites can be used as foam replacements within furniture. Multiknit fabrics have excellent compressibility, low area and bulk density, heat, noise and vibration insulation, excellent mouldability and the potential to be welded if they contain predominantly thermoplastic fibres. This makes them a suitable replacement for PU foams (Anand et al., 2007, p. 219). High loft composite nonwovens made from various nonwoven substrates can also be used as foam replacements. A WIPO patent (www.wipo.int) describes the construction of such a fabric as follows: a needled nonwoven made from a blend of high crimp polyester and bi-component fibres is heated to activate thermal bonding and a thermoplastic layer or film is added to one side; a fabric substrate, which may be a woven, knit or nonwoven (spunbond, spunlace, needle-punch, airlaid, wet-laid or pattern bond nonwoven) material is then needle-punched to the composite; and a further thermoplastic layer is laminated to the other side of the nonwoven. The fabrics produced have been tested as foam replacements and as door panel ornamentals in automotive interiors.

8.5.3

Synthetic leathers

Leather replacement products have been under development since the 1940s for


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use within fashion and interiors. Their production utilizes a number of nonwoven technologies and materials (Assent et al., 2003, p. 537). Although still relatively expensive, these materials can be cheaper than high quality genuine leathers and production has the advantage of quality and waste control. Synthetic leathers can be produced by extruding polymer solutions as film sheeting or fibre matrices. The sheets or matrixes are then bonded to a supporting substrate, such as a spunbond or hydro-entangled nonwoven, which provides dimensional stability. The most common compounds used are polyvinylchloride (PVC) and PU. These compounds can also be developed into an expanded solution that is then applied to a base fabric to produce a synthetic leather material. Grain effects on the surface of the fabrics that give a leather look are achieved through embossing. Synthetic leathers are also commonly produced using hydro-entangling and needle-punching technologies. Further to the traditional methods, synthetic leathers are produced by hydro-entangling splittable bi-component fibres (Anand et al., 2007, p. 292). Needle-punching is used to produce dense fibre constructions that are then impregnated with PU resins. Webs are punched up to eight times using fine gauge needles with small barbs to avoid marking and needle force. The density of the fabric is successively increased through the repeated needling (Anand et al., 2007, p. 253) . To produce fine high-density fabrics single-barb needles with high punching density that require small needle penetrations can be employed (ibid.). Surface area and fabric density can be increased by using a proportion of highshrink thermoplastic fibre within the fibre blend. This induces fabric contraction following heating. Splittable fibres like those used in hydro-entangling have also been developed for use in needle-punch. The fabrics produced using these methods are free from needle marks with a smooth surface and high abrasion resistance (ibid.). The use of microfibril fibres (Assent et al., 2003, p. 539) and air and moisture permeable PU has improved the quality of synthetic leather products. Trade name products such as Clarino®, Alcantara®, Sofrina® and Lorica® are examples of such materials. The improved properties of these materials require a higher market price. The fabrics therefore find application in high-end and luxury products. Alcantara®, in particular, is used in high-end or luxury domestic, contract, fashion and accessories, automotive and interior markets. An example of its application is the development of a range of interior products by Lelièvre, a leading international manufacturer and distributor of fine furnishing fabrics (http://www.lelievre.eu). Laser patterning Lelièvre products include cushions, throws, light shades, curtains and cosmetic bags in various colour palettes and designs that incorporate laser cut and embroidered embellishment. Decorative laser work on Alcantara® has also been utilized in the Mercedes Benz F700 concept car (http://www.carbodydesign.com). Various



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8.4 Sofa upholstered in Alcantara® (image courtesy of Alcantara®, http://www.alcantara.com).

qualities of Alcantara® are produced and used for high-end upholstery applications. As shown in Fig. 8.4, further to cutting, embossing, lamination and finishing can be utilized to produce physical modifications to the surface of nonwovens (Ahmed, 2007, p. 399). Surface patterning using laser marking techniques has also been achieved.

