THE CHEMISTRY AND PROCESSING OF WOOD AND PLANT FIBROUS MATERIALS
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THE CHEMISTRY AND PROCESSING OF WOOD AND PLANT FIBROUS MATERIALS
THE CHEMISTRY AND PROCESSING OF WOOD AND PLANT FIBROUS MATERIALS Editors: JOHN F KENNEDY Director of Birmingham Carbohydrate and Protein Technology Group, Research Laboratory for the Chemistry of Bioactive Carbohydrates and Proteins, School of Chemistry, The University of Birmingham, Birmingham, England and Professor of Applied Chemistry, The North East Wales Institute of Higher Education, Wrexham, Clwyd, Wales GLYN 0 PHILLIPS Chairman of Research Transfer Ltd, (Newtech Innovation Centre), Professorial Fellow of The North East Wales Institute of Higher Education, Wrexham, Clwyd, Wales and Professor of Chemistry, The University of Salford, England PETER A WILLIAMS Head of the Multidisciplinary Research and Innovation Centre and the Centre of Expertise in Water Soluble Polymers, The North East Wales Institute of Higher Education, Wrexham, Clwyd, Wales
WOOI)HI~AI) PUJ3I~ISf-IING lAIl\/lI~I~ED
Oxford
Cambridge
New Delhi
Published by Woodhead Publishing Limited Abington Hall, Granta Park, Great Abington Cambridge CB21 6AH, UK www.woodheadpublishing.com Woodhead Publishing India Private Limited G-2, Vardaan House, 7/28 Ansari Road, Daryaganj New Delhi - 110002, India www.woodheadpublishing.com First published 1996 Reprinted 2001, 2004, 2005, 2010 © 1996, Woodhead Publishing Limited The authors have asserted their moral rights.
This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publisher 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 Woodhead Publishing Limited. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. ISBN 978-1-85573-305-3
Printed in the United Kingdom by CPI Antony Rowe
CELLUCON CONFERENCES AND THE CELLUCON TRUST 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 field of cellulose and its derivatives. This laid the foundation for subsequent conferences in Wales (1986), Japan (1988), Wales (1989), Czechoslovakia (1990), USA (1991), Wales (1992), Sweden (1993) and Wales (1994). They have had truly international audiences drawn from the major industries involved in the production and use of cellulose pulp and derivatives of cellulose, plus representatives of academic institutions and government research centres. This diverse audience has allowed the crossfertilization of many ideas which has done much to give the cellulose field the higher profile that it rightly deserves, Cellucon Conferences are organised by The Cellucon Trust, an official UK charitable trust with worldwide objectives in education in wood and cellulosics. The Cellucon Trust is continuing to extend the knowledge of all aspects of cellulose worldwide. At least one book has been published from each Cellucon Conference as the proceedings thereof. This volume arises from the 1994 conference held in Bangor, Wales, UK, and the conferences planned to be held in Russia, France and Finland, etc, will generate further useful books in the area.
THE CELLUCON TRUST TRUSTEES AND DIRECTORS Prof G 0 Phillips (Chairman) Prof J F Kennedy (Deputy Chairman and Treasurer) Dr P A Williams (Secretary) Mr T Greenway Mr W B Painting Dr C A White
Research Transfer Ltd, UK The North East Wales Institute, UK and The University of Birmingham, UK The North East Wales Institute, UK Akzo Nobel Surface Chemistry Ltd, UK Hoechst (UK) Ltd, UK Fisons Scientific, UK v
CELLUCON CONFERENCES ORGANISING COMMITTEE Prof G 0 Phillips (Chairman) Prof J F Kennedy (Deputy Chairman and Treasurer) Dr P A Williams (Secretariat) Mr H Hughes (Secretariat) Mr P Bale Prof W B Banks Prof C Bucke Dr H L Chum Dr A Fowler Dr K Geddes Mr T Greenway Prof J Guthrie Dr H Hatakeyama Dr M B Huglin Dr P Levison Dr J Meadows Mr W B Painting Mr A Poyner Mr R Price Prof J Roberts Dr J F Webber Dr C A White
Research Transfer Ltd, UK The North East Wales Institute, UK and The University of Birmingham, UK The North East Wales Institute, UK The North East Wales Institute, UK Hercules Ltd, UK University of Wales, UK The University of Westminster, UK American Chemical Society (Cellulose, Paper and Textile Division), USA Courtaulds Ltd, UK Crown Berger Europe Ltd, UK Akzo Nobel Surface Chemistry Ltd, UK University of Leeds, UK Fukui Institute of Technology, Japan University of Salford, UK Whatman International Ltd, UK The North East Wales Institute, UK Hoechst (UK) Ltd, UK Consultant, UK Shotton Paper Co Ltd, UK Institute of Science and Technology, University of Manchester, UK The Forestry Authority, UK Fisons Scientific, UK
Cellucon Conferences are sponsored by: The Biochemical Society, UK - Chembiotech Ltd, UK - Hoechst (UK) Ltd, UK - The North East Wales Institute of Higher Education, UK - The University of Birmingham, UK - The University of Lund, Sweden - USAF European Office of Aerospace Research and Development - US Army Research, Development and Standardisation Group, UK - Welsh Development Agency - Whatman Specialty Products Division, UK.
Cellucon Conferences are supported by: The American Chemical Society (Cellulose, Paper and Textile Division) Aqualon (UK) Ltd - Akzo Nobel Surface Chemistry Ltd, UK - Courtaulds Chemicals and Plastics, UK - Ministry of Defence - Crown Berger Europe Ltd, UK - DOW Chemicals, UK - The Forestry Authority, UK - The Southern Regional Research Center, USA - Shotton Paper Company Ltd, UK - Syracuse Cellulose Conferences, USA. vi
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
1989 Cellucon '89 UK
CELLULOSE: SOURCES AND EXPLOITATION Industrial Utilisation, Biotechnology and Physico-Chemical Properties
1990 Cellucon '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 11 th Syracuse Cellulose Conference
1992 Cellucon '92 UK
SELECTIVE PURIFICATION AND SEPARATION PROCESSES The Role of Cellulosic Materials
1993 Cellucon '93 Sweden CELLULOSE AND CELLULOSE DERIVATIVES Physico-Chemical Aspects and Industrial Applications 1994 Cellucon '94 UK
CHEMISTRY AND PROCESSING OF WOOD AND PLANT FIBROUS MATERIALS The Chemistry and Processing of Wood and Plant Fibrous Materials
The proceedings of each conference were formerly published by Ellis Horwood, Simon and Schuster International Group, Prentice Hall, Campus 400, Maylands Avenue, Hemel Hempstead, Herts, HP2 7EZ and are now published by Woodhead Publishing Limited, Abington Hall, Abington, Cambridge CBl 6AH. 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 The Research Laboratory for the Chemistry of Reactive Carbohydrates and Proteins, The School of Chemistry, The University of Birmingham, Birmingham, B15 2IT, England. Vll
ACKNOWLEDGEMENTS This book arises from the International Conference - CELLUCON '94 which was held at the University of Wales, Bangor, UK. This meeting owed its success to the invaluable work of the Organising Committee.
MEMBERS OF THE LOCAL ORGANISING COMMITTEE - CELLUCON '94 Prof W B Banks (Chairman) University of Wales, Bangor, UK Dr HOmed (Secretariat) University of Wales, Bangor, UK Dr P A Williams (Secretariat) The North East Wales Institute, UK Mr H Hughes (Secretariat) The North East Wales Institute, UK Prof J F Kennedy The North East Wales Institute, UK and (Deputy Chairman and The University of Birmingham, UK Treasurer) Akzo Nobel Surface Chemistry Ltd, UK Mr T Greenway Whatman International Ltd, UK Dr P Levison The North East Wales Institute, UK Dr J Meadows Hoechst (UK) Ltd, UK Mr W B Painting Research Transfer Ltd, UK Prof G 0 Phillips Institute of Science and Technology, Prof J Roberts University of Manchester, UK
Vlll
CONTENTS Preface
XUl
PART 1: THE FIBRE AND NON FIBRE RESOURCES 1 Forestry - Sustainable production and processing J Evans 2 Changing patterns of global wood and fibre supplies . R J Cooper 3 Blackcurrant stems - An agri-waste with potential as a dilutent to existing tree-based fibre sources . D Stewart and R M Brennan 4 Phenolic acid dimers in barley straw cell walls D Stewart and I M Morrison 5 'Non wood plant fibres'. Availability in Kenya and need for maximum utilization . R M urali and J G M wangi 6 Current developments in plant derived gums and resins for the chemical industry in Kenya B Chikamai
PART 2: PULPING. 7 Advances in steam explosion pulping (SEP) . B V Kokta, Y Ben, J Doucet, A Ahmed and D A Sukhov 8 Kinetics and mechanism of wheat straw pulping . A A Baosman, G C Fettis, M J Ramsden and S J Smith 9 Ethanol pulping of pretreated non-wood fibre materials B Lonnberg, M EI-Sakhawy and T Hultholm 10 The chemical composition of tropical hardwoods and its influence on pulping processes . N A Darkwa 11 Pulping characteristics and mineral composition of 16 field crops cultivated in Finland . K A Pahkala, T J N Mela and L Laamanen 12 Screening, purification and characterization of novel xylanases used in pulp bleaching
1
3 13 25 31
37 49
61 63 81
99 III
119 127
B Cuevas, B Bodie, C Wang and M Koljonen 13
Delignification and bleaching of non-wood fibres with peroxycompounds D Stewart and I M Morrison ix
133
x Contents
14 15
Biobleacbing of pulp and paper mill black liquor in fluidized bed reactor tRng immobilized Phanerochaete chrysosporium BKMF 1767 S S Marwaha, R S Singh, P K Khanna and J F Kennedy ViscositylDP relationships for cellulose dissolved in cuprammonium and cupriethylene diamine solvents J H Morton
PART 3: PHYSICAL AND CHEMICAL PROCESSING OF FmRE AND FIBROUS PRODUCTS 16 Property enhancement of plant fibres for industrial use W B Banks 17 Physicochemical aspects of fibre processing . L Salmen and S Ljunggren 18 The effect of acetic anhydride treatments on the mechanical properties, hydrophobicity and dimensional stability of Russian Fifths and Scandinavian pine M J Ramsden, F S R Blake and N J Fey 19 Recovery of packaging laminate components to enhance waste management . E T Evans, M J Kay, N Kirkpatrick and D SWales 20 Celsol - Biotransformation of cellulose for fibre spinning M Vehilainen and P N ousiainen 21 Concurrent modification of wood with phthalic anhydride in composite manufacture R Salisbury, M Lawther and P Brown 22
23 24 25 26
Engineering composites from oriented natural fibres: A strategy. P E Humphrey Reactive cellulosefibres rather than reactive dyes . D M Lewis and Q G Fan The treatment of cotton cellulose with Trichoderma reese; engineered c e l l u l a s e s . . . A Cavaco-Paulo, L Almeida and D Bishop Characterisation of paperboard packages designed for liquid containment C J Harrold and J T Guthrie Biochemical investigation of cellulosic and lineous materials in museum collections M A Robson
PART 4: PHYSICAL AND CHEMICAL PROCESSING OF FIBRE AND NON FIBROUS PRODUcrS 27 Polymeric materials derived from the biomass A Gandini 28 High performance and highly functional polymeric materials from plant components H Hatakeyama
143 151
159 161 173
183
191 197 205 213 221 227 235
243
249 251
263
Contents
29 30
31 32 33 34
Preparation and physical properties of biodegradable polyurethanes derived from the lignin-polyester-polyol system S Hirose, K Kobashigawa and H Hatakeyama Viscoelastic properties of biodegradable polyurethanes derived from coffee grounds K Nakamura, Y Nishimura, T Hatakeyama and H Hatakeyama The fractional composition of polysaccharides in alkaline pretreated and steam pressure treated wheat straw R Sun, J M Lawther and W B Banks Effects of extraction conditions and alkali type on the yield and neutral sugar composition of wheat straw hemicellulose J M Lawther, R Sun and W B Banks Thermodestmction of cellulose and levoglucosone production G Dobele, G Rossinskaja, B Rone and V Yurkjane Star-shaped and crosslinked polyurethanes derived from lignins and oligoether isocyanates S Montanari, B Baradie, J-P Andreolety and A Gandini
PART 5: APPLICATIONS OF CELLULOSE, CELLULOSE DERIVATIVES, LIGNIN AND CELLULOSE-RELATED ENZYMES 35 The alkaline degradation of cellulose relating to the long term storage of radionuclides in cement J Shimizu, J F Kennedy, L L Lloyd and W Hasamudin 36 The use of cellulose and cellulose derivatives in immobilised systems for the removal of colour from textile effluents N Willmott, J T Guthrie, G Nelson and B Burdett 37 New polymer electrolytes based on modified polysaccharides C Schoenenberger, J F Le Nest and A Gandini 38 Thermal and FfIR studies of Tencel-g-co-Hema and Tencel-g-coHema carbanilates M A Kazaure, J T Guthrie and B B Dambatta 39 ESR as a method for monitoring lignins activity during the interaction with monomer and oligomer silicon containing compounds. T Dizhbite, G Telysheva and G Shulga 40 The regularities of lignosulphonate behavior on different interfaces and its alteration by purposeful modification G Telysheva, T Dizhbite, E Paegle and A Kizima 41 Some physicochemical properties of xylanolytic enzymes produced by Aspergillus fumigatus IMI 255091 . L A Hamilton and D A J Wase 42 Endoglucanase j3-D-glucosidase and xylanase induction in Dichomitus squalens (Karst.) Rid . E Resende, M Carolina and N T Rodeia Index
Xl
277 283 291 313 345 351
359 361 369
377 385
393 399 405 413
419
PREFACE This book illustrates what a remarkable resource is offered to us by wood and related plant materials. The aspects described are of an inter-disciplinary character, and will prove of great value to the wood chemist, biochemist and paper technologist. The subject is developed progressively. It starts with the production, management and changing patterns of global wood and fibre resources. Wood pulping is a traditional area of wood utilisation, but throughout the world there is a need for an injection of new technologies to utilise more fully all the lignocellulosic components and to provide improved environmental processes. Thus, steam explosion, ethanol pulping, the role of enzymic and other biological modifications offer exciting new vistas for both wood and non-wood fibrous materials, as do new synthetic pathways to innovative chemical derivatives. New high performance composite materials, chemically modified wood and related cellulosic products receive expert treatment in this volume, Both physical and chemical processing are dealt with, and new biochemical methods for treating wood are described. Increasingly, surplus cellulosic plant fibre wastes offer a raw material for high performance and functional polymers, which are also biodegradable. Vegetable biomass is now being recognised as a unique starting material. These proceedings also celebrate the tenth anniversary of The Cellucon Trust, specifically set up to promote research and communication in cellulose chemistry. The period has witnessed a renaissance in this subject, and The Cellucon Trust can be justifiably proud of its contribution. From the Cellucon and allied meetings with our Japanese, American, Slovakian and Scandinavian colleagues, ten volumes of diverse research findings have been published. New solvent systems have led to new cellulosic fibres, and new chemistry has provided cellulosics with new functional roles and product fields. It was appropriate that this anniversary meeting should have been held in Wales, the traditional home of Cellucon, and in particular the University of Wales, Bangor. Here forestry science and wood chemistry have been a long established speciality. A new established Chair in Wood Science has been inaugurated in Bangor and we are grateful to Professor W Barton Banks, the first holder of the Chair for organising a happy and innovative conference. Again I thank the Secretariat and members of The Cellucon Trust for their unfailing support. Glyn 0 Phillips Chairman, The Cellucon Trust XlII
Part 1: The fibre and non fibre resources
1 Forestry - sustainable production and • processing J Evans - British Forestry Commission, Alice Holt Lodge, Wrecclesham, Farnham, Surrey, aUIO 4LH, UK
Introduction The world's forest resources are under threat, both real and imagined. Owing to tropical deforestation, air pollution and the possible effects of climate change, the well being of trees and forests has risen very much up the agenda of public concern. The objective of this paper is to provide an overview which focuses on the changing nature of the resource, examines the rise in second growth and plantation forests, and addresses the question of sustainability of plantation forestry in particular. In these ways I hope to answer the question, how secure are the world's forests as a continuing fibre resource? Remarks concerning processing, which my title includes, will be confined to generalisations about log size and future wood quality reflecting the changing nature of the forest resource.
Forest Resources of the World Accurate data on forest areas by countries are notoriously difficult to obtain. Both questions of reporting accuracy and definition of what constitutes forest are amongst the largest sources of error. The Food and Agriculture Organisation of the United Nations (FAD) do publish statistics at approximately 10 year intervals and Table 1, which in part derives from FAD (1992,1993a & b), summarises the position for 1990.
3
4 The fibre and non fibre resources
Table 1:
Global and Regional Forest Statistics (1990)
Forest Mha
land
Deforestation Mha/y
New Planting M haly
Forest! capita (ha)
Africa
630
24
4.1
0.1
0.8
Asia & Pacific
350
35
3.9
2.1
0.2
L. America
820
44
7.4
0.4
2.0
15.4
2.6
Tropical
%
1,800
Americas
720
25
0.3
2.6
1.6
Europe & N. Africa
180
27
-
0.2
0.3
E. Asia
170
16
0.8?
2.0?
0.1
CIS & near East
890
35
-
2.2
2.6
Australasia
120
9
-
<0.1
0.5
Temperate & Mediterranean
2,080
27
1.1
7.0
World
3,880
29
16.5
9.6
0.7
(modified from FAD 1992, 1993a & b) The data in Table 1 indicate the order of magnitude, but should not be pressed beyond the first significant digit, except for totals. Moreover, the definition of what constitutes forest needs defining. In the case of the assessment of forest resources in tropical countries forest was defined (FAD 1993a) as "ecosystems with a minimum of 10% crown cover of trees or bamboos, generally associated with wild flora, fauna and natural soil conditions, and not subject to agricultural practices". Thus the data for tropical and subtropical Africa, Asia Pacific and Latin America include savanna woodlands as well as dense forest, but exclude all trees associated with farms. In the case of countries in the temperate and Mediterranean zone the forest area includes forest itself, defined as land with a tree crown cover of more than 20%, and other wooded land which has some forestry characteristics but including open woodland and scrub and shrub and brushland whether or not used for pasture or range (FAD 1992). Thus, the data in Table 1 are not entirely compatible internally. Nevertheless, it is reasonable to conclude that there are about 4 thousand million hectares of forest and wooded land, about 30% of world's land surface, though of this total land surface less than 20%, or only about 2.3 thousand million hectares are of closed forest of what, in Britain, we tend to think of as forest or woodland.
Forestry - sustainable production and processing 5
Patterns of change
The data in Table 1 show that significant deforestation is largely a tropical or developing country phenomenon. In temperate countries forest clearance is almost always followed by regeneration or replanting to forest and, for many countries, there has been an ongoing programme of afforestation leading to a significant net increase in total forest cover. This point bears emphasising. Mather (1993) reports a 2% increase in European forest cover in the 20 years up to the late 1980s. The example of Great Britain further illustrates this with a doubling of forest cover since 1920 while in Ireland there has been a sixfold increase over this period. Over a longer time period, France has almost doubled in forest cover, from 14 to 25 per cent, since the revolution (1789). The other great disparity revealed in the Table is the amount of forest per person with some parts of the world much better endowed than others. In addition to trends reflected by gross data several other changes are evident owing to change in economic aspirations and political priorities. 1.
Significant areas of forest are not only inaccessible owing to physical limitations, but are increasingly designated as reserves for wildlife, wilderness areas, catchment protection, etc.
2.
Public pressure will tend to accelerate the move away from exploitation of old growth, semi-natural or primary forest types.
3.
The economic, political and population pressures causing tropical deforestation are unlikely to abate.
4.
Investment in afforestation and tree planting for industry, carbon offsets and, especially in the tropics, for social and community benefits will rise.
The resource and wood demand
Global production of wood is estimated at about 3.5 million thousand rrr' annually of which about 45 per cent is wood for industrial processing (FAO 1994). The remaining 55 per cent is wood cut for fuel - firewood and charcoal - or used in the round for domestic purposes such as sticks and poles for fencing, stockades for livestock, and, in many tropical countries, for building homes. Most production and consumption of wood for industrial purposes occurs in temperate regions: almost all use of wood for fuel and domestic needs occurs in developing, mainly tropical, countries. The overall annual demand for wood is equivalent to an average increment of just less than one cubic metre per hectare of the world's forests. Almost all natural woodland types, including open forest formations achieve this, and managed forest and plantations exceed it by several times (Wood, 1975). Globally there is no shortage of forest to provide the world's wood requirement. There is, however, marked regional variation from acute wood deficiency to surplus (Table 1). Moreover, as noted, remaining natural forest may neither readily, nor desirably, be exploited and increasingly wood supply will be obtained from second growth and plantation forestry, whether industrial crops or plantings for social and community purposes in rural development.
6 The fibre and non fibre resources
Environmental threats
In addition to continuing deforestation in the tropics, there is considerable concern about forest health and long-term well being arising from air pollution. Annual surveys of forest condition and direct experiments to study pollutant injury, suggest that at most ambient levels effects are likely to be small and secondary to the impact of drought or poor matching of species with site. Kallio's (1987) pollutant determined increment loss in the IIASA model is probably pessimistic. Indeed in Germany, according to Kandler (1993), average wood increment of forests has been greater in the last 30 years than the preceding decades. The impact of global climate change owing to the rise in carbon dioxide and other 'greenhouse' gases, such as methane and CFCs, is less clear. A substantial fertilising effect from high carbon dioxide concentrations is now largely discounted for long lived forest crops, and the resilience of trees and forests to climatic variations from one year to the next does not point to wholesale, widespread declines in the short term. Disease and pest problems may become more severe, as warmer temperatures or drier conditions may stress some tree species and, for example, accelerate some insect reproduction rates. More likely is disturbance in tree reproduction, such that species at the edge of their natural range may be threatened.
Second Growth Forest and Plantations Across the world as a whole the area of untouched forest is now relatively small. Even in the tropics, where large tracts of forest remain in Amazonia and Zaire, it is now clear that few areas have been entirely devoid of man's influence. According to Poore (1989) more than half of all remaining rainforest has had some significant intervention. In temperate regions data about degrees of intervention in forests are unavailable - even a forest now set aside for national parks and reserves may have been worked in the past. But it is apparent that even countries such as Scandinavia, France and Germany with much forest have a long history of intensive management. Indeed, most of the Black Forest in Germany and, for example, the Foret de Compiegne in France has been extensively planted with silver fir and Norway spruce, and oak respectively. In western North America the large stands of old growth have either been cut or are now mostly in reserve status and future timber supplies will come from second growth which tends to be more uniform in species composition and tree size and more akin to plantation characteristics. Similarly the second growth hardwood resource of north-eastern USA is becoming increasingly important.
The rise in plantation forestry
In temperate countries significant attempts at afforestation and reforestation by tree planting began about 200 years ago and almost all such countries have an ongoing programme today (Savill and Evans, 1986). The scale of such planting, compared with the natural resource, generally remained small, outside of specialist projects such as shelterbelts and windbreaks, until the 1930s when plantation development was seen as one of the public works to alleviate the depression. In the immediate post-war era plantation development accelerated in many countries and in some, most notably China
Forestry - sustainable production and processing 7
and India, enormous planting programmes were undertaken. Mather (1993) traces the history of afforestation in a dozen countries citing the policy factors which influence the development of this kind of forestry. Plantation forestry in the tropics, although of equally long history as temperate regions, was much slower to develop and even by 1965 only about 7 million hectares were established. Since then afforestation has been rapid and the present estimate (Evans, 1992; FAD 1993a) is a total in excess of 40 million hectares - see Figure 1. Planting in the tropics initially concerned development of fast growing industrial plantations mainly of pines, eucalypts and teak, but in the last 15 years has focused more on planting multi-purpose and especially nitrogen-fixing species for planting in rural development to provide domestic and farm needs. Figure 1.
Areas of tree plantations in the tropics and hotter subtropics (millions ha) 30
25 C'CS
.c en c .2
20
o Latin
America
a Asia-Pacific • Africa
15
·E 10 5 O-t----------....~IIo-----a._-
1965
1980
1990
The total area of plantations amounts, at most, to about 150 million hectares today or about 6 per cent of the world's closed forest. Approximately one-third of plantations are in the tropics and warmer sub-tropics. While growth rates will vary enormously depending on success with stocking and site conditions - many plantings in semi-arid areas are growing very slowly - even a conservative average mean annual increment (MAl) of 8 rrr' per hectare per year points to plantations su pplying one-third of the world's wood requirement. Sedjo and Lyon (1990) highlight this increasingly dominant role which plantation forests are playing, and which is expected to rise in the future. In the foreseeable future plantations will supply half of all wood required and second growth forests virtually all the rest.
8 The fibre and non fibre resources
Qualitative consequences for wood supply
Increasing dependence on second growth and forest plantations for timber has several consequences for the type of product supplied to the processor. 1.
Mean size of log harvested will diminish.
2.
Log quality in terms of freedom from knots, will decline, though in some situations straightness may improve.
3.
Uniformity of product per unit area of forest will increase.
4.
The proportion of juvenile wood will increase.
No comment is made on the balance of softwood to hardwood production though Arnold (1991) suggests that use of non-coniferous species is likely to rise faster than coniferous ones.
Sustainability of plantation forestry This review has demonstrated that throughout the world there is increasing dependence upon intensive forestry practices and, in particular, on the establishment of forest plantations to supply wood requirements. However, plantation forestry practice, compared with utilising natural forest, not only requires large capital investment in establishment and infrastructure but also expects a compensating higher yield from the plantation site. This raises the question, can the much higher yields expected from plantations be sustained in the long term? From a management point of view, will second and subsequent rotations of trees produce as much as the first? Concern over maintaining yields is important not only because of the economics of plantation forestry but because it raises the question of what are the sustainable limits of a site's growth potential? Where natural forest has been converted to plantation or plantations established in preference to managing natural woodland, the reason has been primarily the expectation of superior growth rates and higher yields. And, these expectations have generally been realised. Both in much of the tropics and in temperate regions wood increment in plantations is commonly two to five times that of natural forest. Can ecosystems, low yielding in wood under natural processes, be turned permanently into a high yielding resource through careful selection of species, monoculture, optimum harvesting regimes and the other silvicultural tools a forester uses to maximise yield? Evans (1990) reviewed this subject by looking at the few important examples of where yield decline with successive crops had been recorded. The concern of foresters about the effects of trees on a site goes back over 100 years. Indeed the work of Weidemann (1923) in Saxony appeared to confirm the worst fears, at least for coniferous monoculture, that it led to declining yields with each rotation. Since that time the problem has only come to the fore in a large way on three occasions, in S. Australia, Swaziland and central China, and to a lesser extent in several isolated examples.
Forestry - sustainable production and processing
9
Yield decline in successive crops
In South Australia in the 1960s and 70s young second rotation Pinus radiaia showed an average yield drop of 25-30 per cent on most sites compared with the first rotation. Fundamental to explaining this decline, which occurred throughout the state, was not the effects of the trees themselves but the destruction of organic matter in slash disposal at harvesting and the near stagnation of second rotation growth due to weed infestation, notably by grasses. Today, with good silviculture and genetically improved planting stock, most second rotation pine is superior to the previous crop. The South Australian experience led to comparable fears for the exotic pine plantations of the Usutu Forest, Swaziland. Twenty-five years growth monitoring, over three successive rotations of Pinus paiula, has shown for the most part increasing productivity with each rotation (Fig. 2a) and yield decline confined to small areas of phosphate deficient soils derived from gabbro (Fig. 2b) (Evans, 1993). Again grass competition has been a critical factor because the second and third rotation crops were established in largely weed-free conditions, unlike the first rotation which was planted into the inhospitable southern African grass veld. Research by Morris (1993) suggests that this satisfactory productivity position may not last indefinitely owing to increasing litter accumulations with each rotation and consequent interruptions of nutrient cycling. Figure 2a.
Mean height of three rotations of Pinus patula on granite derived soils in the Usutu forest, Swaziland (average of 26c-sample plots). 20
Mean
15
height
(m)
•
1st rotation
lr2J 2nd rotation
10
o
3rd rota tion
5
6
10
14
age (years)
10 The fibre and non fibre resources
Figure 2b.
Mean height of three rotations of Pinus patula on gabbro derived soils in the Usutu forest, Swaziland (average of 9 sample plots). 20
Mean
15
height (m)
111 st rotation ~ 2nd rotation
10
D 3rd rotation 5
6
10
14
age (years)
In China soil degradation under Chinese Fir (Cunninghamia lanceolata) plantations is an accepted fact (Li and Chen, 1992). Yield declines of 10% and 40% in second and third rotation crops respectively, are regularly observed. Numerous detrimental changes have been recorded in soil parameters. However these changes, which are genuine, may well not arise from the fact that successive crops of Chinese fir are grown in monoculture, but rather from the harmful practices associated with crop harvesting and re-establishment. Every part of the tree including bark, leaves and twigs are removed from site in whole tree harvesting, any remaining debris is burnt and whole hillsides are diligently re-terraced: all practices which, directly or indirectly, maximise nutrient loss, conspicuously fail to conserve organic matter, and provide ideal conditions for grass and bamboo invasion (Evans and Hunter, unpublished results). The review by Evans (1990) revealed that there was little direct evidence that intensive plantation forestry practice will itself lead to decline in productivity with successive rotations. In Britain, for example, it has been found that at restocking no phosphate fertiliser is required even though it was essential for establishing the first crop (Taylor, 1990). However, the use of whole tree harvesting could well be detrimental (Proe and Dutch, 1994). Nevertheless, in almost all locations from where reports emanated in the past indicating concern, the explanation for observed lower yields has become clear with the postulate of site exhaustion or direct nutrient removal low on the list of contributory factors. In most cases the role of weeds, especially grasses, and their effect on moisture status in the early years after planting or replanting is now recognised as most significant, along with minimising disturbance and soil compaction, and conservation of organic matter and harvesting residues between rotations. With attention to the above silvicultural practices the hope of improving yields with successive rotations through tree improvement programmes
Forestry - sustainable production and processing
11
must remain the expectation. Overstress of sites is uncommon and where it does occur should normally be containable. One exception to this conclusion may be very short rotation coppice crops grown for energy. For the moment, however, yield decline is the exception rather than the rule.
Conclusions 1.
The world's forests are not about to become depleted of timber. There is no inherent imbalance between global supply and demand in the foreseeable future.
2.
The nature of wood supplied will change as increasing reliance is placed on second growth and plantation forestry.
3.
Little evidence exists to suggest that intensive forestry practices are likely to pose a major threat to long term productivity.
4.
Factors of air pollution and the related issue of climatic change remain uncertain, and may even possess an element of compensation leading to negligible net effects.
References Arnold, J.E.M. (1991). Forestry Expansion - a study of technical, economic and ecological factors. Forestry Commission Occasional Paper No. 36. Forestry Commission, Edinburgh 1991. Evans, J. (1990). Long-term productivity of forest plantations - Status in 1990. Proceedings of the 19th World Congress, International Union of Forestry Research Organisations, Montreal. Vol.1, 165-180. Evans, J. (1992). Plantation forestry in the tropics. Oxford (2nd Edition).
Evans, J. (1993). Long-term experimentation in forestry and site change. In:JLeigh, R.A. and Johnston, A.E. (eds). Long-term Experiments in Agriculture and Ecological Sciences. CAB International, Wallingford, 1994.
FAD (1994). FAO Yearbook of Forest Products 1981-1992. FAO, Rome. FAD (1993b). FAD Yearbook of Production 1992, Vol. 46. FAO, Rome. FAO (1993a). Forest Resources Assessment 1990 - Tropical Countries. FAO Forestry Paper 112. FAD, Rome. FAD (1992). The Forest Resources of the Temperate Zones. The UN-ECE/FAO 1990 Forest Resources Assessment. United Nations ECE/TIM/62, New York, 1992. Kallio, M., Dykstra, D.P. and Binkley, C.S. (eds.) (1987). The global forest sector: an analytical perspective. John Wiley, New York. Kandler, O. (1993). The air pollution/ forest decline connection: the "Waldsteben" theory refuted. Unasylva No. 174, Vo1.44, 39-49. Li, Y. and Chen, D. (1992). Fertility degradation and growth response in Chinese fir plantations. Proceedings of the 2nd International Symposium on Forest Soils, Ciudad, Guyana - Venezuela, pp.22-29. Mather (1993) (ed.) Afforestation - Policies, Planning and Progress. Belhaven Press, London.
12 The fibre and non fibre resources
Morris, A.R. (1993). Forest floor accumulation, nutrition and productivity of Pinus paiula in the Usutu Forest, Swaziland. Symposium on Nutrient Uptake and Cycling in Forest Ecosystems, Halmstad, Sweden, IUFRO, June 1993. Poore, M.E.D. (1989). No timber without trees. Earthscan, London. Proe, M.F and Dutch, J. (1994). Impact of whole-tree harvesting on second rotation growth of Sitka spruce: the first ten years. For. Ecol. Mgt. 66. 39-54. Savill, P.S. and Evans, J. (1986). Plantation Silviculture in Temperate Regions - with Special Reference to the British Isles. Clarendon Press, Oxford. Sedjo, R.A. and Lyon, K.S. (1990). The Long-term adequacy of world timber supply. Resources for the Future, Washington, DC. Taylor, C.M.A. (1990). Nutrition of Sitka spruce on upland restock sites. Forestry Commission Research Information Note 164.
Weidemann, E. (1923). Zuwachsruckgang und Wuchstockungen der Fichte in den mittleren und den unteren Hohenlagen der Sachsischen Staatsforsten. Tharandt. (Seen in Translation No. 302 U.S. Department of Agriculture, C.P. Blumenthal, 1936). Wood, D.J. (1975). The wood situation as it will affect the U.K. Scottish Forestry, 29, 25-38.
2 Changing patterns of global wood and fibre supplies R J Cooper - School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, Wales
Introduction Over the last 40 years the changing patterns of world wood supplies have had a profound influence on the development of the forest industries and on wood processing technologies.
For example the rapid growth of the wood composites
industries has been stimulated by the relative abundance of small roundwood and
wood residues compared with large diameter timber. Similarly the development of sophisticated sawmilling and mechanical pulping technologies over the last 20 years reflects the need to improve yields on costly raw materials. The influence of raw materials supplies on the development of the forest industries is likely to continue in the future and the purpose of this paper is to discuss some of the changes in wood and fibre supply patterns over the next two decades. However before examining wood supplies a brief review of expected world consumption of wood products is presented to place future supplies in a market context.
World Consumption of Forest Products Table 1 summarises FAO's most recent forecasts of forest products consumption through to 2010. 13
14 The fibre and non fibre resources
Table 1 :
World Consumption of Forest Products and Roundwood in 1991 and 2010
Product Sawn timber Wood based panels Paper and paperboard Roundwood Industrial roundwood Fuelwood
Units
1992
2010
million m 3 million m 3
481 126
745 313
Annual % growth 1990-2010 2.2 4.7
million tonnes
237
443
3.2
million m 3
1,638
2,674
2.5
million m3
1,807
2,395
1.4
Source: FAD, 1993.
It can be seen that a global increase in industrial roundwood requirements of about 1 billion m 3, or over 60%, is forecast over the next two decades. Although these FAD forecasts are higher than the projections of some other agencies there is universal agreement that 1) increasing world population and per capita incomes will result in a rising demand for wood, and 2) that rates of consumption growth will be higher in the developing than in the developed world but from a much lower base. However the bulk of the increases in wood use will occur in the developed world with a forecast increase in annual requirements of 650 million m 3 by 2010. (FAD 1993). The possible responses to this demand growth in terms of wood and timber supplies are now examined. Physical and Economic Supply In discussing wood supplies it is important to distinguish between physical and economic supplies. The potential physical supply of wood is the volume of wood which can be cut as defined in forest management plans. Economic supply is the volume of wood actually cut. At a country level the potential physical cut is often referred to as the Annual Allowable Cut. Differences between the allowable cut and actual cuts are affected by a variety of factors of which wood prices, logging costs and the revenue expectations of forest owners will often be paramount. Most projections of future wood supplies are of physical supply potential because of the great difficulties in developing valid models for forecasting economic supplies.
Global wood and fibre supplies
15
Physical Supply Forecasts Resource data and standards of forest management are generally better in the developed than developing world and most forecasts of physical supply potential therefore relate to the developed world. In the developed world the commercial forest area of most countries has increased over the last 30 years in contrast to the loss of forests in the developing world. More significantly the net annual increment of European, N. American and Russian forests has been increasing faster than timber harvests. In broad terms the net annual increment is used as the basis for calculating the annual allowable cut and if this exceeds the annual cut the result is in an increase in the timber growing stock. The gap between the current harvest and the estimated annual increment is therefore an approximate measure of the potential harvest increase which could occur without depleting the total stock of timber. Table 2 shows these data for the major regions of the developed world.
Table 2:
Net Annual Increment and Wood Removals from Commercial Forests in the Developed World. Million m 3 over bark
Region Europe North America Former USSR Total
Net Annual Increment 584 828 700 2,112
Total Wood Production 1990
Difference
367 677 367
217
1,411
701
15]
333
Sources: Kuusela, 1993, ECEIFAO 1993, FAO 1993. Although these data should be interpreted cautiously there is clearly considerable physical potential to increase the cut within the constraint of sustainable timber supply. In addition to the three major supply regions shown in table 2 increases in the physical cut will also be possible in other developed countries particularly in Japan, Australia, New Zealand and South Africa. In the developing world lack of data on natural forest growth means that it is
16 The fibre and non fibre resources
impossible to give even broadly indicative figures of the potential cut.
In many
developing countries the main potential for increased harvests lies in industrial plantations. These are already important sources of industrial wood in countries such as Chile, Brazil and China and in countries in S.E. Asia and Southern Africa. In the future the physical supply potential in these countries will increase as the plantations reach maturity. This brief review suggests that physical wood supply potential in the developed world is sufficient to meet forecast wood consumption levels in 20 years time. However physical wood availability is merely the starting point in assessing future economic supplies which will be influenced by a variety of economic and environmental factors. Economic Influences Classical economics postulates that price is a prime determinant of supply, and for this reason price elasticity (the sensitivity of supply to price changes) is a key parameter in generating supply forecasts. Evidence from a number of sources suggests that over the last 40 years the supply elasticity values for wood have ranged between 1.5 and 3.0 (Binkley and Dykstra 1987) and based on these sorts of values it has been postulated that real prices of wood will rise at roughly 1% per annum over the next 20 years roughly, the same rate as over the last 40 years (IIASA 1987, Sedjo and Lyons 1990). However there are grounds for questioning whether this level of price increase will induce increased supply in some regions of the world. First much of the potential increase in supplies in Canada and the former USSR will be from remote areas with expensive infrastructural and harvesting costs. With only modest price increases such areas are likely to remain unprofitable to harvest and supply growth may slow down. (Bazett, 1993). Second, in European countries with high percentages of private forest ownership e.g. Scandinavia, current wood prices have proved too low to attract all potential physical supplies to the market.
As private forest owners become more
affluent their reliance on timber revenues diminishes and as a result the margin between actual and potential wood supply widens. Indeed the undercutting of Nordic
Global wood and fibre supplies
17
forests is causing growing concern to many Scandinavian foresters (Kuusela, 1993). Similar problems exist in Japan where present world prices do not justify bringing high cost Japanese wood to the market.
Environmental Influences Environmental constraints on wood supplies will undoubtedly become an increasingly important influence on future supply trends. They will take many forms and four important ones are briefly discussed. First there will almost certainly be increased pressures to remove forests from commercial logging for conservation reasons. A recent well-known example of this which has caused a substantial reduction in harvests is the setting aside of large areas of federally owned forest land in Washington and Oregon to protect the habitat of the Northern Spotted Owl. Indeed there are now strong pressures in the USA and Canada to eliminate logging in all old growth forests and this would very significantly affect timber supplies from Western USA and Canada (Bazett, 1993). There is also likely to be increasing pressure in Europe to set aside more forest land for conservation use. Similar pressures are being exerted on tropical forests. Indonesia, for instance, has recently announced that it will issue no more forest concessions to private operators and plans to reduce its current harvest of 31 million m 3 by 300/0 over the next 5 years. (Asian Timber 1994). A second environmental issue which is likely to influence timber supplies is that of timber certification and labelling. A number of environmental organisations, particularly the W.W.F, have pushed this to the top of their environmental agenda over the last 3 years.
The idea of timber certification is to provide independent
assurance that timber products originate from sustainably managed forests.
A
labelling system complements certification and guarantees to the buyer that a wood based product has been manufactured using timber from a certified source. An agreed certification system still has to be accepted by all interested parties but whatever its final form there can be little doubt that some areas of supply both in the temperate and tropical world will fail to meet the required criteria.
In addition the process of
certification will lead to higher costs for forest owners and concessionaires. Both these factors will tend to limit wood supplies.
18 The fibre and non fibre resources
A third example relates to the growing recognition that non-market benefits of forestry such as wildlife habitat, landscape, recreation, and soil and water protection must be included in forest management decisions. Methods of valuing these benefits are complex and controversial, however their inclusion in an economic assessment of forestry will tend to reduce timber harvests because the financial benefits of logging will often be outweighed by the environmental benefits of abstaining from logging. The role of forests in the global carbon cycle is a fourth example.
Much
research effort has been devoted to quantifying in physical and economic terms the ability of forests to sequester carbon and thereby ameliorate the global warming effect of C02 accumulation. The contribution of commercial forestry to carbon fixation depends on rates of tree growth (faster growth results in higher rates of carbon fixation) and the patterns of use of felled timber. Some wood based products e.g. building timbers will continue to lock up carbon for long periods after felling while others such as fuelwood and packaging will release carbon rapidly. Figure 1 shows typical carbon fixation and decay curves for a Sitka Spruce plantation in upland Britain. Economic models incorporating the value of carbon fixing, based on these sorts of carbon fixing profiles and an assumed value of a tonne of fixed carbon, improve the economic returns of afforestation compared with returns based solely on timber (Canell, 1991, Pearce, 1991). I What will be the effect of accounting for carbon sequestation by forests on future wood supplies?
In the long term if increased
afforestation is carried out to fix carbon this will increase timber supplies, but in most parts of the world such increases are unlikely to reach the market in the next 20 years. In the shorter term the inclusion of carbon fixing values in forest management decisions could lead to a delay in fellings and hence a fall in timber supplies. This might be the case when the optimum timing of felling is determined by discounted cash flow analysis. Because the financial benefits of carbon fixation occur early in the rotation this could have the effect of delaying the need for early timber revenues, thereby postponing felling and reducing timber supplies (Pearce, 1991, Price, 1993). In tropical forest regions the global warming issue has focussed mainly on the need to reduce burning of forests which occurs primarily in connection with agricultural settlement.
However from a timber production point of view various
modifications of current forest management practice are under review to reduce carbon releases associated with logging.
One research programme in Sabah is
Global wood and fibre supplies
19
Figure 1 Profile of Carbon Fixation and Decay for Sitka Spruce Yield Class 12 Grown in Upland Britain Source Pearce (1991).
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20 The fibre and non fibre resources
investigating the effect of "reduced impact logging" on carbon losses. This system of logging involves more careful planning and execution of felling and extraction to reduce damage to the remaining crops, coupled with lower volume removals per hectare (Tay, 1994). The adoption of such approaches to logging would lead to higher logging costs, a reduction in removals per ha and hence a fall in supplies. The economic and environmental influences discussed above suggest that increases in timber harvests will fall well short of physical supply potential. One recent assessment is that over the next 10 years (by 2005) annual industrial wood harvests will increase as follows: (Jaakko Poyry 1994) Europe N. America S. America Former USSR Asia Oceania Africa Total
+ 20 million m3 + 11 million m3 + 27 million m3 + 42 million m3 + 2 million m3 + 11 million m3 + 4 million m3
+ 117 million m3
I Based on 1989/90 prices and a discount rate of 6% the present value per ha of spruce plantations in the UK uplands are as follows: timber production only -£458 timber production plus recreation -£190 timber production plus recreation plus carbon fixing +£20
Pearce 199 I.
Set against the consumption forecasts outlined on table 1 there would appear to be a growing scarcity of wood. To the economist increasing scarcity means rising prices. These in turn can induce different responses in terms of wood demand and supply. From a roundwood demand standpoint rising wood prices could induce: a)
a dampening of consumption growth
b)
improved efficiency of primary wood conversion and product use
c)
substitution of wood products through changes in material use e.g. (steel for wood) and cultural changes (e.g. electronic media for printing papers)
Global wood and fibre supplies
21
On the wood supply side increasing real wood prices could: a)
stimulate further afforestation (but even on the best sites there is likely to be a minimum supply lag of 7 -8 years)
b)
make it profitable to harvest timber in remote regions (again supply responses might be slow because of inadequate infrastructure)
c)
encourage under use of non-wood fibrous materials
d)
stimulate expanded recycling of "waste" fibres
These last two supply responses might be more rapid than the first two options and their role is now examined in the total supply picture.
Alternative Fibrous Materials Non-wood materials currently account for less than 100/0 of the raw materials flowing to the Forest industries.
Future supplies could be drawn from crop residues and
purpose - grown fibre crops. Crop residues such as straw and bagasse are already used to a limited extent in the pulp and composites industries.
Some of these materials are available in large
quantities. For instance in the U.K. out of an estimated cereal straw production of 15 million tonnes about 7 million tonnes are available for alternative uses. (Silsoe 1994). This is approximately 1 million tonnes greater than Britain's current timber harvest. In developing countries other crops are also abundant. For example in Malaysia it is estimated that there are 21 million tonnes of oil palm stem wood, fronds and empty fruit bunches available per annum. (Mohamed 1986). Fibrous materials might also be obtained from purpose - grown crops and in Europe these might be grown on some of the 6.4 million ha of agricultural set-aside land. (AGRA- Europe 1994)., Because of the EO's wood deficit (120 million m3 per annum in roundwood equivalent) trees have been widely advocated by forestry interests as a strategically important use of this surplus agricultural land.
However from the
farmer's point of view the 10-20 year gap between tree planting and his first timber sales makes forestry financially unattractive without subsidies. Crops like flax and hemp yielding annual harvests might be more attractive than trees to both farmers and governments.
22 The fibre and non fibre resources
In considering the future potential for non-food crops in the UK, a recent study placed the pulp and composite board industries as high priority research areas based on the criteria of: potential demand, cost of necessary additional research and development, and benefits to agriculture and the national economy, Hemp and flax were considered the most promising crops for these industries (Silsoe 1994). If it became technically and commercially viable to use crop fibres in paper and board making this could bring about a large and potentially rapid increase in fibre supplies.
Recycled Materials The recycling of materials and industrial waste is a fast growing area stimulated by environmental legislation. The forest industries in the developed world already use most of the wood residues arising from the sawmilling, wood machining and plywood industries. However there is potential to increase the use of wood waste from other industries e.g. non-usable pallets and so boost existing wood fibre supplies. A more significant potential lies with waste paper.
Currently 86 million
tonnes of waste paper are used globally in the rnanufacture of paper, or approximately 36% of the fibre furnish (FAD 1993). This percentage has doubled since 1970. The rate of recycling will almost certainly increase substantially over the next decade in response to increasing waste disposal costs, the banning or restriction of landfill and other environmental legislation. The USA has set a target furnish for waste paper use in paper making of 40% for 1995 compared with 27% in 1990. Most other developed countries have also set themselves higher targets. FAD (1993) predicts that by 2010 waste paper recycling will double to 172 million tonnes from the current level of 86 million tonnes. This increase is the equivalent of approximately 250 million m 3 of wood.
Implications of Future Supply Trends for the Forest Industries This final section discusses some of the implications for the forest industries of the supply trends outlined above. Future growth of the forest dependent industries (as opposed to recycled fibre dependent industries) will be increasingly based on plantation wood because environmental and cost pressures will shift wood supplies to plantation and second
Global wood and fibre supplies
growth sources and away from old growth forests.
23
The most rapid increase in
supplies is likely to be from fast-growing plantations (plantations where net annual increment exceeds 12 m 3/hala) because these plantations will be the most profitable means of growing wood at present day prices. These plantations are mostly in the tropics and sub-tropics and it is estimated that once current fast growing plantations are in production they will yield approximately 250 million m 3 of wood per annum, mostly of pulp wood quality. This increasing contribution of plantation timber will cause spatial shifts in global wood supplies and industrial processing. The areas of fast growing plantations (Southern USA, Australasia, Southern Africa, Brazil, Chile, Venezuela, S.E. Asia, Spain and Portugal) will increase their share of the world harvest and this will be accompanied by an increasing concentration of forest industries in these regions. This movement of forest industries is already apparent in the market pulp industry where countries like Portugal, Spain, Chile and Brazil now hold a significant share of world market pulp production. The same pattern is emerging with M.D.F. Limitations on the cut from old growth natural forests in both temperate and tropical regions will mean slower growth than in the past in the supply of timber for the solid wood processing industries. This will continue to bring about the substitution of solid timber by composite wood products.
This substitution process could be
accelerated if agricultural crops become more widely used as a feed stock for these industries.
Conclusions In the developed world the physical supply potential of exisung forest resources is sufficient to meet forecast demand growth.
However economic and
environmental constraints are likely to mean smaller increases in economic supplies with the fastest supply growth coming from regions with fast-growing plantations. In areas with slower rates of wood supply growth such as Europe, recycled fibres and short rotation crops fibres are likely to become increasingly attractive as alternative sources of raw materials. Despite these changes in wood and fibre supplies the strong environmental advantages of wood and plant fibre materials over metal, plastic and mineral based products should provide the wood and plant fibre industries with a strong base for future development.
24 The fibre and non fibre resources
References Asian Timber. 1994 Vol 13 No 8 Bazett, M.D. 1993. Industrial Wood. Shell International Petroleum Company and World Wide Fund for Nature. Binkley. C.S, and Dykstra D.P. 1987. Timber Supply. The Global Forest Section. Kallio M, Dykstra D.P. Binkley C.S. John Wiley & Sons. Canell, M. and Cape, J. 1991. Forestry Expansion : A Study of Technical Economic and Ecological Factors. International Environmental Impacts : Acid Rain & the Greenhouse Effect. Forestry Commission. ECEIFAO 1993. Forest Resources of the Temperate Zones. United Nations. FAO 1993. Forestry Statistics for Today and Tomorrow. FAO 1993. Kuusela, K. et alia 1993. Policy Implications of the UN ECEIFAO 1990 Forest Resource Assessment. European Forest Institute Working Paper 1. Mohamed, H. et. alia 1986. Availability and potential utilisation of Oil Palm Trunks and fronds up to the year 2000. PORIM Occasional Paper, Kuola Lumpur, Malaysia. Pearce, D. 1991. Forestry Expansion : A Study of Technical Economic and Ecological Factors : Assessing the Returns to the Economy and Society from Investments in Forestry. Forestry Commission. Poyry, J. 1994 Personal Communication. Sedjo, R.A. and Lyon, K.D. 1990. The Long Term Adequacy of World Timber Supply. Resources for the Future. John Hopkins Press. Silsoe Research Institute 1994. Towards a U.K. Research Strategy for Alternative Crops. Silsoe Research Institute. Price, C. and Willis, R. 1993. Time, Discounting and the Valuation of Forestry's Carbon Fluxes. Commonwealth Forestry Review Vol 72 (4). Tay, J. Personal Communication.
