Recent Advances in Environmentally Compatible Polymers: Cellucon '99 Proceedings

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Author: John F Kennedy | Glyn O Phillips | Peter A Williams

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RECENT ADVANCES IN ENVIRONMENTALLY COMPATIBLE POLYMERS

RECENT ADVANCES IN ENVIRONMENTALLY COMPATIBLE POLYMERS Editors: JOHN F KENNEDY Director of the Birmingham Carbohydrate and Protein Technology Group, School of Chemistry, The University of Birmingham, Birmingham B 15 2TT, England UK. and Director of ChembiotechLaboratories, University of Birmingham Research Park. Birmingham B15 2SQ, England, UK and Professor of Applied Chemistry, The North East Wales Institute of Higher Education, Wrexham, Clwyd LLll 2AW. Wales, UK

GLYN 0 PHILLIPS Chairman of Research Transfer Ltd (Newtech Innovation Centre), and Professorial Fellow of The North East Wales Institute of Higher Education, Wrexham, Clwyd, LLll 2AW, Wales, UK and Professor of Chemistry, The University of Salford, England, UK PETER A WILLIAMS Head of the Multidisciplinary Research and Innovation Centre, and the Centre of Expertise in Water Soluble Polymers, and Professor of Polymer and Colloid Chemistry. The North East Wales Institute of Higher Education, Wrexham, Clwyd, LL11 2AW, Wales, UK Guest Editor: HYOE HATAKEYAMA Professor of Applied Physics and Chemistry, Department of Applied Physics and Chemistry, Faculty of Engineering and Graduate School of Engineering, Fukui University of Technology, 3-6-1 Gakuen, Fukui, Fukui 910-8505, Japan

W O O D H E A D PUBLISHING LIMITED

Published by Woodhead Publishing Ltd Abington Hall, Abington, Cambridge CB 1 6AH, England www.woodheadpublishing.com First published 2001 Reprinted 2006 0 2001, Woodhead Publishing Limited The authors have asserted their moral rights

Conditions of sale 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 publisher, 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 the publisher. 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. ISBN-13: 978-1-85573-545-3 ISBN-I 0: 1-85573-545-8

Printed in Great Britain by Antony Rowe Ltd, Chippenham. Wiltshire

CONTENTS Preface .............................................................................................................................

xv

PART 1: AN OVERVIEW OF THE DEGRADATION OF POLYMER MATERIALS 1.

-

Degradation of important polymer materials an overview of basic reactions B R h b y .....................................................................................................................

3

PART 2: SYNTHESIS AND DERIVATISATION OF BIOCOMPATIBLE POLYMERS 2.

3.

4.

5.

6.

7.

8. 9.

Conjugated oligomers bearing furan and thiophene heterocycles: synthesis, characterization and properties related to electronic conduction and luminescence C Coutterez and A Gandini .....................................................................................

17

Polyamides incorporating furan moieties. Novel structures and synthetic procedures M Abid, S Gharbi, R El Gharbi and A Gandini ......................................................

27

Saccharide- and lignin-based polycaprolactones and polyurethanes H Hatakeyama, Y Izuta, T Yoshida, S Hirose and T Hatakeyama .........................

33

Cellulose as a raw material for levoglucosenone production by catalytic pyrolysis G Dobele, G Rossinskaja, T Dizhbite, G Telysheva, S Radtke, D Meier and 0 Faix ...............................................................................................................

47

New ionic polymers by subsequent functionalization of cellulose derivatives M Vieira, T Liebert and Th Heinze .........................................................................

53

Preparation and characterization of carbamoylethylated and carboxyethylated konjac mannan S Takigami, Y Suzuki, A Igarashi and K Miyashita ...............................................

61

Plastification of cellulosic wastes M Durhn, M Moya, E Umaiia and G JimCnez .........................................................

67

Synthesis and thermal properties of epoxy resins derived from lignin S Hirose, M Kobayashi, H Kimura and H Hatakeyama .........................................

73

10. Effect of modification on the functional properties of rice starch M A M Noor and M N Islam ..................................................................................

79

vi

Contents

11. Succinylation of chemically modified wool keratin - the effect on hygroscopicity and water absorption N Kohara, M Kanei and T Nakajima ......................................................................

91

12. Natural polymers for healing wounds J F Kennedy, C J Knill and M Thorley ...................................................................

97

PART 3: PRODUCTION AND USE OF BIOCOMPATIBLE MATERIALS 13. Improvement of alginate fiber mixing with phosphoryl polysaccharides S Tokura, H Tamura, Y Tsuruta, C Nagaei and K Itoyama ..................................

107

14. Preparation of cellulose viscose for various matrices B Lonnberg, S Ciovica, T Strandberg, T Hultholm and K Lonnqvist .................. 1 13 15. Synthesis and properties of novel polyelectrolyte on the basis of wood polymer G Shulga, G Zakis, B Neiberte and J Gravitis ......................................................

123

16. Utilising the potential of wood fibre L Salmtn and U-B Mohlin ....................................................................................

129

17. Composites from banana tree rachis fibers (Musa Giant Cavendishii AAA) M Sibaja, P Alvarado, R Pereira and M Moya .....................................................

139

18. Temperature and concentration dependency on equilibration in polysaccharide electrolyte hydrosol M Takahashi, M Mishima, T Yamanaka, T Hatakeyama and H Hatakeyama ..... 145 19. Hydrolysed lignin. Structure and perspectives of transformation into low molecular products M Ja Zarubin, S R Alekseev and S M Krutov .......................................................

155

20. Products of lignin modification: promising adsorbents of toxic substances T Dizhbite, A Kizima, G Rossinskaya, V Jurkjane and G Telysheva .................. 161 21. Characterisation and adsorption of lignosulphonates and their hydrophobized derivatives on cellulose fibre and inorganic fillers G Telysheva, T Dizhbite, A Kizima, A Volperts and E Lazareva ........................

167

PART 4: BIODEGRADABLE POLYURETHANE-BASEDPOLYMERS 22. Biodegradable and highly resilient polyurethane foams from bark and starch J-J Ge, W Zhong, Z-R Guo, W-J Li and K Sakai .................................................

175

Contents

vii

23. Biodegradable polyurethanes derived from waste in the production of bean curd and beer K Nakamura, M Iijima, E Kinoshita and H Hatakeyama ......................................

18 1

24. Biodegradable polyurethane composites containing coffee bean parchments H Hatakeyama, D Kamakura, H Kasahara, S Hirose and T Hatakeyama ............ 19I 25. Biodegradable polyurethane sheet derived from waste cooking oil S Srikumlaithong, C Kuwaranancharoen and N Asa ............................................

197

26. Biodegradable polyesters prepared with dimethyl succinate, butanediol and monoglyceride Y Taguchi, A Oishi, K Fujita, Y Ikeda and T Masuda .........................................

205

Preparation and thermal properties of polyurethane composites containing fertilizer N Yamauchi, S Hirose and H Hatakeyama ...........................................................

21 I

28. Biodegradable polymers derived from lactide and lactic acid S H Kim and Y H Kim ..........................................................................................

217

29. Biodegradable polyurethane foams from molasses Y Hazutani ............................................................................................................

227

27.

30. Biodegradable polyurethane foams derived from molasses K Kobashigawa, T Tokashiki, H Naka, S Hirose and H Hatakeyama .................. 229 31. Polyurethane from pineapple wastes M Moya. J Vega, M Sibaja and M Durin .............................................................

235

32. Preparation and physical properties of saccharide-based polyurethane foams Y Asano, H Hatakeyama, S Hirose and T Hatakeyama .......................................

.24 1

33. Biodegradable polymer in seed protein from corn J Magoshi and S Nakamura ...................................................................................

247

PART 5: ANALYSIS AND CHARACTERISATION OF NEW POLYMERS AND MATERIALS 34.

The complete assignment of the "C CPMAS NMR spectra of native cellulose by using 13Clabelled glucose T Erata, T Shikano, M Fujiwara, S Yunoki and M Takai .....................................

261

...

Vlll

Contents

35. 13CCPMAS NMR and X-ray studies of cellooligosaccharideacetates as a model for cellulose triacetate H Kono, Y Numata, N Nagai, M Fujiwara, T Erata and M Takai ........................

269

36. Thermal and mechanical properties of cellulose acetates with various degrees of acetylation in dry and wet states T Asai, H Taniguchi, E Kinoshita and K Nakamura .............................................

275

37. DSC and TG studies on cellulose-based polycaprolactones H Hatakeyama, H Katsurada, N Takahashi, S Hirose and T Hatakeyama ........... 28 1

38. TG-FTIR studies on cellulose acetate-based polycaprolactones T Yoshida, H Hatakeyama, S Hirose and T Hatakeyama .....................................

289

Thermal analysis of functional paper by a temperature modulated technique T Hashimoto, W-D Jung and J Morikawa ............................................................

295

40. DSC studies on the structural change of water restrained by pectins M Iijima, K Nakamura, T Hatakeyama and H Hatakeyama .................................

303

39.

41. Thermal properties of wood ceramics by TG-MS and CRTG T Arii and M Momota ........................................................................................... 3 1 42. Application of environment controlled thermomechanical analysis system H Katoh, T Nakamura and N Okubo ....................................................................

3 7

43. Effect of water on molecular motion of alginic acid having various guluronic and mannuronic acid contents M Takahashi, Y Kawasaki, T Hatakeyama and H Hatakeyama ...........................

32 1

44. Effect of the initial state on the sorption isotherm and sorption kinetics of water by cellulose acetate H Gocho, A Tanioka and T Nakajima ..................................................................

327

45. Osmometric and viscometric studies on the coil-helix transition of gellan gum in aqueous solutions E Ogawa ................................................................................................................ 333

46. Weathering analysis of modified poly (2,6-Dimethyl-1,4-Phenylene ether) by thermal analysis Y Nishimoto, K Sato, Y Nagai and F Ohishi ........................................................

341

47. Non-desirable carbohydrate reactions in pulping and bleaching G Gellerstedt and J Li ...........................................................................................

347

Contents

ix

PART 6: BIOENGINEERING OF NEW MATERIALS 48.

49.

Precision analysis of biosynthetic pathways of bacterial cellulose by I3C N M R M Fujiwara, Y Osada, S Yunoki, H Kono, T Erata and M Takai .........................

359

Studies of transglycosylation of cellobiose by partially purified trichoderma viride R-Glucosidase H Kono, M R Waelchli, M Fujiwara, T Erata and M Takai .................................

365

50. Celsol - modification of pine sulphate paper grade pulp with

51.

52.

53.

54.

55.

56.

Trichoderma Reesei cellulases for fibre spinning P Nousiainen and M Vehvilainen .........................................................................

37 1

Formation and characterization of transformed woody plants inhibiting lignin biosynthesis N Morohoshi and Y Tsuji .....................................................................................

379

Characterization and utilization of ligninolytic enzymes produced by basidiomycetes M Kuwahara .........................................................................................................

387

Kinetics of biodegradation of n-alkanes by pseudomonas immobilised in reticulated polyurethane foam M G Roig, J F Kennedy, C J Knill, J M Sanchez, M A Pedraz, H Jerabkova and B Kralova ..................................................................................

397

Biocornpatible aspects of poly (2-methoxyethylacrylate) (PMEA) the relationship between amount of adsorbed protein, its conformational change, and platelet adhesion on PMEA surface M Tanaka, T Motomura, M Kawada, T Anzai, Y Kasori, T Shiroya, K Shimura, M Onishi, A Mochizuki and Y Okahata ............................................

405

Isolation of a lignin-degrading laccase and development of tranformation system in Coriolus Versicolor Y Nitta, Y limura, J Mikuni, A Fujimoto and N Morohoshi ................................

41 1

Effect of biodegradable plastics on the growth of Escherichk coli A Nakayama, N Yamano, S Fujishima, N Kawasaki, N Yamamoto, Y Maeda and S Aiba.. ..........................................................................................

.4 19

Index ....................................................................................................................

425

THE CELLUCON TRUST Incorporating

Cellucon Conferences International Educational Scientific Meetings on Cellulose. Cellulosics and Wood

Cellucon Conferences as an organisation was initiated in 1982, and Cellucon '84, which was the original conference, set out to establish the strength of British expertise in the international field of cellulose and its derivatives. This laid the foundation for subsequent conferences on carbohydrate etc. polymer topics in Wales (1986), Japan (1988), Wales (1989), Czechoslovakia (1990), USA (1991), Wales (1992), Sweden (1993), Wales (1994), Finland (1998), and Japan (1999). These conferences have had truly international audiences drawn from the major industries involved in the production and use of cellulose pulp and fibre derivatives of cellulose, plus representatives of academic institutions and government research centres. This diverse audience has allowed the cross-fertilisation of many ideas, which has done much to give the field of cellulose in its diverse forms the higher profile that it rightly deserves. Cellucon Conferences are organised by The Cellucon Trust, an official UK charitable Trust with world-wide objectives in education in wood and cellulosics. The Cellucon Trust is continuing to extend the knowledge of all aspects of cellulose, lignin, hyaluronan and other national polymers world-wide. At least one book has been published from each Cellucon Conference as the proceedings thereof This volume arises from the 1999 conference held in Tsukuba, Japan and the conferences planned to be held in the UK and in the USA etc, will generate further usehl books in this area

THE CELLUCON TRUST TRUSTEES AND DIRECTORS Prof G.O. Phillips (Chairman) Prof J.F. Kennedy (Deputy Chairman and Treasurer) Prof P.A. Williams (Secretary General)

Research Transfer Ltd, UK The North East Wales Institute, UK, and The University of Birmingham, UK The North East Wales Institute, UK

THE CELLUCON TRUST is a registered charity, UK Registration No: 328582 and a company limited by guarantee, UK Registration No: 2483804 with its registered offices at Chembiotech Laboratories, The University of Birmingham Research Park, Vincent Drive, Birmingham, B15 2SQ, UK.

The 1lthInternational Cellucon Conference

CELLUCON '99

Recent Advances in Environmentally Compatible Polymers

ACKNOWLEDGEMENTS This book arises fiom the International Conference - CELLUCON '99 - which was held at the Tsukuba Center for Institutes, Tsukuba. This Meeting owes its success to the invaluable work of its Organising Committees and its generous sponsors.

SPONSORS OF CELLUCON 99 Agency of Industrial Science and Technology (Japan) Ministry of International Trade and Industry (Japan) New Energy and Industrial Technology Development Organisation (Japan) The Cellucon Trust (UK)

MEMBERS OF THE ORGANISING COMMITTEES - CELLUCON '99

General Chairman Dr M Kubota National Institute of Materials and Chemical Research, Japan

Domestic Organising Committee Chairman Vice Chairman Members

Dr K Ueno National Institute of Materials and Chemical Research, Japan Dr Y Watanabe National Institute of Materials and Chemical Research, Japan Prof H Hatakeyama Fukui University of Technology, Japan Dr S Hirose National Institute of Materials and Chemical Research, Japan Dr M Funabashi National Institute of Materials and Chemical Research, Japan

International Organising Committee Chairman Vice Chairman Members

Prof H Hatakeyama Fukui University of Technology, Japan Prof J F Kennedy The University of Birmingham, UK Prof G 0 Phillips Research Transfer Ltd, UK Prof P A Williams The North East Wales Institute, UK Prof B Lonnberg Abo Akademi University, Finland Prof M Duran Universidad Nacional, Costa Rica Prof M A M Noor Universiti Sains Malaysia, Malaysia Prof E H M Melo Universidade Federal de Pernambuco, Brazil Prof T Hatakeyama Otsuma Women's University, Japan Dr S Hirose National Institute of Materials and Chemical Research, Japan Dr M Funabashi National Institute of Materials and Chemical Research, Japan

Local Committee

Chairman Vice Chairman Members

Dr Y Watanabe National Institute of Materials and Chemical Research, Japan Prof T Hatakeyama Otsuma Women’s University, Japan Prof K Nakamura Otsuma Women’s University, Japan Dr S Hirose National Institute of Materials and Chemical Research, Japan Dr M Funabashi National Institute of Materials and Chemical Research, Japan

Secretariat

Dr S Hirose National Institute of Materials and Chemical Research, Japan Dr M Funabashi National Institute of Materials and Chemical Research, Japan

THE CELLUCON CONFERENCES 1984 Cellucon '84 UK

CELLULOSE AND ITS DERIVATIVES Chemistry, Biochemistry and Applications

1986 Cellucon '86 UK

WOOD AND CELLULOSICS Industrial Technology, Biotechnology, Structure and Properties

1988 Cellucon '88 Japan

CELLULOSICS AND WOOD Fundamentals and Applications


CELLULOSE: SOURCES AND EXPLOITATION Industrial Utilisation, Biotechnology and Physico-Chemical Properties

1990 CeUucon '90 Czechoslovakia

CELLULOSE New Trends in the Complex Utilisation of Lignocellulosics (Phytomass)

1991 Cellucon '91 USA

CELLULOSE A Joint Meeting of: ACS Cellulose, Paper and Textile Division, The Cellucon Trust, and 1I* Syracuse Cellulose Conference


SELECTIVE PURIFICATION AND SEPARATION PROCESSES

1993 Cellucon '93 Sweden

CELLULOSE AND CELLULOSE DERIVATIVES Physico-Chemical Aspects and industrial Applications


CHEMISTRY AND PROCESSING OF WOOD AND PLANT FIBROUS MATERIALS The Chemistry and Processing of Wood and Plant Fibrous Materials

1998 Cellucon '98 F d a n d

PULP AND PAPER MAKING Fibre and Surface Properties and other Aspects of Cellulose Technology

1999 Cellucon '99 Japan

RECENT ADVANCES IN ENVIRONMENTALLY COMPATIBLE POLYMERS

2000 Hyaluronan 2000 UK

HYALURONAN 2000

The proceedings of each conference were formerly published by Ellis Horwood, Simon and Schuster International Group, Prentice Hall, Campus 400, Maylands Avenue, Hennel Hempstead, Herts, HP2 7EZ, UK and from 1993 are published by Woodhead Publishing Limited, Abington Hall, Abington, Cambridge CB1 6AH, UK.

PREFACE Biopolymers such as polysaccharides, lignin, proteins and polyesters are a natural resource, being produced by living organisms. However, these compounds are not always useful for mankind. In order to compensate for the apparent unsuitability and inconvenience of natural polymers, various kinds of synthetic polymers have been developed by using petroleum and coal as raw materials. Recently, however, it has been found that most synthetic polymers are not compatible with the environment, since they cannot be included in the natural recycling system. They have therefore become less popular. Mankind is presented with serious contradictions between the convenience of human life and compatibility with natural circumstances. It is easy to say that we have to return to nature in order to solve the problems of man-made material. However, this means that we lose all the convenient features and materials which science has developed throughout human history. Accordingly, we have to accomplish a form of ‘sustainable development’, maintaining our present life, developed by science, along with compatibility.

In the polymer industry, utilization of plant and animal components is the key to sustainable development. Carbohydrates have already been used significantly in the food, medical and cosmetic industries. Plant materials such as cellulose, hemicellulose and lignin are the largest organic resources but with the exception of cellulose, they are not very well utilized. Hemicellulose is significantly under-utilized. Lignin, production of which is over twenty million tons per year worldwide, is mostly burnt as fuel and only increases the amount of carbon dioxide in the environment, although lignin is one of the most useful natural resources. We have to understand that nature constructs a variety of materials that can be used for human life. Physical properties of biomaterials cover the range from viscous liquids to solids. The complexity of biomaterials is based on the intricacies of their complex molecular architectures. However, scientific advances enable us to understand molecular features of biomaterials through modern analytical methods such as infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermal and mechanical analysis and electron microscopy. Now is the time to consider that the compounds produced through biosynthesis can be used as “ready-made” raw materials for the synthesis of useful plastics and materials for human life. Is it possible for example, to convert plant components to high-performance and highly functional materials? Of course, the answer is ‘Yes’. Major plant components, such as carbohydrates and lignin, contain highly reactive hydroxyl groups that can be used as reactive chemical reaction sites. Using the reaction sites, it is possible to convert carbohydrates and lignin, for example to gels, membranes, functional polymers, engineering plastics and biodegradable polymers that are environmentally compatible. This book, which is the proceedings of the International Cellucon Conference 99 (Japan) is divided into several sections. It commences with the keynote lecture which offers an overview of basic reactions which occur in the degradation of important polymers. The section on Synthesis and derivatisation of biocompatible polymers

xvi

Preface

includes various reaction routes for the production of useful polymers and their derivatives from plant components. The section on production and use of biocompatible materials offers a material design lesson on the architectural methods to relate chemical structures of biocompatible polymers to their physical properties. The section on biodegradable polyurethane-based polymers reports the recent development in preparation and physical properties of polyurethanes from biomass. The section on analysis and characterisation of new polymers and materials covers the application of CPMAS NMR, X-ray analysis, differential scanning calorimetry (DSC), thermogravimetry (TG), TG-Fourier transform infrared spectrometry conversion, modification and characterisation of biopolymers. Collectively, the 56 papers cited in this book provide a perspective on the current state of knowledge of biomaterials science as it affects the structural, synthetic and biotechnological fields of environmentally compatible materials.

Hyoe Hatakeyama Chairman International Organising Committee for Cellucon '99

Part 1

An overview of the degradation of polymer materials

DEGRADATION OF IMPORTANT POLYMER MATERIALS AN OVERVIEW OF BASIC REACTIONS

-

Bengt RAnby Department of Polymer Technology, Royal Institute of Technology, SE-10044, Stockholm, Sweden

1. Introduction The main theme of this conference is related to environmentallycompatiblepolymers. Because most commercial polymer materials are of high molecular mass they have as such insignificantbiological effects. Their degradation products and the additives of low molecular mass may, however, affect the environment. Therefore, it is essential to know the basic reactions of degradation for the important polymer materials used in large amounts. Environmentaleffects of polymer materials are decreased when the materials are reused (recirculated) in some way. To maintain useful properties of the materials degradation should be under control and brought to a minimum, i.e. stability retained. Also during recirculation,it is important to know what basic degradationreactions may occur and affect the properties.

2. Degradation Reactions 2.1. Degradation reactions of polymer materials are initiated in various ways related to the conditions to which the materials are exposed A common first degradation step is radical formation by main valence bond scission which may be caused by high energy radiation, absorption of ultraviolet or even visible light, mechanical stress or a high velocity gradient, molecular motion at high temperature or electron injection at high voltage. The polymer radicals formed react easily with molecular oxygen in triplet (biradical) state which is the ground state for atmospheric oxygen.

2.2 Polymers containing or conjugated double bonds react easily by addition of molecular oxygen in excited singlet state and with ozone (0, which ) decomposes to singlet oxygen and atomic oxygen. This is jhe "ene" with singlet oxygen which causes oxidation and bond scission. Atomic oxygen may abstract hydrogen from the polymer which gives radical formation.

2.3.Polymers containing ester, amide and ether bonds in their main chain degrade by ' hydrolysis. This is which is catalyzed by acid and alkali in the presence of water and is faster at elevated temperature. 2.4 Many polymer materials are degraded in

andtheenzymes involved may have various initiation functions, e.g. catalyze hydrolysis, cause oxidation of C-Hgroups to C-OH,give proton transfer, etc.

The four types of basic degradation reactions will be further described and exemplified for the important commercial polymer makrials.

4


3. Initiation bv Radical Formation 3.1. PhotodegI.adationof PoThe most frequent initiation of polymer degradation in v i m is radical formation by bond scission. Because most polymer materials are exposed to light, especially sunlight, when they are used, photodegradation is a very common and extensively studied reaction as reviewed (1,2,3). The spectrum of sunlight in clear weather extends from ultraviolet light (290-400 nm) to visible light (400-800 nm) with the relation of wavelengths and energy quanta shown in Fig. 1. The bond scission energies for single chemical bonds vary from about 110 kcal/mole for strong bonds to about 50 kcal/mole for weak bonds Fig. 1. This means that most common main valence bonds have bond scission energies correspondingto ultraviolet light quanta. The visible light quanta may only break weak chemical bonds (Fig. 1). Only light quanta which are absorbed may initiate a chemical reaction. The ultraviolet absorption spectra of thin polymer films and the spectral distribution of sunlight are given in Fig. 2. Polyolefms and poly(vinylch1oride)have low absorption of ultraviolet light but show high rate of photodegradation due to their chemical reactivity. Tertiary and allylic hydrogens are easily abstracted. The 0-0bonds in peroxides and hydroperoxides are very weak (Fig. 1). Photodegradation of polymers in air is largely a free radical process with a following oxidation (photo-oxidation)and leads to cleavage of the polymer backbone (chain scission), crosslinking,rearrangement, unsaturation and products of low molecular mass. All these processes may be responsible for the loss of mechanical or other physical properties of a polymer material such as color, gloss, impact strength, tensile strength, elongation at break and increase other properties, e.g., wettability, adhesion, etc. The polymer becomes brittle, cracks and holes are fonned on the polymer surface, oxygen and impurities penetrate into the bulk and the aging process is spreading through the sample.

150

i Fig. 1 Energy quanta ys wavelengths and dissociation energy of common chemical bonds.

I I

200

I

VISIBLE I

400

Wavelength (11111)

I

600

I

I

800

Degradation of important polymer materials

. ...

5

.

in photodegradation was given by Bolland and Gee in the 1940’s (5). It involves free radical formation followed by addition of molecular oxygen to peroxyl radicals which abstract hydrogen and form hydroperoxide groups (equ. 1). hv

+ Pa + Ha P. + o,+ P - 0 PH

P - 0- 0.+ RH-

0.

P - 0- OH + R* hv

PH + 02+

(1)

IPH - o,l-+

IPH

- o,l*+

P.+ H - o - 0-

The initiating free radicals are formed from absorption of light quanta by (i) impurities of low molecular mass, (ii) chromophoric groups in the polymer, or (iii) charge transfer complexes of polymer and oxygen, which upon irradiation or energy transfer break up into polymer and hydroperoxyl radicals (equ. 1).

200

2.0 Q)

3

z B

1.0

40 0

220

-

n

240 260 280 300 320 340 360 380 400 Wavelength (nm)

Fig. 2. Ultraviolet absorption spectra of polymer films (0.04 mm) and the spectral distribution of sunlight (at 41’ north in July at noon): aromatic polyester (AP),polyarylate (PAR), polycarbonate (PC), polyethylene (PE), polyethylene terephthalate (PET), polysulfone (PSF), poly(viny1 chloride) (PVC). Reproduced from ref. 4 by permission of Technomic. The impurities and the polymer chromophores may contain carbonyl (C=O) or aromatic groups or double bonds (C=C) which absorb light quanta. Continued irradiation leads to * . By energy transfer hydroperoxide groups decompose to alkoxyl and hydroxyl radicals which both are Eactive and abstract hydrogen and form new radicals (equ.2). The hydroxyl radicals are so reactive and shortlived that they an difficult to analyze by ESR spectroscopy.

P - 0- OH+

PO.+ HO.

PO*+PH+POH+P* HO.+ PH+

H,O + Pa

(2)

6


In this way one initiated polymer radical (equ.1) may give an increasing number of polymer radicals in the propagation steps (equ.2).

Photooxidation of polyolefins leads to increased amounts of carbonyl groups dong the chains and also unsaturation at the chain ends. In spite of extensive research the mechanism of chain scission for polyethylene is not quite established. The formation of hydroperoxide groups is shown in equ.( 1). The photodecomposition of P-OOH in the polymer phase (PH) would give carbonyl groups and water (equ.3) or chain scission with one carbonyl chain end and one unsaturated chain end (equ.3). The presence of a carbonyl group on the polyolefin chain may also give chain scission (equ.3) by a nonradical rearrangement. Ketone groups have high absorption of UV light and transfer energy to hydroperoxide groups which have low UV absorption.

P - OOH

+P = 0 + H,O

(in cage reaction)

H /

+ v

P-OOH+P,-C

H,C=CH+H,O

(3)

\

P,

0

H /

P=O+P,-C \\

+

0

H,C=CH \

P,

During photodegradation of polyethylene there is an accumulation of carbonyl and vinyl groups, which are formed by "in cage" reactions and chain scissions. Polypropylene is rapidly photodegraded due to the tertiary hydrogens which are easily abstracted. The mechanism is well established by ESR studies of the intermediate radicals and analysis of carbon monoxide and methane during the degradation (6). The mechanism involves abstraction of tertiary hydrogen, formation of hydroperoxide groups as previously shown (equ.1). decomposition of the hydroperoxides and formation of carbon monoxide (CO) and methyl radicals in the cage (equ.4). The result is chain scission to two chain end radicals which together with the methyl radicals are analyzed by ESR spectra. The methyl radicals abstract hydrogen and form methane according to gas analysis. H

0

1

II

- CH, - C - CH, 1

CH,

0 H

- CH, - C - CH, -+- CH, + C + ~ H F CH,

(4)

CH,

The 1 * involves radical combination. Polyethylene radicals form stable C-C crosslinks (equ.5). With sufficient amounts of oxygen present peroxyl radicals form. One peroxyl and one polymer radical or two peroxyl radicals may combine (equ.5). The peroxide groups formed have low light absorbtion and are rather stable. When a polymer peroxyl radical is reacting with a hydroperoxyl radical, a polymer carbonyl group is formed which has high UV absorption and may initiate further photo-


7

degradation as shown in equ.(3). Tertiary peroxyl radicals on polypropylene chains may interact but do not terminate photodegradation by crosslinking. Instead new radicals are formed and the polypropylene chains degrade (equ. 4).

P.+ P-+

P-P

PO2.+Po,.+P-o0-P+O2

PO,.i. P.+P - 00 - P

PO; +Po,.+

P = O + POH + 0,

(5)

PO,.+ HO,---+P = O + H,O + 0,

. .

3.2 2 Most polymer materials degrade when irradiated with high energy radiation, e.g. an accelerated electron beam or gamma radiation from a T o cell. Some crosslinking may occur but chain scission is usually more rapid and prevails. In the case of polyethylene the crosslinking reaction is several times faster than the chain scission. Therefore, electron beam irradiation (EB) has been developed as an established commercial method for crosslinking of polyethylene in hot water pipes and electric wire insulation (7).

In mcdical and food technology high energy radiation is used increasingly for sterilization of disposable items in medical care and for packaging materials. For such applications the radiation dose is optimized to give desind sterilization effects at an acceptable degree of degradation. In these processes the energy of the radiation electrones and gamma particles is 10' to 10' times higher than the dissociation energy of the common chemical bonds. Therefon, a large number of different radicals are formed in the bulk of the polymer and the molecular mechanisms of degradation are difficult to establish as reported in the literature (8). A selected use of EB radiation to initiate polymer surface modification of medical devices has been developed and applied (9).

3.3. High mechanical stress of solid polymer samples and high velocity gradients are reported to cause chain scission. An example is ball milling of polyethylene (10) which gives degradation to a limiting chain length of about 100 carbon atoms. Shorter chains do not degrade by ball milling. It is also reported that polymers added to lubrication oil for viscosity control are degraded when used. Radical formation in stressed polyamide fibers has been observed by ESR measurements (11). Bond scission in a polymer exposed to air forms radicals which react by adding molecular oxygen observed by the emission of light. A simple experiment is rapid peeling a Scotch tape from a solid surface. In the dark a clear light emission is observed and interpreted as rJlemiluminescenceemitted from radical reactions occurring in the process.

.

.

Attempts to study expected chain scissions as of a solid polymer sample have been made (12). Rapid deformation giving a brittle crack of the sample causes emission of light which can be observed in the dark with the naked eye. Dogbone samples of 6.6-polyamide and polypropylene were mounted in an Instron tester and deformed at a rate giving necking of the sample. The stress-induced

8


chemiluminescence at the necking position was measured with a very sensitive photometer constructed for the purpose (12). Simultaneous Insmn measurements of stress-induced chemiluminescence and temperature of a sample at the running neck position (Fig. 3) were interpreted as a reaction of thermally unstable hydroperoxide groups present in the samples (equ.3). Previous heating and treatment with sulfur dioxide which degrades hydroperoxide groups decrease the stress-inducedchemiluminescenceto low values. It is possible that the stress-inducedchemiluminescenceand the thermoluminescence of reacting hydroperoxide groups also initiate chain degradation of the polymer. The alkyl ketone groups (Pa)formed give chain scission by photo-oxidation (equ.3). 500

2ocW

400 -

0

Load

20

60

40 Exleiisioii

80

(IIIIII)

Fig. 3 Simultaneousstress chemiluminescence(SCL)and load-extension curve for an injection moulded polyamide (PA66) specimen. Load, photon counts and temperature sus extension. The temperature curve has been multiplied by a factor three for legibility (ref. 12).

4. Deeradation bv Sinelet Oxygen and Ozone While molecular oxygen in ground state is a triplet, i.e. a biradical state, which reacts with organic radicals according the quantum rules, excited singlet oxygen (lo2) and ozone (0,) react with double bonds in alkenes and dienes in organic molecules (14). Singlet oxygen has an excitation energy of 22,5 kcaVmole and a halflife of 45 min. in pure state. Singlet oxygen is produced, e.g. photochemically by energy transfer from excited dyes, by high frequency electric discharge in an atmosphere of molecular oxygen to2),and by decomposition of various peroxides. The "ene" reactions of singlet oxygen with akenes and dienes give endoperoxides and hydroperoxides (equ.6).

The "ene" reactioii

EticlopeIoxide


9

The hydroperoxides and endoperoxides react further and give chain scission as shown in equ. (3). Ozone (0,)reacts with alkenes by addition to double bonds (equ.7)and forms an intermediate endoperoxide which is unstable and causes chain scission to oxidized end groups (15).

This reaction is rapid and involves intermediateradical formation. Ozone is used as a reagent to test the stability of polydienes to oxidation.

5. Degradation bv Hvdrolvsis. Polyesters, polyamides, polyethers, polyanhydrides,etc. are formed by stepwise polymerization and contain hydrolyzable groups in the backbone chain. They are degraded by hydrolysis in common applications. Hydrolysis is an ionic reaction with rather high activation energy (20-30kcal/mole) which means that the naction rates increase rapidly at rising temper a t m (16).In aqueous solution the hydrolysis is catalyzed by protons (acid solution) and hydroxyl ions (alkaline solution). Also polysaccharidesare degraded by hydrolysis. Hydrolysis of polyesters, polyamides and polypeptides are extensively studied reactions. The reaction mechanisms are well presented in common textbooks. Briefly the bond scission occurs between the CO-group and the oxygen (0)in the polyester chains and between the CO and the amine (NH) group in the polyamide chains. The new endgroups are -COOH, -OH and

-NH,.

6. Biodegradation of Polymers Biodegradation is defined as a chemical decompositionwhich takes place through the action of enzymes associated with living organisms, e.g. bacteria, fungi, higher plants and animals, or their emitted products (17). All enzymes are proteins with active sites which are effective in close contact with the polymer substrate. Most enzymes are effective catalysts for reactions with certain chemical structures. Under favorable conditions, e.g. temperature, pH, added salts etc.. enzymes may increase the reaction rate by several powers of 10. For some common polymer structures like polyolefins, polystyrene and polyvinylchloride,then are no enzymes for direct reaction. In such cases the degradation may start with oxidation as a first critical step. One example is the extensively studied polyethylene which is biodegraded after chain or endgroup oxidation. Even some

10


B

Table e1.v Enzyme class

Reaction catalysed

Oxidoreductase

Redox reactions

t (17). Reactive bonds

,c

1

=0

\

-C / - NH, Transfer of functional

Transferase

PUPS

Hydrolase

Hydrolysis

Lyase

Addition to double bonds

Isomerase

Isomerisation

Ligase

Formation of new bonds

One C-group Acetyl groups Esters Amides

-c=c-

>c=o

Racemaces (d, I-foms)

-c-0-c-s-

-C-N-

native polymers like lignin and polyisopren (cis and trans) are biodegraded only after initial oxidation. Some of the oxidation reactions are specific for the enzyme applied and may involve the insertion of one or two oxygen atoms.

6.1. Classification and Nomenclature for Enzvmes In a recent review of polymer biodegradation Albertsson and Karlsson (17) have classified the main groups of enzymes. The names give the nature of the chemical reaction catalysed and end with "ase". Shorter names are sometimes used for convenience. (Table 1). The mechanisms of enzyme mactions may involve free radical modifications of the substrate or alternative ionic reactions in other cases. Sometimes only the end products a known but not the reaction mechanisms and the intermediates.

6.2. Biological Oxidation enzymes (equ.8) Oxygen has an important role in many enzyme reactions. The incorporate one oxygen group (monooxygenases) while the ~ x v e e n a introduce ~e~ two oxygen atoms, i.e. molecular oxygen (equ.9).

PH, - 0,_$ PHOH + H,O BH,+

B

The oxidation (equ.8) requires a second substrate (BHJ which is oxidized simultaneously,e.g. nicotinamide adenine dinucleotide (NADH), a common hydrogen donor in the cells.


PH, + 0,+ P(OH),

+ PO + H,O or POOH

I1

(9)

The oxygenases are inserting whole oxygen molecules (03as dihydroxyl groups which split off water and form carbonyl groups CO or carboxyl groups (- CO - OH). With another type of oxidases molecular oxygen is not incorporated into the substrate but acts as a hydrogen acceptor (equ.10) and produces water (H,O) or hydrogen peroxide (H,OJ. PH, + M O,+P

PH, + 0, P‘

+ H,O

+ H202

(10)

Oxygenase enzymes may even catalyse the splitting of an aromatic structure like in lignin and produce two > C = 0 groups from each - HC = CH - group.

6.3. Biological Hydrolvsis Proteolytic enzymes catalyse various hydrolytic reactions like breaking of ester groups or amide groups. The mechanism may be analogous with the acid- and basecatalysed hydrolysis and could be written as equ. (1 1):

9

R, - c - o - R, + H,O+

0 R,- C - OH + HO - R,

0 0 (1 1) R, - 6- MI - R,+H,o+R, - OH+H,N- R, Amide groups in the polypeptide chains of proteins are hydrolysed like in synthetic polyamides.

e-

6.4. Oxidative Initiation of Biodegradation

The rate-determining initial step in biodegradation of many synthetic polymers with C - C chains was shown by Scott in 1975 (18) to be oxidation. Albertsson reported in her dissertation in 1977 that oxidized groups on the surface of polyethylene films were selectively removed by microorganisms (19). From the 20 years study of the biodegradation of polyethylene it is concluded that oxidation usually is the initial step (17). In laboratory experiments an atmosphere of molecular oxygen is used. Under anaerobic conditions certain microorganisms are able to utilize oxygen from nitrate, sulfate or carbonate groups for oxidation of a polymer substrate. A more complete mechanism for was presented in 1987 by Albertsson et al(20). The initial step is an * ,which may be and similar to the typical P-oxidation of fatty acids and paraffms (equ.12). Hydroperoxide groups are introduced. They degrade and form increasing amounts of keto groups which react further by adding water and give chain scission. The chain degradation is slow. When the chain length reaches the 40-carbon level, degradation of 3-oxo-carboxylic end groups occurs and gives progressive and complete mineralization (21). CH,

- +H,O+

- CH,

OH

(12)

12


OH

- CH,- C = O + HO - CH, - CH, -

4

CH, = CH

- + H,O + CO,

(12)

The oxidised degradation intermediateproducts may be metabolized and enter the citric acid cycle of the microorganisms. Therefore, complete mineralization to carbon dioxide, water and other inorganic products e.g. of nitrogen, sulfur and phorphorons, does not always occur. Abiotic and enzymatic oxidations of a polymer may occur simultaneously and are not easy to distinguish. The hydrophobic surface of polyethylene is a major obstacle to microbial attack. Addition of surfactants in degradation experiments of polyethylene increased the rate (22). Certain microorganisms like with hydrophobic surface adhere to other hydrophobic surfaces, e.g. silicones, poly(tetrafluorethene),polydienes and LD polyethylene and may enhance biodegradation (23).

6.5. Hydrolysis of Synthetic Degradable Pofvmers Many scientist study hydrolysable polymers for replacement of the present commodity plastics. These are natural polymers like polysaccharides,proteins and polyuronides. There is a special interest in new polyesters like synthetic poly(1actic acid), poly(adipate) and poly(succinate) and their copolymers which are more or less easy to hydrolyse. Polyvinylalcohol (PVA) is degradable after oxidation according to an interesting mechanism reported by Huang et al(24). PVA samples in acid aqueous solution were oxidized with sodium hypochlorite. Ketone groups formed along the PVA chains to a PVA/PVK polymer. The original PVA degraded slowly and the PVAPVK much faster with inoculated microorganisms of which was the most active of four species tested. The mechanism is a P-cleavage between C = 0 and C - OH groups which is catalyzed by enzymes.