8.5.4

Curtains

Nonwovens are used within curtains and blinds as reinforcing linings and as the main outer fabric. As linings, they are usually coated on either one or both sides with a hot-melt adhesive and thermally bonded to the fabric that they are to support (Stein and Slovacek, 2003, p. 520). Spunlaced nonwovens can be used as replacements for traditional curtain nets, roller blinds and shower curtains. For this


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purpose they must have good tear strength and a soft handle, easy care properties, crease recovery and good appearance. One hundred per cent polyester products can be used as they have easy care properties, do not fray and their shrinkage during washing is 1.5% (ibid.). When given a water-resistant finish they can be used as shower curtains or roller blinds. In this case they are bonded with 3–5% acrylate binder (ibid.). However, this impacts negatively on the drape and washability of the products. The use of polyamide, which is bonded with binder fibres rather than acrylate, results in improved properties. Blast proof curtains Nonwoven technologies are emerging in specialist interior products such as blast resistant curtains (http://www.edana.org). The curtains are designed to mitigate flying glass shards and debris caused by bomb blasts. They vent blast loads, capture projectiles and are fire retardant. High strength polyester fibres are utilized for this application.

8.5.5

Durable fabrics

The development of durable nonwovens has opened up the number of appropriate applications within the home furnishings market. Miratec® fabrics, for example, developed using APEX™ technology are suitable for durable and long life products (http://www.pgi-industrial-europe.com). The technology combines advanced web forming techniques and laser technology to create strong, uniform fabrics ranging from 50–400 g/m². The fabrics are reportedly tear, fray and pill resistant. Fabrics with equal durability but lighter in weight than some woven fabrics are achievable.

8.6

Nonwoven textiles in wallcoverings

Nonwovens are now used as replacements for traditional wallcoverings. They are also used as backings for traditional fabric wallcoverings. The nonwovens currently used in this area are predominantly wet-laid but extend to needle-punched fabrics and potentially others. The preferable requirements of nonwovens for wallcoverings are that they have enough dimensional stability and are strong enough to withstand application to the wall whilst maintaining a smooth and consistent surface. Depending on the market (domestic or contract) and specific use the nonwoven may also need to be ‘wipeable’.

8.6.1

Replacements for traditional wallcoverings

Over recent years nonwoven-based substrates have increased in their share of the wallcoverings market (http://www.ahlstrom.fi). Wetlaid nonwovens in higher



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weights have become popular replacements for paper, vinyl and woven substrates due to a number of significant product advantages. Such nonwovens are simpler to hang and remove than traditional substrates. They are pasted and directly applied to the wall without soaking, as traditional substrates need. Systems such a ‘Easylife™’, developed by nonwovens manufacturer Ahlstrom, works on the premise that the wall rather than the covering is pasted, increasing the ease of application (ibid.). Unlike traditional wallcoverings, this type of nonwoven, reportedly, does not shrink or expand when paste is applied due to their dimensional stability (ibid.). This means that the seams do not separate, which gives the impression of a consistent surface rather than distinct strips. Further advantages include superior strength, tear resistance, high opacity and breathability which prohibits fungus growth between the wall and the covering (Bitz, 2003). The ability to control mould and mildew is a distinct advantage within commercial interiors (http://www.hollingsworth-vose.com). Design potential Wet-laid nonwoven wallcovering substrates can be directly printed on. Due to their dimensional stability they do not need PVC coating ,which is advantageous from both manufacturing and environmental perspectives. This enables decorative designs to be easily applied. Other design opportunities include the ability to incorporate long random synthetic fibres, such as sisal or flax, or small objects (for example glass beads) to create visual, textural and structural effects. There is also the opportunity to create various surface effects through special finishing, enabling numerous structure and surface designs to be achieved. Such techniques have been incorporated into design collections by high-end wallcovering producers. Figure 8.5 shows an example of a nonwoven wallcovering design, ‘Vegas’ by Stereo (a British based wallcovering producer). The Vegas design is produced from 100% polyester and is backed with crepe paper and is around 220 g/m² (www.stereowallcoverings.co.uk). It is suitable for use in all areas of domestic and non-domestic buildings and is coated with Teflon to enable easy care (ibid.). The nonwoven, which appears to be a spunbonded structure, is coated with metallic inks to highlight the fibres creating a shimmering effect. The images in Figs 8.6 and 8.7 show the incorporation of long random threads within the nonwoven structure for decorative affect. ‘Filament’ by Muraspec (Fig. 8.6) shows the inclusion of filaments to create a textured effect and the use of a metallic thread to create a design feature. ‘Sirocco’ by wallpaper producer ‘Vescom’, shown in Fig. 8.7 is constructed from 50% polyester, 10% sisal and 40% wood pulp (http://www.vescom.co.uk) and backed with a stabilizing material. The long sisal fibres create a subtle textured effect. A traditional fabric look and feel can also be achieved using nonwoven technologies if desired. Further to this, due to the production methods used, it is possible to work to a much bigger scale than in traditional wallpaper production.