3 Blackcurrant stems - An agri-waste with potential as a diluent to existing tree-based fibre sources D Stewart and R M Brennan* - Unit for Industrial and *Unit of Soft Fruit Genetics, Scottish Crop Research Institute, Dundee DD2 5DA, Scotland
ABSTRACT Debarked stems of blackcurrant (Ribes nigrum L.; cv. Ben Alder) were subjected to alkaline extractions with increasing concentrations of aqueous NaOH. Lignin was extracted by ball-milling in 90% 1,4-dioxane. Analysis of the neutral sugar, lignin and uronic acid contents of the residues and extracts indicated that blackcurrant stem should be considered as a typical hardwood. The principal polysaccharides in all these fractions were glucuronoxylans. Other polysaccharides present were arabinoglucuronoxylan, glucomannan, mannan and substituted galactan. Four distinct cell types were found in blackcurrant stems; tracheids, libriform fibres, vessel elements and ray parenchyma cells. These cell types are also present in a typical hardwood and of a comparable size. Fourier-transform infrared (FT-IR) and 13C nuclear magnetic resonance (NMR) spectroscopic analysis of the isolated lignin indicated that it had a structure indicative of hardwood lignin. The results of the study suggest that blackcurrant stem fibres have the potential to be used along with existing wood-based fibres in the production of pulp for paper manufacture. INTRODUCTION Currently only 8.4% of global paper production is derived from non-tree fibres (1). However the combination of extensive deforestation and increased environmental awareness has resulted in an increased impetus towards the use of such fibres either alone or as diluents to the existing wood derived fibres. 25
26
The fibre and non fibre resources
Blackcurrant (Ribes nigrum L.) is the most widely grown bush fruit in Europe, occupying 3.4 kha annually in the UK alone (2). Production in the UK is mainly based on large plantations grown under contract for juice processing. Pruning of bushes is carried out in the autumn, either by selective removal of appropriate stems or by cutting the entire bush down to ground level every five years or so and allowing the subsequent regrowth of the bush. The waste wood is usually burned. The amount of waste wood produced in Europe annually for the selective and destructive pruning strategies is estimated to be 190 x 103 and 204 x 103 tonnes respectively (Brennan, unpublished). Non-food uses for blackcurrant bushes have already been explored in terms of essential oil production for the perfume and fragrance industry. However, the potential use of blackcurrant stems in the pulp and paper industry has not been tested. As part of a study of novel non-tree fibres and processing methods, the composition of blackcurrant stem wood was investigated to determine its potential of blackcurrant stems as a source of pulp for paper production. EXPERIMENTAL Blackcurrant stem wood was prepared as described by Stewart et al (3). Blackcurrant stems (20.0g) were sequentially extracted with 1 L of 0.1, 1.0 and 4.5M NaOH for 16 hr per extraction. The suspensions were filtered and the filtrates acidified then made up to 80% ethanol to yield the hemicellulose (HlC) precipitates HlC A and B respectively. Extraction with 4.5M NaOH only provided combined precipitate H/C(A+B)3. Cells were isolated from ~ inch chips as described by Stewart and Morrison (4). Lignin was isolated as described by Stewart et al (3). Carbohydrates, lignin and uronic acid were determined as described by Stewart (4). The FT-IR spectrum was obtained on a Broker IFS 66 FT-IR spectrometer and the 13C NMR spectrum on a Broker 250 MHz spectrometer. RESULTS AND DISCUSSION
Cell Types and Dimensions Four distinct cell types were isolated from blackcurrant stems. These were tracheid, libriform fibre, vessel element and ray parenchyma cells respectively. They had mean lengths and diameters of 70, 100, 100, 25 J.1m and 3, 2, 13 and 3 urn, respectively. These cell types, although typical of hardwoods, are comparatively small. These dimensions give length/diameter ratios of approximately 23, 50, 8 and 8 urn respectively, ranges within which the blackcurrant stem cell types broadly fall. This suggests that blackcurrant stem wood may be suitable for pulp blends where a hardwood pulp is added as a filler to a softwood pulp. Residues and Extracts The neutral sugar composition and residual lignin and uronic acid contents of the residues and their extracts are shown in Table 1. A small amount of uronic acid was
Blackcurrant stems
27
present in the control residue. This, and the level of residual xylose, indicates that glucuronoxylan, the principal non-cellulosic polysaccharide in hardwoods (4), is present. Mannose accounts for c.10% of the neutral sugar composition and is almost certainly present in the form of gluco- and/or galactoglucomannan. Alkaline extraction (see below) suggests the former. The lignin content (18.0%) of the control residue is lower than is normally found in hardwoods (20-25%) which is not surprising since the blackcurrant plant is a bush and the requirement for structural support is lower compared to that for trees. In general the neutral sugar composition is broadly similar to that of a hardwood. Extraction with O.IM NaOH had only a minimal effect on the residual neutral sugar composition and was largely restricted to the pentoses. Both H/C A1 and B1 contained xylose as the principal monosaccharide residue. H/C B1 had a xylose level 600/0 greater than that found in HlC A1. Similarly, the uronic acid content of HlC B1 was more than double that found in HlC Al which suggests that glucuronoxylan is predominantly found in the former. This is in agreement with the results of Sjostrom and Enstrom (5) who found that, for all alkali concentrations, the uronic acid content was greater in the HlC B fractions. It is probable that the arabinose residues, along with the glucose and galactose residues, are derived from substituted galactans. Timell (6) reported that tension wood, the wood formed when hardwood is subject to an outside influence, such as physical pressure, was high in glucose substituted galactan. Similarly, Meier (7), in studies on the hardwood European beech, found that it contained tension wood, the H/C of which was predominantly glucose and arabinose substituted galactan. Table 1 The neutral sugar composition and lignin and uronic acid contents of treated and untreated blackcurrant residues and extracts. Ara •
Xyl
Man
Gal
Gle
Ligntn"
Uronie Acid
RESIDUES Control O.IMNaOH 1.0MNaOH 4.5MNaOH
9.2 5.4 5.6 4.2
29.5 28.0 17.4 10.0
9.6 10.0 12.2 8.2
7.0 6.6 5.9 6.5
44.3 50.0 58.9 71.1
18.0 14.4 11.1 7.7
0.5 n.d. n.d. n.d.
EXTRACTS HlCAl HlC Bl HlCA2 HlCB2 HlC (A+B)3
13.6 8.1 2.7 8.9 2.2
49.6 79.9 89.2 91.1 93.5
4.6 n.d. 1.1 n.d. 5.3
16.0 5.4 n.d. n.d. n.d.
16.2 6.6 7.0 n.d. n.d.
1.1 0.3 3.1 0.4 4.1
4.0 9.9 3.5 4.5 1.3
Sample
* Neutral sugars are expressed as % total sugar. Lignin and uronic acid contents are expressed as 0/0 dry weight. HlC - hemicellulose. n.d. - not detected.
28 The fibre and non fibre resources
Extraction with 1.0M NaOH had a more significant effect on the composition of the residue. The most notable change is the reduction in residual xylose by 40% to 17.4%, showing that most of the major (glucurono)xylan was extracted. Xylose is the predominant monosaccharide residue in both HlC A2 and B2 and, as before, is more prevalent in the latter. Similarly the mannose, glucose and lignin contents are greater in the HlC A2 extracts. Indeed neither mannose nor glucose residues were detected in HlC B2 while galactose residues were not detected in either HlC A2 or B2. This suggests that the glucose and galactose residues in HlC Al and A2 were derived, to a large extent, from the tension wood galactan and that the remaining glucose residues in HlC A2 are probably derived from amorphous cellulose. Increasing the NaOH concentration to 4.5M results in a further removal of noncellulosic polysaccharide residues, with the exception of galactose (Table 1). As before, the largest reduction is in the residual xylose level. The neutral sugar composition of the corresponding extract, WC (A+B)3, suggests that it is principally composed of arabinoglucuronoxylans with a low level of substitution and some P(I-4) mannan, a polysaccharide which is known to be relatively resistant to alkaline extraction (5). Lignin The FT-IR spectrum of blackcurrant stem dioxane lignin (Figure 1) shows a strong, unresolved carbonyl absorbance over the frequency range 1770-1650 cm-1• These are separated more convincingly in the 13C NMR spectrum (Figure 2) over the resonance range 184-161 ppm. The resonances at 184, 172 and 168 ppm are due to quinone, uronic acid and (hemicellulose associated) acetyl carbonyl groups respectively. The intensity of the latter two are small reflecting the determined uronic acid and polysaccharide levels of 0.4 and 1-2% respectively. The polysaccharide resonances occur over the region 100-60 ppm.
The regions of interest in each spectra are those over the ranges 1350-1100 cm-1 and 160-100 ppm. These are concerned with the guaiacyl and syringyl C-O/C-C/C-H stretch vibrations and aromatic ring resonances, respectively. The first absorbance in this range of the FT-IR spectrum is at 1350 em", the guaiacyl/syringyl c-o stretch. The next absorbance, at 1290-1270 ern", is associated with guaiacyl C-C stretch. However, since this is also the region of the P-0-4 C-O stretch, a quantitative comparison with the corresponding syringyl C-C stretch absorbance at 1210 cm- 1 is invalid. The 13C NMR spectrum over the range 160-100 ppm is more informative, yielding information on both the distribution of linkages and ring substitution. There is an intense region of peaks centred around 155 ppm representing C-3,5 in etherified syringyl rings (3). The corresponding C-4 resonance is present as the less intense peaks at 140-137 ppm. Significantly, the combined intensities of the corresponding
Blackcurrant stems 29
d8 1,4-dioxane -----.
I
180
160
140
Figure 1. The
120
13C
I
100 p.p.m.
I
80
60
40
20
NMR spectrum of black currant stem lignin
o N
VI
4J
c
::::l
LO
~
U
C :Jo 1:::: .,.....
to ~
a;
-§Ln ~
C)
. . . .--~-----r-----~-------..,_---_----.
1900
1750
1500
1250
1000
Wavenumber em-1
Figure 2. The FT-IR spectrum of blackcurrant stem lignin
700
30
The fibre and non fibre resources
guaiacyl resonances, C-3,4 (149-147 ppm) and C-5 (117-116 ppm), are present at a similar level. This suggests that the lignin is a syringyl/guaiacyl, or hardwood-like, lignin (8). Further evidence for this is that the guaiacyl C-6 (121-119 ppm) and C-2 (113-117 ppm) resonances are present at similar levels to the syringyl C-2,6 resonances (108-103 ppm). The approximately equivalent distribution of guaiacyl and syringyl rings is typical of hardwood lignins (8). It is evident from the 13C NMR spectrum that the common lignin linkages, 5-5' (132 ppm), ~-O-4 (C-a 72-71, C-~ 87-84 and C-y 63-61 ppm) and the less common ~-~ and ~-5 (55 ppm, shoulder on Ar-OCH3 peak) are present. There is also evidence that not all of the double bonds in the lignin precursors have been removed during lignification, although the corresponding resonances at 128 ppm (C-a) and 130 (C-~) are extremely weak.
CONCLUSION The evidence presented suggests that blackcurrant stems are similar to hardwood. Blackcurrant is an angiosperm and the stems have a composition typical of a hardwood. It posses the cell types indicative of a hardwood, although their dimensions are smaller. Progressive alkali extraction showed that glucuronoxylan was the major non-cellulosic polysaccharide while the neutral sugar composition suggested that the other polysaccharides present were arabinoglucuronoxylan, glucomannan, mannan, galactoglucomannan and galactan. Since hardwoods are used extensively in pulp and paper manufacture, further investigations into the use of blackcurrant stems as a source of fibre for paper pulp is merited.
ACKNOWLEDGEMENT The authors would like to thank Professor J.R. Hillman for his continued support and the Scottish Office Agriculture and Fisheries Department for funding this work.
REFERENCES 1. Anon, (1991) Pulp and Paper Capacities; 1990-1995, Food and Agriculture Organization of the United Nations, Rome. 2. Anon, (1993) Agriculture in the United Kingdom: 1992, Ministry of Agriculture, Fisheries and Food, London. 3. Stewart, D., Brennan, R. M. and Provan, G. J. (1994) Phytochemistry, 37, 1703. 4. Stewart, D., Brennan, R. M. and Morrison, I. M. (1994) Cell. Chern. Technol., In Press 5. E. Sjostrom and B. Enstrom, Tappi 50, 32 (1967). 6. T. E. Timmell, T. E. (1964) in: Advance in Carbohydrate Chemistry, Wolfrom, M. L., (Ed), pp.. 299, Academic Pres, London (1964). 7. H. Meier, H. (1962) Acta. Chern Scand., 16, 2275. 8. Stewart, D. (1993) A Physical and Chemical Study ofPlant Fibres, Ph.D Thesis, University of Dundee, Dundee, Scotland.
4 Phenolic acid dimers in barley straw cell walls D Stewart & I M Morrison - Unit for Industrial Crops, Scottish Crop Research Institute, Dundee DD2 5DA, Scotland
ABSTRACT We report the tentative characterization of three groups of alkali soluble 3-0H-4-CH3 substituted phenolic acid dimers in the cell walls of barley straw. The two predominant groups are derived from ferulic acid by photochemical (truxinic/truxillic acids; Fig. lA) and oxidative (aryl-aryl linked; Fig.1B) dimerization. Within the latter group six compounds were identified by GC/MS as having mass spectral fragmentation patterns consistent with ring-linked dehydrodiferulic acids. Assuming the absence of isomerism about the aryl-aryl bond this means that linkages other than 5-5' are present. Due to steric constraints we propose that the other linkage is 6-6'. The third group of dimers appears to be derived from 3(4-hydroxy-3methoxyphenyl)propanoic acid (hydroferulic acid; Fig IC). Four dimers were present at the limits of detection by GC/MS. This again suggests that linkages other than 5-5' are present. No monomeric hydroferulic acid was found. Analysis of the cell walls at various stages of growth showed that, in general, the number of dimer types accumulated with age, and at a given age, were present more in the basal than the apical tissue. Neither truxillic nor truxinic acid derivatives were detected in etiolated tissue, supporting their proposed photochemical origin. Digestion of mature barley cell walls with a purified xylanase followed by alkaline extraction of the soluble digest released the same range of dimers identified after extraction with 1M NaOH alone. Fractionation of the digest using Sephadex LH-20 and subsequent 1M NaOH extraction and GC/MS analysis showed that the dimers were absent from the fraction eluted with water, but, elution with 50% 1,4 dioxane provided the full complement of dimers. This suggests that the dimers, in the digest are attached to relatively small oligosaccharide fragments.
31
32
The fibre and non fibre resources
INTRODUCTION The phenolic acids, ferulic and p-coumaric acid, are present in the cell walls of Graminaea as both ethers (I) and esters (2). Dimeric compounds derived from these monomers by photochemical linking through the double bond sidechains (truxillic and truxinic acids; Fig. IA) and oxidative linking at the unsubstituted ring positions (dehydrodiferulic acid; Fig. IB) have also been reported. In all previous reports of plant-derived dehydrodiferulic it is stated, or assumed, that the aryl-aryl linkage is 5-5'. Both the monomers and dimers are considered to be implicated the physical and biochemical properties of the wall and therefore may be important in determining the pulping the behaviour of Graminaea fibres (3). Previous studies on these dimers have largely concentrated on the alkali extraction of cell walls at one stage of growth. We report here the tentative characterization and distribution of 4-hydroxy-3-methoxyphenyl substituted dimers in the cell walls of barley straw at defined stages of growth.
CH
OH
R
B:
A2
R - CH=CH-C02H
Figure I. Dimers form by the photochemical (AI-2) and oxidative (B) dimerization of ferulic acid, and oxidative dimerization (C) ofhydroferulic acid MATERIALS AND METHODS Isolation ofphenolic acid dimers from barley straw The phenolic acid dimers were isolated and analysed as described by Stewart (4). Briefly the plant material was extracted with 1M NaOH for 16 hr. The extract was
Phenolic acid dimers
33
acidified, extracted into diethyl ether, concentrated, silylated and analysed by GC/MS on a 25m x 0.32mm capillary column with 0.25 urn BP-5 bonded phase. Isolation ofdimers from barley straw enzyme digests Combined 6 month apical and basal barley straw cell walls were digested with a purified xylanase (Pulpzyme HB, Novo-Nordisk) for 72 hr at 30°C. The supernatant was concentrated and purified on a Sephadex LH-20 column eluted with H20 followed by 500/0 aqueous 1,4 dioxane. Selected fractions were pooled and analysed for dimers as above.
RESULTS AND DISCUSSION Characterization of Phenolic Acid Dimers in Mature Barley Straw Cell Walls The presence of both oxidative and photodimers was confirmed from the extraction of barley straw with 1M NaOH for 16 hr at room temperature. The results of this extraction are shown in Table 1. Table 1 The dimers derived from ferulic and hydroferulic acid extracted from mature barley straw cell walls by 1M NaOH. Dimer Retention. time (min)
Cone. (Ilg g-I)
Proposed Linkage
Photochem.
Al A2
29:13 30:12
20.00 150.00
Oxidative
BI B2
27:29 28:38
10.00 30.00
B3
28:56
90.00
5-5'
B4 B5 86 Cl C2 C3 C4
29:05 31:17 31:37 28:43 29:05 31:10 31'42
20.00 200.00 20.00 < 1.0 < 1.0 < 1.0 <10
5-5' 5-5' 6-6' 5-6' 5-5' 6-6' 5-2'
Proposed Isomerism truxinic truxi II ic
6-6' 6-6'
trans-cis trans-trans trans-trans trans-cis cis-cis cis-cis
As expected the most prevalent oxidative dimer derived from ferulic acid was 5-5' linked. However, the fragmentation pattern (not shown; 4) suggests that it is a cis-cis isomer. The corresponding trans-trans isomer comtent is half that of the cis-cis isomer. For all isomers the 5-5' linked dimers predominate. An unexpected discovery during the GC/MS analysis was the identification of peaks which suggested the presence of oxidative dimers of 3-(4-hydroxy-3-methoxyphenyl) propanoic acid (hydroferulic acid). This compound has not previously been reported to
34
The fibre and non fibre resources
be present in the plant cell wall. The 3-(4-hydroxyphenyl) propanoic acid derivative has been reported to be a metabolite of phenylalanine metabolism by rumen bacteria (5). These dimers (Fig IC) were far less prevalent than either of the dimers derived from ferulic acid (Fig 1 AI-2, B), and were present at levels approaching the limits of detection. However, despite exhaustive scanning, no traces of the monomeric acid were found. The presence of the dimer alone remains an anomaly. It is unlikely that it has been produced by the reduction of 5-5' and 6-6' linked ferulic acid dimers in muro since the mildly acidic conditions present in the cell wall would lead to the addition of H20 , rather than H2, across the double bond. Phenolic Acid Dimers in Barley During Growth There appears to be no rigid relationship between the different dimers and the age of the tissue, although there is a general trend for a wider range of the dimers to be detected as the age of the tissue increases (Table 2). A comparison of the 4 and 6 month apical tissue showed, in the latter, the appearance of two new dimers of type B (Fig. 1) (B2 and 6) and three of type C (CI, 3 and 4). Significantly all of these are non-5-5' linked dimers, the 5-5' linked ones appearing at an earlier stage. Similarly the 6 month basal tissue has 2 dimers of type B (Bl and 4) and one of type C (C2) that were not detected in the corresponding 4 month sample. It is only in the former, and most mature, tissue that the full quota of dimers is detected. The only dimer present in all of the barley samples at all stages of growth, including the etiolated tissue, was B5, the cis-cis 5,5' oxidative dimer derived from ferulic acid. This was the most prevalent of the ferulic acid derived oxidative dimers in each tissue. An obvious feature of Table 2 is the absence of the truxinic or truxillic acids in the etiolated sample. The dimers Al and A2 are present in alkaline extracts of all other growth stages including the 2 month old sample. This suggests that these acids are indeed formed photochemically in muro from the monomeric acids. This hypothesis was in some doubt since a short study on the presence of truxinates and truxillates in other plants (Stewart and Morrison unpublished) showed that these dimers were absent from mature flax (Linum usitatissimum L.). Since flax contained the monomers at levels comparable with those of barley straw (ca. 5 mg g-l cell wall), the absence of the dimers had suggested that either their synthesis was enzymic or that the cinnamates in flax were too spatially diffuse to photodimerize. The results from etiolated barley tend to support the latter hypothesis.
Digestion of whole barley straw cell walls with a purified bacterial, cellulase-free xylanase (Pulpzyme HB) produced an extract which contained the full range of dimers which were present in when the straw was extracted with 1M NaOH alone. Fractionation of the digest (Fig. 2), using the lipophilic Sephadex LH-20 support and subsequent GC/MS analysis of the alkaline extracts of the pooled fractions (A-D),
Phenolic acid dimers
35
showed that the water-eluted fraction contained no dimers. However, both p-coumaric and ferulic acid were present thereby contributing to the UV absorbance at 280nm of the pooled water-eluted fractions. Other contributors to this absorbance were the purified xylanase and any lignin, or lignin-like, fragments released by the enzymic treatment. Table 2 The dimers present in barley straw cell walls at different stages of growth and the soluble xylanase digest M+
Sample 674
676
678
Etiolated
B2 (6), B3 (7), B4 (I) B5 (12), B6 (2)
n.d.
Cl, C2, C4
2 months
B2 (6), B3 (10), B5 (25) B6 (2)
Al (I), A2 (10)
Cl,C4
4 months
B3 (20), B4 (4), B5 (54)
Al (4), A2 (31)
C2
4 months (basal)
B2 (15), B3 (70), B4 (13) B5 (112), B6 (4)
Al (10), A2 (90)
Cl, C2, C3, C4
6 months (apical)
B2 (27), B3 (25), B4 (17), B5 (191), B6 (12)
At (12), A2 (127)
Cl, C2, C3, C4
6 months (basal)
Bl (19), B2 (35), B3 (91), B4 (27), B5 (214), B6 (19)
Al (25), A2 (181)
Ct, C2, C3, C4
Pulpzyme digest
Bl (47), B2 (151), B3 (420) B4 (89), B5 (970), B6 (104)
Al (107), A2 (877)
Cl, C2,C3, C4
(apical)
The figures in parentheses are dimer concentrations expressed as ug g-I cell wall dry weight. n.d. - not detected
Elution with 500/0 dioxane resulted in a fraction (E) that contained the full range of dimers (Table 2). Two conclusions can be drawn from this. Firstly, since the dimers were released in a soluble but still bound form by treatment with a cellulase free xylanase, they must be linked to hemicellulose. Secondly, the fragments to which the dimers are attached are relatively small. Large oligosaccharide fragments would tend to give the dimer/saccharide conjugate a hydrophilic nature and the conjugate(s) would elute with water. However no dimers were found in the water eluate only in that eluted with 50% dioxane.
36
The fibre and non fibre resources
The relative ratio of the B-type dimers (ferulic acid derived) extracted from the soluble enzyme digest is significantly different to those found after simple 1M NaOH extraction. Although the dimer B5 is still the most prevelant, the relative proportion of the others has increased significantly, particularly those containing a 5-5' linkage (B3, B4). A D E I B I C
100 (Pooled fractions)
A
50% Dioxane
(280nm)
50
O-+::====~--r--~---r-------..--"""::='-r--':::
o
50
100
150 200 250 300 Retention Time (min)
350
Figure 2. 'The chromatograph of the soluble extract from the digestion of barley straw cell walls with Pulpzyme. Fractions were pooled as shown (A-E) prior to alkali extraction, silylation and GC/MS analysis.
ACKNO\VLEDGEMENT The authors would like to thank Professor J.R. Hillman for his continued support and the Scottish Office Agriculture and Fisheries Department for funding this work.
REFERENCES 1.
2. 3. 4. 5.
Lam, T. B., Iiyama K. and Stone, B. A. (1990) in Microbial and Plant Opportunities to Improve Lignocellulosic Utilization by Ruminants, pp. 43. Elsevier Scientific Publishing Co. Inc., London. Scalbert, A., Monties, B., Lallemand, J. Y., Guittet, E. and Rolando, C. (1985) Phytochemistry 24, 1359. Chesson, A., Gordon, A. H. and Lomax J. A. (1983) J. Sci. Food Agric. 34, 1330. Stewart, D. (1993) Ph.D Thesis, University of Dundee, Dundee, UK. Martin, A. K. (1978) in Essays on the scientific work of the institute, 148. I-Iannah Research Institute, Ayr, UK.
5 'Non wood plant fibres' . Availability in Kenya and need for maximum utilization R M.urali and J G Mwangi - Department of Woodscience & Technology, Moi University, PO Box 3900, Edoret, Kenya
ABSTRACT
Non-wood plant fibres represent a substantial potential source of raw material for the pulp industry. They are being increasingly recognised for a multiplicity of uses. The economic use of these renewable resource has been almost neglected in Kenya. An extensive survey on the availability of various non-wood plant fibres that can be commercially exploited has been carried out, especially for those like bagasse, straw, reeds and grass for which the processing technology is already established and for minor fibres like kenaf, cotton stalk, sisal, pineapple leaves etc. The study has shown at least five small mills of 5 to 10 tons per day capacity can be set up a various locations for pulp production. Other aspects like method of collection, storage, pulping, refining, cost of installation, use of pulp and pollution abatement for each raw material have been discussed. INTRODUCTION
With an increasing demand for cellulose pulp and decreasing supply of wood, many countries allover the world are using various types of agricultural residues, reeds and other plants to produce pulp. All these materials, collectively known as non-wood plant fibres, can be used for the same purposes as wood, especially for the manufacture of pulp, paperboards and news print. The economic use of these important renewable resources has been neglected by most countries in the past. However, as their value becomes increasingly recognised for a multiplicity of uses, they represent a substantial potential source of renewable raw materials for the future. At present the worldwide
37
38 The fibre and non fibre resources
capacity for the production of non-wood plant fibre pulp is about 10 percent of the total world pulp capacity. In some countries non-wood pulp represents more than 50 percent of the overall fibrous furnish for paper and paper-board. The leaders are the People's Republic of China, Ind ia, Tal wan, Mexico and Ital y (1,2). Literature surveys have shown that:Non-wood fibres are used mainly in areas where sophisticated technology Is less readily available, and the mills that use these fibres are generally smaller production unit than those concerned with wood pulp manufacture. A non-wood fibre pulp can be cheaper for local use than imported wood pulp. Locally produced non-wood fibres can save foreign exchange when compared with imported wood pulp. The non-woody fibres in general are less lignified and require less cooking time, milder condition and in most cases can be cooked by simpler and uncomplicated processes. In bleaching, the chlorine dioxide (D) stage common with wood pulp, is generally not needed. They can be bleached to 80% brightness using CEH sequence. This is obviously a great advantage where sophisticated facilities and labour are not available. The criteria which determines the use of fibrous raw material for cellulose pulp manufacture are:- availability, cost, ease of harvesting, pulping methods, yield and final pulp quality. Table 1 lists some of the important non-wood plant fibre currently used in the world, the number of countries which use them and the area of application. It may be interesting to note that some of these raw materials are available in abundance in Kenya and can be a valuable source of revenue. SPECIFIC NON--WOOD FIBROUS RAW MATERIALS RELEVANT TO KENYA
In the present investigation eight non-wood plant fibres relevant to Kenya are discussed. A survey on their annual availability to the pulp industry has been carried out. MATERIALS AND METHODS Bagasse (spontanlum) (2)
Bagasse is a by-product formed when sugarcane (Saccharum officianrum) is used to produce sugar. Bagasse produced is 36 percent of the crushed sugarcane. An average of 40 percent of bagasse is available as surplus after some has been used as fuel in the boilers of the mill for concentration of sugarcane Juice. For this Important raw material to be made available, sugar factories have been forced to use alternate fuels in boilers for concentrating the sugarcane Juice. This factor has been much to their disadvantage. However, with the advent of membrane technology for concentration of sugar juice, the bagasse can be completely utilized by pulp industries. The production of pulp from bagasse is an established technology in countries like Mexico, China,
Non wood plant fibres
39
Cuba and Brazil. Methods of deplthing and treatment of black liquor have been established for this raw material. There are now no technical problems to prevent this raw material from "taking off" in Kenya.
TABLE 1:
ESTABLISHED NON-WOOD PLANT FIBROUS RAW MATERIAL FOR PULP PRODUCTION
·:::::::::::::::r.:::::::m::s:u::::u:::w:::u:u::s:u····::::s:u:::::::::a:u::::::::wW:a:::::U:::::u::l:::::::::::::::::~::::::ll::::::::::::::::=c::~u::::::;::.
IlAW MorDIAL
usn
lOR PULP - PIlODUCTION
O~ber coun~ri.s
'=::::1:::::::::U::::'::::::::::::::::::::::::::I:::::::"'::::::::::::::::::::::::::I~::::~::::::::w:;;::::::;::::;::""
AVAILABILI'I"Y 1M DDA
11&108 USBS
Kenya
......................................................................................................................... ,.
,
,
Baggase
Yes(20)
Negligible Bxtent
Yes
Newspri nt, wrapping, corrugat i ng ledi a liner board, tissue
Wheat Straw
Yes(l7)
Negligible Bxtent
Yes
Corrugat ing led i a, fine paper, paper board
No
Yes
Yes
Yes(15) BaJaboo
Reeds
Yes(lO)
No
Pineapple Leaves
Yes(4)
No Yes
.
Printing & Writing paper, corrugat i ng lIedia Paperboard, Corrugating Media Newsprint, print paper fluting Lace Twines, Ropes, sacks
Sisal
Yes(6)
Cotton Linters
Yes(lO)
Kenaf
Yes(14)
No
Yes
Drawing paper, Auto.obile filters
No
Yes
Newsprint, Packaging Material
No
Yes
...::::wu::::..-::.-::u:::uur.s:a::::.:::::=::uw:w:: ...:=::=::ss::n=w.~:::s::s=:u:::·· • "r.:::r.u::s::::sw::n::U:::::U::-'::::::;=:::::::U::::::::::.:=:.~::w;=:r:-J::::::::''':t::::::u::::::::::::::::::..::::::::::::::U:::::::l:=:Z::S::S::::::S::W:::::l::J:::U:a::.~.m
Table 2 gives the availability of bagasse In Kenya of which seven million tons are available for the paper Industry. It Is the best non-fibrous raw material in terms of fibre length, alpha cellulose and pentosan contents. Bagasse pulp Is a suitable substitute for hard pulps. Hence hardwood trees may be used in other valuable applications as in
40 The fibre and non fibre resources
furniture manufacture where decorative value Is most desired. Bagasse pulp are used In practically all grades of paper Including wrapping, printing, toilet tissue, towelling, glassine, corrugating media, liner boards and newsprlnts. (3,4) TABLE 2: AVAI,-ABILITY OF BAGASSE IN KENYA (1992) :::=::=:s:::::uw::::::s:::z::::::s::::::z:z=::::::::=:=:::=
.':::::;::~::::::::::::.::::::::::::::::::::::::::::.:::.-:::::=::.:::. ...::::::::::'.::::::::::....:::'.:=:::s:=u:,..:::=.::::::::::::::--::::::::::::::r~~:r=:="
GROSS
AREA COVERED BY SUGARCANE FARMERS (NUCLEUS ESTATE & OUTGROWERS)
DISTRICT
Chemelil Muhoroni Mumlas Nzoia
AVAILABILITY OF BAGASSE (IN MILLION TONS)
16118 11868
2.7
36019 14994
6.2
2.1
Miwanl
12345 1781
2.6 2.2 1.2
TOTAL
93125
17.0
Sony
An average of 40~ (Approx. for pulp production.
= 7 million tons/year Is available as surplus
STRAW straw Is an annually renewable material and is In plentiful supply. It is similar to hardwood in composition and fibre length. It adds needed TABLE 3:
AVAILABILITY OF WHEAT STRAW IN KENYA (1992)
DISTRICT
Kajlado Kelyo Marakwet Nandi w.est Pokot Lalklpla Kerlcho Trans Nzola Uasln Glshu Narok Barlngo Nyandarua/Nyerl/Meru Nakuru
TOTAL About 40S production.
AREA COVERED (HA)
GROSS AVAILABILITY (IN MILLION TONS)
28960
0.90 0.70 3.20 0.60 0.60 3.40 3.00
26700 70828 18695 18000 85434 68350 61238 32300
2.70 1.30 0.50 0.40
15295 1204461224
2.00
499068 (Approx.
8
million
tons/years)
19.3
Is
available
for
pulp
Non wood plant fibres 41
characteristic to waste paper for production of excellent corrugating medium. Besides, its utilization has a desirable ecological value. The availability is computed on the food grain production with an average ratio 1 ton of grain to one ton of straw. The development of desilication could revolutionize the use of straw (rice straw in particular) and result in a dramatic Increase in its use. Cereal sraw is used to produce writing paper in Egypt, Indonesia, Sri Lanka, Iraq, Syria, Greece, Romania and Bulgaria. The People's Republic of China is far ahead producing 82 percent of the world's total in 1993. Large quantities of wheat straw are available as shown in Table 3. Small quantities are used by the fibre board and mushroom industries. Recent development in storage methods, desilication, pith removal have established wheat straw as a standard raw material for pulp production. There should be no restrictions in Kenya for the use of this raw material. BAMBOO (A. alpina)
Bamboo are woody plants of the family Gramineae. Native stands of bamboo occur in many parts of the world especially in warm tropical regions. In Africa about 25 species are found in Abyssinia, Congo, Kenya, Sudan, Tanzania, Uganda and Madagascar. Arundinaria alpina is a common species in Kenya. A yield of 200 tons/Ha can be obtained when harvesting is carried out every five years. It is also a major raw material in India, Bangladesh, The Philippines, Chine, Indonesia and Burma (5,6).
TABLE 4: AVAILABILITY OF BAMBOO IN KENYA (1992) REGION
AREA COVERED (HA)
GROSS AVAILABILITY (IN MILLION TONS)
Aberdares Ranges Mt. Kenya/Mau Ranges Mt. Elgon Kaptagat Timboroa Plateau
65000
6.50
51000 354 31000
5.10 0.30 3.10
TOTAL
147354
15.00
I
••::::::::::::::::::::::::::::::::::'-'::::::::::=:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::!::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::.•::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::;;:::::::::::..
Using 90~ of the availability and harvesting after every five years gives the net availability as 2.5 million tons per year. However, these figures can be improved by plantation and cultivation.
Table 4 gives the availability of bamboo in Kenya. Bamboo is neither used by the paper Industry nor is it used in furniture manufacture or construction in Kenya. The forest department has during the last few years Initiated a bamboo conservation project.
42 The fibre and non fibre resources
REEDS
Reeds were the earliest raw materials In paper making. They grow abundantly In swampy lands, river banks and delta areas. Various types of reeds are used to produce commercial pulp In Russia, Rumania, Egypt, Northern China, Korea, Spain, India and Iraq. Reeds are common names for water plants. They do not belong to anyone botanical family In particular. Two major species of reeds are available In Kenya: .IYQhA domlngensls and Cyoerus latlfolius. Typha are cattails, though not In the grass family. They resemble giant grasses. They reoroduce by seeds and rhizome and are notorious for filling shallow water ways. Cyperus 'Iatifollus, Is a sedge belonging to the family Cyperaceae. It Is a perennial and grows In wet swamps on the side of papyrus. Both plants are known to regenerate rapidly, and have a high growth rate of 20cm/week. The Industrial manufacture of pulp from these two raw materials for Kenyan condition has been established and found to be economical (7). Table 5 gives the swampy areas in Uasin Glshu District and the gross availability. TABLE 5:
LOCATION OF THE BLOCKS OF SWAMPY AREAS IN UASIN
GISHU DISTRICT (1992) NAME
Cheptlret Comelek Kaptagat & Gatonye Group Eigeyo Border Klmumu Sergolt Klplombe Klpsangui Sambut
LOCATION
AREA COVERED (HA)
Atnabkol Division Ainabkoi Division Alnabkol Division Kesses Division Molben Division Soy Division Soy Division SOy Division
19,000 1,300 1,400
5,000 1,700 4,400 3,500 2,600 38,900
TOTAL
••:::::::::rr::::::::unuu::::&:::.:t:::::::::uur.:=::U'.::::::::::::::::::::r.:::::=::::u::::::::r.::~.::::::::::::=:;;:::::::~.:::::..:::::::::::::::::::::::::::::::::-.::.:;::::::::::::::::::::::::::::::::::;:::::::::::::::::::::::::::::.::;:::::=:.~.... ,,::::::::::::::::::~:.:=::::::=:::::=::-..:::::::~.:::t::::"''::::'...
Source:
District Agricultural Office, U.G. District POBox 95, Eldoret, Kenya.
Notes: a) b) c)
Earlier studies have established that yield is 50 tons of air dry material/hectare. 25~ swamp area is available for harvesting. Harvesting can be carried out twice a year.
Gross availability is approximately 1 million tons per year. SISAL (Agave Sisalana) Sisal belongs to the family of Agavaceae, with 532 species.
Sisal Is
44 The fibre and non fibre resources
embroidery and lace manufacture. Table 7 gives the availability of pineapple leaves based on 28 percent of fruit weight. The market price of pineapple pulp Is twenty fold of ordinary pulp. One reason for lack of exploitation of the fibre Is that the leaf has a peculiar structure, the toughness is not uniform, hence there Is a high percentage of waste. Another difficulty Is the leaves tend to die out at the tip while still on the plant and harvesting has to be carr-led out accordingly. TABLE 7:
AVAILABILITY OF PINEAPPLE LEAVES IN KENYA (1992) (Availability of leaves based on 28S of fruit weight)
DISTRICT/PROVINCE
AREA COVERED (HA)
Central Province Kericho Uasln Gishu Bungoma Kakamega Busia Killfi Kwale Kisil Kisumu South Nyanza Nyamlra Siaya
4425 125 5 350 450
Eastern Province TOTAL
FRUIT PRODUCTION (TONS)
GROSS AVAILABILITY (TONS)
324321 7426 100 6000 10000
80
1400
957 170 38 392 32 17
31914 1670 2000 1900 2700 544 980
18
86
90809 2093 28 1680 2800 392 8935 467 560 532 756 152 274 24
7143
391091
109502
84
30~
of total available pineapple leaves are used for planting either as grown or suckers and for cattle feed. Thus 70~ of the total net surplus that can be used for pulping is = 76653 tons per year. COTTON LINTERS AND STALKS
Cotton plants are malnly cultivated for their fibres which are used by the textile Industry. The other parts of cotton plants, after separating the cotton, are considered as agricultural waste. cotton linters are the short hair on seed coats. They are short fibres with thicker cell walls, more cylindrical as compared to cotton fibres. However, it is suitable material for pulp production. Both cotton linters and cotton stalk have considerable cellulose contents and can be used In pulp production. Cotton linters pulp have cellulose contents which can be used in special appucetlon while cotton stalk pulp can be used for semi-chemical pulp used in packaging the Industry. Table 8 gives the availability of both these materials In Kenya.
Non wood plant fibres 45
TABLE 8:
AVAILABILITY OF COTTON IN KENYA (1992)
•.•:::::::::::::::::r.n·m·..·'U·,·,···'m···' ..'···n'••- :==: ..:::::n::·"··,·,·..•••..·!t·····'n::.:::::=:::::.::.::::::::~:::::.::::::: ..·:::::t.::::::::::::::.::::::.::~=~:.::::::::::u:::::.:z
DISTRICT
Klrlnyaga Kwale Kllifi Tana River Lamu Talta Taveta Meru Embu Makueni Kltul Klsumu Siaya South Nyanza Busia Bungoma
TOTAL
AREA COVERED (HA)
·······c:::::::.::::::.:::.:::.:a:.:::~::~;:~:::~~::::::::::.:::::::.::;:::::;:··
GROSS
GROSS
AVAILABILITY OF LINT ON 33~ OF SEED COTTON (TONS)
AVAILABILITY OF COTTON STALK. 0.65 TONS/HA
10000 2570
871 255 883 1155 297
650 73 3348 1163 999 1086 2119 2190 2741 4108 5723 1677 5200 6500 1675
60386
8278
39252
1000 113 5152 1790 1538 1670 3260 3370 4218 6320 8805 2580 8000
240 18 680 590 507 331 430 622 556 843
Approximately 47,530 tons/year are available for pulp production.
KENAF (Hibiscus Cannabinus) Hibiscus Cannablnus is a perennial plant which has straight, slender stems that may reach a height of 8-12m or even more. There are many varieties of the plant, some of which show marked differences in their botanical characteristics. H. Cannablnus Is known under many names, the most important being Kenaf, Deccan-Hemp, Jute, Mesta, Dah, and Guinea hemp. However, in recent years, the name kenaf seems to have been universally adopted. Large quantities of kenaf are grown In India and are used as an ad mixture with jute. Other countries which use kenaf are Cuba, Argentina, Peru, Spain and Thailand. Hibiscus sabdarlffa is a native of tropical Africa known as roselle fibre very similar to Hibiscus Cannabinus. Roselle Is used by two mills in India for the manufacture of coarse sacking. It is strong, silky and light in color. Kenaf reportedly has distinctive advantages over other raw materials:Kenaf can be grown almost anywhere, even in waste and barren lands, poor soils, near paper mills, thereby saving costs of transportation. Tropical climate suits the crop Ideally. Kenaf Is resistant to infections and viruses. Unlike other raw materials, It does not require elaborate storage facilities.
46 The fibre and non fibre resources
Besides having comparable strength and fibre characteristics, the yield of by-products such as 011 cakes (cattle feed) makes It attractive even for small manufacturers to undertake the production of paper. Kenaf pulp when mixed with other pulps gives certain distinctive advantages' such as: greater tear resistance, more folding strength and more bonding strength. There are some problems in mesta or kenaf pulping: The crop Is very susceptible to monsoons. It is affected by heavy rains and climate conditions. It has a high bulk. The density of mesta is 150Kg per cubic metre, compared to that of bamboo which Is 200Kg per cubic metre. Therefore, for a 100 T.P.D. plant, a storage area of 165,000 square metres is required. The cultivation of kenaf In waste or barren lands and semi arid lands need Immediate attention In Kenya (42 million hectares). It has good prospects for commercial development In this country. However, there are no records of Its availability. RESUL TS AND DISCUSSION
Table 9 gives the oroxtmate chemical analysis of these raw materials. Table 10 gives the revenue analysis if these materials could be used for pulp production. From the present investigation it is very evident that commercial pulping can be carried out from the above mentioned nonwood plant fibres. Presently there is only one integrated papermilt of 200 TPO and three small paper mills of 3-5 TPD using waste paper in the country. These mills meet half the local demand. Various types of pulp and paper products are being imported. About four percent of the land area is covered with forests and fifteen percent by agriculture,
TABLE 9:
PROXIMATE CHEMICAL ANALYSIS (All values are based on oven dry weight expressed as
percent content) RAW MATERIAL
Bagasse Wheat straw Bamboo Cyprus Latlfolius Typha domlngensls Pineapple leaf Fibres Sisal Cotton stal-k Cotton linters Kenaf
..............==m....,..:::r ...:====.
..."._.....- :==:::
CROSS & PENTOSAN BeVAN CELLULOSE
LIGNIN
ASH
30
22
2.3
27
18
25
25
8 2
28 30
30 20
16.3 16.5
5.7 6
45
27 20
45 45 30
55 40 35
Na .::::::::::=::::u:-- • .-....
26 20 Na
18
3
20 20
8 3 2 Na
1.8 Na
Non wood plant fibres 47
hence It Is important that this resource should be used for pulp production. Large amounts of soda-ash deposits are available in the country. Most non-wood plant fibres can be cooked by simple batch process using soda ash. The use of these raw materials for pulp production would help to meet the increasing demand and cut down on the Importation of pulp products.
TABLE 10: REVENUE ANALYSIS ...:::::::::::::::::::::::::.::::::::::::::::::::::::::=::::::::::::::••'::::::::-.:::::::::::::::::::::::::::::::::::::::::'::::l::::::::::::::::r:"':::::::::::::::::::::::::::::::::::::::.::::::::::::::::::::'::::::::::::::::::::::::::::;:::::::::::::~::::::::.::::::::::: ...:::::::::::::::::::;:::::::::::::s::::::::::::::::::::'..
RAW MATERIAL
NET AVAILABILITY (MILLION TONS)
CHEMICAL USED IN PULPING
% YIELD OF
UNBLEACHED PULP AS KNOWN FROM LITERATURE
REVENUE AT PRESENT PRICE OF KSHS 1000/TON
(IN BILLION KSHS)
Baggase Wheat straw Bamboo Reeds Pineapple leaves,Sisal and Cotton
TOTAL
7 8
2.5 1
0.13
Sodium Hydroxide Sodium Carbonate Sodium Hydroxide Sodium Carbonate Sodium Carbonate
60
4.2
60
2.8
50
1.25
60
0.62
50
0.06
10.93
CONCLUSION The annual availability data and revenue analysis clearly indicates that at least three or more small scale pulping units of about 4 TPD can be set up at both the Uasin Gishu District and Central Province in Kenya.
48 The fibre and non fibre resources
REFERENCES 1. 2. 3. 4. 5.
6. 7.
Kirby R.H. Vegetable Fibres, University Press, Aberdeen, 1963. Ashok Kumar, Jindal A.K., and Rae N.J. 'Utilisation of Bagasse for paper Making - A Review', IPPTA Vol. 23, No 4, December 1986. Haines R.W. and Amsteinlye K. Sedges and Rushes of East Africa A Flora of the families Juncaceae and Cyperaceae, Nairobi 1983. Inguber, O.V., A.Ch.E. Symposium Series: New Proeess Alternatives in the Forest Industries, 76,196,1980. Report of an ad-hoe-panel of the Advisory Committee on Technology Innovation Board on Science and Technology, National Academy of Science. Making Aquatic Weeds Useful. Some perspectives for Developing Countries, 1981. The Kenyan Geographer (Special Issue). The Journal of the Geographical Society of Kenya, Vol - 5, Nos 1 & 2 1983, Lengo Press, Nairobi, Kenya. Murali. R. and opar F.M. The Industrial Manufacture of pulp from Typha domingensis. International workshop on small scale chemical recovery, high yield pulping and effluent treatment. UNIDO and C.P.P.R.I. New Delhi, India, September, 1991.
ACKNOWLEDGEMENT The author's express their sincere thanks to Pan Paper Mitis, Webuye and Highland Paper Mills, Eldoret for their encouragement and assistance in this project.
6 Current developments on plant derived gums and resins for the chemical industry in Kenya B Chikamai - Kenya Forestry Research Institute, PO Box 20412, Nairobi, Kenya
Abstract
Kenya has varied geographical and ecological conditions that support diverse flora with potential for production of various plant chemicals. Amongst them are plant gums and resins of which gum arabic, oleoresin, Eucalyptus oil, myrrh and frankincense are of commercial importance. The progress that has been made and
initiatives being undertaken to create awareness and realise jiJII commercial production are the focus of the present paper. 1.0. Introduction Kenya has an agricultural based economy that depends on agriculture and livestock for economic well being though recently the tourist industry is playing a significant role. Unfortunately, the area classified as high potential and one that supports rain fed agriculture is only about 20% of the total land area but with 80% of the human population. It is within this area that forests are found, estimated at
3~~
of the land area
and ones that are relied upon by the relatively well developed wood based industry for the supply of timber beside the conservation role. Most of the industrial uses from the forests
are
conventional
timber
and 49
related
biocomposite
products.
The
50
The fibre and non fibre resources
rest of the land area, approximately 80% is arid and semi arid (ASAL) and used mainly as range lands. However, the country has diverse geographical and ecological conditions that support different flora ranging from aquatic and coastal flora to montane vegetation and from true equatorial forests to ASAL vegetation. These diverse flora contain valuable chemical plant products that hold known or potential promise for various uses in the chemical industry. They comprise of gums, notably, gum arabic and related exudate gums found in the
ASALs~
oleoresin from pinus species in the high potential areas,
essential oils from Eucalyptus species in the high and medium potential areas and finally, resins. The later consist of myrrh and frankincense from Commiphora and Boswellia species growing in the ASALs. At present gum arabic and oleoresin are
produced on a commercial scale while knowledge about the others is becoming increasingly available. The present paper examines taxonomic aspects of these gum and resin resources in Kenya and methods of field production. The physical and chemical properties of the gums and resins are then considered in relation to nomenclature and appropriate commercial usage. 2.0. Plant gums 2.1. Gum arabic
Gum arabic forms the main commercial plant gum produced in Kenya. Commercial production began in 1990, preceded earlier by a consultative meeting of interested groups (researchers, merchants and non-governmental organisations) under the auspices of Ford Foundation. At that time, knowledge about Acacia senegal and gum arabic was scant and mostly limited to non documented information. Since then exploratory studies have been undertaken and useful details as given below gathered. There exist three varieties of Acacia senegal in the country and A. senegal var. kerensis is the main source of commercial gum arabic (Chikamai, 1994a). In Sudan A. senegal var. senegal is the source of the commercial product. The latter variety also grows in Kenya but in environments that receive relatively higher rainfall and with shorter dry season that are not favourable for gum production. The other variety is A. senegal var. leiorachis which is found in small pockets in the eastern and southern districts. It is
known to produce edible gum among the Boran community of Isiolo District.
Plant derived gums and resins
51
Currently all the gum arabic resources are still growing in natural stands and the gum collected from natural exudation. Production from natural stands pose some danger of adulteration while yield from natural exudation is generally low and erratic. Effort is therefore underway to map out gum arabic resources, identify possible contaminants in each area and enlighten local farmers on simple procedures of collection and handling to improve quality and avoid adulteration. Tapping trials are planned to improve yield and quality. Gum from Kenya (A. senegal var. kerensis) differs from the main source of commercial gum arabic (A. senegal var. senegal) in three respects (Table
1)~
it has higher values of
specific rotation, nitrogen content (hence protein) and viscosity (Chikamai and Banks, 1993). Of significance in industrial application are protein content and viscosity. High levels of protein have advantages in uses where emulsification properties are important because of the high emulsification activity and stability associated with it. On the other hand, high viscosity makes the Kenyan gum "stringy" i.e. it behaves like a chewing gum at higher concentrations and is thus less desirable in formulations where current commercial gum arabic is used. However, technologies have been developed for lowering viscosity with enhancement of emulsification functionality which have good future prospects (Chikamai, 1994a).