7. Discussion Oxygen is an important reagent in most degradation processes for polymers both in and in yirn. Initiation by radical formation of various means opens the polymers for oxidation by addition of molecular oxygen in ground state (triplet form, '0,) followed by series of degradation reactions. In radical formation by bond scission, the reactions depend on the dissociation energy of the various bonds. Oxidation is an important initiation reaction also for biodegradation of polymers. There are no enzymes active on long alifatic carbon chains. After initial oxidation which could be abiotic or enzymatic, enzymatic degradation is possible. Even native polymers like poly(is0prene) and lignin ate biodegraded after initial oxidation. The abiotic oxidation may be initiated by radical formation like in photooxidation of polymers. The enzymatic oxidation in yiyn involves specific reactions with insertion of either one oxygen atom (0)or one oxygen molecule to,)according to mechanisms which are not found in YitLQ.


13

Excited states of oxygen, singlet oxygen ('03and ozone (OJ. react with double bonds in akenes and certain aromatic compounds. The "ene" reaction and the formation of endoperoxides initiate chain scission and formation of new oxidized chain ends. Degradation of polymers by hydrolysis of ester, amide and ether bonds in the backbone chains are ionic reactions catalyzed both by acid and base catalysts.

In biological degradation the active enzymes involved catalyze oxidatiodreduction reactions, transfer of groups, hydrolysis, isomerization of d, 1-forms,addition to double bonds and formation of new bonds. The degraded polymer fragments may be incorporated in the metabolism of the living organism or mineralized to carbon dioxide, water and other products containing nitrogen, sulphur or phosphorous.

8. Conclusions The most important degradation reactions of polymers in yipn are inhiikd by radical formation and subsequent addition of molecular oxygen to the polymer radicals. The degradation of the oxidized polymer is p ' by radical combination.

from the modified groups and

Polymer degradation by excited oxygen in singlet form and by ozone are leading to chain scission and formation of oxidized endgroups. Degradation by hydrolysis of polyesters, polyamides, etc. are both by acid and alkali in aqueous medium

catalyzed

Biodegradation of C - C chain polymers hyirp is initiated by abiotic or enzymatic oxidation and by enzyme catalysis. Hydrolysis is catalyzed by enzymes. The enzymatic reactions may involve insertion of one or two oxygen atoms, transfer of groups, isomerization, addition to double bonds and fonnation of new bonds.

In biodegradation of polymers, fragments of the chains may be m&&gd ' inthe '' d to carbon dioxide, water and compounds of nitrogen, organismsor * sulphur and phosphorous.

Acknowledeements This paper is based on current literature and a review of research projects in the department supported by grants and fellowships from the State Board for Technical Development (STU and NUTEK), The Wenner-Gren Foundations, The Carl Trygger Foundation and several companies which all is gratefully acknowledged. My colleagues, Professors Ann-Christine Albertsson, Ulf Gedde and Sigbritt Karlsson and Drs.Bengt Stenberg and Anders WirsCn, have kindly supplied helpful information for the review.

14


References 1.

2. 3. 4.

5.

6. 7.

8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

B.Rhby and J.F.Rabek, Photodegradation, Photo-Oxidation and Photostabilization of Polymers, J.Wiley, Chichester, 1975. B.Rhby and J.F.Rabek, Photodegradation of Polymer Materials in Comprehensive Polymer Science, First Supplement, (S.Aggarwal and S.Russo, eds), Pergamon Press, Oxford 1992, Chapter 12. J.F.Rabek, Photodegradation of Polymers, Spnnger-Verlag, Berlin 1996. N.D.Searle in Proceedings of the International Conference on Advances in the Stability and Controlled Degradation of Polymers, (A.V.Patsis, ed.), Technomic, Lancaster, PA, 1989, p.62. J.L.Bolland and G.Gee, Trans. Faraday Soc. 1946,42,236 and 244 and J.L.Bolland. Quart. Rev. Chem. Soc., 1949, 1,3. H.Yoshida and B.RAnby. J. Polym. Sci. B. 1964,2,1155 and Acta Chem. Scand. (1965). 19,72. Cf.A review by A.Chapiro, Radiation Chemistry of Polymer Systems, Wiley-Interscience, New York, 1962. See further K.Wunsch and H-J.Dalcolmo, Radiai. Phys. Chem., 1992,39,443. HKashiwabara, S.Shimada and Y.HorioJadiat. Phys. Chem., 1991, 37,43. A.WusCn, Heterogeneous Grajting of Acrylamide onto D P E : Kinetics, Morpology and Biomaterial Applications. Diss., KTH. Stockholm, 1995. J.Sohma, Dev.Polym. Deg. 1979,2,99. H.H.Kausch, Polymer Fracture, Springer Verlag, Heidelberg, 1978, Chapt. 7. K.Jacobson, B.Stenberg, B.Terselius and T.Reitberger, manuscript, 1999. K.Jacobson, G.F&nert, B.Stenberg, B.Terselius and T.Reitberger, Polymer Testing, 1999, in print. B.RAnby and J.F.Rabek (eds.), Singlet Oxygen Reactions with Organic Compounds and Pofymers, J.Wdey, Chichester, 1978. See further R.L.Clough, M.P.Dillon. K.K.Iu, P.R.Ogilby, Macromol. 1989,22,3620. J.F.Rabek. J.Lucki, B.Rhby, Europ. Polym. J. 1979,15,1089 and 1101. J.R.Danie1, Encycl. Polym. Sci. Technol. 1985.3, 105, A-C. Albertsson and S.Karlsson, in Chemistry and Biotechnology of Polymer Degradation, (G.J.L.Griffin, ed.),Blackie Acad. Prof., England, 1995, p.7. G.Scott, Polymer Age, 1975,6,54. A-C. Albertsson, Studies on the Mineralization of "C Labelled Polyethylenes, in Aerobic Biodegradation and Aqueous Aging, Diss. ,KTH, Stockholm, 1977. A-C.Albertsson, S.O.Andersson and S.Karlsson, Polym. Degrad. Stab., 1987,lS. 73. A-C-Albertsson and S.Karlsson, in Degradable Materials, (eds, S.A.Barenberg CRC Press, Boca Raton, 1990, p.263. S.Karlsson, 0.Ljungquist. and A-C.Albertsson, Polym. Degrad. Stab., 1988,21,237. U.Husmark, Packmarknaden, 1993,3,34. S.J.Huang, in Modification of Polymers, (eds, C.E.Carraher, Jr and J.A.Moore), Plenum Publ., 1983, p.75.

u,

Part 2

Synthesis and derivatisation of biocompatible polymers

CONJUGATED OLIGOMERS BEARING FURAN AND THIOPHENE HETEROCYCLES: SYNTHESIS, CHARACTERIZATION AND PROPERTIES RELATED TO ELECTRONIC CONDUCTION AND LUMINESCENCE Claire Coutterez & Alessandro Gandini' Matiriaux PolymPres, Ecole Francaise de Papeterie et des Industries Graphiques (INPG), LIP 65, 38402 Saint Martin d'Hdres, France

INTRODUCTION For a long time, the development of polymer science and technology based on petroleum-derived monomers has been the federative working hypothesis of most research on these topics. Today, the precarious state of these fossil materials whose future availability is inevitably limited has led to an alternative strategy based on the exploitation of renewable resources. Indeed, the biomass represents an important ecological and non-polluting raw material which can be submitted to specific transformations. Our laboratory took up this challenge several years ago with the general aim of exploiting these renewable resources as the starting point for the elaboration of original polymeric materials'. Three main areas were, and are being, explored, namely: (i) the chemical transformation of polysaccharides both as a surface or a bulk operation; (ii) the use of lignins as macromonomers for the preparation of polyesters and polyurethanes and (iii) the synthesis and polymerisation of furanic monomers derived from polysaccharides, hemicellulose and sugars. The interest of furanic monomers and the corresponding polymers and copolymers, as well as the chemical modification of macromolecules bearing furan heterocycles, was thoroughly described in a recent review2. This paper is devoted to our recent work on conjugated furan oligomers as novel materials for electronic conduction, luminescence and photoactivity. Conjugated polymers have attracted considerable interest in fundamental and applied research because of their potential use as electronic, optical, optoelectronic and, more recently, luminescence devices. On the one hand, the synthesis and processing methods of numerous conjugated polymers are well established and generally lead to controlled materials in terms of molecular weight and structures. On the other hand, however, the non-systematic reproducibility of some syntheses, the presence of intra- and inter-chain defects, the insolubility, infusibility and instability of many of these polymers, reduce considerably the possibilities of their detailed characterisation and their processability in view of their possible applications. As a consequence, the search for similar structures, albeit precisely defined, more soluble and more stable, such as oligomeric compounds based on the same features, has been the subject of many recent investigations. Indeed, soluble conjugated oligomers not only constitute useful models for the corresponding polymers, allowing the study of structure-properties relationships, but must also be considered a new source of processable materials because of their intrinsic electronic and optical properties.

I8

Synthesis and denvatisation of biocompatible polymers

EXPERIMENTAL Synthesis, purification and structural characterisation of the oligomers Series I oligomers

The experimental procedure was a modification of a method previously perfected in our laboratory for the preparation of poly(2,5-furylene vinylene)3 which was adapted specifically to the synthesis of oligomers. In a previous investigation in our laboratory', a new synthetic route to linear low molecular weight poly(2,5-furylene vinylene) was developed, which involved the basecatalysed polycondensation of 5-methylfuraldehyde (MF), using t-BuOK as a nucleophile. In this preliminary investigation, little attention was devoted to the possibility of preparing and studying isolated oligomeric structures (see Fig. I), except for the dirner 5-[2-(5methylfuryl vinylene)] furfural (MFVF). The main purpose of this study was the preparation and characterisation of the polymers. In the present article, the main emphasis is instead placed on the individual oligomers with regard to their electronic and photoluminescence properties. Moreover, a comparison with the corresponding behaviour of homologous unrnethylated oligomers bearing furan andor thiophene moieties (see Fig. 2)4 is briefly presented.

L

n

Ia: n = I , Ib: n = 2 , Ic n = 3, Id: n = 14-81

Figure 1. Methyl-terminated oligofurylenes vinylenes (series I).

IIe: X, Y, Z = 0 IIf x = s, Y,Z = 0 IIg: x, Y = 0 , z= s In: z = 0, Y = s

IIa: X,Y = 0 I n : x = s, Y = 0 IIc: x = 0, Y = s IId: X, Y = S

x.

IIi Figure 2. Heterocyclic unmethylated oligomers (series II)

Conjugated oligomers bearing furan and thiophene heterocycles

19

In a three neck flask provided with magnetic stirring and kept under a nitrogen atmosphere, 2 mol of monomer MF were mixed with 5 ml of dioxan and a small amount of calcium hydride, used as dehydrating agent. The mixture was then brought to 80°C. Since the potassium terbutoxide (t-BuOK) used as the basic catalyst was poorly soluble in dioxan, a homogeneous catalytic solution of t-BuOK (10 g I-') was prepared in that solvent, using a 18-crow-6 ether, viz. 1,4,7,10,13,16hexaoxacyclooctadecan, as solvating solubilising agent. 22.5 ml of this solution was then added dropwise to the monomer solution. The resulting reaction mixture was left for 1 h under stirring at 80°C. Then, successive quantities of 0.5 ml of monomer and 5 rnl of the catalyst solution were introduced dropwise at the same time every 30-min. and this until a total quantity of 10 ml of monomer had been added. At the end of these additions, the brown mixture was left under stirring once more for 4 h at 80°C. After cooling to room temperature, the reaction mixture was finally filtered, neutralised with concentrated acetic acid, shaken with 300 ml of water, and then extracted with methylene chloride (5 x 250 ml). The organic phase was dried over anhydrous sodium sulphate and concentrated at 1/10 of its initial volume by vacuum evaporation. The residue was then poured into a large excess of methanol and the ensuing precipitate redissolved and reprecipitated into a large excess of a 70/30 mixture of hexane/ethyl acetate. The resulting precipitate was composed of a mixture of higher oligomers (n = 4-8) exclusively (60 % yield) which mainly contained the hexamer and heptamer. The various filtrates, which contained the lower oligomers, were combined, concentrated and submitted to a separation procedure based on flash chromatography on silica gel (SiO2, 230-400 mesh, 60A), using (hexane/ethyl acetate) as eluent. The first fraction (90/ 10 hexane/ethyl acetate) contained exclusively the dimer (yellow, 10% yield), the second (85/15) exclusively the trimer (orange, -10% of yield), the third (80/20) exclusively the tetramer (red, 10% yield) and the last (75-25) consisted of an impure mixture of higher oligomers (brown, 10% yield). Each component was obtained as a crystalline powder. The characterisation of all these products called upon FTIR spectroscopy (KBr pellets, Perkin Elmer Paragon loo0 spectrometer), 'H-NMR spectroscopy (CDzC12, Bruker AC300 instrument at 300 MHz), GPC chromatography (THF, Styragel column for the molecular weight range 100-10,O00), detection by refractometry, elemental analysis (carried out at the Central Analysis Laboratory of the National Research Council of France), mass spectrometry (EI: 70 eV, Nermag R10-1OC spectrometer) and melting points (determined by DSC with a Setaram DSC-92 instrument). All structures were thoroughly confirmed and shown to bear exclusively trans conformations across the alkenyl moieties.

-

-

-

6

7

Trimer Ib

FTIR (vmdX) : Fu : 3121 (vCH), 1451 and 1392 (vFu), 1250 (6CH), 1017 (Fu breathing), 799 and 752 ( C H Fu); C=O : 1664 (vC=O); CH : 2820 (vCH); CH=CH : 1611 (vC=C), 957 (oCH trans); CH? : 2915 (vCH3)cm-'. Rh4N 'H (6) : 9.54 (lH, s, H12) ; 7,25 (lH, d, J = 3.7 Hz, H11) ; 7.09 (lH, d, J = 16.0 Hz, H9 trans) ; 6.92-6.86 (2H, rn, H8 and H5 trans) ; 6.71

20


(IH, d, J = 16.0 Hz, H4 trans) ; 6.55-6.52 (2H, m, H7 and HIO) ; 6.38 (IH, d, J = 3.3 Hz, H6) ; 6.32 ( l H , d, J = 2.9 Hz, H3) ; 6.06 (IH, d, J = 2.1 Hz H2) and 2.34 (3H, s, CH3) ppm. UVvis,(kmJ : 325 (min) and 445 nm ( E : 3.39 ~ lo4 ~ I mol-' ~ cm-I). ~ M.p. : 1025°C. Mass ( d z ): 294 (M'), 165, 147, 115, 77, 43. Elem. An. calculed for CI8Hl4O4 : C : 73.49; H : 4.76; 0 : 21.75 96;found : C : 73.06; H : 4.89; 0 : 21.32 %.

Tetramer Ic

FTIR (vn,.J : Fu : 31 I 1 (vCH), 1442 and 1397 (vFu), 1252 (6CH), 1017 (Fu breathing), 776 and 752 ( K H Fu); C=O : 1669 (vC=O); -CH : 2858 (vCH); CH=CH : 1619 (vC=C), 940 and 960 (oCH trans); CH? : 2927 (vCH,) cm-'. RMN 'H (6) : 9.56 (lH, s, H16) ; 7.27 ( 1 H, d, J = 3.7 Hz, H15) ; 7.1 I (IH, d, J = 16.0Hz, H13 trans); 6.96-6.84 (4H, m, H12, H9, H8 and H5 trans) ; 6.71 (lH, d, J= 15.6 Hz, H4 trans) ; 6.57-6.56 (2H, m, HI1 and H14) ; 6.46 (2H, m, H7 and H10); 6.38 (IH, d, J = 3.2 Hz, H6); 6. 31 (IH, d, H3); 6.06 (lH, d, H2) and 2.35 (3H, s, CH?) ppm. W - v i s . ( L X ): 305(min), 475 and 495 (sh) nm (E475",,, : 4.08 lo4 I mol-' cmI). M.p. : 235°C. Mass ( d z ) : 386 (M"), 193, 165, 115, 77, 43. Elem. An. calculed for :C C24H1805 : 74.63:H : 4.66:O : 20.71 %; found :C : 73.03:H : 5.28:O : 19.50 %.

900

Table 1. Maximum absorption wavelength and molar extinction coefficient in the UV-visible spectra(CH2Clz)of series I oligomers

22

Synthesis and derivatisation of hiocompatible polymers

Table 2. Maximum absorption wavelength of series II oligomers (CH2C12) The obvious implication of this behaviour is that it might be possible to obtain electronic conductivity with these materials. Indeed, a pellet of mixed oligomers [n = 4-81 exhibited, after doping with iodine, a conductivity of 0.4 S cm-' at room temperature, which indicated a typical semi-conducting behaviour. These good conducting properties, related to well-defined soluble low-DP structures, compare very favourably with those of many ill-defined insoluble conjugated polymers and open the way to their possible use as processable conducting materials. As for Series II oligomers, the same bathochromic shift was observed in their neutral electronic spectra, as a function of the DP, as shown in Table 2. The replacement of the furan heterocycle with a thiophene homologue produced a modest but systematic bathochromic shift.

Photoluminescence The photoluminescence of both series of oligomers was also studied. Given the range of absorption maxima reported above, two excitation sources were chosen, namely the 366 nm line of a mercury lamp and the 488 nrn emission of an argon-ion laser. When excited with the 366 nm line, all these compounds displayed some photoluminescence, even if the tetramer and the higher oligomers absorbed poorly at this wavelength. With the 488 nm excitation, the absence of luminescence from the dimer was simply due to the fact that this compound did not absorb above about 420 nm. The first relevant observation was that each compound which absorbed at both excitation wavelengths, gave two identical emission spectra (see Figs. 3 and 4 and Table 3). It is well known that fluorescence and phosphorescence occur essentially after the thermalisation of the excited species, i.e. when the excited molecules have lost their excess rotational and vibrational energy by collision and have thus returned to the 0-0 band level.


3~

450

5~

6~

zo

7~

Ie (nm)

23

eo

Ie (nm)

Figure 3. Emission spectra of series I oligomers (CH2Ch. lcexc =366 nm)

Figure 4. Emission spectra of series I oligomers (CH2Ch. lcexc = 488 n

The second key observation is that. whatever the excitation wavelength. the emission Amax increased with the chain length of the excited oligomer. Indeed. the electronic emission spectra displayed a bathochromic shift of Amax as a function of the degree of conjugation, in the same fashion as already observed for the corresponding absorption spectra. The dimers emitted in the blue or blue-green region, whereas higher oligomers glowed in the red. The emission colours of the trimer and tetramer were intermediary (see Table 3). A decrease in the extent of this bathochromic shift was again observed as a function of a further DP increase, which was in tune with the similar trend discussed above for the absorption spectra. Compound

Amax of emission (nm)

lemax of emission (nm)

(for lcexc =366 nm)

(for lcexc =488 nm)

MFVF (n = I) la

493

-

Trimer (n = 2) Ib

590

590

Tetramer (n = 3) Ie

635

635

Oligomers (n =[4-8]) Id

650

650

Dimer lIa

470

-

Dimer lib

490

-

Dimer lie

485

Dimer lid

490

-

Trimer lie

565

565

Trimer Ilf

565

565

Trimer IIg

595

595

Trimer lib

560

560

Tetramer IIi

650

650

Table 3. Emission wavelength maxima of the oligomers (CH 2Cl2 )

24


Compound MFVF (n = 1) Ia

Quantum yield 0.0 1s

Trimer (n = 2) Ib Tetramer (n = 3) Ic

0.003

Table 4. Emission quantum yields of series I oligomers Switching heterocycles produced the same trend as observed in the absorption spectra, with a small bathochromic effect induced by the thiophene ring. Thus, the use of two structural parameters, namely the DP of the oligomers and the sequence of heterocycles along their chain, constitutes an interesting source of a wide range of emission wavelengths (and therefore of colours) which could find promising applications. particularly if these trends were also displayed by electroluminescence. The emission quantum yields were estimated with a number of oligomers using Coumarine 152 as an actinometer. This reference was chosen for its high absorption at 366 nm, for its emission spectrum, which is intermediate among those of the various oligomers, and for its relatively high quantum yield of emission, viz. about 0.75. The results are reported in Table 4. This luminescence behaviour was unambiguosly assigned to fluorescence because of the good continuity, in all instances, between the highest absorption wavelength and the lowest emission wavelength. This indicated the existence of a 0-0 level frontier. Therefore, the results in Table 4 refer to fluorescence quantum yields. Moreover, the presence of atmospheric oxygen in the sample solutions (permanent contact with air during experimentation) inevitably quenched any possible phosphorescence. Indeed, oxygen is a well known powerful trap of triplet excited states. Experiments carried out in an argon atmosphere did not show any appreciable difference in the emission spectra, which suggested that the contribution of phosphorescence was negligible. However, the photomultiplier used for the detection of the emitted light was not sensitive beyond 900 nm and this leaves open the possibility of phosphorescence appearing in the infrared, if the triplet states of these molecules was associated with a particularly low energy level. Given the low values of the fluorescence quantum yields and the unlikelihood that any undetected phosphorescence would account for much higher quantum yields, the fate of most absorbed photons remains unclear. Two possible photochemical events come to mind: (i) whereas the dimerisation by cycloaddition of an excited species with a ground-state molecule through the external unsaturations was certainly negligible in the specific conditions of these emission experiments (high dilution'); (ii) the trans-cis isomerisation related to the alkenyl moieties seems a much more likely event in this context given the fact that this behaviour was previously observed in dilute solutions of the dimeric species5. No values are available as yet of the quantum yields of these isomerisations. The third type of pathway which could account for the missing contribution to primary quantum yields is that related to non-radiative photophysical events, viz. internal conversion from the first excited singled to the ground state and/or intersystem crossing from the first triplet state to the ground state. The study of the effect of the excitation wavelength on the emission quantum yield would give information about the role and relevance of possible photochemical processes. Except for coumarine, which was used for the 366 nm excitation


25

wavelength, we did not find any other suitable actinometer common to all oligomers, which could respond adequately to the various excitation wavelengths corresponding to their different absorption spectra. Clearly, much remains to be done in order to gain a deeper insight into the photochemical and photophysical behaviour of these conjugated molecules. With both excitation wavelengths, when solutions of trirners were in contact with air, some degradation occurred within a few minutes. Thus, both the emission wavelength and the corresponding intensity declined during the exposure time (see Fig. 5). At the same time, the corresponding absorption spectra displayed a shift to lower wavelengths and a decline in the corresponding absorption intensities (Fig. 6). These changes did not occur when the samples were kept under an inert argon atmosphere, suggesting that when the excited molecules were in contact with air, photooxidation reactions took place leading to irreversible structural modifications. The decrease in the absorption and emission wavelengths, characteristic of a lower extent of conjugation, strongly suggests that the alkenyl unsaturations were the sites of these oxidation reactions. Curiously, no corresponding changes were detected when oligomers, other than the trirners, were studied in the context. The fact that the trimer also gave by far the highest fluorescence quantum yield indicates that this specific molecular structure was particularly apt to undergo radiative and photochemical pathways.

Figure 5. Evolution of the emission spectra of trimer under air (Lxc,tat,on = 366 nrn, CH2C12); (a): initial spectrum, (b) after 10 min, (c) after 3 h.

Figure 6. Absorption spectra of trimer (a) under argon, (b) under air after 3 h of exposure

26


CONCLUSION The possibility of preparing well-defined oligomeric structures related to heteroarylene-vinylenes bearing furan and thiophene rings has provided a series of molecules which could be examined individually in terms of such properties as electronic spectroscopy, luminescence and electrical conductivity. A study of the possible application of these novel materials in advanced technologies is in progress.

Acknowledgements The authors wish to thank the Laboratoire de Spectromttrie Physique, UniversitC Joseph Fourier-Grenoble, and in particular J C Vial for his precious advice concerning the luminescence spectra.

REFERENCES 1. A. Gandini, Polymers from renewable resources, In: Comprehensive Polymer Science, 1" Suppl., G. Allen, S. L. Aggarwal & S. Russo (eds.), Pergamon Press, Oxford, 1992, pp.527-573. 2. A. Gandini & N. M. Belgacem, Furans in polymer chemistry, Progr Polyni Sci, 1997, 22, 1203-1379. 3. C. Mtalares, Z . Hui & A. Gandini, Conjugated polymers bearing furan rings: I . Synthesis ans characterization of oligo(2,5-furylene vinylene) and its thiophene homologue, Polymer, 1996, 37, 2273-2279. 4. C. Coutterez & A. Gandini, Synthesis and characterization of oligo(heteroary1ene viny1ene)s incorporating furan and thiophene moieties, Polymer, 1998, 39, 7009-70 14. 5 . V. Baret, A. Gandini & E. Rousset, Photodimerization of heteroarylene-vinilenes, J Photochem Photobiol, 1997, A103, 169-175.

POLYAMIDES INCORPORATING FURAN MOIETIES. 2. NOVEL STRUCTURES AND SYNTHETIC PROCEDURES Mejdi Abid', Souhir Gharbi', Rachid El Gharbi' and Alessandro Gandini** 'Laboratoire de SynthPse et Physicochimie Organique, Faculte' des Sciences, UniversitP de Sfar, 3038 Sfax, Tunisia 2'

Mate'riaux PolymPres, Ecole Francaise de Papeterie et des Industries Graphiques (INPG), BP65, 38402 Saint Martin d'H2res, France

INTRODUCTION Previous scientific work on furanic polyamides consisted mostly in the synthesis and characterization of structures bearing an alternation of aromatic and heterocyclic moieties, i.e. aramide-type polymers'. The sustained interest of one of us in macromolecular materials incorporating the furan ring2 prompted the present ongoing study devoted to a variety of polyamides in which the furan moiety appears in the polymer backbone either on its own (polymers 1,2, and 5 ) or alternating with aliphatic groups (polymers 3 and 4). The synthesis and characterization of some of the latter structures have already been reported3,but those described here are novel.

1

2

r

1

3

28


5

EXPERIMENTAL Three different procedures were adopted to prepare the furanic polyamides, according to their structures, namely: (i) Conventional interfacial polycondensation for polymers 3-5, since it was found previously that this was the most appropriate way to optimize the molecular weight of furanic-aliphatic polyamides3. Thus, 2,2-bis(5-chloroformyl-furyl)propane(CFP) was dissolved in methylene chloride and the complementary diamine in a NaOH aqueous solution (the furfuryl diamine was synthesized by the condensation reaction of furfuryl amine with acetone in an acidic medium). The two solutions were vigorously stirred at room temperature in the presence of a phase-transfer agent (triethylbenzylammonium chloride) for two hours using a 5 % excess of diamine with respect to CFP. Polymers were isolated by filtration, then washed with acetone and ether before being dried . (ii) Polycondensation of N-hydroxymethyl-2-furamide(HF) for polymer 1. This synthesis was inspired by an old short communication4 and was significantly improved as described below. The major change consisted in carrying out the whole preparation in a single operation involving both the hydroxymethylation of 2-furamide and the ensuing polycondensation between the OH groups and the hydrogen atoms at the C5 position of the heterocycles. A thorough study of both the two-step synthesis (preparation of HF by basic catalysis involving paraformaldehyde followed by acidic promotion of its polycondensation) and the simpler one-step counterpart, revealed the advantages of the latter, particularly in terms of the much higher molecular weights of the resulting polyamide 1. Details of this investigation are given elsewhere', but the best conditions found up to now consist in working in a strong acidic medium at temperature of 60 to 80°C. These polyamides were isolated by precipitation in water. (iii) Polymer 2 was prepared by a totally different method which called upon the synthesis of N-furfuryl-2-fury1 amide (FFA) by the reaction of furfuryl amine with 2furoyl chloride and its subsequent polycondensation reaction with acetone carried out in sulphuric acid. Given the asymmetric character of the furanic comonomer, the reaction of acetone with two such molecules can give three different products and thus the ensuing polyamide is bound to possess a random assembly of these (c triads in its linear structure. However, it was thought that the basic features of these random copolymers could be assimilated, at least in the first approximation, to those of the simplified structure shown for polymer 2. These polyamides were also isolated by precipitation in an excess of water and washed to neutrality. All the polymers prepared in this study were characterized by FTIR and 'H-NMR spectroscopy and by inherent viscosity measurement of their solution in m-cresol (1.5 g/L at 25°C) in order to assess the validity of each structure and estimate the corresponding molecular weight. DSC and TGA analyses completed this preliminary ))

Polyamides incorporating furan moieties

29

evaluation of their properties in terms of crystallinity (if any), glass transition temperature and thermal stability.

RESULTS AND DISCUSSION The three procedures and their ensuing polymers will be treated separately before giving a more general appraisal of the present investigation.

Polyamide 1 The construction of this macromolecule follows the same basic idea as that exploited to polymerise furfuryl alcohol, viz. successive electrophilic condensations between OH and H5 moieties. However, whereas in the latter system the monomeric structure obtained, namely -CH2-2,5-Fu-, is deprived of polarity and is also extremely sensitive to side reactions involving the methylene bridge6, in the present context the polarity is greatly enhanced by the amide function and moreover its presence contributes to reduce very considerably the aptitude of the methylene moiety to promote unwanted structural modifications. Although formally polymer 1 was briefly described previously, its structure had not been proved and the DP obtained in that study was much lower than those reported here. In fact, by using the optimized conditions summarized above, we obtained a polymer with an inherent viscosity of 2.3 dl/g which suggests a reasonably high molecular weight. The FTIR spectrum of this sample was very similar to those of all other samples prepared under a variety of conditions, but which had all lower values of q, and displayed all the expected bands associated with structure 1'. The 'H-NMR spectra of some of these polymers, taken in DMSO-d6 at 300 MHz, were also entirely consistent with the expected structure both in the positions of each proton resonance and in their relative intensity. The strong intermolecular association arising from hydrogen bonding between C=O and N-H functions, typical of all primary polyamides, was verified here by the observation that only highly polar solvents like DMSO, or NMP with LiCl or strong acids like H2S04 dissolved these polymers. We noticed moreover that the higher the value of q, the lower the rate of dissolution. One drawback associated with the use of sulphuric acid as polymerization medium is the fact that the polymer has a dark-brown colour, whereas it has a creamy complexion when it is prepared in other acidic media. Obviously, some side reactions occur in the former conditions, although it is difficult to assess at present to what extent, since no spurious structure could be detected by spectroscopy and even the most deeply coloured samples remained entirely soluble. Work is in progress to determine the physical properties of this novel material which associates all the general features of a classical polyamide with the presence of furfuryl moieties as sole spacers.

Polyamide 2 In order to extend the realm of furanic polyamides incorporating a high content of heterocycles, we used an hitherto unexplored synthetic method, based on a standard reaction, albeit usually applied to simple furans. It is in fact well known that the particular reactivity of this heterocycle promotes a facile condensation of aldehydes and

30


ketones with two rings through their H5 atoms because of the high nucleophilicity of that position. In the specific instance of furan itself, this leads to a series of oligomers arising from successive condensations and we thought therefore that this concept could be extended to the reaction of an amide bearing two furanic end-groups, viz. FFA. The polycondensation of FFA with acetone in sulphuric acid occurred as expected and the ensuing polyamide gave an inherent viscosity of 0.8, suggesting that, even within this preliminary context, the degree of polymerization was relatively high. Figure 1 shows the FTIR spectrum of this polyamide, which is entirely in tune with structure 2 with the typical free and hydrogen-bonded NH peaks at 3300-3400 cm-'; the amide carbonyl peaks at 1660, 1530 and 1320 cm-I; the in-plane and out-of-plane vibrations associated with the furan heterocycle at 3140, around 1600, 1020, around 900 and 780 cm-' and the peaks relative to the methylene and isopropyl groups just below 3000 cm-'. The work in progress on this system focuses on the optimization of the synthetic conditions, particularly with regard to the correct stoichiometry between the monomers, knowing that both monomers are likely to be also consumed in side reactions occurring in sulphuric acid. One possibility is to attempt the synthesis of an A-B type structure in order to dispose of an > monomer.

Polyamides 3-5 The experience acquired in our previous investigation on furanic-aliphatic and furanicaromatic polyamides suggested that the pursuit of this project should be conducted using the technique of interfacial polymerization'. The present addition of three novel polymeric structures was intended to extend our knowledge of structure-property relationships, already established in the homologous series of furanic polyesters', by including cycloaliphatic and furanic co-spacers in the polyamide chains.

-50

t

Y

Figure 1. FTIR spectrum of polyamide 2 (KBr pellet).

Polyamides incorporating furan moieties

31

Polymer 3 was prepared in good yields and, after careful purification of both monomers and optimization of the synthesis, an inherent viscosity of over 1.6 was achieved. However, despite this satisfactory molecular weight and spectroscopic evidence of a regular structure in tune with formula 3, the polymers did not exhibit any crystallinity, even after several heating-cooling cycles, as shown by the corresponding DSC tracings which only exhibited a glass transition occurring at 76°C. It is interesting to compare the morphology of this entirely amorphous polymer with that of its homologue with the same molecular weight, but bearing six methylene groups (instead of two), which readily crystallises, as indicated by the presence of clear melting peaks in the DSC thermograms) The difference in behaviour can hardly be attributed to any difference in macromolecular irregularities for 3, since the same monomer purification and polymer synthetic procedures were applied to both polyamides. It seems more likely that the bulky isopropyl group between the furan rings could play a detrimental role in being an obstacle to interchain organization, and this in a more dramatic way in the case of 3 because of the much shorter aliphatic spacer between the -Fu-C(CH3)2-Fumoiety. In other words, the establishment of regular sequences of N-H",C=O interchain hydrogen bonds, typical features promoting the crystallization of Nylons, would be attained much more easily with the polyamide bearing a sequence of six CH2 groups than with 3. The thermal stability of 3, shown in Figure 2, was entirely comparable to that of its homologues prepared previously3 which constitutes further evidence of its regular structure. The synthesis of polyamide 4 was less successful in terms of both yield and DP. This was attributed to the fact the the diamine used bore now secondary functions in a cyclic structure, i.e. less reactive entities. Despite these drawbacks, the FTIR spectrum of the polymer confirmed the postulated structure with the typical peaks of secondary amide (1630 cm" for the >N-C=O), of 2,5-disubstituted rings (3120, 1520, 1010, 960, 800 and 745 cm-') and of the aliphatic groups at 2860,2925 and 2975 cm-' and between 1300 and 1470 cm-'.

'.

I

t

'O

\

1

Figure 2. TGA thermogram of 3 ([q]=1.6 dug). Heating rate 2O0C/min,NZatmosphere.

32


Finally, the novel polyamide 5 bearing furan rings in both spacers was prepared using a diamine whose synthesis and structure simulated that of the corresponding diacid chloride, except that, because furanic amines are thermodynamically unstable with respect to their tautomeric imines, a methylene group must be interposed between the heterocycle and the NH2 group. The resulting polymer 5 had an inherent viscosity of 1.3 dl/g, which is considerably higher than that obtained in the only previous study of the synthesis of entirely furanic polyamides’. This improvement stems from the detailed approach aimed at optimizing all the parameters related to the conditions of the interfacial polycondensation, as described elsewhere’. The ITIR spectrum of 5, showing again all the features related to the expected structure, is given in Figure 3. Among the five polyamides reported in this study, undoubtedly polymers 1 and 5 are the most interesting both because they possessed high molecular weights and because they were rich in furan moieties. Work is in progress to gain a deeper insight into these systems and to extend the characterization of the polymers to their physical polymers.

4000

3500

3000

2500

2000

1500

1000

500

Figure 3. FTIR spectrum of polyamide 5 (KBr pellet).

REFERENCES 1 A Mitiakoudis & A Gandini, ‘Synthesis and characterization of furanic polyamides’, Macromolecules 1991, 24, 830-841. 2 A Gandini & M N Belgacem, ‘Furans in polymer chemistry’, Progr Polym Sci, 1997, 22, 1203-1379. 3 S Gharbi & A Gandini, ‘Polyamides incorporating furan moieties 1. Interfacial polycondensation’, Acra Polym, 1999, 50, 293-298. 4 V M Mihajlov & N Peeva, ‘Polymerisation of furamide with formaldehyde’ Makromol Chem 1968, 116, 107-111. 5 M Abid, R El Gharbi & A Gandini, ‘Polyamides incorporating furan moieties. 2. Polycondensation of 2-furamide with paraformaldehyde’, Polymer, 2000,4 1, 355-362. 6 M Choura, M N Belgacem & A Gandini, ‘The acid-catalyzed polycondensation of furfuryl alcohol’, Macromolecules, 1996, 29, 3839-3854. 7 A Chaabouni, S Gharbi, M Abid, S Boufi, R El Gharbi & A Gandini, ‘Polyesters furaniques: transitions et stabilitt thermiques’, J Soc Chim Tunisie, 1999, 4, 547-558.

SACCHARIDE- AND LIGNIN-BASED POLYCAPROLACTONES AND POLYURETHANES Hyoe Hatakeyama*’, Yoshinobu Izutal, Takanori Yoshida’, Shigeo Hirose and Tatsuko Hatakeyama

’

‘Fukui University of Technology, 3-6-1 Gakuen, Fukui-city, Fukui 910-8505,Japan 2Nalional Institute of Materials and Chemical Research, 1-I Higashi, Tsukuba, Ibaraki 305-8565,Japan ’Otsuma Women’s University, I2 Sanbancho, Chiyoda-ku, Tokyo 102-8357,Japan

ABSTRACT Saccharide- and lignin-based polycaprolactones were synthesized from glucose-, fructose, sucrose, alcoholysis lignin (AL) and Kraft lignin (KL) by the polymerization of E-caprolactone (CL) which was initiated by the OH group of saccharides and lignins. The CWOH (moVmol) ratios of the saccharide-based PCL’s were changed from 1 to 5 and those for lignin-based PCL‘s were changed from 2 to 25. PU sheets were prepared from the above PCL derivatives by the reaction with diphenylmethane diisocyanate (MDI). Thermal properties of the prepared saccharide- and lignin-based PCL’s and PU sheets were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and TG-Fourier transform infrared spectroscopy (FTIR). Glass transition temperatures (T,’s), cold-crystallization temperatures (T,’s) and melting temperatures (T,,,’s) of saccharide- and lignin-based PCL’s and PU’s were determined by DSC, and phase diagrams were obtained. T,’s decreased with increasing CWOH ratio, suggesting that PCL chains act as a soft segment in the amorphous region of PU molecules. Two thermal degradation temperatures (T,,’s) were observed in TG curves of PU’s from saccharide- and lignin-based PCL’s with low CL/OH ratios. TG-FTIR analysis of PU’s from lignin-based PCL’s suggested that compounds having C-0-C, C=O and C-H groups are mainly produced by thermal degradation of PCL chains in lignin-based PCL’s and PU’s.

INTRODUCTION Since plant components such as cellulose, hemicellulose and lignin are fundamentally biodegradable, biodegradable polymers with plant components have been extensively studied by various research groups [1-15]. Biodegradable polyurethanes (PU’s), have been studied at our laboratory and at the Swedish Forest Products Research Laboratory since 1990 [3-10, 12-13, 151. Thermal and mechanical properties of PU’s derived from saccharide-based polycaprolactones (PCL’s) were also reported [14]. In the present study, PU’s from PCL derivatives which were synthesized from saccharides, such as glucose, fructose and sucrose, and also from alcoholysis lignin (AL) and &aft lignin (KL) were prepared by the reaction of the above PCL derivatives with diphenylmethane diisocyanate (MDI). Thermal properties of the obtained PU’s from saccharide- and lignin-based PCL’s were studied by differential scanning

34

Synthesis and denvatisation of biocornpatible polymers

calorimetry (DSC), thermogravimetry (TG) and TG-Fourier transform infrared spect ro metr y (FTI R) .

EXPERIMENTAL Sample preparation Saccharide- and lignin-based PCL's were synthesized by the polymerization of Ecaprolactone (CL) which was initiated by each OH group of glucose, fructose and sucrose, AL and KL. The amount of CL was varied from 1 to 5 moles per OH group of each saccharide, and was varied from 2 to 25 moles per OH group of each of the above lignins. The polymerizations were carried out for 12 hr at 150 "C with the presence of a small amount of dibutyltin dilaurate (DBTDL). PU's were obtained by the following procedure. Saccharide- and lignin-based PCL's (Sac- and Lig-PCL's) were dissolved in tetrahydrofuran (THF). MDI was reacted with each of the above solutions of Sac- and Lig-PCL's for 30 min at room temperature with stirring. Each of the obtained PU prepolymers was cast on a glass plate and the solvent was evacuated in a vacuum desiccator under dry conditions. The obtained PU's were cured at 120 "C for 2 hr.