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8.5 ‘Vegas’ nonwoven textile wallcovering by Stereo (www.stereowallcoverings.co.uk).

8.6 Filament’ nonwoven wallcovering by Muraspec (image courtesy of Muraspec, www.muraspec.com).



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8.7 ‘Sirocco’ nonwoven wallcovering by Vescom (image courtesy of Vescom, www.vescom.co.uk).

Needle-punched nonwovens made from both natural and synthetic fibres can also be used as wallcoverings. Stein suggests that such fabrics should range between 150 g/m² and 300 g/m² (Stein and Slovacek, 2003, p. 519). Often constructed using a rib structure, a number of such products claim to be acoustically absorbent and, like wet-laid products can be engineered to be stain, mildew and fade resistant (http://www.odysseywallcoverings.com).

8.6.2

Backings

Nonwovens are also used as backings for traditional wallcovering substrates. A range of nonwovens can be used for this purpose including stitch-bonded and needle-punched materials (Stein and Slovacek, 2003, p. 519). Often constructed from polyester, fabric weights range from 40 g/m² to 85 g/m² (www.omnova.com). Nonwovens are used as backings when a higher level of dimensional stability is required than can be provided by a traditional scrim. The selection of nonwoven over a woven product is determined by the registration or distortion potential of the printed pattern. Some producers claim that using nonwoven backings can limit pattern distortion in printing (ibid.). They note that nonwoven backings are very stable in print production compared to wovens. Products made from cellulose and polyester can move through the heat and pressure process with little problem (Moore, 2009).


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8.6.3


Temporary wall partitioning

Further to their use as wallcoverings, nonwovens have been used in the design of temporary wall partitioning for domestic and contract interiors. ‘Molodesign’ have developed a product called ‘soft wall’, which is described as a ‘flexible partition prefabricated from 600 thin layers of a soft translucent nonwoven textile’ (www.molodesign.com). The nonwovens used, made from polyethylene, are arranged to create a flexible honeycomb structure that can expand and contract. It is one inch in length when collapsed and extends to more than 20 inches when expanded. The translucent qualities of the nonwovens are exploited to visual effect within interior spaces. The nonwovens used can be treated to be flame resistant and can be made with 100% recycled content if required.

8.7

Nonwoven textiles for floor coverings

Needle-punch technology is widely used to produce carpets for both the domestic and contract interior sectors. Nonwovens are also widely used as primary and secondary carpet backings.

8.7.1

Needle-punched carpets

Needle-punched carpets usually consist of three layers: a face layer, a scrim and a bottom layer. They are produced using pre-needling, flat needling and often structuring techniques (Anand et al., 2007, p. 253). These carpets have found a place in the floor covering market due to advances in needle-punch technology that enables patterning to be realized (Stein and Slovacek, 2003, p. 517). Both broadloom carpets and carpet tiles are produced using these methods. By using structuring needle looms, surface texture including ribs, velour and colour effects can be achieved (Anand et al., 2007, p. 253). Needle looms with ‘lamella’ strips, brush conveyor belts and fine gauge forked needles are used for this purpose. Pre-needled fabrics are re-punched using forked needles that transport the fibres between the lamella strips, which act as bed plates, to create loop pile effects (ibid.). Depending on the orientation of the needle fork in relation to the incoming fabric, a rib or velour effect can be achieved (ibid.). Patterning is introduced by selecting the position of the needles and controlling the strokes per minute. The height of the pile can be adjusted by raising and lowering the lamella table. Figures 8.8 and 8.9 show needled carpets with different pile heights and constructions. A reinforcing fabric backing or coating is incorporated to achieve high dimensional stability (Stein and Slovacek, 2003, p. 517). Fabric weights are in the region of 300–800 g/m² (Anand et al., 2007, p. 253). Needled nonwoven carpets are commonly supplied as roll goods in widths of 2,000 mm, but widths of up to 5,000 mm are possible (Stein and Slovacek, 2003 p. 517). Carpet tiles commonly have dimensions of 500 × 500 mm or 330 × 330 mm.