2.2. Other plant gums of economic importance Ethno-botanical surveys in the ASALs have revealed existence of other valuable gum
producing species. Among important ones are species in the genus Sterculia and
Astragalus (Stiles, 1988). The former contain species that produce commercial gum karaya of which India is the main producer. Small quantities of gum karaya are said to be exported from Kenya but information concerning species and production are scanty and focus for future investigation. Astragalus species produce gum tragacanth used in processed foods of high value. The commercial product comes from Turkey, Iran and Syria. Several species of Astragalus are said to occur in Kenya (Stiles, 1988) though additional details are lacking.
52 The fibre and non fibre resources Table 1: Analytical data of gum arabic *
Loss on drying (%) Total ash (%) Specific rotation (degrees) Nitrogen content (%) Hence protein (N x6.63) Intrinsic viscosity (ml/ g) Emulsification activity Emulsification stability (~IQ)
Kenya
Sudan
Nigeria
14.7
13.0 3.6 -30 0.34 2.3 16.0 1.60 95
13.0 3.7 -30 0.35 2.3 18.0 nd nd
3.0 -34 0.44 2.9 21.9 1.66 93
* Chikamai and Banks, (1993) nd ~ not determined
2.0. Pine oil
Pine oil is classified into three categories depending on the method of production; oleoresin (or gum naval stores), wood resin (wood naval stores) and tall oil (sulphate naval stores). Oleoresin is obtained by tapping living trees, wood resin from solvent extraction of wood and tall oil is recovered as a by-product of kraft (sulphate) pulping. Oleoresin and tall oil are the main sources of commercial pine oil and in terms of world trade, China is the leading producer of oleoresin while USA leads in the production of tall oil. In general, oleoresin is produced in countries where labour costs are low and tall oil in industrialised countries with sufficient pine resources. Oleoresin is the only source of pine oil produced in Kenya. Production started in 1987 after installation of a rosin plant. Pinus elliottii is the main source of oleoresin but occupies about 2% of the total pine plantations and thus does not guarantee long term sustainability. The company has expanded its recent tapping operations on P. caribaea (which is also grown on a small scale) and P. radiata (Wason, 1994; personal communication). The latter species covers a large area (18% of pine plantations) and will provide sufficient oleoresin once field tapping procedures are fully established. Other species with potential are P. pinaster and P. kesiya which however, are on small scale and experimental basis respectively. P. patula is the main species of pine grown but does not yield suitable oleoresin in both amount and quality. Table 2 provides a breakdown of the pine species grown in Kenya.
Plant derived gums and resins
53
Table 2. Pine species grown in Kenya * Species
Area (ha)
Pinus patula Pinus radiata Pinus elliottii Pinus halepensis Pinus canariensis Pinus caribaea Other pines
44,691 10,388 1,224 362 255 118 460
* --+ Forestry Dept.;
1991
Field tapping is based on the Portuguese method that advocates for narrower face width. Recent studies on profitable oleoresin tapping (Chikamai, 1994b) have shown that: · higher yields are obtained from trees
~ 30
em dbh
· two faces of 7 em width per tree per period result in good yield with minimum damage to the tree · weekly streaks and application of acid result in higher yield though use of acid paste would give even higher yield and reduce the frequency of
working
on
the
trees. The season for tapping has also been determined. For P. elliottii growing on the hills in Machakos and Taita Taveta Districts, higher yield is obtained during the drier and warmer months than during the rains or cooler months. The former conditions were therefore recommended for tapping while the rain and cooler seasons were to be set aside for plantation maintenance. In the case of P. caribaea which is a lowland species, higher yield is obtained during the drier months which were recommended for tapping setting aside the rain season for maintenance of the plantations. Studies on yield between species have shown that P. caribaea yields more oleoresin ( about twice) than
P. elliotii. Long term sustainability for the rosin industry will therefore depend on successful tapping of P. radiata. This will require establishing suitable procedures for tapping including the use of acid paste. 2-Chloroethylphosphonic acid paste (CEPA) which has been successfully developed (McReynolds and Rossuth, 1985) will need to be tested. Additionally, areas under P. elliottii and P. caribaea will have to be increased in future
54 The fibre and non fibre resources
planting programmes. Meanwhile to overcome conflict of interest on the utilisation of pine resources in the country, a tapping cycle should be incorporated into the management plan to run alongside either the sawnwood or plywood/veneer cycles. Oleoresin from the field contains two commercial products; turpentine and rosin. The approximate composition is 15-20% turpentine, 70-75% rosin with 5-10% representing foreign matter notably, debris and water. Turpentine is the volatile component (essential oil) after distillation. It consists of monoterpenes with elementary formula C 1OH 16 and sesquiterpenes (C ISH24), the actual composition depending on the species. Main constituents are pinenes, carene with minor constituents of camphene, longifolene, limonene etc. The best quality turpentine in the USA contains high content of a- and
~-pinenes.
Studies on the composition of Kenyan turpentine has been
determined for P. radiata (Coppen and Robinson, 1988) which was found to be of good quality with high content of pinenes (Table 3). All the turpentine currently produced is used as a solvent in the paint and varnish industries. Application of the turpentine in the pharmaceutical or as starting material in other industries has been hampered by lack of a fractionation plant. Rosin constitutes the solid residue after distillation of the turpentine. It consits of a mixture of resin acids and small amount of esters. The major types are pimaric acids that are characterised by both methyl and vinyl subsitituents at the C- 7 position and Abietic acids bearing only a single isopropyl group at C-7 (Sjostrom, Table 3: Constituents of turpentine and rosin from P. radiata* Turpentine composition % 28.2 68.4 0.5 1.0 0.6 ~-Phellandrene 0.9 Terpinolene 0.1 a-Terpineol O. 1 Others 0.2 * Coppen and Robinson, 1988
Component a-Pinene ~- Pinene Camphene Myrecene Limonene
Rosin Component composition % 9.9 Pimaric acid 50.3 Levopimaric 4.3 Isopimaric 4.6 Dehydroabietic 7.1 Abietic 19.3 Neoabietic 4.5 Others
Plant derived gums and resins
55
1981). Like turpentine, the composition is characteristic of the species. The rosin of P.
radiata from Kenya is rich in Levopimaric and Neoabietic acids accounting for about 700/0 (Table 3). In general, the physical properties of Kenyan rosin i.e. high acid and saponification numbers but low unsaponifiable matter makes it of good quality comparable
to
acceptable
international
standards
(Wason
1994,
personal
communication). All the rosin produced is consumed by the paper industry as adhesive.
3.0. Eucalyptus oil Not much has been done to utilise Eucalyptus oil in Kenya though Eucalyptus species form the third major plantation species after cypress and pines. And when the area under farm forestry is taken into account, Eucalyptus species are the most widely grown species. The species are grown for poles and posts, fuel wood, timber and to a lesser extend decorative veneer. Various species have been tried though the following are the principal ones: Eucalyptus saligna, E. grandis, E. maculata, E. paniculata, E.
camaldulensis, E. tereticornis, E. citriodora and E. globulus. Based on studies elsewhere, E. camaldulensis, E. tereticornis, E. citriodora and E. globulus are potential sources of Eucalyptus oil (Eucalyptol). Various factors would favour a Eucalyptus oil industry in the country. First, the main source of oil are leaves which are not in current use. The leaves could be gathered after harvesting the stem or from pollarded branches and thus do not pose direct competition to the primary product i.e. wood. This would allow dual management of Eucalyptus plantations or wood lots for wood and oil. Secondly, apart from managament for timber or veneer, the other uses are for short rotation cycle with a maximum of 12 years which are more compatible with management for oil. Most species begin to produce oil at 3 years. Finally, the ability of the species to coppice allows leaves to be harvested 3 or 4 times before the farm is replanted or replaced. This has advantage as additional costs for further establishment are avoided in the short run. Eucalyptol is an essential oil with an oil content varying between 1.oa~ and 9.0 % (Maitai et al, 1983) and containing up to 30 different compounds. Yield and composition are species specific. For commercial utilisation, Eucalyptol is classified into pharmaceutical and perfumery oils solely on the basis of cineole content. Oil with a cineole content
~
600/0 is used in the pharmaceutical industry and priced higher.
Cineole is used as an expectorant, antiseptic and in the manufacture of deodorants
56
The fibre and non fibre resources
(Panda and Panda, 1987). Various species of Eucalyptus are grown in Swaziland and Zimbabwe in southern Africa for the production of cineole rich oil (Coppen, 1990). Table 4 lists some of the main species rich in Eucalyptol. Some species produce Eucalyptol low in 1, 8 - Cineole but containing high amount of other compounds with a distinct odour suitable for perfumery industry. Among these are E. citrodiora with a high content of Citronellal and Citronellol and E. tereticornis whose level of Cineole is not high enough for use in the pharmaceutical industry (Table 4). In addition, the latter species has a high proportion of a-pinene, an important
component in the perfumery industry. Citronellal is an optically active aldehyde used as a starting material for manufacturing various compounds while Citronellol has been used to prepare various esters possessing different odours. Table 4: Yield and composition of major constituents of Eucalyptol by species Species
oil yield (mfb) Major component (%, v/w)
E. radiata
9.9
1, 8 - Cineole
67.4*
E. smithii
5.0
1, 8 - Cineole
70.7*
E. sideroxylon E. citriodora
2.7
1, 8 - Cineole
Citronellal
69.1 * 72.8**
J3-Citronellol
14.5**
1,8 - Cineole
37.5**
a-pinene
13.1 **
E. tereticornis
mfb
~
composition (%)
moisture free basis
* ~ Coppen, 1990, **
~
Panda and Panda, 1987
Initiative is needed to screen Eucalyptus species with potential for oil in the country for a Eucalyptus oil industry.
Plant derived gums and resins
57
4.0. Myrrh and Frankincense Myrrh and frankincense, like gum arabic, are articles of commerce since ancient times and remain important products in specialised industries. Until recently Somalia was the leading producer accounting for 80% of the world market (Ali, 1986). Myrrh (from latin word myrrha) is derived from species of the genus Commiphora of the Burseraceae family. There are about 46 species of Commiphora indigenous to Kenya (Dale and Greenway, 1961) though the main myrrh producing species are less than six and confined to the ASALs. Frankincense (meaning pure incense in French) is derived from species of the genus Boswellia of the Burseraceae family. Three species are indigenous to Kenya. General knowledge of myrrh and incense in the country is still poorly understood both in terms of their availability or economic value. Most of the collection is done by local herdsmen and women while looking after livestock or for fuel wood which is then sold on local markets as incense. However, there is now increasing awareness about the commercial importance of the products, thanks to the effort of a number of groups. Taxonomic difficulties which initially hampered adequate identification of myrrh and incense by source has been resolved following the recent publication of "The flora of Tropical East Africa on the Burseraceae" (Gillet, 1991). Market and ethno botanical surveys have identified the main myrrh and resin producing species (Chikamai and Gachathi,
1994~
Stiles, 1988). It
has been found that an unknown quantity of the products is exported to China and Japan mostly through Somalia. The following species have been identified as sources of myrrh and incense: Commiphora myrrha - is the source of true myrrh. It is said to be quite variable with different forms merging imperfectly that recognition of intraspecific taxa is not practical (Gillet, 1991). It produces myrrh commercially called "molmol" in Somalia.
C. incisa - produces resin which hardens to yellowish red. C. confusa - easily confused with C. africana (hence the epithet). It produces highly valued incense among the Borana community of northen Kenya.
C. holtziana - produces gum resin used by the local communities as insect repellent and treatment offoot rot in sheep. Two subspecies i.e. subsp.
58
The fibre and non fibre resources
holtziana and subsp. microphylla are recognised and both are found in
Kenya.
C. habessinica - considered to produce an inferior type of myrrh of commerce. Two subspecies have also been recognised; subsp. habessinica is found in Kenya and Ethiopia while subsp. tanganyikensis is found in Tanzania. Boswellia neglecta - exudes a fragrant gum resin collected and sold under
various local names. The incense is commercially called "Olibanum". The next step on the resource aspect is to carry out resource surveys to map out source locations, carry out inventories and evaluate the commercial availability for tapping. In terms of chemical composition, myrrh is a natural oleo-gum-resin comprising about 3-8% essential oil, 30-60% water soluble gum and 25-40% alcohol soluble resin (Tucker, 1986). The essential oil and resins are of more commercial significance. Like most plant products, their nature and composition are species specific. Some preliminary studies have been carried out to determine the resin and oil components of three Kenyan species. C. myrrha and C. ho/tziana were found to be rich in sesquiterpinoids with oil yield of 7.6% and
5.4~~
respectively (Provan et aI, 1987a).
The main resins in both species were Elamanes, Eudesmanes and Germacranes. C. campestris was found to have an oil content of 4.8% and rich in monoterpenes notably,
pinenes and sabinenes (Provan et aI, 1987b). Frankincense is also a natural oleo-gum-resin comprising about 85~~
5-9~o
essential oil, 65-
alcohol soluble resins and the remaining as water soluble gums. True olibanum is
said to come from Boswellia carteri and B. frereana growing in Somalia. Chemical characterisation of the oil from commercial incense has revealed high proportions of monoterpenes notably, pinenes, limonene, phellandrene, cadenene, camphene etc. (Tucker, 1986). Commercial Indian olibanum is from B. serrata. Chemical composition of the oil shows that it is rich in o-thujene which accounts for 61.4% with small amounts of a-pinene (7.7%), sabinene (5.1%) and P-cymene (4.3%) (Varghese et aI, 1987). Preliminary analysis of B. neglecta from Kenya has shown that it is rich in monoterpenes (Provan et al, 1987b). It has a mean oil yield of 4.4% with a-pinene, athujene and p-cymene as major components. More studies are still needed on the chemical characterisation of both myrrh and incense.
Plant derived gums and resins
59
References Ali, A. F. (1986). The State of Forestry Research in Somalia. In Conf. on For. Res. in Afirica. 8p. Chikamai, B. N. and Banks, W. B. (1993). Food Hydrocolloids, 7,521. Chikamai, B. N. (1994a). PhD Thesis, University of Wales, UK. Chikamai, B. N. (1994b). E. Afri.Agri. For. 1. In press. Chikamai, B. Nand Gachathi, F. N. (1994). E. Afri.Agri. For. 1. In press. Coppen.J. J. W. and Robinson, 1. M. (1988). Terpenoid constituents and properties of xylem oleoresin from exotic Pinus radiata. Naval stores review, March/April. Coppen, J. J. W. (1990). Analysis of oils from leaf samples ofEucal)'Ptus species growing in Zimbabwe. Unpublished report, NRI, UK. Dale, I. R. and Greenway, P. 1. (1961). Kenya Trees and Shrubs, Buchanan's Kenya Estates Ltd., Nairobi. Gillet, 1. B. (1991). Flora of Tropical East Africa; Burseraceae. A. Balkama, Rotterdam. Maitai, C. K.; Talalaj, S. and Talalaj, D. (1983). Aromatic plants of East Africa. National Council of Science and Technology, Kenya. McReynolds, R. D. and Rossuth, S. V. (1985). Southern Journal of Applied Forestry, 9, 170. Panda, R. and Panda, H. (1987). The Indian Forester, 113,437. Provan, G. J.; Grey, A. I. and Waterman, P. G. (1987). Flavour and Fragrance 1.,2, 109. Provan, G. J.; Grey, A. I. and Waterman, P. G. (1987). Flavour and Fragrance 1.,2, 115. Stiles, D. (1988). Desertification Control Bulletin, 17, 18. Sjostrom, E. (1981). Wood Chemistry: Fundamentals and Applications. Academic press. Tucker, A. O. (1986). Economic Botany, 40, 425. Verghese, J. and Joy, M. T. (1987). Flavour and Fragrance 1.,2,99.
Part 2: Pulping
7 Advances in steam explosion pulping (SEP) *B V Kokta, **y Ben, **1 Doucet, *A Ahmed and ***0 A Sukhov*Centre de recherche en pates et papiers, Universite du Quebec a Trois-Rivieres, Trois-Rivieres (Quebec) G9A 5H7 Canada; **Departement des sciences du bois, Faculte de Foresterie, Universite Laval, Ste-Foy (Quebec) GIK 7P4 Canada; *** Technical Institute of Pulp and Paper Industry, St-Petersburg, 198092 Russia
INTRODUCTION Steam explosion pulping process consists of chemical impregnation of chips, cooking with saturated steam for a short period of time followed by a rapid pressure release, atmospheric refining and bleaching. This process is suitable for both hardwood and softwood (1). Impregnation of wood chips with Na2S03 is essential to obtain ultra-high-yield pulp and preserve a high brightness level. To ensure good swelling of chips, NaOH is usually added, especially during the hardwood cooking. The presence of NaOH proved to be beneficial to the paper strength increase as well as to the decrease of specific refining energy (2,3). In the negative side, both optical properties as well as yield were adversely affected by the presence of NaOH (2). It is believed that the high alkalinity of the impregnation solution contributed to higher yield and brightness losses. For better understanding the correlation between the chips chemical pretreatment and resulting paper properties, yield and specific refining energy, this study was mainly focused to the following aspects: i) the effect of chemical pretreatment on physico-chemical changes of fibers. ii) the correlation between physico-chemical changes of fibers and paper properties. iii) the optimal impregnation system.
63
64
Pulping
EXPERIMENTAL Materials Freshly cut aspen trees (populus tremuloides Michx) from the Joliette region were debarked, chipped and screened ala Station Forestiere, Duchesnay, Quebec. Afterwards, all chips were shredded at the Centre de Recherche et Developpement, Consolidated-Bathurst Co., Grand-Mere (Quebec). The chips were shredded to facilitate the impregnation of chemicals. The average chip size, after screening, was as follows: length 2.5 to 3.75 em, width 1 to 2 em and thickness 1 to 9 mm.
Chemical impregnation Aspen chips (150 g at a 50% dryness level) were mixed in plastic bags along with 150 g of a solution made up of different concentrations of chemical products such as Na2S03 alone or with NaOH, NaHC0 3, MgC03; NaOH with MgC1 2. The liquor/chips ratio was 3:1. The time of impregnation was 24 h and the temperature of impregnation 60°C.
Cooking Cooking was carried out using saturated steam in a laboratory batch reactor of 300 mL built by Stake Tech. Co. Temperature was 190°C and time of cooking 4 min unless otherwise specified. Cooking was preceded by a 1 min steam flushing phase at atmospheric pressure. After cooking, pressure was instantaneously released, and chips which exploded into the release vessel were washed with tap water and subsequently refined after being stored in a cold room. Cooking under CMP mode was carried out at 150°C for 30 min in vapor phase using the same reactor as in the case of explosion pulping. Yield was measured as follows: exploded chips (75 g) were washed with 1 L of tap water and subsequently defibrated for 90 seconds in a laboratory blender at a 2% consistency level. The resulting pulp was washed once again with 1 L of water, dried at 105°C to constant weight and compared to the initial 0.0. weight of chips. Laboratory refining was also done with a domestic blender, Osterizer B-8614, at a consistency level of 2%. Defibration and refining energy was measured using a EW-604 wattmeter. Relative specific refining energy was calculated by subtracting the blending energy of fully heated pulp from the total energy needed to refine and blend the fiber suspension.
Property evaluation Paper sheets were prepared and tested according to standard CPPA testing methods on 1.2 g sheets. Brightness of paper was evaluated on 3 g paper sheets made with deionized water. Ionic content (sulphonate and carboxylate ions) was determined by means of conductometric titration (4).
Bleaching Bleaching was carried out according to previously published procedures, in one stage, using 2% of hydrogen peroxide, 20% bleaching consistency at 80°C and 3 h bleaching time (5).
Steam explosion pulping
Lignin in aspen and pulps Total lignin content is equal to acid insoluble and acid soluble lignin. They are determined separately according to Tappi standard methods.
ESCA analysis The ESCA spectrometer used in this study was an ESCALAB MKII spectrometer fitted on a microlab system V.G. scientific and equipped with a dual Mg-AI anode X-ray source, non-monochromatized. Kinetic energies were measured using a hemispherical electrostatic analyzer with a 150 mm radius working in a constant pass energy mode (20 ev for CIs and 0ls peak, 50 ev for S2p and for survey spectra). No flood gun was utilized. The vacuum in the test chamber was maintained at 10-8 Torr. Liquid nitrogen was used to cool the sample. Spectra were produced using the Mg anode at 300 watt. For peak synthesis, curve fitting technique was used for resolving the complex spectra, employing the computer with VGS 1000 software. The ratio of Gaussian to Lorentzian function was 60%. For the spectrometer and conditions used in this study, the ratio of oxygen atoms to carbon atoms and sulfur atoms to carbon atoms can be estimated from their respective peak intensity areas by the following equations: NJNe = 10"2.85 r, NslN e =0.523 IslI e where NJNe is the atomic ratio of oxygen to carbon NslN e is the atomic ratio of sulfur to carbon 10 is the normalized integrated area of 0ls peak Ie is the normalized integrated area of CIs peak Is is the normalized integrated areas of S2p peak So the various atomic ratio can be calculated directly from their peak area.
Infrared spectroscopy analysis Circular specimens of 10 mm in diameter cut from the handsheets of grammage 10 g/m 2 were covered with KBr powder on both sides and the sandwich like specimens was pressed to 1556 Kpa. Infrared spectra were recorded in absorbance units in the frequency range of 4000 to 400 cm- 1 with a FTS-60 Digilab spectrometer. The spectrometer was equipped with a nitrogen source, a computer control and a DTGS detector.
FTIR - RAMAN Spectroscopy Evaluation of crystallizing was done using qualitative methods as described by Sukhov et al. (6).
RESULTS AND DISCUSSION Pulp and lignin content The total lignin content (acid soluble and acid insoluble) of aspen chips was 19.6%. The effect of different forms of chemical treatment during impregnation on
65
66
Pulping
the resulting pulps' yield and lignin content was verified. The lignin content of the pulp based on initial wood shows that the quantity of lignin remained in the pulp is virtually same irrespective to the pretreatment system. About 2% of the total lignin is removed from the chips under explosion pulping conditions. Yields were highest for the pretreatment system as: 8% Na2S03 + 1% MgC0 3 (yield 93%) and 8% Na2S03 + 1% NaHC0 3 (yield 90.5%). The lowest yield 87% was obtained with 8% Na2S03 + 1% NaOH. The yield drop is mainly due to the partial dissolution of hemicellulose, especially xylan, during impregnation and high temperature steam cooking. The removal of wood extractive and acid soluble fraction of the lignin also contributed to the yield lost. Figure 1 shows that impregnation solution pH should be in the range 9 - 10.5 in order to obtain a 90% yield or higher. The highest yield (93%) produced with 8% Na2S03 + 1% MgC0 3 at pH 10.8 can be related to the protective effect of magnesium carbonate against carbohydrate hydrolysis, oxidation and degradation.
FTIR results Fourier transformation infrared spectroscopy showed some differences in relative intensities for a band at 1735 crrr! due to C=O stretching vibration of acetyl and carboxyl in xylan of hemicellulose. The intensity of this band is much weaker for the pulps. The absorption band at 1735 crrr! for the pulps was weak even after a mild acid wash which confirms elimination of both the uronic acid group and xylan. Furthermore, the decrease of absorption band 1735 crrr'! concorded with the weakened absorption intensity at 1235 cm-l due to C=O stretching of acetyl and carboxyl in xylan. The bands at 1593 and 1504 cm-l ascribed to C=C stretching vibration in benzene rings showed no significant variation for different pulp samples.
Optical properties Brightness values of pulps, before and after bleaching, as a function of chemical pretreatment are shown in Figure 2. It is obvious that pH control when using carbonates and bicarbonates with Na2SO 3 resulted in a slight initial brightness increase compared to Na2S03 used alone, and in a substantial (4-5%) brightness increase compared to the Na2S03 + NaOH system.
Paper properties and specific refining energy The pulp properties, yield and refining energy consumption depend significantly on pretreatment chemicals. As shown in Figure 3, breaking length for all CSF range increased with the presence of NaOH, NaHC0 3 or MgC0 3 in comparison with Na2S03 alone. Furthermore, it is obvious from Figure 4 that breaking length is not at all a function of yield, since the system with MgC0 3 with a yield of 93% had a strength level similar to that of NaOH with a 87% yield.
Steam explosion pulping
LIGNIN CONTENT (%) YIELD (%) 25 , . - - - - - - - - - - - - - - - - - - - - - - - r - 100
20
·.1
95
15 90 10 85
5
-+- YIELD
LIGNIN ~CONTENT
-
o
80 7
Figure 1
7,5
8
8,5
9
9,5 10 10,5 11 11,5 12 12,5 13 13,5 14 pH
Influence of impregnation liquor pH on pulp yield and lignin content.
BRIGHTNESS (%)
A
A+l~N.OH A+l~NaHC03 A+l~MIC03 B+l~MICIt
A:
Figure 2
8~
Na2S03
B:
3~
No chemical
NaOR
Influence of different chemical impregnation system on pulp brightness.
67
68
Pulping
BREAKING LENGTH (krn)
8 ,.--------------------------..,
6
4
8% Na1S01
-+-
8% Na1S J+
-S- 8% Na1S0J+ 1% NaHCOJ
~ 8% Na1S0J+ 1% MgCOJ
2
~ 3% NaOH + 1% MgCL1
~ No chemical O;-----.--~---.----,-----yo--~--~--..---.----------!
o
50
100
150
200
250
300
350
400
450
500
CSF(ml) Figure 3
Influence of impregnation chemical on resulting pulp's breaking length at various CSF levels.
Breaking length (km)
8r---------------------------
*
Na2S~+ NaHCO~8+1)
+
0 Nag803+ MgCO i8+1)
N~S03+ NaOH(8+1)
I I I 4"----.-..--....L---..:....-----L-_....:-_ _..l...-_~_ ___1.._ _..l.__
85
86
87
88
89
90
91
92
Yield (%) Figure 4
Relation between breaking length and pulp yield.
93
94
___J
95
Steam explosion pulping
As observed in Figure 5, the presence of swelling agents NaOH, NaHC0 3 or MgC0 3 in pretreatment solution improved the tear values of the resulting pulp for similar breaking length. Results appearing in Figure 6 indicate that the presence of swelling agents results in a considerable specific refining energy decrease compared to Na2S03 alone. This is in agreement with results obtained from semi-industrial trials with or without NaOH (3,7,8). It is important to mention that the specific refining energy decrease is similar for NaHC0 3 or MgC0 3 as in the case of NaOH even though their yields are from 3 to 6% higher. It is quite clear from Figure 7 that specific refining energy is independent of yield. This fact is in complete agreement with the work of Carrasco et al (9) as well as with Kokta et al (10). Breaking length as a function of specific refining energy is plotted for different forms of chemical treatment in Figure 8. The presence of NaOH, NaHC0 3 or MgC03 have substantially increased paper strength at a constant specific refing energy. The same paper strength could have been achieved with substantially lower specific refining energy, when the pretreatment solutions contain swelling agents in addition to Na2S03' Once again, these results are in agreement with semi-industrial trials carried out with Na2S03 alone or with NaOH (3,8). The presence of swelling agents enable faster chemical diffusion, fiber softening and facilitate higher total ionic content on fiber surfaces. As a consequence, this leads to easier defibration along with lower specific refining energy and to higher long-fiber content expressed as L factor. The L factor is directly correlated with tear values of the paper, as shown in Figure 9.
Tear index (mN. m 2 / g)
91
Na2S~+
NaOH(8+1)
8.5 8
Na2S03+ NaHC0 3(8+1) _,/
Na2S03+ MgC03(8+1) t;'
7.5 7
6.5 6L-------:....---...:..---~---~--~---....:...----.-;..------'
4
4.5
5
5.5
6
6.5
Breaking length (km) Figure 5
Tear index as a function of breaking length.
7
7.5
8
69
70
Pulping
RELATIVE SPECIFIC REFINING ENERGY, MJ/kg
4 -.,.-------------------------.
3.5
3 2.5
~
2 1.5
-+-
8% Na2S0J+ 1% NaOH
-e-
8% Na2S0J+ 1% NaHCOJ
~
8" Na2S0J+ 1% MgCOJ
~
3% NaOH + 1% MgCL2
--A- No chemlal 1-+-----r-----,---r---...,..----r---~----r--~-.,....---..------I
o
50
100
150
200
250
300
350
400
450
500
550
CSF(ml) Figure 6
Specific refining energy as a function of CSF of pulp obtained with various impregnation chemicals.
RSRE (MJ Ikg)
4,------------------------------..
"*
0 Na2S03+ Mg C0 3( 8 +1)
11-
I
o~-----.&....--...o..------"-----------"----'-----------
85
86
87
88
89
90
91
Yield (%) Figure 7
Specific refining energy as a function of yield.
92
93
94
9S
Steam explosion pulping
, Na2S03+ NaHC0 3(8+1) NaaS03+ MgCO~8+1)
7
6
s
____"__
4L--..!.----L----l...._--..l.._----I~_.J...__~_~
1.5
1.7
Figure 8
8
1.9
2.1
2.3
2.5
2.7 2.9 3.1 RSRE (MJ/kg)
3.3
3.5
___'''''"''__ _
3.7
3.9
Breaking length as a function specific refining energy.
GLEN GTH (km) -BREAKIN -r----------
L·FACTOR (%) -,
60
55 6 50 4
45
40 2
3S
A
A+tt,NaOH A+lt,NaHCO.A+lt,MICO, B+lt,MICIt No chemical
A:
Figure 9
8~
Na 2SO a
B:
3~
NaOH
Influence of L-factor on pulp breaking length.
71
72 Pulping
Correlations between physico-chemical changes and paper properties Effect of bulk ionic content Carrasco et al. (9) showed that the most important fiber change, which explains more than 80% of paper properties is fiber ionic content. In Figures 10, 11, paper strength properties are related to sulfonate and total ionic content. Figure 10 indicates that the highest breaking length could be correlated, in case of NaHC03, with the higher values of sulfonate content. The correlations expressed in Figure 11 show that paper properties increase with total ionic content of the pulp. Effect of surface composition It is well known that adhesion based paper properties like breaking length, burst index, stretch etc. are directly related to interfiber contact surfaces. Therefore, ESCA (electron spectroscopy for chemical analysis), a surface sensitive technique, was applied to evaluate the surface characteristic of pulps. Breaking length is presented, in Figure 12, as a function of chemical treatment as well as O/C ratio and C 2 peak area. The presence of swelling agents (NaOH, NaHC0 3 and MgC0 3) in Na2S03 impregnation solution resulted in a higher O/C ratio and C 2 peak area compared to Na2S03 alone or other chemicals. This clearly indicated a higher percentage of carbohydrate on the fiber surface which lead to higher adhesion potential between OH groups and, therefore better strength.
BREAKING LENGTH (km)
SULFONATE (mmol/kg)
8 - , - - - - - - - - - - - - - - - - - - - - - - - - - = - . . : . . . - 70
60 6
so 40
4
30
20
2
10
A
A+ICJ,NaOH A+ICJ,NaHCq. A+l~MICG.4 B+ICJ,MIC~ No chemical
A:
8~
Na 2S03
B: 3911 NaOH
Figure 10 Influence of sulfonate content on breaking length of pulp.
Steam explosion pulping
73
BL,KM It BURST INDEX,KPa m 1/ g TEAR INDEX, mN .m 1 / g 14 , . - - - - - - - - - - - - - - - - - - - - - - - - - - - - , 8
-t
+ 12
7
+
10
6
+ BREAKING LENGTH
8
-+6
5
TEAR INDEX
-*4
4
3
2
CSF ..:. 100 ml
o 70
80
90
100 110 120 130 140 1S0 160 170 TOTAL ION CONTENT (m mol/kg)
Figure 11 Effect of total ionic content on pulp tear index, breaking length and burst index.
AREA(%) It O/C RATIO 8 TB_R_E_A_K_IN_G_L_E_N_G_T_H_(k_m~) ;:-- C2 PEAK ....:...:..-=-=-==.:.:.::.:...::::.....::..:..::~~~ 70
6
60
4
so
2
40
A
Figure 12 Effect of C2 peak area (%) and ole ratio on breaking length.
2
180 190
74
Pulping
The strength properties for all forms of treatment are plotted in Figures 13 and 14 as a function of O/C atomic ratio or C 1 peak area fraction. As mentioned earlier, the higher O/C ratio correlated extremely well with adhesion properties such as breaking length and burst index, but did not correlate to tear values to any great extent. BL,km & Burst index,KPa.m 2/ g 10
Tear index, mN.m 2/ g 8
·1·
,1.J. .-:Ll:.----=1=---.---- - 7
8
-6
-I-
CSF = 100 ml
6 ~~
*
;:~.
-5 - 4
BREAKING LENGTII
-1- TBARINDBX ~iE-
BURST INDEX
/'
3
o
2
1 - l__ L_...J-l_L.-l-J_
35 37 39 41 43 45 47 49 51 53 55 57 59 O/C KfOMIC RKfIO X 100
Figure 13
Effect of O/C ratio on breaking length, tear index and burst index of pulp.
BL,km & Burst Index,KPa.m 2/ g
Tear index,mN.m 1/ g
10...---------------,. 8 ~
~
8 -
-1- .
-I :---':"I:":'~:I _ -1---',. ~- 7
'"
.........
.
-..~ -I-6 6~ '~. ~ ~s 4-
~
'1'~4
2 -
~~
o --I_.I_I_I_I_l.-L-J_....J __ I.---L-L-1
CSF = 100 ml BRBAKING LBNGTII -1- TBAR INDEX -;'t~ BURST INDEX
- 3
2
20222426283032343638404244464850 C PEAK AREA PRAC'flON
Figure 14 Effect of C 1 peak area fraction on pulp breaking length, burst index and tear index.
Steam explosion pulping
The C1 peak area fraction can only be found in lignin and extractives present on the surface. Extractives, as well as lignin, provide amount of potential hydrogen bonding OH groups at least three times lower than cellulose and therefore, should negatively influence adhesion strength. This is confirmed in Figure 14 where both burst index and breaking length drop with a C1 peak area fraction increase. It is well known that sulfonation of lignin improves the adhesion interfiber forces. It is not surprising that the increase in SIC atomic ratio leads to higher breaking length, as shown in Figure 15.
SIC ATOMIC RATIO X 10000 BREAKING LENGTH (km) 8 - r - - - - - - - - - - - - - - - - - - - - - - - - - - r - 30
7
25
6
20
5
15
4
10 CSF ~ 100 ml
3
--*-
5
BREAKING LENGTH SIC ratio
2
...... 0
-+--------r--------r-----~-----._------::~
A
A+l~NaOH
A+l~NaHC03
A:
Figure 15
8~
Na 2S03
A+l~MIC03
B+l~MIC~
No chemical
B: 3% NaOn
Influence of SIC ratio on pulp breaking length.
Effect of high temperature cooking on cellulose structure Sukhov et al (6) have proposed a four-component model structure definition of cellulose material by means of combined FTIR and Raman spectroscopy. They have shown that CI leads to higher degree of interfiber bonding than CII and in consequence sheets made of CI results in tensile strength more than twice the value of that made from mercerized cellulose of CII. The above mentioned phase changes were observed in pulp samples prepared at various pulping conditions. As shown in Figure 16, cooking temperature leads to ell disordered decrease and CI ordered increase. Careful observation reveals that there is a sharp increase in CI value (Figure 17) or sharp decrease (Figure 18) in CII value occuring at the cooking temperature 190°C and cooking time at least 2 min. It seems that this structural changes may at least partially explain better bonding of SEP pulps.
75
76
Pulping
o CTMP 128°C/4 min.
0.75 -
• CMP 150 oC/30 min. oC/1 • SEP 180 min. SEP-N 180 oC/1 min. o SEP 180oC/2 min.
•
o
0.70 -
• SEP 180o C/4 min. • SEP-N 200 oC/4 min. )IE BASE EXP 1900C
w
• WATER EXP 190°C + SEP 190°C/I min SEP 190o C/2 min X SEP-N 190oC/2 min • SEP 190o C/4 min + SEP 200°C/I min
en
9::JQ> j.65 -
e
X
....J"O
...J~
wg
()~
••
0.60 I
0.06
I
1
I
I
• SEP 200 oC/2 minoC/4 • SEP 200 min
•
0.08 0.10 0.12 0.14 0.16
0.18
CELLULOSE I ordered Figure 16 Structural changes in CTMP, CMP and SEP of aspen.
0.17 0.16 0
w 0.15 a: w 0.14
0
a: 0.13 0
w 0.12
SEP
(J)
0
-J
~
0.11
...J
0.1
UJ
0.09
-J
o
0.08 0.07 100 110 120 130 140 150 160 170 180 190 200 210 TEMPERATURE (0 C) Figure 17 Effect of temperature on cellulose I.
Steam explosion pulping
0.78 0
RMP
0.76
w a: 0.74 w 0
CMP
a: 0.72 0 en 0
-W
0.7 0.68
CTMP SEP
en 0.66 0 -' :J 0.64 .....J .....J
w 0.62
o
0.6
100 110 120 130 140 150 160 170 180 190 200 210 TEMPERATURE (0 C)
Figure 18 Effect of temperature on cellulose II. In Figure 19, breaking length value of SEP is compared as a function of different cooking time as well as cooking severity. An increase in paper strength is observe with the rise of cooking time from 1 to 2 min at 195°C, when compared the pulp at the same ionic content as well as the same chemical pretreatment. At the cooking temperature 200°C, the cooking time of 1 min seems to be sufficient for properties increase because it leads to required CI increase and CII decrease (Figure 16). Effect of pulpin~ conditions on surface chemical composition as well as cQ'stallinity In comparative semi-industrial trials, Barbe et al. (3) showed that SEP exhibited much higher strength than CMP at comparable total ionic content and yield. In order to explain the fundamental factors which may contribute to the higher strength level of SEP, both SEP and CMP taken from the Barbe et al. (3) trials were examined by ESCA(ll). In Table 1, kraft aspen pulps were compared to water exploded aspen chips (SEP-H 20), SEP (8+1), and CMP (8+1). SEP (8+ 1) revealed a higher O/C content on the surface than CMP (8+ 1) did, which indicates better bonding surface characteristics. Lower percentages of C1and 01 (found mostly on lignin or non-cellulosics) for SEP, as opposed to CMP, also indicate a lower amount of lignin on the surface, even though the bulk percentages of lignin are the same for both SEP and CMP (10). Finally, the higher SIC found for SEP, compared to CMP, indicates a higher level of surface lignin sulfonation for steam explosion pulps. It seems that a higher percentage of carbohydrates and a higher percentage of sulfonated lignin on the fiber surface of SEP (compared to CMP) can partially explain superior adhesion when related to strength properties.
77
78 Pulping
8
EXPLOSION PULPING OF ASPEN: TOTAL IONIC CONTENT VERSUS BREAKING LENGTH AT CSF 100 - EFFECT OF OPERATING CONDITIONS
2000C I'
E
o =8%No ZS0 3 =40%O.o.C.
.~
~
190°C 2'
180°C 5'
J 8;::::
1700C II'
6
::I:
o
I~
tt!)
:z
lLLJ ,..J
y
4
o
:z
I
::lIl:::
x~
x-16°/oNo2S03 == 32°/00.D.C
12%No2S03=24%0.D.C.
8°1o N02S03 ==IG%OD.C.
oct
:~
~x
x 195°C
2
ltD
I'
o
195°C 2'
o
195°C 3' 200°C 75"
A
O-t---~--,r----,.----r----...----Y----r---
120
160
200
240
TOTAL IONIC CONTENT (mmol/kg)
Figure 19 Effect of operating conditions and total ionic content on the breaking length of pulp (SEP) at 100 CSF level.
Table 1 ESCA Spectroscopy of Ultra-High Yield Aspen Pulps Pulp
Yield (%)
Total Ionic Content (mmol/kg)
Sulfonic
Cl
01
(%)
(%)
0.59
20.0
7.7
OIC
(mmol/kg)
Kraft
SIC
BL (km)
Spec. ref. Energy (MJlkg)
SEP (8+1)
92
174
43
0.52
33.9
10.3
3.08
7.2
3.0
eMP (8+1)
89.9
190
53
0.41
43.1
14.3
2.22
4.7
9.7
SEP (H2O)
91
85
0.34
55.6
22.7
4.1
8+ 1: 8% Na2S03 + 1% NaOH; SEP: 195°C; 1 min; CMP: 150°C; 30 min
Steam explosion pulping
In Table 2, cellulose crystallinity I index as well as crystallite sizes were compared for aspen fibers, CTMP (5+5), CMP (8+1) and SEP (8+0) and SEP (8+1), all prepared in semi-industrials (3,6,7). It was shown (9) that CTMP or CMP aspen treatment increases C 1 cellulose crystallinity from 56% to 71.50/0 or 71.3%. In the case of SEP submitted to a temperature above the glass-transition of lignin, crystallinity C1 increases to 75.90/0 irrespective of the chemical treatment. It seems that crystallinity and crystallite sizes, being 21.4 A for aspen and 27 A, 27 A for CTMP or CMP and 31.5 or 31.5 for SEP (8+0) or SEP (8+0.5), are a function of temperature rather than the type of chemical treatment. Table 2 X-Ray Diffraction Parameters Aspen Fibers
CTMP 128°C; 10 min 5% Na2S03 5% NaOH
CMP 150°C; 30 min 8% Na2S03 1% NaOH
SEP 194°C; 1 min 8% Na2S03
SEP 194°C; 1 min 8% Na2S03 0.50/0 NaOH
Crystallinity Index (Cr.I) (%)
56.0
71.5
71.3
75.9
75.9
Crystallite Sizes (002) (A)
21.4
27
27
31.5
31.5
CONCLUSIONS The presence of NaOH, NaHC0 3 or MgC0 3, as opposed to Na2S03 alone or other chemical systems, leads to a higher sulfonate and carboxylate content, although the bulk lignin content of SEP pulps did not show much difference. The physical strength of paper and its brightness improves when the pulp has higher hydrophilic group content. The presence of NaOH, NaHC0 3 or MgC0 3, as opposed to Na2S03 alone or other chemical system trials, led to a lower relative specific refining energy consumption and better physical strength. In addition, the presence of NaHC0 3 or MgC0 3, compared to Na2S03 alone or with NaOH or other chemical systems, resulted in an increase in brightness of up to 4% as well as a 3% to 6% yield increase. Excellent paper strength and low specific refining energy similar to the one obtained with NaOH can be produced with either NaHC0 3 or Na2S03. The strength values of SEP compares well to those of low yield hardwood industrial kraft pulp (8). At the same time, NaHC0 3 can protect yields well over 90% and brightness levels 64%. Better bonding of SEP fibers may be at least partially explained by a higher O/C ratio on the fiber surface, by a higher level of SIC ratio as well as by a higher percentage of bonding CI crystallinity in SEP when compared to CMP.
79
80
Pulping
ACKNOWLEDGEMENT We wish to thank the NSERC, FCAR, Stake Technology Limited for their financial supports.
REFERENCES 1. Kokta, B.V., Process for Preparing Pulp for Papermaking, Can. pat. # 1,287,705 (Aug. 20, 1991) 2. Kokta, B.V., Ahmed, A., Zhan, H. and Barbe, M., "Explosion Pulping of Aspen" Paperija Puu-Paper and Timber, (9):1044-1055 (1989). 3. Barbe, M.C., Kokta, B.V, Lavallee, H.C. and Taylor, J.,"Aspen Pulping: A Comparison of Stake Explosion and Conventional Chemi-mechanical Pulping Process" Pulp and Paper Canada, 91(12), T395-T403, December 1990. 4. Katz, S., Beatson, R. and Scallan, A.M., "The Determination of Strong and Weak Acidic Acid Groups in Sulphite Pulps, Paprican PPR, 408 (1982). 5. Kokta, B.V. and Daneault, C., "Brightening Ultra-High-Yield Hardwood Pulps with Hydrogen Peroxide and Sodium Hydrosulfite" TAPPI, 69(9), 130133 (1986). • 6. Sukhov, D.A., Zhilkin, N.A., Valov, P.M. and Terentiev, O.A. "Cellulose structure in relation to paper properties" Tappi, 74(3) 201-204 (1991). 7. Kokta, B.V., Ahmed, A., Garceau, J.J. and Chen, R., "Progress of Steam Explosion Pulping: an overview, Lignocellulosics: Science, Technology, Development and Use, Kennedy, Phillips and Williams, Editors; Ellis Horwood Series in Polymer Science and Technology, pp. 171-212 (1991). 8. Kokta, B.V., "Steam Explosion Pulping of Aspen: Results from Semiindustrial Trials" Poplar Council of Canada Newsletter, 2. pp. 9-14, June (1991). 9. Carrasco, F., Kokta, B.V., Ahmed, A. and Garceau, J.J., "Ultra-High-Yield Pulping: Relation between Pulp Properties and Fiber Characteristics by Multiple Linear Regression." Preprint of 1991 Pulping Conference, pp.407417, Orlando, Nov. (1991). 10. Kokta, B.V., Ahmed, A., Garceau, J.J., Carrasco, F., Zhai, D. and Huang, G.Q., "Steam Explosion Pulping of spruce and Aspen: Optimization of the Process", Proceedings of 78th. Annual CPPA Meeting, vol. 1, A91-AI05, Montreal, Jan. (1992). 11. Hua, X, Kaliaguine, S., Kokta, B.V. and Adnot, A., "Surface Analysis of Explosion Pulp by ESCA", Wood Science and Technology, (in press 1994).
8 Kinetics and mechanism of wheat straw pulping A A Baosman, G C Fettis, M J Ramsden and S J Smith - Chemistry Department, University of York, Heslington, York YOI 5DD, England
2.1
ABSTRACT
This paper describes the first part of an intended in depth study of the kinetics of pulping Saudi Arabian wheat straw with caustic soda solution in a rotating steel reactor of 250 ml total capacity. The work is of current relevance in the UK because there is renewed interest in finding uses for waste straw which can no longer be burned in
fields after harvesting the grain crop. potential outlet.
Paper production from straw pulp is one
The extent of dissolution of lignin during pulping was measured in the temperature range 25°C to 170°C using the standard Klason method of analysis for lignin. In a few runs residual caustic soda was titrated with acid. Some NMR and IR studies were also done on straw before and after pulping and on lignin. In order to avoid all possibility of mechanical pulping it was necessary to cut the straw prior to reaction neatly into 2-3 em lengths and avoid grinding it for the kinetic studies. Titration of residual caustic gave variable results initially. This was shown to be due to strong absorption of some of the caustic by straw. Multiple washing by water was necessary in order to recover it quantitatively. The rate of delignification reaction was found to be first order with respect to lignin and 0.6 order with respect to caustic soda. Values were obtained for the rate constants 81
82
Pulping
at a number of temperatures and the activation energy was found to be 14 ± 3kJ mol". This low value is indicative of the rate controlling step being physical rather than chemical in nature, e.g. diffusion of caustic within the structure of the straw.
2.2
INTRODU<:TION
One of the many measures which have resulted from legislation to protect the environment has been the banning in the UK and elsewhere of the burning of straw in the fields after harvesting the grain crop. As a result there is renewed interest in finding outlets for waste straw. Manufacture of paper from straw pulp was quite widely practised in Europe and the USA prior to the Second World War but dwindled post-war. Paper making from bagasse and other fibrous non-wood materials such as rice and wheat straw has long been carried out in China, India and other Eastern countries. However, only about 3 % of paper pulp is currently made world wide from straw!' 2. Processes for pulping straw have nevertheless been under continuous development. Amongst the most recent innovations has been the "Alcell" process which uses hot aqueous alcohols in a continuous fashion to extract lignin and hemicelluloses", The most traditional processes all involve the use of aqueous caustic soda as pulping agent either on its own (TheSoda Process) or with e.g. anthraquinone or sodium sulphite. The Soda Process is still the most widely used. 4 This paper reports the first part of an intended in depth study of the kinetics and mechanism of wheat straw pulping using aqueous caustic soda on its own. Saudi Arabian grown wheat (from the North-west region) has been chosen as the substrate for study, principally because one of the co-authors, A.A. Baosman, is domiciled there. Also fewer quantative studies have been reported on Saudi straw compared with e.g. Chinese or European grown straw. Saudi Arabia is in fact a significant grower of wheat. The quantity of by-product wheat straw processed there in 1987 was estimated at 3.6 million tonnes':''. A number of kinetic studies have been done on alkaline straw pulping by other workers, particularly ChineseI''' There are also numerous studies on wood pulping which are of some relevance particularly Russian? and early work by Kleinert!". None of the studies on straw have been sufficiently comprehensive to elucidate the overall reaction mechanism for soda pulping and none has been on Saudi wheat straw which has a higher than average lignin content (,.; 23 %) compared with wheat straws from many other countries (,.; 20% or less). It should be noted at this point that throughout this paper the lignin referred to is so called Klason or acid insoluble lignin. In addition Saudi wheat straw contains
Wheat straw pulping
83
approximately 1.5 % non-Klason acid soluble lignin which was not detected by the method of analysis used.
2.3
EXPERIMENTAL
The pulping runs were carried out in a specifically designed stainless steel cylindrical reaction vessel of total capacity 250 ml. Throughout the runs the reactor was rotated about its horizontal axis inside an electric furnace to achieve good mixing of the reactants at controlled temperatures. The sample of wheat straw was denoded and cut neatly into sizes of 2 cm - 3 cm in length (grinding the straw caused mechanical pulping and gave variable results). The straw was washed with water, dried to a constant weight in a vacuum oven and a known weight was then mixed with caustic soda. 55 ml deionized water was added and after dissolution of the caustic the mixture was transferred to the reactor. A standard weight of 4.23 dry straw was used. Caustic ranged from 0.045 g to 4.45 g. The temperatures covered were 25°C, 80 -c, 125°C, 150 °C and 170°C for reactions times of 10 min - 6 hr depending on the level of caustic used. After cooking the pulp was cooled and filtered off. In later experiments the pulp was repeatedly washed with water to recover all the residual caustic which was found to be strongly absorbed to the pulp and unreacted straw. This caused variable results in earlier experiments before the washing step was introduced. 30% of the filtrate was used to determine the alkali content by titration with dilute acid (O.IM H 2S04 or O.IM CH 3COOH) using phenolphthalein as indicator. In some cases as a check titrations were also carried out on the unfiltered reaction mixtures. The standard Klason method was used for the determination of lignin dissolved in the remaining 70 % of the filtrate from pulping runs II . The liquid volume was first reduced 5-fold using a rotavapor (vacuum). The concentrated extract was then acidified with mineral acid (H 2S0 4) to give a precipitate of lignin which was separated by filtration. The precipitate was washed with water and dried. The weight of lignin was then calculated gravimetrically'? Untreated straw was found to contain 6.3% ash. Selected samples of lignin were washed and all found to contain less than 1% ash except samples from pulping runs at 170°C at 1.5 hr or more reaction time where up to 24% ash was found and a correction was made on the lignin analysis. Lignin analysis was also done on a number of repeat samples of untreated straw. To a ground sample of clean dry straw (4g) in a 250 ml round-bottomed flask was added 24 ml of 72 % (12M) H 2S04 . The contents of the flask were stirred for 1 hour at 30 "C and then diluted with 800 ml 3 % H 2S0 4 in a 1 litre flask. The mouth of the flask was covered with aluminium foil tied with cotton and then autoclaved for 1 hour at 125 °C.