Measurements Differential scanning calorimetry (DSC) was performed using a Seiko 220 at a heating rate of 10 "C/min under a nitrogen flow (flow rate = 30 ml/min). Sample mass was ca. 5mg. Aluminum open pans were used. The samples were heated to 120 "C and quenched to -150 "C. Melting temperature (TJ, melting enthalpy (AH,,,), cold crystallization temperature (T& glass transition temperature (TJ and heat capacity gap at Tg (AC,) were determined by the method reported previously [16]. Thermogravimetry (TG) was performed using a Seiko TG 220 at a heating rate of 10 "C/min in the temperature range from 20 to 800 "C under a nitrogen flow (flow rate = 200 ml/min). Sample mass was ca. 5mg. TG curves and derivatograms (DTG) were recorded. Mass residue (WR) was calculated according to the equation: WR = (mT/m,,) x 100 (%) where mT is mass at temperature T and mzois mass at 20 "C. In order to analyze gases evolved by thermal degradation, TG-Fourier transform infrared spectroscopy (FTIR) was performed using a Seiko TG 220 - JASCO ETIR-420 system at a heating rate of 20 "C in the temperature range from 20 to 800 "C under a nitrogen flow (flow rate = 200 ml/min).

RESULTS AND DISCUSSION Fig. 1 shows the schematic chemical reaction for the synthesis of saccharide-based PCL's. The results of the characterization of glucose-, fructose- and sucrose-based PCL's have been reported elsewhere [14]. The obtained saccharide-based PCL's were reacted with MDI according to the conditions mentioned in the Experimental Section. Fig. 2 shows the schematic chemical structure of the PU from sucrose-based PCL. The length of the PCL chains attached to the sucrose core structure is shown as "m" in the diagram. (The number "m" was controlled by the initial amounts of CL which are shown as "n" in Fig. 1.) TgyS were observed in all of the PU samples from saccharidebased PCL's. Tg decreases with increasing CL/OH ratio in PU's from ca. -15 to -60 "C in the case of PU's from glucose- and fructose-based PCL's and from ca. -40 to -60 "C

Saccharide- and lignin-based polycaprolactones and polyurethanes

3S

in the case of PU's from sucrose-based PCL's. The above facts suggest that PCL chains with saccharides act as soft segments in PU networks and that this softening effect of caprolactone chains was enhanced progressively with increasing chain length of CL chains.

Sucrose

E:

-Caprolactone

CH,OR

~~ ~~rn,o,

° b~L-ln( RO

Sucrose-based PCL CH20H O

~

H20 H O

~

OH

HO

HO

OH

HO

Glucose

Figure 1.

CH,OH -

OH

OH

Fructose

Schematic chemical reaction for the synthesis of saccharide-based PCL's (CO(CH2),O)m-CONHRNHCOO-

I

(CO(CH2)SO)m-CONHRNHCOO-

o

I

~H2

I

tR- ~ CH2

o

o

/

-oocm"'HNOC-JO(H,C),OC)

0

I

-OOCHNRHNOC-m(O(H2C),Oq

CHp

0

I

(CO(CH"O).-CONHRNHCOO-

I

(CO(CH2),O)m-CONHRNHCOO(CO(CH2),O)m-CONHRNHCOO(CO(CHi>sO)m-CONHRNHCOO-

Figure 2.

Schematic chemical structure of the PU from sucrose-based PCL

36


The DSC curves representing each PU from saccharide-based PCL’s with CL/OH ratio 5 showed a prominent exothermic peak due to cold crystallization at around -20 “C. A peak of melting of crystals was also observed at around 40 “C. The DSC curve representing each PU from saccharide-based PCL’s with CL/OH ratio 4, which was annealed at room temperature, showed a melting peak around 40 “C. The above results suggest that the PU’s derived from the saccharide-based PCL’s with CL/OH ratios over 4 have a crystalline region in the molecular structure. Fig. 3 shows the schematic chemical reaction for the synthesis of lignin-based PCL’s. The obtained lignin-based PCL’s were reacted with MDI according to the conditions mentioned in the Experimental Section. Fig. 4 shows the schematic diagram for the preparation of lignin-based PCL’s and also for the preparation of PU’s from lignin-based PCL’s. The schematic chemical structure of the obtained PU from ligninbased PCL is shown in Fig. 5. The length of the PCL chains attached to the lignin core structure is shown as “m” in the figure. (The number “m” was controlled by the initial amounts of CL which are shown as “n” in Fig. 3.)

H

O

I-

-

/40CH3 C ~ ~ O

H

0

+ n

Figure 3.

0 I1

Schematic chemical reaction for the synthesis of lignin-based PCL’s


&aft Lignin

*

Alcell Lignin Benzene

&aft Lignin

Alcell Lignin -caprolactone catalyst

E

Lignin-based Polycaprolactone

I

I-

Polyurethane Sheets

Dissolved in Dioxane

1

m’

NCO / OH ratio = 1,2 CL /OH ratio (mol/mol) = 2-5, 10,15,20,25 Figure 4. Schematic diagram for the preparation of lignin-based PCL’s and also for the preparation of PU’s from lignin-based PCL’s

O(CH2)~0)m-CONHRNHCOO-

I (CO(CH2)50)m-CONHRNHCOO-

(CO(CH2)50)m-CONHRNHCOO-

Figure 5. The schematic chemical structure of the obtained PU from lignin-based PCL

37

38


Fig. 6 shows representative DSC curves of AL based PCL (ALPCL) with various CUOH ratios of 10, 15 and 20. A marked change in baseline due to glass transitjon was observed in each DSC curve. 7,’s were determined by the method reported previously [ 161. T, decreases with increasing CUOH ratio from 2 to 10 in PU’s from Lig-PCL’s, since caprolactone chains with lignin act as soft segments in PU networks. However, as shown in Fig. 6, when the CUOH ratio was 10 to 25, T, increased. In the case of the DSC curves representing AL-PCL’s with CUOH ratio 15, a prominent exothermic peak due to cold-crystallization of h P C L and also a prominent peak due to melting of crystals are observed at around 40 “C when CUOH ratio \was over 15. The above results suggest that the PU’s derived @omALPCL’s with CUOH ratios over 15 have a clear crystalline region in the molecular structure. A similar phenomenon was observed in PU from KL-PCL’s with CUOH ratio 10. Fig. 7 shows the changes of Tg’sofPU’s from A L and KLPCL’s. The TI markedly decreases with increasing CUOH ratio in the region where CUOH ratio below 15 and then the T, increases with increasing CUOH ratio in the region where CUOH ratio exceeds 15. The increase of T, over CUOH ratio = 15 suggests that by the introduction of long PCL chains the crystalline region increased and this restricted the motion of PCL chains. Fig. 8 shows the changes of T,’s, cold-crystallization temperatures (Tab) and melting temperatures (T,,,’s),against CUOH ratios of PU’s derived fiom A L and KLPCL‘s (KLPCL PU’s). The change of TI’Sis almost the same for the A L and KLPCL PU’s. Ta’s and T,’s slightly increase with increasing CUOH ratio in the region over CUOH ratios over 15, suggesting increasing crystallized area of PCL chains in the AL and KLPCL PU’s.

0 D

w“

I

I

-100

I

-50

T

I

I

0

50

/“C

Figure 6. DSC heating curves of PU’s from &based PCL Numerals in the figure show CUOH ratio and arrows indicate T“s. Tr glass transition temperature; T , cold-crystallization temperatures; Tm,melting temperature


0 0

.

-20

,o M

h

-40 .

-60

-

-80 0

I

I

I

I

I

5

10

15

20

25

30

CL / OH ratio / (mol/mol) Figure 7. Relationship between Tg’sand CUOH ratios in AL and KL-PCL PU’S

0 AL-PCLPU

Figure 8.

0 KL-PCLPU

Phase diagram for AL-and KL-PCL PU’s showing Tp T, and T,,,

39

40


--I0

-20 100

I

I

I

200

300

400

T I'C

Figure 9. TG and DTG curves of AL-PCL PU's with CUOH ratios of 10,15 and 20 rnolhnol 400

350 0

" R, 3m:%-8--

250

200

I

0

5

I

1

1

1

10

15

20

25

30

CL/ OH ratio / (rnol/rnol) Figure 10. Change of Tdland Td2with CUOH ratios of AL- and KL-PCL PU's.

0 AL-PCL PU T,,

w

0 AL-PCL PU Td2

0 KL-PCLPU T,j,

KL-PCL PU T,,


41

Fig. 9 shows TG and DTG curves of AL-PCL PU’s with CUOH ratios of 10, 15 and 20. Two kinds of thermal degradation temperatures, Tdl and Tdz are observed. Similar TG and DTG curves of KL-PCL PU’s were also obtained. Fig. 10 shows the change of Tdl and Td2with CUOH ratios of AL- and KL-PCL PU’s. Matsuzak et al. reported that some urethane bonds in PU’s dissociate to form hydroxyl and isocyanate groups at about 200 “C [17]. Dornberg et al. proposed a mechanism where a dehydration reaction of hydroxyl groups in alkyl groups and heterolysis and homolysis dissociation of P-aryl ether bonds in lignin occur initially at about 200 “C [ 181. Accordingly, it is considered that Td, may reflect the degradation of lignin parts in AL- and KL-PCL PU’s. We reported that the Td of cellulose acetatebased polycaprolactones increased from 350 to 390 “C with increasing CUOH ratio from 2 to 20 [19]. The above change of Td accords well with the change of T d 2 of ALand KL-PCL PU’s, as shown in Fig. 10. Accordingly, it is considered that Tdz may reflect the degradation of PCL parts in AL- and KLPCL PU’s. Fig. 11 shows the change of WR at 420 “C with CUOH ratios of AL- and K L P C L PU’s. PU’s with various KL contents from 0 to 50 % in polyethylene glycol which was obtained by the reaction with MDI showed that the W R of the PU’s increased with increasing KL contents [18]. This suggests that the lignin part in PU’s derived fiom lignins constitutes a significant part of the residual products. It is also obvious that the WR’s of AL and KL-PCL PU’s decrease with decreasing lignin core structure in the lignin-based PCL PU’s. Accordingly, it is considered that a significant part of the residual products of AL- and KL-PCL PU’s may consist of core lignin structure.

50

40

t3 1

s

30

20 0

10

20

30

CL /OH ratio / (mol/mol)

Figure 11. Change of WR with CWOH ratios of AL- and KL-PCL PU’s WR at 420 “C A AL-PCLPU A KL-PCLPU

42

Synthesis and derivatisation of bioeompatible polymers

O.OS 0.04 III

-
B-rrGlcpn-(l-3>B-o-G.IIHAc-(~chondroitin: W=H. R'=H chondroitin+rulphate (A): R'-S03H. R'-H chondroitinhulphata (C): R'=H. R"= S q H

r

L

1

An

keratan sulphate 3 ~ p - D - G a l p ( 1 4 ~ p - D G l c p N A c ~ S 0 3-H ( l

4)-p-DGlcpA-(l-4~ u-DGk~SO~KBS03K(I-

heparin disaccharide repeating units

Figure 2.

Sulphated polysaccharides with wound management potential.

Natural polymers for healing wounds

103

Sulphated poiysaccharides 27

The group of naturally occumng sulphated polysaccharides including heparin , chondroitin (sulphate), dermatan sulphate and keratan sulphate (Figure 2) exhibit extensive biological activity. Some or all show anticoagulant activity, lipemia clearing activity, interaction with growth factors and fibronectin, and in some cases an anti-HIV effect. It is proposed that their biological activity is due to their anionic nature. Although there is little reported research with respect to their application in wound management, they will undoubtedly find application in the not too distant future since the healing of wounds is accompanied by an increased biosynthesis of the sulphate-containing glycosaminoglycans, within a zone adjacent to the edge of the wound '*. Complex heteropolysaccharides

Research is now focusing on the suitability of more complex polysaccharides for use in wound management aids. An example of this is branan ferulate, a substituted arabinoxylan isolated from high fibre corn bran by alkaline extraction (Figure 3) 3,29. Branan ferulate has also been incorporated into alginate fibres 24@). The ferulate ester groups in branan ferulate are enzymically cross-linked (using a peroxidase / hydrogen peroxide system) to form a commercial hydrogel product, Sterigel" (SSL International), which is used as a wound management aid ". U-L-AIaj 1

a-D-GlcpA 1

4

4

2 2 +4)-P-D-Xylp( 1+4>P-D-Xylp-( 1+$)-f%-D-Xylp-(l+4>P-D-Xylp-(1+ 3 3

t

t

1 a-D-Galp-( 1+2)a-L-Araf 5

1 U-L-kaf 5

Figure 3.

t

t

fedate

ferulate

The structural features / monosaccharide configuration in branan ferulate

REFERENCES 1.

2.

3. 4. 5. 6. 7.

G. D. Winter, Formation of the scab and the rate of epithelializationof superficial wounds in the skin of the young domestic pig, Nature, 1962,193, 293-294. S. Thomas, WoundManagement and Dressings, PharmaceuticalPress,London, 1990. L. L. Lloyd, J. F. Kennedy, P. Methacanon, M. Paterson & C. J. Knill, Carbohydratepolymers as wound management aids, Curbohydr. Polym., Special Issue Gluportwo, 199ft,z, 315-322. S. Dimitriu, P. F. Vidal & E. Chornet, Hydrogels based on polysaccharides, In: Polysucchurides in Medical Applications, S . Dimitriu (ed.),Marcel Dekker, New Yo&, 1996, pp. 125-241. R J. Schmidt, Xerogel dressings - an overview, In: Advances in WoundManugement,T. D. Turner, R J. Schmidi & K. G.Harding (eds.), Wiley, Chichester, 1986, pp. 65-71. P. M. Collins (ed.),Dictionary ofcurbohydrutes, Chapman & Hall,London, 1998. (a) E. E. Treiber, Formation of fibres from cellulose solutions, pp. 455479; (b) L. C. Wadsworth 8z D. Daponte, Cellulose esters, pp. 344-362; (c) M. D. Nicholson & F. M. Merritt, Cellulose ethers, pp. 363-383; In: Cellulose Chemistry and its Applications, T. P. Nevell & S. H. Zeronian (eds.), Ellis HorwOOQChichester, 1985.

-

104

8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

20.

21. 22.

23. 24.

25.

26. 27. 28. 29.

30.


British National Formulary, The Pharmaceutical Press. London, 41, March. 2001. D. N . 4 . Hon, Cellulose and its derivatives: structures: reactions, and medical uses, In:Polysacchandes i n Medical Applications, S . Dimitriu (ed.),Marcel Dekker, hc.. New York. 1996, pp. 87-105. A. N. de BeIder, Dextran, In: Industrial Gums:Polysaccharides and Their Derivatives, R. L. Whistler & J. N. BeMiller (eds.),Academic Press, New York, 1993, pp.399-425. T. Kuge. K. Kobayashi, S. Kitamura & H. Tanahashi, Degrees of longchain branching in dextran. Carbohydr. Rex, 1987,160,205-214. A. J. Howcroft, A controlled trial of Dextranomer (Debrisan) in burns of the hand, Bums. 1979,6, 12-14. C. A. Blanclaneister & D. H. Sussdorf, Macrophage activation cross-linked dextran, J. Leukoc. Biol., 1985. 37,209-219. B. A. Stone & A. E. Clarke, Chemistry and Biology of (1 -+3)-~Glucans,La Trobe University Press, Victoria, 1992. S. J. Leibovich & D. Danon, Promotion of wound repair in mice by application of glucm, J. Reticuloendothel. Soc., 1980,27, 1-11. P. C. Berscht, B. Nies, A. Liebendorfer & J. Kreuter, In vitro evaluation of biocompatibility of different wound dressing materials. J. Mat. Sci. Mater. Med.. 1995, fj,201-205. R A. A. Muzzarelli, M. Mattioli-Belmonte, A. Pugnaloni & G. Biagini, Biochemistry, histology and clinical uses of chitins and chitosans in wound healing, In: Chitin and Chitinases, P. JolKs & R. A. A. Muzzarelli (eds.),Birkhiiuser Verlag, Basel, 1999, pp. 25 1-264. Y. Q n & 0.C. Agboh, Chitin and chitosan fibres: unlocking their potential, Medical Device Technoloo, 1998, December,24-28. (a) Y. Qn. 0. C. Agboh, X. Wang & D. K. Gilding, Novel polysaccharide fibres for advanced wound dressings, pp. 15-20; (b) Y. Le, S. C. Anand & A. R Horrocks, Using algmate fibre as a drug carrier for wound heahg, pp. 21-26; In: Medical lextiles 96, S . C . Anand (ed.), Woodhead Publishing, Cambridge, 1997. R. A. A Muzzarelli, G. Biagini, A. Damadei, A Pugnaloni & J. Da Lio, Chitosans and other polysaccharidesas wound dressing materials, In: Biomedical and BiotechnologrcafAdvances in Industrial Polysaccharides, V. Crescenzi, I. C. M. Dea,S . Paoletti, S. S. Stivala & I. W. Sutherland (eds.), Gordon & Breach, Amsterdam, 1989,pp. 77-88. L. L. Balassa & J. F. Prudden, Applications of chitin and chitosan in wound-healing acceleration, In: Proceedings of The First International Conference on Chitin/Chitosan, R. A. A. Muzzarelli & E. R Pariser (eds.), Massachusetts Institute of Technology Sea Grant Report, MITSG 78-7,1978, pp. 296-305. (a) G.Biagini, R. A. A. Muzzarefi, R. Giardino & C.Castaldini, Biological materials for wound healing. pp. 16-24, (b) K. Kifune, Clinical application of chitin artificial skin (Beschitin W), pp. 9-15; In: Advances in Chitin and Chitosan, C. J. Brine, P. A. Sandford 62 J. P. Zikakis (eds.),Elsevier Applied Science, London, 1992. R. A A Muzzarelli, Chitin and chitosan: unique cationic polysaccharides,In: Towards a carbohydrutebased chemise, Report EUR 12757 EN, Commissionof the European Communities, Luxembourg, 1989, Pp. 199-231. (a) X. Chen. G. Wells & D. M. Woods. Production of yarns and fabrics fiom alginate fibres for medical applications; (b) M. Miraftab, Q. Qao, J. F. Kennedy, S. C. Anand & G. Collyer, Advanced materials for wound dressings: biofunctional mixed carbohydrate polymers, pp, 164-172; In: Medical Textiles, S . C. Anand (ed.),Woodhead Publishing Ltd, Cambridge, 2001. (a) P. H. Weigel, S. J. Frost, R. D. LeBoeuf & C. T. McGary, The specific interaction between fibrin(ogen) and hyaluronan: possible consequences in haemostasis, inflammation and wound healing, pp. 247-264; (b)E. A Balazs & I. L. Denlinger, Clinical uses of hyaluronan, pp. 265-280; In: The Biology of Hyaluronan (Ciba Foundation Symposium 143), John Wiley & Sons,Cluchester, 1989. D. Williams. The engineering of polysaccharides,Medical Device Technology, 1997, September, 8-11. B. Casu, Structure andbiological activity of heparin, Adv. Carbohydr. Chem. Biochem., 1985,43,51-134. R. A. Carlsen, P. Helin & G. Helin, Glycosaminoglycan formation around the linear wound, J. Invest. Dermatol., 1973,6l. 7-1 1. J. F. Kennedy, M. Paterson, C. J. Knill & L. L. Lloyd, The diversity of properties of polysaccharides as wound management aids, and characterization of their structures, In: Proceedings of the 5'h European Conference on Advances in WoundManagement, G. W. Cherry, F. Gottrup. J. C. Lawrence, C. J. Moffatt & T. D. Turner (eds.),Macmillan Magazines Ltd, London, 1996, pp. 122-126. J. F. Kennedy, P. Methacanon, L. L. Lloyd, M. Paterson & C. J. Knill, The chemical structure of a novel polysaccharide, Sterigel, suitable as a wound management aid, In: Proceedings ofthe 61h European Conference on Advances in WoundManagement, D. J. Leaper, G. W. Cherry, C. Dealey, J. C. Lawrence & T. D. Turner (eds.),M a d l l a n Magazines Ltd, London, 1997, pp. 141-147.

Part 3

Production and use of biocompatible materials

IMPROVEMENT OF ALGINATE FIBER MIXING WITH PHOSPHORYL POLYSACCHARIDES Seiichi Tokura'*, Hiroshi Tamura', Yukihiko Tsuruta', Chisato Nagaei2and Kouki Itoyama2 Faculo of Engineering and HKC. Kansai University, Suira, Osaka 564-8680, Japan Institute for Research and Development, Fuji Spinning Co. Ltd., Oyama, Shizuoka 410-1394, Japan

ABSTRACT Chitin and cellulose were converted to water soluble materials and to calcium specific adsorbents by introducing phosphoryl groups into sugar the residues. Phosphoryl chitin (P-chitin) or phosphoryl cellulose (P-cellulose) was mixed with alginate aqueous solution before spinning and then spun into calcium chloride aqueous solution under similar conditions as those for alginate filament spinning. The P-chitin mixed alginate filament was shown to have improved wet tensile properties in addition to the softness of filament, whereas P-cellulose mixed alginate filament showed less knot strength than that of Pchitin mixed filament.

,&!7+/&7&7j NHCOCH,

NHCOCH,

NHC0CH3

NHCOCH,

P-Chitin

'

,

COOH

Alginic acid

,g?&7&&-7 OH

OH

OH

P-Cellulose

Figure 1. Polysaccharides used in this study.

OH

108


INTRODUCTION As alginate is known to be one of the biological polysaccharides biocompatible the fiber or membrane is used for biomedical purposes I . Chitin is also expected to be used as biomedical materials due to its biodegradability and low toxicity 2.3. However, the stiffness of alginate filaments and wet tensile properties of chitin filaments can be improved by substituting hydroxyl groups with functional groups. We have prepared chemically modified chitin derivatives, which possess good solubility in many kinds of solvents and characteristic functions, in order to promote the usefulness of this polysaccharide resource. In the course of this project, the acylation reactions in methanesulphonic acid were found to be efficient, and many kinds of acyl-chitins, such as sulfate, and carboxymethyl chitins, soluble in organic solvents were successfully prepared by this method 4.5. Recently, the reaction of chitin with phosphorus pentoxide by this method was found to give water-soluble phosphoryl-chitin (P-chitin) of sufficiently high degree of substitution (DS). In our preliminary experiments, it was found that P-chitin forms a gel in the presence of calcium ions as well as the alginate. We gave attention to the fact that both polysaccharides have the same coagulation condition and performed the mixed spinning of P-chitin with alginate using calcium chloride as coagulant. The properties of mixed spun filament were compared with those of the mixed spun filament of P-cellulose with alginate.

EXPERIMENTAL Materials P-Chitin fine powder originating from squid bone was obtained from Nippon Suisan Co. Ltd., and vacuum dried at 60 "C for 1 day. P-cellulose was purchased from Wako Pure Chemicals Co. Ltd. N,N-dimethylfomamide (DMF) was dried over potassium hydroxide and vacuum distilled before use. Orthophosphoric acid was prepared by adding diphosphorous pentoxide to 85% phosphoric acid followed by refluxing at 110 - 120 "C for 12 h. Other chemicals were purchased from Wako Pure Chemicals Co. Ltd. and used without further purification.

Synthesis of P-chitin and P-cellulose P-chitin was prepared by the orthophosphoric acid method using P-chitin from Squid bone. P-chitin of fine powder was stirred in urea-DMF solution, and reacted with orthophosphoric acid at 150°C for 3 h. P-cellulose was also prepared by the same method as the P-chitin applying P-cellulose of lower substitution.

Mixed spinning of filament Mixed solutions of P-chitin (DS=1.4) and alginate where P-chitin contents of 50,33,20 and 0 % were prepared. This solution was excluded out using air pressure through a nozzle (0.lmm diameter, 50 holes) into 3% calcium chloride solution to coagulate. The filament was wound up, using mini-spinning machine, with the first roller rate set at 4.9 d m i n and with a magnitude of elongation of 1.2 (Fig. 2). The obtained filament was extensively washed with water and methanol, and air dried at room temperature. Mixed spinning of P-cellulose with alginate was also performed in a similar manner as the Pchitin mixed alginate filament.

Improvement of alginate fiber mixing

109

PehStin(%) 0 20 33 50 Alglnate(%)lW 80 67 50 \

Wind-up rdler Stretching roller

1st roller rate :4.9 m/mln Stretching ratlo : 1.2

3% CaCh aq. soin.

Figure 2. Spinning machine.

Tensile strength The stress-strain diagram of the filament was measured by the JIS 1013-7.5 and 7.6 methods using Tendon RTA-250 apparatus. The initial sample length was 20.0 m m and the stretching rate was 20.0 d m i n . The force at the breaking point was taken as the tensile stress, which was transferred to tensile strength and Young's modulus.

RESULTS A N D DISCUSSION Synthesisof P-chitin and P-celldose

The introduction of phosphate groups was confirmed by FT-IR and I3C NMR spectra. The IR spectra of P-chitin with various DS show that as the DS increases there is a corresponding decrease in the absorption due to the hydroxyl group (1310cm-') and new absorption frequencies characteristic for stretching of the phosphate groups appear at 124Ocm-'and 920 cm". The proton decoupled 'CNMR spectra for two kinds of P-chitins (DS = 0.22 and 1.26) measured in D,O at pD 7.0 showed that the carbons which attach to the substituted hydroxyl groups are clearly distinguished from the non-substituted ones. It was also found that the introduction of phosphoryl groups into the 6 position took precedence over 3 the position. When the reaction was carried out using orthophosphoric acid, DS increased with increase of the urea-DMF. In contrast to the conventional methanesulfonic acid method, no decrease of MW of the P-chitin was found. There is a good correlation between MW and DS against Urea/DMF ratios suggesting the possibility of regulation of the DS by changing this ratio. This result suggests that destruction of the hydrogen bonds in p-chitin is performed by urea which is known as a general hydrogen bond breaking reagent. The commercially available water insoluble P-cellulose was further phosphorylated to become water soluble applying the similar procedure as the P-chitin.

I10


Mixed spinning of filament Mixed spinning of P-chitin with alginate was successfully performed using calcium chloride as coagulant using the mini-spinning machine, because P-chitin forms gels in the presence of calcium ion as well as alginate. The obtained filaments were lustrous and smooth with a size of 3-6 denier/g. The P-chitin mixed alginate filament was more flexible than the alginate filament itself. Scanning electron microscope observations of the filaments with different contents of P-chitin indicated that the diameter was around 10 p m and the surface of the filament became rough as the content of the P-chitin increased. The same calcium absorption behavior of P-cellulose made it possible to perform mixed spinning of P-cellulose with alginate successfully to give the fine filament as well.

Tensile strength of filament Tensile strength of the P-chitin mixed alginate filament under dry conditions increased with the increase of the content of the P-chitin and that under wet conditions decreased. Thus, the dry-wet ratio in tensile strength was about 30-40% as shown in Fig. 3. Elongation of the filament in this condition is around 6 - 8 % both in dry and wet conditions with the same strength as rayon and wool. Knot strength was also measured applying the filament in the knot condition. Knot strength is an important characteristic factor for filaments because this character reflects characteristics such as stretching, compressing, bending and torsion. Although knot strength of the filaments decreased to 20-30 % compared to tensile strength, dry-wet ratios of the knot strength of them were 100 - 200 % (Fig. 3).

Figure 3. Dry-wet ratio of P-chitin mixed alginate filament measured in tensile strength and knot strength.

Improvement of alginate fiber mixing

I

0.50

P-chitin

0

11 1

I

P-cellulose

20 33 Content of P-saccharide (96)

50

Figure 4. Comparison of knot strength between P-chitin and P-cellulose mixed aiginate filaments.

These results suggest that the present mixed filament of alginate with P-chitin have excellent properties under wet conditions. The filament properties of alginate filament containing P-cellulose were also performed. The comparison of the knot strength between P-chitin and P-cellulose mixed alginate filament is shown in Fig. 4. It was found that the P-chitin mixed alginate filament is superior to the P-cellulose in knot strength. In addition, reduced antigenic, blood coagulation properties suggest that alginate filament containing P-chitin have the possibility of becoming a new biomedical material, such as wound dressing.

CONCLUSION Mixed spinning of P-chitin with alginate was successfully performed because both of the Pchitin and alginate coagulate under similar conditions. The obtained filament showed soft feeling and flexible, and has an advantage in knot strength especially in the wet condition. The comparison of the filament properties between P-chitin and P-cellulose mixed alginate filament indicates that the former is superior to the latter in the knot strength probably due to the strong interaction with alginate molecule.

ACKNOWLEDGEMENTS This research was partly supported by the Kansai University Special Research Fund, 1999 and also a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, and Sports, Japan (Grant 09240103).

112


REFERENCES 1.

2. 3.

4.

5.

6.

S. Ohlson, P.-0. Larsson & K. Mosbach, Steroid Transformation by Living Cells Immobilized in Calcium Alginate; European J. Appl. Microhiol. Biotechnol., 1979,7, 103-107. F. G. Pearson, R. H. Marchessault & C. Y. Liang, Infrared Spectra of Crystalline Polysaccharides. V. Chitin, J. Polym. Sci. 1960, 38, 101-116. N. Nishimura, S . 4 . Nishimura, N. Nishi, F. Numata, Y. Tone, S . Tokura, & I. Azuma, Adjuvant Activity of Chitin Derivatives in Mice and Guineapigs, Vaccine, 1985, 3, 379-384. K. Watanabe, I. Saiki, Y. Uraki, S. Tokura & I. Azuma, 6-0-Carboxymethyl-chitin (CM-chitin) as a Drug Carrier, Chem. Pharrn. Bull., 1990, 38, 506-509. S. Tokura, Y. Miura, Y. Kaneda & Y. Uraki, Two-step Hydrolysis of a Polymeric Drug under a Model System, Carbohydr, Polym. 1992, 19, 185-190. Japanese Standards Association, Japanese Industrial Standard JIS L 1013, 1992, pp. 1-8.

PREPARATION OF CELLULOSE VISCOSE FOR VARIOUS MATRICES B Lonnberg’, S Ciovica’, T Strandberg’, T Hultholm’ and K Lonnqvist2

’ Abo Akademi University, Faculty of Chemical Engineering, Laboratoy of Pulping Technology, Porthansgatan 3, FI-20500 TurkdAbo, Finland Cellomeda @, Tykistokatu 6 A. FI-20520. Turku, Finland

ABSTRACT

New medical and clinical applications of regenerated cellulose matrices require also new and better properties. There are different ways to achieve them. Plant cellulose is a natural, pure and mostly crystalline material that can be dissolved and regenerated to form various products (threads, membranes and sponges). The properties of the cellulose viscose and hence the final regenerated cellulose will evidently be affected also by the cellulose source (wood, grass), the pulping method (sulphite, haft) including bleaching, One approach is to find acceptable products by just doing the processing in a better way than before, which implies process modification. In this case, the pulping was made by a new sulphur-free alkaline pulping method called the IDE- process ‘72. The first capital I stands for the ‘impregnation’of the cooking chemicals into the fibre material, D stands for ‘depolymerization’of the lignin and E for the ‘extraction’ of it. Thus IDE forms a special delignificationconcept providing controlled pulping. In this study, a commercial dissolving pulp and bleached IDE-pulps were processed into cellulose viscose and to membranes for comparison of certain chemical and physical properties. The work was considered an exploration of the most proper cellulose regeneration for certain matrix properties. INTRODUCTION

Currently, cellulose matrices are studied in the form of membranes or sponges for use in various clinical and medical products 3,4, since cellulose is a natural material and thus considered pure and biocompatible. Although it is very inert, due to its high degree of crystallinity, and subsequently resistant to acids and alkali, the cellulose may be modified after treatment with strong alkali with the aim of activating the cellulose. Thus the alcoholic hydroxyl groups become accessible and can be substituted with a number of functional groups to give the cellulose modified properties. The classical way of preparing a solution of cellulose is to treat the alkali cellulose with carbon disulphide to form a xanthate soluble in dilute alkali. The cellulose solution or viscose is finally coagulated and regenerated to provide a pure cellulose preferrably in a physical form easy to study. Therefore, the viscose was cast as a film or membrane for the regeneration. Since some medical products require biodegradability, new cellulose materials must be developed, and it is believed that IDE cellulose might fulfil such requirements.

114


Table 1. Cooking conditions for the softwood IDE pulps. Cook

1 stage')

No.

Temp.

"C IDE-06 IDE-11 IDE-16

D stage Time min

Temp. "C

Time min

Temp.

"C

Time min

90

180 170 165

60 180 180

130 130 130

1x0 1xo 1x0

100 100 100

')

E stage

YO

90

Two-stage procedure under similar conditions

EXPERIMENTAL Pulping and bleaching Pulping conditions Softwood haft and IDE pulps were made in the laboratory under well controlled conditions. The haft pulping conditions were normal (kappa number 24), as the sulphurfree TDE pulping started with a two-stage alkali impregnation at 100" C and continued with a depolymerization stage containing alkali, anthraquinone as a catalyst, water and ethanol and carried out at different temperatures as shown in Table 1. The extraction stage finally carried out with water and ethanol for effective extraction of depolymerized residual lignin was constant in all experiments.

Bleaching conditions The pulps were bleached according to a common ECF bleaching sequence, which was DEDED (DI-I11 for chlorine dioxide, EI-I1 for alkaline extraction). The total chlorine dioxide charge was 13% as active chlorine and the alkali charge 4%, see Table 2.

Table 2. DEDED-bleaching conditions for the softwood haft and softwood IDE pulps.

Stage

act. C1 %

D1 EI DII El1 DIII

NaOH 5%

Pulp cons.

Temp.

%

"C

x 2

4 8 4 4

65 20 65 20

4 4

2 5

65

Time min 60

45 60 45 60

Preparations of cellulose viscose

115

Table 3. Unbleached and bleached softwood haft (K-2) and softwood TDE pulp properties. -

PULP SAMPLES K-2

IDE-06

IDE- 1 1

IDE- 16

-

UNBLEACHED PULPS: Total yield, % Screenings, % Kappa number Acetone extractives, % Viscosity’), mL/g

45.7 0.03 24.2 0. I 1007

49.1 0.08 25.6 0.2 746

47.5 0.02 23.5 0.2 798

47 .O 0.06 28.5 0.1 915

453 1078 8.3 6.6

325 773 9.4 7 .O

330 785 8.9 6.6

371 897 8.6 6.6

BLEACHED PULPS: Viscosity‘),mL/g DP” Slo Solubility3’,% S I S Solubility? %

SCAN-CM 15:88;

DP = (viscosity)/0.42; 3, SCAN-C 2:61

Pulp properties Table 3 presents the pulp yields and kappa numbers. All pulps, including the haft pulp (K-2) and the IDE pulps (IDE-06, IDE-11 and IDE-16), had an unbleached kappa number close to 25. It should be emphasized that the IDE pulp yields were significantly higher than those of the haft pulp, as again the viscosity was much lower, also after bleaching.

Viscose preparation The cellulose viscoses were produced in the laboratory starting with the bleached softwood haft and softwood IDE pulps described earlier, and with a bleached commercial softwood dissolving pulp as a reference pulp. The conditions are shown in Table 4. The alkalization was made with a 20% NaOH solution, which produced an alkali cellulose providing the degree of pressing Pd = 2.8 (weight of pressed alkali cellulose relative to the initial cellulose weight). The final viscose contained 9% cellulose and 6% NaOH. Some of the viscoses were coagulated and regenerated into membranes as to enable a study of the viscose process and the cellulose strength properties.

116


Table 4. Conditions for preparation of the cellulose viscose.

Procedure

Conc./Charge %

Alkalization (NaOH-c.) - ageing Xanthogenation (CS2-ch.) - dissolution Viscose" ageing

')

To a final DP 400 (see Table 6 )

20

35

Temp. "C

Time

40 23

60

30

60

10 20

(24 h)

min

1)

90

Composition: 9% cellulose and 6% NaOH

Determinations

Fibre dimensions The original bleached pulps as well as the corresponding alkali celluloses were analyzed by the Kajaani FiberLabB Analyzer for fibre and particle dimensions as length, width, wall thickness and coarseness (weight/length). Before running the tests, the alkali celluloses were thoroughly washed, acidified as to exclude the bound sodium ions and washed again to complete neutrality. The fibre dimensions were determined following normal procedures implying that thousands of fibres were measured and reported as distribution curves and average values. The fibre length measurement interval covered the range born 0 to 7.6 mm and the fibre width accordingly from 0 to 200 pm, the resolutions being 50 and 1 pm respectively.

'

Infra-red spectra IR-spectra were taken on the bleached pulp samples (K-2, IDE-06, IDE-1 1 and IDE16, and the commercial dissolving pulp as a reference) as to determine the crystalline and amorphous domains of the cellulose, and to provide a measure of the crystallinity index. The absorption of the 1375 cm-' wavelength was considered reflecting the crystalline part and that of 2900 cm-' wavelength the amorphous part of the cellulose '; thus the ratio between these two absorptions would provide an approximation of the crystallinity index.

RESULTS AND DISCUSSION Cellulose crystallinity The IR spectra taken are given in Fig. 1, and the computed crystallinity indices are compiled in Table 5. It appears that the IDE pulps provided quite low crystallinity indices according to the method applied. The IDE-06 pulp which was cooked at a high temperature of 180' C appeared to be particularly low in crystallinity.

Prcparations of cellulose viscose

1 I7

I

I

Figure 1. IR spectra of the softwood DEDED-bleached haft (K-2) and IDE pulps as well as of the commercial reference pulp. Ageing of alkali cellulose Cellulose depolymerization took place during the ageing of the alkali celluloses obtained. The degree of depolymerization (DP) was computed from the viscosity divided by 0.42. Both DP and lnDP decreased linearly as a function of the ageing time with R2 clearly exceeding 0.95. Table 6 shows the ageing time required to obtain DP 400, and also the coefficients a and b of the equation lnDP = a - b t, as well as the R2 value. Fig. 2 provides an example with IDE-06, which had a low crystallinity index.

Pulp fibre dimensions The pulp fibre dimensions, i.e. fibre length, fibre width and fibre wall thickness and their respective distributions, were determined with the FiberLab Analyzer.

Table 5. Softwood haft (K-2) pulp, softwood IDE pulp and commercial dissolving pulp crystallinity indices evaluated from the IR spectra. Pulp

K-2 IDE-06 IDE- 1 1 IDE- 16 Reference

Al3WA29OO

0.8 1 0.35 0.67 0.57 0.7 1

118

Production and use of biocornpatible materials

Table 6. Ageing characteristics of the alkali celluloses including that made of the

dissolving pulp as a reference.

K-2

37.5 6.94 -0.025 0.98

Time to DP 400, h Coefficient a Coefficient b R2

IDE- I 1

IDE-06

27.5 6.66 -0.024 0.YY

26.3 6.66 -0.025 0.99

IDE- 16

Reference

27.7 6.76 -0.028 0.98

lY.O 6.29 0.016 0.96

Measurements were performed on the celluloses (initial pulps), on the alkali celluloses (celluloses after alkali treatment) and on the treated alkali celluloses (celluloses after alkali treatment, pressing and shredding). The ratio between fibre width and fibre wall thickness was computed and reported.

Fibre length The fibre length (weighted by length) is shown in Fig. 3 for the IDE-06 cellulose, the corresponding alkali cellulose, and the treated (pressed and shredded) alkali cellulose. It may be seen that the treatments decreased the average fibre length, which is further itlustrated in Fig. 4. If the cellulose was given the arbitrary average fibre length of 1, it was slightly exceeding 0.8 for the alkali cellulose and even lower after further treatment of the alkali cellulose (pressing and shredding). The trend was about the same for all other celluloses studied in this context, and thus the conclusion may be drawn that particularly the alkali treatment decreased the fibre length, as did also combined pressing and shredding, but to a lower extent, see Table 7.

IDE-06 Alkali cellulose

P

n

C

6.7 6.6 6.5 6.4 6.3 6.2 6.1 6

+ 6.6689 R 2 = 0.9951

y = -0.0246X

I

0

i

10

20

30

Ageing time, h

Figure 2. Ageing rate of the IDE-06 alkali cellulose.

Preparations of cellulose viscose

119

-

IDE-06

rn

1.o

0.0

I

2.0

3.0

4.0

5.0

6.1

Fibre length (length weighted), rnrn

Figure 3. Fibre length distributions for the IDE-06 cellulose, the corresponding

alkali cellulose and the further treated alkali cellulose.