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8.8 ‘4200 Sidewalk’ needled carpet with a ribbed surface by Burmatex (www.burmatex.co.uk).

8.9 ‘5500 Luxury’ needled carpet with a pile surface by Burmatex (www.burmatex.co.uk).


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8.10 ‘3230 Classic’ fibre bonded sheet carpet by Burmatex (www.burmatex.co.uk).

Needled floor coverings are commonly produced using PP, polyamide (PA) or blends of the two which are spun dyed and blended prior to carding. PET can be used in products where less wear resistance but greater softness is required (Anand et al., 2007, p. 253). Sometimes small quantities of fibres such as viscose are added for comfort. The durability and compression recovery properties of the carpet can be adjusted by blending fibres with different linear densities (ibid.). Linear densities are in the range of 12–20 denier (ibid.). When producing covering that incorporates two layers it is possible to use fibres reclaimed from textile waste for the bottom layer. Needled carpets suitable for both the domestic and contract markets can be produced. For both sectors the carpets must be stable enough so as not to undergo any dimensional changes during cutting and laying and it must be possible to lay the carpet without any bubbles or creases (Stein and Slovacek, 2003, p. 517). In terms of the contract sector, end uses include flooring for hospitals, schools, exhibition centres, airports, office buildings and so on. Within this sector the main demand on the product is high wear resistance. The wear resistance of needled carpets can be increased by needling on both sides (Anand et al., 2007, p. 253). Further to durability, coloured carpets in the contract sector must have high light fastness (Stein and Slovacek, 2003, p. 517). Easy care, stain and flame resistance properties can be built into needle-punched



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carpets through finishing. Specific properties are required in certain areas of this sector, for example, the need for antistatic properties for carpets used in computer rooms. Careful consideration is now given in the design of new buildings to aspects such as ventilation, static and moisture control due to the impact that this can have upon users’ health. Reduced levels of static, catalysed by the careful design of elements such as floor covering, can, it is claimed, improve conditions for users (http://www.marlings.co.uk). Figure 8.10 shows a needle punched carpet constructed from 85% polypropylene and 15% nylon. The product is needled from both sides and impregnated with a synthetic resin. Designed specifically for computer rooms in the contract market, the carpet performs well in static electricity tests (IBM and ICL) and is durable to withstand heavy traffic from castor chairs.

8.7.2

Backings

Nonwovens are commonly used as the primary and secondary backing for traditional tufted carpets. Tufted carpets are comprised of three elements: the pile, the tufting substrate, which is also referred to as the primary backing, and a secondary backing. The primary backing is located between the carpet pile and the secondary backing. The backing is a key factor in determining the final properties of the carpet and also the success of the different construction stages of the carpet including tufting, dyeing and when necessary coating (Slovacek, 2003, p. 522). Primary backings are commonly produced using PP and PET in spunbond processes. Both virgin and recycled fibres can be used as appropriate. Fabric weights in the range of 150–200 g/m² are commonly produced. Both woven and nonwoven substrates can be used as primary backings and each has particular advantages and disadvantages. The multidirectional distribution of filaments in spunbond structures creates an isotropic fabric and therefore good dimensional stability. Further to this they do not fray. These two factors affect the number of points at which the filaments bond. The disadvantages of nonwovens in comparison to wovens are that pile anchorage and tear resistance are less than that of woven substrates (Slovacek, 2003, p. 522). Nonwoven primary backings are suitable for use in broadloom carpets, carpet tiles, car carpeting, dust control mats and bath mats within both the domestic and contract sectors (Slovacek, 2003, p. 522).