84
Pulping
While the resulting hydrolysis mixture was still warm the acid in soluble material was filtered off and thoroughly washed with water. The filtrate was dried at 75 °C for 15 hours and then weighed as Klason lignin 13,14. The Klason lignin content of the straw based on 5 replicate analyses was 22.9 % w/w.
Solid-stat.e NMR Solid-state NMR spectra were obtained with use of the CP/MAS technique. A Bruker 300 MSL NMR spectrophotometer operating at 67.8 MHz for 13C equipped with high power amplifier and a narrow-bore probe was employed for this purpose. The samples were packed in a 5mm Kel-F rotor and spun at 5 KHz. Data were collected by taking 3556 scans using a 4.5 J.1.s 90 0 pulse, a 5-ms contact time and a 6-s delay time. The data were processed with 30-Hz line broadening to improve the signal-noise ratio. The spectra were referenced to poly(dimethylsilane) (Petrarch System, Inc.,) at 1.84 ppm with respect to Me4Si by placing 5 mg of the reference (wrapped in Teflon tape) at one end of the rotor.
Solution NMR Spectroscopy Solution NMR spectra were obtained on a FX-90 Q Jeol spectrophotometer operating at 22.85 MHz for 13e. The sample was dissolved (50 mg/0.5 ml) in Me 2SO-d6 with about 1 % Me 4Si added as an internal reference at 0 ppm. Infrared Spect.roscopy Infrared (IR) spectra were obtained on an Analect FX-6160 FT-IR spectrometer. Samples were run in the single-beam transmission mode as KBr disks (2 mg of sample /58 mg of KBr). Each spectrum was the result of 128 scans of IR-grade KBr under ambient conditions. Spectral data were accumulated at 4 cm' resolution over the range 4000-450 cm'. Kinet.ics and Mechanism In order to derive rate constants for the delignification reaction it was necessary to postulate a reaction scheme. The following basic scheme was adopted for the uncatalysed reaction".
kL or kLb. Cr
+
slNaOHs L = lignin
where kL
.
IS
lee or
kC,b
Lp dissolution of lignin Cp dissolution of carbohydrates
C = carbohydrate
h ~. -dL t e rate constant lor reaction (If
Wheat straw pulping
-d[NaOH] dt
85
for lignin
-ac Cit -d[NaOH] dt
for carbohydrate
n 1 and s 1 are moles of NaOH which react with 1 mole of lignin or carbohydrate respectivel y. -dL (If
If a and b are the initial concentrations of lignin and caustic respectively and x is the amount of lignin reacted at time t then: when caustic is in excess -dL (If
or
-dL (If
where kL is the pseudo order rate constant and kL For first order in L, m
=
1 and integrating In
Plot of In a-x vs. t slope
=
=
a a-x
-k L[b] 1l
For initial reaction rate first order in lignin
if [a] is kept constant and b is varied in separate runs constant [b]O
kL[b]O
86
Pulping
where constant = kL[a] log
n log [b]
+
log constant
Plot of log (initial rate) versus log (initial caustic concentrate) has slope n and intercept log kL[a]
2.4
RESULTS AND DISCUSSION
2.4.1 Lignin Characterisation The structure and composition of three samples, the ground wheat straw, the pulp (after delignification) and the extracted lignin were first investigated spectroscopically by solid-state NMR since it is a non-destructive method of analysis (Figure 1).
.~
ro
E o
:{ u eu
roc o
(5
0..
c Carbohydrate
-'--,60..-----,60r-
,~o
,~o
00 '
'---;00 (ppm)
FIGURE 1.
Sol id Stn t e NMR Spec t r a of: A Wll(~nt Strnw;
n
Pulp;
C Lf gn in
60
40
Wheat straw pulping
87
The solid-state NMR spectrum for the extracted fraction of WS after cooking in the metal reactor contained primarily lignin. This was indicated by signals in the regions 50-65; 70-90; 95-130; 130-140 and 140 -160 ppm in the spectrum (Figure 1). These are primarily due to aromatic methoxyl, protonated aliphatic, protonated aromatic, nonprotonated non-oxygenated aromatic and phenolic non etherified and etherified aromatic carbons respectively. These signals are consistent with the signals previously obtained in the solid-state NMR spectra of lignin 15-19. The spectrum of the original wheat straw shows strong bands in the region 65-110 ppm which are characteristic of carbohydrates. Bands for lignin in the straw are much less pronounced (Figure 1). The pulp spectrum gives similar results to the straw. The presence of significant levels of phenolic groups in lignin will help render it soluble. The extracted fraction of lignin was further subjected to solution 13C NMR spectroscopy. The sample was first dissolved in DMSO-d 6t. Most of the signals were assigned in accordance to the previously assigned data of lignin 15,17. The spectrum (Figure 2) generally reflect the same signals observed in the solid-state NMR except that they are more resolved and have somewhat different relative intensities. The signals are also shifted between (3-4 ppm), in general from those in the solid-state NMR. There are also additional signals detected for lipids or waxes (22-35 ppm)20,21 and acetic acid or acetate (21 and 174 ppm) that were not visible by solid-state NMR. Also, there is signal for the solvent DMSO-d 6 at 40 ppm which was not present in the solid-state NMR. DMSO
PHJr
OOCH]
COC~
200
150
100
50
o
FIGURE 2. Solution 13 C NMR spectra of the extracted lignin in metal reactor(bomb). Key: TMS = tetramethylsilane, COCH 3 = methyl in acetyl, DMSO = dimethylsulfoxide, OCH 3 =.methoxyl, POA = protonated oxygenated aliphatic, PAr = protonated aromat~c, PhOH = phenolic (non-etherified), PhOR = phenolic (etherified) CO = carbonyl, COCH) = carbonyl in acetyl. '
88
Pulping
In order to have additional information, infrared spectra were also taken for the three samples i.e. the ground wheat straw, the delignified pulp and the extracted lignin. These spectra are shown in Figures 3 and 4 and the bands were identified by their wave numbers. The assignments of the bands are in accordance with those of lung and Himmelsbach. 15 The region of absorption ranged from 450-4000 ern", the bands at 1715 and 1658 cm' have been assigned to carbonyl stretching in unconjugated ketone and carboxyl groups.P The band at 1590-1596 cm' (ring stretch associated with C-O stretch) has been assigned to syringe! and to the coniferyl groups. The prominent broad absorption at 2980-2993 cm' was observed for the hydroxyl and aliphatic C-H stretching. 15
203JE== -----~--_.------------~----------;
H
H
I I
%T
(2)
0(-1 F I CURE J.
I j{ SI'I':CTRA OF 1 WIIEAT STRAW;
2 PULP
Wheat straw pulping
~-r~{[-'-~~~-~~--'-'~~=~:=~=~~.=-=--=~~=~~=--=~==~~=~~~=~
173. riO-
89
----=ri
. . --
J6O-1
l~i %T
130-
II
96.6_ ..... _.. '" ...... 1'......
··T
r··
. ··r···········
3..">00
-1000.0
3000
2500
·····T
2000.0
1000
-r····--··-r·····-····-I-··· 1~oo
1600
1200
----r·.···--.-I-·· 1000
000
600
·-~
~50 . 0
04-1 n(;URI~
I,.
1 R SPECTRUM 010' I. lGN 1N
Rate of Delignification Reaction (:~ Figures 5 and 6 show typical plots of residual % lignin on straw versus time of cooking. 24
...----.--....,..-..---.---r---,..--,.-~-_,._--,r__-,
22
20 18 16
%L
o
14
o
12
10 24 , . . - - - r - - r - - - - , - - - - r - - . - - . - - - , . - - - - ,
6
o
.2
.4
.6
.8
FIGURE 5. 25°C; WS 4.23 g;
t]
1
1.2
1.4
1.6
22
1.8
20
hours
NaOH 4.45 g;
18
H 55 ml 20
16 %L
14
o
12
10
d.L-_l--_.L..-_.l..--_L.--._'------"_ _' - - - _
·0 FIGURE 6.
.5
1.5
BOoC; WS 4.23 g;
t]
2
2.5
3.5
hours
NaOH 4.45 g;. H
20
55 ml
90
Pulping
Figures 7-13 show first order plots of In residual lignin on straw (In a-x) versus time using excess caustic (2.25 g and 4.45 g) at 25°C - 170°C. The data shows a reasonable fit to first order kinetics, though there is scatter in some cases. Attempts to obtain second order and fractional power plots gave a much poorer fit than the first order ones.
3.5 T
3.0 2.5
-=----____
~2.0
~ .~
~
,.... 1.5 >:<
~
.5
Gradient =-O.53±O.09
.~.
•
1.0 0.5 0.0 0.0
0.5
1.0
1.5
20
2.5
3.0
Time (h)
FIGURE 7. 25 DC; WS 4.23 g; NaOH 4.45 g; H 55 ml 20
3.5 T 3.0 • c:::
~
2.5 2.0
~ 1.5
= .----.----.-----.----
Gradient -O.6O±O.04
.-----.-----.
";( ~
:s
1.0 0.5 0.0 +------+0-----+-0-----+--------4 0.0 1.0 2.0 1.5 0.5 Time (h)
FIGURE 8. 80°C; WS 4.23 g; NaOH 4.45 g; H20 55 ml
Wheat straw pulping
3.5
T
3.0 • 2.5
.~
2.0
~
";<
1.5 1.0
.5
0.5
~
$
0.0
Gradient =-1.79±O.49
• .J----~~---_t_----_t_----~----t
0.5
-0.5 -1.0
Time (h)
FIGURE 9. 125°C; 4.23 g; NaOH 4.45 g; H 0 55 ml 2
3.5 3.0 •
·a
.~
2.5 2.0 1.5
0
~
1.
~
0.5 0.0
>?
Gradient =-2.73±O.38
.5 -0.5
+---------~-----_t"----....:::_--_,
0.5
1.0
-1.0
•
-1.5 Time (h)
FIGURE 10. 150°C; WS 4.23 g; NaOH 4.45 g; H 0 55 ml 2
91
92 Pulping
3.5 T
-"~radient =-2.62±036
3.0
2.5
c
""'"
~
].2.0 ~
-____
.1.5 )(
Gradient =-O.62±O.06
------.
0.5
--------------
0.0
...----~~----+--...;..--_t_---___t
~ 1.0
0.5
0.0
1.5
1.0
2.0
Time (h)
FIGURE 11. 170°C; WS 4.23 g; NaOH 4.45 g; H20 55 ml
3.5 T 3.0 • ~ c 25 ·2 2.0 ~
)(
1.5 ~ .5 1.0 0.5
=
Gradient .0.31
0.0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (h)
FIGURE 12. 25°C; WS 4.23 g; NaOH 2.25 g; H20 55 ml
3.5 T ~
3.0·~ 2.5
••••
c
'c 2.0 ~
9~ .5
1.5 1.0
Gradient =-0.62
0.5 0.0 +-----4-----+-----~t__----. 20 1.0 3.0 4.0 -0.5
Time (h)
FIGURE 13. 25°C; WS 4.23 g; NaOH 4.45 g; H20 55 ml
Wheat straw pulping
93
The pseudo first-order rate constants when using excess caustic and the true reaction rate constants derived from Figures 7-13 are given in Table 1. Figures 14 and 15 show plots of residual lignin on straw versus cooking time at 80°C for four levels of caustic. The initial rates
-~~
derived from Figures 14 and 15 are plotted in
Figure 16 against log of the initial caustic concentration (log[NaOH]i)' The slope of the graph indicates that the order of caustic in the delignification reaction was 0.6. This was the figure used to derive the true delignification rate constants given in Table 1.
~ c
FIGURE 14. 80 °C; WS 4.23 g; ~aOH 4.45 g & 0.45g; H20 55 ml
Gradient =-7.64
20
.~
15
'c 00
a
::i 10
0.205 MNaOH
n
Gradient = -17.97
c
c
2.023MNaOH 0 O.S
0
2.5
2
1.5 Time (h)
1425 • Gradient =-5.46
20 ~
FIGURE 15.
---~
15
c
'cco 10
BO °C; WS 4.23 g;
•
0.455 1-1 NaOH
a
~aOH
1 g & 2.25 g;
H20 55 ml
::i
1.023 M NaOH
Gradient= -24..54
0
0
1.5
2
0 0.5
-5
Tune (h)
15 1.6
1.4 1.2 1 Sco 0.8 .9 0.6
FIGURE 16. Plot of Data from Figures 14 & 15
'S
0.4 0.2 0 -}
-0.5
0 Jog([NaOH])
0.5
94 Pulping
TABLE 1.
Delignification Rate Constants 4.23 g WS; 55 ml H 20
Temp
kL
NaOH
(dm3) O.6 mo)-o·6 h- 1
g
°C
25
4.45
0.53
0.34
2.25
0.31
0.31
80
0.60
0.39
125
1.79
1.16
150
2.73
1.77
170
2.62
1.70
25
From the intercept in Figure 16
log kL[a] and
kL
=
1.1
= 0.55 at 80°C
This compares with the value of 0.39 for k L at 80 de given in Table 1. The fact that these values are reasonabl y comparable indicates that the rriechanism of the reaction is 'similar from the initial stages (Figures 14 and 15) through to a residual lignin of 7% on straw (Figures 5-13) and over a ten-fold range of caustic levels (0.205 - 2.023 M). Figure 11, runs with excess caustic at 170 "C differs from the runs at lower temperatures by displaying a change of slope to a slower reaction which appears at 7% residual lignin on straw. This changes from so called bulk to residual delignification as has been observed by. other workers, as has also the finding that the change, if any, is less pronounced at lower temperatures. 7 "Figure 17 shows the Arrhenius plot for kL in the temperature range 25°C - 170°C. The activation energy derived from the plot is 1~± 3 kJ mol- l for the delignification reaction. This is unusually low to represent a chemical reaction and indicates that the rate controlling step ~ay be physical in nature, e.g. the rate of diffusion of caustic
Wheat straw pulping
95
within the straw structure as postulated by other workers for the pulping of bagasse". The fact that caustic is 0.6 order reflects the heterogeneous nature of the reaction. 0.3 0.2 0.1
o
~ -0.1 eo
.s
-0.2 -0.3 -0.4
-0.5 -0.6 -0.7 - + - - - - - - - + - - - - - - - + - - - - - - - f 3.5E-03 3.0E-03 2.5E-03 2.0E-03
Iff (jK) FIGURE 17.
Arrhenius Plot
Though the rate controlling step or steps may be physical, the NMR and IR studies clearly show that the production of lignin involves significant chemical change. The rates of these chemical reactions must be higher or comparable to those for the physical mechanism postulated at least over part of the temperature range studied if the physical reactions involved are rate controlling.
2.4.3
. -d[NaOH] Rate of Caustic Removal ( dt )
Figure 18 shows a typical plot of the rate of reaction of caustic with time of cooking 80°C using excess straw (4.23 g) with an initial weight of caustic of 0.045 g. at The initial rate of caustic removal was very rapid compared with the rate of the delignification reaction shown in Graph 2. 1.2 1.0 ~
~ 0.8
en
.5 :I: 0cU
Z
~
0.6 0.4 0.2 0.0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Tune (h)
FIGURE 18. 80°C; WS 4.23 g; NaOH 0.045 g; H 55 rnl 20
96
Pulping
Rapid initial consumption of alkali by wheat straw has been observed by other workers24 who correlated the rate of reaction of alkali with carboxylic and other acidic groups on straw. Alkali is also consumed in dissolving hemicellulose from straw. 9 The authors of the latter paper postulated that the delignification and hemicellulose reactions take place in parallel but more work is needed to elucidate the overall reaction scheme and determine the rate of the reactions which result in caustic consumption.
2.5
CONCLUSIONS
The lignin produced by the laboratory scale pulping of Saudi wheat straw with NaOH was significantly different chemically than in the untreated straw. The rate of the delignification reaction was found to be first order with respect to lignin and 0.6 order in caustic. The activation energy determined over the temperature range 25 - 170°C was only 14 ± 3 kJ mor ' indicating that the rate controlling step might be physical rather than chemical in nature.
REFERENCES 1.
Agarwal, J.C., IPPTA, vol. 8 p.3. (1971).
2.
Atheison, J.E., Ind. Pulp Paper, 78, 10 (1974).
3.
Hartley, B.S., Society of Chemical Industry Symposium. Present and Future uses for Straw. Jan, 1991.
4.
Pira, Research Association for the Paper and Board Printing and Packaging Industries, Leatherhead, Surrey, Internal Report, (1988).
5.
Fakeeha, A.J., Farag, A.A., Abu-Khalaf, A. and Al-Jobailie, A., Sci. Int., 2 (2) 139, (1900).
6.
Statistical Year Book, 23rd issue Ministry of Finance and National Economy, Kingdom of Saudi Arabia (1987).
7.
Hongguang, T. and Gurangrui, C., Pulping Conference, 371 (1986).
8.
Chen Fang, Huang Wenlan, Wang Linong, Yu Jialuan and Chen Jialuan, Cellulose Chern. Technol. 25, 383 (1991).
Wheat straw pulping
97
9.
Pen, R. et al., Khirn Drev., 6, 31 (1989).
10.
Kleinert, T.N., TAPPI, 49, 53 (1966).
11.
TAPPI Standard T222, New York, TAPPI.
12.
Trivedi, M.K., IPPTA, XII (4) (1975).
13.
Bethge, P.O., Gran, G. and Ohlsson, K.E., Svensk Papperstidning 20, 31 (1956).
14.
Theander, 0., and Westterlund, E.A., J. Agri. Food Chem., 34,330 (1986).
15.
Jung, H.G. and Himmelsbach, D.S., J. Agr. Food Chem., 37, 81 (1989).
16.
Maciel, G.E., O'Donnell, D.J., Ackerman, J.J.H., Hawkins, B.R. and Bartusa, V.J.A., Chern. 182,2297 (1981).
17.
Himmesbach, D.S. and Barton, F.E. II, J. Agri. Food Chem., 28, 1203 (1980).
18.
Hatfield, G.R., Maciel, G.E. and Erbatur, G., Anal. Chem., 59, 1729 (1987).
19.
Leary, G.J., Morgan, K.G. and Newmen, R.J., Pinus Radiata Wood Appita, 40, 181 (1987).
20.
Barton et al. (1975).
21.
Barton et al. (1978).
22.
Sarkanen, K.V., Ludwig, C.H., Lignin: Occurrence, Formation, Structure and Reaction.
23.
Sabatier, J., Peniche, C. and Fernandez, N., Holgfarochung, 47,313 (1993).
24.
Pavlostathis, S.G. and Gossett, J.M., Biotechnology and Bioengineering, 27, 346 (1984).
9 Ethanol pulping of pretreated non-wood fibre materials B Lonnberg", M EI-Sakhawy** and T Hultholm* - *Abo Akademi University, Laboratory of Pulping Technology, Abo, Finland, **National Research Center, Cellulose and Paper Department, Cairo, Egypt
ABSTRACT
Lately economical, environmental and technological requirements have led to development of a number of solvent pulping processes. It is supposed that a solvent pulping process could be economically feasible even as a relatively small
unit in comparison with the common kraft pulping process. It has been demonstrated on a large scale that ethanol as such is able to delignify hardwood species under certain conditions, although softwood species also seem to require alkali in the pulping system. It was observed for non-wood materials that pulping by ethanol and water reduced the final pH to a level of about 4 leaving the final lignin content at extremely high values even for a fiberised pulp. This problem was reduced by carrying out ethanol extraction subsequent to the pulping stage, which resulted in some lower, but still high chlorine numbers of 8 - 9. By introducing alkali and anthraquinone in addition to the ethanol and water the delignification resulted in chlorine number levels below 5 without final extractions. The choice of pulping method is highly dependent on paper grade targets, i.e. bleachability and papermaking properties of the fibres. Application of the impregnation-depolymerisation-extraction concept on wheat straw gave promise for a suitable pulping method.
99
100 Pulping
INTR()DUCTION Delignification of lignocellulosic materials by application of simple alcohols, such as methanol, ethanol, propanol etc, or fatty acids, such as formic acid, acetic acid etc, has been of interest for a long period of time. The main goal has been to replace inorganic chemicals for organic compounds easily recoverable by for example distillation. The search for environmentally sound pulping processes without sulphur and chlorine has been a driving force, as well as the possibilities of fractionating the wood or non-wood biomass into fibres, lignin and other chemicals, such as furfural and acetic acid. In. Finland, however, the goal was to develop a pulping process for production of papermaking fibres from softwoods which form the main fibre source. Byproducts should not be generated primarily, but the dissolved part of the lignocellulosic material should be converted into energy (1). Initial studies on both acidic and alkaline alcohol pulping methods for softwood indicated that the acidic methanol and ethanol pulping processes produced sulphite-like pulps, as the alkaline methanol and ethanol pulping processes resulted in kraft-like, easily bleached pulps (2, 3, 4). In order to improve the acidic ethanol extraction, flow-through pulping conditions were applied with the aim of eliminating lignin "condensation" that occurs particularly at pH < 4; it was obvious that this technique would provide effective pulping as regards the final lignin content (5). Finally, subsequent to effective alkali impregnation, proper depolymerisation of the lignin and final extraction a kraft-like softwood pulp was produced at a high pulp yield and reasonably low residual lignin content (6). The pulping concepts mentioned above have been applied on non-wood raw materials, such as wheat straw, cotton stalks and tall fescue. Wheat straw is available world-wide, cotton stalks constitute so far a minor pulp fibre resource and tall fescue is together with reed canary grass a potential fibre crop for fallow fields.
EXPERIMENTAL
Fibre raw material. Wheat straw (Triticum aestivum L.), cotton stalks (Gossypium arboreum L.) and tall fescue (Festuca arundinacece Schr.) were investigated and reported in this work. The wheat straw and the tall fescue were delivered by the Agricultural Research Centre of Finland in Jokioinen, as the cotton stalks of Giza 75 type were delivered from a Cairo university farm in Egypt. The spring wheat straw and the cotton stalks were harvested in the autumn 1993. The fibre raw materials were characterised by determination of some basic
Ethanol pumping
101
properties, such as lignin content, average fibre length and silica content; see Table 1.
Table I. Analysis of the non-wood fibre raw materials studied.
Lignin content, 0/0 Av. fibre length, nun Silica content, % *)
Wheat straw
Cotton stalks
Tall fescue (7)
20.6 1.60 2.8
21.7 1.00 1.9*)
18.8 0.7 3.1
Ash content
Pulping methods. The following pulping methods were tested on the fibre raw materials: ethanol/water (EtOH/H20) pulping, ethanol/water/sodium hydroxide/anthraquinone (EtOH/H20/NaOH/AQ) pulping and impregnation-depolymerisation-extraction (IDE) pulping. The pulping experiments were conducted on a laboratory scale by application of a 0.2 L autoclave charged with 20 g of fibre raw material calculated as oven dry material. The autoclave was moved back and forth during pulping with the aim of maintaining good mixing of the pulping liquor. At the end of the digestion the liquor was drained from the autoclave through a cooler, after which the autoclave was opened and the pulp was washed or extracted for removal of dissolved lignin. After cleaning, the entire pulp was fiberised and dried for determination of the total pulp yield. Finally, the dried pulp was rewetted and disintegrated and screened by application of a flat screen with 0.15 mm slits in order to determine the rejects.
The EtOH/H20 pulping conditions were as follows:
fibre raw material EtOH/H20 liquor/raw material time of rise maximum temperature time at max. temp.
wheat straw; cotton stalks 50/50; 40/60 %/% by volume 7/1 L/kg 30 min 175; 190 C 120 min 0
The EtOH/H20/NaOH/AQ pulping conditions were as follows:
102
Pulping
fibre raw materials EtOH/H20 liquor/raw material NaOH concentration AQ charge time of rise maximum temperature time at max. temp.
wheat straw; cotton stalks 50/50; 40/60 %/% by volume 7/1 L/kg 0.3 - 0.8 mol/L 0.1 % on fibre raw material 30 min 140; 180 C 90; 120 min 0
The impregnation-depolymerisation-extraction pulping conditions were basicly as follows:
fibre raw material impregnation:
tall fescue
N~C03
0.5 mollL 20 C
temperature time depolymerisation: EtOH/H2 liquor/raw material time of rise maximum temperature time at max. temp. extraction: EtOH/H20 temperature time
°
0
24 h
50/50 %/% by volume 8/1 L/kg 30 min 170 C 60 min 0
50/50 %/% by volume 20 C 0
12 h
After the extraction the pulp was drained and washed with a 50/50 ethanol/water mixture, and finally fiberised in a 25n5 mixture. Also wheat straw pulps were prepared in a 2 L digester with forced recirculation (160 g o.d. fibre raw material), but under modified IDE conditions.
RESULTS AND DISCUSSION The fiberising and delignification conditions were determined by pulping of various non-wood raw materials on a laboratory scale. For this purpose, pulp yield, rejects and lignin content were measured on the pulps for evaluation of the process. In future works, bleachability and papermaking properties of the pulps will be determined after pulping on a larger scale.
Ethanol pumping
103
EthanollWater pulping. Figs. 1 and 2 present the screened yield and the level of rejects of wheat straw and cotton stalks. Yield and rejects are given in percent of the charged fibre raw material. The wheat straw was pulped at 175° C maximum temperature, and the cotton stalks at 190 C; there was also a slight difference in the ethanol/water composition. As visible, the wheat straw provided significantly higher screened yield, as the cotton stalks gave larger rejects despite the higher pulping temperature. When considering the total pulp yield (screened yield + rejects) there is still a clear difference between the raw materials in favour of the 0
60
A
50 ~ 0
-0
40
""0
30
CD .~ (],)
c
(],) (],)
'-
0 en
20 10
0 0
2
3
4
Time at max. temp., h
Fig. I. Screened yield of acidic EtOH/H20 pulps made from non-wood fibre raw materials.
wheat straw. The pulps contained much lignin; measured as the chlorine number 13 - 15 % for the wheat straw pulps and 17 - 21 % for the cotton stalk pulps. Such pulps seem less suitable for paper grades that require highly bleached pulps, but probably they could be used as such in various board grades. As known, the rapid change from a solvent liquor system to an aquatic system "condensates" the dissolved lignin resulting in high lignin contents. Hence, by introduction of extraction stages subsequent to the pulping stage the lignin content could be diminished. Extractions as follows were tested (EtOH/H20 50/50 %/% by volume, 150 C, 60 min, one or two steps), and it was found that the lignin content could be reduced to chlorine numbers of 8 - 9 for wheat straw pulps. 0
The ethanol/water pulping ended up at acidic pH- levels round 4.5 - 5.0 for the
104 Pulping
wheat straw black liquors and 4.1 - 4.2 for the cotton stalk black liquors. The low pH is due to formation of various organic acids in the black liquor, mainly formic acid and acetic acid that according to analyses and simulations amount to about 18 and 14 kg/t of pulp respectively (8).
30 , . . . . - - - - - - - - - - - - - - - - - ,
~ 0
20
C/,'0 Q)
00)
a: 10
oL..--J.--L..-..L-----:I::=::::x==:Q=:=t:=::=O o 2 3 4 Time at max. temp., h
Fig. 2. Rejects formed in acidic EtOH/H20 pulping of non-wood fibre raw materials.
Ethanol/Water/NaOH/AQ pulping. When designing pulping processes with alkaline delignification and bleaching stages with oxygen and peroxide respectively, the pulping process itself might be alkaline as well. The use of both alkali and alcohol provides a relatively complicated recovery system for both inorganic and organic pulping chemicals. Figs. 3 and 4 illustrate the screened yield and the rejects of wheat straw and cotton stalks when pulped by the alkaline ethanol process. The wheat straw produced also now significantly higher screened yields, but the rejects were roughly equivalent. Fig. 5 representing the interrelationship between screened yield and the chlorine number indicates that the selectivity and pulping economy would be far better for wheat straw, and the reasonably low lignin contents (chlorine number 2 - 3) could be achieved by application of 0.4 mol NaOH/L for wheat straw, as cotton stalks would require 0.8 mol NaOH/L for the same lignin content, although the cotton stalks were pulped at a much higher temperature and for a longer time.
Ethanol pumping
60
~ 0
-0
Q)
.~
~
50
cott~
40
"0 Q)
c: Q) Q)
wheat straw
30 0
'-
0 CJ)
20 0 0
0.2
0.4
0.8
0.6
NaOH-conc., molll
Fig. 3. Screened yield of alkaline EtOH/H 20 pulps made from non-wood fibre raw materials.
30
,------------------..,..r-t I I I
~ 0
I
20
cotton stalks /
....en
/ /
0
Q)
/
'0)
a:
/ /
10
pi /
wheat straw
/'
O~-oI...---'iillIIIIIo--"'-A~----'---~........-
o
2
4
6
..........- - -
8
10
Chlorine no.
Fig. 4. Rejects formed In alkaline EtOH/H20 pulping of non-wood fibre raw materials.
105
106 Pulping
60 , . . . - - - - - - - - - - - - - - - - - - . ~
eft
wheat straw
50
-ci' Q)
.s;..
40
-0 Q)
C
Q)
~
o
30
o
Cf)
20
........- . . & . - - I - - ' " - - - I . . - . . & . - - . & . - - - - . . - . . . . I
O~-L-
o
2
4
6
8
10
Chlorine no.
Fig. 5. Pulping selectivity for alkaline EtOH/H20 pulps made from nonwood fibre raw materials.
Impregnation-depolymerisation-extraction pulping. A new pulping concept (6) was applied to the non-wood fibre raw materials in order to see whether it could provide some advantages in comparison with alkaline EtOH/H 20 pulping. Table 2 compiles some typical pulping results obtained with tall fescue. The results indicate that it may be very important to fractionate the fibre raw material with the aim of improving the economy of the pulping process and the pulp quality as well. It seems that the total raw material comprises a large number of non-fibrous cells that easily can be lost from the fibre fraction into the black liquor. Removal of the leaves would significantly improve the screened yield. By further optimisation of the pulping conditions even better yields are expected. Initial results obtained with wheat straw were positive. The impregnation stage has been developed in order to diminish both the rejects and the chlorine number, and also to increase the screened yield; see Table 3. The results reveal that the IDE concept would provide highly delignified pulps at screened yields clearly lower than that of the alkaline ethanol pulp, which may be explained by the comparatively high temperature of the depolymerisation stage.
Ethanol pumping
107
Table 2. Impregnation-depolymerisation-extraction pulping of tall fescue.
Black liquor pH Screened yield, % Rejects, % Chlorine number
Total fescue (straw + leaves)
Straw of fescue
10.7 25.2
I.X
10.4 37.7 6.7
1.7
3.5
Table 3. IDE pulping of wheat straw (impregn.: 100 C, 30 min, 15 b). 0
Impregnation liquor N~C03
NaOH mol/L
mol/L
0.75
0.25
0.50 0.25
0.25 0.25
0.30
Screened yield %
Rejects
46.8 46.0 48.9 54.0
1.0 1.4 2.1 2.4
Chlorine number
Remark
1.0 1.9 1.7 4.3
Ref.
0/0
Ref. EtOH/Hl)jNaOH/AQ: 90 min at 140 C 0
CONCLUSIONS This study concludes the initial work on the optimisation of the delignification and fiberising of certain non-wood species, of which wheat straw, cotton stalks and tall fescue are reported in this context. The fibre raw materials were charged as such, i.e. including leaves and straw as well as bark (in the case of cotton stalks), into a laboratory scale digester. Ethanol/water was found to result in fiberised pulps though containing large quantities of lignin unless the pulping stage was followed by high-temperature ethanol extraction steps. Even after that treatment, however, the chlorine number was far exceeding the level typical for bleachable pulp grades. Anyhow, these pulps constitute a potential for unbleached board grades. The cotton stalks yielded much less pulp than wheat straw with simultaneously high rejects despite the high pulping temperature. Alkali was introduced with anthraquinone as a catalyst in the ethanol/water
108 Pulping
process thus giving potential for effective alkaline delignification. A new pulping concept called the IDE (impregnation-depolymerisation-extraction) process was also tested. As expected the lignin was removed effectively due to proper depolymerisation of the lignin in combination with maximum swelling of the fibre wall structures. As a matter of fact the dissolved lignin is supposed to comprise a considerable proportion of low molecular lignin (MW 200). The alkaline pulps with screened yields exceeding 50 % are consequently suitable for lignin removing bleaching. The work indicates that unbleached and bleachable pulp grades may be produced by application of both acidic and alkaline ethanol pulping methods. The future studies within the Non Food Production Research Programme will concentrate on further optimisation of the pulping conditions for obtaining bleachable and strong pulps that would substitute bleached birch kraft in certain paper grades. This goal requires not only good pulping systems, but also working chemical recovery systems irrespective of pulping process. Further, the fibre raw material itself must fulfil certain prerequisites what concerns removability of the lignin, final fibre length distribution and silica content.
ACKNOWLEDGEMENTS The financial support from the Ministry of Agriculture and Forestry is gratefully acknowledged. Wheat straw and tall fescue has been delivered by the Agricultural Research Centre of Finland, Institute of Crop and Soil Science, Jokioinen, and the cotton stalks by the National Research Center, Cairo, Egypt.
(1)
T. Laxen and J. Halttunen, Organosolvkeitot (Organosolv pulping), Publications of the Water and Environment Administration - series A 119 SYTYKE, The Environmental Research and Development Programme for the Finnish Forest Industry - Project 21, Helsinki 1992, 48 p.
(2)
J. Aittamaa, T. Laxen, B. Lonnberg and R. Sjoholm, Studies on the alcohol pulping processes, xxn EUCEPA Conference, Florence, October 6 - 10, 1986; Proceedings Vol. I No. 1 - 21.
(3)
B. Lonnberg, T. Laxen and R. Sjoholm, Chemical pulping of softwood chips by alcohols, 1. Cooking, Paperi ja Puu - Papper o. Tra 69(1987):9, 757, 759-762.
(4)
B. Lonnberg, T. Laxen and A. Backlund, Chemical pulping of softwood
Ethanol pumping
109
chips by alcohols, 2. Bleaching and beating, Paperi ja Puu - Papper o. Tra 69( 1987): 10, 826-830. (5)
D. Valtakari, Organosolvkok som motstromskok (Organosolv pulping in counter-current flow), M.Sc. Thesis, Department of Pulping Technology, Abo Akademi University, 1992, 52 p.
(6)
M. Backman, B. Lonnberg, K. Ebeling, K. Henricson and T. Laxen, Impregnation - Depolymerization - Extraction Pulping, Paperi ja Puu Paper and Timber 76(1994): 10, 644-648.
(7)
J. Janson, T. Jousimaa, M. Hupa and R. Backman, The use of Festuca
arundinacece: Pulping, bleaching, papermaking and spent liquor recovery EWLP '94, 3rd European Workshop on Lignocellulosics and Pulp, Stockholm, 28-31 August 1994, Poster presentation. (8)
T. Laxen, J. Aittamaa and B. Lonnberg, Chemical pulping of softwood chips by alcohols, 3. Solvent recovery and energy consumption" Paperi ja Puu - Papper o. Tra 70( 1970): 10, 891-894.
10 The chemical composition of tropical hardwoods and its influence on pulping processes N A Darkwa - Forestry Research Institute of Ghana, University Box 63, Kumasi, Ghana
ABSTRACT: The chemical composi tion of some Ghanaian hardwoods are described as well as investigations into their pulping characteristics. The results show that the chemical composition of these hardwoods are as varied as their densities. Klason lignin values cut across the whole range of values for both temperate softwoods and hardwoods. The cellulose contents range from as low as 33.0% to 53.1%. The extractive contents are also high compared to temperate woods. The results of the pulping studies reveal that these tropical hardwoods could be pulped individually and in mixtures with soda process at 20% alkali on wood to produce pulps with total yields ranging from 45.93 to 53.2% and kappa numbers of 20 to 55. INTRODUCTION: Forcast of the available pulpwood resources in the temperate areas shows that these alone cannot support the future global demand of the raw material needs for pulp and paper industry. As such tropical hardwoods have
111
112 Pulping
emerged as a potential source of raw material for the pulp and paper industry, this is examplified by the number of tropical hardwoods being used in the industry at the moment, in such countries as Brazil and Nigeria. But most tropical forests contain a mixture of hundreds of species with varied morphological and chemical properties. These have precluded the utilization of these forests for pulp production, except where the virgin forest has been cleared to give way to mono-culture as pertain in the temperate regions. While such mono-culture might not be a problem for the pulpwood as these are harvested at most after 15 years, it represents a serious problem for the forester as some of these species begin to die off when occurring in mono-culture as examplif ied by example(2). I. Thus the problem of tropical countries has been finding a way to utilize the mixed species as occurring in the natural forest as raw material for pulp and paper production. In this article an attempt is made to relate the morpholopical and chemical composition of tropical woods to the pulping processes with particular reference to percentage yield and kappa number of the alkaline process on a number of wood species. DISCUSSION:
A. Morphological Properties
It will be observed from Tables 1 and 2 that the fiber lengths of the Ghanaian hardwoods are about equal to most of the temperate hardwoods except that of wawabima which appears to be longer than most of these woods / but are surely shorter than the fiber lengths of temperate softwoods. Figures on lumen width and cell-wall thickness indicate that except for otie and funtum, these fibers have wide lumen and thin cell-walls. As the flexibility ratios indicate, most of these Ghanaian hardwoods would completely collapse during the consolidation process thus giving the sheets high strength properties and good opacity, properties that are characteristics of printing and writing papers.
Tropical hardwoods
Table I Local Nale
Morphological Properties of Some Ghanaian Hardwoods Botanical Nale
Fi be r length
LUlen Wi dth
Fiber DiaIeter
Wall thick ness
Dens 1ty gl. CC
(u)
(.1 ) (~ )
Hex;bilit Y Rat; 0 2w I L
Ot i e
P.angoLensis
1. 45
13.45
23.65
9.82
0.35
0.71
AKonkoree
B.Buonopozense
1. 76
32.25
38.41
6.16
-
0.19
Fun tUI
F.elastica
1.04
17.32
26.63
6.23
0.27
0.48
Odwulla
M.cercropiodes
1.25
18.88
25.11
6.23
0.27
0.3
Onyina
C.pentandra
1. 83
27. 35
32.82
5.47
0.26
0.20
Wawa
T.seleroxylon
1. 33
40.94
47.49
6.55
C.19
0.16
Ngo-ne nkyene
(.patens
1. 55
45.69 I 51.63
5.94
C.22
o• ~ 3
~akabima
S.rhincpetala
2.07
14.15
'9. ,a
4.95
0.76
J. 35
Em 1re
-.:vorens;)
1. 2~
; 4.55
~
9.50
4.95
0.37
0.34
40.60
7.32
0.29
0.22
i
S;nd ru Lbone; 1.45 32.28 *Source : Anatomy Section of FORIG, KUMASI.
Table 2
: Morphological Properties of
Species
Fiber length (rom)
Some
temperate Woods
Fiber diameter (11 ) range
Quaking aspan
1.04
10-27
Yellow birch
1.85
20-36
Beech
1.2
16-22
Sweetgurn
1.7
20-40
Longleaf pine
4.9
35-45
Black spruce
3.3
25-30
Douglas-fir
3.9
35-45
6.1 Redwood 50-65 *Source : "The chenustry of wood" Ed. B.L. Brownmg pp. 29
&
33
113
114 Pulping
B. Chemical Composition The chemical composition as seen on Table 3 and 4 is very varied wi th the percentage lignin varying from 22.7 for ceiba to 39.2 for kaku. These figures cut across the whole range of lignin percentages for both temperate hardwoods and softwoods with averages at 20% and 28% respectively. This will mean that woods with lower lignin percentage would need lower charge of alkali, as compared to those of higher lignin percentage, to produce pulp with a good kappa number for bleaching. This is clearly shown by the kappa numbers of onyina and odwuma in Table 5. For at 19% sodium hydroxide on wood the onyina pulp had a kappa number of 30 while that of odwuma was 47, their respective Klason lignin percentages are 22.4 and 25.9. If the relationship kappa x 0.14 = % lignin (4) is assumed to be true for tropical hardwoods then the reduction in lignin content during the pulping process is 81.3% and 74.6% for onyina and odwuma respectively. This shows more lignin has been removed from the lower lignin content wood than the higher. Table 3
Chemical CoIIp>sition of Some TeQ?erate woods
Species
A:B Extract
Cellulose %
Red pine
Klason lignin %
Hemicellulose %
9.7
47.8
23.4
15.1
Douglas-fir
-
57.2
28.4
14.1
Western hemlock
-
51.6
30.4
15.5
Yellow birch
3.4
42.6
18.8
26.6
Beech
2.0
43.6
22.2
23.6
Sugar Maple
2.7
46.8
21.1
22.2
*Source
"The Chemistry of Wood" Ed. B.L. Browning pp.66-67
Tropical hardwoods
Table 4:
Local Trade
Chemical COIIIX>Sition of
Botanical Name
Name
115
sane Ghana Hardwoods
A:B Extract
cellulose
%
%
Klason lignin %
Pento san %
Esa
C.rnildbraedii
-
40.6
25.1
22.2
Onyina
C.pentandra
-
33.0
22.4
18.7
Bese
C.nitida
-
41.0
25.8
19.0
Kusia
Nauclea spp
9.5
44.8
38.1
-
Edinam
E.angolense
3.2
50.3
27.6
15.2
Kaku
Lophira spp
2.5
39.5
39.2
-
Africa Walnut
C.edulis
3.4
45.3
27.8
15.8
Odwuma
M.cecropiodes
3.3
53.7
24.6
16.1
Otie
P.angolensis
1.1
53.5
23.8
18.7
Ofram
T.superba
3.4
48.5
29.2
16.4
Wawa
T.sceroxylon
1.4
41.5
34.3
17.4
9.6 T.ivorenses Emire 42.0 30.5 11.9 *Source : The Chernlstry Sectl0n of Forestry Research Institute of Ghana, Kumasi, Ghana.
Therefore to achieve the same degree of delignification the charge would have to be increased or time lengthened, for the higher lignin content woods. The percentage of the alkali-resistant cellulose of the tropical hardwoods range from as low as 33.0 for onyina to 53.7 for odwuma. The values here also cut across the averages for both temperate hardwoods and softwoods at 42% and 48% respectively. These values reflect very much on the percentage screened yields of the pulps produced from these woods. Thus odwuma and onyina at 19% alkali on wood gave pulp yields of 50.90 and 42.15 respectively.
116 Pulping
c.
Alkaline Pulping Process
Table 5 shows the alkaline pulping characteristics of some tropical species in singular and in mixture. Work done by Darkwa on emire (2) and Smith and Primakov on odwuma and emire (5) indicate that there is nothing unusual with the alkaline pulping of these species in singular. However as shown on Table 5, at the same alkali charge odwuma gives higher % yield and higher kappa number than onyina. The difference in yield could be explained in part by the high difference in cellulose content of the two species at 53.7% for odwuma and 33.0% for onyina. their lignin % are very similar, and their specific gravity also similar. When they were mixed in equal proportions for pulping (Mixture 1 on Table 5), the resultant pulp and % yield between the two species in singular while the kappa number was significantly lower than both species in singular. Table 5:
Akaline Pulping of Odwurna, Onyina, Emire and Mixture of these Species.
Species (Mixture)
% NaOH on Wood
Screened Yield
Rejects
%
%
Total Yield i
Kappa Number
47
OdVUlia Onyina Emire
19 19 20
50.90 42.15 41.80
0.76 0.00 0.12
51.56 42.15 41.92
26.4
Kixt\i.re 2 :El1ire tObe 1:1)
20
44. 73
0.77
45.50
35
Mixture 3 (OdiUla + Onyina + hire 1" Otie
20
44.70
1.70
46.40
33
20
45.79
D.H
49.93
20
30
1:1:1 :1)
Mixture 1 (Odwulla + OnyiJa 1:1)
=
*Cooks were perforlled in 15 litre digester heated externally. Liqour: Wood 4: 1, Time to max. Temp. of 170oC= 45 minutes and Time at Max Temp. = 90 minutes.
In mixture 2 where the specific gravity of the two species were higher than those in mixture 1, there was an increase
Tropical hardwoods
117
in % rejects and decrease in % screened yield with increase in kappa number, when compared to mixture 1. When all four species were mixed together (mixture 3) the % screened yield remained the same with mixture 2 with increase in % rejects while the kappa number of mixture 3 was 2 points below that of mixture 2 but 13 points above mixture 1. Of the four species mixed together, otie and odwuma have similar % cellulose and lignin except that otie is medium density wood while odwuma is low density wood. Onyina on the other hand has low density, low cellulose and lignin contents while emire is medium in density and high in lignin content and medium in cellulose content. Smith and Primakov (6) working with a mixture of odwurna, emire and wawa stated that as the ratio of odwuma increased in the mixture, the % yield increased and the Kappa number decreased. Emire and wawa have high lignin and medium cellulose content. Thus with increasing amount of odwuma in the mixture, the % yield should increase with decreasing kappa number. CONCLUSION: The overall results of this work indicate that yield and kappa number may be attributed to the chemical composition of the individual species present in the mixtures but the most favourable mixture from tropical species is one in which a species with high cellulose content dominates. REFERENCES 1. Browning, S.A.; (1966) Pulping Process, Interscience Publishers, New York. pp.142. 2. Darkwa, N.A. (1971) - "Pulping Characteristics of Ernire - "Technical Newsletter (FPRI) Vol.S Nos. 3 & 4. 3. Ofosu-Asiedu, A and Phil Cannon, (1976) "Terminalia ivorensis decline in Ghana" PANS 22 (2): 239-272. 4. Rydholm, S.A. (1966) Pulping Processes, Interscience Publishers, New York. pp.142. 5. Smith, J.B. and Primakov (1977) Appita 30 (5),405. 6. Smith J.B. and Prirnakov (1978) Appita 32 (2), 113.
11 Pulping characteristics and mineral composition of 16 field crops cultivated in Finland K A Pahkala, T J N Mela and L Laamanen - Institute of Crop and Soil Science, Agricultural Research Centre of Finland, FIN-31600 Jokioinen, Finland
1. INTRODUCTION An active search is underway in finding raw material other than wood for pulp production. One proposed alternative for hardwood in printing papers is nonwood fibres from herbaceous field crops. Promising species for fibre production have been found in the plant families Gramineae, Leguminosae and Maluaceae (1). Within these, the closest attention in recent years has been paid to grasses and other monocotyledons (2, 3) and to flax and hemp (4). The pulping properties of grass and straw are similar to those of hardwoods, but the amount of lignin is lower than in woody species, which means that they are easy and cheap to pulp (5). The mineral concentrations are higher in nonwood species than in wood. Elements that are not desired in the alkali circulation system include potassium, chlorine, aluminium, iron, silicon, manganese, magnesium, calcium and nitrogen. Most of these originate from the raw material and are found in small amount in birch chips, too (6). The chemical and pulping characteristics of herbaceous fluctuate more than those of woody species (5, 7), since the plant properties vary with growing conditions, e.g., soil type, fertilization, climate and plant age, as well. The aim of the Agrofibre Project, begun in 1990, was to develop profitable ways of producing specific, short fibre raw material from field crops available in Finland, and to process this for use in high quality papers. The project as a whole has been described in an earlier paper (8). Our first task in 1990 was to choose the most promising crop species for further study. The properties considered important were the fibre yields and quality and the mineral composition of the 119
120 Pulping
plants. This paper presents the results of our evaluation of potential fibre plant species.
2. METHOD OF APPROACH During 1990, data were collected from field trials including 16 field crops and from one wild species to determine the fibre yields and quality and the mineral composition of the plants (Table 1). Grasses were harvested in July or August at full flowering or seed ripening stage. Straw of cereals, oilflax, rape and turnip rape were harvested in September. The effect of plant age was studied at four different harvest times: at the beginning of flowering in June, at full flowering in July, at seed maturity stage in August and in the following spring when the plants were dead. The non-wood species were compared with birch, the common raw material of short fibre in Finnish pulp mills.
Table 1. Plant species in the preliminary screening, trivial and latin names Trivial name Reed canarygrass Tall fescue Meadow fescue Timothy Common reed Winter rye, straw Oat, straw Spring barley, straw Spring wheat, straw Goat's rue Red clover Lucerne Oilflax, straw Fibre hemp Nettle Spring turnip rape Spring rape Birch
Latin name
Type
Phalaris arundinacea L. Festuca arundinacea Schr. Festuca pratensis Huds. Phleum pratense L. Phragmites communis Trin. Secale cereale L Avena sativa L. Hordeum vulgare, L. Triticum aestivum, L. Go/ega orientalis L Trifolium pratense L. Medicago sativa L. Linum usitatissimum L. Cannabis sativa L Urtica dioica L Brassica rapa L. Brassica napus L. Betula spp. L.
perennial monocotyledon perennial monocotyledon perennial monocotyledon perennial monocotyledon perennial monocotyledon winter annual " annual monocotyledon annual monocotyledon annualrnonocotyledon perennial dicotyledon perennial dicotyledon perennial dicotyledon annual dicotyledon annual dicotyledon perennial dicotyledon annual dicotyledon annual dicotyledon deciduous tree, dicotyledon
To evaluate the pulping characteristics, the plant material was cooked for 10 minutes at 165°C in NaOH solution (16% of dry matter) with anthraquinone (0.1% of dry matter). The sorted pulp yield, the uncooked rejects, the viscosity, the fibre length and the kappa number were determined after cooking. The concentrations of Fe, Mn and Cu were measured by flame-AAS and the concentration of silica (Si0 2 ) by gravimetry, in both cases after dry ashing. Nitrogen content was determined by Kjeldahl method.
Field crops
121
3. RESULTS AND DISCUSSION
3.1 Pulping studies Cooking of grass biomass and cereal straw was easy and fast compared with the processing of wood pulp, which took at least 90 minutes. Only small differences between the monocotyledonous species were found. Pulp yields were 33 - 400/0 of dry matter for grasses, 42-48% for straw (Table 2). Pulp yields for dicotyledons were much lower. The amount of uncookable rejects which is insignificant in commercial birch sulphate pulp was 0.1-1.2% for grasses, 11.8% for reed, 0.62.6% for straw and 13-41% for dicotyledons. Common reed gave a pulp yield nearly as high as the cereal straw, but the amount of rejects showed that the cooking procedure was not well suited for reed (Table 2).