IDE-06 ............

Cellulose

Alkali Treated cellulose alkali cellulose

Figure 4. Average fibre lengths for the IDE-06 cellulose, the corresponding alkali cellulose and the further treated akali cellulose. Table 7. Average fibre lengths (in arbitrary units: 1 for the initial cellulose) for the softwood haft (K-2) and IDE celluloses, and the dissolving cellulose, the corresponding alkali celluloses and the further treated alkali celluloses.

Pulp

Cellulose

K-2 IDE-06 IDE- 1 1 IDE- 16 Reference

1.oo 1.oo 1.o0 1 .00

1.oo

Alkali cell.

‘Treated alk. cell.

0.85

0.78 0.78

0.85 0.85 0.90 0.62

0.78 0.82 1x1

120


0.0

Figure 5. Fibre width distributions for the IDE-06 cellulose, the corresponding alkali cellulose and the further treated alkali cellulose. Fibre width

A similar evaluation of the fibre widths was made on the celluloses, the corresponding alkali celluloses and the further treated alkali celluloses. Fig. 5 showing the fibre width distribution and Table 8 providing the average fibre widths - presented also in Fig. 6 indicate that the alkali treatment appeared to cause some s w e h g to the material, but not as much as to the reference dissolving cellulose.

Fibre wall thickness The fibre wall thickness index behaved in a similar way as the fibre width. The ratio between the fibre wall index and the fibre width may provide some further information

I

IDE-06

3 1.02 --

Cellulose Alkali Treated cellulose alkali cellulose

Figure 6. Average fibre widths for the IDE-06 cellulose, the corresponding alkali cellulose and the further treated alkali cellulose.

Prteparations of cellulose viscose

121

Table 8. Average fibre widths (in arbitrary units: 1 for the initial cellulose) for the softwood haft (K-2) and IDE celluloses, and the dissolving cellulose, the corresponding alkali celluloses and the further treated alkali celluloses. Pulp

K-2 IDE-06 IDE- 11 TDE-16 Reference

Cellulose

Alkali cellulose

Treated alkali cellulose

-

1.oo 1.00 1.oo 1 .oo 1.oo

1.02 I .0:3 0.99 1.04 1.13

0.98 0.96 0.94 0.97 nd

on the fibre swelling, see Table 9. It appears that the IDE celluloses would have a higher relative fibre wall swelling than the reference dissolving cellulose.

Strength properties Some strength properties were determined on membranes made of the cellulose viscoses produced of the softwood haft and IDE pulps. The filtration of the haft pulp viscose was difficult, and no membrane was thus prepared. The results compiled in Table 10 indicate that the membrane stretch, tensile work and stiffness were similar for the IDE celluloses and the reference, as the tensile strength showed some differences.

Table 9. Ratio between the fibre wall index and fibre width (in arbitrary units: 1 for the initial cellulose) for the softwood haft (K-2) and IDE celluloses, and the dissolving cellulose, the corresponding alkali celluloses and the further treated alkali celluloses. Pulp

Cellulose

Alkali Treated alkali cellulose cellulose

K-2

1.oo 1.oo 1.oo 1.oo 1.OO

1.06 1.02 1.oo 1.02 0.95

IDE-06 IDE- 11 IDE- 16 Reference

0.96 0.95 0.96 0.97 nd

Table 10. Strength properties of cellulose membranes made from softwood IDE pulp and dissolving pulp as a reference.

Property

IDE-06

IDE- 1 1

IDE- 16

Reference

Strength, kN/m Stretch, % Work, J/m' Stiffness, I r N h

3.4 1 4.8 162 286

3.21 4.4 144 292

4.57 3.6 156 312

4.26 4.8 158 304

122


CONCLUSIONS This study indicated that softwood pulps cooked to kappa number 25 by application of the sulphur-free IDE cooking concept, DEDED-bleached and finally converted into cellulose viscose (for medical and clinical membranes or sponges) might provide an interesting cellulose material. Dependent on the D stage temperature from 165" -180" C the crystallinity index and cellulose membrane strength may vary, but it appeared that a high temperature provided a low crystallinity index and a low temperature again a high membrane strength, In general, the pulp yield was very high for the IDE pulp, but the pulp viscosity (DP) was low compared with those of the haft pulp and the commercial dissolving pulp as il reference. The regenerated celluloses will in the future be developed towards good hydrophilicity and suitable biocompatibility.

REFERENCES 1. M. Backman, B. Lonnberg, K. Ebeling, K. Henricson & T. Laxen, Impregnation Depolymerization Extraction pulping, Paperi ja Puu, 1994,76 (lo), 644-64

2. T. E. M. Hultholm, K. B. Lonnberg, K. Nylund & M. Finell, The IDE process: a new pulping concept for nonwood annual plants, In: Proceedings of Pulping Conference, Chicago, Oct. 1-5, 1995, Book I , TAPPI Press, Atlanta, 1995, pp 85-89. 3. 0. Pajulo, B. Lonnberg, K. Lonnqvist & J. Viljanto, Development of a high grade viscose cellulose sponge, In: The M V I I Congress of the European Societyjor Surgical Research (ESSR),Turku-Finland, May 23-26, 1993. Abstract Book, P- 156. 4. S. Ciovica, B. Lonnberg & K. Lonnqvist, Dissolving pulp by the IDE concept, Cellulose Chem. Technol., 1998, 32 (3-4), 279-290.

5. Valrnet Automation Kajaani Ltd, FiberLab installation and operation manual W4230467 V1.3, June 1998, Kajaani, Finland. 6. O'Connor et al., Text. Res. J., 1958 28: 383, In: H. A. Krassig, Cellulose Structure, Accessibility and Reactivity, Gordon and Breach Sci. Publ., 1993, p. 125.

SYNTHESIS AND PROPERTIES OF NOVEL POLYELECTROLYTE ON THE BASIS OF WOOD POLYMER Galia Shulga'"', Girt Zakis', Brigita Neiberte', Janis Gravitis2 'Latvian State Institute of Wood Chemistry, 27 Dzerbenes St., Riga LV-1006, Latvia; 'United Nations Universi& Institute ofAdvanced Studies, 53-67Jingumae 5-chome. Shibuya-ku, Tokyo 150-8304, Japan;

ABSTRACT

In this work, diluted reaction aqueous mixtures, containing polymer cation (PC), a weak polymer base, and sodium salt of birch nitrolignin (Na-Mig) in a composition range of 0.1 5 Z I 5. where Z = [pC]/[Na-Nlig] have been studied. Nitrolignin is an environmentally compatible by-product of the nitrate pulping process and possesses pronounced biostimulating action. The presence of various ionogenic groups imparts polyelectrolyte properties to the lignin macromolecule. It has been shown that the interaction between the reaction mixture components proceeds according to an electrostatic mechanism and results in the formation of novel polyelectrolytes (NPE), differing from Na-Nlig and PC, in terms of their behavior in aqueous media. The water solubility of the W E formed is determined by the composition of the reaction mixture and depends on the extent of conversion in the interpolyelectrolyte reaction. An enhanced ability of adsorbing on the liquidgas and liquidhquid interfaces is conditioned by the presence of hydrophobic domains in NPE structure formed by the interacted regions of polycation and lignin-polyelectrolyte macromolecules. It has been shown that it is possible to regulate the hydrophilic-hydrophobic balance of the water soluble NPE structure by varying the extent of conversion in the interpolymer reaction. The last feature is of interest from the viewpoint of the use of NPE as a regulator of surface tension on various interfaces.

INTRODUCTION Reduction of available oil resources worldwide will gradually reveal lignin, a biomass constituent, as a very important starting material for production of polymers. Chemical modification will play a key role in the development of novel polymer products based on lignins - the by-products of various industrial processes of wood delignification. Therefore, environmental demands, economic realities and a high efficiency of the biomass conversion will be integrated in the process of creation of a new generation of high-performance, high quality and environmentally compatible polymers and plastics. The results reported may be regarded as one of the numerous steps made by the State Institute of Wood Chemistry in accordance with its program "New Materials of Wood and Plant Origin", and the United Nations University in UNU/ZERI (Zero Emissions Research Initiative) concept development based on the strategy of the high efficiency of the biomass conversion into value added chemical products [l]. Nitrolignin (Nlig) is a by-product of a pulping process with nitric acid. It has been shown that nitrolignin formed possesses pronounced biostimulating action. Owing to the

124


presence of a considerable amount of carboxyl and phenolic hydroxyl groups, Mig is one of the representatives of lignin-polyelectrolytes. One of the interesting reactions, which allow to modification of lignin-based polyelectrolytes, is an interaction of such polyelectrolytes with polymer or oligomer cations. These reactions proceed in aqueous, aqueous-salt, or aqueous-organic media at room temperature and normal pressure and lead to formation of polymer products [2,3). The goal of the present work was to study of the interaction between nitrolignin and polymeric cations in dilute aqueous mixtures, and to investigate the properties of novel polymer products formed.

MATERIALS & METHODS Mig was obtained as a result of a delignification process of birch wood 1431. The pulping process included the following stages: impregnation of birch chips with 12.5 g dl-' HNO3 at 323 K for 4 hours; cooking of chips in a sharp steam reactor at 323 K for 1 hour; leaching of chips with water and alkaline extraction with 2.5 g di-' NaOH at 323 K for I hour. Mig was isolated from the spent liquor by precipitating with the universal ion-exchange resin at 293K. Its purification was carried out by selective dissolution in an aqueousalcohol solution with further lyophilic drying. The elemental and functional analyses of Nlig have shown the following average formula of its phenyl-propane unit: C ~ H ~ . S ~ ( O C H ~ ) O . ~ ( O H ~ ~ . ~ ~ ( ~ ~ ~[S] ~. ~ The ~ content )~.~~(~O of ionogenic groups was estimated from potentiometric and conductometric titration curves of Nlig. Its average molecular mass value equal to 3500 was calculated from viscometry data [6]. As the polymer cation (PC), the weak polybase with a molecular mass 50,000 was chosen. It possessed a branched structure and contained up to 75% of primary and secondary amino groups. The novel polyelectrolyte products WE) were synthesized by mixing of diluted initial aqueous solutions of Na-salt of NLig and PC at 293K. The composition of the reaction mixtures was expressed by the Z=[PC]/wa-Nlig]] value, a ratio of the molar concentrations of oppositely charged fimctional groups. Surface tension equilibrium values IS of the aqueous polymer solutions were found according to the Wilhelmy method at 293K. A concentrated oiVwater type emulsion (75 mass p a d 25 mass part) was chosen as the liquid disperse system. The emulsion was obtained by mechanical dispersing of n-heptane in the stabiliser-containing water. The coalescence time (5, min) of equal-volume emulsion samples served as a criterion of aggregative stability. RESULTS & DISCUSSION Intermacromolecular interaction between wood and synthetic polyelectrolytes in aqueous solutions

It has been established that the interaction between the polymer components in the reaction mixtures has an electrostatic mechanism and results in the formation of the novel polyelectrolytes, differing from Nlig and PC, in terms of their behavior in aqueous solution.

Synthesis and properties of novel polyelectrolyte

125

An interpolyelectrolyte reaction of the NPE formation can be represented schematically in the following manner:

Na-Nlig

where A'

PC

NPE

- COO-, O'f, .

The NPE macromolecule formed can be regarded as a special macromoleculepolyampholyte, containing both hydrophilic chains with charged fiinctional groups of diverse nature and hydrophobic domains formed by macromolecule fragments of the interacted polymer cation and nitrolignin. The aggregative stability of the NPE is determined by the composition of the reaction mixtures Z and depends on the extent of conversion (0) in the interpolyelectrolyte reaction calculated fiom the potentiometric titration curves of the polyelectrolytes mixtures [2]. The profiles 0@H) of intermacromolecularreaction are characterized by the steep slope, which is generally typical for cooperative transitions. Initial values of 8 in the Na-NLig - PC interpolymer reaction for reaction mixtures with 0.5 5 Z_O) and & (>O) represent the

(5) N - N, or No + Nu repeating units is expected to change with annealing &me t by the &sociation of polysaccharide molecular assemblies and subsequent homogemzation. We assume the simple relation to describe the time evolution of N - N,.

rate constants for adsorption and desorption of water molecules.

d(N - NJdt = - a! (n q,(T)) ~

Here,

a! (>O)

(4)

is the phenomenological constant, and n,(T) the equilibrium value of n at

the annealing temperature T.

The eq. (1) is derived from equations (Z), (3) and (4).

The solution of eq. (1 ) n=Cexp(-y t)cos(w t + 6 ) + n e ,

(5)

describes well the anomalousbehaviour of non-freezing water [4, 51. In h s study, Tg-s measured by FBM increased with the increase of the anneahg temperature and the concentration

On the other hand, the rate of change of non-freez&g

water increased with the increase of the annealing temperature, but the obvious dependency of the change of non-freezing water on the concentration was not observed in the measured concentration region. From the above physical pictures and the experimental results, the structure formed

in the annealing process is considered as follows. At low anneJng temperature, dissoaation of the assemblies of polysaccharide molecules is incomplete and the homogeneity partly remains in the system However, at h g h annealing temperatures, homogeneity m the systems almost disappears. The annealing temperature difference of the gel-sol transition temperature s e a m to be due to the ddference of the shucture in the systems or the Uference of the attainment of the equilibration of systems.

As for the

Temperature and concentration dependency

I53

concentration dependency, it is very difficult to discuss the concentration dependency because of the narrow region of measured concentrationsince it is generally impossible to prepare completely homogeneous aqueous solutions of plysaccharide electrolyte with concentration larger than 10 wt%. However, the dependency on concentration should be strong if the concentration fluctuation which causes the structural change in the

annealing process is based on the translational &fusion of plysaccharide electrolyte chains, i.e. the reptational motion of polysacchande electrolyte chams in concentrated aqueous solmons. Therefore, it may be concluded that the structural change in annealing process is caused by the molecular motion in the microscopic domain which is smaller than the dimension of plysaccharide electrolyte chains.

ACKNOWLEDGEMENTS This work was supported by Grant-in-Aid for COE Research (10CE2003) and that of (C) (No. 11650925)by the Ml~llstryof Education, Science and Culture of Japan.

REFERENCES 1) F. X. Qum,T. Hatakeyama, M. Takahashi and H. Hatakeyama, ‘The effect of annealing on the conformationalproperties of xanthan gum hydrogels’ , Polymer, 1994,

35, 1248-1252. 2) T Yoshida, M. Takahashi, T. Hatakeyama and H. Hatakeyama, ‘Annegelationof xanthadwater systems’ , Polymer, 1998, 39. 1119-1122.

induced

3) T. Yoshida, M. Takahash T Iwanami R. Tanaka, T Hatakeyama and H. Hatakeyama, In: StdsticrJ Physics. Experiments, Theotiesa d Computer Simulcrions, M Tokuyama and1 Oppenheim(eds.), 1998, World Scientific, Singapore, pp61. 4) M. Takahash, T. Hatakeyama and H. Hatakeyam, ‘phenomenological theory describing the behaviour of non-freezing water in structure formation process of plysaccharide aqueous solutions’ , Carbohydr. Polym., 2000, 41, 91-95. 5) J. Fujwara, M. Takahashi, T. Hatakeyama and H. Hatakeyama, ‘Gelation of HyaluronicAcid by Annealing’ , to be publishedin Polym. International. 6 ) S. B. Ross-Murphy, V. J. Morris and E. R Morns, ‘Molecular Viscoelasticity of XanthanPolysaccharide’ , Faraday Symposia of thechemical Society, 1983, 18, 115129. 7) K. Nishmari, ‘Gel Formation of Natural Polymers’ , Sen-i To Kogyo, 1993, 49(3), 84-93. 8) G. Cuveir and B. Launary, Carbohydr. Polym, 1986, 6,321. 9) R. K. Richardson and S . B. Ross-Murphy, Intenlahod Journal of Biological

154


Macromolecules, 1987,9 , 257. 10) M M a s , M. Rmaudo, M Kmpper and J. L Shuppiser, ‘Flow and Viscoelastic Properties of Xanthan Gum Solutions’

,

Macromolecules, 1990,23, 2506-251 1.

11) P. A. Williams, S. M. Clegg, D. H. Day, K. Nishuran and G. 0. Phillips, In:

”

Food Polymers, Gels, and Colloids,” E. hckurson (eds.), RSC Publication. Cambridge,

1991,pp. 339-348. 12)P. A. Williams, D. H. Day, M J. Langdon, G. 0.Phillips and K. Nishinari, ‘Synergistic interaction of xanthan gum with glucornannans and galactomannans’ , Food Hydrocolloids, 199 1,4, 489-493. 13) P. A. William, P. Annable, G. 0. Phdlips and K. Nishinari, In: Food Hydrocolloids: Stmdure, Propetties cprd Functions, K. Nishinari and E. Doi (eds.), 1994,F’lenumF’resss, New York, pp.435-449.

14)S. C. De Srnedt, P. Bckeyser, V. Fhbitsch, A. Lauers, J. Demeester, Biorheology, 1993,30, 31. 15) T. Yanalu and T. Yamaguchi, ‘Temporary Network Formation of Hyaluronate Under a Physiological Condition 1. Molecular Weight Dependence’ , Biopolymers,

1990,30, 415-425. 16)J. E. Scott, C. CUmnnngs, A. Brass and Y . Chen, ‘Secondary and tertiary structures of hyaluronan in aqueous solution investigated by rotary shadowing-electron microscopy and computer simulation’ , Biochem J. , 1991,274,699-705.

17) J. Fujiwara, T. Iwanami, M. Takahash, R. Tanaka, T. Hatakeyama and H. Hatakeyama, ‘Structural Change of Xanthan Gum Association in Aqueous Solutions’ to be published in Thennochimica Acta.

18) F. X. Quinn, T. Hatakeyama, H. Yoshida, M. Takahashi andH. Hatakeyama, ‘The Conformational Properties of GeUan Gum Hydrogels’ , Polymer Gels and Networks,

1993,1 , 93-1 14. 19) H. Yoshda and M. Takahash, ‘Structural change of gellan hydrogel induced by annealing’ , Food Hydrocolloids, 1993,7,387-396. 20) T. Hatakeyama, K. Nakamura and H. Hatakeyama, ‘Determination of Bound Water Contents Adsorbed on Polymers by Dfferential Scanrung Calorimetry’ , Netsusokutei, 1979,6, 50-52. 21) K. Nakamura, T. Hatakeyama and H. Hatakeyama, ‘Studies on Bound Water of Cellulose by Differential Scanning Calorimetry’ , Text. Res. J _,1981,5 1, 607-613. 22) K. Nakarnura, T. Hatakeyama and H. Hatakeyama, ‘Relationship between Hydrogen Bonding and Sorbed Water in Styrene-Hydroxystyrene Copolymers’ , K o h b w h Ronbunshu, 1982,33,55-58, 23) K.Nakamura, T. Hatakeyama and H. Hatakeyama, ‘Effect of Water on Polymers’ Sen-i Gakkaishi, 1985,41, 369-378.

,

HYDROLYSED LIGNIN. STRUCTURE AND PERSPECTIVES OF TRANSFORMATION INTO LOW MOLECULAR PRODUCTS. M.Ja. Zarubinl, S.R. Alekseevl, S.M. Krutovl. 1

Department of Chemical Engineering, St. Petersburg Forestry Technical Academy 194021 St. Peterburg, Russia.

ABSTRACT Because of the large volume of wasty produced by the Russian wood hydrolysis industry the utilization of hydrolized lignin has emerged as a scientific problem. As of yet, this problem has not been solved due to the lack of detailed structural knowledge. Based on literature data and newly emerging experimental data, a hypothetical structure for hydrolysed lignin i s proposed which opens new opportunities for its practical use.

INTRODUCTION In Russia, wood hydrolysis is conducted by cooking wood in 0.5% HzS04 at I800 C. The hydrolysis process of hydrocarbons has been mastered sufficiently to consistently produce monomeric fragments which are quantitatively fermented to alcohol 111. During hydrolysis, the number of C-C bonds has been shown to increase. They are formed on account of the splitting of mainly a-n base groups, with carbocations forming benzyl type matemals and secondary condensation products [21. As a result the structure of hydrolysed lignin is more condensed in comparison with native lignin. The proposed reaction figure for the conversion of various lignin structure units, which contain a-n base linkages, is presented below (figure 1):

Figure 1. Proposed convertion figures for various lignin structural units containing a-n base groups.

156


OC H3

r-

OH [OR1

Figure 1. (continued).

H+

Hydrolysed lignin

H

F

T

H3C

HOH2C-HC-HC'

-

C

0

Figure I . (continued). The last two steps are dominent in strongly acidic environments and, hence, are not produced during wood hydrolysis conducted at 0.50/0H S 0 4 . It is well-known from literature data [3,4], and as it is seen in figure 1, etheral bonds in lignin are well preserved during acid hydrolysis: mainly p-ether, 4-0-5 biphenylic, a-0-y in the pynoresinol structures and also a-0-4 bonds in phenylcumaran structures. Splitting of the final reaction product does not result in lignin like fragments. Rather the most likely fate for hydrolysed lignin is to be split into low molecular weight products at the p - 0 4 bonds. The splitting mechanism of these bonds is well-known for model compounds in lignin chemistry 151. We believe that hydrolysed lignin P-ether bonds are split by alkali via the proposed figure 2:

157

T H

158


Figure 2. The P-ether bonds splitting in technical hydrolysed lignin. The P-ether bonds split in the presence of ZnClz are believed to proceed via the proposed mechanism shown in figure 3 161:

H [OR1

[OR1

[OR1

bH [OR1

Figure 3 The P-ether bonds splitting in the presence of ZnCh The proposed mechanism agrees with the results of experiments conducted on hydrolysed lignin fragments under basic conditions in alkaline solutions at high temperatures, and under acidic conditions in the presence of ZnCb in 00 C C H C O O H solutions.

EXPERIMENTAL Treatments of hydrolysed lignin samples (Klason lignin 72%) were conducted in 5% NaOH at 170 t o 180° C for 180 min. The yield of substances dissolved in alkali was more than 90%. Increases in the processing time did not result in increases in the yield of dissolved substances. Catalysts introduction in the form of soft-bases (HS- and anthraquinone) resulted in a reduced yield 161.

Hydrolysed lignin

159

The yield of dissolved substances for reactions conducted in the presence of ZnClz was found to be less than 10%. This can be explained by the steric hindrance experienced ZnClz in approaching the P-ether bond [6]. Further studies are planned to determine the influence of increasing concentrations of ZnClz and temperature treatments on the yield of soluble products (experiments will be conducted in autoclaves at increased boiling temperat ures of CH3COOH). The basis of calssification of alkali dissolved reaction products is shown in figure 4:

1 HYDROLYSED LIGNIN ethanol-benzene extract ion

(volatile fraction

-l UNDISSOLVED FRACTION

1

soluble fraction

II

soluble fraction

DISSOLVED FRACTION

I

HCl addition to p H 1

to p H 7 and evaporation separation to

C,H,OH (tainled with HCI) extraclion

r - i WATER-SOLUBLE FRACTION

Figure 4. The classification of alkali dissolved reaction products.

RESULTS AND DISCUSSION As shown in figure 4, alkali dissolved reaction products were separated into the following fractions: acetone soluble, acetone insoluble, and water soluble substances. The dominant fraction was found to be the acetone soluble fraction (36.4%). According to TLC data, this fraction consists of 6 major components. By comparison of the experimental Rf values with lignin model compound Rfvalues,

I

160


a similarity was found between the most polar acetone soluble compound and diisoeugenol. Six preparative chromatographical separation zones were selected. IR-spectra of separated zones indicate that these compounds were of a phenolic nature, and possessed carbonyl and alcoholic groups. This interpretation agrees with those of other researchers 171. The TLC data for the water soluble fraction (18.1%) showed that this fraction is comprised of 5 major components. Hence, 5 preparative chromatographical separation zones were selected. The most polar compound in the water soluble fraction was found to be similar to guaiacylpropanol in Rfvalue. IR- and UVspectra indicated an aromatic nature of the analyzed compounds, and the presence of hydroxyl groups. The extractive substances (15.5%) were separated to a steam-volatile fraction (0.9%), an ether soluble fraction (27.30/9), and an acetone soluble fraction (58.8Y0). As preliminary reseach showed, the steam-volatile fraction consists of monoterpenes, ether-soluble substances (resin acids and polymerisation products of terpenes), acetone-soluble substances (likely gumification products of hydrocarbons). The extractives fraction, according to the TLC data, consists of 5 major comounds, or zones. Analysis by IR- and UV- spectra indicated the total absence of the aromatic compounds. The more polar compounds were shown to contain carbonyl groups.

CONCLUSION The results of this research showed the possibility of the fragmentation of hydrolysed lignin. The splitting of hydrolysed lignin under these conditions was found to proceed to a great extent. In the future, the products of the splitting reaction will be resolved and analyzed t o determine their molecular structures.

REFERENCES 1. U I Cholkin, m e hydrolysis manufactures technology, Forest industry, Moscow, 1989.

2. M Ja Zarubin, M F Kirushina, V V Troitskiy, K A Savov, V N Oparin, M I Ermakova, The lignin acid-base nature role in spite of the wood chemical process, Wood Chemistry, 1983, (9,3-24. 3. J Gierer, Svensk. Papperstidor. 1970, (73), 57 1. 4. J Gierer, I Noren, Acra Chem. Scand., 1976, (1962), ( I 6), 171 3. 5. K V Sarkanen, K H Ludvig, Lignins: structure, properties, reactions, (Translated into Russian by A.V. Obolenskaya et al.), Wood Industry, Moscow, 1975. 6. A Nikandrov, R M Sevillano, G Mortha, D Robert, M Ya Zaroubin, Lachenal

D, Characterisation of residual lignins from oak kraft pulps isolated by acetic acid and ZnClz.’ Conference Proceedings: Advances in Lignocellulosics Chemistry for Ecologically Friendly Pulping and Bleaching Technologies. August 30 - September 2, 1998, University of Aveiro, Portugal, 165-169. 7. S R Alekseev, Research into the structure of technical hydrolysed lignin, Masters Thesis, St. Petersburg Forestry Technical Academy, St. Petersburg, Russia. 1998. 8. Y L Stephen, Methods in Lignin Chemistry, C.W. Dence (eds), 1992, SpringerVerlag, Berlin.

PRODUCTS OF LIGNIN MODIFICATION: PROMISING ADSORBENTS OF TOXIC SUBSTANCES Tatiana Dizhbite(*), Anna Kizima, Galina Rossinskaya, Vilhelmina Jurkjane & Galina Telysheva Latvian State Institute of Wood Chemistry, 27 Dzerbenes St., Riga, LV-1006, Latvia

ABSTRACT In the present work, the interactions of water insoluble lignins (haft lignin and hydrolysis lignin) with oppositely charged water-soluble surfactants, quaternary ammonium salts (QAS), were investigated with the aim of producing new materials with enhanced adsorption and antiseptic properties. It has been shown, that lignin provides a matrix for holding alkylammonium cations owing to strong coluombic, complexing and hydrophobic interactions. Bonds formed are stable in aqueous and aqueous-basic media in the presence of low-molecular electrolytes. Using ESR (spin-probe technique), X-ray analysis and water vapour sorption it has been found that the main impact of modifications under investigation is an increase in hydrophobicity of lignin and its mesoporosity. Adsorbents obtained are characterized with a high adsorption capacity towards phenols, namely twice as large as that of a standard commercial active carbon and close to the well known polymer adsorbent Amberlite XAD-4.

INTRODUCTION The use of polymeric adsorbents is a promising option for the removal and recovery of organic contaminants from polluted water. It is known that the relatively low solubility and the presence of significant amounts of different oxygen-containing groups in lignins, the matrix of which is characterized with a cross-linked structure are prerequisites for sorption activity by mechanisms such as physical adsorption, hydrogen bonding, co-ordination and covalent linking, and acidicbasic interactions. Hydrolysis lignins, the major by-product of the conversion of lignocellulosic biomass to ethanol, were proposed as sorbents of various organic dyes, phenol from the wastewater of phenol-formaldehyde resins production, cleaning and discolouring of wastewater and enterosorbents for medicine and veterinary Regarding the porous structure, hydrolysis lignins can be characterized as sorbents whose porous structure is not enough developed. According to mercury porometry data the hydrolysis lignins contain pores with radii from 3.3 up to 3.6*104 nm and the maximal share belongs to pores with radii of 500-5000 nm. The total volume of hydrolysis lignin pores defined by the benzene vapours sorption, was found to be 1.7 cm3/g, and specific surface 3.7 m21g. The specific surface of hydrolysis lignins, found using nitrogen sorption, was 5-8m2/g '. It has been demonstrated that, among different methods increasing sorption activity of lignins towards organic compounds/contaminants,modification by organic cations is an easy and effective technique '. Use of quaternary ammonium salts (QAS) for

-

162


modification enhances sorption activity of both insoluble lignins isolated from plant tissue and lignins in lignocellulose complexes. Besides, application of quaternary ammonium salts which exhibit the high bacteriostatichactericide effects there is also an opportunity to design sorbents with antimicrobial properties on the basis of biomass processing wastes. The main objective of the present work was an investigation of the regularities of heterophase interaction of lignins with quaternary ammonium salts differing by the structure of organic moieties, and assessment of the change in the lignin structure aimed at obtaining sorbents of high efficiency towards phenols which are wide spread contaminants. MATERIALS & METHODS Lignins Hydrolysis lignins: HL70 - commercially available lignin obtained by dilute sulhric acid hydrolysis, Klason lignin content 70%, carboxyl groups content 1.5%, phenolic hydroxyl groups content 5.0%; HL52 - lignin obtained in a pilot plant by the combination of diluted sulfbric acid hydrolysis and steam explosion procedure, Klason lignin content 52%, carboxyl groups content 0.4%, phenolic hydroxyl groups content 1.7%; HL98 - lignin obtained by concentrated hydrochloric acid hydrolysis in a pilot plant, Klason lignin content 98%, carboxyl groups content 4.3%, phenolic hydroxyl groups content 4.4%, Kraft lignin KL89 - commercially available lignin, Klason lignin content 78%, carboxyl groups content 3.2'0, phenolic hydroxyl groups content 4.6%. Quaternary ammonium salts (QAS) Hexadecyl trimethylammonium bromide (HDTMA-Br), trimethylbenzylammoniium bromide (TMBA-Br) and dimethylethylphenylarnmoniumbromide (DMEPhA-Br) were obtained from Sigma. Methods The modification procedure was carried out as described in 4, by stirring the lignin suspension in the QAS aqueous solution varying the duration, pH of the aqueous medium and temperature of interaction (6-120 h, pH 4-10 and 20-60°C). The degree of modification, a,expressed as the molar ratio of QAS cations introduced to the phenyl propane units of lignin was determined from the nitrogen content in the modified lignins. The nitrogen content in the samples was determined by the Kheldal method Klason lignin content was determined by the TAPPI method T 222 om-88. The sorption capacity of lignins and products obtained for phenol was examined under static conditions at 22-23OC from aqueous solutions of 10 g/Lconcentration. To characterize hydrophobic/hydrophilic properties of lignins and their derivatives, water vapour sorption isotherms were measured at 20-2 1"C. X-ray analysis and ESR spin probe measurements were used for monitoring changes in

Products of lignin modification

163

lignin microstructure as the result of modification. X-ray diagrams of lignin samples (pellets) were recorded within the range of 28 values fiom 6 to 50” using difiactometer DRON-2 (C& radiation, Ni-filter). An average distance, d, between planes of mesomorphous microregions was estimated as described in A spin probe, 2,2,6,6-tetramethylpiperidine-l-oxyl,was introduced into the lignin samples from gas phase ESR spectra were recorded at 20fl”C on an ES1006 X-band spectrometer using the following instrumental parameters: scan width, 125 G, time constant, 0.25 s, scan time, 4 min, modulation amplitude, 0.33 G, microwave power, 10 mW, modulation fiequence, 100 Hz. The rotational correlation time of the probe was estimated according the method

’.

‘,

’.

RESULTS & DISCUSSION Analytical data obtained have shown that electrostatic interaction and formation of heteropolar bonds involving carboxyl and phenolic (at pH>10) groups of lignin are the main type of interactions in the heterogeneous system lignin - aqueous QAS:

(Lignin)-COOH + R’R”.R”’3-. N H d 4 (Lignin)-COOR’R’’,,R”’3.. N’ + HHal (Lignin)- OH,h, + R’R”.R”’3.. NHal-+ (Lignin)-COR’R”.R’”3.. N’ + Hhal It has been established that at the reaction temperature 20”C, the amount of QAS coupled to lignin does not exceed 0.6 mole per 1 mole of phenyl propane units of lignin even if QAS is used in sufficient surplus. The pH change fiom 7.5 to 10, extension of the reaction duration to 120 h and temperature elevation within the interval 20-60°C does not influence the lignin modification degree (Fig. 1). The relationship between degree of modification and reaction time can be linearized in the coordinates of the Erofeev-Kolmogorov equation:

a=l-e

kt”

8

-__

0

I 0.1

0.3

0.5

0.7

0 .§

c , st.

Figure 1. Kinetic of interaction between hydrolysis lignin (HL98) and hexadecyltrimethylammonium bromide (HDTMA-Br). Reaction temperature: (1) 20°C, (2) 3OoC, (3) 40°C. pH=lO. EA=50.1 kJ*mole-’. Topolunetic parameters: (1) n=1.13, K=O. 12 h-’; (2) n=l. 10, K=O. 16 h’; (3) n=0.95, K=0.30 K’.

164


Topokinetic parameters of the process, n and k, were determined on the basis of the equation 111, while the rate constant K=nk”” and effective energy of activation were calculated using Sakovich and Arhenius equations, respectively In spite of their formal character, the results obtained (Fig. 1) revealed that the process is chemically controlledg. Based on the results obtained, the formation of a new insoluble lignin-quaternary ammonium salt can be described as a frontally extended ion exchange reaction. The organic cation transfer into the lignin matrix occurs via interchange between an already formed lignin-organic cation complex and free fragments of the lignin network, i.e. by “jumping” of the cation from one lignin segment to another localized further from the surface. The bonds between lignin and quaternary ammonium cations are rather stable to hydrolysis in water-alkaline medium containing 0.1 M NaCl (pH=lO): after a 12-h hydrolysis the content of quaternary ammonium cations in the products of reaction between TMBA-Br, DMEPhA-Br and HDTMA-Br was 93.5, 94 and 96% (in terms of the cation content in the products prior to the hydrolysis), respectively. The stability of lignin quaternary ammonium derivatives is determined not only by the electrostatic interaction but also by forming other types of bonds between the coreagents. The chemical structures of QAS under investigation are characterized by the presence of hydrophobic organic radicals, which enable QAS molecules to associate in aqueous solutions and immobilizing them in the Iignin matrix by hydrophobic interaction. Besides, formation of charge transfer complexes between lignin aromatic moieties and quaternary ammonium cations reveals itself in the 2 - 3 fold increase in the content of stable paramagnetic centres after lignin modification The stability to hydrolysis of lignin quaternary ammonium derivatives may result in a formation of a “barrier layer” (after establishing a certain polyaniodcation ratio in the reaction product), which hinders further penetration of new QAS molecules and formation of the product with an equimolar ratio of polyanion and cation units. Analysis of water vapour isotherms for initial and modified hydrolysis lignins (Fig. 2) gave evidence of increasing hydrophobicity of the lignin surface as a result of modification. Parameters of water adsorption by lignins decreased after modification: the specific water accessible surface by 8.5%, monolayer capacity by 19.7%, surface concentration of hydrophilic groups by 12.3% and BET equation energy constant by 37%, indicating that the energy of water interaction with sorption centres of the lignin surface diminished. The amount of inclusion water during desorption also decreased (the sharp narrowing of the hysteresis loop in the Fig. 2, b). X-ray analysis showed, that the lignin supramolecular structure changed significantly as a result of transport of voluminous QAS cations into the lignin matrix. The X-ray diagrams for both the initial lignins and their modified products showed one difisive reflex in the 28 20-21”. It has been shown ’,lo, that this reflex is attributed to the diffusion of the planes, formed by benzene rings. As a result of the modification, the average distance between the plains increased from 0.42 nm for lignin (HL98) up to 0.56 nm for HL98-HDTMA (a = 0.12) and sizes of the mesomorphous microregions decreased by 30%. Significant increase in the mesopore volume in the lignins after modification with QAS has been shown by the water sorption-desorption isotherms as well as ESR spin probe method. The average size of these mesopores has been estimated by the adsorption isotherms methods as - 100 - 150 A.

’.

Products of lignin modification

165

180

160 140

120 zll

100

E 6 80 60

40 20 0 0

02

OA

0.6

Od

1

0

0.2

0.6

0.8

1

PtPD

PfpD

Figure 2.

0.4

(a) (b) Adsorption-desorption isotherms of water on (a) lignin, HL98 and (b) modified lignin HL98 - HDTMA (a=O. 12).

The analysis of the ESR spectra of the modified lignln products containing the spin probe showed, that these spectra corresponded to the spin probe with relatively free movement within the microcavities. Taking into account the size of the spin probe, the average diameter of these microcavities could be estimated as 2 100 A. The sorption activity of lignins modified with QAS towards phenol, increases significantly (Fig. 3) as the result of lignin matrix hydrophobization and the changes in the lignin supramolecular structure. Efficiency of the long chain quaternary ammonium cation (HDTMA) is higher than shorter chain cations (TMBA and DMEPhA). Evidently, the more pronounced hydrophobic character of the surface of lignin-HDTMA favours adsorption of phenol from water.

KL89

HL52

HL70

HL98

Arnbdlte

BAC

m-4

Figure3. Evolution of phenol uptake onto lignins, as a result of modification - 0.20) with hexadecyltrimethylammoniumbromide (HDTMA-Br); comparison with commercial sorbents (Amberlite XAD-4 and BAC). (a=O. 18

166


In order to exceed the phenol sorption activity which has commercial birch active carbon (BAC) and obtain indices of Amberlite XAD-4, the well known high-efficiency towards phenol polymers, only a low degree of modification (a=O.14-0.17) of hydrolysis lignin with 78-98% content of Klason lignin is necessary.

CONCLUSIONS The proposed concept of modification of insoluble IigNns via heterophase interaction with cation surfactants, quaternary ammonium salts, gives the possibility of the design (synthesis) of high efficient sorbents for application in aqueous media. The modification, which is carried out under mild conditions and at low demand of a modifier, provides an increase of sorption efficiency owing to hydrophobization and development of mesoporosity as a result of quaternary ammonium cations diffusion into the lignin/lignocellulose matrix.

REFERENCES 1. M. Wayman & S. R. Parekh, Biotechnologv of Biomass Conversion, Open University Press, Milton Keyness, 1990. 2. N. A. Belyakov (ed.), Enterosorption, Center of the Sorption Technologies, Leningrad, 1991 (in Russian). 3 . V. P. Levanova, Medicine Lignin, Center of the Sorption Technologies, St.Petersburg, 1992 (in Russian). 4. T. Dizhbite, G. Zakis, A. Kizima, E. Lazareva, G. Rossinskaya, V. Jurkjane, G. Telysheva & U. Viesturs, ‘Lignin - a useful bioresource for the production of sorption-active materials’, Biores technol, 1999, 67, ( 3 ) , 22 1-28. 5. M. Ya. Ioelovich, G. M. Lebedeva, G. P. Veveris & G. M. Telysheva, ‘Study of the

supramolecular structure of organic-silicon lignin derivatives’, Khimiya drevesiny w o o d Chemistry), 1991, (I), 100-4. 6. T. Dizhbite-Scnpchenko, G. Domburg, J. Lebedev & V. Sergeeva, ‘A possibility of the spin probe method application for investigation of lignin microstructure’, Khimiya drevesiny (Wood Chemistry), 1975, (4), 75-9. 7. A. N. Kuznetsov, A. M Wasserman, A. U. Volkov, N. N. Korst, ‘Determination of rotational correlation time of nitric oyde radicals in a viscous medium’, Chem. Phys. Lett., ’, 1971, 12, (l), 103-6. 8. E N Eremin, Fundamentals of Chemical Kinetics, Vysshaya Shkola, Moscow, 1976 (in Russian). 9. G M Panchenkov and V P Lebedev, Chemical Kinetics and Catalysis, Khyrniya, Moscow, 1985 (in Russian). 10. J. Haggin, ‘Lignin in native wood tissue has ordered structure’, Chem. And Engng News, 1985, 63, (18), 33-4.