8.8

Summary

As outlined in this chapter, nonwovens have established a central role within the interior textiles sector. Within bedding, nonwovens play a key role as component materials and as economic alternatives to facing fabrics. In upholstery they are important as support materials but are emerging as appealing fabrics that afford design possibilities for visible furnishings applications. In wallcoverings,


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nonwovens are now established as a credible and often superior alternative to traditional substrates as both backing and facing materials. In floor covering, nonwovens provide durable solutions, particularly for the contract market. Key to the role of nonwovens within the domestic and contract interior market is the continued development of new products underpinned by new and developing technologies and design innovation. As discussed, such products include anti-microbial bedding, blast proof curtains, static control carpets, expandable partitioning, laser patterned fabrics and decorative nonwoven wallcoverings. The opportunities afforded by the development of durable nonwoven fabric structures has opened up application areas that can be consolidated through innovative and creative design.

8.9

References

Ahmed, A. I. 2007. Chapter 8, ‘Nonwoven fabric finishing’, Russell, S. J. (ed.) in Handbook of Nonwovens, Woodhead Publishing Limited, Cambridge. Anand, S. C., Brunnschweiler, D., Swarbrick, G., Russell, S. J. 2007. Chapter 5, ‘Mechanical bonding’, Russell, S. J. (ed.) in Handbook of Nonwovens, Woodhead Publishing Limited, Cambridge. Assent, H. Cl., Hasse, J. Stoll, M., Brodtka, M. 2003. Chapter 14 , ‘Nonwovens for Apparel’ Albrecht W., Fuchs, H., Kittelmann, W. (eds) in Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Processes, pp 523–544, WileyVech, Weinheim, Germany. Bitz, K. 2003. ‘Nonwovens hit the wall’, Nonwovens Industry, October 2003, http:// www.nonwovens-industry.com/articles/2003/10/feature1, accessed 10.12.08. Chapman, R. 2007. Chapter 7, ‘Chemical Bonding’, Russell, S. J. (ed.) in Handbook of Nonwovens, Woodhead Publishing Limited, Cambridge, p. 365. Engqvist, H. 2005. ‘Index 05 to showcase developments in nonwovens for the home’ Technical Textiles International, March/April. Fletcher, K. 2008. Sustainable Fashion and Textiles, Design Journeys, Earthscan, London, p 105–106. Gopalakrishnan, D., Aswini, R. K. ‘Antimicrobial finishes’, Fibre2Fashion, http:// www.fibre2fashion.com/industry-article/textile-industry-articles/antimicrobial-finishes/ antimicrobial-finishes1.asp, accessed 18.02.09. Kittlemann, W., Dilo, J. P., Gupta, V. P., Kunath, P. 2003. Chapter 6, ‘Web Bonding’, Albrecht W., Fuchs, H., Kittelmann, W. (eds) in Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Processes, pp 269–408, WileyVech, Weinheim, Germany. Moore, R. 2009. Email correspondence with OMNOVA Solutions Inc, 18.02.09. Morris, D. 2008. CIRFS, ‘The World Markets for Interior Textiles to 2012’, 77th International Wool Textile Organisation Congress, Beijing, People’s Republic of China, April, 2008, http://www.cirfs.org/press/the%20world%markets%20for%20interior%20textiles %20to%202012.pdf. Nonwovens Industry. 1999. ‘There’s no place like home’ Nonwovens Industry, April Issue, Rodman Publishing, Ramsey, New Jersey, http://www.nonwovens-industry.com/articles/1999/04/theres-no-place-like-home, accessed 03.09.08. Stein W., Slovacek, J. M. 2003. Chapter 13, ‘Nonwovens for home textiles’ Albrecht W.,



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Fuchs, H., Kittelmann, W. (eds) in Nonwoven Fabrics, Raw Materials, Manufacture, Applications, Characteristics, Testing Processes, pp 512–522, Wiley-Vech, Weinheim, Germany. Yeager, J. I., Teter-Justice, L. K. 2000. Textiles for Residential and Commercial Interiors, 2nd Edition, Fairchild Publications, New York.