Table 2. Sorted pulp yield, rejects, kappa number, viscosity and fibre length (LW) for crop plant samples taken in 1990 and for commercial birch sulphate pulp. Species Reed canarygrass Tall fescue Meadow fescue Timothy Reed Rye Oat Barley Wheat Goat's rue Red clover Lucerne Oilflax Fibre hemp Nettle Turnip rape Rape Birch
Sorted pulp Rejects % % 36.9 0.3 32.6 0.1 -0.3 40.1 33.7 1.2 38.1 11.8 48.2 2.6 42.3 0.6 48.3 2.0 43.4 2.1 13.7 24.2 23.9 13.4 20.9 17.2 13.0 35.7 13.4 41.0 9.9 21.5 16.4 36.7 12.3 38.5 50.0
Kappa number 9.1 10.2 12.0 13.5 31.7 12.5 14.4 19.9 10.0 45.5 63.4 65.0 80.2 49.2 78.7 78.9 74.7 17-20
Viscosity
LW
1090 910 1080 1020
mm 0.57 0.60 0.72 0.60
1100 1180
0.90 0.80
790 850 810 760 1100 610 590 690 >1000
0.70 1.08 0.42 0.83 0.90
The kappa numbers indicating lignin content were lower for grass pulp than wood pulp. Grasses harvested during the growing period were easily cooked to kappa number 9-14 (Figure 1), which was lower than the kappa number for commercial birch sulphate pulp (17-20) [fable 2) and the kappa numbers for the other plants tested. Viscosity of the pulp made of grass, straw or hemp was similar to that of birch pulp.
122
Pulping
TALL FESCfJE
%
45 40 35 30 25 20 15 10 5 0
%
A
B
~pulp
30 25 20 15 10 5 0
D C -rejects
A
C B ga kappanumber
D
RED CLOVER 45 40 35 30 25
90 80 70 60 50
% 40 30
% 20
15 10 5 0
20 10 0
A
o pulp
B
A
D
C
• reJects
B
C
D
~ kappanumber
Figure 1. The effect of plant age on pulp yield, amount of rejects and kappa number in tall fescue and red clover. Samples taken A=at the beginning of flowering (June), B=at full flowering (July), C=at seed maturity (August), D=in following spring.
Table 3. Pulp yield, rejects, kappa number and viscosity for goat's rue and red clover after pulping in different amounts of NaOH. Species
NaOH- NaOH% residue
Pulp %
Rejects Kappa Viscosity LW % number mm
gil
Goat's rue
Red clover
16.0 20.0 24.0
2.6 6.5 11.7
13.7 18.3 22.5
24.2 15.7 11.6
45.5 38.2 34.7
790 970 920
1.01 0.92
16.0 20.0 24.0
0 4.7 9.7
23.9 22.8 24.8
13.4 9.7 7.7
63.4 48.5 46.2
850 890 930
0.70 0.87 0.89
Field crops
123
The amount of NaOH (16% of dry matter) used in trials was too low for dicotyledons. In the case of red clover and in goat's rue the pulp yield, amount of rejects and kappa number became more acceptable when the dose of cooking chemical was increased to 20 or 24% of dry matter (Table 3).
3.2 Mineral concentrations The mineral concentrations were higher in the non-wood species than in birch and the concentrations in grasses and cereals differed from those of dicotyledons (Table 4). The silica concentration of grasses ranged between 0.9 and 6.1 % and that of dicotyledons between 0.2 and 0.8%, being lowest in oilflax straw «0.1%). The ash content was lowest in straw of oilflax and hemp (3.8-3.9%). In some species plant age was important for mineral content (Figure 2). The effect of plant age on chemical and pulping properties of several non-wood plants has been discussed in detail in papers published earlier (9, 10).
Table 4. Mineral concentrations in dry matter of crop samples taken in 1990. Species, harvesting
Ash
Fe mg/kg
%
Reed canarygrass Tall fescue Meadow fescue Timothy Rye Oat Barley Wheat Reed Goat's rue Red clover Lucerne Oilflax Fibre hemp Nettle Turnip rape Rape straw Birch
Mn mg/kg
5.09 5.31 9.10 10.03
2.63 2.42 1.52 0.88 3.61 3.68 6.13
101.5 100.3 53.6 131.3 159.0 48.6
24.0 61.9 42.4 38.0 18.8 46.2 15.3
5.41
3.52
97.3
7.79 6.93 6.22 6.83 3.93 3.75 12.13
3.30 0.27 0.31 0.38 <0.1 0.19 0.78 0.14 0.36 <0.1
51.3 109.0 91.2 118.5
8.76 9.54
7.62
6.10 6.82 0.41
56.7
54.6 87.3 100.7 74.5 351.2 22.3
Cu mg/kg 7.05 5.50 5.03 4.42
N %
4.95 3.29
1.73 2.47 1.28 1.10 0.52 0.96 0.33
13.0
1.76
0.54
13.4 17.6 24.0 16.9 87.3 11.2 102.7 14.0 25.8 114.0
3.58 7.95 7.64 7.04 6.09 4.05 6.92 3.27 3.66 0.90
1.06 1.96 1.83 1.89 0.99 0.56 2.70 0.96 0.83 0.11
3.26
4. CONCLUSION
In this study the most suitable species for alkali cooking were the grass and cereal crops, which gave the highest pulp yield and the lowest amount of rejects. Common reed gave pulp yields nearly as high as the cereal straw. At least with
124 Pulping
the tested. cooking method, the dicotyledonous plants did not show much promise as fibre crops. On the basis of our results, we selected the following species for further study: reed canarygrass, tall fescue, meadow fescue and spring barley. Because they have the favourable property of not requiring nitrogen fertilization, goat's rue and red clover were included in some of the further studies, too. The values reported are useful for comparison and preliminary evaluation but do not sufficiently take into account the regeneration process with a higher amount of minerals. This problem will be studied separately.
TALL FESCUE
, %
Ash
12 10 8 % 6
4
4
2
2 -
o
o A
B
c
-+----------ir--------+-------j
B
A
D
c
D
RED CLOVER 1
12 10 8
Si0 2
0.8 %
0.6
% 6
0.4
4 2
0.2
o
Ash
-t--------+----f---------i
A
B
c
o
-----+---------+-
DAB
C
---j
D
Figure 2. The effect of plant age on silica and ash contents in tall fescue and red clover. Samples taken A=at the beginning of flowering (June), B=at full flowering (July), C=at seed maturity (August); D=in following spring. 5. REFERENCES
1. Nieschlag, H.J., Nelson, G.H., Wolff, LA. and Perdue, R.E. (1960) TAPPI, Vol. 43, 3, 193-201. 2. Kordsachia, 0, Baum, N. und Patt, R. (1992) Das Papier 6,257-264.
Field crops
3.
125
Olsson, R., Torgilsson, R. and Burvall, J. (1994) Pira International, Conference Proceedings Vol. 1, Paper 6,8 p. 4. anna, M, van (1994) Pira International, Conference Proceedings Vol. 2, Paper 18, 15 p. 5. Judt, M. (1993) Industrial Crops and Products 2,51-57. 6. Keitaanniemi, O. and Virkola, N.-E. (1982) TAPPI Vol. 65, no. 7,89-92. 7. Wisur, H., Sjoberg, L.-A. and Ahlgren, P. (1993) Industrial Crops and Products, 2, 39-45. 8. Mela, T. (1993) 2nd European Symposium on Industrial Crops and Products, Pisa, Italia. Abstract No. 72. 9. Pahkala, K. and Mela, T. (1993) 2nd European Symposium on Industrial Crops and Products, Pisa, Italia. Abstract No. 83. 10. Pahkala, K., Mela, T. and Laamanen, L. (1994) Maatalouden tutkimuskeskus, Tiedote 12/94,56 p .
12 Screening, purification and characterization of novel xylanases used in pulp bleaching B Cuevas, B Bodie, C Wang and M Koljonen - Genencor, International, 180 Kimball Way, South San Francisco, CA 94080, USA
ABSTRACT Five xylanases were purified from culture supernatants produced by the actinomycete Microtetraspora flexuosa. These xylanases were assayed for alkalinelthennostability and partially characterized. Two were subsequently tested for pulp prebleaching efficacy. Physical characteristics of the five xylanases varied substantially with respect to thermo stability, molecular weight and isoelectric point. The two xylanases increased brightness of chemically bleached pulp by 0.4 to 2.1 ISO units, depending on pH and temperature used.
INTRODUCTION The paper industry'S use of xylanases to assist in pulp bleaching has becorre commercially significant in recent years [1]. By cleaving reprecipitated xylans associated with chromophoric lignin on pulp surfaces, pretreatment of pulp with xylanase disrupts bonding between lignin and cellulose thereby improving lignin extractability and lowering the amount of chlorine and chlorine compounds required to achieve bleaching [3]. In addition to chemical cost savings, the use of xylanase also significantly reduces levels of hazardous waste released into mill waste streams, halogenated organic compounds being major byproducts of chlorine bleaching [2]. As environmental regulations concerning pulp mill eftluents increase, the paper industry will have to employ chlorine-free alternatives for pulp bleaching.
127
128
Pulping
During the alkaline cooking (kraft) process most commonly used in mills, the pulp mixture must be cooled and its pH lowered prior to pretreatment with current heat and alkaline labile xylanase products. An aIkalineIthennostable xylanase product which can be fed directly into the pulp cooking process with little or no process modification is desirable. Identification of such a xylanase requires enzyme screening and purification for effective characterization. After performing well in bleaching tests, the enzyme would be cloned and produced in a high expression production strain, formulated and provided to pulp mills. These steps can be summarized as follows:
Grow Culture: plates, shake flasks, small scale fermentors
. . . ._ ---..@ No
Xylanase Producer? -azo birchwood xylanase assay Yes Protease Present? -skim milk assay No
Purify Xylanase to Homogeneity, N-terminal sequence for DNA probe, Clone gene into high expression production strain
Purify Xylanases
~-.--.ot
Perform Application Studies On Each, Identify Potential Candidate(s), if any
Many fungal and bacterial strains were screened for the production of alkaline/thermostable xylanases. One such organism, the bacterium Microtetraspora flexuosa, was found to produce xylanases of interest. Microtetraspora flexuosa is a thermophilic actinomycete. Actinomycetes include a wide range of branching bacteria with great morphological variation. These organisms are Gram positive and mostly slow growing. It is the nocardioform actinomycetes and the common sporoactinomycetes, bacteria with branching hyphae and specialized spore-bearing
Xylanases used in pulp bleaching
129
structures, that have attracted considerable interest from biotechnologists, geneticists and ecologists. The following describes steps taken in the development of an industrial enzyme, specifically an alkaline/thermostable xylanase used in pulp bleaching. Techniques involving the purification and characterization of potential bleaching alkaline/thermostable xylanases from the actinomycete Microtetraspora flexuosa will be described.
METHODS Strains. Microtetrasporaflexuosa ATCC 35864, obtained from the American Type Culture Collection (Rockville, Maryland, USA). Media used was 3X XPYB (IX XPYB is 10 goat spelt xylan, 5 g trypticase peptone, 5 g yeast extract, 5 g beef extract, 0.74 dihydrocalcium chloride per liter, pH 7.2). Culture grown in 141 fermentor, 45°C, 72 hours. Analytical Methods. Isoelectric focusing (IEF) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) were carried out using a PhastSystem (Pharmacia) as per manufacturer's instructions. Markers used for pI determination were a broad pI kit pH 3.59.3 (Pharmacia Biotech). Molecular weight markers used were from Sigma Chemical Co. (St. Louis, MO). Visualization of proteins was by PhastSystem development silver staining, as per instructions. Protein concentrations were determined using a BCA method (Pierce). Molecular weight determinations were accomplished by SDS-PAGE and mass spectroscopy (MS). MS was performed by Charles Evans and Associates (301 Chesapeake Drive, Redwood City, CA 94063, USA). Xylanase activity was determined using a remazol brilliant blue dyed birchwood xylan (RBB-xylan) substrate (Megazyme, Sydney, Australia). Samples, 200 ul, were mixed with 250 ul of substrate solution (2 % (w/v) RBB-xylan in 50 mM sodium citrate pH 6.5) and incubated at 37 °C for 10 minutes. Undigested xylan was precipitated by the addition of 1 ml 95% ethanol and removed by centrifugation. Released dye remaining in solution was quantified by spectrophotometry (OD590) and was proportional to xylanase activity. Activity was quantified using a standard curve and is reported as XAU/ml (xylanase activity units per milliliter). Thermostability and alkaline stability was determined by adjusting described temperature and pH and assaying as above. A gel overlay method for detecting the presence of multiple xylanases and to determine their isoelectric point (pl) was also developed using RBB-xylan substrate. IEF gels, pH 3-9, were overlaid with a melted agarose-substrate suspension (4 % (w/v) agarose, 7 mgIml RBB-xylan, 0.5 % (v/v) glycerol in 50 mM sodium citrate, pH 6.5) and incubated at 37 °C. After 1 hour xylanase activity was evident as clearing zones. Gels were allowed to dry completely and stored. Xylanase pI was determined by comparison with identically run IEF gels containing silver stained pI standards. Purification Methods. A combination of ion exchange and hydrophobic interaction chromatography (IEC and mc, respectively) were used to purify all five xylanases (xylanases "1-5"). Briefly, fermentation broth (ca. 14 XAU/ml, 12.5 mg/ml total protein)
130 Pulping
was concentrated 5 X using ultrafiltration (Amicon stir-cell, 350 ml, PM-l0 membrane). All samples were filter sterilized. IEC was used to copurify xylanases 1 and 2. Concentrated sample was dialyzed completely against 10 mM tris-HCI, pH 9.0 and 50 ml were applied to a Pharmacia C 16/40 column packed with Q-Sepharose lIP (Pharmacia). The column was washed then eluted with a 400 ml 0.25 M NaCI gradient. Xylanases 1 and 2 co-eluted from the column with the break-through (i.e. were unbound by the column), relatively pure, while the vast remainder of protein was eluted by the salt gradient. Hydrophobic interaction chromatography (mC) was used as a second step to purify xylanases 1 and 2. Active fractions were pooled and brought to a final (Nl4)2S04 concentration of 0.2 M by the addition of 2 M
RESULTS AND DISCUSSION Microtetraspora flexuosa produced thermostable xylanase activity in liquid culture (data not shown). When dosed as a whole, M. flexuosa culture supernatant containing xylanase activity was shown to enhance the chemical bleaching of softwood pulp at elevated
Xylanases used in pulp bleaching
131
temperatures and pH (table 1). Supernatant effected a 3.6 % ISO and a 1.7 % ISO brightness increase at pH 8, 70 C and pH 9, 70 C, respectively. Gel overlay analysis revealed the presence of five xylanases, pI 8.5, 7.5, 6.2, 5.8, and 5.3 (xylanases "1-5", respectively, data not shown). Protein purification methods employed proved to be effective, resulting in homogeneous or near homogeneous xylanases (figure 1). Characterization of individual purified xylanases revealed significant differences with respect to molecular weight and thermostability (table 2). Microtetraspora flexuosa xylanases 1 and 2 were chosen for bleaching studies based on their high thermostability and low molecular weight. After preparative purification, the two xylanases were used to prebleach hardwood kraft pulp at elevated temperatures and pH as high as 90 °C and pH 8 (table 3). Xylanase 1 performed better than xylanase 2, effecting a brightness increase of 2.0 % ISO at pH 8, 90 °C over reference levels (no enzyme). The two enzymes performed better than current xylanase products at pH and temperatures studied, offering promising potential for future alkaline/thermostable xylanase pulp bleaching products. 0
0
Table 1. Bleaching experimental results using whole culture supernatant. Oxygen delignified I . D-E-D bleac hinl~. soft wood kraft PUlppnorto Brightness Change Temperature ( °C) Brightness (% ISO) Enzyme pH (% ISO) Reference Irgazvrre 40* Microtetraspora jlexuosa
7.5 10 7.5 7.5
7.5 7.5 8 9 10 *Commercial xylanaseproduct.
50 70 50 70
74.4 74.3 78.7 79.2
+4.3 +4.9
80
76.0 74.7 77.9 76.0 75.2
+1.7 +0.4 +3.6 +1.7 +0.9
90 70 70 70
Ta ble 2 . Purified X yJIanase c haractensncs. I temperature ( °C)
pH xylanase
pI
MW(kD)method
optimum
stability range
optimum
stability (half-life at 80°C, min.)
1 2 3 4 5
8.5 7.5 6.2 5.8 5.3
33.1-MS 13.3-MS 31-SDS 50-SDS 35-SDS
7.0-7.5 7.0-7.5 7.5 7.5 7.5
6-8.5 6-8 6-9 6-9 6-9
70 65 65 65 70
110 45 30
90 30
132
Pulping
Table 3. Bleaching results using purified xylanases 1 and 2. Oxygendelignified hardwoodkraft pulp prior to D-E-D bleac• .
EnzymeIRefecence Treanreet pH Reference
xylanase2
Brightness Change (% ISO)
83.0 83.0 83.3 83.4 85.1 85.3 83.6 84.8 83.6
+0.4 +2.1 +2.0 +0.6 +1.8 +0.3
(eC)
'E 90 70 90 90 70 90 90 70 90
5 7 8 5 7 8 5 7
xylanase 1
Fmal Brightness (%ISO)
8
Figure 1. Isoelectric focusing gelanalysisof purifiedenzymefractions. 2
3
4
5
7
6 .~
pI
....~
.•~.~"...
,~
.,.........
..
....
8.45 8.15
7.35 6.85 6.35
Key: 1) originalculture supernatant, 1:10
2) xylanase1 3) xylanase2 4) xylanase3 5) xylanase4 6) xylanase5 7) pI standards
5.85
"
:'15.2 '.'
4.55
SilverstainedPhannaciaPhastGel, pH 3-9. Map bands identified as xylanase by overlay technique.
REFERENCES
[1] Wong, K . K. Y., and Saddler, J. N. In: Coughlan, M.P., Hazlewood, G.P (eds.), Hemicellulose andHemicellulases (1992), pp. 127-144, London, Portland Press. [2] Viikari, L., Kantelinen, A., Sundquist, J., and Linko, M., FEMS Micro. Rev. (1994), 13,335. [3] Kantelinen, A., Hortling, B., Sundquist, J.,Linko,M., and Viikari, L., Holsforschung (1993),47, 318.
13 Delignification and bleaching of non-wood fibres with peroxy-compounds D Stewart and I M Morrison - Unit for Industrial Crops, Scottish Crop Research Institute, Dundee DD2 5DA, Scotland
Abstract Barley and forage rape straw and flax fibre were treated with Oxone under the following conditions: Oxone 0-200 gl-l, 30-l00°C, H2S04 0.0-4.0M. Delignification was followed by extraction with 1.OM NaOH. After delignification the residues were analysed for residual lignin and neutral sugar composition and by Diffuse Reflectance
Fourier-Transform Infrared (DRIFT) spectroscopy. In general, increasing Oxone concentration and temperature were accompanied by decreasing residual lignin and non-cellulosic polysaccharides for all three fibre sources, after alkali extraction. However, increasing temperature during forage rape treatments, although resulting in a reduced residual lignin content, also reduced the anhydro-glucose (cellulose) level. The optimum temperature for delignification of barley straw was 70°C, whereas the optimum temperature for anhydro-glucose (cellulose) was 100°C. The corresponding temperatures for forage rape and flax fibre were 70°C and 30°C, respectively.
Introduction Increasing environmental awareness concerning deforestation and pollution, and the need to develop profitable non-food industrial crops has meant that there is an increasing impetus to find and develop non-wood fibre sources and pulping and bleaching processes. Two such fibre sources are cereal straw (barley) and forage rape stems. These, along with the cellulosic textile fibre, flax, were subjected to a series of 133
134 Pulping
treatments with peroxymonosulphate anion (HSOs-) in the form of Oxone, a triple salt (2KHSOs.KHS04.K2S04 ) . The effect of peroxymonosulphate has previously been studied on wood fibres (1-2) but not those derived from non-wood sources.
Experimental Mature, dry barley straw and forage rape stems were hammer-milled, water and acetone extracted and freeze-dried. These served as the control materials. The retted and scutched Belgian flax fibre was a gift from Craigview Mill, Inverbervie, Scotland. Samples (2.0g) were suspended in the appropriate acid solution (0-4.0M H2S04) to which was added Oxone (Dupont, USA; 0-200 g I-I). This was shaken at a fixed temperature (30-100°C) for 90 mins then filtered, washed with water, freeze-dried and analysed for lignin, residual neutral sugar composition (RNSC) and by diffuse reflectance FT-IR (DRIFT) spectroscopy as described by Stewart and Morrison (3-4). The samples were then extracted with 1M NaOH at 50°C for 60 mins then washed and analysed as before.
Results and Discussion Barley Straw Table 1 shows the effect of treating barley straw with different concentrations of Oxone in O.05M H2S04 and at different temperatures on the lignin content. Also shown is the effect of a subsequent extraction with 1.0M NaOH on the lignin content. The general trend for both pre- and post-NaOH extraction is a decrease in lignin content with increasing Oxone concentration. Considering first the samples prior to alkali extraction, over the Oxone concentration range 0-20 g I-I there is a relatively small drop in the lignin content of the treated residues: 0.6% at 30°C, 1.6% at 50°C, 3.0% at 70°C and 2.1% at 100°C. Increasing the Oxone concentrations, to 100 g 1-1, results in a more pronounced temperature dependence and drop in lignin content to give reductions in residual lignin contents of 1.7% at 30°C, 5.2% at 50°C, 10.7% at 70°C and 13.2% at loooe. Delignification reaches a maximum in this series with the treatment conditions 200 g 1-1 Oxone/0.05M H 2 S0 4/100°C, giving a lignin content of 2.5%. Since the control sample at this temperature has a residual lignin content of 18.2% this represents a removal of 86% of the lignin. This degree of delignification, although impressive, requires a high concentration of Oxone.
The combination of Oxone treatment and alkali extraction, however, allows the concentration of Oxone to be lowered without any detrimental effects on the extent of delignification. A comparison of the residual lignin contents before and after alkali extraction shows that the latter are all, without exception, lower. This occurred even for the control samples which were treated in the absence of Oxone but was to be expected since the alkali solubility of gramineae lignins and associated phenolic constituents has been widely reported (5) and is seen here as a decrease in the lignin content of approximately 3-4%. The advantage of using an alkali extraction step can be
Delignification and bleaching
135
seen by comparing the concentrations of Oxone, at a fixed temperature, needed to give similar residual lignin contents for a sample which had only the Oxone treatment and one which had both Oxone and alkali treatment. The samples treated with 200 g I-I Oxone/0.05M H 2S0 4/50°C/pre-alkali extract and 2.5 g I-I Oxone/0.05M H 2 S0 4/50°C/post-alkali extract have residual lignin contents of 10.8% and 10.90/0 respectively. This means that the alkali extraction step reduced the concentration of Oxone needed for an equivalent delignification by 80 fold.
Table 1 Lignin content (% dry matter) of Oxone-treated barley straw pre- and post-NaOH extraction Oxone (gl-l)
pre
30°C post
0 2.5 5 10 20 50 100 200
17.2 16.8 16.6 16.2 16.6 17.5 15.5 14.7
14.4 14.0 13.1 13.0 12.2 11.2 8.6 6.3
pre
17.6 17.0 16.3 16.2 16.0 15.8 12.4 10.8
50°C post
pre
post
100°C pre post
13.1 10.9 10.6 10.3 9.4 7.7 4.8 2.9
16.4 15.3 14.6 14.4 13.4 10.4 5.7 3.1
11.1 9.6 9.1 7.1 4.8 1.5 0.5 0.3
18.2 18.5 17.9 18.0 16.1 11.3 5.0 2.5
70°C
15.1 14.4 14.0 13.9 11.2 4.2 1.4 1.0
This direct relationship between Oxone concentration and delignification can be seen in Fig 1. The important frequencies are those at 1510 and, to a lesser extent, 1595cm- l , the lignin absorbances. The spectra show that, as the Oxone concentration is increased from 0 to 5,50 and finally 200 g I-I, the absorbances at 1510 and 1595 crrr! decrease and are essentially. absent at the higher Oxone concentrations. This correlates well with the residual lignin contents of 11.1, 9.1, 1.5 and 0.3% respectively. The absorbance at 1735 cm-', however, appears to increase. This is due to aryl aldehyde formation (6) and is indicative of the oxidative nature of Oxone. Another trend apparent in Table 1 is the effect of temperature on delignification. In general the progression from 30 to 70°C is accompanied, for both the pre- and postalkali extracted samples, by a reduction in lignin content. This is particularly evident at the higher Oxone concentrations. Under the conditions 100 g 1-1 Oxone/0.05M H2 S0 4/post-alkali extraction the residual lignin contents for the samples treated at 30, 50 and 70 0 e are 8.6, 4.8 and 0.5% respectively. The increase in temperature from 70°C to 100 oe, however, does not follow this trend giving a residual lignin content of 1.4%. At a given Oxone concentration the residual lignin contents of the majority of the samples treated at lOOoe are higher than those for treatments at 70 0 e and SO°C.
136 Pulping
This anomalous temperature relationship might imply that a competitive reaction involving the HSOs- ion is occurring at 100°C, but this can be ruled out since it also occurs when Oxone is absent and only 0.05M H2S04 is present. Another possible explanation may be found in the behaviour of lignin in aqueous H2S04 • Under these conditions the hydroxyl and ether substituted aromatic rings in lignin undergo additional oxidative reactions. These new linkages further cross-link the macromolecule. The traditional method of lignin determination, Klason lignin, depends, to a large extent, on this phenomenon to give a water-insoluble material that can be analysed gravimetrically. A feasible explanation is that these oxidative coupling reactions, although occurring at 30-70°C, become far more prevalent at 100°C, both hampering and competing against the axone delignification reactions by producing a more tightly cross-linked lignin macromolecule which is both less readily penetrated by axone and less readily extracted by alkali.
Q)
o
c:
ca
'0
~
~ Q)
> ~
Q)
0:
1800
1600
1400
1200
1000
800
Wave number (crn-t)
Figure 1. The DRIFT spectra of barley straw treated at 70°C with 0.05M H 2 S0 4 and 0, 5, 50 and 200 g I-I axone, and extraction with 1 M NaOH. This anomaly aside, the importance of this temperature-delignification relationship, particularly to industry, is further exemplified by the samples treated with 200 g I-I Oxone/0.05M H 2S0 4 at 30°C and 10 g I-I/0.05M H2S04 at 70°C, then alkali extracted giving residual lignin contents of 6.3 and 7.1% respectively. This means that increasing the reaction temperature by 40°C from 30°C to 70°C has allowed the concentration of Oxone needed for a comparable level of delignification to be reduced by 95%. The variation of both Oxone concentration and temperature had a pronounced effect on the residual neutral sugar composition (Table 2). The residues obtained after treatment with 0.05M H2S04 in the absence of Oxone then alkali extracted showed a
Delignification and bleaching
137
reduction in the amount of residual hemicellulose (arabinose plus xylose) with increasing temperature. The acid lability of arabinofuranoside residues has been well reported (3-4). This is seen as the temperature is increased from 30°C to 50°C. The residual arabinose content drops by a third from 10.20/0 to 6.80/0. A further increase in temperature to 100°C reduces this by a further 440/0 to 3.60/0. The residual xylose content follows a similar pattern dropping from 30.5% at 30°C to 21.3% at 50°C then finally to 9.6% at 100°C. Increasing axone concentration, like temperature, causes the amount of residual hemicellulose to decrease. An interesting feature is that, at a given temperature, as the axone concentration increases the drop in the level of residual hemicellulose is due predominantly to a loss of xylose residues. At 30°C an increase in axone concentration from 5 to 200 g }-1 results in a reduction in the residual xylose of 10.4% and arabinose by only 0.60/0, while at 70°C the same axone concentration increase causes losses of 8.7 and 0.90/0 respectively. This effect is repeated for all the temperatures studied and suggests the linkage point ofNCP to lignin is through arabinose residues. Treatment of the cell walls with axone results in oxidation of the lignin at the edges of the macromolecule: the buried lignin-NCP interface, however, would remain untouched.
Table 2 The effect of axone and temperature on barley straw cell wall composition. Oxone (g 1-1)
Temp. (OC)
0 5 50 200 0 5 50 200 0 5 50 200 0 5 50 200
30 30 30 30 50 50 50 50 70 70 70 70 100 100 100 100
Control
Ara *
9.1 10.2 10.0 9.8 9.6 6.8 6.8 6.6 5.1 7.1 3.4 3.0 6.2 3.6 5.9 5.0 3.6
Xyl
32.2 30.5 29.0 25.0 20.1 21.3 17.2 13.0 13.9 21.8 19.5 15.2 14.0 9.6 8.5 6.8 5.6
Gle
58.5 59.3 61.0 65.2 70.3 71.9 76.0 80.4 81.0 71.1 77.1 81.8 79.8 86.8 85.6 88.2 90.8
Lignin"
15.2 14.4 13.1 11.2 6.3 13.1 10.6 7.7 2.9 11.1 9.1 1.5 0.3 15.1 14.0 4.2 1.0
*The residual neutral sugar composition (RNSC) and lignin contents are expressed as % total sugars and 0/0 dry weight respectively.
138 Pulping
The combined effects of temperature and Oxone concentration reach a maximum loss in hemicellulose with the conditions; 200 g 1-1 Oxone/lOO°C/0.05M H2S04/post alkali extract. This resulted in a residual hemicellulose content of only 9.2%. However, at 1.0%, these conditions did not give the lowest level of residual lignin. This was achieved by the similar treatment at 70°C which gave a figure of 0.3%. Acid concentration, like temperature, had a definite effect on the efficacy of Oxone delignification. Unlike temperature, however, the progression from low to high acid concentration showed no anomalies, the residual lignin level decreasing with increasing acid concentration. The step from O.OOM acid (distilled water) to 0.05M H2S04 is the most significant with a relatively large percentage of the lignin being lost. At 50 and 70°C this transition reduces the residual lignin content from 13.3 and 6.7% to 7.7 and 1.5% respectively. The progression to 4M H2S04 (an 80 fold increase) only reduces these figures to 4.0 and 0.9%. The residual neutral sugar composition, as with the residual lignin content, changed most significantly on the transition from O.OOM (distilled water) to 0.05M H2S04 • For example, the residual xylose content for treatments at 70 and 100°C dropped from 21.0 to 15.2% and 15.3 to 6.8% respectively. The net effect, therefore, is a progressive loss of hemicellulose as the acid concentration increases.
Flax Fibre The RNSC and lignin contents of the treated flax fibre samples are shown in Table 3. Treatment of flax fibre with 0.05M H2S04 alone had no significant effect on the residual lignin level. However the use of increasing Oxone concentrations resulted in a general trend of increasing delignification. For example, increasing the Oxone concentration from 0 to 200 g 1-1 at 30, 50 and 70°C resulted in a reduction of the residual lignin contents by 30, 32 and 74% respectively, reaching a maximum after treatment with 200 g 1-1 to give a residual lignin content of 0.4%. The combined Oxone and 1M NaOH treatment had a significant effect on the RNSC. All the samples treated at 30°C experienced losses of NCPs, particularly those containing arabinose and xylose residues. Increasing Oxone concentration during pretreatment had minimal effect on the residual mannose and galactose levels suggesting that the NCPs containing arabinose and xylose are those principally attacked by Oxone. The resistance of flax mannans and rhamnogalacturonans to alkali extraction has previously been reported (7). As the temperature of Oxone pre-treatment increased to 50 then 70°C, the loss of NCP became almost exclusively confined to arabinose and xylose. However, at these temperatures increasing Oxone concentration produced a progressively greater loss of xylose, a phenomenon reported earlier in the barley straw/Oxone studies, suggesting that arabinose is again present at the lignin-carbohydrate interface.
Delignification and bleaching
139
Forage Rape The RNSC and lignin contents of the forage rape samples after treatment with Oxone and 1M NaOH are shown in Table 3. The effect of increasing Oxone concentration on the residual lignin content was similar to that seen in the earlier studies on barley straw and flax fibre, i.e. increasing delignification with increasing Oxone concentration. However the scale of the reductions in lignin levels accompanying the treatment were unexpectedly small. An appreciable level of delignification was only evident after treatment at 50 and 70°C/200 g I-I Oxone and 70°CISO g I-I Oxone followed by alkali extraction.
Table 3 The effect of Oxone and temperature on flax fibre and forage rape cell wall composition. Oxone (g I-I) Flax Fibre
Forage Rape
Control 0 5 50 200 0 5 50 200 0 5 50 200 Control 0 5 50 200 0 5 50 200 0 5 50 200
Temp. (OC)
30 30 30 30 50 50 50 50 70 70 70 70 30 30 30 30 50 50 50 50 70 70 70 70
Ara*
Xyl
Man
Gal
Gle
Lignin*
2.3 2.2 1.0 1.1 n.d, 3.3 2.1 2.1 2.2 1.7 1.0 2.4 1.1 6.9 1.5 1.8 3.2 1.8 3.5 2.4 1.9 2.2 3.5 3.6 3.1 2.1
2.3 1.6 3.6 1.4 n.d. 1.2 1.3 1.8 1.4 1.0 0.5 0.7 0.4 30.1 6.4 6.7 6.1 5.0 10.0 8.3 5.8 6.6 12.3 11.8 10.1 9.9
6.0 3.8 4.2 2.6 4.4 5.5 4.4 5.4 6.8 5.0 6.6 7.4 6.1 7.1 3.7 4.7 4.5 5.6 4.8 4.6 7.6 7.7 8.0 7.7 7.9 6.9
4.0 2.0 2.5 2.4 1.5 5.3 5.3 3.4 4.9 6.1 4.2 7.3 4.2 n.d, n.d, n.d, n.d, n.d, n.d, n.d.
85.4 90.4 88.7 90.5 94.1 84.7 86.9 87.3 84.7 86.1 87.7 82.2 88.2 56.0 88.4 86.7 86.2 87.6 82.7 84.7 84.7 83.5 76.2 76.9 78.9 81.1
2.0 0.6 1.0 1.0 0.7 0.9 1.3 0.8 0.4 2.0 0.8 0.6 0.4 10.0 9.0 8.9 8.3 7.0 7.6 7.0 6.1 3.5 6.8 6.2 3.8 0.4
*The RNSC and lignin contents are expressed as % total sugars and
n.d. n.d, n.d. n.d,
n.d, n.d, %
dry weight respectively.
140
Pulping
These produced residues with lignin contents of 3.5, 0.4 and 3.8% respectively. The inactivity of the forage rape lignin to both Oxone pre-treatment and alkali extraction suggests that it is different to other plant lignins. This agrees with the observations of Morrison and Burrows (8) who found that both chlorinated and oxygenated delignification methods performed poorly with several forage rape genotypes as the raw fibre. As before there was a positive relationship between delignification and both temperature and Oxone concentration. At a given Oxone concentration an increase in temperature from 30 to 50°C, or 50 to 70°C was accompanied by a reduction in the residual lignin content. The principal effect of Oxone treatment on RNSC was xylose removal. The xylose:arabinose ratio prior to alkali extraction was roughly 5-7 (not shown), whereas, after extraction, this was reduced to around 3-4. This suggests that, like the barley straw and flax fibre, at least some arabinose is present at the lignin-NCP interface and is therefore resistant to both Oxone and alkali treatment. Similarly the residual mannose level was relatively unaffected and, in some cases, even increased after treatment with Oxone and 1M NaOH again reflecting the intractability ofmannans.
Conclusions Oxone proved to be an effective agent for the delignification and bleaching of barley straw and flax fibre. This was verified by DRIFT spectroscopy. The results presented here merit further study into the effect of Oxone on the physical properties such as tensile strength, elasticity etc. These studies are currently underway. The treatment of forage rape with Oxone, however, was less successful producing limited delignification and minimal bleaching. However, these results were useful in that they support the proposal by Morrison and Burrows (8) that the forage rape lignin is different to other plant lignins. A more in-depth account of this work has been published (1-2).
Acknowledgement The authors would like to thank the Scottish Office Agriculture and Fisheries Department for funding this work and Professor J. R. Hillman for his interest and advice.
References 1. 2. 3. 4. 5.
Springer, E. L. (1990) Tappi J., January 175-178. Minor, J. L. & Springer, E. L. (1993) Paperi Ja Puu, 75(4) 241-246. Stewart, D. & Morrison, I. M. (1993) Cell. Chern. Technol., 27(4) 419-427. Stewart, D. & Morrison, I. M. (1995) Cell. Chern. Technol., 29 In Press. Lapierre, C., Jouin, D. & Monties, B. (1989) Phytochemistry, 28(5) 14011403.
Delignification and bleaching
6.
Bennett, J. E., Gilbert, B. C. & Stell, J. K. (1991) J. Chern. Soc. Perkins Trans 11,1105-1110.
7.
8.
MacDougall, G. J. (1993) Carbohydr. Res., 241 227-233. Morrison, I. M. & Burrows, S. E. (1993) Industr. Crop Prod., 2 171-177.
141
14 Biobleaching of pulp and paper mill black liquor in fluidized bed reactor using immobilised Phanerochaete chrysosporium BKMF 1767 S S Marwaha,* R S Singh,* P K Khanna** and J F Kennedy*** *Department of Biotechnology, Punjabi University, Patiala-147002, India; **Department of Microbiology, Punjab Agricultural University, Ludhiana-141004, India; ***Research Laboratory for the Chemistry of Bioactive Carbohydrates and Proteins, University of Birmingham, Birmingham B15 2TT, UK
ABSTRACT
Phanerochaete chrysosporium immobilized in calcium alginate gel was used in a fluidized bed reactor for the biobleaching of black liquor. The alginateentrapped mycelium was activated for 6-24 h in the bioreactor, and different flow rates (10-30 ml h- 1) were studied for the continuous biobleaching of black liquor. All the activation periods with different flow rates, resulted in poor reduction in colour and chemical oxygen demand than batch system. 1. INTRODUCTION
Environmental pollution is a world wide problem of all the industrialized countries. Some of the large scale industries have been set up during the last two decades in India. The pulp and paper industry is one of the such upcoming industries in the country in general and Punjab in particular. India is achieving about 288 paper and pulp units with installed capacity of 27.5x10 5 tonnes of paper per year [1]. This industry is partially or completely dependent upon lignocellulosic crop residues as raw materials. Most of the pulp and paper mills in Punjab manufacture paper using agro-residues mainly from cereal straws which rank high both in terms of water usa~e and pollution load. The pulp and paper industry on an average uses 273-450 m of fresh water per tonne of paper manufactured [2], nearly 70% of which is discharged as effluents [1]. The pollution potential of the paper mill is negligible as compared to a pulp mill. It is the pulp making process which is responsible for the pollution problems associated with
143
144 Pulping
integrated pulp and paper mills. The pollution potential of small mills is greater than that of large mills as they lack proper effluent treatment and chemical recovery units. The waste water from pulp and paper mills is dark brown in colour and associated with high biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solids and organic carbon [3,4]. The main contributors to the colour are water soluble, polymeric, chlorinated and heavily oxidized degradation fragments of lignin with low aromatic contents [5,6,7]. In most of the mills, these effluents are first treated in the primary clarifiers and then subjected to some biological oxidation process. The lignin derivatives are highly resistant to microbial attack and consequently escape through the biological waste water treatment technologies, into the receiving water, thereby resulting in environmental pollution. White-rot fungi are the promising group among the lignin degrading microorganisms for dealing with this. The ability of white-rot fungi to degrade lignin and lignin derivatives is well characterized [8]. These fungi possess an active lignolytic system [9,10] which is able to degrade protolignins as well as heavily modified lignins, such as kraft lignin and chlorinated lignins [11]. The potential of some white-rot fungi in decolourizing the effluents of pulp and paper mills has been recently demonstrated [4,7,12]. The black liquor constitutes only 10-15% of the total waste water but attributes approximately 95% of total pollution load of pulp and paper mill effluents [13]. Therefore keeping this in view and the advantage of the immobilized cell system over free cells, the present investigations were carried out to develop an immobilized whole cell technology employing white-rot fungi for biobleaching and consequently diluting the pollutants of pulp and paper mill effluent.
2. MATERIALS AND METHODS 2.1 Collection and storage of black liquor: Black liquor of stage-I was periodically collected from Shreyans Paper Mills Ltd., Ahmedgarh, Punjab, India, in air tight plastic containers (10 L capacity) and stored at 4± 1°C. 2.2 Organism : Phanerochaete chrysosporium BKMF 1767, a white-rot basidiomycete, was obtained from Professor T.K. Kirk of Forest Products Laboratory, US Department of Agriculture, USA. The fungal culture was maintained on potato dextrose agar (PDA) Slants. 2.3 Immobilization of Phanerochaete chrysosporium BKMF 1767 : The gel entrapment method was used for the immobilization of P.chrysosporium as follows. 2.3.1 Preparation of mycelial suspension: Phanerochaete chrysosporium was grown on patato dextrose (PD) broth (50 ml contained in 250 ml conical flasks) for seven days under stationary conditions at 30°C. The fungal mats were recovered, washed with sterilized distilled water, suspended in sterile distilled
Biobleaching of black liquor
145
water and macerated aseptically using a homogenizer. The resultant mycelial suspension was used for immobilization. A known volume of mycelial suspension was filtered using pre-dried and pre-weighed Whatman filter paper No.1, which was then dried in an oven at 60°C to a constant weight to calculate the dry weight of fungal biomass. 2.3.2. Entrapment of P. chrysosporium in alginate: The mycelial suspension of P. chrysosporium was thoroughly mixed with sodium alginate (5% w/v). The resultant mycelium-alginate slurry was extruded as drops into calcium chloride solution (0.075 M) at room temperature. To obtain the beads in uniform. size (av.diam. 5.00 mm), the slurry was extruded through a sterilized glass syringe (20 ml capacity). The beads were left suspended in calcium chloride solution (0.075M) for 24 h to allow complete gelation. The beads were washed with saline immediately prior to their use to remove excess of calcium ions and untrapped cells. 2.4 Fabrication of fluidized bed reactor: An acrylic tube 22.08 em long having 8.90 cm J.D. was used to fabricate a fluidized bed reactor (Fig.1). The inlet for the untreated effluent and outlet for the treated effluent was given at a distance of 2.00 cm and 16.08 cm respectively, from the bottom. The bottom plate of the reactor was fitted with a rotating device containing a 5.00 em long teflon coated magnetic bar. The reactor was operated on a magnetic stirrer to achieve agitation. Provisions for different probes to monitor the operation of the reactor were also made through top plate of the reactor. The temperature was maintained at 30°C by placing the bioreactor in a BOD incubator. Fig. 1 : Schematic diagram of experimental set-up for fluidized bed reactor. (A) : Magnetic stirrer (B) : Teflon coated magnetic-bar (C) : Alginate beads containing immobilized mycelium (D) : Sites for probes in top plate (E) : Effluent reservoir (F) : Peristaltic pump (G) : Treated effluent reservoir
c
G
E
2.4.1 Biobleaching of black liquor using immobilized P. chrysosporium in a fluidized bed reactor : The black liquor was filtered through oridinary filter paper, diluted to 5% v lv, supplemented with dextrose (1 %w/v) and adjusted to pH 5.5 was used for its biobleaching in the fluidized bed bioreactor having the void volume 800 ml. The reactor was loaded with the beads containing a known weight of the entrapped mycelium.
146 Pulping
2.4.2 Activation vs. substrate feed rate in bioreactor : The alginate entrapped mycelial beads were maintained for 6-24 h in the bioreactor for the activation of the entrapped mycelium. These were then used to optimize the flow rate to develop a continuous process of biobleaching. The flow rates of the black liquor were regulated to 10,15,20,25 and 30 ml h-1 in fluidized bed reactor, by using a peristaltic pump (Miclins PP-10, India). The treated effluent samples were collected at one hour intervals and assayed for pH, colour and COD, until a steady state was achieved. A steady state was assumed when the colour and COD levelled off as evidenced by assays of five successive samples. 2.4.2.1 Colour: CPPA standard method [14] was used for measuring the colour units of black liquor. 2.4.2.2 Chemical oxygen demand (COD): The COD of black liquor was determined following the procedure of APHA [15].
3. RESULTS AND DISCUSSION The immobilized fungal biomass (6g dry weight) loaded in a fluidized bed reactor was activated for 6-24 h. Then the different flow rates (10-30 ml h- 1) were monitored for the continuous biobleaching of diluted black liquor. The observations after attaining the steady state for the monitoring parameters at all the flow rates were made. The results obtained are presented in Figures 2-4. 16.,-----·------------., 14
12
I t~~~ ~:..
o
II 1:i~~I,. t;·:=,~.:;~.':j
!
10
...
~: ~~.~
••.,.... ?#~
15
~
~
"'r.3:~..
.......·r,:·.·:
.....
20 flOW RA~
I~l~ COlOUR . . coo Fig. 2 Fig. 2 & 3:
30
:::: .... ... ....:.;...:
1.5
~i
25
(mllh)
3C
10
15
20
25
now RATE (mllh)
30
I~;,:if~~ COLW< . . coo Fig. 3
Influence of different flow rates on colour and COD reduction of black liquor in fluidized bed reactor system, loaded with entrapped mycelium activated for 6 & 12 hours respectively.
The. entrapped mycelium activated for 6 h resulted in a colour reduction of 15.3% with corresponding decrease in COD by 5.9% at all the flow rates (Fig. 2). The respective values for the culture activated for 12 h were 34.3% and 22.6% (Fig.3). However, the reduction in colour and COD at different flow rates achieved, while using culture activated for 18 and 24 h were almost similar. At all the flow rates tested for the two activation periods, the reduction in colour and COD achieved were 58.6% and 42.2%, respectively (Fig.4).
Biobleaching of black liquor
147
«50..,------------------, 50
I~?~?~: caW' III coo Fig. 4 Fig. 4:
Influence of different flow rates on colour and COD reduction of black liquor in fluidized bed reactor system, loaded with entrapped mycelium activated for 18 & 24 hours.
However, in the experimentation in flask culture and in the batch system on the bench scale, the colour reduction was 91.73% with corresponding decrease in COD by 67.04%, under stationary conditions after 24 h of treatment. It has been established that P. chrysosporium required a non-agitated mode for enhanced lignin degradation [9,16,17,18]. In the pneumatic devices, the yield of lignin and manganese peroxidases as well as extracellular proteins was more as compared to mechanically agitated bioreactors [19]. However, degradation of lignin by submerged pellets in agitated cultures has been achieved by using a mutant strain [20]. The agitation induced suppression and its alleviation have not been explained. However, the extent of agitation on lignin degradation may need reassessment [21,22,23]. The poorer levels of colour and COD reduction in the continuous fluidized bed bioreactor than the batch system, are justified in the light of the observations made by earlier workers.
4. ACKNOWLEDGEMENT The financial support to RSS in the form of Senior Research Fellow from CSIR, New Delhi is duly acknowledged.
REFERENCES [1] [2] [3] [4]
Gokhale, S., Kapadnis, B.P., Patil, S.F. Impact of paper and pulp industry effluents on environment. NIE.J., (1992), 10, 6. Subrahmanyam, P.V.R. Colour removal from kraft pulp mill waste water. IPPTA Souvenir, (1975), 58, 108. Khanna, P.K., Mittar, D., Marwaha, S.S.,Kennedy, J.F. Characterization and biobleaching of paper pulp mill effluents. Biopapers J., (1990), 10, 16. Singh, R.S. Marwaha, S.S.,Khanna, P.K., Kennedy, J.F. Pulp and paper mill effluent biobleaching using immobilized Phanerochaete chrysosporium
148 Pulping
[5]
[6] [7]
[8]
[9]
[10]
[11]
[12]
[13] [14] [15]
[16]
[17]
[18]
BKMF 1767. In: Cellulosics : Pulp, Fibre and Environmental aspects (Eds.,Kennedy, J.F., Phillips, G.O. and Williams, P.A.), Ellis Horwood, Chichester, (1993), 485. Bennet, D.J., Dence, C.W., Jung, F.L., Luner, P., Ota, M. The mechanism of colour removal in the treatment of spent bleaching liquors with lime. Tappi J., (1971), 54, 2019. Kirk, T.K., Jefferies, T.W., Leatham, G.F. Biotechnology applications and implications for the pulp and paper industry. Tappi J., (1983), 66, 45. Royer, G., Livernoche, D., Desrochers, M., Jurasek, L., Rouleau, D., Mayer, R.C. Decolourization of kraft mill effluent: Kinetics of continuous process using immobilized Coriolus versicolor. Biotehnol. Lett., (1983), 5, 321. Bajpai, P., Mehna, A., Bajpai, P.K. Decolorization of kraft bleach plant effluent with white not fungus Trametes versicolor. Process Biochem., (1993), 28, 377. Kirk, r.x., Schultz, E., Connors, W.J., Lorenz, L.F., Zeikus, J.G. Influence of culture parameters on lignin metabolism by Phanerochaete chrysosporium. Arch. Microbiol., (1978), 117: 277. Paice, M.G., Jurasek, L., Bourbonnais, C. Ho. R., Archibald, F. Direct biological bleaching of hardwood kraft pulp with the fungus Corio Ius versicolor. Tappi.J., (1989), 72, 217. Chang, H.-m., Joyce, T.W., Campbel, A.G., Gerrad, E.D., Huynh, V.-b, Kirk, T.K. Fungal decolourization in bleach plant effluents. In: Recent Advances in Lignin Biodegradation Research (Eds. Higuchi, T., Chang H.m.and Kirk, T.K.) VnL Publ. Co., Tokyo, (1983), 257. Livernoche, D., Jurasek, L., Desrochers, M., Veliky, LA. Decolourization of a kraft mill effluent with fungal mycelium immobilized in calcium alginate gel. Biotechnol. Lett., (1981), 3, 701. Rangan, S.G. Pollution abatement in paper industry. IPPTA Conventional Issue, (1987), 87, 141. CPPA Technical Section Standard Method H 5 P," Colour of pulp mill effluents". 1974. American Public Health Association. Standard Methods for the Examination of Water and Waste water, American Public Health Association, Washington, (1989). Yang, H.H., Effland, M.J., Kirk, T.K. Factors influencing, fungal degradtion of lignin in representative lignocellulosic thermomehanical pulp. Biotechnol. Bioeng., (1980), 22, 65. Reid, I.D., Abrams, G.D., Pepper, J.M. Water soluble products from the degradation of aspen lignin by Phanerochaete chrysosporium. Can.J.Bot., (1982), 60, 2357. Reid, I.D. Solid state fermentations for biological delignification. Enz. Microb. Technol., (1989), 11, 786.
Biobleaching of black liquor
149
[19] Bonnarme, P., Delattre, M., Drouet, H., Corrieu, G., Asther, M. Towards a control of lignin and manganese peroxidase hypersecretion by Phanerochaete chrysosporium in agitated vessels. Evidence of superiority of pneumatic bioreactors on mechanically agitated bioreactors. Biotechnol. Bioeng., (1993), 41, 440. [20] Gold, M.H., Kowahara, M., Chui, A. A., Glen, J.K. Purification and characterization of an extra-cellular H2 02 requiring dianalpropane oxygenase from white-rot basidiomycete. P.C. Arch. Biochem. Biophy., (1984), 234, 353. [21] Reid, J.D. Chao, E.E., Dawson, S.S. Lignin degradation by Phanerochaete chrysosporium in agitated cultures. Can. J. Microbiol., (1985), 31, 88. [22] Buswell, l.A., Odier, E. Lignin bio-degradation. Crit. Rev. Biotechnol., (1987), 6, 1 [23] Kirk, T.K., Farell, R.L. Enzymatic Combustion: the microbial degradation of lignin. Ann. Rev. Microbiol., (1987), 41, 465.