CHARACTERISATION AND ADSORPTION OF LIGNOSULPHONATES AND THEIR HYDROPHOBIZED DERIVATIVES ON CELLULOSE FIBRE AND INORGANIC FILLERS Galina Telysheva'(*), Tatiana Dizhbite', Anna Kizirna', Alexander Volpertsl & Elena Lazareva' 'Latvian State Institute of Wood Chemishy, 27 Drerbenes St., Riga, L V-1006, LATVIA 2Depar!menrof Chemism, Moscow State Universiv, Vorob 'evy goiy, Moscow, Russia

ABSTRACT The adsorption of lignosulphonates (LS) at the water-solid interface is characterized by a high value of the free energy of adsorption. The LS adsorption behaviour can be controlled by varying the LS macroion negative charge density, either changing the solution pH or increasing LS hydrophobicity, e.g. modifying with aluminum containing silicon-organic oligomers. At low concentrations,LS adsorb in a flat conformation owing to electrostatic (in the case of an oppositely charged surface) or chemisorption (in the case of identically charged surfaces) interactions. With an increase in the level of surface coverage LS macromolecules form a mobile pseudo-liquid microphase at the water-solid phase boundary. In the case of LS modified with silicon-organic oligomers, the microviscosity of the adsorption layer tends to increase. The adsorption behavior of LS and their hydrophobized derivatives at the water-solid interface corresponds to that predicted for polyelectrolyte adsorption by the self-consistent field model.

INTRODUCTION Lignosulphonates (LS), formed as a by-product of the process of cellulose manufacture, are widely used as technical surfactants with dispersing, stabilizing and adhesive abilities'32.In recent years the role of LS as auxiliary substances for papermaking and paper coating is increasing. A few types of LS based products, mainly LS purified and fractionated by ultrafiltration, now are proposed to improve coating properties and to retain fine cellulose material and fillers in the pape?&. In these cases LS adsorption on the solid components of paper composition is an important factor of their activity. Besides, LS can affect the adsorption of various auxiliary substances, e.g. rosins or starch, on fiber and filler particles during papermaking thus influencing paper strength. The majority of work concerning lignin ad~orption''~~ describe LS behavior as corresponding to the Langmuir model. Alongside that, the polylayer nature of LS adsorption on kaolin surfaces and the description of the process according to a network polylayer adsorption model have been proposed'. The present work develops our previous investigations aimed at generation of the background for purposeful alteration of the LS efficiency as auxiliary substances at different stages of papermaking'9'0. It is focused on the main features of LS adsorption onto solid components of paper composition and their relationship with characteristics of adsorption centers on solid surfaces under study.

168


MATERIALS & METHODS A commercial sodium lignosulphonate LS purified by ultrafiltration and containing less than 1% of carbohydrates as well as the products of their modification with sodium alumoethylsiloxanolate or sodium diethylalumoethylsiloxanolate(MLS) were used in the work as adsorbates. Bleached sulphate cellulose from coniferous wood (a-cellulose content 98%), kaolin, titanium dioxide (rutile) and calcium carbonate were applied as adsorbents. LS adsorption isotherms from aqueous solutions were obtained at 20fl°C and thermodynamic characteristics of adsorption as well as changes in thermodynamic functions along with increase in the level of sorbent surface coverage were calculated using the Aranovitch model of polylayer adsorption". The sorption of different organic compounds from aqueous solutions on solid surfaces under study was determined by measuring their equilibrium concentrations under conditions where the interaction between sorbate molecules could be disregarded (coverage 8>titaniumdioxide2kaolin>>calcium carbonate.

TOTAL S C A N WIDTH.

125 G

\t

Figure 2. ESR spectra of 4-benzoyloxi -2,2,6,6-tetramethylpiperidine-1-oxyl coadsorbed with LS on cellulose surfaces at coverage 0 = 0.2 (a) and 0 = 0.9 (b).

Characterisationand adsorption of lignosulphonates

171

Higher enthalpy values for LSMLS adsorption on the kaolin and cellulose compared to CaC03 (weaker surface negative charge) indicates specific interaction of LS with adsorptive centers on the formers. High values of the nonionic energy of the LS segment adsorption interaction with kaolin and cellulose (4.8 kT and 7.4 kT, respectively) calculated on the basis of the experimental data give evidence of possible Coulomb repulsion forces compensation. Thermodynamic characteristicsof LS and R4LS adsorption on splids. Table 2. Adsorbate

LS

MLS

Adsorbent Cellulose Kaolin Ti02 CaCO3 Cellulose Kaolin Ti02 CaCOj

-AG~~, kJ/moll 9.5 5,6 6-8 296 10,7 798 470 3,7

-m0I,

kJ/moll 21,9 14,3 16,3 10,5

28,2 19,6 123 14,4

42, kJ/moll 48,l 32,9 33,2 n.d. 51,2 34,3 25,4 n.d.

' -AGO,-AHo ((pure))values of the free Gibbs energy and adsorption enthalpy, correspondingly

'Aq,-

energy of bonding between adsorbate and adsorbent surface

The adsorption centres of the surfaces under investigation were characterized via the relationship of maximum adsorption of organic compounds vs. their ionization potentials, a=f (I,,). The results obtained suggest a specific: interaction of sulphonate and carboxyl LS groups (ionization potential 9.5 eV) with adsorption centers of kaolin and cellulose, which have a resonance potential of 9.5 eV. High content of aluminum in kaolin permits formation of surface metal-LS sr-complexes. The possibility of such an interaction is due to the resonance potential at 10.1 eV for kaolin and values close to it of the first and the second ionization potentials of the aromatic compounds relative to lignin. In the case of cellulose, the maxima on the curve of the relationship a=f (I,,) at 7.8 and 8.1 eV, which were not observed on the correlation dependencies for the nonorganic surfaces, correspond to potentials of x-ionization of some lignin model compounds, namely aromatic acids, alcohols and ketones. A significant increase in the adsorption plateau and heat and free energy of adsorption interaction as the result of LS modification by the silicon-organic oligomers indicates the possibility of regulation the adsorption behavior and structure of the adsorption layer of LS. The presence of the polyvalent metal in the silicon-organic block permits the adsorbate molecules approaching closer to the negatively charged adsorbent surface than in the case of LS. CONCLUSIONS The adsorption of the LS at the water-solid interface is characterized by high values of the non-electrical portion of the free energy of adsorption, which provide effective adsorption on the surfaces charged similarly to LS. Balance of the LS adsorption forces can be regulated by the change of the density of the negative macroion charge, variation of solution pH, or by modification, for example, by silicon containing organic oligomers. At the low concentrations in the solution, LS adsorbs in a flat conformation due to electrostatic (oppositely charged surfaces) or chemisorption (similarly charged surfaces) interactions. With an increase in the degree of coverage LS macromolecules adsorb

172


forming a mobile pseudo-liquid micro-phase. Modification of the LS by the siliconorganic oligomers increases microviscosity of this layer. Depending on the specific characteristics of the adsorbent surface, lignin adsorption occurs via ion exchange or chemisorption due to hydrogen bonding and formation of donor-acceptor complexes with participation of Ic-orbitals of the aromatic lignin structures.

REFERENCES I . G. M. Telysheva & N. I. Afanas’ev, ‘Surface-active properties of lignosulphonates aqueous solutions’, Khim. Drev., 1990 (l), 3-1 1 . 2. V. Hornof, ‘Lignosulphonates application for enhanced oil recovery”, Cell Chem Technol, 1990.24 (3), 407-15. 3. P. Sennert, Use of high molecular weight sulfonate as auxiliary dispersants for structured kaolins, US Patent, No. 4 859 246, August 1989. 4. G. Telysheva, T. Dizhbite, J. Hrol, M. Akim & E. Kurkova, ‘Application of modified lignosulphonates in paper production’, In: Int. con$ PaprFor ’93, VNIIB, St.Petersburg, 1992, 103-4. 5. F. A. Adamsky & B. J. Williams, ’Effect of new drainage, retention, and formation technology for improving production rates and runnabihty of recycled fiber cylinder machines’, Tappi J , 1996, 79 (8), 175-82. 6. G. Telysheva. T. Dizhbite & M. Akim, ‘Lignin based auxiliary substances for paper and board production’, In: Proc. 4Ih Europ. Workshop Advances in characterization andprocessing of wood, non-woody and secondaryfibers, Streza, 1996,5 18-23. 7. J. C. Le Bell, B. Bergroth, P. Stenius & B. Stenlund, ‘The adsorption of sodium lignosulphonates on kaolin’, Paperi j a Puu, 1974,56 ( 5 ) , 463-71. 8. P. Dilling & H. Eicke, “Adsorption of lignosulphonates to disperse dye substrates’, Colourage, 1990, (3), 37-47. 9. N. I. Afanas’ev, G. M. Telysheva. N. A. Makarevich & Yu. S. Hrol, ‘Adsorption of the fractionated lignosulphonates on kaolin’, Khim Drev, 1990, (2), 85-92. 10. G. Telysheva. T. Dizhbite, E. Paegle & A. Kizima, ‘The regularities of lignosulphonates behaviour on different interfaces and its alteration by purposehl modification’, In: The Chemistry and Processing of Wood and Plant Fibrous Materials, J. Kennedy, G. 0. Phillips & P. A. Williams (eds.), Woodhead, 1996, 3394. 1 1 . G. L. Aranovich, ‘The determination of adsorption heat from adsorption isotherm at infinitively little coverage’, Zhurn Fiz Khim, 1990,64 (I), 161-65. 12. Yu. Tarasevich, E. Nechaev, V. Rudenko, Z. Ivanova & B. Kats, ‘Preparation and properties of carbon-mineral sorbents’, Kolloidn Zhurn, 1995,57 (2), 240-46. 13. J. Yao & G. Strauss, ‘Adsorption of quaternary ammonium surfactants on poly(tetdluoroethy1ene) surfaces‘, Langmuir, 1991,7 (lo), 2353-57. 14. C. G. Pin, J. W a g , S. S. Shab, R. Sik & C. F. Chignell, ‘ESR spectroscopy as a probe of the morphology of hydrogels and polymer-polymer blends’, Macromolecules, 1993,26 (9), 2 159-64. 15. G. J. Fleer & J. M. H. M. Scheutjens, ‘Modeling polymer adsorption, steric stabilization and flocculation’, In: Coagulation and Flocculation, B. Bogus (ed.), Schpringer, Basel, 1994, 105-83. 16. P. Luner & U. Kempf, ‘Properties of lignin monolayers at the air-water interface’, Tappi J, 1970, 53 (1 l), 2069-76.

Part 4

Biodegradable polyu rethane-based polymers

BIODEGRADABLE AND HIGHLY RESILIENT POLYURETHANE FOAMS FROM BARK AND STARCH J-J Gel, W Zhong’, Z-R Guol, W-J I,il and K Sakai2* Laboratory of Molecular Engineering of Polymers, Department of Macrmlecuiar Science, Fudan UniversiQ Shanghai 200433. P. R . chi^ Department of Forest Products, Faculty of Agriculture. Kyushu University, Fukwka 812-8581,Jqxm

ABSTRACT Liquefaction of the Acacia meamsii bark (BK) and cornstarch (CS) has been conducted by using a solvent mixture consisting of polypropylene glycol (PPG), glycerol and sulfuric acid with a weight fmction of (9445/1) at 150 C. Solubilities of BK and CS were about 80% for 60 min and 1 W o for 20 min in the same solvent, respectively. Highly elastic or highly resilient polyurethane foams (PLIFs) for car-seat cushions have been prepared from the liquefied BK and CS without removing insoluble residue from the liquefaction mixture. About 20% insoluble residue from BK contributed remarkably to the improvement of flame resistance of the resulting PUFs. PUFs having better resilience properties were prepared using PPG of molecular weight around 4OO0, as compand with polyethylene glycol having the same hydroxyl value. PUFs were synthesized from three BKs with different tannin contents to evaluate the effect of tannin content on their performances of resilience. Both the resilience value and density of the PUFs increased with increasing BK content for all BK systems. A BK with the largest tannin content, 48.5%, provided PUFs possessing tbe best resilient property. Density and flame resistance are the important properties for commercialization, f m cost and burning safety points of view, respectively. When CS replaced partly BK, the density and compressive strength of the PUFs decreased with increasing CS proportion whereas resilience value had its maximum value when the weight ratio of CS:BK was 1:l. The PUFs were to some extent biodegradable, the average weight loss of samples buried in soil for 6 months was 15.6 wt %. Keyword: bark, starch, polyurethanefoams, biodegradability.

INTRODUCTION Polyurethane foams (PUFs) are used widely in many fields as structural, cushion, insulation, electrical, flotation and packaging materials. Much attention is paid on introducing plant sources into PUFs production. The materials prepared from biomass not only open a new and efficient way to use renewable natural sources, but also possess a great potential for bio- and photodegradability. The latter advantage is more striking in the urgent need of environmental protection.” Natural polymers containing more than one hydroxyl group in the main chain are expected to be utilird as polyols for polyurethane preparation*;(’. We have prepared PUFs with moderate strengths and biodegradab~ties from wattle tannin (WT) or the Acacia meanrrii bark (BK) and diisocyanate in the presence of synthesized polyester.CXI

176

Biodegradable polyurethane-based polymers

It was proved that WT which is the main component of BK m t e d with diisocyanate as crosslinking agent in polyurethane molecules through careful studies on model

reactionM'and that the W component improves the compressive properties of the PUFs."" However, the density of tannin PUF was higher than those of the commercially produced PUFs; this may lead to higher production cost. Recently, Nakashima et aL9) prepared low-density rigid PUFs from polyol mixtures of barks of Acacia mearmii or Crypfomeriujaponicu with polyethylene glycol (PEG) 400. Yao et al.'" repoited the method to prepare PUFs from combined liquefaction of wood and starch in a PEG 400/glycerol blended solvent using sulfuric acid as catalyst. But those methods are not suitable to prepare flexible PUFs because polyol with larger molecular weight is indispensable in preparation of the flexible PUFs. Flexible PUFs for car cushion use has attracted more and more attention recently. For this purpose PUFs need a high crosslinking density to afford a high resilient property. Component with benzene rings and flexible configurations such as diethanolamine are usually introduced into PUFs formulations as crosslinking agents to improve the compressive strength and resilience."' In this study, a new kind of effective, environmentally safe and low-cost crosslinking agent BK was introduced in the preparation of high resilient flexible PUFs. The liquefaction of BK in a solvent mixture consisting of larger molecular weight polyether polyols and glycerol with sulfuric acid as catalyst has been investigated. We also report the preparation of high resilient flexible PUFs from the obtained liquefaction mixture. The properties needed for cushion material are discussed.

EXPERIMENT Materials and chemicals BK (Acacia meamsii De Wild 80 mesh pass) and cornstarch (CS) were dried in an oven at 105@ for 24 h before use. Polypropylene glycol (PPG) (GEP-330N, Hydroxyl group value 33.5-36.5 mgKOWg, Viscosity: ~ 1 o o cP/25@) O was kindly supplied by No.3 Chemical Plant of Shanghai Gao Qiao petrochemid Co. Other chemicals used were reagent grade and obtained from commercial sources.

Liquefaction solvent and procedure Liquefaction was conducted by the acid catalyst method given by Yao et al.,"' using a liquefaction mixture consisting of PPG, glycerd and sulfuric acid with a weight fraction of (94/S/1). The solvent and the catalyst were premixed thoroughly in a three-necked flask equipped with a mechanical stirrer and a nitrogen inlet. Then the BK powder in the flask was heated to 150T within 30 minutes. The liquefaction mixture was maintained at this temperature with stimng and refluxing under a nitrogen atmosphere for 30 min and followed by adding a predetermined amount of the CS as the second biomass component at this temperature for another 20 minutes if needed. After that, the flask was cooled down to mom temperature, the excess sulfuric acid was neutdized with an equivalent amount of sodium hydroxide aqueous solution (48 wt 96). The hydroxyl value of a liquefaction mixture was determined by the method described by Yao et al.'')

Determination of the liquefaction extent of the biomass The liquefaction extent of the biomass was determined after a prescribed liquefaction

Biodegradable polyurethane foams

177

time by the diome/water binary diluent method described by Yao et d.') That is, the liquefied mixture was diluted by an adequate amount of dioxandwater (8/2), stirred with a magnetic stirrer for more than 4 h, and then vacuum filtrated through a Q/XHJ3017 filter paper. The residue was rinsed by the diluent repeatedly until a colorless filtrate was obtained, and then the residue was dried to a constant weight. The residue content of biomass was calculated by the following equation. Residue content = (weight of residudweight of total biomass) x 1 W o Preparation and characterization of PUFs

A standard formulation for PUF syntheses was as follows, unless otherwise noted Isocyanate index 1IWO;diethanolamine 0.5%; dibutyltin dilaurate 0.32%; water 0.4%; triethylenediamine 0.03%; silicone oil (Y10366) 2.0%. The definte amounts of biomass polyol, catalyst, surfactant, water, and other additives, if any, were premixed thoroughly in a paper cup with a mechanical stirrer. To this mixture, a calculated amount of tolylene diisocyanate (TDI) was added and stirred at 2400 rpm for 10-15 seconds. The mixture was then poured immediately into a 12~12x10 cm mould and was allowed to rise at room conditions. The resulting foam was removed from the mould after one hour and was allowed to cure at room temperature for one week before cutting into test specimens. The ball rebound resilience value, flammability and compressive strength of the PUFs were measured according to ASTM D 357481,GB 8410-94 and the method described in a previous report," respectively. The isocyanate index are defined as follows: Isocyanate index = [MTDI x Wmd (Mmx WID+ 2118 x WW)]x 100 Where MTDIis the isocyanate group contents in TDI (moUg), Wm is the weight of TDI (g), Mu, is the hydroxyl group contents in liquefied biomass (moVg), WIDis the weight of liquefied biomass (g), and W w is the weight of water in the foam formulation (8).

RESULT AND DISCUSSION Effect of liquefaction solvent composition

PUF prepared from polyether such as PPG or polyethylene glycol has comparatively low density and high resilience because of the low viscosity of polyether prepolymer and the low rotation hindrance of ether bonds in the main chain. However, the high chain flexibility also leads to low compressive strength. Usually there ~IEtwo ways to improve the compressive strength; first, introduction of aromatic groups to the main chain to improve the chain rigidity, and second, increasing the amount of crosslinking agent such as diethanolamine and trimethylol propane to increase the crosslinking density of the polymer chain."' In previous work, we reported that tannin and tannin-containing BK became effective crosslinking agents in preparing PUFs6". In this paper, it is expected that BK can impmve the strength and resilience of PUFs because tannin has not only phenyl groups for the improvement of chain rigidity and ether bonds for the change in the chain configuration but also enough active hydroxyl groups to form crosslinks as shown in Fig.1. BK should be liquefied in larger-molecular-weight poXyols so as to produce flexible PUFs. Two kinds of polyether polyol, PEG and PPG having the same hydroxyl value, 35 mgKOWg, were used for preparation of PUFs from BK. The PUFs from PPG gave higher resilience values than those from PEG at given BK contents (data not

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Figure 1 Structure of condensed tannins.

Figure 2 Effect of molecular weight of PPG on the solubility of BK and on the resilience values of PLJFs.

shown). On the other hand, solubilities of BK were about 85%, 80% and W o in PPG with molecular weight 3000,4000 and 5oO0,respectively. However, the resilience values of PUF showed a maximum value at molecular weight of 4OOO as shown in Fig. 2. Thus, poly-ether PPG GEP-330N with Mn 4OOO and viscosity 800 CPwas selected to prepare highly resilient PUFs in the further work.

Effect of tannin content in bark on resilience value and density of PUFs in order to evaluate the effect of tannin content on the resilience of PUFs, we synthesized PUFs from three BKs with different tannin contents, that is BKO (tannin: 0%, residue after tannin extraction), BK1 (tannin: 43.0%),and BWtannin: 48.5%);the results are shown in Fig. 3. Both the resilience values and densities of the PUFs increased with increasing BK contents for all BK used. The densities of PUFs from BK2 were slightly larger than those of BK1 and BKO at given BK contents. However, the former had larger resilience values than those from BK2 and BKO. Since both resilience value and density are important properties of PUFs, the resilience valuddensity (RID) ratio was calculated. The larger the RID ratio, the better the PUF properties for car-cushion use. RID of PUFs from BK2 possessed the best values at given BK content (data not shown). This can be ascribed to the presence of the aromatic structure in tannin. BK2 was chosen for all the synthesis described hereinafter.

Effect of cornstarch content in biomass on resilience of PUFs. Cornstarch can easy be dissolved in a PEG 4Wglycerol mixture’), and there are a lot of glycoside bonds in its main chain that may contribute to the resilience of PUF, so we tried to use CS as the second biomass component. It can be totally dissolved in the liquefaction mixture within 20 rnin. at 1 5 0 C From Figs. 4 and 5, it can be seen that when CS replaced a part of BK, densities and compressive strengths of the PUFs decreased with increasing CS proportion whereas resilience value showed a maximum at CS/(CS+BK) 50%, that is 1: 1 of CS:BK .

Effect of insoluble bark residue on flammability of PUFs Flame resistance is an important property from safety points of view. We find that

Biodegradable polyurethane foams

179

62 60-

L

2 c O

P

A . 56' 54-

C

52-

O"

50-

.

20 io

30 i

i40o ia do 50 00 70 CS/(CS+BK) (WT%)

80 do

Figure 4 Effect of CS contents in total biomass on resilience values and densities of PUFs. J 80-

6040 -

Figure 3 Effect of BK contents on resiiience values and densities of PUFs.

20 -

0CS/(CS+BK) (wt96)

Figure 5 Effect of CS contents in total biomass on compressive strengths of PUFs.

8070 -

*\

-+PUFS with BK

8050-

40-

30-

0 4 8 12 16 20 Insoluble Reaidw in Lquefklion M i u m (M%)

Figure 6 Effect of the amount of insoluble bark residue in liquefaction mixture on the flammability of PUFs. flammability of the PUFs derived from BK is remarkably better than PUF without BK. More interestingIy, the insoluble BK residue plays an important role on flame resistance properties of BK-derived PUFs. The insoluble residue removed from a liquefaction mixture of BK was partly added back to the liquefaction mixture containing no insoluble residue, then PUFs were prepared from the mixture. The flammability was plotted against insoluble residue contents in the liquefaction mixture as shown in Fig.6. It can be seen that the flammability of PUFs decreased with increasing the insoluble residue in PUF. This improvement of flame resistance may be caused by the inorganic components in BK, though more detailed study is necessary for clarifying its mechanism.

I80


Biodegradability Three categories of PUFs, the first one derived from 30% BK, the second one from 15%BK and 15%CS, and the third one commercially purchased, were buried in soil. Their weight loss was observed every month. Weight losses of two PUF samples derived from biomass increased with increasing periods of soil-microbial treatments (data not shown). The PUFs containing BK and CS showed a slightly faster weight loss behavior than those only containing BK. These results indicate that the CS component in PUFs is easier to be decomposed by soil microorganisms than the BK component. On the other hand, almost no change was observed in the weight of commercially obtained PUF. The above-mentioned results indicate that the biomass components contribute mainly to the biodegradability of the PUFs. 4. CONCLUSION

Highly elastic or highly resilient polyurethane foams (PUFs) suitable for car-seat cushions can be prepared from the liquefied BK and CS. Insoluble residue from BK liquefaction contributed remarkably to the improvement of flame resistance of the resulting PUFs. When CS replaced part of BK, the density and compressive strength of the PUF decreased with increasing CS proportion whereas resilient ratio had its maximum value when the weight ratio of CS:BK was 1:1. The PUFs were to some extent biodegradable, the average weight loss of samples buried in soil for 6 months was 15.6 wt %. Acknowiedgment

This work was aided by N o 3 Chemical Plant of Shanghai Gao Q a o petrochemical Co and Shanghai Yan Feng automotive trim Co., Ltd. in material supplying and testing of mechanical properties of PUFs, respectively. We are indebted to the financial aid from the Scientifc Research Fund of the Shanghai Educational CommiW and Shanghai Environment Protecting Ministry. The authors thank Mr. R. M. Gu for the synthesis of polyether polyol. REFERENCES 1 Y Yao, M Yoshioka and N Shiraishi, Mokuzai Gakkaishi, 19!B 39, 930-938. 2 S Hirose, T Tokashiki, H Hatakeyama, 39&Lignin Symposium, Fukuoka, 1994 p.59-62. 3 K Nakamura, R Morch, A Reinmann, K Kringstad, H Hatakeyama, Wood Processing and Utilization, J F Kennedy, Ed, Ellis Horwood, 1989 p. 175-180. 4 R L Cunningham, M E Cam, E B Bagley, JAppl Polym Sci, 1992 44, 1447- 1483. 5 N Shiraishi, Cellulose Utilization;Research and Rewards in Cellulosics, H Inagaki, and G 0 Philips,.Ed, Elsevier Appl Sci, 1989 p.97-109. 6 J-J Ge and K Sakai, Mokuzui Gukkuishi, 1993 39,801-806. 7 J-J Ge and K Sakai, Mokuzai Gakkaishi, 1996 4 2 , 8 7 9 4 . 8 J-J Ge and K Sakai, Mokuzai Gukkuishi, 19% 42,417-426. 9 Y Nakashima, J-J Ge and K Sakai, Mokuzui Gdkuishi, 1996 42, 1105-1112. 10 Y Yao, M Yoshioka, N Shiraishi, Mokuzui Gukkuishi, 1995 41, 659-668. 11 Y S Fang, R M Zu: "Polyurethanefoam (in Chinese)",J Q Cai Ed. Beijing,1996 p .74-77.

BIODEGRADABLE POLYURETHANES DERIVED FROM WASTE IN THE PRODUCTION OF BEAN CURD AND BEER Kunio Nakamural, Mika Iijimal, Emiko Kinoshital arid Hyoe Hatakeyamaz

’ Otsuma Women‘s Universi@, 12, Sanban-cho, Chiyoah-ku, Tokyo 102-8357, Japan Fukui University of Techrwlogy, 3-6-1, Gakuen, I W u i 910-0028, Japan

SYNOPSIS From the viewpoint of the recycling of bio-based resources and development of environmentally friendly polymers, polyurethanes (PU’s) were prepared from polyethylene glycol (PEG) containing fine powder of bean curd refuse (BCR) or beer grains (BG) (waste derived from beer production) , and diphenylmethane diisocyanate (MDI). Mechanical and thermal properties of the PU’s were measured and biodegradability of the PU’s was also examined. Stress at break and Young’s modulus of the PU’s increased with increasing waste contents of BCR and BG in PU’s. The maximum stress at break was observed at about 0.5 (gig) of BCRPolyol and BGPolyol ratios. Glass transition temperature (TJ increased with increasing BCRPolyol and BGPolyol ratios. It is found from these results that the fine powder of BCR and BG acts as a hard segment in PU’s and that BCR and BG fine powder contributed effectively to an improvement in the mechanical and thermal properties of PU’s. The weight loss percentage of PU samples after biodegradation tests in soil increased with testing time and depended on the waste materials. SEM observation suggested that PU’s were degraded by microorganisms in soil.

1. INTRODUCTION World production of plastics is about 140 million tons a year and about 65% will be waste [l].These waste plastics are ordinarily burned or buried. It is considered that waste plastics cause global environmental problems, such as global warming, and acid rain caused by sulfur dioxide (SO,) and nitrogen oxides (NO,). Recently, there have been many reports concerning endocrine-disrupting chemicals [21 such as dioxin, nonylphenol and bisphenol A which affect human beings and the ecological system. Polyurethanes (PU’s) are one of the most useful multi-purpose polymers, since they can be used in various forms such as sheets, foams, paints etc. From the ecological viewpoint, PU’s containing natural polymers are beneficial, since natural polymers are generally recognized as biodegradable polymers. We have developed biodegradable polyurethanes (PU’s) derived from various natural polymer wastes, such as lignins [3-61, brewer’s grains [7], coffee grounds [8,9], edible fat and oil [lo] and other waste materials Ill-141. It has been reported that the mechanical and thermal properties of PU’s derived from waste materials increased with the introduction of plant components, which have pyranose rings and phenyl groups. From the viewpoint of the recycling of bio-based resources and development of environmentally friendly polymers, polyurethanes (PU’s) were prepared from polyethylene glycol (PEG) containing fine powder derived from bean curd refuse (BCR) or beer grains (BG), and diphenylmethane diisocyanate (MDI). Mechanical and thermal properties of the PU’s were measured and biodegradability of the PU’s was also examined.

I82


2. EXPERIMENTAL

2.1 Chemical reaction of PU’s Table 1 shows the production and components of bean curd refuse and beer grains. The production of bean curd (TOFU) and beer is 70 thousand tons / year and 7 million kl / year in Japan and the amounts of bean curd refuse and beer grains produced by the industry are 80 thousand and 20 thousand tons/year, respectively. Bean curd refuse and

Table 1. Production and components of bean curd refuse and beer grains.

Resources

Production Waste (looot) (1Ooot)

Protein Lipid Saccharide Ash (%)

(a)

(%I

(%)

Bean-curd refuse

700

800

25.4

19

51.4

4.2

Beer grains

7000

200

27.1

9.8

58.7

4.4

beer grains have not been used since no methods were found for effective utilization. The main chemical components of dry bean curd refuse and beer grains are polysaccharide 50-60%, protein 26%, lipid 10-20%, and ash 4 % as shown in Table 1. Figure 1 shows the reaction scheme of PU consisting of PEG-MDI system. PU’s have been synthesized using various types of polyols and isocyanates. In the reaction to form the urethane linkage between isocyanate and waste materials, the hydroxyl groups in wastes act as reaction sites. The MDVpolyol ratio and BCR and BG contents (BCR/polyol and BG/polyol) were defined as the following equations. MDVpolyol = mass of MDI / mass of polyol BCWpolyol = mass of BCR / mass of polyol BG/polyol = mass of BG / mass of polyol

Figure 1.

(1) (2) (3)

Reaction scheme of PU derived from PEG and MDI.

Biodegradable polyurethanes from waste

183

2.2 Samples Bean curd refuse and beer grains were obtained from Sugimoto Tofuten, Tokyo and Asahi Beer Co. Ltd., respectively. Polyethylene glycol (PEG) with molecular weight of 400 and crude diphenylmethane diisocyanate (MDI) were obtained from Mitsui Toatsu Chemical Co. Ltd. Figure 2 shows the preparation scheme of PUS containing waste materials. In order to prepare PU films containing waste materials, a certain amount of waste materials which passed through 200 mesh filter of diameter = 75 pm was mixed well with PEG (Mw = 400). The polyol mixture was mixed with a trace amount of catalyst (di-nbutyltin dilaurate) and MDI in tetrahydrofuran (THF).MDI/polyol ratio was 1.0. The mixture was reacted at room temperature for about 1 2 hours under stirring. Then the mixture was cast on a glass plate and THF was slowly removed in a desiccator. PU films were dried in air, cut for testing and treated at 120 "C for 5 hours in an electric oven. The thickness of PU films derived from various wastes was about 0.1 0.3 mm. The colors of PU films were derived from the original colors of the wastes.

-

-

I

Waste materials

Drying at 1Zo'C

I

-

Crushed by mixer Filtering

Original polyol PEG 400

Polyol Sn catalyst

-

L-THF

StirringStirring cast

MDI

-

Homogenized

-

Homogenized

-

Surfactant + H@

MDI

Heat treatment Drying Humidity control

P Measurement

Figure 2. Preparation scheme of PU's derived from various wastes.

I84


2.3 Measurement

Tensile properties of PU films were determined using a tensile test machine (TENSILON RTA-500, Onentec Co. Ltd.) at 25°C. The strain rate was 5 mm/min. The gauge length was 30mm. Tensile stress at break and Young's modulus were calculated from stress-strain curves. The width and thickness of samples were 5 mm and 0.1 to 0.3 mm, respectively. Thermal properties of PU's were measured by a differential scanning calorimeter (DSC 220C, Seiko Instruments Inc.). Scanning rate was 10"C/min. 2.4 Biodegradation tests

Biodegradation tests were canied out in a field at Otsuma Women's University, Sayamadai campus where there is good sunshine and good drainage. PU films were kept between stainless steel nets and were buried under the ground.

3. RESULTS AND DISCUSSION 3.1 Mechanical properties Figure 3 shows the stress-strain curves (S-S curve) of PU films derived from BCR (BCR-PU) obtained from tensile tests. The similar S-S curves were obtained in the case of BG-PU systems.

50

I

I

BCR/Polyol=0.6

40

d 30 I

. m

0.1 (22.3MPa,6E.l0h)

m

g 20

v)

0.05(22.7MPa,104.3%)

10

PEG-MDI (28.2MPa,l W h )

0

0

2

Figure 3.

4

6 Strain / Yo

8

10

Stress-strain curves of BCR-PU systems.


50

5000

185

50

5000

(b) 1B P U G --

p”;

0

0

0.6 0.8 (BCWPolyol) I 8.9-’

0.2

Figure 4.

0.4

1.0

0

0.2

0.4

0.6

0.8

1.0

(BGIPolyol) I pQ1

The relationship between stress at break (a,)and Young’s modulus (E) of (a) BCR-PU and (b) BG-PU films, and BCWpolyol and BGfpolyol ratios.

and Young‘s modulus Figure 4 shows the relationship between stress at break (q) (E) of PU films and BCWpolyol and BG/polyol ratios. In both cases of BCR-PU and BG-PU systems, both 0, and E show similar relations. q, and E increased until about 0.5 g/g and then decreased with increasing BCWpolyol and BG/polyol ratios. However, oband E of BCR-PU were higher than those of BG-PU. The results indicate that the BCR and BG components act as a hard segment and that PU’s in the glassy state are hardened with increasing waste content. Moreover, BCWpolyol of 0.5 g/g represents the borderline between ductile fracture and brittle fracture of PU films. Polyols of BCR-PU and BG-PU consisted of PEG for soft segments and BCK and BG fine powder for hard segments. An appropriate balance between molecular flexibility from soft segments and rigidity from hard segments in PU’s was obtained at 0.5 g/g of BCWpolyol and BG/polyol ratios.

3.2 Thermal properties Figure 5 shows the DSC curves near the glass transition (T,) of BCR-PU systems. T,’s of BCR-PU systems increased with increasing waste content of BCR. In the case of BG-PU systems, similar DSC curves were obtained. Figure 6 shows the glass transition temperature (T,) estimated from DSC heating curves of BCR-PU and BG-PU systems as a function of BCWpolyol and BG/polyol ratios. The values of Tg gradually increased until about 0.5 g/g and then rapidly increased with increasing BCWpolyoI and BG/polyol ratios. The inflection point of 0.5 g/g agreed well with the borderline between ductile and brittle fractures which is obtained from tensile test of PU films.

1 86


5 BCR/P0lyol=0.05 0.2

0 Y

7 BCR-PU 0

-50

Figure 5.

50 100 150 Temperature / "C

200

250

DSC curves near T, of BCR-PU.

(b) BG-PU 200

200

0 - 0

0

0.2

0.4

0.6

0.0

(BCWPolyol) / g.g-7

Figure 6.

1.0

(BG/Polyol) I g.g-1

T,'s and ACp's of (a) BCR-PU and (b) BG-PU plotted against waste content.

Biodegradalble polyurethanes from waste

187

3.3 Biodegradability of PU's Figure 7 shows the relationship between weight loss by biodegradation test in soil and testing time. The weight loss rapidly increased until about 50 days and then gradually increased with increasing testing time. Weight loss also increased with increasing waste contents of BCR and BG. However, comparing the weight loss at the same waste contents of BCR and BG, weight loss of BCIR-PU was higher than that of BG-PU. 30

30

I (a) BCR-PU I

/

(b) BG-PU

I

=E0

BGlpolyol=O.?

01-

O

15

gm10 5

5

I

0

0

I

I

5 0 1 0 0 1 5 0 2 0 0 2 5 0 Time / day

Figure 7. The relationship between weight loss by biodegradation test in soil and testing time. Figure 8 shows the relationship between weight loss and particle size of BCR fine powder and depth under the ground of BG-PU test films. Weight loss decreased with increasing particle size of BCR fine powder because the. surface area of wastes in PU films increased with decreasing particle size. From Figure 8(b), the weight loss changed in the order of 15cm > 5cm > 30cm depth in soil. The maximum weight loss was obtained at the depth of 15 cm under the ground. It is considered that good conditions for microorganismsare formed at this depth.

(b) BG/POIYOI~O.~

deDth=l5cm

J 'Ah

1

5cm

PEG-MDI PU

50

100 Time I day

150

Figure 8. The relationship between weight loss and (a) particle size of BCR fine powders and (b) depth under the ground of BG-PU films.

200

1 88


Before biodegradation tests

After 90 days

(a) PEG-MDI PU

(b) BCR-PU

I

(c) BG-PU

Figure 9.

The SEM photographs of (a) PEG-MDI PU, (b) BCR-PU and (c) BG-PU films before and after biodegradation test in soil.

Figure 9 shows the photographs of PEG-MDI, BCR-PU and BG-PU films before and after biodegradation tests in soil. The surface of the films gradually changed with increasing testing time. In the first stage, microorganisms come into contact with the wastes in PU films. Finally, many small holes in the films were observed. A clear


189

difference was not observed in PEG-MDI PU without wastes, but a clear difference was observed in BCR and BG PU’s before and after biodegradation tests.

3.4 Physical properties of the PU films after biodegradation Figure 10 shows the relationship between stress at break and Young’s modulus of BG-PU films after biodegradation tests and the testing time. Both stress at break and Young’s modulus obtained from the stress-suain curves of PU’s after biodegradation tests increased with increasing testing time until about 30 days and then decreased. Figure 11 shows the relationship between T of BCR-PU films after biodegradation tests and testing time. T slightly decreased with increasing testing time in the case of BCR-PU. While Tg of PhG-MDI PU increased with increasing testing time. Tg of BGPU also increased until about 60 days and then decreased although the figure is not shown here. It is considered from these results that PU films became stiff during biodegradation tests. This means that PU molecules were affected not only by microorganisms but also by water in soil. Concerning these results, further investigation is necessary. 5

600

BGPU

70

BG/PolyoI=O.5

60

r t

i

50

9 40 \

p30 20

10 0- 0

0

I BCR-PU 1st run

0

30

60 90 Time I day

120

0

50

100 150 Time I day

I 200

~

~~

Figure 10. The relationships between Figure 11. The relationship between Tg stress at break and testing of BCR-PU films and testing time of biodegradation. time of biodegradation. 4. CONCLUSIONS

From the above results, the following conclusions are obtained. (1) Bean curd refuse and beer grains can be used as a part of polyols in polyurethanes. (2) Bean curd refuse and beer grains act as hard segments in polyurethanes. (3) Stress, Young’s modulus and glass transition temperature of polyurethanes derived from bean curd refuse and beer grains have almost the same values as those of ordinary polymers. (4) It is considered that environmentally friendly polyurethanes can be prepared from bean curd refuse and beer grains.

190


5. REFERENCES

1. S. Yamauchi, Statistics of Plastics and Related Materials, Tokyo, NIKKAN PLASTICS, 1996. 2. T. Colbom, D. Dumanoski, and J. P. Myers, Our Stolen Future, New York, PLUM PENGUIN, 1996.