Web references http://www.ahlstrom.fi/modules/page/show_page.asp?id=F98B2FAA7510478AB9A771A 9885447B2&tabletarget=data_1&MENU_2_activeclicked=E3B8B35FDD454DA9AD0 DE310D4B3A9E4&pid=02CCFAD536644D13BFB7E705C9A87673&layout= ahlstrom06, accessed 10.12.08. http://www.carbodydesign.com/archive/2007/09/26-mercedes-benz-f700-concept-design/, accessed 06.10.08. http://www.edana.org/Content/Default.asp?PageID=151, accessed 31.12.08. http://www.edana.org/objects/4/images/GraphB.gif, accessed 15.12.09. http://ec.europa.eu/enterprise/textile/development.htm, accessed 18.08.08. http://www.hollingsworth-vose.com/products/industrial/wallcovering/commercial_ applications.htm, accessed 10.12.08. http://www.inda.org/enduses/homefurn/application.html, accessed 03.09.08. http://www.lelievre.eu/decoration/alcantara.html, accessed 06.10.08. http://www.marlings.co.uk/index.php. http://www.molodesign.com/en/products/soft/overview.html, accessed 08.10.08. http://www.odysseywallcoverings.com/skyline.html, accessed 12.12.08. http://www.omnova.com/products/wallCovering/backings.aspx, accessed 12.12.08. http://www.pgi-industrial-europe.com/pid39.mid25.html, accessed 08.10.08. http://www.stereowallcoverings.co.uk/technical_pdfs/vegas_tech.pdf, accessed 12.12.08. http://www.vescom.co.uk/frameset.asp, accessed 12.12.08. http://www.wipo.int/pctdb/en/wo.jsp?wo=2008036119&IA=WO2008036119 &DISPLAY=DESC, accessed 19.09.08.


9 The use of nonwovens as filtration materials S. Z O B E L and T. G R I E S, RWTH Aachen University, Germany

Abstract: Textile fabrics are used as filter media. Depending upon the filtration application, different requirements have to be fulfilled. A number of standards exist for the development of filters and filter media for different applications. Sometimes it is necessary to combine different filtration media to best fit the application’s requirements (e.g. textile filter and membrane). As well as describing the standards, the structural design of the filters and their manufacturing technologies are discussed. Some technological priorities that have arisen due to the introduction of stringent environmental regulations are discussed and future trends are documented. Key words: filter, filtration, depth filtration, surface filtration, nonwoven filter, filter cell, cartridge filter, bag filter, filter application.

9.1

Introduction

This chapter deals with filtration and specifically the use of nonwovens in filtration. The term ‘filtration’ has been defined as: The separation of particles from a fluid–solid suspension of which they are a part by passage of most of the fluid through a septum or membrane that retains most of the solids on or within itself. The septum is called a filter medium, and the equipment assembly that holds the medium and provides space for the accumulated solids is called a filter. The fluid may be a gas or a liquid (Anon., 2007). The particles may be solid, liquid or gaseous substances. There is a huge variety of filter media available. Textile fabrics, porous foams, films and sands can be used as filter media. Depending upon the filtration application different requirements have to be fulfilled. Sometimes it is necessary to combine different filtration media to fit best the application’s requirements (e.g. textile filter and film). The choice of the filter medium depends on the properties of the particles that need to be separated (e.g. particle size, potential for agglomeration, particle concentration) and the surrounding medium (e.g. temperature, flow velocity, etc.). When nonwovens are used as filters, they offer a range of advantages above 160 © Woodhead Publishing Limited, 2010