15 Viscosity/DP relationships for cellulose dissolved in cuprammonium and cupriethylene diamine solvents J H Morton - Buckeye Cellulose Corporation, 1001 Tillman St,
Memphis, TN, 38108-0407, USA
ABSTRACT Conversion equations have been determined which relate the solution viscosity of cellulose pulps to the weight average degree of polymerization of their cellulose tricarbanilate derivatives. OPw's were determined by laser light scattering, and the viscosity determinations were made by 0.5% CEO capillary viscometry and cuprammonium ball fall test methods. These results extend the range over which an accurate prediction of the degree of polymerization of cellulosic fibers can be made from routine viscosity testing to 7000 - 7500, the highest level commercially available in cellulose pulps.
INTRODUCTION Buckeye Cellulose Corporation has been producing purified cellulose pulps since 1920, and is unusual in that it produces these pulps from both wood and cotton linters raw materials. One of the key attributes of cellulose pulps intended as a chemical feedstock for polymeric derivatives is the degree of polymerization (OP) of the starting cellulose. The DP affects processing characteristics of the raw material and properties of the derived cellulose derivatives.
BACKGROUND Historically, the easiest way to measure and control DP during processing is by dissolving the cellulose fibers in a solvent and measuring the viscosity of the derived solution. Traditional solvents for measuring differences in OP are cuprammonium and 151
152
Pulping
cupriethylene diamine [1]. For the control of cotton linters pulp processing, Buckeye adopted and modified the procedure described in 1929 [2] by the analytical committee of the ACS cellulose chemistry division. This method is a rapid control test which uses a solution that is 20 gpl in copper(ll) and 200 gpl in ammonia. Cellulose samples of various weights are dissolved in cuprammonium, and the time required for a ball to fall 20 cm. through this solution is measured. (Higher DP samples are tested at lower concentrations to maintain pseudo-Newtonian fluid response.) The actual time is converted to a 2.5 gm., i.e. 2.5% cellulose, basis and the viscosity reported as "2.5 gm. ACS seconds". (This procedure has been submitted to ASTM for publication as a standard method.) Process control of wood pulp production is based on the Tappi CED method [3]. This procedure uses a solvent that is 0.5 Min copper(II), 1.0 M in ethylene diamine, and 0.5% in cellulose. The viscosity is measured in a capillary viscometer. The size of the capillary tube is varied depending on the viscosity of the 0.5% solution. The efflux time is converted to centipoise or rnillil'ascalesec, These methods have been used for many years. Several methods for converting the viscosity of cellulose dissolved in these solvents to a degree of polymerization have been published. Buckeye participated in the development of one of the early methods [4] sponsored by ACS. This procedure is based on preparation of the cellulose nitrate derivative, determination of its viscosity in ethyl lactate or ethyl acetate, conversion to a specific viscosity (11 sp' equation #.1), and calculation of an estimated intrinsic viscosity ([11], equation #.2). The intrinsic viscosity is converted to a DP based on equation #.3. 11sp = (solution viscosity/solvent viscosity) -1 [11]= (11sp/ c)/ (1+k'11sp); k'= 0.4 for ethyl lactate, 0.35 for ethyl acetate DP = K[11]; K= 85 for ethyl lactate, 75 for ethyl acetate
(#.1) (#.2) (#.3)
This gives the average DP of the starting cellulose sample. If the nitrate is dissolved in acetone, it can be fractionated by sequential dilution with water. By determining the nitrate DP of each fraction, it is possible to plot the Molecular Weight (or DP) Distribution of the starting material. Buckeye scientists used this method to establish relationships between the solution viscosity of cellulose pulps and the nitrate DP described above. These results were used to prepare a sliderule relating DP to solution viscosity which was publicly released in 1957. The regression equation derived for CED testing is given by equation #.4, and plotted in Figure 1a. DP = -387.4 + 1439log1o (CED)
(#.4)
Development of new methods and new cellulose solvents [5] indicated that the work summarized above may underestimate the DP. For this reason, the above work was reevaluated with samples similar to ones used previously by measuring their intrinsic viscosity in CED and cadoxen (cadmium ethylene diamine). DP was calculated from the Mark-Houwink equation #.5, shown below, using coefficients reported by Brown [6].
Viscosity/DP relationships
153
Figure 1b
Figure1a
... ... ... ...
VlscosIt)itP ConYersions
..
Vlscoslt)«)P Conversions
................... ...
19:9
..... ............. ... .... .--1957 . . .. . SlICJefUe
/
~
1969 sliderule
(
sliderUe
1000
I
o
o
o ~
~
~
~
~
~
~
o
1000
0.6%CEOViscosity (cp)
2(XX)
seoo
«XX)
5000
&XX)
ACSseconds
Intrinsic viscosities in CED were converted to a cadoxen basis by using Henley's [7] ratio of 1.23.
[1'))
= K(M)
K'(DPv)
= 0.0184, a = 0.76
(#.5)
These results were again issued publicly as the 1969 Buckeye sliderule. (See Figure la for CED, and lb for cuprammonium testing. Figure la also includes the 1957 nitrate DP relationship.) The regression equations are given below as #.6 and #.7, respectively. The new method gave a significantly different prediction of the degree of polymerization, and provided better agreement with other laboratories. DPw = -2953 + 2523.8 (CED)o.25 - 0.021425 (CED)2 DPv = 807*loglo CuAm + 389.36*(CuAm)O.25- 266.4
(#.6) (#.7)
NEED FOR NEW WORK Improvements in equipment and methods have greatly enhanced the capability to preserve DP through the cotton linters process, as shown in Figure 2, such that higher viscosity grades extend beyond the range of the original regression work. In addition, it is desirable to extend the CED conversion beyond wood pulp ranges to include the much higher viscosities associated with cotton linters products. The 1969 regression equation #.6 cannot accurately predict high viscosities. Figure 3 indicates there is a point of inflection at about 220 cp., and the DP actually returns to 0 at about 700 cpo EXPERIMENTAL Wood and cotton linters based pulps, which spanned a very large DP range, were chosen for the new work. A direct method (laser light scattering) was chosen for determining weight average DP. Since previous work, in house, had indicated that nitrate derivatives gave poor light scattering results, the tricarbanilate derivative [8,9] was chosen for the scattering experiments. These derivatives are stable, easy to prepare and purify, are non-degrading, and exhibit good scattering response due to a high dn/dc
154 Pulping
Figure 3
Figure 2
en
18000 16000 14000
..,...----------~a___-__.,
+--------~~-----~
+--'-------#-----If--
~1~ 81ססoo : ~
__~:
~ ~
~
6000
-
--t: L
- t - - - - - -_ _I - -
<1:4000
---I
:
2000
........ .
6Ooo~------------,
.
5Ooo+---:'OIIiIL-----~---~
•
4Ooo4-.---~InM---------~
Sllderule ~30oo-+-4----------~ 2000~---------~
1000
...-.---------~
O...L----.....L....---~----'----J
o HVE Viscosity Improvements
o
200
400
600
0.5% CEO Viscosity (cp)
value. The experimental plan involved making multiple (4-6) viscosity determinations for each sample by both the cuprammonium ball fall and Tappi CED tests. Cellulose tricarbanilates (CTC's) were to be prepared and assayed for purity (see below) from each sample. Impure CTC's were to be discarded and the procedure continued until 3-5 derivatives were prepared from each sample. Finally, the light scattering DP w values and viscosity data would be related by regression equations. The experimental procedure used for tricarbanilation preparation (Figure 4) is: 1. 2. 3. 4.
Shake dry cellulose sample in dry pyridine overnight without heat. Add excess phenylisocyanate and heat to 90 0 C. with shaking for 24 hours. Add methanol to decompose unreacted phenylisocyanate. Precipitate from 70:30 methanol/water (v/v), to which has been added 2% glacial acetic acid. 5. Filter, wash with methanol, dry, and determine purity by nitrogen and UV analyses. 6. Dissolve in THF (1-4 days) and filter ( 0.45 u).
+
3
crN=C=O-
Cellulose Tricarbanilatc if:
R
O-R R
=H
n
O-R
n
RF\
=
-C-i-~ H
Figure 4: Reaction of cellulose with isocyanate to form urethanes (tricarbanilates)
Tricarbanilate purity was assayed by nitrogen analysis and UV absorption in spectral grade THF. Nitrogen level was converted to Degree of Substitution (8.09%= 3 DS); UV extinction coefficients were measured at 280 om and 235 nm, and compared to values obtained from pure, recrystallized cellulose tricarbanilates. CTC's which exhibited DS = 2.8-3.1 and were >90% UV pure at both wavelengths were used for
Viscosity/DP relationships
155
light scattering. Filtered stock solutions in THF were made from each sample. Light scattering experiments were carried out at 5 concentrations in batch mode using scintillation vials, and analyzed by Zimm plots. A dn/dc value of 0.163 (10) for cellulose tricarbanilate dissolved in THF was used in calculations. RESULTS AND DISCUSSION The results of viscosity and light scattering determinations are given in Table 1. To derive especially low DP materials, three wood pulps were steeped in caustic and aged for 24 hours to reduce their DP, as is done in the viscose process. The alkali cellulose was carefully neutralized to regenerate the "aged wood pulp" samples listed in the table. The parent wood pulps and seven cotton linters pulps were also evaluated. These samples span a very large range of viscosities and degrees of polymerization. They represent high purity dissolving pulps used for such diverse applications as low viscosity rayon or acetate products to very high viscosity cellulose ether derivatives.
Table 1: Results of Laser Light Scattering and Viscosity Testing LSOP
CEO
CuAm
Aged Wood Pulp 1
635
(nm) 39.7
(cp) 3.8
(ACS sec.) 1.44
Aged Wood Pulp 2 Aged Wood Pulp 3
679 852
4.1 5.1
1.97 3.6
Wood Pulp 1 Wood Pulp 2
856 1140
5.3 7.1
6.49 9.04
Linters Pulp 1 Linters Pulp 2
1347 1433
42.5 48.8 48.2 61.7 71.5 66.7
8.4 9.7
13.31 16.96
Wood Pulp 3 Unters Pulp 3 Linters Pulp 4 Unters Pulp 5
1606 2272 3603 5020 6475 7208
76.5 97.0
10.8 18.5 52.8 88.8 284.0 355.2
21.84 70.32
Sample
Linters Pulp 6 Linters Pulp 7
133.2 150.8 184.7 241.3
532.4 1070.8 10930 14234
The results, when plotted, suggested a power function. Log and quadratic regressions gave good fits, but less than the 99% predictability target. A "log quadratic" model exhibited the proper form, and gave the level of fit desired, without being overly complicated. Regression results for the data shown in Table 1 are given in Tables 2a & 2b, respectively. These results lead to the following conversions for our CED (equation #.8), and cuprammonium (equation #.9) viscosity test methods. DPw DPw
= 118.019*ln2 CED + 598.404*ln CED - 449.61 = 47.485*ln2 CuAm + 243.745*ln CuAm + 422.04
(#.8) (#.9)
156 Pulping
Plots of these regression equations, along with points from the previous conversions are given in Figures Sa and Sb. A comparison of these results with those previously obtained, indicate that the light scattering results agree very well with the cad oxen and CEO intrinsic viscosity results over the limited range for which the 1969 sliderule was valid. In addition, this new work greatly extends the range of viscosity/DP for which there is a valid relationship. As shown in Figure 5, the CED range was extended from 60 cp to about 400 cp, and the cuprammonium range from 6000 ACS seconds to > 16000 ACS seconds.
Table 2: Regression results for light scattering DP and solution viscosity 2a: CEO Ln Quadratic Regression Coefficients Intercept -449.6 In 598.4 (In)1 118.0
ANOVA Sum of Source Sguares
R~gression 6.3E'
Error Total
R2 99.6%
2.7Es 6.3E'
:F
1145
Std Error 282 192 27
M 2 10
I
Residuals 76 49 13 -20 -37 -11 -87 -37 -29 -178 409 -222 73
PredIcted 560 630 839 877 1177 1358 1519 1643 2301 3781 4611 6697 7135
2b: CuAm Ln Quadratic Regression Coefficients Intercept 422.0 243.7 In (10)1 47.5
ANOVA Source Regression Error Total
Sum of Squares
6.2E' s 5.7E 6.3E'
R2
F
99.1%
545
Std Error 176 94 9
M 2 10
I
Residuals 118 70 39 -188 -49 -24 -60 -19 146 -220 586 -320 112
PredIcted 517 609 812 1044 1189 1371 1493 1625 2318 3823 4433 6795 7096
Figure 5a: CEO, New & Old
8000 7000 6000 5000 D. c 4000 3000 2000 1000 0
1957 1969 1994
CTC light scattering
1957 ;,~ t •• 4
0
sliderule
100
200
300
O.5°k CEO Viscosity (cp)
400
Viscosity/DP relationships
157
Figure 5b: CuAm, New & Old 8(XX)
-r------------------------,
70C1J
-+-----------=--~---_____1
«:rJJ
-+--
~ ~,~~:~:iaC· ..~:. : . .-:- - - - - - - \ - - - - - - - - - - - - 1 ~C".,..
...,
CTC light sea ermq
aoo !~ 'VVV\
LlA./V fV'V\
1969
~~~'"---~~_::__+~--------------_1 ....
e
·1· ....
•• \AAJ - . I r . T . , . - - - - - - - - - - - - - - - - - - - - - - - - - i
1
O--+-------...----------,.-----...-----------i
o
5COO
1CXXX)
l5COO
ACS seconds CONCLUSIONS Laser light scattering of cellulose tricarbanilates provides a powerful technique for determining the relationship between solution viscosity and the weight average degree of polymerization of cellulose raw materials. This method was used to establish new viscositylDP equations relating CEO and cuprammonium testing to the weight average DP of cellulose dissolving pulps derived from wood and cotton linters. The equations are valid from low to very high viscosities (DP's). The CTCILALLS technique is consistent with the predictions of cadoxen and CED intrinsic viscosity methods, but provides an alternate, direct method of determination which can be coupled with size exclusion chromatography to gain polydispersity data. ACKNOWLEDGMENTS I would like to thank our Vice President of Product Development, Dr. Jerry Huff, for sponsoring this work and supporting its publication. I would like to thank the Cellucon Trust for accepting this paper. I would like to thank Dr. John May, for help in initiating this project and assistance in light scattering analysis. I would like to thank Dr. William H. Boyd for statistical advice and carrying out SAS regression analyses. I would like to thank Mrs. Algenner Jackson for preparing tricarbanilates, performing nitrogen analyses, and helping develop the UV-concentration assay.
158 Pulping
REFERENCES Macdonald, R. G. (Ed.) (1969), in "Pulp and Paper Manufacture", Vol. 1 (Chapter 2), McGraw-Hill. Carver et al. (1929) Ind. Eng. Chem., Anal. Ed., 1,49-51. Tappi Standard T230 om -89 Mitchell, R. L. (1953) Ind Eng. Chem., ~ 215-217. Jayme, G. (1971) in Cellulose and Cellulose Derivatives, Part 4, Bikales, N. M. and Segal, L., (Eds.), Chapter XIV, Interscience, New York. 6. Brown, W. 1. (1966) Tappi Journal, 49(8), 367-373. 7. Elmgren, H. and Henley, D. (1960) Svensk Papperstid., g 138-142. 8. Schroeder, L. R, and Haigh, F. C., (1979) Tappi Journal, 62(10), 103-105. 9. Evans, R, Weame, R. H., and Wallis, A. F. A. (1989)J. Appl. Polym. Sci., ~ 3291-3303. 10. Cael,1. 1., Cannon, R. E., and Diggs, A. O. (1981) in Solution Properties ofPolysaccharides, Brandt, D. A., (Ed.), Chapter 5, ACS Symposium Series No. 150. 1. 2. 3. 4. 5.
Part 3: Physical and chemical processing of fibre and fibrous products
16 Property enhancement of plant fibres for industrial use W B Banks -- School of Agricultural & Forest Sciences, University of Wales, Bangor, Wales
INTRODUCTION Increasingly since the Rio Conference, held in 1992, concern is being expressed about the environmental impact of mankind's industrial activity. There is criticism pointed at much forest exploitation and there is no doubt that some of it is merited. However it is important to recognise that : i) ii)
forests managed wisely for timber/fibre production are often environmentally benign well managed plantations planted on appropriate sites are sustainable through many rotations (1).
There are good arguments therefore to support the idea of switching some materials technology from non renewable mineral to sustainable plant fibre based resources. In order to make rational decisions about development of industrial materials it is essential to be aware of long term security of supply and of basic material properties. The availability and supply side of the problem are dealt with elsewhere in this book. This paper is focused on plant fibre properties and on the potential to derive innovative products from these materials.
PROPERTIES OF FIBRES There is abundant evidence that fibre reinforced composite materials are competing successfully in many areas with metals and timber e.g. in aircraft and road vehicle structures; in leisure
161
162 Physical and chemical processing of fibre and fibrous products
products e.g. small boats, gliders, racquets. The basic properties of a selection of fibres used in such products are compared with natural fibre properties in Table 1 below. Table 1
Material
Cotton
Spruce kraft 300 fibril angle Spruce kraft 50 fibril angle Nylon Glass Carbon Steel
Mechanical properties of selected fibres
Dry Properties Stiffness (dry) Tensile strength (dry) initial specific initial specific km MPa (km) GPa 860 64 11 825 1000 70 30 240
1800
127
70
4930
420 3000 3200 4000
42 135 190 57
11 70 500 210
1090 3160 29600 3000
From (19) From Table 1 it can be seen that the properties of plant fibre are generally of similar magnitude to those of synthetic materials used in high performance composites. The exception to this generality is the case of stiffness of carbon fibre which outperforms all natural fibres and the other synthetics by a large amount. Nonetheless, the data of Table 1 do suggest that the natural fibres have tensile properties which could allow them to compete with synthetics in high performance materials. PERFORMANCE OF WOOD In order to understand quantitatively the potential for plant fibre to perform in structural composites, it is useful to try to understand the behaviour of wood itself viewed as a fibre reinforced composite material. From a knowledge of the strength of the covalent bonds within the polymer molecule and the aggregate strength of the hydrogen bonds between adjacent cellulose molecules the tensile strength of pure native cellulose microfibrils is estimated to have a maximum value of about 7GN/m2 (2)
The tensile strength of unfilled phenolic resins is cited as approximately O. 05GN/m 2 and that of non fibrous cellulose derivatives in the order of 0.05 - 0.1 GPa (3). On the average therefore, a reasonable value for wood matrix substance tensile strength is in the order of 0.08 GPa. It is well established that the tensile properties of fibre reinforced composites obey a "law of mixtures". That is, in the direction parallel to the fibre axis,
Where Tc
tensile strength ofthe composites
Property enhancement of plant fibres 163
tr and tm =
tensile strength of fibre and matrix respectively
Xf and x m = volume fractions of fibre and matrix within the composite
The cellulose content of conifer wood is approximately 45% by volume. Hence, where the tensile load is applied normal to the micro fibril, wood fibre strength is given by: 0.45 x 7 + 0.55 x 0.08 GPa 3.15 + 0.04 3.2 GPa
Tc
In the direction normal to the fibre direction tensile strength is given by :
Abbreviations are as defined above. Hence in this plane
Tc = 0.14 GPa
In fact microfibril angle varies considerably across the cell wall in conifer wood from around 100 to 90 0 (see Table 2 below).
Table 2-
Microfibrillar orientation in cell wall layers in spruce wood*
Wall layer Primary
SI S2 S3
*
From (5)
% thickness 5
9 85 1
Angle to fibre axis Random 50 0 - 700 100 - 30 0 600 - 90 0
164 Physical and chemical processing of fibre and fibrous products
The relationship between tensile strength and "fibre" angle is indicated in Fig. 1 below.
IIItill 0°
co
CL ~
1400
45°
s:
"5 c Q)
"-
en
1050
~
en c
~
700
Tensile strength (M Pa) Fig. 1 Relationship between fibre angle and fibre reinforced composite tensile strength. (From Ref. 4) From the Fig. it can be seen that a shift in fibre angle from 0 to 300 reduces tensile strength by some 50%. At angles greater than about 600, the reduction is in the order of 85%. Bearing this in mind it is perhaps more realistic to take the following as a model for the wood cell wall. • Cellulose fibre 45%; of which 85% is well orientated. Hence strongly orientated fibre content approximately 38%. The rest of the cell wall substance (less orientated cellulose, hemicellulose and lignin) is treated as matrix. •
Mean fibre angle 200 (from cell axis). :. Tc
0.38 x 7 + 0.62 x .08 2.66 + 0.05 2.7 GPa
Property enhancement of plant fibres
165
Now, from Fig. 1 it can be seen that a fibre angle of 200 reduces tensile strength by some 37%. Hence, the best estimate of wood fibre tensile strength, normal to the fibre axis (assuming an average microfibrillar angle of 200 from the fibre axis) is equal to
2.7 x (1 - 0.37) = 1.7 GPa
Experimental weight is given to the powerful effect of microfibril angle in data reported by Baum (19). These data show spruce kraft fibre dry tensile strength to be 1.8 GPa where microfibril angle = 50, reducing to 1.0 GPa at a microfibril angle of 300. Given the high degree of approximation in the above calculations the predicted value of fibre tensile strength (1.7 GPa) compares well with those measured experimentally (1.0 - 1.8 GPa). Wood also has composite properties at a second level. It is comprised of elongated cells (lignocellulosic fibres) embedded in a (largely) lignin matrix - the middle lamella. Microscopic examination shows that the middle lamella occupies a maximum of 10% of conifer wood volume. The law of mixtures can be applied at this level, precisely as described above. Taking the experimental average value for fibre tensile strength (1.4 MPa) and assuming lignin tensile strength = 0.08 GPa, then wood tensile strength, parallel to the fibre direction is given by
Tc
0.9 x 1.4 + 0.08 x 0.1 1.26 + 0.008
i.e. approximately 1.2 - 1.3 GPa This is much higher than the experimental value determined for spruce wood (- 0.14 GPa. (5». This order of magnitude difference between experimental and theoretical values for spruce wood needs consideration.
It is well established in materials science theory that the law of mixtures breaks down outside certain critical limits :
i)
where matrix content is less than 20-30% of composite volume. This is because at lower levels, the matrix binder fails effectively to surround the fibre.
ii)
at low fibre length: diameter values (aspect ratio). For example, in a carbon fibre/nylon composite, increasing the carbon fibre aspect ratio from 30 to 800 brings about an increase in composite tensile strength from 110 to 240 MPa. (4)
The volume of intercellular material (i.e. the fibre-fibre bonding substance) is about 10% or less in wood (Fig. 2).
166 Physical and chemical processing of fibre and fibrous products
.---.' .\(=~.: .·.<·l~~~j;~!·~\f.~>\"".~ Fig. 2
Softwood cross section showing cells and intercellular-bonding region.
In synthetic composites this is too low to give optimal performance. It must be borne in mind however, that in wood, the matrix substances are produced molecule by molecule alongside the fibre. Hence, the fibre coating process is much more sophisticated than simple random mixing as in man made materials. At cell level, the "fibres" are discontinuous and their aspect ratio is quite low i.e. about 50. The example cited above (4) suggests that this is too low for best composite performance (see general materials science texts, e.g. (4». Both factors may well contribute to the less than predicted tensile properties of wood. In the growing tree, wood serves a dual function : i) support for the crown; ii) conduction of soil water and nutrients from root to leaf. It is self evident that the stem fills this function adequately. Hence, it may well be that strength properties, beyond those necessary for crown support have not evolved in wood.
THE PRESENT GENERAnON OF WOOD BASED COMPOSITES Leaving aside laminates of various types, wood based composites are based on either particles or fibres. Geometry ofthese fibrous elements are given below in Table 3. Table 3Board type Flakeboard Chipboard Fibreboard
Wood based composites - fibrous element geometry
Approx. fibre length (mm) 30 5 - 10 2-3
Approx. fibre thickness (microns) 300 300 50
Property enhancement of plant fibres
167
The tensile strength of these board materials is not often measured. However, some tensile data are available for chipboard. Here, the tensile strength parallel to the plane of the board is estimated to be in the order of 0.01 GPa (6). If it is assumed that whole wood strength is O. 14 GPa and wood fibres strength is 1.4 MPa (see above), then the predicted strength of chipboard (assuming 10% resin loading) is approximately 0.1 GPa and of fibreboard approximately strength is 0.7 GPa. These values assume random "fibre" orientation. It is clear therefore, that the strength achieved in wood based composites is nowhere near that predicted. The reasons for this are almost certainly associated with the two strength limiting factors discussed above in relation to whole wood; i.e. aspect ratio and fibre : matrix ratio.
Fig. 3 Edge view ofMDF showing relatively sparce fibre-fibre bonding area. sparsness of fibre-fibre contact.
n.b
relative
It is certain that increase in matrix volume to around 30%, dramatically improves the properties of plant fibre composites (see Table 4). Table 4-
Bending strength of some wood based products
Material Douglas fir wood Wood fibre board (10% resin) Wood fibre/phenolic resin (35% resin content by volume)
Bending strength GPa 0.08 0.02 0.11
Bending load is of course much more complex than tensile. It is built up of tensile, compression and shear elements. Nonetheless, at order of magnitude level it provides a useful means of performance comparison. It is noteworthy that increase in resin volume from 10% to 35% results in 5 fold increase in bending strength (Table 4).
168 Physical and chemical processing of fibre and fibrous products
It is also of relevance to note that at this higher resin loading, the manufactured composite is stronger than a relatively strong natural timber (Douglas fir). This is in spite ofthe fact that the fibres (cells) ofthe timber are oriented in the direction of the tensile element of load, whereas in the composite, the orientation is near random. What might be achieved by increase in fibre aspect ratio is not known. If it is assumed that increases similar to those reported in this paper for the carbon/nylon composite (4) might be achieved, then attention to this factor might be beneficial indeed. Apart from mechanical properties, natural fibre composites have two drawbacks in comparison to those based on synthetics : i) ii)
The fibres are extremely water reactive. The products are bio-degradable
WATER SENSITIVITY Because of the abundance of hydroxyl groups present throughout plant 0011 walls, they have a strong affinity for water. This' leads to two deleterious effects. First, as water is absorbed, it occupies space within the cell wall, leading to swelling stresses which are often of sufficient magnitude to rupture fibre-fibre bonds. This is reflected in the high degree of swelling in the thickness direction of such boards when exposed to severe swetting conditions, and the accompanying major decrease in mechanical properties (Table 5). Table 5-
Relative humidity (0/0) 65
90 100 (water soak)
*Change in properties of u.f. bonded wood particleboard due to moisture sorption (From Ref 7) MOR(MPa) 17 10 - 14 3.5 - 8.5
Approximate thickness swell (0/0)
o 5 30
From the above, it is clear that attention is needed to improve water resistance before such chipboards can be used in exterior applications. In their unmodified state wood based boards have similar susceptibility to decay organisms as the wood from which they are formed (8). In practice this is rather irrelevant because at moisture contents where decay is likely to occur (2530%), simple moisture sorption will have already caused major reduction in mechanical properties (see Table 5). FUTURE DEVELOPMENTS So long as the wood board industries continue along the conventional route of high volume, low matrix, low cost production there are severe constraints on market development. It is likely that total market growth will be strongly linked to general construction industry activity and competition will be largely internal - between different board types. This has been observed over a considerable period of time with chipboards and flakeboards taking over traditional plywood markets and latterly, medium density fibreboard making inroads into some chipboard markets.
Property enhancement of plant fibres
169
There may be opportunities for plant fibre based composites to compete for higher value markets with synthetics like carbon and aramid fibres. For this to occur it will certainly be necessary to move into the area of high matrix materials, i.e. where the matrix volume fraction is approximately 35% of the composite. A further constraint on level of performance is fibre aspect ratio. It is noted above that this lies in the region of 10-100 and well below the level where stress transfer is sufficient to give optimal performance. Incorporation of a higher level of matrix resin is not a technological, but simply an economic problem. In order to justify it, it is certainly necessary to move significantly from low cost largely interior grade building boards selling at $300 - 400/tonne towards higher value sports or vehicle products commanding a price of $3,000 - $30,000 per tonne (18). To be acceptable in this market products must be durable in wet environments. It has been shown that significant improvement in moisture resistance of wood based boards can be achieved by substitution of hydroxyl groups with ester, carbamo ester or epoxide groups (Rowell, Tillman, Zhengtion 1986, Youngquist, Krzysik, Rowell 1986, Martins, Banks 1991, Tillmann 1988). (9, 10, 11, 12). More recently work is reported on fibre modified by etherification with glycidyl methacrylate and subsequently bonded with poly (methyl methacrylate) (13). Boards produced by this process show significant improvement in stability, especially in the irreversible part of the dimensional change (Table 6). Once water resistance is imparted to natural fibre composites, the question of bio resistance becomes important. Wood fibre and particle chemically modified by several systems has been shown to become resistant to decay by several wood destroying fungi (14, 15, 16). It is likely that a "cocktail" could be devised to impart dimensional stabilising and wood preservation properties by a single process. Perhaps the most challenging aspect of property enhancement to be addressed is that relating to aspect ratio.
Table 6-
Poly (methyl methacrylate) bonded boards - swelling data
Total swell 0/0 Wetting cycle 1 2 3 4 5 6
modified 8.5 10 8 8 8 9
nonmodified 11 12.5 13.5 15 15 16.5
Reversible swell 0/0 modified 6.5 9 7
8 8 9
nonmodified 8.5 8 9 9 9 II
Irrev. swell 0/0 modified 2 1 1 0 0 0
nonmodified 2.5 4.5 4.5 6 6
5.5
170 Physical and chemical processing of fibre and fibrous products
FIBRE ASPECT RATIO The obvious way to improve aspect ratio is to dissolve the natural fibre and regenerate it into fibre of indefinite length. This of course is an established industrial practice in the traditional viscose process and the newer Courtauld "Tencel" system. This approach in many areas where a pure cellulosic fibre is needed, is attractive. Its disadvantage is that it requires significant purification of the fibre (removal of lignin and hemicellulose) in order to be worked effectively and sophisticated chemical engineering plant for fibre dissolution and regeneration. An alternative approach may be feasible. That is one based on "chemical welding" of short natural fibres into networks. Strict orientation is lost by this approach, but effective fibre length may be dramatically increased with a matching improvement in aspect ratio (Fig. 4).
",
"" I
I
""
I
/ /
/
/ /
/
---
/
"
".
Fig.4 Effective fibre length increase by chemical welding. (n.b. hatched zones represent "welds") A distinction is drawn between the chemical "weld" and the adhesive bond between fibre and matrix. The intentions in the weld is to develop a covalently bonded system with the inter fibre bond being of similar strength to that of intra fibre bonds. In the matrix-fibre bond, phase differences allow crack stopping to occur, increasing toughness, whilst allowing the development of sufficiently strong fibre-matrix bonds to ensure the efficient transmission of stress between adjacent "effective" fibres. In plant fibre technology, this is a relatively untested concept. Some evidence that it may be effective is provided in the work of (13). In this work glycidyl methacrylate was bonded to fibre through the glycidyl epoxy group, leaving the methacrylic group free. This was then reacted with methyl methacrylate (MMA) so that a chemical bond forms between fibre and the polymerising MMA. The resulting composite, bonded with poly (methyl methacrylate) was significantly stronger than a control material made from unmodified fibre bonded with the same matrix resin (Table 7).
Property enhancement of plant fibres 171
Table 7-
Modulus of rupture of wood fibre - poly (methyl methacrylate) composite
Control (non modified fibre) Fibre modified with glycidyl methacrylate
MOR (dry) (GPa) 25.9 39.6
The potential for further development of plant fibre based composites is high. Technologically it seems that it may well be feasible to develop a new generation of high performances composites based on plant fibres,. Such development is most desireable. The fibres can be produced sustainably in an environmentally benign fashion. Processing of them requires much less energy input than does synthetic fibre. For example, it is calculated that switching from glass to plant fibre for composite production in Western Europe might lead to an energy saving equivalent to Y4 - Y2Il1 tonnes of coal per annum (17). To enable such technological development to occur, research is needed in the following areas: i)
Effective fibre length increase of plant fibre for use in composites
ii)
Reduction in moisture sensitivity of plant fibre, especially in relation to dimensional properties.
iii)
Development of processes allowing stress relaxation to occur in fibre/particle during composite foming.
iv)
Enhancement of matrix - fibre bonding to reduce the likelihood of adhesive bond failure by a preferential wetting process.
References 1)
Evans,1. 1990, Proc. 19th IUFRO World Congress, Montreal, 1, 165-180.
2)
Mark R.E. 1967, Cell Wall Mechanics of Tracheids Yale Univ, Press, New Haven & London.
3)
Saunders, KJ. 1988 Organic Polymer Chemistry (second edition). Chapman & Wall, London, New York.
4)
Askeland D.R. 1988. International, London
5)
Dinwoodie J.M. 1981 Timber, its nature and behaviour. Van Nastraud Reinhold, New York. London.
6)
Dinwoodie, J.M. 1994, Personal communication, Building Research Esv. Garston, Watford, U.K.
The Science and Engineering of Materials Van Nastraad
172 Physical and chemical processing of fibre and fibrous products
7)
Banks W.B. & J.M. Lawther 1994 Derivazation of wood in composites, in Cellulose Polymers ed. R.D. Gilbert Hanser, Munich, Vienna, New York.
8)
Eaton, R.A. & M.D.C. Hale 1993 Wood, decay, pests and protection Chapman & Hall, London.
9)
Rowell, R.M., Tillmann, A.M., Liu-Zhengtian, 1986. Wood Science & Tech. 20, 8395
10)
Youngquist, lA., Krzysik, A., Rowell, R.M. 1986. Wood Fiber Sci, ll, 90-98.
11)
Martins, V. Banks, W.B. 1991. Wood Protection 1,69-75.
12)
Tillman, A-M. 1988. Jnl. Wood Chern. ~, 235-259.
13)
Banks, W.B. Rozman Hj Din, Lawther lM. 1992 in Plackett o.v & E.A. Dunningham, FRI Bull 176, New Zealand Forest Research Inst, Ratorua, New Zealand.
14)
Kalnins, M.A. 1993, Wood Sci., li, 81-89
15)
Cardias, M.S., Hale, M.D. 1990 Roo. Ann. Cony. BWPDA, 48-56
16)
Rowell, R.M., Youngquist, lA., Imamura, Y. 1988. Woods Fiber Sci 20,266-271.
17)
Banks, W.B. 1994. University ofWales, Bangor, inaugural professoriallectur.
18)
Marsh, P. 1990 New Scientist 217, (9th June), 58-60.
19)
Glomb, J.W. and Mulligan D.O. 1994 in Concise Encyclopedia of Composite Materials ed. A. Kelly, Elsevier Science Ltd. Oxford.
17 Physicochemical aspects of fibre processing L Salmen and S Ljunggren - STFI, Box 5604, S-114 86 Stockholm, Sweden
INTRODUCTION The wood fibre has a complicated structure, evolved by nature to meet the various demands of life on earth. This structure, not yet fully discerned, influences both the physical and chemical behaviour of the wood. It will also greatly influence any chemical or mechanical processing to which the wood is subjected. In order to be able to utilise the fibre resources better and to target process conditions to the particular fibre source, it is important to gain deeper knowledge regarding the wood fibre structure itself and to identify the main factors influencing fibre processing. In general terms, fibre processing or rather the product quality obtained from a particular wood source depends on the fibre length distribution, i.e. the dimensions of the fibre of the particular raw material, whether as a variation between stands or as a variation in age, juvenile and mature wood. This kind of variability is to some extent utilised when slab wood is used to obtain good tearing resistance while core wood is used when the demand for tensile strength is higher. One can also foresee that a development whereby it would be possible to separate earlywood fibres from latewood fibres would mean a considerable improvement in quality for certain paper grades. This summary will concentrate, however, on the physicochemical aspects of the variability of the fibres, and does not further consider the variations in dimensions of the fibre source. The heterogeneous structure of the wood fibres has long been a research subject for wood scientists, but there is still uncertainty concerning their composition in detail. The lamellar structure with cellulose microfibrils at different angles is well established, but the organisation of the surrounding matrix material of lignin and hemicelluloses is still quite uncertain. Another factor of importance for the subsequent processing is the abundance of compression wood in trees. The structural difference between compression wood lignin and that of normal fibres influences its properties, a fact which is often overlooked. 173
174 Physical and chemical processing of fibre and fibrous products
It is not often recognised that wood is an "ionomer", i.e, that its polymers contain ionisable functional groups whos counterions will affect properties. In native wood, it is mainly the carboxylic acids of the xylan and the phenolic hydroxyls of the lignin that dissociate with increasing alkalinity. These three aspects of the nature of the wood fibre material, the distribution of the wood polymers in the fibre wall, 'the structural molecular differences of lignin in different parts, and the effect of ionasable groups in the wood polymers, are discussed in this paper. WOOD FIBRE MORPHOLOGY The structural arrangement of the wood polymers within the fibre wall is extremely complicated. Although the spatial arrangement of the cellulose microfibrils in different lamellae is fairly well established, the structure of the cellulose crystals is still a matter for debate. The possible conversion of the cellulose crystalline forms from 10. to Ip during processing as recently indicated (1) may certainly have an influence on fibre properties, but will not be further dealt with here. Knowledge is less precise as to how the matrix materials, the lignin and the hemicelluloses are intermixed and distributed through the cell wall. The question also arises as to what extent these two components are covalently bonded to each other. If this is the case, dissolution of lignin should be affected. Physical properties such as softening and swelling may still be unaffected, as these properties depend on the sizes of the domains of the individual components, which may be sufficiently large for them to act separately. These aspects are dealt with below. Wood polymer distribution The composition of the wood polymers has been shown to vary somewhat between the 51, 52 and 53-layers, but the distribution within the layers at the cell wall level is in general considered to be rather homogeneous. However, microscopic observations point to the occurrence of concentric layers within the 82 wall (2, 3)indicating a variation in structure and/or component distribution. Studies by Daniel and Nilsson using biological decay organisms have also shown the development of pronounced concentric slits within the S2 layer, indicating weak regions with a non-homogeneous distribution of the wood polymers (4, 5), see Figure 1. Takabe et al. also found a heterogeneous distribution of the polysaccharides in the secondary wall and they concluded from deposition studies that the deposition process was different for cellulose and hemicelluloses(6). The existence of such regions could mean that a specific attack could lead to good flexibility properties in the fibres without the removal of all the lignin. Transmission electron microscope studies of wood treated with lignin-degmding fungus indicate on the other hand that there is a close association of hemicelluloses and lignin down to the microfibrillar level (7). Considering the mechanism of biogenesis, Terashima postulates a close association between hemicelluloses and lignin in the space of 3 to 4 nm between microfibrils (8). It is also probable that during the formation of the cellulose microfibrils, hemicelluloses must be deposited at the same time acting as spacers to hold the microfibrils apart. Analysis of hemicelluloses in the fibre walls also suggests that both xylan and glucomannan are distributed evenly throughout the cell wall in proportion to the cellulose content (9). This close association between hemicelluloses and cellulose has led to the suggestion that some of the hemicelluloses act as coupling agents between cellulose and lignin (10). It is also fairly clear that some of the hemicelluloses are oriented parallel to the cellulose microfibrils (11, 12). This strict
Physicochemical aspects of fibre processing
175
Figure 1. Schematic picture of the presence ofconcentric inhomogeneous layers as viewed by light microscopy, after Daniel and Nilsson (4, 5). organisation is plausible considering the sequential organisation of oriented carbohydrates in the primary wall which has been established by cell culture studies (13).
With an assumption that the gaps between microfibrils contain similar amounts of lignin and hemicelluloses, only about 4 to 7 lignin chains would fit into the available space. As the domain size generally required for polymers to act separately mechanically is of the order of 50 to 150 A (14, 15), it is plausible to expect the lignin and hemicelluloses to act as a homogeneous matrix material within the space between microfibrils. NMR- measurements showing the similarity of relaxation constants for the polymers also suggest an intimate mixing of the major hemicellulose component and the lignin in both hardwood and softwood species (16). On the other hand, mechanical softening measurements show no evidence of such an intimate mixing, although detection of a pure hemicellulose transition is rare. Kelley et a1. have for moist wood detected transitions that they attribute to the separate transitions of hemicelluloses and lignin (17). By selective extraction of the wood polymers from high yield pulp fibres it has also been concluded that on the dry papers there are separate transitions for hemicelluloses, lignin and amorphous cellulose (18), see Figure 2. From DSC measurements, on the other hand, transitions for lignin and hemicelluloses, have only been detected for the isolated components whereas for wood only the lignin transition is detectable (19, 20). From dissolution studies on pulps, it has been shown that the lignin diffusing out of the fibre wall has a molecular weight corresponding to a spherical diameter of 3.5 to 6.0 nm for CTMP (21) and of about 10 nm for unbleached kraft (22). This suggests that at least the lignin component may exist in large enough regions to exhibit a mechanically separate behaviour while the hemicelluloses are perhaps too closely associated with the cellulose (23) as the schematic picture in Figure 3 indicates.
176 Physical and chemical processing of fibre and fibrous products
175 ..........
0
205 0
I
230°C
, ' ..................... ,
.....................
delignified o
"'lo
, 1':>.
'- <,
'
...............' \
... ......
hemiextracted', \
~100
200 temperature
o I
C
Figure 2. The identification of separate transitions for hemicellulose at 1750C,for lignin at 2050C and for amorphous cellulose at 23()OC in the elastic modulus temperature curves for extracted papers (18)
Cellulose
Cellulose Hem;t:ellutos~·····.,····• • •-
Lignin ?
Figure 3. Schematic picture ofthe organisation ofthe cell wall components in the secondary wall ofwood fibres.
Physicochemical aspects of fibre processing
177
For the mechanical properties of the cell wall, this question of compatibility is of prime importance since the elasticity is to some extent governed by the stiffest component. If the components are miscible, the stiffness will be very drastically reduced at the plasticized softening temperature, otherwis a more gradual softening will occurr separately for each of the components. In mechanical pulping, a vital question is whether the hemicellulose is a component of importance for the softening and defibration properties of the wood, a question which ought to be studied further.
Existence of lignin-carbohydrate complexes The question of whether or not there are covalent bonds between lignin and hemicelluloses, LCC, has been investigated for some time. It is clear that such bonds may be formed in the process of pulping (24, 25, 26, 27) but also that they' do exist natively to some degree (28, 29). Presumably the frequency of these bonds is so low that no mixing on the molecular level is to be expected, merely that domains of the two polymers are connected to each other. The association is also demonstrated in the fact that the leaching of hemicelluloses and lignin is always simultaneous (30, 31). The consequences for pulping of the existence of LCC in the fibre wall may be a slower degradation and dissolution of lignin and less extensive delignification. This may result in a lower selectivity of the process. The presence of LCC, whether native or formed during the process, naturally also affects the efficiency of bleaching of the pulp in a negative way, and the prevention of the formation of such bonds would probably be a major advancement in bleaching technology. Fibre wall layers The composition of the outer fibre wall layers, i.e. the primary wall, and the middle lamella differ significantly from that of the rest of the fibre wall. The primary wall has a high content (up to 15%) of protein (32) and contains pectic substances. The protein is indicated to be highly associated with the lignin in the primary wall (33, 34), to such an extent that these polymers form a mechanically homogeneous mixture. A result is that the softening temperature of the lignin in the primary wall is substantially lower than that of other fibre wall layers, as the protein functions as a softener (33, 36). Mild chemical attacks on the primary wall seem also to be especially advantageous in promoting fibre separation and thus enhancing mechanical pulping (33, 37, 38). For the middle lamella, the most significant difference may be that its lignin is more condensed or cross-linked and probably has a higher molecular weight than the lignin in the other fibre walls (39). The middle lamella should thus have a slightly higher softening temperature than the other fibre walls. For chemical pulping, the secondary wall lignin is easier to degrade chemically and thus to dissolve than the middle lamella lignin (40). The structural differences of lignin, e.g. more reactive phenolic groups in the secondary wall and less cross-linking have substantial effects upon the course of delignification (41, 42). Furthermore, secondary wall lignin seems to contain much more cleavable bonds of the dominating 13-0-4 linkages between lignin units (43). This means that the delignification preferably occurs initially from the secondary wall lignin. However, it is still not known how the different cooking chemicals affect the kinetic course of delignification from the various fibre wall layers.
178 Physical and chemical processing of fibre and fibrous products
COMPRESSION WOOD LIGNIN STRUCTURE Compression wood is considerably more abundant than is generally realised. For Scandinavian spruce the content of compression wood is about 19 to 30% (44) and for pine 8 to 45 % (45). This is also true for normal straight trees as a deflection of only a few degrees causes the formation of compression wood (46). Since the top of the tree is more exposed to wind it generally contains a larger portion of compression wood. Compression wood contains more lignin and a lignin that is more cross-linked than the normal type of lignin (47). Consequently the content of cellulose is lower. Also the angle of the microfibrils is considerably higher in compression wood than in normal wood even in conditions where the typical morphological features of cell wall cavities in compression wood have not developed. The larger amount of cross-linking in the compression wood lignin is due to a much higher percentage of p-hydroxyphenyl units (up to 70%) than in normal softwood guaiacyl lignin units (48). Recently it has been shown that oxidatively coupled pcoumaryl alcohol units occurring in compression wood are probably precursors for the formation of chlorinated dibenzodioxins and dibenzofurans during the chlorine bleaching of pulp (49). Negligible amounts were obtained from the methoxylsubstituted coniferyl alcohol units present in guaiacyllignin in softwood. Compression wood gives pulp of substantially lower yield and quality. However, comparing the delignification kinetics with that of normal wood no difference is found, only that more chemicals are needed to reach the same kappa number due to the higher content of lignin in compression wood (50).
90 0 0
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,...
'-""
80
c.
E CI) .., m
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'I-
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60 +---.--.-.......---......--r--...---r-~-..-~......----r--~-1 100 120 140 160 180 200 60 80
methoxyl group content, mol% Figure 4. The softening temperature ofwood, determined by mechanical spectroscopy at 1 Hz, as a function ofthe methoxyl content ofthe lignin phenylpropane units ofthe lignin (51).
Physicochemical aspects of fibre processing
179
In terms of quality, it is however noticeable that the viscosity is significantly lower for this pulp than for pulp of normal wood. The more cross-linked nature of compression wood also means that it has a higher softening temperature, as this is directly related to the content of methoxyl groups (51), Figure 4. Mechanical pulping properties are thus adversely affected by the content of compression wood (52).
INFLUENCE OF IONISABLE GROUPS The fact that the wood polymers contain ionisable groups, mainly carboxylic acid groups in the xylan and phenolic hydroxyl groups in the lignin, makes their properties especially sensitive to the pH of the surroundings, as these groups may dissociate (53). Also, the type of metallic counterion to these ionisable groups has an influence on the properties. Native softwood contains about 100 uekv/g of carboxylic acid groups connected mainly to the xylan (54). The dissociation of these carboxylic acid groups leads to a greater swelling of the wood, and this gives the fibre a higher flexibility and mechanical pulps with improved tensile properties (55). The dissociation of the carboxylic acid groups in the xylan does not however affect the softening properties of the wood. This again indicates that the softening of the wood is purely associated with the softening of the lignin, and thus that the association between the lignin and the xylan is not so intimate that the polymers are intermixed on a molecular level, i.e. mechanically they behave as separate components. If ionisable groups on the other hand are introduced into the lignin by sulphonation or peroxide bleaching (introducing carboxylic acidgroups) the softening of the wood, i.e, of the lignin, becomes highly dependent on the dissociation as well as on the type of counterion present. Chemimechanical pulping for example at a normal pH of 9 to 6 is highly influenced by the type of counterion present in the system. In sulphonated wood material with a lower pH of about 4, the lignin is highly softened due to the dissociated sulphonic acid groups, and this gives good fibre separation properties. The carboxylic acid groups on the other hand remain undissociated, so that the hemicelluloses are stiff, which is probably the reason for the good fibrillation occurring in refining rendering the pulp good optical properties. The dissociation of phenolic hydroxyl groups only occurs at pH-values above 10 so that generally only conditions during alkaline chemical pulping are affected. However for chemical pulps also, especially bleached pulps, the dissociation of the carboxylic acid groups is important for the swelling of the fibre. In general, for good swelling it is favourable to have a low concentration of electrolytes to avoid "shielding effects" of the counterions and thus collapse of the fibre (30). Donnan equilibria also play an initial role in the delignification processes in pulping and in bleaching. It is important for impregnation (diffusion) of the cooking chemicals and for dissolution of lignin fragments out of the fibre wall. The ion-distribution and the rate of delignification are affected by the presence of a Donnan-like gel system in the fibre wall. The pH-value in the internal region of the pulp/water system can be up to four units lower than the external pH (56). Also, large differences in the distributions of the anions of the added reactant (X-) inside and outside the fibre wall can be observed. Thus equilibrium in wood-alkali interactions is important when determining the real alkali (and sulphide) consumption during kraft pulping, which has been reported to differ by as much as 58%, due to ionic dissociation equilibrium and the Donnan equilibrium (57, 58). If the pKa-values of the COOH and OH groups of the polysaccharides and lignin are known, together with the charged and actual alkali concentra-
180
Physical and chemical processing of fibre and fibrous products
tions of the outer solution, the Donnan equation can be utilised to calculate the hydroxyl ion concentration of the inner solution. The delignification process ought consequently to be controlled by this lower alkalinity of the inner solution in the fibre wall. An increase in the electrolytic content, i.e. addition of sodium salt to the system reduces, however, the Donnan equilibrium. At a high concentration of electrolyte (1-2 mol/kg H20), the alkali concentration of the inner solution approaches that of the outer solution. As already mentioned, raising the electtolyte concentration results in principle in a shielding of the repelling ionised groups that lead to a decrease in fibre swelling. This affects lignin dissolution negatively, i.e. it lowers the dissolution. A suitable adjustment of the electrolyte balance is thus necessary to achieve an optimal dissolution from the pulp.