Compression 3. K. Nakamura, R. Morck, A. Reimann and H. Hatakeyama, Properties ofpolyurethane foam derived from kraft lignin. in "Wood Processing and Utilization", J. F. Kennedy, G. 0. Phillips and P. A. Williams Eds., P.175, Ellis Horwood, Chichester , 1989. 4. K. Nakamura, R. Morck, A. Reimann, K. P. Kringstad and H. Hatakeyama, Mechanical Properties of Solvolysis Lignin-derived Polyurethanes , Pol ym. Adv. Technol., 1991,2,41. 5. S. Hirose, K. Nakamura H. Hakakeyama, J. Meadouws, P. A. Williams and G. 0. Phillips, Preparation and Mechanical Properties o f Polyurethane Foams From Lignocellulose Dissolved in Polyethylene Glycol, CELLULOSICS : Materials for Selective Separations and Other Technologies, Ellis Horwood, London, 1993. 6. K.Nakamura, H.Hatakeyama, J. Meadows, P. A. Williams and G. 0. Phillips, Mechanical Properties of Polyurethane Foams Derived From Eucalyputus Kraft Lignin, CELLULOSICS : Materials for Selective Separations and Other Technologies, Ellis Horwood, London, 1993. 7. K. Nakamura, E. Kinoshita and H. Hatakeyama, Physical properties and Biodegradability of Polyurethanes Derived from Brewers grains, Sen-i Gakkai Preprints, 1998, G-254. 8. K. Nakamura, Y. Nishimura, T. Hatakeyama and H. Hatakeyama, Viscoelastic properties of biodegradable polyurethanes derived from coffee grounds, The chemistry and processing wood and plant fibrous materials (J. F. Kennedy, G. 0. Phillips, P. A. Williams), 1996. 9. K. Nakarnura, Y.Nishimura, T. Hatakevama and H. Hatakevama. Preparation of biodegradable polyurethanes derived from coffeegrounds, International 'Workshop, Tsukuba. 1993.239. 10. K. Nakakura &d Y. Nishimura, Polyurethane Foam Derived from Waste Vegetable Oil, Kobunshi Ronbunshu, 1993,50,881. 11. Y. Tamai, Y. Sasaki and K. Nakamura, Utilization of By-product(Shir0-Kasu)from Wheat Starch lndusfryfor Polyurethane, SEN-I GAKKAISHI, 1997,53, 381. 12. H. Hatakeyama, S. Hirose, K. Nakamura and T.Hatakeyarna, New types o f polyurethanes derived from lignocellulose and saccharides, CELLULOSICS, 1993. 13. K. Nakamura, Y. Nishimura, T. Hatakeyama and H. Hatakeyama, Mechanical and Thermal Properties o f Biodegradable Polyurethanes Derived f m m Sericin, S EN-I GAKKAISHI, 1995,5 1 , 11 1 . 14. K. Nakamura and Y. Nishimura, Thermal Properties o f Polyurethanes Derived from Tea Grounds,Netsu Sokutei, 1995,22, 114 15. M. Iijima and K. Nakamura, Mechanical Properties o f Polyurethanes Derived from Bean-Curd Refuse, Nihon Kasei Gakkaishi (J. Home Econ. Jpn.), 1999,50, 6

BIODEGRADABLE POLYURETHANE COMPOSITES CONTAINING COFFEE BEAN PARCHMENTS Hyoe Hatakeyama”, Daisuke Kamakura’, Hideyuki Kasahara’, Shigeo Hirose’ and Tatsuko Hatakeyama’ I

Fukui Universiry of Technology, 3-6-1 Gakuen, Fukui-city, Fukui 910-8505, Japan

’National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

’Otsuma Women’s University, 12 Sanbancho, Chiyoda-hi, Tokyo 102-8357, Japan ABSTRACT Polyurethane composites were prepared using coffee bean parchments (CBP) mixed with a molasses-polyol (MP) consisting of molasses and polyethylene glycol (PEG-200). The content of CBP in the polyol was varied from 0 to 90 wt %. The above mixture was reacted with diphenylmethane diisocyanate (MDI) with the presence of a catalytic amount of dibutyltin dilaurate (DBTDL) to form polyurethane composites. The compression strength ( u ) and the compression modulus (E) was almost constant in the region of CBP content lower than 50 9%. When the CBP content exceeds 60 %, u and E increase prominently with increasing CBP content, reaching a maxima at CBP content = ca. 70 %., and then decreasing with increasing CBP content. The derivative thermogravimetry (DTG) curve of the obtained CBP composites showed two kinds of the thermal degradation temperatures: DTd, and DTd2.DTdldecreased with increasing CBP content. DTdz increased slightly with increasing CBP content, reaching the degradation temperature of coffee bean parchments.

INTRODUCTION In the past 15 years, various synthetic polymers, whic:h can be derived from plant components such as saccharides and lignin, have extensively been studied by various research groups [l-81. We have paid attention to composites which were obtained from fine parchments the diameter of which was less than 2 ~ l land l thickness was 0.09 m. In the present study, PU composites were prepared from ground plant particles, such as coffee bean parchments, mixed with a molasses-polyol (MP) solution consisting of molasses and polyethylene glycol (PEG-200). Mechanical and thermal properties of the above composites were studied. EXPERIMENTAL Sample preparation Coffee bean parchments were kindly provided by the National Federation of Coffee Growers of Colombia. The particles were 2 111111 in diameter and 0.09 mm in thickness for coffee bean parchments. A molasses polyol (MP, molasses mixed with polyethylene glycol 200, Tropical Technology Center Co.) was used as a polyol and diphenylmethane

192


diisocyante (MDI, Mitsui Chemical Co.) was used an isocyanate.

Measurements Apparent density ( ,n ) was measured using a Mitsumoto A B S digital solar caliper and an electronic balance. The size of the sample was 40-60 rnm (length), 20-30 (width) and 20-30 nun (thickness). The unit of apparent density was g / cm3. Compression measurements were carried out using a Shimadzu Autograph AG 2000D at room temperature. Test specimens were a rectangular solid, and the added stress was less than 10 MPa / min. Compression strength ( 0 )was defined as the value of highest point of the linear part in the stress-strain curve. Static Young's modulus ( E ) was calculated using the initial stage of compression curves. Conditions in detail accorded with Japanese Industrial Standards (JIS 2-2101). Thermogravimetry (TG) was carried out in nitrogen flow using a Seiko TG 220 at a heating rate of 20 "C / min in the temperature range from 20 to 500 "C. Sample mass was ca. 5 mg. TG curves and DTG curves were recorded. Mass residue was indicated as ( mT / m m ) x 100 (%), where mT is mass at temperature T and m, is mass at 20 "C. Mass residue was evaluated at 450 "C.

RESULTS AND DISCUSSION

As shown in Fig. 1, CBP was mixed with polyol and suspensions were obtained with various mixing ratios from 10, 20, 30, 40, SO, 60, 70, 80 and 90 wt 96. Acetone was added to each mixture in order to control the viscosity of the suspension. MDI was added to the suspension under stirring and coffee bean parchment-PU composites were obtained. After drying for 3 days at room temperature, the sample was cured at 120 "C for 2 hrs. Fig. 2 shows the relationship between density ( p ) of PU composites and coffee bean parchment contents. The density reaches a maximum when the content of parchments in the composites is ca. 70 76. Coffee bean parchments

I added Molasses polyol mixed Suspension

I reacted with MDI

rn PU composites

NCO/OH =1.2 Material content = 10-90 wt%

Figure 1.

Preparation scheme of polyurethane composites (PU composites)

Biodegradable polyurethane composites

0.80

0.00

,

193

-

' 0

20

40

60

80

100

coffee bean parchments content I %

Figure 2.

Relationship between density ( p ) of PU composites and coffee bean parchment contents

Fig. 3 shows the relationship between compression strength ( u ), modulus of elasticity ( E ) and coffee bean parchment content in PU composites. As seen from the figure, both compression strength ( CJ ), and modulus of elasticity ( E ) increase with increasing coffee bean parchment content in PU composites and reach a maximum when powder content is ca. 70 $5. 20.0

800.0

16.0 600.0 rJ

12.0

2

2.

400.0

2 --. rrl

8.0 200.0 4.0

0.0

0

20

40

60

80

1Oil

coffee bean parchments content 1 %

Figure 3.

The relationship among compression strength ( u ) modulus of elasticity (E) of PU composites and coffee bean parchment contents 0 compression strength ( u ), o modulus of elasticity (E)

194


20.0

800.0

15.0

600.0

cd

rj

a

a

5 10.0

400.0

5 4

b

5 .O

200.0

0.0

0.2

0

0.4

0.6

0.8

P ~g-cm-~

Figure 4.

The change of compression strength ( u ) and modulus of elasticity ( E ) with density ( p ) of PU composites from CBP 0 compression strength ( u ), o modulus of elasticity ( E )

content I %

3

200

300

400

5

T i "C TG heating curves and derivative curves of CBP-MP type PU composites containing various amounts of coffee bean parchment

Biodegradable polyurethane composites

1-

370.0

195

370.0

330.0

9 \

cn 290.0

'------I

250.0

0

20

40

60

80

250.0

100

coffee bean parchments content / 9%

Figure 6.

Change of Td and DT, with coffee bean parchment content in PU composites a DT,,, CBP 100%DT,,, A Tdl, + CBP 100% T,, 0 DT&, 0 CBP 100% DTa, A Ta, C) CBP 100% Tdz

Fig. 4 shows the change of compression strength ( u ) and modulus of elasticity (E) with density ( p ) of PU composites obtained from coffee bean parchments. As seen from the figure, both compression strength ( u ), and modulus of elasticity (E) increase with increasing density ( p ) of PU composites. The above results suggest that the highest mechanical properties of PU composites from CBP properties are observed when the density of PU composites reaches the highest value. Fig. 5 shows TG curves and DTG curves of PU composites from CBP. As seen from Fig. 5, DTG curves show the presence of two kinds of thermal degradation corresponding to DTdland DTc DTdz seem to be specific to the degradation of CBP, since the DT,,peak becomes prominent when CBP content in PU composite are over 30 5% and this is very clear when coffee bean parchment content is 100 %. Fig. 6 shows the change of Td,,Ta, DT,, and DTdZwith the coffee bean parchment contents. Both degradations may be mainly caused by the degradation of CBP, since both are observed when the coffee bean parchment content is 100%.

CONCLUSIONS (1) Polyurethane composites were prepared using coffee bean parchments (CBP) mixed with a molasses-polyol (MP) consisting of molasses and polyethylene glycol (PEG200). The content of CBP in the polyol was varied from 0 to 90 wt%. (2) The compression strength ( (T ) and the compression modulus (E) was almost constant in the region of CBP content lower than SO 5%. When the CBP content exceeds 60 96,CJ and E increase prominently with increasing CBP content, reaching maxima at CBP content = ca. 70 %, and then decreasing with increasing CBP

196


content. (3) The DTG curves of the obtained CBP composites showed two kinds of thermal degradation temperatures: DTdl and DTa. DTdl decreased with increasing CBP content. DTdz increased slightly with increasing CBP content, reaching the degradation temperature of coffee bean parchments.

ACKOWLEDGEMENT The authors would like to thank the National Federation of Coffee Growers of Colombia, for providing coffee bean parchments.

REFERENCES 1. V. P. Saraf and W. G. Glasser, ‘Engineering plastics from lignin. 111. Structure Property Relationship in solution cast polyurethane films’, .I. Appl. Polym. Sci., 1984, 29, 1831-1841. 2. V. P. Saraf, W. G. Glasser, G. L. Wilkes and J. E. McGrath, ‘Engineering plastics from lignin. a.Structure Property Relationship of PEG-containing polyurethane networks’, J . Appl. Polym. Sci., 1985, 30, 2207-2224. 3. W. H. Newman and W. G. Glasser, ‘Engineering plastics from lignin. XI. Synthesis and performance of lignin adhesives with isocyanate and melamine’, Holzforschung, 1985,39,345-353. 4. A. Reimann, R. Morck, H. Yosida, H. Hatakeyama and K. P. Kringstad, ‘Kraft lignin in polyurethane. 111. Effects of the molecular weight of PEG on the properties from a kraft lignin-PEG-MDI system’, J . Appl. Polym. Sci., 1990, 41, 39. 5. K. Nakamura, R. Morck, K. P. Kringstad, H. Hatakeyama, ‘Compression properties of polyurethane foam derived tiom kraft lignin’, Wood Processing and Utilization (J. F. Kennedy, G. 0. Phillips and P. A. Williams, Eds.), Ellis-Honvood, Chichester, 1989, 175-180. 6. H. Hatakeyama, S. Hirose, K. Nakamura and T. Hatakeyama, ‘New type of polyurethanes derived from lignocellulose and saccharides’, in Cellulosics: Chemical, Biochemical and Material Aspects ( J . F. Kennedy, G. 0. Phillips and P. A. Williams, Eds.), Ellis-Honvood, Chichester, 1993, 525-536. 7. N. Morohoshi, S. Hirose, H. Hatakeyama, T. Tokashiki and K. Teruya, ‘Biodegradabability of polyurethane foams derived from molasses’, Sen-i Gakkuishi, 1995, 51(3), 143-149. 8. K. Nakamura, Y. Nishimura, T. Hatakeyama and H. Hatakeyama, ‘Viscoelastic properties of biodegradable polyurethanes derived from coffee grounds’, the Chemishy and processing of wood and plunt firous materials (J. F. Kennedy, G. 0. Phillips and P. A. Williams, Eds.), Woodhead Publishing Ltd., Cambridge, England, 1996. 283-290.

BIODEGRADABLE POLYURETHANE SHEET DERIVED FROM WASTE COOKING OIL Sumalai Srikumlaithong*, Chulaporn Kuwarananchrroen* and Narongdej Asa* Thailand Instilute of Scientif?cand Technological Research, 196 Phahonyothin Rd, Chatuchak, Bangkok 10900, Thailand

ABSTRACT Experiments on the preparation of biodegradable polyurethane sheet derived from waste cooking oil were carried out. The major factors affecting its properties were casting conditions, the amount of waste cooking oil, additives used and NCO/OH ratio. The products prepared by casting into a mould at ambient temperature gave more even properties and higher hardness than that using hot mould. When silica and fibre glass were applied as reinforcement, the result of polyurethane sheet containing fibre glass possessed higher hardness and lower elongation at break than those with silica at amounts of 2, 4, 6 and 10 parts by weight (pbw). The additives used improved the quality of products prepared at NCO/OH ratio 1 to a certain extent but they were not good enough for commercial applications. The effect of NCO/OH ratio on mechanical properties was also studied. The product obtained at NCO/OH ratio of 1.6 containing 30 pbw waste cooking oil gave properties that complied with the requirement. Preparation of polyurethane sheet with properties complying to standard was accomplished by blending 30 pbw oil, 70 pbw PEG and 79.7 pbw MDI (NCO/OH ratio of 1.6), casting into a mould at ambient temperature and hot air post-curing at 120'C for 4 h.

INTRODUCTION Waste cooking oil from the food industry and restaurants is increasing substantially every year. The waste which could be collected was 42,000 metric tons in 1995, thus resulted in environmental pollution. Fats and oils are the ester of glycerol consisting of hydroxyl groups (Schauerte. 1985). Hatakeyama (1991) and Nakamura (1993) preliminary investigated its utilization for production of biodegradable polyurethane. Polyurethanes composing of carbonate groups in their backbone structure (Wood 1987) were produced by the reaction of isocyanate with more than one reactive isocyanate group per molecule (a diisocyanate or polyisocyanate) and alcohols having two or more reactive hydroxyl groups per molecule (diols or polyols). The molecular weight of the effective polyols should be 200 -10,000, depending on their applications (Schauerte 1985). All types of polyurethanes are based on the exothermic reaction of diisocyanate or polyisocyanate with polyols. Mechanical properties of urethane are influenced directly to NCO/OH ratio and the excess of isocyanate groups is able to take part in the crosslinking reaction through the formation of allophanate or biuret linkages (Nierzwichi et al. 1980). It was found that the increase in NCO/OH ratio results in the increase of hardness, tensile modulus, tensile strength and elongation properties. To enhance a wide range of applications, additiies - catalyst, chain extenders, crosslinking agents and fillers - may be used to control and modify both the reaction and properties of the final polymer. In this study, waste cooking oil from the food industry

198


utilized as polyols for production of biodegradable polyurethane. The effect of NCO/OH ratio, and amount of oil and additives on its properties were assessed.

EXPERIMENTAL

Materials 1. Polyols 1.1 Waste cooking oil fiom a restaurant was filtered and its properties are presented in Table 1.

Table 1. Properties of waste cooking oil Characteristics Moisture, % w/w Acid value, mg KOWl g oil Saponificationvalue, mg KOWl g oil Hydroxyl number Molecular weight (av.)

Waste cooking oil

0.1 3.39 207.57 61.80

2,723

1.2 Polyethylene glycol (PEG) with properties are shown in Table 2.

Table 2. Properties of polyethylene glycol (PEG) Characteristics Molecular weight (av.) Hydroxyl number Acidity pH (5% aq. soln.) Degree of polymerization (n)

PEG

400 28 1 0.1 5.5 9

2. Isocyanate Diphenylmethanediisocyanate (MDI) with average molecular weight of 250 and NCO content of 3 1% 3. Additives 3.1 Silica with particle size less than 45 micron as reinforcement 3.2 Fibre glass as reinforcement 3.3 Silane A 1100 as coupling agent 3.4 Vulkanox BMT as antioxidant 3.5 DioctylphthalateP O P ) as plasticizer 3.6 Releasing agent A-F- 1

Methods 1. Material preparation Waste cooking oil, PEG and MDI were dried and deaerated in an vacuum oven with a reduced pressure of 5- 10 inch Hg at 105-110°C for 15 min, 1 h and 2 h respectively. MDI was cooled in a vacuum chamber at a reduced pressure of 1-2 inch Hg for 2 h.

199

Biodegradable polyurethane sheet

2. PUsheetpreparation

PEG solution was prepared by mixing dried oil and hot PEG at 90°Cfor 5-10min and cooled in a vacuum chamber with a reduced pressure of 1-2inch for 2 h. PU sheet was achieved by prepolymerization of PEG solution and MDI at ambient temperature. The speed and time consumed are indicated in Table 3, 4,and 5. The solution was casted on glass plates coated with releasing agent at the size of 10~15~0.20 cm3, followed by curing at 120°Cfor 1.5-4h. The product was released out of the mould and left for 2 weeks to complete the crosslinking reaction. Table 3. Weight of oil and casting conditions at NCO/OH ratio 1 Ingredients Experiment No. 1 2 3 4 30 20 30 @bw) 20 Oil

5 40

6 50

PEG400

(pbw)

80

80

70

70

60

50

MDI

@bw)

55.10

55.10

49.80

49.80

44.70

40.70

Speed of mixing (rpm) Mixing time

Curetime

30

70

55-80

80

hot

cold

hot

cold

.

Cure temperature (“C)

115-120 115-120 hot

hot

120 1.50

(h)

200-225 200-230 200-230

200

(sec.)

Mould

200

200

b

1 .so

4

1.50

1.50

4

Table 4. Additives for property improvement of PU sheet at NCO/OH ratio 1 Ingredients Experiment No. 1 2 3 4 5 6 7 8 9 10

NCO/OH

1

1

1

1

1

1

1

1

1

1

(pbw) 20

20

20

20

20

20

20

20

20

20

30

PEG400

(pbw) 80

80

80

80

80

80

80

80

80

80

70

MDI

(pbw) 55.1 55.1 55.1 55.1 55.1 55.1 55.1 55.1 55.1 55.1 49.80

Silica

(pbw)

-

Fibreglass

(g)

-

SilanellOO

(pbw)

-

ratio Oil

1

11

V U ~ ~ ~ O (pbw) X BHT DOP (Pbw) Speed of mixing Mixingtime

2

2

4

6

10

20

-

2.75 1.67 2.88 2.50

0.12 0.12 0.24 0.36 0.36 0.12 0.24 0.24 0.24 0.24

-

0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25

(rpm.)200 200 200 200 200 210 450 (sec.)

60

60

70

95

100 70

70

-

1

-

200-250 70

60

60

b

75

200


Mould Cure temperature Cure time

("C)

.

hot mould

120 b

1.50

(h)

3.50 1.00 t

4 4

t

Table 5. Variation of NCO/OH ratio and oil Ingredients Experiment No. 1

2

3

4

5

6

7

8

9

10

1

1

1.2

1.2

1.4

1.5

1.6

1.6

1.6

1.6

NCO/OH ratio Oil

(pbw)

20

30

20

30

30

30

20

30

40

50

PEG 400

(pbw)

80

70

80

70

70

70

80

70

60

50

MDI

(pbw) 55.10 49.80 66.20 59.80 69.80 74.80 88.20 79.70 71.10 65.12

Speed of mixing Mixingtime

(rpm.) 200

200

200

200

200

200

200

200

200

200

70

80

72

76

70

78

66

78

84

90

(sec.)

Mould Cure temperature Cure time

4

Cold mould

t

("C)

4

120

+

(h)

4

4

b

3. Study on the effect of oil, additives and NCO/OH ratio on properties of PUsheet 3.1 Oil

PU sheets were prepared by using an isocyanate to hydroxyl group (NCO/OH) ratio of 1 and 1.6 while the weight of oil was varied from 20% to 50% of PEG solution. The experimental conditions are presented in Table 3 and 5 . 3.2 Additives

Silica and fibre glass were used as reinforcement in PU sheets. Prior to mixing with PEG solution, silica was pretreated with water (6%) and dried at 110°C for 24 h. Fibre glass was coated with silane containing a small amount of water (8% of fibre glass) before application. 3.3 NCO/OH ratio

PU sheets were prepared at a NCO/OH ratio of 1, 1.2, 1.4, 1.5 and 1.6. The weight of oil, PEG and MDI used are shown in Table 5. 4. Testing

Tensile strength and elongation at break were measured according to ASTM D 412-80. Hardness and Izod impact strength were determined by the method of ASTM D 2240-81 and ASTM D 256-92 respectively.


201

RESULTS AND DISCUSSION

Utilization of cooking oil waste for the preparation of PU sheet has been accomplished, resulting in both environmental protection and value added of the waste. The effects of various parameters consisting of casting conditions, the amount of oil, additives and NCO/OH ratio used were studied.

Casting conditions Polymerizationis an exothermic reaction which leads to heat evolution and results in a high rate of reaction. Hence, the setting took place rapidly before homogeneous mixing was ready while casting with hot mould. Whereas PU sheet casted with cold mould could yield homogeneousproperties (Table 6).

Table 6. Effect of oil and casting condition on PU properties at NCO/OH ratio 1 Experiment Mould Oil Tensile strength Elongation at Hardness (Pbw

No. 1

2 3 4 5 6

hot cold hot

20

Wa) 0.84-1.44 1.08-1.44 1.08-2.54

cold

30

1.82-1.89

hot hot

40

0.54- 1.22 0.44-1.35

50

(”/)

57-90 49-68 33-1 15 43-46 47-1 13 63-99

(shore A) 33-42 51-52 33-63 62-63 10-40

7-20

Effect of oil on PU properties at a NCO/OH ratio of 1 Table 3 shows that the higher the amount of oil used, the longer the time of mixing. The oil increased with the decrease of PEG and MDI at NCO/OH ratio of 1, thus resulting in a slower rate of reaction. Hardness of PU sheet substantiallydecreased when the weight of oil used increased as presented in Table 6.

Additives for property improvement Silica and fibre glass were added as reinforcements to increase the tensile strength and hardness, an antioxidant to prevent product degradation caused by reaction with atmospheric oxidation, and a coupling agent to increase level of bondmg in polymer. (Lutz 1989). PU sheets prepared 6pm NCO/OH ratio of 1,20 pbw oil and silica at the weight of 2, 4,6, 10 pbw possessed no significant difference in tensile strength and elongation at break but hardness decreased as shown in Table 7. At 20 pbw of silica, tensile strength of the sheet was relatively high. Fibre glass ranging fiom 1.67 to 2.88 pbw strengthened the hardness of PU sheets but decreased in elongation at break. However, the property of PU sheet embedded with either silica or fibre glass was improved to some extent but not sufficient for commercial applications.

Table 7. Effect of silica and fibre glass on PU properties at NCO/OH ratio 1 Experiment Additives Tensile strength Elongation at Hardness break No. (pbw) @Pa) (%) (shore A) 1 0.841.44 57-90 33-42

202

Biodegradable pol yurethane-based polymers

2

Silica 2

0.33-0.68

52-66

15-19

3

2

0.40-0.72

82-107

15-22

4

4

0.67-1.12

65-84

14-20

5

6

0.65-1.40

65-87

14-25

6

10

1.07-1.17

34-37

19-50

7

20

1.94-2.16

38-45

40-45

8

FG 2.75

1.92-5.22

4-6

37-62

9

1.67

1.25-4.16

5-6

63-68

10

2.88

0.91-2.13

6-15

46-58

11

2.50

1.70-4.13

5-10

55-59

Effect of NCO/OH ratio and oil on PU properties The ratio of NCO/OH influences the ultimate properties of polymer (Nakamura et al. 1992). The PU sheets were prepared at a NCO/OH ratio of 1, 1.2, 1.4, 1.5 and 1.6 with 30 pbw of oil. Tensile strength and hardness increased with the increase of NCO/OH ratio (Table 8 and Fig. 1). The product obtained at NCO/OH ratio of 1.6 containing 30 pbw waste cooking oil gave properties that complied with the requirement. To make use of more waste cooking oil, PU sheets at NCO/OH ratio of 1.6 were produced from the oil at a weight of 20,30,40 and 50 pbw. Their mechanical properties decreased with the increase of oil used as shown in Fig. 2. Oil at 30 pbw possessed the properties of PU sheets that complied with the requirement.

Table 8. Effect of NCO/OH ratio and oil on PU properties Experiment NCO/OH Tensile Elongation Hardness No. ratio strength at break (MPa) (YO) 49-68 51-52 0 1 1 1.08-1.44 2

1

1.82-1.89

43-46

62-63 0

3

1.2

5.32-6.57

44-49

81-84

4

1.2

6.60-8.23

29-40

83-87

5

1.4

11.94-14.22

18-33

44

6

1.5

18.50-19.88

7-9

52-53 A

7

1.6

23.8 1-31.08

5-12

58-63 A

8

1.6

22.81-33.82

6-9

62-64 A

9

1.6

21.66-25.15

3-6

52-59 A

10

1.6

16.20-19.62

3-4

51-52 A

~

0 shore A A

shore D

Impact strength (J)

A

0.1


NCO/OH ratio Figore 1.

Effect of NCO/OH on PU properties at 30 pbw oil.

Figure 2.

Effect of oil on PU properties at NCO/OH ratio of 1.6

203

204


CONCLUSION The effect of casting conditions, the amount of waste cooking oil, additives and NCO/OH ratio on mechanical properties of PU sheets was studied. PU sheets with properties complying to the standard was accomplished by blending 30 pbw oil, 70 pbw PEG and 79.7 pbw MDI (NCO/OH ratio of 1.6), casting into a mould at ambient temperature and hot air post-curing at 120°C for 4 h.

REFERENCES 1 . K. Schauerte, M. Dahm, W. Diller, and K.Uhlig, Raw Materials in Polyurethane Handbook By Gunter Oretel, Munich, Copyright Carl Hauser, 1985. 2. H. Hatakeyama, S . Hirose and K. Nakamura, Biodegradable Polyurethanes and Manufacture, Jpn., Kokai Tokyo Koho, P 05, 186, 556,1991. 3. K. Nakamura and Y. Nishimura, Polyurethane foam derived fiom waste vegetable oil, Kobunshi Ronbunsh, 1993,50(1 l), 881-886. 4. G. Wood, ICI Polyurethane Book, New York, John Wiley & Sons Inc., 1987. 5. W. Nierzwicki and E. Wysoaka, Microphase separation and properties of urethane elastomer, J Appl Polym Sci,1980,25,739-746. 6. J . T. Lutz, Jr., lllennoplastic Polymer Additives, New York, Marcel Dekker, IncJ989. 7. K. Nakamura, T. Hatakeyama, and H. Hatakeyama, Thermal properties of solvolysis lignin-derived polyurethanes, Polymersfor Advanced Technologies,1992,3, 15 1- 155.

BIODEGRADABLE POLYESTERS PKEPARED WITH DIMETHYL SUCCINATE, BUTANEDTOL, AND MONOGLYCERIDE Yoichi Taguchi', Akihiro Oisht, Ken-ichi Fujita', YosMazu Ikeda' and Takashi Masuda' I National Institute of A4aterials and Chemical Research. 1-1, Higashi. Tswkuha-shr. Iharah-ken. 305-8565, Japan

INTRODUCTION

Aliphatic polyesters are well known to be biodegradable and environmentally compatible polymers. Above all, poly(buty1ene succinate) which is produced by the polymerization between succinic acid derivative and 1,4-butanediol is known to be an excellent biodegradable polyester with a high melting point and good mechanical strength, while the properties are not always optimal properties for use. Therefore, many kinds of improved copolymers based on poly(buty1ene succinate) have been reported [I]. On the other hand, monoglycerides such as monolaurin, monostearin, and monoolein can be derived from natural oils and fats whch are renewable resources, and have two reactive alcohols per molecule. It was reported that a high molecular weight poly(buty1ene succinate) could be obtained from transesterification between dimethyl succinate and 1 ,Cbutanediol [2]. Therefore, the copolymers prepared with dimethyl succinate, butane diol, and monoglyceride was expected to be biodegradable polymers with good properties for use (Scheme I). In this paper, copolymers were produced from dimt9hyl succinate, 1,4-butanediol, and monoglyceride, and their properties were compared with the properties of poly(buty1ene succinate) homopolymer.

EXPERIMENTAL Materials

Dimethyl succinate, 1 ,Cbutanediol, and titanium tetraisopropoxide were reagent grade chemicals from Wako Pure Chemical Industries Ltd., and monolaurin, monoolein, and monostearin were reagent grade chemicals from Tokyo Kasei Kogyo Ltd.. Measurement

GLC was carried out using a Shmazu GC-14 chromatograph (FID) with a capillary column (J&W Scientific DB-I, 0.541 mm x 30 m). Distillates of the

206


H2c-CooMe + HOfCH&OH H2C-COOMe

+

HO-CHp-CH-OH 942

li(O-i-Pr)4 c

- MeOH

0I C=O c1lH23

0 C=O CllH23 Scheme 1

polymerization were analyzed at a temperature increasing from 100°C to 300°C at a rate of S"C/min (injection and detector temperature: 320°C). Number (Mn) and weight (Mw) average molecular weights of the polymers were measured by Toso GPC-8010 system using TSK gel column (G2000HR + G3000HR + G4000HR + G5000HR) and monodisperse polystyrenes as standards at 40°C. Chloroform was used as an eluant at 1 ml/min. The differential scanning calorimetric and thermogravimetric studies were carried out using Seiko SSC-5200. Tensile tests were carried out according to SS-207-EP on Toyo Baldwin tensile testing machine. 'H NMR spectra were measured in CDCL using a Bruker AC200 (200 MHz) spectrometer. Preparation of copolymer including monoglyceride The typical procedure was as follows. The solution of dimethyl succinate (180 mmol), butane diol (187 mmol), monolaurin (0.9 mmol), and titanium tetraisopropoxide (0.1 mmol) as a catalyst was heated at 160 "C for 1 h, and then the temperature increased gradually to 200 "C and was maintained for 30 min. The

methanol generated by transesterification was removed through a glass condenser. In the next stage, the prepolymer was further polymerized at 215 "C under 0.1 mmHg for 5 h A part of the obtained copolymer was dissolved in chloroform, and the solution was poured into MeOH to induce the precipitation of polymer. The precipitant was h e d under vacuum at 60°C for one day, and it was used for 'H Nh4R and GPC measurements.

RESULTS Table 1 shows the effect of the amount of monolaunn on the molecular weight and thermal properties of the copolymer. Monolaurin in the range of 0.1 % to 10 % molar ratio against methyl succinate was used for copolymerization. 'H N M R spectra of copolymers showed peaks for methylene and methyl protons of laurate respectively at about 1.2 ppm and 0.9 ppm. This fact shows that monolaurin component is

Biodegradable polyesters

Transesterification

~yH-O~

207

H3C-O-~-C11H23

o

CH2

6

c=o

C"H23

Scheme 2

included in the copolymer. A little amount of methyl laurate was detected by GLC analysis of distillates during the polymerization reaction. When more than 2 % of monolaurin to methyl succinate was used for copolymerization, gelation took place (Run 6-8). These results show that dodecanoate in copolymer is replaced with a corboxylate of the other polymer by transesterification to give a three dimensional polymer network and a methyl laurate (Scheme 2). The molecular weight distribution increased with increasing amount of monolaurin in the copolymer. These copolymers had similar thermal properties to homopolymer (Run I). Table 1. Properties of copolymers including monolaurin *: Dimethyl succinate: butanediol : monolaurin

Run I

2 3 4 5 6 7 8

Molar Ratio* 180 : 188 : 0 180: 187: 0.21 180 : 187 : 0.53 180 : 187 : 0.91 180 : 185 : 1.81 180: 184: 3.61 180: 178: 9.00 200 : 188 : 20.0

Mn 32,400 35,000 46,200 52,200 22,200 gel gel gel

Mw Mn 1.63 1.80 2.10 2.91 3.93 x x x

Tg

Tm

·C

·C

- 39.9 - 37.6 - 35.9 - 38.8 - 40.0 - 35.4 - 39.8 - 42.0

114.1 114.1 113.7 114.1 114.9 112.8 105.4 96.7

aHm Td mJ/mg (2%) 110.1 322.2 92.4 314.3 72.0 311.8 106.4 320.0 107.7 309.0 100.5 311.0 106.2 306.5 65.5 297.6

Table 2. Tensile test of copolymers including monolaurin *: Dimethyl succinate: butanediol : monolaurin

Run Molar Ratio* 180: 188 : 0 I 180: 187: 0.21 2 180: 187: 0.53 3 180: 187: 0.91 4 180 : 185 : 1.81 5 180: 184: 3.61 6 180: 178: 9.00 7 200 : 188: 20.0 8

Elastic MPa 333 375 292 344 330 brittle brittle brittle

Yield Stress Break Stress MPa MPa 29.9 32.4 29.2 29.8 28.5 31.4 32.9 30.0 25.8 28.0 x x x x x x

Break Strain % 119.3 14.3 250.0 190.4 42.6

x x x

208

Biodegradable pol yurethane-based polymers

Table 2 shows the results of the tensile tests of copolymers including monolaurin, elastic strain, yield stress, and break stress of copolymers were not so different to thehomopolymer. However, the break strain of copolymers was greatly dependent on the amount of monolaurin. Copolymers including 0.3 % and 0.5 % of monolaurin had larger break strains than the homopolymer (Run 3 and 4). Table 3 shows the number average molecular weight and molecular weight distribution of copolymers including 0.3 % and 1.0 % monostearin (Run 3 and 6) and monoolein (Run 4 and 7). 'H N M R spectra of copolymers including monostearin and monoolein also showed that stearate and oleate were included in the obtained copolymers. These copolymers had similar molecular weight to copolymers including monolaurin (Run 2 and 5). Table 4 shows thermal properties of copolymer including monostearin (Run 3 and 6) and monoolein (Run 4 and 7 ) . These values were similar to the values of FHp-OH CH-OH CHZ-O-C-C~ iH23

0 Monolaurin

I

Run 1 I 2 3 4 5 6 7

CHp-OH CH-OH

CHp-OH

CH-OH CHp-O-C-Cq7H35

H H

-CH*

CH2 - 0 - C

,c=c,

CHz-CH3

0

0 Monostearin

Monoolein

Molar Ratio* 180 : 188 : 0 (Homowlvmer) 180 : 187 : 0.53 (Monolaurin) 180 : I86 : 0.55 (Monostearin) 180 : 186 : 0.55 (Monoolein) 180 : 185 : 1.81 (Monolaurin) 180 : 186 : 1.81 (Monostearin) 180 : 186 : 1.83 (Monoolein)

f

I

MwfMn 1.63 2.10 1.80 1.77 3.93 2.19 1.48

Mn 32.400 46,200 37,200 34,400 22,200 33,900 25,000

Table 4. Thermal properties of copolymers including monoglyceride *: Dimethyl succinate : butanediol : monoglyceride

I

I

Run Molar Ratio* 180 : 188 : 0 (Homopolymer) 1 I 2 1 180 : 187 : 0.53 (Monolaurin) 1 180 : 186 : 0.55 (Monostearin) 3 4 180 : 186 : 0.55 (Monoolein) 180 : 185 : 1.81 (Monolaurin) 5 6 180 : 186 : 1.81 (Monostearin) 7 180 : 186 : 1.83 (Monoolein)

Tg "C - 39.9 - 35.9 - 38.9 - 38.5 - 40.0 - 35.3 - 37.0

I 1

Tm "C 114.1 113.7 115.0 115.0 114.9 113.7 116.1

1 I

AHm mJ/mg 110.1 72.0 76.7 74.2 107.7 71.3 80.6

I I

Td(2%) 322.2 314.3 301.9 304.4 309.0 298.3 304.4

1

Biodegradablepolyesters

209

Table 5. Tensile test of copolymer including monoglyceride *: Dimethyl succinate: butanediol : monoglyceride

Run Molar Ratio· 180: 188 : 0 (Homopolymer) I 2 180 : 187 : 0.53 JMonolaurin) 3 180 : 186 : 0.55 (Monostearin) 4 180: 186: 0.55 (Monoolein) 5 180: 185 : 1.81 (Monolaurin) 6 180 : 186 : 1.81 (Monostearin) 7 180 : 186 : 1.83 (Monoolein)

Elastic MPa 333 292 316 309 330 330 350

Yield Stress Break Stress

MPa 324 28.5 26.3 26.. 0 28.. 0 26.. 9 29.6

MPa 29.9 31.4 32.2 37.7 25.8 26.4 23.1

Break Strain

% 119.3 250.0 386.8 384.3 42.6 201.1 33.6

homopolymer (Run I) and copolymers including monolaurin (Run 2 and 5). Table 5 shows the results of tensile test of copolymers including monolaurin, monostearin, and monoolein. Although elastic strain, yield stress, and break stress ofcopolymers including 0.3 % monoglyceride were not so different with homopolymer, the break strain of copolymers was larger than the homopolymer (Run 2, 3, and 4). In particular, copolymers including monostearin and monoolein had superior values of break strain. This means that break strain of copolymer is dependant not only on the amount of monglyceride but also on the chain length of the fatty acid of the monoglyceride. CONCLUSION Aliphatic polyesters were produced from dimethyl succinate, butanediol, and monoglyceride with a long-chain fatty acid. IH NMR spectra of copolymers showed that the monoglyceride component was included in the copolymers. Three dimensional networks were built up by transesterification of a part of the monoglyceride component, and gelation occurred if more than 2 % of monolaurin was used for copolymerization. The number average molecular weight and thermal properties of copolymers were unchanged by the amount and type of monoglyceride if less than 2 % of monoglyceride was used. Molecular weight distribution increased with increasing amount of monoglyceride in the copolymer. The elastic strain, yield stress, and break stress of copolymers were similar to the homopolymer. The tensile tests showed that the break strain of the copolymer was very dependent on the amount of monoglyceride. Copolymers including 0.3 % of monoglyceride had larger break stresses than the homopolymer. In particular, break stress of copolymers with 0.3 % monostearin and monoolein were superior. REFERENCES [1] For example, M. Kadobayashi, I. Takahara, Biodegradable polyesters with high molecular weight and their manufacture, Jpn. Kokai Tkkyo Koho JP 09 40,762,

2 10


February 1997; E. Takiyama, T. fujimaki, Y. Hatano, and R Ishioka, Manufacture of biodegradable aliphatic polyesters with hlgh molecular weight and good transparency, Jpn. Kokai Tokkyo Koho JP 09 31,176, February 1997; I. Takahashi, K. Kawamoto, A. Matsuda, and T. Masuda, Biodegradable high molecular weight aliphatic copolyesters with good modability and their preparation, Jpn. Kokai Tokkyo Koho JP 08 31 1,181, May 1995; T. Ooyama, H. Isozaki, S. Morita, and K. Sueoka, Thermal contractive aliphatic polyester films and their manufacture, Jpn. Kokai Tokkyo Koho JP 09 57,849, March 1997. [2] Y. Kawaguchi, N. Migita, H. Shiraharna, and H Yasuda, Synthesis and biodegradability of aliphatic polyesters prepared by polycondensation, Polymer I'reprmfs, .Jupun, 1994, 43 (1 I), 4048-49; Y. Imada, Y. kajikawa, M. Taniguchi, K. Koumoto, I. Takahashi, and T. Masuda, Synthesis of aliphatic polyester and Enzymatic Hydrolysis, Kohunshr Ronhunshu, 1998, 55 (8), 497-99.