161

Others 4.70% Agriculture 1.40%

Unidentified 0.50%

Automotive 3.50% Civil engineering/ underground 4.50%

Hygiene 33%

Building/roofing 12.70%

Air and gas filtration 2.40% Liquid filtration 3.90%

Medical/surgical 3.10%

Floor coverings 2.10%

Wipes for personal care 7.70%

Upholstery/table linen/ household 5.90% Coating substrates 1.80%

Wipes – others 7.20%

Garments 1% Shoe/leather goods 1.80% Interlinings 1.90%

9.1 Nonwoven applications (EDANA; Anon., 2006b).

other filter media. For example, nonwovens offer large and adjustable surface properties and can be adapted to different filtration requirements. Depending upon the filter requirements, different textile or plastic grid structures can be combined together to form a sandwich structure (e.g. backing fabric and nonwoven). Compared to other filtration media like membranes, wire cloth and monofilament fabrics, nonwovens offer a thicker cross-section and bulk (Gregor, 2004). This provides the opportunity to use nonwovens as a structure that can fulfil the requirements and boundary conditions of all types of applications. To influence the structure of the nonwoven media, different manufacturing methods are used to manufacture filters for diverse applications. Nonwovens offer high permeability and surface area, which are further enhanced by pleating of the material. Also the wide range of fibre materials available offers good mechanical, chemical and physical thermal properties. Thus, the production of nonwovens for filtration applications is very efficient and can be very economic depending on the fibre material and process steps used. According to Gregor (2004), nonwoven filters are the material of choice when large quantities of particulate loading, long life or where general clarification of a liquid or gas stream is required. In 2005, 4000 t of nonwovens were produced worldwide (Anon., 2006a). In


162


(Million US$)

16000 12000 8000 4000 0 North America

West Europe 2001

Asia-Pacific region 2006

Other regions

2011

9.2 Trend of world filter demand (Anon., 2008).

Europe a total of 1399 t of nonwovens was produced for various applications (Schumann and Erth, 2006) including 3.9% for liquid filtration and 2.4% for gas and air filtration (see Fig. 9.1). Increasing demand and ongoing development of new applications continues to fuel an increase in growth of the use of nonwovens in filtration. As can be seen from Fig. 9.2, growth is expected not only in America and Europe but also in Asia and other regions (Anon., 2008). Rigby (2003) showed that the annual growth rate of nonwovens in filter applications in 2005 was expected to be 8% and to reach a growth of 8.6% by 2010. For comparison the growth rate of general nonwovens production, independent from application was expected to increase by about 4.7% by 2005 and about 5% in 2010 (David Rigby Associates, 2002). Thus, the use of nonwovens for filter applications is one of the fastest growing sectors in the nonwoven market.

9.2

Classification of filters

When choosing the appropriate filter for an application the properties of the fluid surrounding the filter have to be considered. The following features of the surrounding fluid are important: • • • • •

temperature humidity flow condition mass flow chemical composition.

These qualities affect the filter’s performance. In addition the fibre material used, the assembly and the forces and stress exercised on the filter during operation need to be considered. Finally, also the particle properties, for example particle size, particle size distribution and particle material, have to be considered. Taking into account these manifold types of requirements and boundary conditions the available filter media can be classified.



163

For the classification of filter media different methodologies are used. According to the Filters and Filtration Handbook (Dickenson, 1997), filters can be classified in four main categories. These categories are solid–gas separation, solid–fluid separation, liquid–liquid separation and solid–solid separation. Albrecht et al. (2000) add one more separation type, the gas–gas separation, so that filter media are categorised into five different types. The most common methodology for the classification of filter media, which is described in this chapter, is as follows. The filter media are classified depending on: • the nature of the surrounding medium (dry and wet filtration) • surface filters or depth filters • particle size to be filtered (e.g. micro-, ultra-filtration).

9.2.1

Dry and wet filtration

Dry filtration deals with the separation of solid, liquid or gaseous substances from a solid or gaseous medium. These substances are dispersed in the solid or gaseous medium. For example, for solid–solid separation the finer particles are separated from the larger particles by means of a multiple stage sieving process. This procedure determines the grain size distribution of different soils used. For the separation of solids or liquids from a gaseous medium, filter fabrics (e.g. nonwovens, wovens) are used. The fluid with the substances to be filtered out is passed through the filter. Depending on the structure of the filter the particles can be deposited on the surface (surface filtration) or inside (depth filtration) the filter medium installations. Dry filters are usually voluminous structures. The air and gas filtration market includes domestic filters, industrial filters and automotive filters. Domestic filters are used in heating, ventilation and air conditioning (HVAC), cooking, vacuum cleaners and various portable filters in the market. Industrial filters are in general used in (HVAC), high efficiency particulate airfilter (HEPA) and ultra low penetration air (ULPA) filters, dust removal for power stations, incinerators, paint spray house and many industrial processes, where air is contaminated and needs to be cleaned, or a very clean environment is required for the production of, for example, electronic components. Automotive filters include engine air filters (intake and exhaust) and cabin air filters. Wet filtration deals with the separation of solid, liquid or gaseous substances from a liquid medium. The materials to be filtered are usually suspended in the medium. In the case of the separation of a liquid–liquid mixture the boiling point of the different liquids is taken into consideration. By evaporating one of the components of the liquid mixture, the separation can take place. Solid–liquid separation by deposition occurs due to the deposition of the solid particles at the bottom of the container (e.g. sewage treatment). In addition to