REFERENCES 1. Lennholm, H. (1994) Investigations of cellulose polymorphors by 13C-CP/MASNMR spectroscopy and chemometrics. Ph. D. dissertation KTH, Stockholm. 2. Bailey, I. W., Kerr, T. (1935) J. Arnold Arboretum 16, 140. 3. Bailey, W. (1938) Industrial and Engineering chemistry 39,40. 4. Daniel, G., Nilsson, T. (1985) Studies on Wood Fiber Using Biological Decay Organisms, Int. Symp. Wood & Pulping Chern. (Vancouver) Tech. Papers Vancouver, p. 173. 5. Daniel, G., Nilsson, T. (1984) The Swedish University of Agricultural Sciences, Department of Forest Products, Studies on the S2 layer of Pinus silvestris . 6. Takabe, K., Fukazawa, K., Harada, H. in Plant cell wall polymers N. G. Lewis, M. G. Paice, Eds. (American Chemical Society, Washington DC, 1989), vol. 399, p.47. 7. Ruel, K., Bamoud, F., Eriksson, K.-E. (1984) Holtforschung 38,61 . 8. Terashima, N., Fukushima, K., He, L.-F., Takabe, K. (1973) in Forage cell wall structure and digestibility) ASA-CSSA-SSSA, Madison, WI, 1993) p. 247. 9. Hardell, H.-L., Westermark, U. The carbohydrate composition of the outer cell walls of spruce fibers., International Symposium on Wood and Pulping Chemistry. Stockholm, 1981, vol. 1, p. 32. 10. Page, D. H. (1976) Wood and Fiber 7,246. 11. Albersheim, P. (1975) Sci. Am. 232, 81. 12. Liang, C. Y., Bassett, K. H., McGinnes, E. A., Marchessault, R. H. (1960) Tappi 43, 1017 . 13. Keegstra, K., Talmadge, K. W. Bauer, W. D., Albersheim, P. (1973) Plant Physiol 51,188. 14. Kaplan, D. S. (1976) J. Applied Polymer Science 20, 2615. 15. Schick, C., Donth, E. (1981) Physica Scripta 43, 423. 16. Newman, R. H. (1992) Holzforschung 46, 205. 17. Kelley, S. S., Rials, T.G., Glasser, W.G. (1987) J. Mater. Sci. 22,617. 18. Salmen, N. L. (1979) Trans. Tech. Sect. (Can. Pulp Pap. Assoc.) 5, 45. 19. Irvine, G. M. (1984) Tappi J. 67,118. 20. Ostberg, G., Salmen, L., Terlecki, J. (1990) Holzforschung 44, 223. 21. Willis, J. M., Yean, W. Q., Goring, D. A. I. (1987) J. Wood Chem. Technol. 7, 259. 22. Favis, B. D., Yean, W. Q., Goring, D. A. I. (1984) J. Wood Chem. Technol. 4, 313 . 23. Atalla, R. H., Hackney, J. M., Uhlin, I., Thompson, N. S. (1993) Int. J. Bioi. Macromol. IS, 109. 24. Gierer, J. W., Wannstrom, S. (1986) Hotzjorschung 40, 347. 25. Ohara, S., Hosoya, S., Nakano, J. (1980) Mokuzai Gakkaishi 26. 26. Iversen, T., Wannstrom, S. (1986) Holzforschung 40, 19.
Physicochemical aspects of fibre processing
181
27. Tanaka, K., Nakatsubo, F. (1979) Mokuzai Gakkaishi 25, 653. 28. Leary, G. J., Sawtell, D. A., Wong, H. (1983) Hoizforschung 37,11. 29. Katayama, Y., Morohoshi, N. (1980) Mokuzai Gakkaishi 26, 414. 30. Lindstrom, T., Ljunggren, S., de Ruvo, A., Soremark, C. (1978) Svensk Papperstidn. 81, 397. 31. Willis, J. M., Delafield, C., Goring, D.A.I. (1986) Pulp Pap. Canada 86, TIOI. 32. Westennark, U., Hardell, H.-L., Iversen, T. (1986) Holzforschung 40, 65. 33. Salmen, L., Pettersson, B. (1995) Cellulose Chem. Technol. Accepted for publication. 34. Lamport, D. T. A., Catt, J. W. (1981) Encycl Plant Physiol. 138, 133. 35. Gellerstedt, G., Lindfors, E.-L. (1984) Holzforschung 38, 151. 36. Ostberg, G., Salmen, L. (1988) Nordic Pulp Paper Res. J. 3, 8. . 37. Westennark, U., Samuelsson, B., Simonson, R., Pihl, R. (1987) Nordic Pulp Pap. Res. J. 2, 146. 38. Axelson, P., Simonson, R. (1982) Svensk Papperstidn. 85, R132. 39. Sorvari, J., Sjostrom, E., Klemola, A., Laine, J. E. (1986) Wood Sci. Technol. 20, 35. 40. Whiting, P., Goring, D. A. I. (1981) J. Wood Chem. Technol. 1, 111. 41. Westennark, V., Samuelsson, B. (1986) Holzforschung 40, 139. 42. Berry, R. M., Bolker, H. I. (1986) J. Pulp Pap. Science 12, J16. 43. Lange, H., Wagner, J. F., Kaler, E. W., McCarthy, J. L. Computer modelling: The structure of gymnosperm lignin and the delignification of hemlock wood, 1989 International Symposium on Wood and Pulping Chemistry (Tappi, Raleigh, NC, 1989), p. 577. 44. Young, W. D., Laidlaw, R. A., Packman, D. F. (1970) Holzforschung 24, 86-98. 45. Low, A.J. (1964) Forestry 37, 179-201. 46. Timell, T. E. Recent progress in chemistry, ultrastructure and formation of compression wood., International Symposium on WQOd and Pulping Chemistry Stockholm, 1981), vol. 1, p. 99. 47. Timell, T. E. (1982)Compression Wood in Gymnosperms Springer Verlag, N.Y. Vol. 1, 359. 48. Nimz, H. H., Robert, D., Faix, 0., Nemr, M. (1981) Holzforschung 35,16. 49. Hrutfiord, B., Negri, A. R. (1992) Chemosphere 25, 53. 50. Kask, T. (1993) MSc Diploma work, Royal Institute of Technology, KnI, Stockholm. 51. Olsson, A.-M., Salmen, L. in Cellulosics: Chemical, biochemcal and material aspects J. F. Kennedy, G. O. Phillips, P. A. Williams, Eds. (Ellis Horwood Ltd, Chichester, 1993) p. 255. 52. Pillow, M. Y., Schaefer, E. R. (1936) J. C. Pew, Paper Trade Journal, 220. 53. Lindstrom, T. (1992) Nordic Pulp Pap. Res. J. 4, 181. 54. Sjostrom, E., Janson, J., Haglund, P., Enstrom, B. (1965) J. Polym. Sci 5, 221. 55. Htun, M., Salmen, L., Eriksson, L. in Energy efficiency in process technology P. A. Pilavachi, Eds. (Elsevier Appl. Sci., London, 1993) p. 1086. 56. Haglind, I. A. K., Kringstad, K. P., Almin, K. A. Donnan equilibria in pulping and bleaching; some considerations, International Symposium on Wood and Pulping Chemistry (Tappi, Raleigh, NC, 1989), p. 635. 57. Pu, Q., Sarkanen, K. (1991) J. Wood Chem, Technol. 11, 1. 58. Pu, Q., Gustafson, R., Sarkanen, K. (1993) J. Wood Chem. Technol. 13, 1.
18 The effect of acetic anhydride treatments on the mechanical properties, hydrophobicity, and dimensional stability of Russian Fifths and Scandinavian pine M J Ramsden, F S R Blake and N J Fey - Department of Chemistry, University of York, Heslington, York YOl 5DD, UK
1 ABSTRACT Strips and blocks of Russian Fifths and Scandanavian Pine were acetylated over different periods of time. These, along with control samples, were tested for their tensile modulus, hydrophobicity and dimensional stability. The modulus of elasticity (tensile modulus) for each sample was derived using a statistical approach and was calculated from the extension/force graphs, the samples' dimensions and the parameters of the material testing machine. The observations in this work suggest the acetylation process significantly reduces the tensile modulus of the woods compared to their untreated state in an irreversible manner, and that the extent of the deterioration in tensile modulus is a function of the acetylation conditions. Acetylation improved significantly the hydrophobicity and the dimensional stability of the woods. It appears therefore that acetylation using acetic anhydride in xylene has an optimum set of reaction conditions that compromise between the gains in water repellence and dimensional stability with the deterioration in mechanical properties.
2 INTRODUCTION It is known that wood can be acetylated by reacting the hydroxyl groups on holocellulose, hemicellulose and lignin with acetic anhydride. This forms ester bonds between the acetic anhydride and the hydroxyl groups in the cell walls of the wood
183
184 Physical and chemical processing of fibre and fibrous products
and the intercellular regions, creating stable acetate groups which are resistant to hydrolytic attack (1). Measurements of the long term stability of acetylated wood have been carried out and have found that under accelerated environmental conditions the wood retains its stability and has enhanced protection against environmental degradation (2). Much of this work was done on softwoods. These are used extensively in the construction industry where wood's cost-effective mechanical attributes are exploited, and where treatments such as acetylation may further enhance wood's merits by improving the resistance to changes caused by the presence of water. The effect of the removal of water from the structure on the mechanical properties has been measured before (3) and this work examines the effect of the replacement of the water in the wood structure with acetate groups. Measurements of the longitudinal tensile modulus (referred to hereafter simply as tensile modulus), a measure of the wettability and swelling of Russian Fifths pine and Scandinavian pine were made. Roll angle testing was investigated to see whether surface hydrophobicity could be measured indirectly. 3 EXPERIMENTAL WOOD SPECIMENS: Lengths of Scandinavian pine and Russian Fifths 2.4 m x 50 mm x 25 mm were obtained from builders' merchants. Samples were taken from a single piece of wood that was cut into strips between 1.0 mm and 1.5 mm thick. Templated shapes in the form of dumbbells (to create probable fracture points between, rather than inside, the jaws of the testing machine) with standard lengths of 40 mm to 110 mm were cut from the knot-free sections of these strips and then dried prior to treatment and mechanical testing. Between 14 and 20 of these strips were processed in the same acetylation reaction mixture to assess the change in tensile modulus under those acetylation conditions. Blocks (-20 mm x -45 mrn x -25 mrn) were prepared from a single piece of wood. The blocks were dried in an oven at 378 K for 12 h. This reportedly gives a moisture content between 2 % and 5 % which is the optimum level required for the best reaction conditions; if the water content is above 5 % the water hydrolyses the acetic anhydride to form acetic acid (1). The rate of acetylation is also decreased as the moisture content of the samples increases (4). ACETYLATION OF WOOD: The acetylation technique was based on that reponed by Youngquist (5). The blocks and strips were held submerged in 500 ml of 50 % (v/v) acetic anhydride (SLR, Aldrich) in xylene (OPC, Aldrich). The solution, under a nitrogen purge, was brought to reflux at 418 K for periods ranging from 0.5 h to 4.0 h. After a controlled period of cooling, the samples were removed and vacuum dried at 30 mm Hg and room temperature for 1 h, then dried in an oven for 12 h at 378 K. Control samples were air dried or treated only with 500 ml xylene. TENSILE MODULUS The control and treated strips of knot-free wood were mounted individually between the jaws of a material testing machine (Instron 1122). The lower jaw was fixed, and a load was applied by moving the upper jaw (mounted on a crosshead) at a rate of 0.5 mm min-to A load cell measured the force being applied. The tensile modulus of the sample was calculated from the resulting chart of force versus extension, accurate dimensions of each sample (measured to ±O.05 mm using a micrometer) and the chart speed. The deformation in the testing machine, a significant: factor when testing materials such as wood, was taken into account.
Acetic anhydride treatments
185
WETTABILITY ANALYSIS: Two tests were used to measure the wettability of the wood surfaces: the drop test and the measurement of the roll angle. THE DROP TEST: A 15 Jll droplet of aqueous propan-2-o1 (IPA) (SLR, Aldrich) solution was dropped on the end grain of treated and untreated blocks. A range of 0 to 100 % aqueous IPA solutions was used. ROLL ANGLE: A 20 Jll droplet of 20 % IPA _was dropped at one end of the longitudinal surface of treated and untreated blocks. The end was elevated at intervals of 5 creating an angle between the horizon and the edge of the block, referred to as the "roll angle". Samples with high hydrophobicity caused the drop to have a high contact angle and the drop would therefore roll at lower angle of inclination than less hydrophobic surfaces. 0
DIMENSIONAL STABILITY: Treated and untreated blocks were weighed then immersed in 5 dm 3 of distilled water for 24 h. When the blocks were withdrawn, surface water was removed and the blocks re-weighed. The dimensions of the blocks before and after immersion were also measured with a micrometer. The heterogeneity of wood poses problems for all those involved in the field, and this work has used a statistical approach based on multiple replication to investigate the effects of acetylation. Where ranges are quoted in this paper, they refer to the standard error of the means. 4 RESULTS AND DISCUSSION TENSILE MODULUS: Determination of tensile modulus before and after acetylation was used to assess the change in the mechanical properties of wood. By combining results obtained for each strip (Figure 1) it was possible to calculate the modulus of elasticity for each treatment process and compare treated with untreated. These values (shown in Table 1) ill ustrate that a modification has taken place. Moduli for both Scandinavian and Russian Fifths treated samples were higher than those observed for dried untreated control samples. It was found that strips of less than -1.0 mm thickness gave inconsistent and irreproducible results. This was attributed to the cellular structure of pine. In softwoods, the two types of cells are the tracheids and the parenchyma. The tracheids run vertically through the wood to transport mineral solutions and are 2 mm to 4 mm in length with an aspect ratio of about 100: 1. The parenchyma are much smaller and act as food stores; they are aligned horizontally and measure about 200 urn x 30 urn, The samples which were less than 1 mm thick would have contained only about 20 to 30 cells at most and would therefore be expected to be more susceptible to variation than thicker samples. The results show that acetylation for up to 1 h produced a significant increase in the tensile modulus of the wood samples compared to the air dried samples. However, the tensile modulus then apparently falls as the duration of the acetylation increases. Compared to the untreated woods, there was a significant reduction in the tensile modulus at all levels of treatment.
186 Physical and chemical processing of fibre and fibrous products
Type of wood
Treatment Reaction Acetic anhydride Roll angle Wettability (% IPA) time (h) concentration (
0
)
(M)
Tensile modulus (OPa) ± s.e.
± 2.7
55
10
4.9
Pine: RF Xylene only
4.0
0.0
55
10
7.8 ±0.8
Pine: RF Acetylated
0.5
5.3
45
10
8.6± 1.1
Pine: RF Acetylated
1.0
5.3
45
10
10.7 ± 1.3
Pine: RF Acetylated
2.0
5.3
40
20
8.5 ± 1.5
5.3
40
20
Pine: RF Air dried
8.4
± 1.7
Pine: RF Acetylated
4.0
Pine: Sc
Untreated
0.0
15.1 ± 1.4
Pine: Sc
Air dried
0.0
7.0 ± 1.0
Pine Sc
Xylene only
4.0
0.0
Pine: Sc
Acetylated
0.5
5.3
Pine: Sc
Acetylated
4.0
5.3
10 30
Table 1. Results from samples acetylated in xylene at 418 K. (RF Sc = Scandinavian pine).
± 1.5 12.6 ± 1.2 7.9 ± 0.7
10.0
= Russian Fifths;
4.0E-6
en
>
(1.)
~
~ 0
c.....
e
~
(5 c::
0 0: .;;;
c.....
0
c Q)
~.....
2.0E-6
C
~
><
t.tJ
•
3.0E-6
1.0E-6
•
• ~f: ~. .~.~
..
.~~
..
0
O.OE+O - t - - - - + - - - - + - - - - + - - - - - + - - - - - t 4,000 8,000 12,000 16,000 20,000 24,000 Ratio Of X-Sectional Area To Original Length (m)
Figure 1: Results for strips treated with acetic anhydride in xylene for 2 h at 378 K.
The correlation of moisture content of a wood and its tensile strength has been noted elsewhere (6). At moisture contents below about 30 % (wt) the tensile modulus increases linearly. This has been attributed to the removal of hydrogen-bonded water
Acetic anhydride treatments
187
which allows the intercellular distance to fall (accompanied by the shrinkage of the wood); as the distance between the cell walls falls, intercellular hydrogen bonding can take place which is assumed to result in an increase the tensile modulus. Reducing the moisture content of wood from 30 % to 5 % has been shown to increase the tensile modulus of softwoods by about 20 % (5). As the water content of the samples of acetylated woods that were tested in this work was small, any subsequent uptake of ambient moisture may reduce the tensile modulus still further.
Scandinavian pine
,-.16 ~
Russian Fifths .....---t--------------r~~------------
-+--:::1::--------.....----- . . ------==--~~-----8 -+----="--o----::l::---~--~-- -+---........----------0--
2,12 ~
~
"8
E
~ 4 c::
~
-+---.....------------ . . - -------------
o -+---1---+---+---+---+---+----1 +---+---+---+---+---+---i~-t
Figure 2: Comparison of tensile moduli of treated Russian Fifths and Scandinavian pine (* = approximate range of literature values for softwoods at -10% moisture content (Reference 1, page 57)).
The tensile modulus of the air dried samples used in this work were measured to be lower than the untreated wood. No explanation of this observation is available at present. CHANGES DURING ACETYLATION: Figure 3 shows the weight change during acetylation. The increase in wood volume during the acetylation process is equal to the volume of chemical added (Reference 7) and hence the weight gain is an indication of the degree of acetylation. The acetylated samples were very slightly darker than the original wood, and the darkening was more noticeable with the longer acetylation times. The acetylating solutions and xylene also became slightly yellow. This was attributed to the dissolution of organic material from the wood. DIMENSIONAL STABILITY: A change in the dimensional stability of Russian Fifths and Scandinavian pine is observable when treated samples of both pines are compared with untreated samples (Figures 4, 5). Under the acetylation process the wood volume increased to close to its original value as the hydroxyl sites became acetylated. Hence when immersed in water, the additional swelling due to the uptake
188 Physical and chemical processing of fibre and fibrous products
of water was minimal. This is consistent with other workers' observations (Reference 8). Thus the reduction in the availability of si tes for hydrogen bonding leads to an increase in the dimensional stability of acetylated woods.
c:
40
40
.2
"0
~
>.. ~eu
30
s:: 20 .t:
-:0 ~
~
10
~
~
~
35
~
;j
be)
.n eu (l)
~
'C'U
37.5
I./)
be)
s::
~0
0
[J
32.5 30
[]
27.5
0
2
3
4
2
0
3
4
Acetylation Time(h)
Acetylation Timc(h)
Figure 3. Mass gained by Russian Fifths samples during acetylation.
Figure 4. Uptake of water as a function of time of acetylation of Russian Fifths.
WETTABILITY: The two tests to measure the wettability of wood surfaces showed that the measurement of the roll angle is a more sensitive technique than the drop test. The drop test showed little variation with the duration of the acetylation (Table 1), whereas the roll angle appears to correlate with the mass gained during the acetylation as indicated by the comparison of Figure 3 with Figure 6.
Duration Of Acetylation At 418 K (h)
[] Scandinavian pine • Russian Fifths
Figure 5. Effect of acetylation on dimensional stability of treated wood.
Acetic anhydride treatments
189
OPTIMAL ACETYLATION CONDITIONS: The weight gain during acetylation (Figure 3), the uptake of water after treatment (Figure 4), the volume change on immersion in water (Figure 5) and the roll angle on the longi tudinal surface (Figure 6) show that the changes are rapid initially, and then slow down, consistent with standard chemical reaction kinetic behaviour. This would be consistent with a mechanism in which most of the available hydroxyl groups were acetylated within two hours. Prolonging the treatment beyond this period provides only marginal improvements in water resistance and dimensional stability. The changes in the mechanical properties during this period indicate that there is an initial 2-hour period when the tensile modulus increases from its dried state. This is then followed by a slow deterioration. The wood also becomes rnore discoloured.
60 55 -..<:,)
eo c
50
«
'0 45
0
x
40
0
35 0
2
3
4
5
Acetylation Time (h)
Figure 6. Correlation of roll angle of samples of Russian Fifths with treatment time.
5 CONCLUSI()NS The roll angle and water weight gain during swelling tests indicate an improvement in the water repellence properties of both woods. This agrees with the findings of earlier workers that the weight gain due to acetylation is sufficiently high to be near the saturation point of the wood and hence excess water is unable to form hydrogen bonds successfully with the cell wall. However, the observations in this work suggest the acetylation process significantly reduces the tensile modulus of the woods in an irreversible manner, and that the extent of the deterioration in tensile modulus is a function of the acetylation conditions. It appears therefore that acetylation using acetic anhydride in xylene has an optimum set of reaction conditions that compromise between the gains in water repellence and dimensional stability with the deterioration in mechanical properties.
190 Physical and chemical processing of fibre and fibrous products
REFERENCES 1
Rowell, R. M.: Distribution of acetyl groups in southern pine reacted with acetic anhydride. Wood Sci. 1982. (15): 172-182
2
Rowell, R. M.; Lichtenberg, R. S.; Larson, P.: Stability of acetylated wood to environmental changes. Wood Fiber Sci. 1993. (25) 4:359-364
3
Gerhards, C C; Effect of moisture content and temperature on the mechanical properties of wood. Wood and Fiber. 1982 14 (1) 4-36
4
Tarkow, H.; Stamm, A. J.; Erickson, E. C. 0.: Acetylated wood. Forest Prod. Lab. Report No. 1593
5
Youngquist, J. A.; Krzysik, A.; Rowell, R. M.: Dimensional stability of acetylated aspen flakeboard. Wood and Fiber Sci. 1986. (18) 1:90-98
6
Dinwoodie, J M: "Wood: Nature's Cellular Polymeric Fibre-composite" 1989, Published by The Institute Of Metals, London
7
Rowell, R. M.; Gutzmer, D. 1.; Sachs, 1. B.; Kinney, R. E.: Effects of alkylene oxide treatments on dimensional stability of wood. Wood Sci. 1976. (9): 51-54
8
Rowell, R. M.; Ellis, W. D.: Determination of dimensional stabilization of wood using the water-soak method. Wood Fiber. 1978. (10): 104-111
19 Recovery of packaging laminate components to enhance waste management E T Evans,' M J Kay," N Kirkpatrick? and D S Wales' 'British Textile Technology Group, Didsbury, Manchester, M20 2RB, UK; 2Pira International, Leatherhead, Surrey, KT22 7RU, UK
Introduction
Packaging laminates are extremely versatile and are cost-effective in their use of raw materials. The properties offered by laminates include those of a barrier nature against moisture, oxygen, microorganisms and dust together with those properties related to the physical characteristics ofthe packaging such as support (stiffuess) and durability. In the EC draft Directive on packaging and packaging waste (92/C 263/01), the following hierarchy for management of packaging waste is indicated: prevention at source, re-use, recycling, incineration with energy recovery, incineration without energy recovery and finally disposal via landfill as a last resort. The draft Directive specifies that not later than 10 years after the Directive comes into force, 90% by weight of the packaging waste output is removed from the waste stream for the purpose of recovery and that 60% by weight of each material in the recovery target shall be removed from the waste stream for the purposes of recycling. Recycling can be classified as 'primary recycling' whereby materials are recycled into the same type of product or 'secondary recycling' whereby materials are recycled into lower grade (decreased value) products which do not resemble that form from which the raw materials came. Secondary fibre is a valuable raw material, representing some 37% of the fibre which is currently used to make paper and board products worldwide. In the ~ secondary fibre utilisation has even greater economic .significance, with 86% of the fibre which is used for packaging and board manufacture being derived from wastepaper. It is predicted that over the next 15-20 years secondary fibre usage will grow at twice the rate ofvirgin fibre and by the year 2001,41% of the world's fibre for paper and board manufacture will be derived from secondary fibre [1j. 191
192 Physical and chemical processing of fibre and fibrous products
Laminated structures which comprise paper and/or board complexed with aluminium foil have excellent barrier properties which has resulted in their widespread use as packaging materials. In this study, the recovery of cellulosic fibre and aluminium from this type oflaminate has been investigated.
Methods Re-pulping of cellulosic fraction. Oven dry laminate (60g) was tom into pieces (2cm2 ) and added to tap water (20 litres) to give a final consistency of 3% (w/v). The sample was pulped for 25 minutes in a SPEA disintegrator at ambient temperature. Fibre was recovered using a Sommetville screen system (screen slot size - 0.23mm). Assessment of fibre strength properties. Tensile strength properties of paper and board were determined according to BS 4415 [2]. Determination of the internal tearing resistance of paper was carried out to BS 4468 [3]. Bursting strength of paper and board was measured using BS 3137 [4]. Laboratory sheets were prepared for physical testing by the method specified in ISO 5269 [5] Assessment ofvisual characteristics.Optical properties of paper and board were determined according to BS 4432 [6,7]. Assessment of machine runnability properties. Determination of drain ability of pulp was carried out by the Schopper Reigler method [8]. Ash content of paper and board was measured using BS 3631 [9]. Chemical analysis of process waste water. The presence of soluble and insoluble carbohydrate was determined according to the test methods detailed in Roff and Scott, 1971 [10]. Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were determined according to standard test methods [11,12]. Clean-up of pulped composite laminate.Composite of a known amount from which cellulose fibre had been removed by pulping, was added to distilled water (60ml). Commercial enzyme (O.lg) was added and the sample incubated as specified in the results. The sample was harvested by filtration and ashed at 575°C for 4 hours. The percentage non-ashable residue was then calculated.
Results and Discussion
Recovery ofcellulosic fibre Table 1. Fibre and Contrary Recovery from a Cellulose/ Aluminium Foil Laminate.
Raw material Fibre Contraries Solubles
Weight (g) 558.0 443.5 100.7 13.8
% raw material 100 79.5 18.0 2.5
A high yield offibre was recovered (80%) following the repulping and screening
Recovery of packaging laminate components
193
operation (Table 1). Using parameters which considered burst index, tear index, breaking length and tensile index, the recovered fibre was found to compare favourably with the results for an unrefined and refined virgin eucalyptus pulp, an inexpensive fibre alternative to fibre derived from waste paper (Table 2). Table 2. Strength Properties for Fibre Recovered from a Cellulose/Aluminium Foil Laminate Strength property
Fibre recovered from laminate
Burst index (kPam2g- 1) Tear index (mNm2g- 1) Breaking length (km) Tensile index (Nmg- 1)
2.04 8.07 3.34 32.8
Eucalyptus hardwood pulp unrefined refined 1.2 2.1 4.2 5.2 2.5 4.0 39 26
Ash in recycled pulps is normally derived from inorganic fillers (chalk/china clay) and coatings which are added to the paper during manufacturing or converting. In the studies presented here it is considered that ash may also arise from aluminium metal impurities which were not recovered during the screening process. Relatively low ash values were recorded indicating the relative purity of the recovered fibre (Table 3). Data provided by the Schopper Reigler analyses support these results, with drainability for the recovered fibre being comparable with that recorded for the unrefined eucalyptus pulp.
Table 3. Paper Machine Runnability Properties. Sample
Fibre recovered from laminate
% ash
6.6 19.0
SR
o
Eucalyptus hardwood pulp unrefined 1.0 20.0
refined 1.0 30.0
Effluent analysis The results of preliminary studies to characterise the unrecovered material present in the process waste water which resulted following initiation of the screening process are presented in Table 4. Non-ashable material accounted for over 77% by weight of the suspended solids and the results of BOn and COD indicated that approximately 15% of the material in the process water was biodegradable. Evidence was noted for the presence of insoluble carbohydrate ('fines').
194 Physical and chemical processing of fibre and fibrous products
Table 4. Analysis of Effluent 0.080 0.062 lthiourea
BOD
43.2 331
+ <0.2 Recovery of aluminium After recovery of the cellulose fibre, the effects of temperature, incubation time and degree of mechanical agitation on the rate of enzymatic digestion of the contaminating cellulose component and adhesive at pH 4.5 were investigated using commercially available mesophilic cellulolytic enzymes (Table 5). Table 5. Percentage Non-Ashable Residue of Pulped Composite
,
, tationary Incubation Time (Hours)
% NonAshable Residue
0
44.0 44.0 45.6 49.9 52.1
I
3 6 24
% NonAshable Residue (Controls) 44.0 44.0 44.0 44.1 44.2
% NonAshable Residue 44.0 44.1 49.5 49.8 54.3
• -1 revsmm % NonAshable Residue (Controls) 44.0 44.0 44.0 44.0 44.1
, % NonAshable Residue 44.0 44.5 48.0 51.0 71.0
• -1 revsmm % NonAshable Residue (Controls) 44.0 44.0 44.0 44.0 44.2
From these results it can be seen that there was negligible difference in the percentage non-ashable residue after 24 hours between stationary flasks and shaking flasks (50 revs min-I) at 28°C in the presence ofa commercial cellulolytic enzyme, optimum pH 4.5. To date, the optimum incubation conditions achieved for 'clean-up' of the contraries fraction are 28°C, 100 revs min-I, pH 4.5 for 24 hours after which time 71% of the residue was non-ashable (aluminium fraction).
Conclusions The results demonstrate that the major components ofpackaging laminates constructed from aluminium foil laminated to board (usually with a printed paper outer) can be
Recovery of packaging laminate components
195
recovered using the process outlined in Fig. I.
Packaging Laminate
Pulping using Secondary Board · Conditions
Separation of Cellulose Fibres and Contraries
Contraries
Recovery of Fibre
Enzymatic 'Clean-up' of Contraries
EfIluent (suspended solids 0.03 0.08 g/IOOml)
Clean Aluminium
Aluminium with some Remaining Contamination
Effluent (not analysed)
Fig 1. Proposed recovery process/or cellulose/aluminium/oil containing packaging laminates. Fibre recovery from a cellulose/aluminium foil laminate could achieve a dual role by providing both an alternative source of secondary fibre and meet the environmental pressures to increase the level of recycling of packaging materials. The recovered fibre is of sufficient quality for re-use in either paper or board. The value of the recovered aluminium will vary depending on its purity, but is in the range £400 £600 per tonne. The economics of the process have yet to be finalised, but will include investigation of enzyme recycling for the 'clean-up' of the contaminated aluminium resulting from the pulping of composite containers, and further analysis of the two liquid effluent streams.
196 Physical and chemical processing of fibre and fibrous products
Acknowledgements This work was supported by the Department of Trade and Industry. Support from several industrial sponsors including Lawson Mardon Packaging and Fasson BV is gratefully acknowledged. References [1] [2]
[3] [4] [5]
[6]
[7]
[8] [9]
[10] [11]
[12]
Cathie, K Secondary fibre treatment. Pira Reviews of Pulp and Paper Technology. Pira International, Leatherhead, UK, (1994). Anon. Determination of the tensile properties of paper and board. Constant rate of loading method, BS 4415 : Part 1. The British Standards Institution, (1992). Anon. Determination of the internal tearing resistance of paper, BS 4468. The British Standards Institution, (1990). Anon. Determination ofbursting strength of paper and board, BS 3 137. The British Standards Institution, (1972 (1987». Anon. Pulps - preparation of laboratory sheets for physical testing. Conventional sheet former method, ISO 5269 : Part 1. International Organisationfor Standardization, (1979). Anon. Measurement of the diffuse blue reflectance factor (ISO brightness) of paper and board, BS 4432 : Part 2. The British Standards Institution, (1980). Anon. Determination of opacity (paper backing) of paper and board by the diffuse reflectance method, BS 4432 : Part 3. The British Standards Institution, (1990). Anon. Schopper-Reigler method, BS 6035 : Part 1. The British Standards Institution, (1988). Anon. Determination of ash of paper and board, BS 3631. The British Standards Institution, (1984 (1989». Roff W.J. and Scott, J.R Fibres, Films, Plastics and Rubbers Butterworths, London, (1979). Anon. 5 Day biochemical oxygen demand (BODs) with dissolved oxygen in waters, ammendments. Methods for the examination of waters and associated materials. Second edition. Her Majesty's Stationary Office, London, (1988). Anon. Chemical oxygen demand (dichromate value) of polluted and waste waters. Methods for the examination of waters and associated materials. Second edition. Her Majesty's Stationary Office, London, (1986).
20 CELSOL - Biotransformation of cellulose for fibre spinning M Vehvilainen," P Nousiainen,* H Struszczyk,** D Ciechafiska,** D Wawro** and G East*** - *Fiber, Textile and Clothing Science, Tampere University of Technology, Tampere, Finland; **Institute of Chemical Fibres, Lodz, Poland; ***Department of Textile Industries, University of Leeds, Leeds, UK
ABSTRACT The well-known ability of various cellulase enzymes to degrade cellulose has already been applied in order to improve the conventional cellulose xanthate process. The aim of the present CELSOL-research is to develop a method for making cellulose directly soluble in aqueous sodium hydroxide, without chemical substitution of the cellulose. The method is based on a combination of mechanical and biochemical treatments though efficient dissolution of hardwood pulps requires an additional chemical pretreatment. The effect of combined treatments on the supermolecular structure of common pulps was measured by the change in the degree of polymerisation and by the solubility of the cellulose in 9wt% aqueous sodium hydroxide. The celluloses treated by above methods are characterized to be highly soluble and the alkaline solution, containing 3-7 w/w% cellulose, can be regenerated to films and fibres.
1.
INTRODUCTION
The aim of this work is to develop an environmentally safer method for dissolving cellulose and, further, to spin cellulosic fibres from this solution. The most successful method to produce high-quality cellulose fibres has been the viscose process. However, there are environmental problems associated with this process which make it important to find alternative solvents and dissolving methods for cellulose. Our work is based on a combination of mechanical, chemical and biochemical treatments of cellulose. The cellulase enzymes play the most important role in this 197
198 Physical and chemical processing of fibre and fibrous products
procedure. The degrading effect of cellulase enzymes on cellulose has been investigated for decades (1-6). The well-known synergistic relationship between the actions of endoglucanase (EG) and cellobiohydrolase (CBB) enzymes is crucial for efficient cellulose degradation. Figure 1 illustrates a scheme of cellulase action in which endo1,4-b-o-glucanase (EC 3.2.1.4) randomly cleaves internal glucosidic bonds within an unbroken glucan chain. The newly created non-reducing chain ends then become the substrate for 1,4-b-o-glucan cellobiohydrolase (EC 3.2.1.91), which cleaves cellobiose dimers from the glucan chain and releases them into solution. The hydrolysis of cellulose into the glucose end product is completed by (3-glucosidase (EC 3.2.1.21), which splits cellobiose into glucose monomers. The creation by endoglucanase of nonreducing glucan chain ends that are sites of catalytic action for cellobiohydrolase leads to a synergism in the overall rate of cellulose degradation.(7)
A
B
~
-------.;:..~---
ceDoblose
<:t~
QP~
]
Glucan chain
HO
tnon-redUCIng end
Figure 1. The mechanism of enzymatic degradation of cellulose (7). (See text for explanation).
Celsol
199
However the overall degradation of cellulose is not our goal, but the biotransformation of its supermolecular structure that allows the preparation of a directly alkali soluble cellulose. The method was first reported in 1991 by Struszczyk et at (8,9). In this work we have studied the action of two enzymes produced by different fungi, on two different kinds of dissolving pulps; hardwood and softwood. In this stage of the work we have used the enzyme from Trichoderma reesei for hardwood pulp and the enzyme from Aspergillus niger for softwood pulp. The reverse combinations are under investigation and the results will be available in forthcoming papers. We also studied the solubility of celluloses in sodium hydroxide after biotransformation treatments and the spinnability of the solutions according to the patent application (10). It has come obvious during the work that the mechanical pretreatment of the pulp before further treatments has a significant effect in the biotransformation of cellulose. In the case of hardwood pulp, an additional chemical treatment was also needed before enzymatic hydrolysis. The treated pulps are characterised as having a high solubility in 9% aqueous sodium hydroxide and the alkaline solutions prepared have high transparency and spinnability.
2.
MATERIALS AND METHODS
The celluloses used are dissolving pulps from the eucalyptus/acacia mixture and from the southern pine. The characteristics of the pulps are presented in table 1. T able 1 Th e charactenstics 0 f pu IpS PULP Character Raw material Process Producer Alpha content Ash content Resin content
SI8 S10 DPw TAPPI viscosities
Hardwood SAICCOR eucalyptus/acacia 3: 1 Ca/Mg - (7/3) sulphite Saiccor Ltd, South-Africa 92% 0.09% 0.12% 5.0% 9.8% 690 17 -18 cP
Softwood FffiRANIERJ southern pine prehydrolyzed sulphate lIT Rayonier, USA 960/0 <0.1 % 0.01 % 3.00/0 4.9% 756 17 - 18 cP
The enzyme used for hardwood pulp was produced by fungus Trichoderma reesei and was specially formulated for these trials by The Research Laboratory of Alko, Finland. The enzyme used for softwood pulp was produced by fungus Aspergillus niger and was formulated by Institute of Technical Biochemistry, Technical University of Lodz, Poland. The activities of the enzymes are presented in table 2.
200 Physical and chemical processing of fibre and fibrous products
TahIe 2 1"'he enzyme activines. ENZTIvIE
ECU/ml
FPU/ml
Trichoderma reesei Aspergillus niger
40250 18
3.3 0.012
2.1
Mechanical pretreatment
Mechanical pretreatment of sheet form cellulose was carried out on a laboratory shredding machine. Cellulose sheets were pre cut into small pieces by hand, immersed in distilled water and kept in a refrigerator for about 20 hours before shredding. The mixture containing 30 w/wOlo cellulose was shredded for 3·hours and then dried at room temperature.
2.2
Chemical pretreatment
When required, cellulose samples (5g) were treated with O.IM sulphuric acid (100 ml) at 900C for 20 minutes using a shaker. After treatment the cellulose was washed with cold, distilled water and dried at room temperature or put into a buffer solution, pH 4.8, for enzymatic treatment.
2.3
Enzymatic treatment
Cellulose samples (5g) were placed in a 0.05M sodium acetate buffer (100 ml) and stored overnight in a refrigerator. The cellulose was separated from the buffer and added to the enzyme solution (100 ml). The mixture was shaken for varying lengths of time from 2-24 hours whilst maintained in a water bath at 50°C. After the required time the cellulose was separated from the solution, treated with hot distilled water for 5 minutes and washed with cold, distilled water. The treated cellulose was dried at room temperature. The enzyme solution was prepared by introducing a suitable amount of concentrated enzyme into a 0.05 M sodium acetate buffer, pH 4.8. The average molecular weights (DP) after the different kinds of pretreatments and after enzymatic hydrolyses have been measured by GPC in the Institute of Chemical Fibres, Lodz, Poland.
2.4 Preparation of cellulose solutions A cellulose solution of treated hardwood was prepared by introducing a suitable amount of wet cellulose into a reaction flask containing 9 wt% aqueous sodium hydroxide (-SOC). The mixture was stirred keeping the temperature at -SoC until the cellulose had dissolved. For fibre spinning, the solution was deaerated, poured into the reservoir, the pressure was set and the spinning was started immediately. A cellulose solution of treated softwood was prepared as explained above, but the solution was left standing at a low temperature « +10 °C) for 24 hours before further processing.
Celsol
201
2.5 Solubility determinations Mixtures of cellulose (1.35g) and 9wt% aqueous sodium hydroxide (40 ml) were stirred at -50C for 30 minutes. The solutions obtained were centrifuged twice using 'MSE Mistral 1000' centrifuge at a speed of 3600 rpm for 15 minutes. The undissolved part was separated after both centrifugations, washed with 5wt% aqueous sodium hydroxide and centrifuged for a further 5 minutes to obtain purer undissolved cellulose. The dissolved cellulose from all separations and the undissolved cellulose after washing were treated with 3 % sulphuric acid, washed with distilled water and ethyl alcohol and dried at 105°C for at least 4 hours. The solubility of cellulose was calculated as a percentage using the following equation: [1] where Wd = weight of dissolved cellulose and Wu= weight of undissolved cellulose.
2.6 Fibre spinning Fibres from both types of cellulose solution were produced. In the case of the hardwood cellulose solution the spinning line consisted of the reservoir, volume 300 ml, pump, capacity 0.3 ml/revolution and spinneret, 8 x 250 urn. In the line there was one wire core filter, mesh 50 and two polyester fabric filters with seals. The pressure of the line was set approximately to 30 psi using nitrogen. The spinning bath was placed horizontally; its volume was about 6 litres and length 1.2 meters. The fibres were collected either directly on one godet or after stretching, on a second godet. In the case of the softwood cellulose solution the spinneret used was 1 x 500 urn. The fibres obtained were washed until neutral and dried either from water/acetone mixture (hardwood) or from water (softwood).
3.
RESULTS AND DISCUSSION
3.1 Pretreatment and solubility Two different dissolving pulps, hardwood sulphite and softwood prehydrolyzed sulphate, were transformed into alkali soluble forms by a combination of mechanical, chemical and enzymatic treatments. The type of pretreatment played an important role in the solubility of cellulose. Mechanical and enzymatic treatments alone were not enough to produce a good, spinnable solution for hardwood, since the DP w of the cellulose did not decrease to the required level. On the other hand the softwood pulp did not need any chemical pretreatment before enzymatic hydrolysis since the enzymes had a greater effect on the DP w (12). The data are given in table 3.
202 Physical and chemical processing of fibre and fibrous products
Table 3 l"heeffiect 0 f pretreatment on t e so u I Ity and DPw o f ceIIuIosee Pulp Pretreatment
Hardwood, Saiccor solubility
% 32 37 45 61 47 67 64 80
DPur
wt loss %
-
Softwood, Fibranier J wt loss % DP ur
-
756 690 None 684 608 Mechanical 400· Chemical 2.1 393 1.2 Mechanical and chemical 604 656 Enzymatic 585 493 2.8 10 Mechanical and enzymatic 430· 4.7 Chemical and enzymatic 420 Mechanical chemical and enzymatic 2.7 • Not measured; estimated from the DP w of cellulose after mechanical and chemical pretreatments
-
-
-
-
The compositions of hardwood and softwood before pulping are significantly different, in that the softwood has a higher lignin content and the hardwood has a higher cellulose content. These differences become more important after pulping prior to enzymatic hydrolysis since the supermolecular structure and especially the capillary structure of these two materials are different. It is well-known that direct physical contact between the enzymes and the substrate is a prerequisite to hydrolysis (12). Since cellulose is an insoluble and structurally complex substrate, this contact can be achieved only by diffusion of the enzymes into the cellulose matrix. Any structural feature that limits the accessibility of cellulose to enzymes will diminish the susceptibility of cellulose to hydrolysis (13). After pulping, the softwood has a more porous structure than the hardwood because the lignin is removed during the process. According to our results in table 3 the softwood also seems to be accessible enough to enzymes after mechanical pretreatment only, whereas the hardwood pulp is less affected and needed an additional treatment. The mild acid hydrolysis was chosen as the second treatment. The main effect of mechanical shredding is to subdivide cellulosic material into fine particles which are highly susceptible to acid or enzymatic hydrolysis. The smaller particles have a large surface-to-volume ratio, thus rendering the cellulose more accessible to hydrolysis. The effects of acid hydrolysis, specially with mild sulphuric acid, are claimed to be the creation of micropores by the removal of hemicellulose, a change in crystallinity and a reduction in the DP (14). According to our results the chemical pretreatment had the greatest effect on the DP w, but the enzyme treatment caused the largest increases in solubility. The combinations of mechanical / enzymatic and chemical/enzymatic treatments did not give as good solubility as with both pretreatments together, prior to enzymatic hydrolysis. Without enzymes the solubility of cellulose increased with decreasing DPw, which is in
Celsol
203
accordance with the studies of Schleicher and Lang (15). However enzyme-treated cellulose always showed a higher solubility at a given DP w' The next question to be asked: 'How do the enzymes work?' Kamide et al. (16) studied the alkaline solubility of cellulose as well as the solubility of treated natural cellulose and concluded that the solubility is greatly dependent on the degree of break-down of an intramolecular hydrogen bond (03 ...05)' Further, Yamashiki et al. (17) studied the alkali solubility of cellulose having crystal form I after reduction of the intramolecular hydrogen bonding by physical treatment and obtained a solubility of nearly 100%. We speculate that the break down of the intramolecular hydrogen bonds might be one of the mechanisms that is employed by enzymes as well. This suggestion is supported by the fact that the DP w of cellulose does not always decrease significantly during the enzymatic hydrolysis. 3.2 Fibre spinning Fibres from both types of cellulose solution were spun. One spinning from hardwood was made without chemical pretreatment and another with it. The DP of the cellulose was reduced from 684 to 393 by the chemical treatment; during enzymatic hydrolysis the DP increased to 420 probably due to the loss of low molecular weight cellulose. In all the trials the solvent used was 9% NaOH, but in experiment 2 (table 4) a further additive was present in the solution. The properties tested were tensile strength and extensibility. The parameters and results offibre spinning are given in table 4. T ahI e 4 Th e parameters an d resu ts 0 ffib re spinmng. Cellulose
Spinning parameters
pulp
chern. pretr,
enz.
DP w
1. Sa
no
TR
585
cell. cone % 3.00
bath content
draw
spinneret
%
Fibre properties T Ext. cN/dtex %
-
-
8x 12 H?S04 10% Na,.S04 200/0 250 um 2. Sa yes TR 420 8x 24 0.76 11 H?S04 10 % * 4.50 250J.lm Na?S04 1~% 3. Fi no AN 455 5.00 Ix no 0.40 H?S04 10% Na,S04 2O% 500 JlIIl AJ,,(SOA)'l 16% 4. Fi no AN 386 3.50 Ix no 0.5-1.0 H?S04 10% Na,S04 8% 500 J.U1l Sa = Saiccor cell., Fi = Fibranier cell., TR = T. reesei, AN =A. niger, * Alkaline solution: NaOH +additive, T = tensile strength, Ext. = extensibility
-
-
204 Physical and chemical processing of fibre and fibrous products
From the results in table 4 it can be seen that cellulose with a higher DP w than used in the viscose process can be dissolved in 9wt% NaOH. In this early stage of the studies neither the alkaline ratio nor the fibre properties are as good as in the viscose process.
4.
CONCLUSIONS
The effect of different enzymes based on Trichoderma reesei and Aspergillus niger was investigated in order to obtain cellulose soluble in 9OA. aqueous sodium hydroxide. The pulps investigated were hardwood sulphite (Eucalyptus/acacia) and softwood prehydrolysed sulphate (Southern pine). Both pulps proved to be biotransformable into a soluble form in 9% aqueous sodium hydroxide after combined treatments. The cellulose from a prehydrolyzed process was easier to transform; however, the hardwood sulphite needed an additional chemical treatment and special formulation of cellulase activities. Results from fibre spinning proved that it is possible to produce cellulosic fibres from biotransfonned cellulose, though further studies on various pretreatments, coagulation mechanisms and spinning parameters are needed in order to develop the CELSOL method further. References 1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17
Li, L.H., Flora, R.M. and King, K.W., Arch.Biochem. 1II(1965),p.439 Selby, K. and Maitland, C.C., Biochem.J. 104(1967), p. 716 Wood, T.M., Biochem.J. 109(1968), p.217 Erikkson, K.E. and Rzaedowski, W., Arch.Biochem.Biophys. 129(1969), p.683 Wood, T.M. and McCrae, S.L, Biochem.J. 128(1972), p.1183 Reese, E.T., in "Biological Transformation of Wood", 00. Liese, W., Springer Verlag, Berlin 1975, pp. 165-181 White, A.R., in "Cellulose and Other Natural Polymer Systems", Edit. Brown, R.N., Jr., N.Y., 1982, pp. 489-509 Struszczyk, H., Nousiainen, P., Wawro, D., Ciechanska, D. and Dolle M., Cellucon Conference, December 2-7,1991, New Orleans, USA Struszczyk, H., Nousiainen, P., Ciechanska, D., Wawro, D. and Matero, M., Cellucon Conference, June 3-6, 1993, Lund, Sweden Kemira Fibres and Institute of Chemical Fibres, Fin.Pat, application, 91-1408, March 22, 19.91 Nousiainen, P., Matero, M., Struszczyk, H. and East, G., Akzo Nobel Viscose Chemistry Seminar, May 30 - June 3, 1994, Stockholm, Sweden Fan, L.T., in "Adv, Biochem. Eng., vol 14", ed.Fiechter A., Springer, Berlin Heidelberg New York, 1980, p.lOI Biotechnology Monographs: "Cellulose hydrolysis", 00. Aiba, S., Fan L.T., Fiechter, A., Klein, J., and Schugerl, K., Springer-Verlag Berlin Heidelberg New York, 1987 Knappert, D., Grethlein, H. and Converse, A., Biotech. and Bioeng., Vol 22, 1980, pp.I449-1463 Schleicher, H. and Lang, H.,International Conference on Advanced Polymer Materials, September 6.-9., 1993, Dresden, Germany Kamide, K., Okajima, K., Matsui, T. and Kowsaka, K., Polym.J., 16, 857 (1984) Yamashiki, T., Kamide, K., Okajima, K., Kowsaka, K., Matsui, T. and Fukase, H., Polym.J.,vol. 20, no 6, pp. 447-457 (1988)
21 Concurrent modification of wood with phthalic anhydride in composite manufacture R Salisbury,* M Lawther* and P Brown** - *The BioComposites Centre, University of Wales, Bangor, Gwynedd LL57 2UW, Wales; **BP Chemicals Ltd, Hull Research Centre, Saltend, Hull HU12 8DS, UK
Abstract Phthalic anhydride (PA) is a well-known commodity chemical which is low cost and low hazard. PA can be used to improve the properties of wood particleboard made with phenolformaldehyde (PF) resin. The greatest improvement is in resistance to the effects of water, but initial properties also show some improvement. PA can be used to pre-treat the wood particles, but can also be added during board manufacture, eliminating the need for separate chemical processing. Boards made with unmodified wood and PF resin show improved properties at lower material cost when part of the PF resin is replaced by PA. The reactions of PA with PF, and with individual wood components, were investigated. It is shown that the improvement in board properties is not due to effects of PA upon the PF resin or the wood alone, but to result from an interaction between all three components.
Phthalic anhydride Phthalic anhydride is a major commodity chemical which finds applications as a difunctional intermediate with ultimate applications mainly in the plastics industry (e.g. polyester resins, paints and phthalate ester plasticisers). Current European production is of the order of 800,000 tonnes per annum. The material is commercially available in bulk as molten PA at 1600C (freezing point is or as a solid flake in pack sizes down to 25 kgs. Current price levels are approximately £500/tonne. 1310C)
PA is classified as an irritant, but causes no handling problems provided basic industrial practices are followed.
205
206 Physical and chemical processing of fibre and fibrous products
General considerations It has long been known that acid anhydrides react with wood, and many attempts have been made to improve the properties of composites using this reaction. PA has not been a popular choice of reagent, probably for two reasons. Firstly, it is not very reactive in the conditions usually applied, and secondly, all the results have shown that phthalylation increases the hygroscopicity of wood. On the first point, Rowell has suggested (1) that useful modification of wood must take place at 1200C or less, because the wood deteriorates above this temperature. However, in view of the fact that wood is subjected to temperatures of 20()OC during board manufacture, this seems unnecessarily restrictive. The only true measure of the usefulness of a reaction is the effect on the properties of the final composite. If excessively harsh reaction conditions are used, the composite will lose bending strength and stiffuess. Removing the 1200C restriction allows us to dispense with solvents and catalysts, and to react wood directly with powdered PA, which melts at 13IOC. In practice, we mixed ovendry softwood shred with powdered «400J.1) PA in a metal container which was closed but not sealed, and then heated it in an oven at 1600C for 1 hour. Non-leachable weight gains of more than 10% were easily obtained. The reaction of wood with an anhydride is usually represented as:
~o
o +
wood-OH
o
O-wood OH
> o
[1] In the case of a cyclic anhydride, the carboxyl group formed remains attached to the wood, as shown, which explains the greater hygroscopicity of wood so modified. That the above representation is correct is shown by the use of the carboxyl group for grafting on further polymers (2).