PREPARATION AND THERMAL PROPERTIES OF POLYURETHANE COMPOSITES CONTAINING FERTILIZER Nobuyuki Yamruchi', Shigeo Hirose', Hyoe Hatrkeyama3 'Taki Chemical Co.,Ltd,2-1-6Sengeih Tsukuba, Ibaraki 305-0047,Japati ZNatio,ia[ ItistitUte of Materials atrd Chemical Research,l-1 Higashs Tsukuba,

[baraki 305-8565, Japan 'Fukui UiiiVersilyof Technology, 3-6-1 Gnkuen, Fukui-ciry, F i h i 910-8505,

Japan

ABSTRACT Polyurethane foam composites containing fertilizer were prepared as follows. Fertilizer particles (urea, diameter:0.2-2.0mm) were mixed with a polyol consisting of molasses polyol, polyethylene glycol, with a molecular weight of 200 (PEG200) and polypropylene glycol with a molecular weight of 3000 (PPG3000 triol). The above mixture was reacted with diphenylmethane diisocyanate (MDI) in the presence of a catalyst to foam polyurethane form composites. The content of fertilizer in the composites was varied from 0 to 15wtY0. The thermal properties of composites were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG). Glass transition temperatures (7'' 's) were determined by DSC. T, 's increased with increasing fertilizer content and with decreasing particle size. Thermal decomposition temperatures (Td's) were determined by TG. Three Td's were observed in TG curves. Td)swere almost constant regardless of fertilizer content. KEYWORDS Polyurethane, composites, degradation temperature

fertilizer,

glass transition

temperature, thermal

INTRODUCTION Polyurethanes are recognized as one of the most important polymeric materials since they can be produced in various forms such as fibers, films and sheets. We have extensively studied the biodegradable polyurethanes which can be derived from plant components such as saccharides and lignin[ 1-51, In the above studies, polyurethanes from molasses showed excellent thermal and mechanical properties and also showed biodegradability with relatively high degradation rates. In the present study, molasses

2 12


based PU foams containing solid fertilizer of urea were prepared. The thermal properties of the obtained PUF composites, were studied by DSC and TG. The relationship between thermal properties of PUF and content and particle size of fertilizer is discussed in this study

EXPERIMENTAL Materials Molasses pol yo1 (MOL) consisting of sucrose, glucose and other saccharides was obtained from Tropical Technology Center Ltd. Water in obtained MOL was removed by evaporation and, PPG and PEG were used as received. Commercial grade polymeric MDI was obtained from Mitsui Chemical Industries Co.

Preparation of Polyurethane Composites Polyurethane composites were prepared by the following procedure. MOL (lowto/) was mixed with PPG (8Owt%), PEG (lOwt%)(MOL solution). Fertilizer (urea) or Barium Sulfite (BaSO, as a standard), small amounts of silicone oil (surfactant), 1,8Diazabicyclo [5,4,0] -7-undecene (catalyst : 0.2wtY0against total polyol weight) were mixed with MOL solution using a mechanical stirrer. The obtained solution was reacted with MDI (NCO/OH=I . l ) at room temperature. After the foam sample was obtained in a vessel, the sample was allowed to stand overnight at room temperature. In the above process, the NCO/OH ratio was calculated as follows: where NCOiOH is the molar ratio of isocyanate NCO/OH=(M,,,xWm,) / (MhZOLxWivlOL) and hydroxyl groups per gram of MDI (7.4mmol/g), W,, the weight of MDI, M,, the number of moles of hydroxyl groups per gram of MOL solution.

Measurements DSC measurements were carried out using a Seiko DSC 220. Samples of ca.5mg were heated at a heating rate of 10"C/min in nitrogcn. A Seiko TG 220 was used for TG measurements. Samples of ca. 5mg were heated in nitrogen at a heating rate ol' 10°C /min.

RESULTS & DISCUSSION Phase transition of polyurethane composites was studied by DSC Fig.1 shows DSC curves of PU composites having various fertilizer contents. In each DSC curve, the gap in the baseline due to glass transition is observed. The glass transition temperatures

Polyurethane composites containing fertilizer

2 I3

(T,’s) were determined by a method reported by Nakamura et a1 [ 6 ] . Fig.2 shows the change of Tg’s plotted against filler contents. As shown in Fig.2, TR’s increase more markedly with increasing fertilizer contents when the particle size of fertilizer is decreased i.e. surface area of urea fertilizer is increased. The increase in 7‘’’s of PU composites with BaSO, is smaller than those with fertilizer. The above results suggest that the polyurethane chains interact with urea molecules on the surface of the fertilizer and the main chain motion. The relationship between A : f s of polyurethane composites and filler content is shown in Fig.3 T was calculated as follows[7] : A T = T, - Zg I“, g: Extrapolated End Temperature Tg:Extrapolated Initial Temperature AT increases with increasing filler contents and the walues of PU composites with fertilizer are larger than those with BaSO,. A T values increase with the decrease in particle size of fertilizer i.e. with the increase in surface area of fertilizer. This result suggests that main chain motion of PU’s is a effected by the interaction with urea molecules and the distribution of the units for main chain motion of PU’s becomes broader.

I

I

-70

I

-50

-30

Temperature / “C

Figure 1.

-52

DSC curves ofPU composites containing fertilizer

J

L 0

..

5

10

15

Filler Contents (wt%)

Figure 2. Change of T,’s plotted against filler contents

0

5

10

1s

Filler Contents(wt%)

Figure 3. Change of A T s plotted again st fi 11er contents

214


The thermal decomposition behavior of polyurethane composites was studied by TG. Fig.4 shows TG and differential TG (DTG) curves for fertilizer. TG curves show a twostep decrease in the temperature range below 500 . Fertilizer decomposed completely at 500°C. Fig.5 shows TG and DTG curves for polyurethanes containing fertilizer. TG curves show a three-step decrease in the temperature range below 500°C. Thermal decomposition temperature ( Td) was determined as the temperature of the crosspoint of extrapolated baseline and tangent line at the peak temperature of DTG curve as shown in Fig.4 The first decomposition temperature (Td,)at around 160-170°C is the decomposition temperature of fertilizer as shown Fig.4. It is known that saccharides such as sucrose and glucose start to decompose at around 200°C and to form caramel[8]. It is also known that urethane bonds dissociate to form hydroxyl and isocyanate groups at around 250°C [9]. Therefore, it considered that the second decomposition temperature (T,) is mainly related to the decomposition of urethane bonds and molasses, while the third decomposition temperature (Ta) is related to the decomposition of the remaining components. Fig.6 shows TG and DTG curves for polyurethane containing BaSO,. TG curves show a two-step decrease in the temperature range below 500°C. It is considered that Td is mainly related to decomposition of urethane bonds and molasses, T, is related to decomposition of remaining components, since BaSO, is stable up to 500°C.

"c

I 20

I 1W

13 75

p

so

50

175

n

0

I 0

I

I

I

I

IW

200

ml

rm

l 5 yn

Telllprralure I 'C

Figure 4. TG and DTG curves of fertilizer

Figure 5. TG and DTG curves of Polyurethane containing fertilizer (diarneter:O.O2mm)

Polyurethane composites containing fertilizer

400 10

im

-__I-

-

-

-

350

\

2 15

Td3

13 75

z .

E 75

YE4

I25

o

0

: restricted water by hydrophilic

>freerestricted water in the volume of CA :

Figure 6a. The low DS CA

Figure 6.

Figure 6b. The high DS CA

The molecular models of interaction between CA and Water.

Glass Transition Figure 7 shows the DSC curves of the dry CA films and Table 2 shows the Tg values. The Tg's decreased with increasing DS of CA. This means that the increase of Tg is caused by the increase of hydrogen bonds between hydroxyl groups of CA and that molecular motion was easily occurred by introduction of large acetyl groups. Figure 8 shows the relationship between Tg of CA and Wc. Tg rapidly decreased at low amounts of sorbed water and then gradually decreased in the region of Wc more than 2.0 g / g. The effect of water on the Tg's of CA decreased with increasing DS because of the decrease of hydrogen bonds.

Stress at break Figure 9 shows the relationship between stress at break (a,)of CA films at various RH and DS. Figure 10 shows the relationship between the a b ratio of wet and dry states of CA films and RH. As shown in Fig. 9 and Fig. 10, u b decreases in the presence of water, and the decrease of ab is much more significant in the case of CA containing low DS. It can be ascertained that intermolecular hydrogen bonds are broken by water molecules and hence ub decreases. Table 2.

Tg of dry CA films.

DS

2.42

2.75

2.81

2.92

Tg("C)

185.0

181.2

177.3

173.7

New polymers arid materials

280

200

1

1 fllm (dry)

160

I

170

180

200

190

0'

0

Temperature I 'C

I

0.2

0.6

0.3 0.4 0.5

wc I g l'g Figure 8. The relationshipbetween Tg of CA films and Wc.

Figure 7. The DSC curves of dry CA films. 120

0.1

110,

m 100

n

. g, z Y

c 0 u) u)

2

60

/OO%

40 2.4

2.6

2.8

! :t

3.0

DS Figure 9. The relationshipbetween q,of CA and DS.

4u ' 0

,

20

film

. 40 60 RH 1'3'0

80

100

Figure 10. The relationshipbetween awe, /udvratios of CA and RH.

CONCLUSION It is concluded that there are two types of sorbed water in CA molecules. One is restricted by the hydrogen bonds between hydroxyl groups and water molecules, and the other is restricted by the free volume of CA which is formed by acetyl and hydroxyl groups. The results of the increase of u b and Tg of CA at dry state suggest that the intermolecular hydrogen bonds between free hydroxyl groups of CA decrease with increasing DS. However, intermolecular hydrogen bonding is broken by sorbed water.

REF'ERRENCE 1. T. Hatakeyama, K. Nakamura, H. Yoshida and H. Hatakeyama, ThermochimicaAcfa, 'Phase transition on the water-sodium poly (styrenesulfonate)', 1988, 88,223 - 228.

DSC AND TG STUDIES ON CELLULOSE-BASED POLYCAPROLACTONES Hyoe Hatakeyarna', Hitoshi Katsurada', Nobuhide Takahashi',Shigeo Hirose', and Tatsuko Hatakeyama' 'Fukui University of Technology, 3-6-1 Cakuen,Fukui-cify,Fukui 910-8505, Japan 'National Institute of Materials and Chemical Research,1-1 Higashi,Tsuhba, Ibaraki 305-8565, Japan 'Otsuma Women's Wniversify,12 Sanbancho,Chi+-ku,

Tokyo 102-8357, Japan

ABSTRACI' Cellulose-based polycaprolactones(CellPCL's) were synthesized from alkali cellulose by the polymerization of E-caprolactone (CL) which was initiated by the OH group of cellulose in the presence of crown ether (18-crown-6) in dimethylsulfoxide at 80 "C. The ratios of CL to OH groups in cellulose (moVmol) were varied fiom 1 to 20 mol/moI. Differential scanning calorimetry (DSC) and thennogravimetry (TG) were performed using the CellPCL samples. The relationship between the chemical structures and thermal properties is discussed in this study.

INTRODUCTION In the previous studies [l-51,we have prepared saccharide-, lignin and cellulose acetatebased polycaprolactones and their molecular properties have been studied. In the present study, we have tried to prepare cellulose-based polycaprolactones (CellPCL's) directly from cellulose. They are expected to have molecular properties such as thermoplasticity and biodegradability. Thermal properties of the obtained CellPCL's were analyzed by differential scanning calorimetry (DSC) and thennogravimetry (TG).

EXPERIMENTAL Sample preparation Fig. 1 shows the preparation scheme in order to obtain CellPCL's. Cellulose powder (Arbwell) was kindly provided by Miki Sangyo Industries. The cellulose powder was immersed in 30 76 potassium hydroxide (KOH)aqueous solution and kept for 5 hr. at room temperature. The obtained alkali cellulose was washed with ethanol several times and then it was dried in vacuum. The dried alkali cellulose powder was dispersed in dimethylsulfoxide (DMSO) and was reacted with distilled & -caprolactone (CL) using crown ether (18-crown-6) (Merck Co. Ltd.) as a catalyst at ca 80 "C for 24 hrs. The CJJhydroxyl group (OH) ratio was changed from 1 t o 20 mol/mol. The obtained CellPCL's were precipitated by adding water and then were dried in vacuum for 48 hrs at room temperature. The obtained crude CellPCL's were pursed by the precipitation method which was carried out as follows: CellPCL's were dissolved into DMSO and then

282

New polymers and materials

[

Cellulose (Arbocel)

Alkali Cellulose DMSO E

-caprolactone

crown ether

Cellulose-based Polycaprolactone CL / OH Ratio (moVmol) = 1, 2, 3, 5, 10, 15, 20 Fig. 1 Preparation of cellulose PCL derivatives

3-f' 1 \ X

=

8

-fC(CH&d)Ti

caprolactone chain

n = 1,2,3,5,10,15,20 Fig. 2 Synthetic scheme of cellulose PCL derivatives were precipitated by putting their solution in water dropwise. The obtained Cell-PCL was dried in vacuum for 48 hrs at 60 "C. Fig. 2 shows the schematic chemical structure of the obtained cellulose PCL derivatives.

Measurements Differentialscanning calorimetry (DSC) measurements were carried out in nitrogen flow using a Seiko DSC 220C at a heating rate of 10 "C/min under a nitrogen flow. Sample mass was ca. 5 mg. Aluminum open pans were used. At first the CellPCL samples were heated to 120 "C and then quenched to -150 "C. DSC heating curves of the quenched

Cellulose-based polycaprolactones

283

samples were used for analysis. The melting temperature (T,), melting enthalpy (AH,), cold crystabtion temperature (TJ,glass transition temperature (TJ and heat capacity gap (AC,)were determined by the methods reported prewiously [ 6 ] . Thermogravimetry (TG) was carried out in nitrogen flow using a Seiko TG 220 at a heating rate of 20 "C/min in the temperature range 6om 20 to 500 "C. Sample mass was ca. 5 mg. TG curves and derivatograms were recorded. Mass residue (WR) was indicated as (mT/ mm)x 100 (%), where mT is mass at temperature T and mm is mass at 20 "C.

RESULTS AND DISCUSSION fig. 3 shows DSC heating curves of CellPCL derivatives with CUOH ratios of 1, 10 and 20 mol/mol. Numerals in the figure show CUOH ratio. The samples were heated to 120 "C and quenched at the cooling rate of 40 "C/min to -120 "C. Glass transition is recognized as the endothermic deviation of each DSC curve. Glass transition temperatures (T,'s) of CellPCL derivatives were observed in the temperature range from ca. -70 to -60"C, depending on CUOH ratios. A broad exothermic peak observed in the temperature range 6om -50 to -10 "C in each CellPCL derivative shows cold c r y s t a t i o n . By introduction of PCL chains, it is clear that a part of the amorphous chains rearranges and crystallizes. Peak temperature of cold crystallization (Ta)was observed from -38 to -25 "C depending on CUOH ratio. Melting peak (Tm)was observed as the endothermic peak of each DSC curve in a temperature range 6om ca. 30 to 40 "C. It is known that cellulose shows neither glass transition nor melting in the dry State 171 . The fact that T, is observed by the introduction of CL chains suggests that the main chain becomes less restricted and that some parts of the main chain can rotate 6eely. At the m e time, the introduced PCL chains associate and form the crystalline region. When the sample is quenched in the conditions as outlined above, a part of the amorphous chains rearranges during heating. It is also observed that cold crystallization occurs in a broad temperature. This indicated that the higher order structure of amorphous chains of CellPCL's is distniuted in a wide range when the sample is quenched from the molten state. As shown in our previous study [3] , it was found that cellulose acetate-based PCL showed T,at around -70 to do "C. In cellulose based polycaprolactones (CAPCL's) 3 hydroxyl groups per each glucose unit of cellulose are substituted by C L Accordingly, it is reasonable to consider that the molecular chains of CellPCL are bulky enough to show low T,value, even if CUOH ratios are low. Fig. 4 shows the relationship between T, , d C pand ClJOH ratio of CellPCL samples which were cooled at 40 "C 6om 120 "C to -120 "C. This figure shows T i s of CellPCL's increased and reached a maximum at 5 moVmol and then decreased with increasing CUOH ratios over 5. However, dC, of CellPCL's decreased in the CUOH ratios below 5 and then increased in the CUOH ratios over 5. This suggests that the matrix of CellPCL's becomes slightly flexible due to side chain association when CUOH ratios are over 5. When CL /OH ratios are below 5 the crystalline region increases by the increase of side chain, molecular packing. A slight decrease of T, at a high CUOH ratio can be explained by the molecular distortion of molecular chains in the amorphous region that exists between the crystallites. Fig.5 shows the relationship between T,, dH,and CUOH ratio of CellPCL samples which were cooled at 40 "C /min from 120 "C to -220 "C. This figure shows T , ' s with CellPCL's slightly increase with increasing CUOH ratio. The increase of both T,,, and AH, indicates that the crystalline regionincreases with increasing CWOH ratio.

284


1 -so

-100

o T /·C

so

100

Fig. 3 DSC heating curves of cellulose PCL derivatives (Cooled at 40°C /min to -120°C)

-55

0.5 0.4

-60

blI

E

p

I I I

\

40

>

\

.. \

\

I

-.

\

\ \ ....... ..\

60

- -_-.\

\

\

80

100

"C

Stability of Relative Humidity as a function of temperature

Thennomechanical analysis system

d

3 19

e C

\

(II

4-

u1

0.1

1 x108 -

0.02 10

20

30

40

50

60

70

80

T / "C

Figure 3.

Dynamic viscoelastic properties of nylon 6 conditioned at various humidity

MEASUREMENT EXAMPLE Fig. 3 shows the DMA curves of nylon 6 measured with the DMS6100 under humidity controlled environments. Storage modulus E' and tan 6 measured at 1 Hz are plotted as a function of temperature at 0, 20, 40, 60, and 80%RH, respectively. It is evident from the data that glass transition temperature decreases with increasing relative humidity. The moisture absorbing properties of nylon have been widely studied and are well known. The amide group (-NH-CO-) acts as a hydrophilic: functional group. A humidity controlled system to study such properties not only provides a critical means for quantitative measurement of this shift, but also gives an insight to plasticization effects on such polymers.

REFERENCES 1. S . Yano, M. Kodomari, N. Okubo, The dynamic viscoelastic properties of hydroxypropyl cellulose/silica-gel hybrid, In: The Pacific Conference on Rheology and Polymer Processing '94, 1994, pp. 309-310 2. Y. Ichimura, In: Handbook of Calorimetry Measurement and Thermal Analysis, The Japan Sociaty of Calorimetry and Thermal Analysis, Maruzen, Tokyo, 1998, p. 240 3. H. Kato, T. Nakamura, N. Okubo, Application of Thermomechanical analysis with controlled atmosphere system, In: The 341hJapanese Conference on Calorimetry and Thermal Analysis, 1998, pp. 236-237

EFFECT OF WATER ON MOLECULAR MOTION OF ALGINIC ACID HAVING VARIOUS GULURONIC AND MANNURONIC ACID CONTENTS *Masato Takahashi'), Yuka Kawasaki", Tatsuko Hatakeyama') and Hyoe Hatakeyama" ')DepartmentofFine Materials Engineering, Faculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Ue& Nagano 386-8567, J q o n

''Department of Textile Science, Faculty of Home Economics, Otsuma Women's University, 12 Sanhancho, Chiyoda-ky Tokyo 102-8357, Japan

"Depmfment of Physics and Chemistry, Farulty of Engineoing, F u h i University of Technology, 3-6-1, Gakuen, Fukui 910 -8505, Japan

ABSTRACT The effect of water on the molecular motion of alginic acid (Alg) was investigated by differential scanning calorimetry. Alg is a copolysaccharide consisting of guluronic (G) and mannuronic acid (M). A phase diagram of water-Alg with various M/G ratios, such

as 1.20, 0.88 and 0.18 , was established over a water content (= W, = gram of water/gram of dry Alg) ranging from 0 to 3.0 g/g. When the system was quenched from 50 to -1OO"C, glass transition, cold crystallization, pre-melt crystallization, melting and liquid crystal transition were observed from the low to high temperature side. The Wc range where the glassy state and liquid crystalline state are formed increased with increasing M/G ratio. This suggests the molecular flexibility of M constituent is higher than that of the G constituent, since the hydroxyl groups of the M acid are located to facilitate easy contact with water molecules. This is also supported by the fact that the amount of bound water in the systems increases with increasing M/G ratio.

INTRODUCTION Alginic acid (Alg) is a polysaccharide extracted from seaweed. Morns and coworkers studied the conformational structure of Alg and suggested that Alg is the copolysaccharideconsisting of guluronic acid (G) and mannuronic acid (M) [ 1-31. The

322

New polymers and matenals

physical properties of Alg/water systems depends on the M/G ratio.

In our previous

studies, phase diagrams of various polysaccharide-water systems have been investigated

as a function of water content W, (= weight of water in gram / weight of dry plysaccharide in gram) by differential scanning calorimetry (DSC) [4-201. In general, glass transition of water-plysaccharide complex domain, cold crystallization, melting of water and liquid crystal transition were observed from low to high temperature side in the phase diagrams.

Therefore, it is very important to investigate the effect of M/G ratio on

the transition temperatures described above. In this study, phase diagrams of water-Alg with various M/G ratios were determined by differential scanning calorimetry (DSC), and the effect of water on the molecular motion of Alg with various M/G ratio is discussed.

EXPERIMENTAL Alg was supplied by &bun Food Chemical Co. The values of G/M-ratio and limiting viscosity Q are listed in Table 1. The sample was prepared in an aluminum

(Al)sealed pan. The solvent used was pure water, provided by Wako Pure Chemical Industries L.t.d. The desir'ed amount of dry Alg and excess amount of water were put into an Al sealed pan, and then sealed when the water content Wc reached the desired amount by the evaporation of water.

The experimental procedure is reported elsewhere

in detail[6, 8, 9, 111. The water content is defined by

Wc = weight of water in grams 1weight of dry Alg in gram (1) The sample was annealed at 40 "C for 1 hr in order to ensure homogeneity before DSC measurements.

Table 1. Values of M/G ratio and limiting viscosity Code Name

M/G

350M 500M

0.88

350G

0.18

1.28

Q

of Alg samples used. 7) (CP)

380 550 355

In DSC measurements, the measurement was carried out in a N2 atmosphere. The sample was cooled to -150 at 10 "Clmin and then heated to 85 at 10 "C/min after

"c

holding at -150 "C for 10 min.

"c

After the measurement was completed, a small pinhole

was made and the sample dried in an oven.

The final value of Wc was determined by

Effect of water on alginic acid

4

323

.1 Y

w

w

120

175

230

285

- 175

I

I

120

T(K)

230 T(I0

285

340

Figure 1. DSC curves of SOOM/water systems with W, = 0.56: (a) and 1.83: @) measured in heating process at 10 "C/min.

sz

250

200 150 100

i

0 0.5

A

1

1.5

2

2.5

Tpc Tcc

3 3.5 4

wc (dg)

300 jC"250

F 200 150 100

Figure 2. Phase diagrams of Aldwater systems composed of 350G: (a), S00M (b) and 3SOM: (c) determined by DSC measurements.

324


weighing the dried sample.

RESULTS AND DISCUSSION Figure 1 shows DSC heating curves of SOOM/water systems with Wc = 0.56 g/g.

As shown in Figure

l(a),

glass transition

(T,),

cold

crystallization

(To),

premeltcrystallization (TJ, melting of water (TJ and liquid ~ ~ y s t to a l isotropic liquid transition (T*) temperatures were observed from low to high temperature side. T,,,,, are hardly observed for the sample with Wc as shown in Figure. l(b).

T,, and

Figure 2 shows phase diagrams of water/Alg systems with three different M/G ratios. From the phase diagrams thus obtained, the following results were obtained. transition temperature T, increased with the increase of M/G ratio.

Glass

Wc range, where the

glassy state and liquid crystalline state are formed, increased with increasing M/G ratio. On the other hand, the Wc range where the premelt crystallization temperature Tpcwas

observed decreased with the increase of MIG ratio. 350

300 250

-.

200

ol

1

150

I

a

100

so 0 0

0.5

1

1.5

2

2.5

3

3.5

4

wc (919)

3 50

300 250

-.

Figure 3 . Relationship between the enthalpy of melting, A H,, of Aldwater

200

0

LI

2

systems composed of 3SOG: (a), 500M: @) and 3SOM: (c) and Wc.

150

r

a

100

50 0

0

0.5

1

1.5

2

2.5

wc (919)

3

3.5

4

Effect of water on alginic acid

325

Figure 3 shows Wc dependence of the enthalpy of melting of 1 mg of water in systems with various M/G ratios. From Figure 3, it is concluded that the W, range where all

-

-

water molecules behave as non-freezing water increased with the increase of M/G ratio, i.e. 0 0.3 for 350G, 0 0.4 for 500M, 0 -0.5 for 350M. The experimental results obtained here seem to show that the molecular flexibility of the M constituent is higher than that of the G constituent, since the hydroxyl ;groupsof M acid are located to facilitate easy contact with water molecules.

ACKNOWLEDGEMENT This work was supported by Grant-in-Aid for COE3 Research (10CE2003) by the Ministry of Education, Science and Culture of Japan.

REFERENCES 1). E. D. T. Atkins, I. A. Nieduszynkins, W. Mackie, K.. D. Parker and E. E. Smolko, ‘Structural Components of Alginic Acid. , The Cryslalline Structure of Poly-P-D Mannuronic Acid. Results of X-ray Diffraction and Polarized Infrared Studies’,

Biopolymers, 1973, 12, 1865-1878. 2). E. D. T. Atkins, I. A. Nieduszynkins, W. Mackie, K. D. Parker andE. E. Smolko, ‘Structural Components of Alginic Acid. . The Crystalline Structure of Poly-a-LGuluronic Acid. Results of X-ray Diffraction and Polarized Infrared Studies’, Biopolymers, 1973, 12, 1879-1887. 3). A. Haug, B. Larsen and 0. Smidsrod, Acta Chem. Scand., 21,691 (1967). 4). K. Nakamura, T. Hatakeyama, and H. Hatakeyama, ‘Studies on Bound Water of Cellulose by Differential Scanning Calorimetry’, Text. Res. J., 1981, 51, 607-613. 5). K. Nakamura. T. Hatakeyama, and H. Hatakeyama ‘Effect of Bound Water on Tensile Properties of Native Cellulose’, Text. Res. J., 1983, 53, 683-688. 6): T. Hatakeyama, K. Nakamura, H. Yoshida and H. Hatakeyama, ‘PHASE TRANSITION ON THE WATER-S ODIUM P IDLY(STYRENESU LFONATE) SYSTEM’, ThermochimicaActa, 1985, 88,223-228. 7). T. Hatakeyama, H. Yoshida, and H. Hatakeyiuna, ‘A differential scanning Calorimetry study of the phase transition of the water-sodium cellulose sulphate system, Polymer, 1987, 28, 1282-1287. 8). T. Hatakeyama, K. Nakamura and H. hatakeyama, ‘DETERMINATION OF BOUND WATER CONTENT IN POLYMERS BY DTA, DSC AND TG’, Thermochimica Acta, 1988, 123,153-161. 9). T. Hatakeyama, K. Nakamura, H. Yoshida, and H. Hatakeyama, ‘Mesomorphic

326


properties of highly concentrated aqueous solutions of polyelectrolytes from saccharides ’, Food Hydrocolloids, 1989, 3, 301-31 1. 10). H. Yoshida, T. Hatakeyama and H. Hatakeyama, ‘Glass Transition of Hyaluronic Acid Hydrogel’, Kobunshi Ronbunshu, 1989, 46, 597-602. 11). H. Yoshida, T. Hatakeyama, and H. Hatakeyama, ‘Phase transition of the waterxanthan system’, Polymer, 1990, 31, 693. 12). K. Nakamura, T. Hatakeyama, and H. Hatakeyama, ‘Formation of the Glassy State and Mesophase in the Water-Sodium Alginate System’, Polym. J . , 1991, 23, 253. 13). T. Hatakeyama and H. Hatakeyama, Polym. Adv. Technol., 1,305 (1991). 14). T, Hatakeyama, N. Bahar, and H. Hatakeyama, ‘LIQUID CRYSTALLINE STATE OF WATER-CARBOXYMETHYLCELLULQSE SYSTEMS SUBSTITUTED WITH MONO- AND DIVARENT CATIONS’, Seni-Gakkaishi, 1991, 47,417-418. 15). K.Nakamura, T. Hatakeyama, and H. Hatakeyama, ‘FORMATION OF THE LIQUID CRYSTALLINE STATE IN THE WATER-SODIUM ALGINATE SYSTEM’, Sen4 Gakkaishi, 1991, 47,421-422. 16). T. Hatakeyama, H. Hatakeyama, and K. Nakamura, ‘Non-freezing water content of mono- and divarent cation salts of polyelectrolyte-water systems studied by DSC’, Thermochim. Acta, 1995, 253, 137-148. 17). T. Hatakeyama, H. Yoshida, and H. Hatakeyama, ‘The liquid crystalline state of water-sodium cellulose sulphate systems studied by DSC and WAXS’, Thermochim. Acta, 266,343 (1995). 18). K. Nakamura, Y. Nishimura, T. Hatakeyama, and H. Hatakeyama, ‘Thermal properties of water insoluble alginate films containing di- and trivalent cations’, Thermochim. Acta, 1995, 267,343-353. 19). J . Ratto, T. Hatakeyama, and R. B. Blumestein, ‘Differential scanning calorimetry investigation of phase transitions in waterkhitosan systems Polymer, 36, 2915 (1995). 20). T. Hatakeyama, K. Nakamura and H. Hatakeyama, ‘Glass Transition of Polysaccharide Electrolyte-Water Systems’, Kobunshi Ronbunshu, 1996, 53, 795-802.

EFFECT OF THE INITIAL STATE ON THE SORPTION ISOTHERM AND SORPTION KINETICS OF WATER BY CELLULOSE ACETATE Hiromi Gocho', Akihiko Taniokaz*, and Toshinari Nakajima3 'Department of Food and Nutrition, Seitoku Jr. College of Nutrition 1-4-6 Nishishinkoiwa, Khtsushika-ku, Tokyo 124-8530, Japan 'Department of Organic and Polymeric Materials, TokyoInstitute of Technology 2-12-1 Ookayama, Meguro-ku Tokyo 152-8S52, Japan 3Doctoral Course of Science for Living System, Showas Women's University 1-7-57 Taishido,, Seiagaya-ku, Tokyo 154-8S33, Japan

INTRODUCTION Cellulose acetate is in a glassy state near room temperature, since its glass transition temperature is about 150°C. Sorption experiments of water by cellulose acetate are performed at 20°C to 30°C because cellulosic materials are usually used around these temperatures. If sorption kinetic measurements of water using this polymer are done in this state, the shape of the sorption kinetic curve strongly depends on the initial state of the sample and the sorption history of the sample. After repeating the same sorption experiments several times, we can obtain data which can be used for the analysis. The sorption isotherm of water using a glassy polymer shows a sigmoid shape' and strongly depends on the state at 0% relative humidity, which is determined by the drying procedure. These problems are due to the fact that the state of the glassy polymer is determined not only by the state variables, i.e. pressure (p) and temperature (T), but also requires a third state variable, the so-called ordering parameter (5)for full characterization of its statezv3. In this study, the sorption kinetics and sorption isotherm phenomena of water using cellulose acetate are examined based on non-equilibrium thermodynamics' though there are no optimum methods to exactly determine the 5 parameter at this time.

EXPERIMENTAL Samples A commercial cellulose triacetate film, whose acetyl group degree of substitution was 2.71, was partially hydrolyzed in a 1N NaOH aqueous solution at 25°C. The reaction times were 0, 1, 3, 5 and 7 days in order to obtain samples which had various degree of acetylation, that is 42.2%, 38.9%, 32.2%, 27.6% and 11.8%, respectively. After the hydrolysis, the cellulose acetate film was immersed in benzene for 1 hr and ethanol for 1 hr, and subsequently washed in distilled water. The prepared samples were then kept in water at 80°C for 3 hr before air drying. The degree of acetylation was determined using the acetyl group microanalysis method based on saponification and successive titration by NaOH.

328


Measurements of sorption kinetics The measurement of the sorption kinetics was made using the spring balance method. Seventy mg rectangular-shaped samples were hung at the bottom of the quartz spring balance in the vacuum chamber made of Pyrex glass connected to a vacuum pump and humidity controller via glass cocks. The temperature in the vacuum chamber and the humidity controller was kept at 20°C by circulating water around them. First the vacuum chamber was evacuated by the vacuum pump for several hours and successively the water vapor at 44% R.H. was introduced into it. The relativc humidity (R.H.) was controlled by a saturated K2C0, aqueous solution. The change in the length of the quartz spring balance according to the water vapor sorption by cellulose acetate was measured with a cathetometer as a function of time and converted to the weight change from the calibration curve between length and weight. After a sorption kinetics measurement, the sample was dried in order to make the next measurement of sorption kinetics. The measurements were repeated several times before obtaining a reproducible curve.

Measurements of sorption isotherm Samples dried by three different procedures (A, B and C) in weighing bottles were placed in desiccators for 10 days where the humidities were controlled by various saturated aqueous salt solutions. The weighing bottles with the samples were removed from the desiccator for quick weighing. After weighing, the bottles were This placed back in the desiccator. After 10 days, they were again weighed. procedure was repeated every 2 or 3 days until the weight change was within t0.05%. The measurement temperature was 2O0CkO.2"C. The water content in the polymer (water regain), V, was represented by the weight of sorbed water (8) per weight of dried polymer (g) as a function of Telative vapor pressure, x. Sample A is the sample that was dried by P,O, at 20°C. Sample B is the sample that was evacuated for 2hr at 105°C and Sample C is the sample that was first dried by P,O, at 20°C and successively cvacuated for 2hr at 105°C after once sorbing water. The degree of acetylation for the sample, which was used in this experiment, was 27.6%.

RESULTS AND DISCUSSION In Fig. 1, the changes in the adsorbed water (Q: g/g-dry polymer) by the cellulose acetate film with a 42.2% degree of acetylation are shown as a function of time (t: min). The experiments were repeated 7 times before obtaining a reproducible curve. Sorption kinetic curves for the samples with 38.9%, 32.2% and 27.6% degrees of acetylation are very similar to those in Fig.1. In Fig. 2, Q is shown for the film with an 11.8% degree of acetylation as a function of t. The repeated experiments were done only 4 times. Since the glass transition temperature of cellulose acetate is about 150"C, these samples are in glassy state before water sorption and still with a low water content. The shape of the sorption kinetic curve strongly dcpends on the initial state of the sample and the sorption history of the sample. Aftcr repeating the experiments several times, the curve is summarized in its final form. This situation is affected by the acetyl content. The state of the glassy polymer is determined not only by the state variables, is., pressure (p) and temperature (T), but also requires third state variables, the so-called ordering parameters (t,,E2 5,) for full characterization of its state.

-

Sorption isotherm and sorption hnetics of water

329

These ordering parameters are defined by the affinity (A,) of the actual state of the polymer membrane where A, is equal to the chemical potential difference of the polymer in its actual state, ~.lp(T,p,E,),minus the chemic:al potential of an equilibrium state, pp(T,p,C=O), of the polymer. The sorption isotherms and the sorption kinetics of water by cellulose acetate were analyzed by the model based on nonequilibrium thermodynamics. If the degree of acetylation decreases, we can reduce the number of

0.05 C

a

E n

0.04

0.03

2

.

P 0.02 CI)

z

CI)

0.01

0 0

50

100

150

200

t (min)

Fig. 1 Sorption kinetic curves of water by cellulose acetate film with 42.2% degree of acetyla-tion as a function of time (min) at 20 "C. Q is the amount of sorbed water ( g ) per dry polymer (g). The sorption experiments are repeated 7 times with the same sample and under the same conditions. 0 indicates the 1st sorption experiment, the 2nd, X the 3rd, 0 the 4th, A the 5th, A the 6th and 0 the 7th. 0.05 L h L

'

0.04

21 -

2

P

0.03 0.02

0)

v

0

0.01 0 0

50

100

150

200

t (min)

Fig. 2 Sorption kinetic curves of water by cellulose acetate film with 11.8% degree of acetyla-tion as a function of time (min) at 20 "C. Q is the amount of sorbed water (8) per dry polymer (g). The sorption experiments are repeated 4 times with the same sample and under the same conditions. 0 indicates the 1st sorption experiment, the2nd, X the3rdand 0 the4th.

330


!i

-

0.08 -

) .

g

0.06

-

2

u 0.04 m m

. * ;

0.02

1

0 0

10

20

30

40

50

Degree of Acetylation (%)

Fig. 3 Amount of saturated sorbed water per dry polymer (Q,) during the final stage of the repeated sorption experiment as a function of the degree of acetylation. repeated experiments before obtaining the final curve. Fig.2 shows that the curves for four trials had the same value, which is similar to the case for a rubbery polymersolvent system. In Fig. 3, the amount of saturated sorbed water Q, (gig-dry polymer) during the final stage of the repeated experiments are shown as a function of the degree of acetylation. R decreases with increasing degree of acetylation because the sample, which has the high acetyl content, is hydrophobic. Sorbing the water by cellulose acetate decreases the glass transition temperature. The sample with degree of acetylation 11.8% seemed to have become rubbery with the high water content because we cannot observe a large difference between each trial. In Fig. 4, the ratio of the sorbed water at time t to the saturated sorbed water for various samples, QJQ,, with different degrees of acetylation are plotted as a function of tin. These curves are not linear at the early sorption times, which indicates that they are not Fi~kian'.~. However, we can estimate the apparent diffusion coefficient of water through the cellulose acetate, Dapp,from the curve whose degree of acetylation is 38.9% because the linearity is higher than that of the other curves. Therefore, Dapp was determined to be about 3 ~ 1 O ' ~ c m ~ / s . Taking into account the QJQ, -tlR curve for the 11.8% degree of acetylation, it shows a typical non-Fickian figure though we cannot find the deviation among the curves as shown in Fig. 2. In this case, it is suggested that the distribution of the ordering parameter is very low. Fig. 5 shows the sorption isotherms for the cellulose acetate films for various drying procedures. The degree of acetylation for this sample is 27.6%. A shows the sample which was dried using P,O, at 20"C, B shows the sample which was evacuated for 2hr at 105"C, and C shows the sample which was first dried using P,O, at 20°C and successively evacuated for 2hr at 105°C after sorbing water one time. The amount of water sorbed by each sample is in the order C>B>A. The shape of the sorption isotherm strongly depended on the initial state of the sample, which was determined by the drying procedure. Applying the modified n-th layer BET equation as shown in

Sorption isotherm and sorption kinetics of water

331

equation (1) below to the sorption isotherm, the total number of adsorption sites in the

0.8 0.6

~

9

U-

0.4

0.2 0

5

0

t 112

10

15

Fig. 4 Sorption kinetic curves as a function of tln at 20°C for various samples with different degree of acetylation. QJQ, indicates the amount of sorbed water at time, t, shows the sample whose degree of per amount of saturated sorbed water. accetylation is 42.2%, 38.9%, X 32.2%, 0 27.6% and A 11.7%.

0.1

L

0.08

a,

0.06 Q

z

6 0.04

. 0)

0)

iF 0.02 0

0

0.2

0.6

0.4

0.8

X

Fig. 5 Sorption isotherms for the cellulose acetate films using various drying procedures. R is the amount of sorbed water per dry polymer at the sorption equilibrium. The degree of acetylation for this sample is 27.6%. .(A) shows the sample which was dried for 10 days using P,O, at 20°C, H(B) evacuated for 2hr at 105"C, and X(C) first dried for 10 days by P,O, at 20°C and successively evacuated for 2hr at 105°C after sorbing water one time.

332


polymer, V,, the interaction energy between water and adsorption sites, K, and the number of adsorbed layers, n are calculated4,’and listed in Table 1.

(1) where x corresponds to the relative vapor pressure (= p/p,), and (2) K = fmoHC,oH + fmAcCiac fmOHand fmAcare the fractions of unadsorbed sites of the hydroxyl groups and acetyl groups relative to the total number of unadsorbed sites, respectively, and C,, and CIA, are the C parameter in the original BET equation. The following relationship is found between fmOH and fmAc, (31 fmOH + fmAC= 1 According to Table 1 , K and n are constants for drying procedures, A, B and C. On the other hand, V, increased in the order of A, B and C. It suggests that the adsorption site increases if the sample in a glassy state is completely dried as much as possible. In eq.(2) C,, and CIA, should be constant even if the drying procedure is altered. Therefore, fmoHand fmAcare also constant though the number of adsorption sites is changed according to the drying procedure. This result indicates that the existing ratio of the hydroxyl groups and the acetyl groups in the film is not affected by the drying procedure.