164


separation by deposition, filter fabrics (e.g. nonwovens, wovens) are used for wet filtration. Wet filters offer the possibility for fluid permeability and at the same time provide the impermeability for particles that need to be filtered. Nonwoven filter media offer the possibility of collecting the particles on the filter surface (surface filtration) and in the filter medium installation (depth filtration). Wet filtration media are usually very thin and compacted media. Liquid filtration is a fast growing market for nonwovens. It includes water filtration (tap and waste water), food and beverage filtration, pharmaceutical and electric processes, blood filtration, tea bags and coffee and juice filters, cooking oil filters and oil/fuel filters for automotives. Nonwovens have been successfully used in the industry as membrane support for micro-filtration, ultra-filtration and reverse osmosis filtration.

9.2.2

Surface filters and depth filters

Filter media can be classified into surface filter and depth filter media. It has to be mentioned that mostly, both surface and depth filtration occur in the filter medium. The classification of whether the filter medium is a surface or depth filtration medium depends on the preferred deposition area of the particles. Surface filtration is characterised by a deposition of particles or aerosols, whose diameter is greater than the pore size of the filter, on the filter surface (see Fig. 9.3). On one hand the particles can clog and block the filters, which would result in high fluid resistance across the filter, at which point the filter would need to be either cleaned or changed. On the other hand the deposited particles on the surface of the filter can result in the formation of a layer of substrate that has lower pore size than the filter itself, thus facilitating filtering. This layer of substrate is commonly known as a filter cake. Many surface filters function most effectively when the filter cake is developed on the filter. A filter cake is compressible and its filtration efficiency decreases with increasing pressure and reduction of the pore volume. This effect increases the separation until the filter cake is completely blocked (Hoeflinger and Pongratz, 2000). The filtration through a filter cake functions as a depth filter, where the filtered particles are mechanically held or adsorbed into the the cake. For surface filter media only a few particles penetrate into the interior of the filter and remain there. Hence surface filters can be cleaned and reused multiple times. Surface filters usually have a smooth, paper-like surface and are very thin. Filters are generally compared based on their filtration area and the degree of separation possible. According to the Filters and Filtration Handbook (Dickenson, 1997) surface filters have the following properties: • low pressure loss compared to depth filters • high filtration reproducibility with a narrow pore size distribution. In the case of depth filters, the filtered particles of different dimensions settle and


The use of nonwovens as filtration materials Cake formation

165

Suspension

Filter Filter cake Filter

Blocked filter Filtrate

9.3 Surface filtration. Suspension Mechanical filtration

Filter

Filter

Particle absorption Filtrate

9.4 Depth filtration.

deposit themselves within the pores of the filters (see Fig. 9.4). Depth filters are normally used for applications where there is a large difference in particle size. They are usually very thick and can have a progressive density of pore structure. This leads to the interception of very coarse particles in the upper layers of the filter. In subsequent layers, finer particles can be intercepted. Thus coarser particles are separated mechanically and finer particles are filtered due to their adsorption. The pressure difference and the fluid flow rate remain almost constant. Depth filters are difficult to clean and can be reused only under specific circumstances. Criteria for comparison are pore volume, the filter thickness and degree of separation. Depth filters are characterised using the following properties: • suitability for the filtration of difficult filterable solids (e.g. particles of different dimensions); • high filtration efficiency over a wide range of particle sizes. Through the combination of surface and depth filters, it is possible to separate coarser particles by surface filters and the finer particles through depth filters from the fluid stream. This results in high endurance and maintains the throughput performance of the filter media.


166


9.5 Filter media categorised by particle size.

9.2.3

Particle size

When selecting filter media the particle size, particle size distribution, particle type and particle concentration must be taken into account. Large particles are normally intercepted on the surface and finer particles within the filter medium or a filter cake. Based on the particle size, one can categorise currently available filter media useful for different types of filtration processes (see Fig. 9.5). These include for example filter media for reverse osmosis (particle size

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