Table 1 Parameters of modified BET equation (V,,,, K and n) for the cellulose acetate films’)for three drying procedures*)at 20°C

B 0.034 3.1 3

A v m

K n

0.028 3.2 3

C 0.037 3.2 3

1) The degree of acetvlation this sarnole is-27.6%. . .for .~ ~ ~. ~ . ~ . . .~ 2) A m e s s thesample which was dried for 10 days usin P 0 at 20°C B evacuated for 2hr at 105°C. and C first1 dried for 10 days using P,& at 2 k and kcessively evacuated for 2hr at 105.6 after one water sorptxon. ~~~~~

~

~

REFERENCES 1. T Nakajima and H Gocho, ‘Sorption of the water vapor by vinyl acetate-vinyl alcohol copolymers’, Nihon Kagakukaishi, 1978, 10, 143 1- 1436 2. S Motamedian, W Pusch, A Tanioka and F Becker, ‘Sorption isotherms of gases by polymer membranes in the glassy state; An explanation based on the nonequilibrium thermodynamics’, J. Colloid and Interface Sci., 1998,204, 135-142 3. R N Haward, Ed., The Physics of Glassy Polymers, Applied Science, London, 1973 4. H Gocho, A Tanioka and T Nakajima, ‘Sorption isotherm analysis of water by hydrophilic polymer composed of different adsorption sites using modified BET equation’,J. Colloid and Interface Sci., 1998,200, 155-160. 5. J Crank and G S Park, Ed., Diffusion in Polymers, Academic, London, 1968 6. J Crank, The Mathematics of Diffusion, Clarendon, Oxford, 1975 7. H Gocho, H Shimizu, A Tanioka, T -J Chou and T Nakajima, ‘Effect of acetyl content on sorption isotherm of water by cellulose acetate: Comparison with the thermal analysis results’, Carbohydrute Po(ymers, 1999,41,83-86

OSMOMETRIC AND VISCOMETRIC STUDIES ON THE COIL-HELIX TRANSITION OF GELLAN GUM IN AQUEOUS SOLUTIONS Etsuyo Ogawa' I Showagakuita Jr. College, Higashisugano, Ichikawa, Clriba 272-0823, fopan

ABSTRACT Conformational behavior of sodium type gellan gum in aqueous solutions was studied by osmometry and viscometry. Osmotic pressure and intrinsic viscosity mcasuremcnts were carried out in the range from 45 to 15"Cfor aqueous solutions with NaCl (concentration Cs=25, 50, and 75 mmoVdm3). It was found that the Mn values obtaincd at 45, 40, 36, 28, and 25°C with different Cs agreed with cach othcr and the averagc Mn values above 36°C wcrc almost half the valucs obtained at 28 and 25"C, suggcsting association of two molecules. At 32°C unassociated molecules seems to be in simultaneous equilibrium with associated molecules. By lowering tempcrature, the viscosity numbers, vsp/c, of three solutions with different Cs remained almost constant over higher temperature regions but increased rapidly between the regions of 40-35, 3832, and 34-28 "c for the NaCl solutions of Cs= 75,50, and 25 mmoVdm 3 , respectively, and below these temperature regions the values remained again almost constant (NaCI solutions of Cs=75 and 50 mmoVdm3) or increascd gradually (NaCI solutions of Cs=25 mmoVdm3). These variations of vsp/c could be interpreted as a reflection of the conformational transition and association of helices observed from osmometry .

INTRODUCTION Gellan gum is an extracellular microbial polysaccharide produced by fermentation of the organism Pseudomonas Elodea. It has potential applications in the food and biotech-

nological industry because it forms transparent and heat- and acid resistant gels.1 Jansson ct al. established that the chemical structure has a tctrasaccharide rcpcating unit,-.3)- B -D-Glcp-(l-4)- P -D-GlcpA-(14)- B -D-Glcp-(l-+4)- a -L-Rhap-(1-, as shown in Fig. 1. The gelation mechanism of gellan gum solutions has been the subject of controversy, but now it is accepted that gellan gum shows a thermorevwsible conformational transition from a disordered state (single coil) at high tempcrature to an ordercd state (doublc hclix) at low tcrnperature, and junction zones of gellan gcls arc formcd by aggregation of doublc helical gellan molec~les.~-11 Thus, helix formation is a pre-requisite for gel formation.4 The conformational transition temperature of gellan gum has been reported to be around 30"C.s The detailed mechanism, however, has not bccn clarified sufficiently. *13

COI M

CHPH

~

o

&

o

&

o

CHPH

~

o

-

-

HO OH

OH

OH

HO

OH

Figure 1. Rcpcating units of a gcllan gum M =Na molecule.

334


Previously we studied the coil-helix transition of tetramethylammonium gellan gum (TMA-gellan) and sodium gellan gum (Na-gellan) in aqueous solutions by osmometry.12-16 In the present study, the temperature dependence of the conformational properties of Na-gellan in aqueous NaCl solutions by osmometry and viscometry has been investigated.

MATERIALS & METHODS Substrates The sample of Na-gellan were prepared from deacetylatcd gcllan gum, kindly supplied by San-Ei Gen F.F.I., Inc. Osaka, Japan (Lot 62058A), by passing through a column of cation exchangc rcsin (Ambcrlitc IR120B) at 6Ooc.17-J6 Thc conversion to Na salts was checked by measuring the ionic contents of the Na-gelIan samples (Table 1). The Na-gellan was dissolved in aqueous NaCl and stirrcd 2 hours at 60°C. In the case of the osmotic pressure measurements, the Na-gellan solutions were dialyzed for 3-5 days at 45°C against aqueous NaCl and diluted with this dialyzing solvent. Measurements Osmometry was carried out using a Hewlett-Packard High-speed Membrane Osmometer, Model 503, having a special type of glass tube. 12-16 Viscometry was made using an Ubbelohde-type viscometer. The flow time for water in the viscometer utilized was about 250 sec at 20°C.

RESULTS & DISCUSSION Osmotic pressure measurements were carried out at 45 to 25°C for the three solutions (NaCI concentration Cs= 25, 50, and 75 mmovdm3). The n / C plots are shown in Figures 2a-c. x is the osmotic pressure and C the polymer concentration. The 7r /C values increased almost linearly at 45, 40, and 36°C (except for the solution of Cs=75 mmoVdm3 at 36°C) in the observed concentration region. While at 28 and 25°C (and 36°C at CS=75mmoVdm3), the n /C values deviated downward above around C=O.20.4 (lOKg/m3) and the lowest polymer concentrations at which these deviations were observed decreased with increasing NaCl concentrations. In these solutions, we noticed a small increase in the solution viscosities at the same concentration regions. It is supposed that interchain aggregation, which should be responsible for gel formation, may occur at least partly. During the measurements, howevcr, thc solution was stablc as a whole without gelation and good reproducibility of the data was obtaincd. Thcrcfore,

Table 1 . Metal Contents in the Gellan Gum and Na-Gellan Samples.

Sample

Na

K

ca

Mg

Gellan g u m ( h t 62058A)

4300

5YY00

8000

( fl g/g) 1600

Na-gellan gum

300 300 30 36800 Metal contents were measured by flame spectrophotometry (Na,K) and flame atomic absorption spectrometry (Ca,Mg).(Perkin Elmer Model 3100)

Coil-helix transition of gellan gum

a, 25

20

CJrnniol dm-3

335

I

i-.

50

3

15 75

d 10

0

7s

k

45°C

O

- 5

m

0 0 0

28°C

L . . . . . . & A

0 0.0

b,

c/lOKg m-3

CJmmol dm-3

0.2 0.4 c/lOKg m-3

25°C

0.6

Figure 2. (a) Plots of ~r/c VS. C for NaCl solutions of Na-gellan at 45, 40, and 36°C. The solid lines denote the values calculated from eq.2 using the values of M, and A2 at 40°C shown in Table 2. (b)Plots of n / C vs. C for NaCl solutions of Na-gellan at 32°C. The solid line is the values calculated from eq.2 using the values of M, and A2 at 32 "C shown in Table 2 (25mmoVdm3) and an empirical fit to the data (50 and 75 mmol/dm:i). (c) Plots of 7r /C vs. C for NaCl solutions of Na-gellan at 28 and 25°C. The solid lines denote the values calculated from eq.2 using the values of M, and A.2 at 28°C shown in Table 2.

336


below 28°C (and the solution of Cs=75mmoVdm3 at 36°C ) the data in the low concentration region below C = 0.25-0.4 (10Kdm3) were used for the following calculations. It is known that osmotic pressure for the polymer solutions is expressed by the following equation with appropriate value of g.17 E /C = (RT/Mn)[l+A2MnCtg(A2Mn)'C'] t11 Here R is the gas constant, T the absolute temperature, Mn the number average molecular weight, and A2 the second virial coefficient. The parameter g in equation [I] is related to the third virial coefficient, & by: g=A3/A2M. To diminish the third virial contribution, the empirical value g=1/4 is often used. For the Na-gellan aqueous NaCl solutions of Cs= 25, 50, and 75 rnmoUdm3, we showed previously that g values obtained by osmometry were close to 1/4.13-15 By assuming g=1/4, equation 1 can be rewritten in the following form. ( r/C)"2 = (RT/Mn)l/' (1+A2MnC/2) PI Plots of ( i-r /C)1/2 VS. C for the Na-gellan solutions are shown in Figs. 3a and b. The Mn and A2 obtained respectively from the intercepts and slopes of the straight lines are shown in Table 2. The M n values obtaincd above 36°C in three different NaCl solutions were almost coincident and the average values obtained above 36°C were almost half the

b, 5

CJ mmol dm

3 2

3

c/lOKg

m-3

Figure 3 . (a)Plots of ( ~ / C ) 1 / 2vs. C for NaC1 solutions of Na-gellan at 45, 40, and 36°C. @)plots of ( i-r /C)l/2 vs. C for NaCl solutions of Na-gellan at 28 and 25°C.

Coil-helix transition of gellan gum

337

Table 2. Number-Average Molecular Weights and Second Virial Coefficients for the Na-Gellan in NaCl Solutions. CS (mmoUdm3) 25 50 75 CS (mmoUdm3)

25 50 75

M,,

~10-4

-

25

28

32

36

40

9.6 9.4

9.3 9.2 9.6

5.6

4.3 4.4 4.7

4.5 4.5 4.9

II>

.Q

'C

e '" co

I

'C

e '"c-

:l

,

I

..., >.

: I

1

10

I

Co Co

0

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expos~re

periJd (yearf

5

Figure 20 Changes in apparent complex modullus and loss energy with outdoorexposure period.

:

4

r-----;:::==========:::;J _

~

_

-

10

loss energy . Oyear

loss energy - 3yeat'S

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i t~ l_.J..--+--r=======i x2

I

1

o

o

100

200

300

400

0 500

thickness scraped off from the exposed surface(~ m)

Figure 3. Apparent complex modulus and loss energy of samples without surface.

Figure 40 Infrared spectra of the gases evolved from the unexposed and 5 years exposed samples from exposed surface to 100JUIl depth at 300 'C and 400 'Co 3. Weathering analysis of m-PPE using FT IR and SEC SEC is one of the most useful methods for determination of average molecular weights and molecular weight distributions of polymers. Fig.5 shows the changes in number average molecular weight of the scraped powder sample from the exposed

Poly (2,h-Dimethyl- 1,4-Phenylene ether)

345

surface and apparent complex modulus of specimen whose surface layer scraped from the exposed surface. The 3 years exposed sample shows remarkable changes in number average molecular weight within l o o p from the exposed surface, whereas in the case of the unexposed sample, these values were almost constant. These results show good agreement with the result from the DL-TMA method. It was demonstrated that the apparent complex modulus and loss energy from the DL-TMA method correlated fairly we11 with the number average molecular weight or weight average molecular weight (Fig.6).

-! r 1.2

0

Y

canplexmoblu

i E

1.10'

f

l.' 1

x

8

0.9 0.8

$a g 0.7

n

0.6

Figure 5. Changes in number average molecular weight of scraped powder and apparent complex modulus of scraping layer from the exposed surfice

5

-L

4

.-0

3

0.8

1

12

Mn / 10*

1.4

1.6

Figure 6. Relationship between number average molecular weight and apparent complex modulus and apparent loss energy.

I

-C

2Ou m-80u rn

v

2

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expos&

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4

5

Figure 7. Change in gelation ratio of whole samples with increase of outdoor exposure period.

O

'

exporufe penod(year) 4

5

Figure 8. Relationship between IR absorbance ratio (173Ocm"/ 7OOcm-') and outdoor exposure period.

It was observed that the gelation ratio of the whole Sample increased remarkably at the initial degradation period (Fig.7). In the case of m-PPE, it was reported that the

346


increase in the absorption at 3400cm.' (OH) or 1730cm" ( G O ) owing to thermal degradation or photo oxidation [6,7]. In this study, the increasing in absorbance at 173Ocm.' with outdoor exposure period was found. It was observed that the IR absorbance ratio of the sample from the surface to 2Op.m thickness increased remarkably at the initial degradation period, while the absorbance ratio increase was found only after 3 years exposure in the case of the thickness of 20pn to 80pm (Fig.8).

CONCLUSION We measured the degraded surface of the m-PPE by number average or weight average molecular weight, IR spectrum and gelation ratio. It was shown from these experiments that the degradation of the m-PPE used in this study occurred in the range of about l00p.m depth from the exposed surface. It was found that the results from this DL-TMA method have close relation with the molecular weight. The molecular weight of exposed sample changes are associated with the cross linking reaction or main chain scission by degradation in the region of the surface. The gelation ratio of whole exposed samples increased according to the outdoor exposure period. The evolution of H20 and C02 from the exposed sample was found to be more than that from the unexposed sample in the initial thermal decomposition state. From these results, it was considered that both the cross linking and main chain scission occurred in the region of the surface of exposed m-PPE. It was proved that surface degradation is detectable with high sensitivity by this DL-TMA method.

ACKNOWLEGEMENTS The authors wish to thank GE Plastics Japan Ltd. for gifts of samples. The authors would like to thank Japan Weathering Test Center for outdoor exposure test. The authors are indebted to Mr. Y. Ichirnura of SEIKO Instruments Inc. for obtaining the DMA and TG-FT IR data.

REFERENCES l)I.C.McNeill, M.H. Mohammed, Polym. Degrad. Stab., 1997,56,191 2)S.Zulfiqar, M.Rizvi, A.Ghaffar, I.C.McNeill,I. Polym. Degrad. Stab.. 1996,52,341 3)Y.Nishimoto, H.Nagata, Y.Nagai, F.Ohshi, Kobunshi Ronbunshu, 1997,54,119 4)S.H.Hamid, and W.H.Prichrd, Polym. Plast. Technol. Engng, 1988,27,303 5)M.Suzuki, and C.A.Wilhe, Polym. Degrad. Srab., 1995,47,217 6)T.Tanakq T.Fujimoto, K .Shibayama, Kohunshi Ronhunshu, 1977,34,377 7)J.D.Cooney, Polym. Eng. Sci., 1982,22,492

NON-DESIRABLE CARBOHYDRATE REACTIONS IN PULPING AND BLEACHING Goran Gellerstedt'. and Jiebiiig Li' 'Department of P u b and Paper Chernishy and Technologv Royai Instiiute of Technology,SE-100 44 Stockholm. Sweden

ABSTRACT

The remaining lignin content in chemical pulps is usually measured as the "Kappa Number" and, fiequently, this number has been transformed into a corresponding amount of residual lignin. In this paper it is demonstrated that the kappa number does not correlate exactly with the amount of remaining lignin Other oxidizable groups present in the pulp carbohydrates can also contribute and the extent of this contribution can vary largely depending on wood species and pulping procedure. In a subsequent bleaching operation these carbohydrate derived structures may or may not react depending on the bleaching agent(s) employed. This, in tim can result in bleached pulps still having considerable amounts of reactive but colourless structures being chemically attached to the fibre polysaccharides. The major contribution fiom the carbohydrates to the kappa number is hexenuronic acid which is formed under alkaline pulping conditions. In addition, other, still unknown, carbohydrate structures formed in the pulping process can contribute to various extents depending on the process and wood species. In the paper, a summary of our present knowledge concerning the structure of the carbohydrate derived reactive structures in haft pulp fibres, unbleached and bleached, is presented.

INTRODUCTION In haft pulping, wood is delignified at around 160-170 "(3 by the action of strong alkali which, together with hydrogen sulfide ions, promote cleavage of the lignin macromolecule into smaller alkali soluble hgments. The resulting unbleached kraft pulp is brownish in colour and still contains around 2-5% lignin attached to the fibres. In a subsequent bleaching operation, this lignin is removed leaving a colourless cellulosic fibre. The colour of haft pulps has usually been attributed to the presence of lignin which in the pulping process is modified such that chromophoric groups are introduced (1). In a model experiment with cellulose this view has, however, been modified (2). Thus, haft pulping of pure cellulose results in a certain formation of chromophores in the resulting "pulp" although the same experiment carried out in the presence of lignin gives an even more discoloured pulp. In the same investigation it was also shown that krafi pulping of cellulose in the presence of either xylan or glucomannan likewise gave rise to a discoloured cellulose. The results are summarized in Fig. 1 which also shows the UV-absorption curves of the pulping liquors corresponding to the various experiments described above. From the UV-spectra it can be seen that experiments carried out with only polysaccharides present result in an absorption maximum around 300 nm whereas the experiment with lignin gives a maximum around 280 nm. The latter

348


is well-known and attributed to the lignin aromatic ring while the identity of the former

Polymer

Brightness of "pulp"

UV-spectra of liouors Absorbance

A. Cellulose

80.1

B. Cellulose t Lignin (25%)

65.6

C. Cellulose + Xylan (25%)

69.5

r

\

D. Cellulose + Glucomnnnan (25%) 72.2

230

250

270

290

310

1.nm

Figure 1. Brightness of the resulting "pulp" as well as UV-spectra of the resulting pulping liquors after kraft pulping of pure cellulose (cotton linters; original brightness 90.5%) in the absence/presence of either lignin, xylan or glucomannan (2). is unknown. The figure also shows one further absorption maximum, viz. at around 260 nm,in the experiment with xylan (curve C). In fiuther work, Theander et a1 were able to demonstrate that simple sugar molecules like glucose or xylose to a small extent can be converted to a variety of aromatic and olefinc structures by treatment with alkali at an elevated temperature (3). These structures are shown in Fig. 2. Such and similar structures have also been found in the black liquor from kraft pulping of pine (4) and it was recently shown that at least the cyclopentenone structures are formed early in the h a f t cook (5), i.e. in that part of the cook when the majority of the hemicelluloses are degraded (Fig. 3). Treatment of birch cnm

won

on

Figure 2. Conversion of either D-glucose or D-xylose to aromatic and olefinic structures by the action of alkali at an elevated temperature (3).

Non-desirable carbohydrate reactions

Krnft rook

+ Black liquor

Pine wood +White liquor --->Pulp R!

349

,OH

Figure 3. Cyclopentenones found in the black liquor after kr& pulping of pine wood (4, 5).

kraft pulp with strong alkali at an elevated temperature has also been shown to result in the formation of cyclopentenone structures. In this case it is not known, however, if these compounds were present in the pulp or formed during the treatment (6). The ability of 4-0-methyl-uronic acids to yield the corresponding unsaturated hexenuronic acid by loss of methanol has been known b r a long time. In pulping, this reaction was fmt described in a model experiment by the use of 2-0-(4-O-methyLP-Dglucopyranosyluronic acid)-D-xylitol(7). When treating this compound with alkali at 150 OC, the corresponding unsaturated compound was found and identified as hexenuronic acid-D-xylitol. In its protonated form, this acid exhibits a UV-absorption maximum at around 230 nm whereas in alkali the maxinium is shifted to 260 nrn (8), i.e. the value found by Theander (see Fig. 1). More recently, the presence of hexenuronic acid as part of the xylan in krafi pulps has been thoroughly investigated by Buchert et al(9). By employing enzymatic techniques coupled with N M R the hexenuronic acid moiety could be identified and quantified directly on pulp samples. Contrary to the traditional sugar analysis based on acid hydrolysis, this type of analysis does not result in any degradation of the acid sensitive hexenuronic acid. Alternative analytical methods for the quantificationof hexenuronic acid in pulp samples have been developed and give results in good agreement with each other (10). In chemical pulping, the kappa number is fiequently used as a tool for process control. The method is based on the oxidation of a pulp .sample with an excess of acidic potassium permanganate, which, under specified conditiims, is allowed to react with the pulp. After 10 min, the unreacted permanganate is determined and the permanganate consumption is calculated. Although the method states that there is no direct relationship between kappa number and lignin content, a conversion factor is often used to calculate the lignin content of the pulp. Kappa number measurements are also used fiequently in technical investigations on pulping and bleaching processes in order to evaluate the degree of delignification. The results are used in e.g. comparisons of the influence of different pulping and bleaching parameters imd of different bleaching agents. As discussed above, there are, however, reasons to believe that not only lignin but also a variety of carbohydrate derived structures may contribute to the kappa number

350


measurement since permanganate is a powerful oxidant. Furthermore, the carbohydrate derived structures may have a different reactivity as compared to lignin thus giving rise to suboptimization of e.g. a bleaching stage if only the kappa number is used for process evaluation. Therefore, an attempt has been made to identify and quantifL different types of structures that can contribute to the kappa number in unbleached and bleached chemical pulps thereby facilitating a more thorough understanding of the chemical structures and changes that take place in the fibres when going from wood to bleached chemical pulp.

RESULTS AND DISCUSSION In order to determine the contribution to the kappa number h-om different types of structural units in chemical pulps, a series of oxidation experiments were carried out using lignin model compounds as well as isolated lignins and a variety of other compounds containing oxidizable functional groups. Based on these experiments, it was found that lignin, irrespective of type and origin, gave a consumption of permanganate in the kappa number method of approximately 11.6 equivalents of permanganate per mole of phenylpropane units. For hexenuronic acid, the corresponding value was found to be around 8.5 equivalents; a value based on both model experiments and on experiments with pulp samples (1 1). Other types of structuresKunctiona1groups can, however, also contribute as shown in Fig. 4. Although the presence of some of these in unbleached pulp fibres have not been unequivocally identified, they all constitute possible structures based on the discussion above. In a series of unbleached chemical pulps, the contribution to the kappa number was determined using the values for lignin and hexenuronic acid shown in Fig. 4.The amount of lignin in the pulps was determined as Klason lignin and recalculated as kappa number. For hexenuronic acid, the recalculation was based on the amount of hexenuronic acid, analysed as described in Ref 12. On all pulps, the kappa number was

1-

1 1 ~ . polymeric lignin

~ ~ ~ _ _ ..._... _ . _ _ _ _ _ _ _ _

-t -____

-0

8

0

E

- 6

0

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____....!?&8:6

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hexeneuronic acid

7.7

\

0 .0 05

0.22

0.14

0.081

a

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04

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5.7

Small contributors

t

Noticeable contributors

:

2.0

n

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Figure 4. Different types of structuredfunctional groups that consume permanganate

when subjected to a kappa number determination.


35 1

0 other non-lignin mHaxaneuronic acid

Figure 5. The contribution to kappa number fiom Klason lignin and hexenuronic acid with all values re-calculated in kappa number units. The values for "other non-lignin" structures are taken by difference to the analysed kappa numbers in the pulps. also measured directly. As shown in Fig. 5, all pulps gave calculated values that were lower than the actual measured ones with a discrepancy in the order of 2-4 kappa number units, referred to in the figure as "other non-lignin" structures. It can also be seen that the contribution fiom hexenuronic acid varies widely depending on both pulping process and wood species. Thus, soda based processes seem to promote a dissolution or degradation of the hexenuronic acid which, consequently, is present in a very small amount. In birch kraft pulps, on the other hand, the contribution fiom hexenuronic acid is substantial and may, in fact, exceed that fiom lignin. In birch haft pulps, the total contribution to the kappa number fiom lignin is rather small and, consequently, the kappa number does not at all reflect the degree of delignification. Based on the results presented above, a m h e r series of pulp samples was analysed with respect to the contribution to kappa number fiom hexenuronic acid (Table 1). In agreement with the well-known fact that birch kr& pulps usually contain much more xylan and, consequently, more uronic acid groups than pine and spruce pulps it was found that the kappa number contribution was higher for the former. When these pulps

Table 1.

The contribution to kappa number fiom hexenuronic acid (HexA) groups present in some unbleached and bleached hiiftpulps. Bleaching with oxygen (0),ozone (Z) and hydrogen peroxide (P). Q denotes a treatment with chelating agent; n.d. = not determined.

Pulp Unbleached, pine 0-bleached, pine OZQP-bleached, pine OQPQ(PO)-bleached, pine Unbleached, birch OQP-bleached, birch

Kappa No 18.4 10.4 n.d. n.d.

14.5 4.5

HexA contribution 2.3 2.3 0.3 1.9 4.9 3.4

352


-+

Unbleached pulp bleaching

h,,H COOH

Equivalentslrnole

10.8

RxcooH

R

I d c o o H LOOH co

COOH

9.2

4.2

2.0

Figure 6. Consumption of permanganate in the oxidation of various structures assumed to be present in bleached chemical pulps. were subjected to bleaching, none of the investigated sequences was able to completely eliminate the hexenuronic acid, however. Thus, despite being a powerhl oxidant for hexenuronic acid groups in addition to lignin (13), ozone bleaching (2)of a pine kraft pulp sample did not result in a complete elimination of these groups. For bleaching agents like oxygen (0)and hydrogen peroxide (P) which are used in alkaline medium, the kappa number reduction proceeds smoothly but the amount of hexenuronic acid in the pulp is only affected to a small extent (12). The fact that bleaching of krafi pulps does not result in a complete removal of hexenuronic acid (and possibly of other non-lignin structures) is supported indirectly by studies on the heat-induced yellowing tendency of such pulps. Thus, it has been demonstrated that the yellowing tendency of a variety of bleached pine and birch kraft pulps can be reduced after subjecting the pulps to treatment with xylanase (14). In agreement with the discussion above, the birch pulps showed the greatest reduction of yellowing after this treatment. The chemical reactions of lignin in bleaching have been elucidated in a large number of studies both with lignin model compounds and with isolated lignin samples (1 5 ) . In summary, it can be concluded that the aromatic rings generally are the most reactive structures present in the lignin. Chlorine and ozone as well as chlorine dioxide and oxygen are all oxidants which are able to degrade the aromatic ring albeit with very large differencies in reactivity. Hydrogen peroxide, on the other hand, does not react with aromatic rings, whether phenolic or not, unless the peroxide is allowed to decompose into radical species. This bleaching agent is, however, superior in eliminating chromophoric groups and it may also degrade lignin through oxidation reactions in the side chains. In the bleaching of chemical pulps, a successive oxidation of the remaining lignin will thus take place with formation of degraded and partly degraded aromatic rings and/or side chains. At the same time, it can be anticipated that oxidizable non-lignin structures and hexenuronic acid will or will not react depending on the chosen bleaching agent. In the kappa number determination, intact aromatic rings consume 1 1.6 equivalents of permanganate per mole of phenylpropane units as shown in Fig. 4. The contribution &om some other possible structures in unbleached pulps are also shown in that figure. Some other types of structures assumed to be present in bleached or partly bleached pulps give, when subjected to permanganate oxidation, the results shown in Fig. 6. The frst two of these structures are known to be formed when lignin is oxidatively degraded whereas the presence of the furan derivative is more uncertain. The a-ketoacid structure may be present in oxidized carbohydrates. All of these structures contribute to a

Non-de:sirable carbohydrate reactions

353

consumption of permanganate although the number of equivalents is different from that of aromatic rings. The fact that even fully bleached pulps, irrespective of the bleaching sequence, usually have a measurable kappa number can, however, be expIained. In order to further detail the contribution fiom various,structures to the kappa number in chemical pulps, a modified kappa number determination procedure has been developed (16). This is based on the fact that mercury (11) can be used to eliminate double bonds in the so-called oxymercuration reaction. Ifthis is followed by a demercuration step, i.e. a treatment with sodium borohydride, almost all interfering structures can be eliminated leaving the aromatic rings as the sole source of permanganate consumption in the kappa number determination. The reaction sequence, denoted Ox-Dem kappa number, is outlined in Fig. 7. In the first reaction step, hexenuronic acid is eliminated fiom the pulp and dissolved. Other types of double bonds also add mercury(T1)-ions and, after hydroxylation, the mercury(I1)-ions are reductively eliminated by the action of borohydride. At the same time, keto groups present in aldehydes and ketones are reduced to the corresponding alcohol groups. The effects of applying the Ox-Dem kappa number to some unbleached birch krafl pulps are shown in Fig. 8. In these two series of pulping experiments, birch wood was used and the krafi cooks performed under identical conditions with exception of the concentration of alkali. The reaction time at the maximum temperature was varied and is expressed as the H-factor. From both series of cooks, the normal as well as the OxDem kappa number was measured on the resulting pulps. It can clearly be seen that a

Llgnin containing pulp + exceaa of KMnO, Determination of unreacted KMnO,

Figure 7. The reaction sequence employed to selectively analyse the content of lignin in chemical pulps by kappa number determination;the "Ox-Dem" kappa number.

354


160 "C,(HO-]= 0.6 M

160 "C, [HO-J= 1.0 M

Figure 8. Normal and Ox-Dem kappa numbers of two series of birch kraft pulps prepared with variation of cooking time at two different alkalinity levels. large discrepancy exists between the two measured values in any given pulp. An increased alkalinity during the cook results, as expected, in an enhanced delignification rate but it is also obvious that, at a prolonged cooking time, there is a tendency for an increase of the apparent lignin content in the pulp. The reason for this is not known but reactions of the type discussed above (see Fig. 1 and 2) may well be responsible. Two of the birch pulps, both having a normal kappa number around 16, were chosen and subjected to bleaching in an OQP sequence. As before, both the normal and the OxDem kappa number was measured after each bleaching stage. The results are shown in Fig. 9 and demonstrate that the large difference between the two types of kappa number, 18

2 '

I

Unbleached

* 140 C,

(OH-)= 0 . a cook Kormal Kappa No.

* 160 C,

(OH-)= I.0M cook K o m l Kappa No.

1

Aftcr 0 2

I

After OQP 140 C, (OH-I=0.6M COOL

Ox-Dcm-Kappa No.

* Ox-Dcm-Kappa 160 C, (OH-]=1.OM COO^ No.

Figure 9. Normal and Ox-Dem kappa number of birch krafi pulps after bleaching in an OQP sequence.


355

observed after the cook, still remain after the subsequent bleaching operation. Thus, the oxygen (0)bleaching stage is an efficient delignification stage, particularly if the preceding cook is carried out at the lower alkalinity 1evt:l. The hydrogen peroxide (P) stage, on the other hand, does not give much lignin dissolution but it can be seen that the normal kappa number is lowered indicating the presence of structures in the pulp being non-aromatic but reactive towards hydrogen peroxide. These structures are still unknown since it has been shown in other work that hexenuronic acid does not react with hydrogen peroxide under bleaching conditions (1 1, 12).

CONCLUSIONS Based on the results presented in this work as well as the earlier work on conversion reactions of carbohydrates in alkaline pulping, it can be concluded that carbohydrate structures contribute to the kappa number and possibly also to the colour of unbleached chemical (haft) pulps. A major portion of the non-lignin related kappa number originates from hexenuronic acid, formed through elimination of methanol from the uronic acid moieties in xylan. Other non-lignin structures are, however, also present in the pulp in amounts that vary with pulp type and wood species. Indications have been obtained that pulping under non-optimal delignification conditions may result in a formation of new structures in the pulp which behave like lignin in the kappa number measurement. Oxygen is an efficient delignification agent but neither oxygen nor hydrogen peroxide is able to degrade hexenuronic acid thus giving bleached chemical pulps still containing a considerable amount of this structure.

ACKNOWLEDGEMENTS Financial support to one of us (JL) f?om The Swedish Pulp and Paper Research Foundation, Grants No 87 and 21 1, is gratefully acknowledged. The authors are also much indebted to professor Olof Theander for generously sharing his knowledge about carbohydrate reactions in pulping with us.

REFERENCES 1.

J Gierer, The reactions of lignin during pulping, Svensk Papperstidn, 1970 73 571-596.

2.

0 Theander, in S.S. Stivala, V. Crescenzi and I.C.M. Dea (Eds.), Industrial Polysaccharides. The Impact of Biotechnology and Advanced Methodologies, New York, Gordon and Breach Science Publishers, 1987, pp 481-492.

3.

I Forsskal, T Popoff and 0 Theander, Reactions of D-xylose and D-glucose in alkaline aqueous solutions, Carbohydr Res, 1976 48 13-2 1.

4.

K Niemelii,The formation of 2-hydroxy-2-cyclopenten-1-ones from - polysaccharides during haft pulping of pine wood, Carbohydr Res, 1988 184 13 1-137.

5.

F Berthold and G Gellerstedt, Reactive structures formed during the initial phase of a haft cook, 7" int conf Wood and Pulping Chemistry,Beijing 1993. Proceedings 3 160- 163.

356


6.

G Gellerstedt and J Li, Extraction and fractionation of residual lignin from birch kraft pulp, 3'* European Workshop on Lignocellulosics and Pulp, Stockholm 1994. Proceedings 2 15-218.

7.

M H Johansson and 0 Samuelson, Epimerization and degradation of 2-0-(4-Omethyl-a-D-glucopyranosyluronicacid)-D-xylitol in alkaline medium, Carbohydr Res. 1971 54 295-299.

8.

A Torngren and G Gellerstedt, The nature of organic bound chlorine fiom ECFbleaching found in kraft pulp, 9" int symp Wood and Pulping Chemistry, Montreal 1997. Proceedings 1M2- 1--4.

9.

J Buchert, A Teleman, V Harjunpw M Tenkanen, L Viikari and T Vuorinen, Effect of cooking and bleaching on the structure of xylan in conventional pine krafi pulp, Tappi J, 1995 78:ll 125-130.

10.

M Tenkanen, G Gellerstedt, T Vuorinen, A Teleman, M Perttula, J Li and J Buchert, Determination of hexenuronic acid in softwood krafi pulps by three different methods, J. Pulp Paper Sci. 1999 25 306-3 11.

11.

J Li and G Gellerstedt, The contribution to kappa number from hexenuronic acid groups in pulp xylan, Carbohydr Res, 1997 302 213-2 18.

12.

G Gellerstedt and J Li, An HPLC method for the quantitative determination of hexenuronic acid groups in chemical pulps, Carbohydr Res, 1996 294 41-51.

13.

N - 0 Nilvebrant and A Reimann, Xylan as a source for oxalic acid during ozone bleaching, 4h European Workshop on Lignocellulosics and Pulp, Stresa 1996. Proceedings 485-491.

14.

J Buchert, E Bergnor, G Lindblad, L Viikari and M Ek, The role of xylan and glucomannan in yellowing of krafi pulps, 8' int symp Wood and Pulping Chemisw, Helsinki 1995. Proceedings 3 43-48.

15.

C W Dence and D W Reeve, Pulp Bleaching. Principles and Practice, Atlanta, TAPPI PRESS, 1996.

16.

J Li and G Gellerstedt, Oxymercuration-demercuration-kappanumber; A more accurate estimation of lignin content in pulps, 5h European Workshop on Lignocellulosics and Pulp, Aveiro 1998. Proceedings 28 1-284.

Part 6

Bioengineering of new materials

PRECISIOh ANALYSIS OF BIOSYNTHETIC PATHWAYS OF BACTERIAL CELLULOSE BY l 3 C NMR Masashi Fujiwara, Yoshiko Osada, Shunji Yunoki, Hiroyuki Kono, Tomoki Erata and Mitsuo Takai Division of Molecuhr Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan

ABSTRACT The biosynthetic pathways of bacterial cellulose (BC) in Acetobacter xyfinum were precisely examined by using culture media containing D-( 1- ” C)glucose, (2- l 3 C)glucose or (6-’’C)glucose as the carbon source. Quantitative analysis of the NMR spectra of the glucose hydrolyzed from synthesized BC allows us to estimate the percentage of which metabolic pathway the fed glucose pass through, such as the pentose phosphate cycle (PC) and Entner-Doudoroff (ED) pathway. The results indicated that the rate of direct polymerization (DP) of glucose intensely increased to 47% by ethanol addition compared to the standard (16%). The other pathways (PC and ED) decreased to 30% from 35%, to 8% from 41%, respectively. From these results, it is considered that the role of ethanol is to act as the energy source for proliferation of cells instead of PC or ED pathways and a large part of the glucose which does not pass through PC or ED is used for BC production through DP. Keywords; Bacterial cellulose, Acetohucter xylinum, Biosynthetic pathways, Labeled ethanol, Labeled glucose, I’ C NMR spectroscopy

INTRODUCTION Bacterial cellulose is an extracellular polysaccharide produced by some species of Acetobacter xylinum. Recently, bacterial cellulose is expected to be one of the novel industrial materials due to its excellent properties, such as high mechanical strength, high biodegradability and so on. However, the production cost for bacterial cellulose is considerably high in the present state to realize mass production. For its efficient production, it would be n,ecessary to elucidate the mechanism of cellulose biosynthesis in microorganisms. The biosynthetic process of cellulose in Acetobacter xylinum has been investigated using 14C-specificallylabeled carbohydrates by Minor and Greathouse et al. in the 195Os[1-5]. Minor et a l . [ l ] found that the presence of ethanol in the culture medium increased the yield of cellulose and the quantity of l 4C labeling in cellulose. Recently investigations using I’ C-labeled glucose as the carbon source with or without addition of ethanol have been reported by Arashida and Kai et af.[6-71.They succeeded in the quantitative I’ C labeling analysis of cellulose dissolved in N-methyl morpholine oxide / dimethy sulfoxide-d6 by I’ C NMR spectroscopy. They showed that the direct polymerization l(DP) of introduced glucose was mainly found, especially with the addition of ethanol. Their technique is useful for estimating the ” C labeling on cellulose, however. there has been a problem that the resonance of the C-6 carbon of anhydroglucose units of cellulose which completely overlapped with that ofN-morpholine

360

Bioengineering of new materials

(a) Glucose from standard BC

I

I

concluded that the carbon of the added-ethanol did not directly incorporated into cellulose molecule.

I

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

Cellulose from the medium containing l 3 C-glucose

L

(b)Glucolu from labeled BC aynthuled from (1-1JC)dhaMl.

Fig. 2 shows the ''C NMR spectra of the labeled glucoses prepared by cellulase-hydrolysis of the I I . i . ir. i. ." . ". i. . . c . P. . . .n . b. . .A i b h L. labeled cellulose produced w from the culture medium Fig. 1 1 X NMR spectra of glucose obtaincd from hydrolysis of bacterial cellulose. Bacterial cellulose is designated as BC. containing D-(1- I' C) glucose, D-(2- C)glucose or D-(6- I ' C)glucose. All the l 3 C signals for each carbon of glucose were previously assigned[9], and their assignments are indicated in Fig. 2. For calculating the percentage of the biosynthetic pathways of cellulose, I' C-labeling ratio (LR, the ratio of introduced C intensity, i.e. observed intensity minus the natural abundance of carbon to that of I

Y

1.

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.

.

a

.

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s

Chemical shift (ppm)

Fig. 2 1 X NMR spectra of glucose obtained from hJdrolysis of bacterial cellulose. The culture medium contained (a) unlabeled glucosc, (h) D-(l-lJC)glucose.(c) I)-(2-l3C)glucose. (d) D-(6-13C)glucose.

Precision analysis of biosynthetic pathways

361

oxide, suggesting that no information was obtained from the C-6 carbon resonance of cellulose. In order to avoid the overlaps between the signals for cellulose and those for the solvents and to estinisite the correct labeling of C-6, we adopted ” C labeled glucoses hydrolyzed from I’ C labeled cellulose by cellulase enzyme for ” C NMR spectroscopic analysis in deuterium oxide. In this paper, the possibility of direct incorporation of added ethanol into cellulose was examined using (1 -I’ C)ethanol. The percentage of the respective pathways for cellulose biosynthesis in .4cetobucter xylinum were precisely determined by our method using D-(l-” C)glucose, Cb(2-I’ C)glucose or D-(6-” C)glucose as the carbon source with or without ethanol. Frorn these results, the mechanism of the increase of cellulose production by ethanol is discussed. EXPERIMENTAL For biosynthesis of C-labeled cellulose, Acetohucter xylinum ATCC 10245 was grown statically in 15ml of Hesrrin-Schramm medium[8] containing D-( I-‘‘ C)glucose, D-(2”C)glucose or 0-(6-”C)glucose (Isotec Inc., Ohio, USA) as 10% of the carbon source. The isotopic purity of the labeled glucoses was 99.0, 98.7, and 99.8%, respectively. In the case of “C-labeled dhanol, 1 (v/v) % of ethanol containing 10 (w/w)% of ( I I’ C)ethanol (Isotec Inc., Ohio, USA) was added in the Hestrin-Schramm medium. After 7days of cultivation at 28 “C, the biosynthesized cellulose was purified by boiling in 1 ( w h ) YOaqueous NaOH solution, thoroughly washed with distilled water, and freeze-dried. The purified cellulose were completely hydrolyzed to glucose units with cellulase (Cellulase ONOZUKA R- 10, manufactured by Yakult Co. Ltd.). The solution of labeled glucose was concentrated using a rotary evaporator, filtered through a

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