Phthalic anhydride in boards The BioComposites centre, started working with PA in 1991. Phthalylated wood made into a board with phenolic resin was found to have greatly increase water resistance.
In an attempt to show that wood modification was a key component of this effect, we also made boards in which the PA was simply added in various ways to the board furnish. Unfortunately for our theory, these boards also showed improved properties. A full study was carried out using a resin (J2005A) which had proved to be satisfactory in earlier work. This was not the best resin, but one which was easy to work with and readily available. We chose to work with wood shred rather than fibre or flakes, for ease of handling.
Modification with phthalic anhydride
207
Outline of trial At this time, we were assuming an analogy between PA and acetic anhydride, so the amount of chemical used was quite high: 10%, 14% and 18%. Two series of boards were made, one with wood that was modified with PA beforehand, the other with PA being added with the resin. Sufficient boards of each type were made to provide enough material for British Standard tests of : thickness swell, linear expansion and water uptake from manufacture to conditioning at 65% relative humidity at 20°C from conditioning to 1 hour water soak at 20 0C from conditioning to 42 hour water soak at 20°C from conditioning to conditioning at 93% relative humidity at 20 0 e from conditioning to 2 hours boiling after V313 cyclical testing during repeated boiling and drying at 105°C weight loss due to V313 cyclical boiling internal bond strength at 65% relative humidity at 20 0 e at 93% relative humidity at 200C after 1 hour soak at 20°C followed by reconditioning after 24 hours soak at 20°C followed by reconditioning after 2 hours boiling followed by drying and reconditioning after V313 after cyclical boiling three-point bending tests at 65% relative humidity at 20 0 e after 24 hours soak at 20 0 e weight loss due to biological challenge by Coniophora puteana Gleophyllum trabeum Pleurotus ostreatus
Results All the properties were improved by PA, whether it was reacted with the wood before board manufacture or added with the resin. The figures for the physical testing are not presented here, because they have been superceded by later work. The results of the biological testing are shown in Tables 1 and 2, because no further trials have been made.
208 Physical and chemical processing of fibre and fibrous products
Table 1.
Table 2.
Weight loss due to fungal attack: wood modified by PA fungus\amount of PA
none
10%
14%
18%
Coniophora puteana
25.4
7.14
2.27
.44
Gleophyllum trabeum
4.8
0.15
-0.09
-0.35
Pleurotus ostreatus
13.34
-0.47
-0.56
-0.47
Weight loss % due to fungal attack: PA added with resin fungus\amount of PA
none
10%
14%
18%
Coniophora puteana
25.4
2.82
1.92
1.43
Gleophyllum trabeum
4.8
-0.57
-0.45
-0.06
Pleurotus ostreatus
13.34
-0.57
-1.03
-1.17
The physical testing results also showed that reaction during manufacture was nearly as good as prior modification, and also suggested that much lower levels of PA would also be effective. We therefore made boards using PA to replace some of the phenolic resin, and did a more restricted set of tests on them. The tests were not to British Standard, but were designed to give maximum information from the minimum of material. It was found that the best results were obtained by replacing about 20 - 25% of the resin (dry weight) by PA. The improvements obtained are summarised in the table.
Table 3.
Relative improvements achieved in chipboard properties by replacing about 20% of PF resin by PA Property IBS - conditioned IBS - boiled IBS- retention thickness swell - cold soak thickness swell - 2 hour boil bending strength - conditioned bending stiffitess - conditioned bending toughness - conditioned bending strength - boiled bending stiffness - boiled bending toughness - boiled
Improvement factor 2.1 14 9 1.2* 1.8* 1.3 1.3 1.6 1.5 1.5 1.9
* ratio of log reciprocal
swell
Modification with phthalic anhydride
209
These are not minor improvements, and any proposed mechanism must be able to account for the scale of these effects. It was found that all the properties were highly correlated with initial IBS, and this property only is used in the graphs below.
Possible mechanisms PA could be acting as an accelerator for the resin, producing more complete cures before the wood starts to deteriorate. A series of trials showed (Figure 1) that PA does act as an accelerator, but not a very powerful one, and the properties of boards made with PA go on increasing with pressing for longer:
Effect of press time
onlBS 0.6 .....- - - - - - - - - - - - - - -...... 0.5
+----------=-"'=---.-.:::::::::~---t
0.4
-I--
---I
---,~L.._
Ci
[J
Q.
~0.3 +--~--~~--------~~ UJ ~
• 20%PA
0.2
+-_~-_-----::..-c::;;.---------I
0.1
-I-----""7"'--~~---------...;;~
noPA
• 20% PA, boiled no PA, boiled
0.0 .....- - . . . - . -......- -......- - - . . - - -......- ---'1 o 10 20 30 40 50 60 press time
at 200°C (mins)
Figure 1 PA could be acting to improve the resin in some other way. We investigated this by making boards with vermiculite replacing wood and also by testing resin-impregnated strips of glass fibre filter paper. PA was detrimental to all the properties except dry strength. However, when cellulose filter paper or newsprint was used to make the strips, PA improved the strength and stiffness of the strip, both when dry and when soaked.
Table 4
Effect of PA on properties of resin strips control = 100
support
dry strength
dry stifthess
wet strength
wet stiffness
glass fibre
136
99
96
79
cellulose
107
110
109
116
newsprint
III
108
212
201
210 Physical and chemical processing of fibre and fibrous products
The effect of PA on resin cannot explain the greatly increased water resistance of boards, so what about the effect upon the wood? A set of boards was pressed at 20O<>C for ten minutes with or without 2% PA, but with no resin. As made, these were of the same thickness and density. After conditioning, the boards bad picked up about the same amount of moisture, but the control boards had swelled more. On soaking in cold water, the control boards immediately started to swell at a rate of about 100/0 per minute, and continued to do so for 7 Y2 minutes, when measurements were stopped. The board with PA initially swelled at a much' slower rate, about 1% in the first minute, but after 4 minutes it too was swelling at 10% per minute. The overall delay amounted to about 1 minute. This difference may be chemical, or may be due to the PA decreasing to porosity of the board. In either case, such a minor difference cannot explain the greatly improved resistance of boards made with PA to two hours of boiling. A further set of boards made without resin was cut into blocks immediately after pressing and cooled in a dessicator. They were then quickly measured and mounted for internal bond measurement. The board containing PA was no stronger than the board without it. PA is clearly not acting as a binder. The effect of PA cannot be explained by its action on either wood or resin, it must involve an interaction between all three components. Boards are sensitive to water content. Perhaps the PA "locks up" the water in some way and stops it interfering. A series of boards have been made and tested, and the results are shown in the Figure 2. It is not possible to translate the curve for the boards with PA onto the control curve by a horizontal movement only ~ so PA is not acting only to reduce the effects of moisture.
Phthalic anhydride addition.
Effect of mattress moisture on 18S. '1.6 .....- - - - - - - - - - - - - - - - - -..
"1.4
+--------~------------4
1.2
-+---------~------------I
(i1.0
+----------~~---------I
0...
•
~O.8 +-----------~--------4
2%PA
~ 0.6 +-------~-----~=-------I
control
)(
(/)
0.4 -+-0.2
-..--;:l~---------I
~---------------===-~--I
------"'1.....-----.. .
0.0 ......- - - - -..... o 5
10
moisture content of mattress (%)
Figure 2
15
Modification with phthalic anhydride
211
Chemical considerations The resin is in aqueous solution and has a high pH. The board is pressed at high temperature. In these conditions the PA cannot survive long before being hydrolysed to acid, and some will be converted to phthalate ion. On the other hand, phthalic acid is thermolabile, and could start to dehydrate to PA. A phthalate ion from di-sodium phthalate, on the other hand, would have to grab two protons from the alkaline surroundings, and hold onto them long enough to be dehydrated. This seems unlikely. Dehydration is a mechanism that is not available to terephthalic acid (the para isomer) either.
Spectroscopic evidence The reactions of PA, phthalic acid and sodium phthalate with wood components were also investigated using FTIR. There is good evidence of reaction of PA and phthalic acid with all components at 1800C or less. Sodium phthalate does not appear to react even with lignin. FTIR spectra show that when PA reacts with wood at 1600C only di-ester is formed, no acid is detectable. Phthalic acid reacts just as thoroughly at 1800C. This shows that benzenecarboxylic acids can react directly with wood, without forming an anhydride. Futher studies confirmed that terephthalic acid also reacts with wood at 1600C, but in this case acid groups remain. However, sodium phthalate shows no reaction even at 200 0C. That relevance of these reactions was confirmed since it was shown by spectroscopy that phthalate is also present exclusively as di-ester when PA is added to a board with the resin.
r
We conclude that equation 1], derived from studies using anhydrous solvents, does not represent the reaction of PA with wood when the two are simply heated together, or pressed together in a board. This can be confirmed by looking at the affinity of the product for water. Whereas a carboxyl group is more hygroscopic than the hydroxyl it replaces, a di-ester should be much less hygroscopic than two hydroxyls. The equilibrium moisture content at 65% r.h. of wood modified with 2% PA was found to be 7.5%, compared to 9.2% for untreated wood. Once the di-ester is formed, it is unlikely to react further in board pressing, but boards made with this material show the property enhancements. It therefore appears that we have a chemical reaction between PA and wood, and a physical interaction between the modified wood and the resin.
Comparison of different additives We would expect, from the reaction information, that phthalic acid should be comparable in its action to PA. Terephthalic acid may also have an effect, but di-sodium phthalate should have none. A series of boards, all using the same amount of resin, were made to test this. The results (Fig 3) are not in full agreement with the prediction. Terephthalic acid is harmful. Phthalic acid is comparable to PA. But di-sodium phthalate is also beneficial. Whatever the mechanism, it seems unlikely that wood modification is involved.
212 Physical and chemical processing of fibre and fibrous products
Comparison of additives.
Effect on dry and boiled 18S. 0.8 ~------------------------..
0.6
....-......-_4----------------------___
~
ca :i ~ 0.4 ....... .....---."""'....---+--4-------------------D.
tJ)
m 0.2
phthalic anhydride
phthalic acid
sodium phthalate
control
terephthalic acid
Figure 3
Summary PA greatly improves the properties of particleboard made with PF resin, both when it is used to pre-modify the wood and when it is added with the resin. There is little difference in the effects, so there is probably little difference in the mechanism. PA does not significantly improve the properties ofPF resin or of wood alone.
In solvent-free conditions, PA reacts with wood completely to give di-ester. The product is not hygroscopic. No further reaction with the resin is likely, so the board improvements must result from a physical interaction. Sodium phthalate also improves board properties, but does not react with wood. different mechanism must be involved, which probably also contributes when PAis used.
A
There is clearly much more work to be done before this system is fully explained.
We acknowledge the contribution of Dr H Earl at the start of this work, and the help of Dr D Gerrard ofBP with the spectroscopy.
References (1) R M Rowell, (1983) Chemical modification of wood. Forest Products Abstracts Vol.6 No.12,363-383 (2) H Matsuda, (1987) Preparation and untilisation of esterified wood bearing hydroxyl groups.
Wood Science and Technology 21:75-88
22 Engineering composites from oriented natural fibres: A strategy P E Humphrey - Oregon State University, Corvallis, Oregon, USA
1 INTRODUCTORY SYNOPSIS Most plant fibres which have rigid walls consist of highly evolved arrangements of lignocellulosic (LC) sub - elements. The impressive physical properties of these fibres are, however, rather poorly utilized in present-day composites. It will be argued here that such fibres could be used in some quite revolutionary ways, and looking to nature's solutions to her engineering problems may help us in this endeavour. The internal micro-structure and external shape of mammalian bones are, for example, tailored to the mechanical and biological demands placed upon them. It is this principle of judiciously manipulating overall shape and the spatial distribution of properties therein which will be contemplated here. New types of molded engineering components incorporating spatially oriented and modified LC-fibres could be the result. Products so derived may partially replace environmentally less attractive materials, including pressed steel, aluminium alloys and some polymers, in a diverse range of engineering applications. We will see that property control within the proposed engineered components may be achieved by manipulating a combination of the following: i) spatial distribution of fibre type; ii) spatial distribution of fibre orientation; iii) spatial distribution of localized conditions (thermodynamic, chemical, stress) to which pre-formed fibre networks are exposed during consolidation processes.
213
214 Physical and chemical processing of fibre and fibrous products
It is well known that the structures of conventional wood-based composites (mainly panel products) are greatly influenced by physical mechanisms that occur within them during their consolidation (hot pressing; item iii) above). These mechanisms include unsteady-state heat and moisture transfer, rheology (densification and stress relaxation) and adhesion. Some models which simulate material behavior during the pressing process will be summarized here, and their possible use (albeit in much modified form) to aid in developing ways to form the new molded components will be considered. Let us start by considering some general principles upon which the design of engineering components often depend, before going on to look at some possible ways of synthesizing new and useful objects from natural fibres.
2 Design rationale for engineering components: the way engineers usually do it Most components used in engineering applications are designed using shape as the principal variable. This usually follows some type of materials selection activity which is done in light of the anticipated demands in service versus the attributes of a range of candidate materials. Desired combinations of attributes are clearly diverse, usually including load bearing properties, density and cost, but also often including thermal properties, factors such as machinability, finishing, wear, and means of connection. In more forward looking design groups, some form of environmentally inclusive life-cycle analysis may be made when allocating cost (4,14). With the ever increasing demand for efficient designs, much attention of late has been given to optimizing shape, and this has led to the evolution of quite sophisticated design strategies using numerical methods of analysis. "Shape Optimal Design", or SOD, using FEM and, more recently, Hereditary algorithms (6) are, for example, now being used in diverse engineering fields as well as in the aerospace industry where they originated. Furthermore, greater care is being taken in identifying performance criteria for materials which are to be used in particular combinations of in-service demand. Pioneering in these approaches to materials selection is the work of Ashby and his co-workers (1). They have developed well founded rationales for identifying performance indices. Mass-to-strength and mass-tostiffness ratio manipulation under specific demand conditions are common concerns when using such approaches. Many combinations of factors (such as mechanical, thermal, aerodynamic, and vibrational ones) may, however, all come together to affect an optimal selection in this strategy .. Even in Ashby's approaches, almost all of the materials considered in the data base upon which the approaches depend are assumed to be homogeneous in nature, or at least orthotropic. This is in contrast to many materials and micro-structures which occur naturally in plants and animals and which perform highly specialized functions therein.
3 Nature's solutions to engineering design In the above, it is largely assumed that a homogeneous material structure, or a regularly repeating micro-structure, be employed and that the shape of the object is the only aspect that may be varied very much once a selection of material is made. One only needs to
Composites from natural fibres
215
consider the structure of even the most primitive plant genera to realize that nature's solution to the task of efficiency in design is much more sophisticated and leads to some elaborate multi-functional and tailored solutions (11). Microscopic examination of trees or animal bones or insect shells soon shows that the internal structure of such objects are elaborate and involve complex mixing of diverse cell types and orientations (12). Such structures lie within objects which themselves are not of simple geometric shape. In other words, through the power of natural selection, nature combines the concept of "shape optimal design" (SOD) with that of internal structure control, and thence spatial property distribution control. Together, these two concepts yield natural systems which are significantly more efficient and viable than almost any human construct. The concept of manipulating the spatial distribution of properties within an object will here be termed "Internal Property Distribution Control" or IPDC.
4 Can we combine SOD and IPDC in human-made composite components? Some attempts have, of course, already been made to control both shape and properties in human-made objects. This has mainly been in fibre re-enforced polymer products where mandrel windings or wovens of long strands of carbon, glass, boron etc are formed into relatively simple shapes. The winding or weaving or lay-up configurations within such objects are usually selected in the light of stresses anticipated in service. Spatial gradients of property change achievable in such approaches are, however, largely limited by the formation method and truly three-dimensional control over internal structure remains illusive. A couple of rather interesting examples of shape and property control are to be found in the wood utilization field. Both spatial property distribution (by lumber selection and subsequent placement) and shape are, as we well know, controlled in glu-Iaminated beam design. On a rather smaller dimensional scale, density profile (cross-sectional mass distribution) in hot pressed panel products is increasingly acknowledged as being an important factor in affecting the efficiency with which we tailor panel design to in-service demands (7). The transformed section of a panel may be likened to the shape of an "I" beam and thence, for example, effect its ability to span floor joists in a building. This particular paradigm will be taken further in the discussion to follow, in which an extension of the mechanisms used to affect density profiles in panel products will be considered for the development of new natural fibre based engineering components. As mentioned above, one may apply the principle using a diversity of raw materials -synthetic or elemental fibres, particles etc in conjunction with diverse matricizing agents and processing methods. Natural fibres do, however, have some special attributes which may offer us special opportunities. They lend themselves especially well to in-process modification; this is unlike most other fibrous materials which are relatively inert. Before looking at this aspect in a little more depth, let us first list some of the primary attributes of plant fibres (at least those with rigid walls) which may effect their behavior during processing and in subsequent service. For our purposes, it is convenient to boil down the fibres' attributes to the following: •
permeable to gases and liquids due to the presence of the lumen (and inter-fibre spaces in fibre networks);
216 Physical and chemical processing of fibre and fibrous products
•
wall accessible to, and reactive with, some molecules - particularly small polar ones and this makes the fibre amenable to modification in-situ;
•
wall therefore hygroscopic and this makes unmodified fibres dimensionally unstable (below wall saturation) and, more encouragingly, an active player in the convection of polar vapours and the bound diffusion of adsorbed molecules;
•
hygro-thermo-viscoelastic and this makes the fibre amenable to structural modification (deformation, densification) in-situ (particularly by manipulating thermodynamic and chemical conditions while applying stress);
•
anisotropic in terms of mechanical and translational properties (particularly axially versus transversely);
•
has significant specific (density corrected) axial load-bearing properties and toughness.
5 Structural changes that occur within wood-based composites during consolidation Our looking at the mechanisms operative within conventional wood-based panel products during pressing has provided some of the groundwork upon which to base processing innovations in the present strategy. For this reason, a very brief overview of the mechanisms and our modelling of them will be given here before going on to identify some opportunities for innovation The above listed fibre attributes should be remembered from henceforth. Heat and moisture move throughout conventional wood based composites during pressing. This is principally by means of thermal conduction and the convection of water vapour. The water vapour gradients are generated within the pore spaces of the hygroscopic fibre network since some form of phase balance is maintained localI y between water adsorbed in the fibre walls and that existing as vapour in the pore spaces; local energy content dictates the phase balance and temperature of the solid-gas combination. As a consequence of heat and moisture transfer and phase change, an ever changing spatial distribution of temperature, adsorbed (fibre wall) moisture and within--void partial pressure of water vapour occurs within the composite as pressing proceeds. Since the fibre network is hygro-thermo-viscoelastic, it densifies differently in different locations depending on the time-temperature-moisture history sustained and the stress applied from the platens of the press. As one would expect in flat pressed panels, the induced property gradients are most extreme in the compression direction (usually through the thickness) and the density profile is a consequence. It is this density profile which effects the flexural properties of the products, for there is usually a strong correlation between density (level of consolidation) and mechanical properties for assemblages of bonded natural fibres or particles. In the pressing process, rheological changes (which affect the density profile changes as pressing proceeds) directly influence the translation properties of the furnish material (principally permeability to water vapour and thermal conductivity). It is, however, temperature and moisture which influence the densification process. In other words, there is a high degree of linkage between the mechanisms that occur within the fibre network as pressing proceeds. For this reason, numerical methods of simulation have been used to
Composites from natural fibres
217
account for the interactions, and the resultant algorithms are now being used as tools to aid in optimizing the production of conventional composites and the development of new machines for their production (approaches such as continuous steam injection pressing). The interdependencies among mechanisms in wood-based composites during pressing are represented schematically as Figure 1. A range of example predictions of the models which simulate heat and moisture movement, rheological behavior and adhesion development are to be found in publications and ones in preparation (3,7). One typical set of model predictions for the thermodynamic (heat and moisture transfer) aspect of the system applied to the consolidation of a homogeneous mat of wood flakes is presented as Figure 2. Following this (Figure 3) is a predicted density profile development plot using the same model, but this time applied to the pressing of a homogeneous mat of thermo-mechanically produced wood fibres and fibre bundles. It is this plot that most clearly demonstrates the potential for using the modelling techniques to aid in controlling the structure (and thence properties) within natural fibre composites by manipulating pressing conditions.
HEAT AND MOISTURE TRANSFER Thermal conduction, phase change, and vapor convection affect local temperatures, MCs, and vapor pressures. Local balance between temperature, MC, and vapor pressure is maintained.
Figure 1. The mechanisms operative within dry-formed composites during pressing.
218 Physical and chemical processing of fibre and fibrous products
_--------,160
0.0 UPPER PLATEN
0.5
1.0 LOWER P\.ATEN
1--------,..f20 10
/:.(0.0
0.5
1.0
UPPER PLATEN
LOWER PLATEN
0.0 UPPER PLATEN
1.0 LOWER PLATEN
Figure 2. Predicted variations of cross-sectional (consolidation direction) distributions of temperature [A], vapour pressure [B], and adsorbed moisture (on a dry basis) [C], with simulated pressing time. These data relate to a mattress of Sitka spruce flakes, initially at 11 % moisture content, pressed to a mean density of 650 kg m? with 1600C platens (8).
Simulated Density Profile Development 900
Density (Kg/ m3)
Thickness
Elapsed Time (Sec.) o
Figure 3. Predicted cross-sectional (consolidation direction) density distributions with simulated pressing time. These data relate to a mattress of thermo-mechanically produced Douglas-fir fibres, initially at 11 % me, pressed to a mean density of 650kg m? with 160°C platens. An extended form of the simulation model used to generate the data of Fig. 2 was used here (5). Note: Total mattress thickness decreased from an initial value of 42-mm (150kg m") to a constant value of 16-mm (650-kg m") in the first 37 seconds of simulated pressing. This variation is not represented graphically here; equal mass was, however, conserved in each of the ten cross-sectional modelling regions.
Composites from natural fibres 219
In order to simulate such processes, a range of materials properties input data for networks of fibres, particles and the like has to be provided. A suite of miniaturized techniques have been developed to provide such data. These include, but are not limited to, techniques to explore the following: •
Gas permeability of natural fibre networks and particle mats as functions of flow direction and level of consolidation (density) (2);
•
Thermal conductivity as a function of fibre moisture content, direction and level of consolidation (density);
•
Rheological properties (viscoelastic with micro-fracture) as functions of fibre moisture content, temperature and level of consolidation (density) (13);
•
Bonding reactivity (for a given adhesive and adherend) as a function of temperature and moisure content (preliminary and simplistic at this stage!) (9,10).
6 A possible sequence of fibre processing stages to form the new materials The insights gained in studying the behaviour of conventional composites will aid in the formulation of the new ones. A strategy now under detailed development is including (but is not limited to) the stages listed below. •
Fibre separation and selection: This may be from naturally occurring populations (eg extracted from trees of a single specie), or by species-dependent ranges in properties. Natural and man-made fibres may ultimately be combined. Very rapid but accurate fibre sorting techniques are being considered.
•
Fibre modification prior to re-constitution: This may encompass a diversity of chemical and mechanical treatments to impart desirable properties to the fibres prior to their being further modified during the re-constitution phase to follow. Clearly, in present products, adhesive is the main additive at this stage (although fibres used in papers and the like are modified in a wider range of ways). In the proposed composites, alternative treatments may be warranted. For example, the application of very small quantities of a ferromagnetic element renders the fibres amenable to subsequent orientation in a magnetic field (see below.)
•
Creation of a pre-form which consists of fibres spatially oriented in two or three dimensions within a simple or complex shape: Preliminary experimentation suggests that magnetic means have potential (15), although a range of possibilities are being explored.
•
Consolidation of the pre-form to create a component with controlled shape and internal structure: It is proposed to consolidate the pre-form in a sealed pressing system to affect the thermodynamic and chemical environment in such a way as to trigger a
220 Physical and chemical processing of fibre and fibrous products
desirable range of reactions. In other words, concentrations of reactive vapours will be transtluxed through the porous matrix of fibres. This could stimulate reactions which affect localized densification, adhesion, dimensional stabilization and the like. Zoned injection and removal offers the potential for spatially controlled reactions and thence final structure.
CONCLUSIONS Biological parts are, in certain respects, the antithesis of most objects fabricated by engineers from commodity materials. The formidable power of natural selection tailors the former to very specific demands, while the latter often perform moderately well in a wider range of uses. With improvements in our design ability and the advent of sophisticated process control in manufacturing, it may become feasible to form highly tailored objects which resemble their natural counterparts. This opens up exciting design opportunities which may have aesthetic as well as functional ramifications.
REFERENCES (1) Ashby, M.F. 1992 Materials Selection in Mechanical Design. Pergamon Press, London. (2) Bolton, A.J. and P.E. Humphrey. 1994. The permeability of wood-based composites. Part I. A review of the literature and some unpublished work. Hotsforschung, 48(suppl.):95-100. (3) Bolton, A.J., P.E. Humphrey and P.K Kavvouras. 1988-1989. The hot pressing of dryformed wood-based composites. Parts 1 to VI. Ending with: Holl,{orschung,43(6):406-410. (4) Chapman, P.F. and Roberts, F. 1983. Model Resources and Energy. Butterworths, London. (5) Haselein, C. 199-. Modelling the formation of advanced natural fibre composites (provis. title). Doctoral Thesis, Oregon State University, Corvallis, Or., USA. (6) Hedberg.S. 1994. Emerging Generic Algorithms. AI Expert. 9 (9): 25-29. (7) Humphrey, P.E. 1992. Pressing issues in panel manufacture: internal behaviour during pressing. Proceedings of the 25th. Particleboard symposium, March 1991, Pullman, WA. (8) Humphrey, P.E., and A.J. Bolton. 1989. The hot pressing of dry-formed wood-based composites. Part Il, A simulation model for heat and moisture transfer, and some typical results. Holzforschung, 43(3): 199-206. (9) Humphrey, P.E. and D. Zavala. 1989. A technique to evaluate the bonding reactivity of thermosetting adhesives. J. Testing and Evaluation (ASTM), 17(6):323-328. (10) Humphrey, P.E. and Ren, S. 1989. Bonding kinetics of thermosetting adhesive systems used in wood-based composites: the combined effect of temperature and moisture. J. Adhesion Sci. and Technology, 3(5):397-413.
(11) Mattheck, C. 1990. Why they Grow, How they Grow:
the Mechanics of Trees.
ArboriculturalJournal. 14,1-17. (12) Neville, A.C. 1993. Biology of Fibrous Composites. Cambridge Univ. Press, Cambridge. (13) ReD, S. 1992. Thermo-hygro-rheological behavior of materials used in wood-based composites. Doctoral Thesis, Oregon State University, Corvallis Or., USA. (14) Van Griethuysen, A.J. 1987. New Applications of Materials. The Hague, Netherlands. (15) Zauscher, S. 1992. Orienting lignocellulosic fibres by means of a magnetic field. Masters Thesis, Oregon State University, Corvallis, Or., USA.
23 Reactive cellulosic fibres rather than reactive dyes D M Lewis and Q G Fan - Department of Colour Chemistry, Leeds University, Leeds LS2 9JT, UK
Abstract In order to overcome the disadvantages of reactive dyeings of cellulose substrates, the concept of reversing the conventional system by incorporating the nucleophilic group in the dye and the reactive group containing the electron deficient carbon atom in the fibres is explored with compound A: 2,4-dichloro-6-(2'-pyridinoethylamino)-s-triazine chloride (DCPEAT) and compound B: 2-chloro-4-(2'-pyridinoethylamino )-6-(4" vinylsulphonyl-anilino)-s-triazine chloride (CPVT). Cotton was pre-treated either by an exhaustion method or a pad-batch method. The dyeing was carried out using the bisaminoalkyl derivative ofC. I. Reactive Red 120. The results indicated that the modified cellulose dyeing process is successful with the quaternary reactive compounds, giving high uptake of dyes in the absence of salt and a high degree of dye-fibre covalent bonding.
1. Introduction Reactive dyes are extremely popular for dyeing cellulosic fibres because of the bright colours, wide shade ranges, easy application and more importantly their excellent wet fastness of the reactive dyeings. However, reactive dyes are vulnerable to hydrolysis under conditions where the dyes are applied to cellulose substrates thus lowering the fixation efficiency resulting in problems of coloured effluents with high salinity harmful to both the environment and the sewage system.
221
222 Physical and chemical processing of fibre and fibrous products
During the reactive dyeing process, two fundamental elements play an important role. They are: • an electron deficient reactive atomic centre, usually the carbon atom(s) adjacent to an electron withdrawing group in the dye structure; • an electron rich nucleophilic atomic centre, usually the hydroxyl group in cellulosic fibres or the amino group in the wool fibre. In order to overcome the disadvantages of reactive dyes, the concept [1] of reversing the above system by incorporating the nucleophilic group in the dye and the reactive group containing the electron deficient carbon atom in the fibre is further explored with two compounds having following structure:
,
CI
N--< W-CH2-CI12-NH~ 0N=(
CI- 'I
N
CI
compound A 2,4-dichloro-6-(2'-pyridinoethylaminoj-s-triazine chloride (DCPEAT)
compound B 2-chloro-4-(2' -pyridinoethylamino )-6-( 4" -vinylsulphonylanilino)-s-triazine chloride (CPVT) Cotton was activated to make it subsequently dyeable by amino or aminoalkyl dyes such as the bis-aminoalkyl derivative of C. I. Reactive Red 120 (MR120) of the following structure:
Dye: MR120 The practical application of the two reagents, DCPEAT and CPVT, involved two steps. Firstly, cotton was treated using one of the reagents under the same conditions as reactive dyeing. The activated cotton was then dyed with modified C. I. Reactive Red 120 (MR120).
Reactive cellulosic fibres
223
Once DCPEAT or CPVT is fixed onto the cotton, the substantivities of anionic dyes to the reactive cotton are greatly improved because of the charge attraction between the cationic pyridinium centre of the reagent and the anionic sulphonate group of the dye. In this way, high exhaustion of dye can be achieved. On the other hand, due to the resistance of amino or aminoalkyl dyes to hydrolysis, it can be expected that this modified cotton dyeing process could greatly decrease the waste of dye by raising the fixation efficiency of dyes. Overall, this system can render the following advantages over the conventional reactive dyeing procedure whilst maintaining the same high wet fastness profiles of the final dyeings: • • •
excellent pad-liquor stability, zero electrolyte use" less washing-off time.
2. Experimental 2.1 Pre-treatment of Cotton by a Long Liquor Process (Exhaustion) Cotton was treated with the reagents" either at pH 9 (DCPEAT) or pH 11.5 (CPVT), at a liquor ratio of20: 1 at 50°C for 90 min.
2.2 Pad-Batch Pre-treatment of Cotton Cotton was padded to 90% pickup with pad liquor containing either Na2C03 20 gil (DCPEAT) or Na3P04 10 gil (CPVT) and Sandozin NIE (Sz) 10 gil, then rolled, sealed and batched for 24 hours at 30°C. Following batching the samples were thoroughly rinsed in running cold water for 5 minutes.
2.3 Dyeing of Activated Cotton Dyeing was carried out using 20/0 owf MR 120 at pH 9 at a liquor ratio of 20: 1 at the boil for 1 hour. Unlike "standard" reactive dyeing" no salt was added.
2.4 Dyebath Exhaustion (OAt) Exhaustion values were obtained by measuring the absorbance of the dye liquor at the maximum absorbance wavelength (Amax = 520 nm for MR120) before and after dyeing.
2.5 Dye Fixation (%) This was obtained by measuring the K/S values of samples before and after soaping which was carried out by boiling in a solution containing Sandozin NIE (Sz) 5 gil and sodium carbonate 2 gil for 15 minutes.
224 Physical and chemical processing of fibre and fibrous products 3. Results and Discussion The results showing the effect of the pretreatment and subsequent reactive dyeing procedures on dye exhaustion and fixation are shown in Figures 1- 4.
100
~ o ........
80 60 40
20
o
untreated
4 %owf
6 %owf
8°A>owf
DCPEAT Concentration I
Figure 1
[J
EXh~usti~nOfDye. Fixation of Dye~
Effect of DCPEA T concentration (exhaust application) on dyeing
100r
~ o ........
1-----I
20 gIL
30 gIL
40 gIL
50 gIL
DCPEAT Concentration
~I=:J Exhaustion of Dye III Fixation of Dye Figure 2
Effect of DCPEAT concentration (pad-batch application) on dyeing
Reactive cellulosic fibres 225
;e 108~' o
~
60
4020 ~
O~--4 %owf
6 %owf
10%owf
8O/oowf
CPVT Concentration
Figure 3
Effect ofCPYT concentration (exhaust application) on dyeing
100 r '
\---
t
80l L
60t f
40t 20f i ~ L
OL-- 20 gIL
30 gIL
40 gIL
50 gIL
CPVT Concentration Exhaustion of Dye
Figure 4
~
Fixation of Dye-I _. .
-------~
Effect ofCPYT concentration (pad-batch application) on dyeing
It is obvious that the modified cotton dyeing process is successful especially where CPVT was applied by the exhaust method at concentration ~ 8% owf It is especially worth noting that the high degree of dye exhaustion and fixation (> 95%) was achieved in the absence of salt. The likely reaction scheme is shown in Scheme 1, in the case of CPVT application.
226 Physical and chemical processing of fibre and fibrous products
+
HO-eell
j
Scheme 1
4. Reference [1] I). M. Lewis and X. P. Lei, Book of Papers of American Association of Textile Chemists and Colorists, Annual Conference and Exhibition, Atlanta, (1992)259.
24 The treatment of cotton cellulose with Trichoderma reesei engineered cellulases A Cavaco-Paulo,* L Almeida* and D Bishop'[ - *Dep Eng Textil, Universidade do Minho, 4810 Guimaraes, Portugal; tDept Textiles & Fashion, De Montfort University, Leicester LEI 9BH, UK
I-INTRODUCTION Controlled enzymatic hydrolysis can provide ecologically acceptable routes to finishing cellulosic textiles (1). The most widely used application is the replacement of the stone washing process to produce the fashionable aged appearance of denims. Other cellulase treatments are used to improve the appearance of cotton fabrics by removing fuzz fibre and pills from the surface. Such processes also modify the fabric mechanical properties in ways which lead to the perception of improved handle, particularly of improved softness (2). Increasing use is being made of cellulases in domestic fabric washing products where they are claimed to aid detergency (3), as well as removing damaged fibrillar material from cotton fibre surfaces. This improves fabric appearance, colour brightness and softness (1). Cellulase enzymes have a specific catalytic action on 1,4-(3-D glycosidic bonds of the cellulose polymer, which apart from 6-8% of moisture, is essentially the sole constituent of scoured and bleached cotton. Cellulase, by definition, consists of a complex mixture of three major enzyme types: endoglucanases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91) and cellobiases (EC 3.2.1.21) (4). A general model for action of these enzyme components on cotton cellulose is that the endoglucanases (EGs) cause random hydrolytic chain scission at the most accessible points of long cellulose polymers, while the cellobiohydrolases (CBHs) split cellobiose from the "non reducing end" of cellulose molecules. The cellobiase hydrolyzes cellobiose to glucose. Improvement in purification and analysis techniques have lead to the isolation and study of the pure components and new models have been proposed. It is now clear that the mode of action of the pure cellulase components cannot be classified simply as "endo" or "exo" in type (5). A synergism between the different components has been observed, but the detailed mechanism of their action is not yet fully understood (5).
227
228 Physical and chemical processing of fibre and fibrous products
The cellulolytic complex of Trichoderma reesei is one of the most extensively investigated fungal enzyme systems (5). It is known to contain at least one cellobiase, CBH I, CBH II, EG I and EG Il. The genes of these hydrolases canbe manipulated such that some activities are deleted to produce new cellulase combinations (6). Furthermore it has been reported in recent literature (7, 8) that two more cellulase components known as EG III and EG V are always present in the crude mixtures from Trichoderma reesei. In the present work, cotton degradation was studied after short (as made in textile applications) and extended periods of cellulase hydrolysis. Comparisons were made between the effects of crude cellulase mixture from Trichoderma reesei (TC), and mixtures in which the activities of EO I and EO II (C-EGs) or the activities of CBH I and CBH II (C-CBHs) had been deleted. 2-EXPERIMENTAL Cellulases: All enzyme samples are from Primalco Ltd., Rajamaki, Finland. These were: CE 883042 (Total crude), CE 519/92 (Crude-EGs) and CE 523/92 (Crude-CBHs). Enzyme Activity: The activities per gram of crude were measured towards carboxymethylcellulose (CMC), phosphoric acid swollen Avicel (PASA) and cellobiose, at pH=5, as described previously (9). The activity towards scoured cotton fabric was also determined by measuring weight loss. Cotton Satnples: All samples used were 100% cotton fabrics after industrial scouring and bleaching. Treatments~
Shm1: The fabrics were treated with the enzyme (dilution factor, 1/500) using the ratio: l g of fibre to 20 ml of bath; buffer pH = 4.8 (acetate, 0.5 M), temperature 50 oC. The fabrics were treated during 30, 60, 120 and 240 minutes. The treatments were stopped by addition of a solution of sodium carbonate (10 %). The fabrics were washed after treatment with hot and cold water. The treatments were carried out in the stainless steel pots of a Linitest machine rotating at 65 rpm. Long: The fabrics were treated with the enzyme (dilution factor, 1/60 for the CrudeCBHs and 1/120 for the Total crude and Crude-EGs) using the ratio: l g of fibre to 50 ml of bath; buffer pH=4.8 (acetate, 0.5 M), temperature 50 0C. The fabrics were treated without agitation for 3, 6 and 13 days in a beaker inside an incubator. The fabrics were washed after treatment with hot and cold water. Weight Loss was determined by weighing the samples before and after treatment, after conditioning for 24 hours at 20°C and 65 % of relative humidity. Mean Chain Len~th: Mean chain lengths were determined by the weight difference taken from weight loss calculations and measuring in solution the reducing ends of the leaving sugars as cuprous neocuproine complex in alkaline media at 95 0C. Cotton Reducing Power: The reducing ends of the cotton fibres were also quantified via the cuprous neocuproine complex in alkaline media at 95 0C. Viscosity nleasurements: Fluidity and specific viscosity were measured as described (10), on cuproethylenediamine (CED) solutions of cotton cellulose. Breaking Load Loss (%) was measured relative to the untreated fabric in an Instron machine, model 4204. Bending Hysteresis of the Fabrics was measured on KES-FB2 from Kato Tech. Co, Ltd. Crystallinity Index by X-ray diffraction measurement was obtained by the method described by Chidambareswaran and others (11). The X-ray diagrams were obtained using a Philips Analytical PWI7IO diffractometer with a X-ray tube using Ni filtered Cu Ka,radiation and the limits were 10° and 3()O.
Trichoderma reesei 229
Scannin~ Electron Microscopy Photo~aphs (Leica Cambridge Stereoscan 360) were taken after 2 minutes of gold metalization (Bio-Rad SC 502). Enyironmental Scannin~ Electron Microscemy (Electron Scan, Mod 3) A video-tape was recorded during the drying of cotton fibres, which had never been dried after the cellulase treatment. The pressure of the chamber during drying was brought down from 6 Torr to 2,5 Torr.
3-RESULTS AND DISCUSSION The measured activities of C-CBHs towards CMC and of C-EGs towards PASA were greater than those of TC (tab. 1). These results illustrate the expected increments in classical endo and exo type activities for C-CBHs and for C-EGs respectively (12). While TC was found to have lower measured activity than C-EGs towards cellobiose, CMC and PASA, it caused consistently greater cotton weight loss than C-EGs in both long and short treatments (tab. 1 and fig. 1). This apparent contradiction shows that care should be exercised in predicting cellulase activity on cotton, from data obtained using other forms of cellulose or its derivatives. The result also points to the importance of synergy between the various components in the hydrolysis of cotton cellulose. Substrate \ Enz me Cellobiose a) CMC b) PASA b)
The deletion of CBH I and CBH II activity from the total crude mixture dramatically reduced the rate of cotton weight loss (fig. 1) thus confirming the importance of exo type activity in solubilization of the polymer. The deletion of EG I and EG II activity also caused some reduction in the rate of cotton weight-loss, and this is expected from the synergy between endo and exo type activity. Nevertheless, it is clear that C-EGs and TC can both bring about complete dissolution of cotton cellulose, albeit in somewhat longer reaction times, as shown by the SEM photos after 6 days of degradation (fig. 2a). The surprisingly high activity of C-EGs may possibly due to the previously reported synergy between the two CBH components (13) and, or, to some endo activity in our C-EGs. The latter may be accounted for either by remaining EGs such as EO III and V or by some endo characteristics of the CBHs themselves (5, 14). Weight Loss (%) - LONG TREATMENT 80
~------------.
--a--0~
Total Crude Crude-CBHs Crude-EGs
Weight Loss (%) - SHORT TREATMENT
3.....------------2
10 20 100 200 Time (days) Time (min) Figure 1 - Relation between weight-loss and treatment time.
300
230 Physical and chemical processing of fibre and fibrous products
In the short hydrolysis, the relative activity of C-CBHs is higher and the relative activity of C-EGs is lower, when compared with the longer hydrolysis. This seems to be due to the rotation of the reactor where the hydrolysis takes place. The agitation is known to increase the weight loss ( 15) and to have a synergistic action with an endo type cellulase (16). However the main structure of the fibres remains unchanged (fig. 2b).
Figure 2 a) Scanning electron microscopy photographs of long treated fibres
Figure 2 b) Scanning electron microscopy photographs of short treated fibres
SEM photos (fig. 2) showed that the short treatment caused the changes only at the fibre surface, while the long treatments also affected the internal structure of the fibre.
Trichoderma reesei
231
Mean Chain Length Leaving Sugars - SHORT TREATMENT
4...------------------.., --0--0-3
~
Total Crude Crode-CBHs Crode-EGs
2
o
100
200
300
Time (min) Figure 3 - Relation between mean chain length of the leaving sugars and treatment time.
In treatments with C-CBHs, the mean chain length of the leaving sugars (fig. 3) decreased from 3.4 (30 min) to 1.7 (240 min) showing endo character when compared with the other mixtures where the mean chain length was about 2 throughout. The results show that the soluble cellooligosaccharides resulting from TC and C-EGs hydrolysis are readily broken as they are produced to a mean length of 2, while those resulting from C-CBHs are slowly broken. The slow decrease of the mean chain length of the soluble cellooligosaccharides caused by C-CBHs is believed to be due to the lower cleavage frequencies of EGs compared with those of CBHs (14), on the soluble cellooligosaccharides. The low cellobiase activity of these cellulase mixtures is also reflected in the results. Specific Viscosity (0 sp , - LONG TREATMENT
Cotton Reducing Power (mg gli/g eel)
1 , 2 . . . - - - - - - - - - - - - -.....
0,7
~====~~=====n---""
1,0 0,8 0,6
0,4
- - 0 - Total Crude --0-- Crode-CBHs
0,6 Total Crude Crode-CBHs Crode-EGs
°
~
Crude-EGs
0,5 ............-........--..--...................-...........-...........--1 20
40
60
80
0
20
40
60
80
Weight Loss (%) Weight Loss (%) Figure 4 - Relation between cotton reducing power and between specific viscosity with weight-loss
In spite of causing low weight loss, the C-CBHs enzyme produced higher concentrations of terminal reducing groups in the cotton fibres and a large decrease in the viscosity of their CED solutions (fig. 4). TC and C-EGs also produced appreciable quantities of terminal reducing groups but the viscosity of CED solutions of the treated celluloses changed only slightly, even at a weight loss greater than 50 %. These results confirm the increased endo type activity of C-CBHs in causing random cellulose chain scission, (hence a large reduction in CED solution viscosity) and the sequential nature of exo type activity, (hence little change in mean polymer chain length or CED solution viscosity). These effects are further illustrated in figure 5, where an increasing slope of the plot of cotton fluidity versus cotton reducing power indicates increasing randomness of cellulolytic attack. Thus C-CBHs is shown to cause the most random hydrolysis and CEGs to cause the most localized attack, with TC having an intermediate effect. While the randomness of cellulolytic action of different cellulases is commonly measured in this
232 Physical and chemical processing of fibre and fibrous products
way by using CMC as a soluble substrate (17) these relationships have not previously been reported for cotton cellulose. Fluidity (lin sp 1,9
1,8
D
1,7
o
1,6
6
1,5 1,4
- LONG lREATMENT
~--~---------------.
e:===-.!r---6--__J
b ....
-+---.~......----r--r----r-~_,.-~....,.-_r_..,.___t
0,4
0,6
0,8
1,0
1,2
Cotton Reducing Power (mg gli/g eel) Figure 5 - Relation between cotton reducing power and specific viscosity
It is interesting to note that the relative randomness or localization of cellulase action on cotton and the extent of the produced damage (fig. 2) did not change the measured crystallinity of the fibre (tab. 2). A similar result has previously been observed for complete cellulases (18). Thus the present work tends to confmn the view that the action of cellulase is not confined initially to non-crystalline regions, irrespective of the cellulase components present. It has also been reported (19) that the hydrolysis of cellulose by cellulase concentrates of Trichoderma viride is first order with respect to substrate. This suggests uniform reactivity of (crystalline and amorphous) cellulose and therefore implies that no change in crystallinity should result from cellulase hydrolysis. 1 ABLE 2 - CrystallInIty Index (WeIght-Loss) Untreated 83% (0%)
TC C-CBHs C-EGs 240min 240min 240min 83% (23%) 83% (09%) 83% (1,8%)
TC
6 days 83% (63%)
C-CBHs 6 days 83% (3%)
C-EGs 6 days 81% (52%)
Cellulase hydrolysis reduced the tensile strength cotton fabrics as shown in figure 6. Recently a possible relation between loss in tensile strength and endo activity has been reported (16). The present results support this to the extent that C-CBHs caused much greater strength loss at low weight loss than the other cellulase mixtures (fig. 6). On the other hand C-EGs did not show reduced strength loss for a given weight loss in comparison with TC. This may however be due to the effects of the residual EGs (III and V) in the present C-EGs sample. Breaking Load Loss (%) - LONG lREATMENT Breaking Load Loss (%) - SHORT lREATMENI 100 40 --0-- Total Crude 80 30 ---0-- Crode-CBHs Total Crude Crode-CBHs Crode-EGs
60 40
~
Crode-EGs
20 10
20 0 .......-.................-.---.--...--........-....--.......
o
20
40
60
80
o .w-=~=!:~-....----.-J 0
1
2
Weight Loss (%) Weight Loss (%) Figure 6 - Relation between breaking load loss and weight -loss
3
Trichoderma reesei
233
We have observed before (16) that for short cellulase treatments the changes in bending hysteresis of cotton fabrics, related to internal friction of the fibrous assembly, are due to the formation of microfibrils on (or their removal from) the fibre sutface. The small changes in bending hysteresis, for the short treatment, are consistent with what can be seen in SEM photos (fig. 2b). The large decrease in bending hysteresis for higher weight loss (long treatments) observed here is mainly due to the reduction in the number of fibres in a yarn and reduction of its diameter, as shown by SEM photos (fig. 2a). In as far as low bending stiffness/hysteresis is correlated with perceived softness, TC and C-EGs would be preferred over C-CBHs for their cotton fabric softening effects. This is consistent with a previously reported observation (16) that endo activity with high mechanical action led to the formation of microfibrils on fibre surface and caused increased inter-fibre friction, and hence an increase in bending hysteresis.
TABLE 3 • Bending Hysteresis (gf.cm/cm) Untreated 0.050
TC 240min 0.043
C-CBHs 240m in 0.053
C-EGs 240min 0.045
TC 2 days 0.015
C-CBHs 2 davs 0.048
C-EGs 2 days 0.019
Examination of the wetting (swelling) and drying (collapsing) behavior of untreated and cellulase treated cotton fibres by ESEM revealed that the fibre twisting and retraction behavior in untreated fibres is absent after long cellulase treatments. It is therefore postulated that a cellulase treatment may be beneficial to achieving stable, fully-relaxed dimensions in knitted cotton textiles.
CONCLUSIONS Crude cellulases from Trichoderma reesei have been used to investigate the mechanisms of cellulase hydrolysis of cotton cellulose in the form of scoured and bleached fabric. Predictions of the general model for cellulase action were largely confirmed. An EG "rich" crude, from which CBH I and CBH II activity had been deleted showed typical endoglucanase activity, causing random chain scission which led to a rapid rise in fluidity and high strength loss but did not solubilize cotton. A crude, from which EG I and EO II activity had been deleted, caused less random hydrolysis (i. e. increased exo type activity) than the total crude mixture. Nevertheless, it solubilized cotton as effectively as the total crude mixture. This C-EGs did however retain some endo type activity which was possibly due to the endo character of both CBH I and II and also due to the undeleted EO ill and V. Since it is important to maintain fibre strength in most textile applications it does not appear to be appropriate to increase the endo activity of cellulases intended for cotton processing. There may however be advantages for low endoglucanase or endoglucanase free mixtures especially where substantial weight loss may be required to achieve softness or de-pilling without serious loss of strength. The short treatments, as used in textile applications, keep the changes at the fibre surface while the long ones affect the internal structure of the fibre. ESEM studies have revealed that the fibre retraction and twisting behavior of untreated fibres is absent after long treatments.
ACKNOWLEDGMENTS We thank Primalco Ltd for kindly supplying the special crude cellulase mixtures used in this work. We also thank Dr. C. Carr of UMIST and Mr. C. Gilpin of the Electron Microscopy Unit, Biological Sciences Department, Manchester University, for their
234 Physical and chemical processing of fibre and fibrous products
help with the ESEM work. The authors are grateful to the British Council/Portuguese Universities Rectors Council for the grants under the Treaty of Windsor scheme which enabled the development of this paper.
REFERENCES 1 .. Cavaco-Paulo, A. and Almeida, L., (1994) Nova Textil, 32, 34-38 2·· Almeida, L. and Cavaco-Paulo, A., (1993) Melliand Textilber., 74, 404-407 3 .. Murata, M., Hoshino, E., Yokosuka, M. and Suzuki, A., (1993) Jour. Am. Oil Chem. Soc., 70, 53-58 4 - Enzyme Nomenclature (1978), Academic Press, New York 5 .. Enari, T. and Niku-Paavola, M., (1987) CRC Critical Reviews in Biotechnology, CRC Press 5(3) 67-87 6 .. Nevalainen, H., Pentilla, M., Harkki, A., Teen. T. and Knowles J., (1991) In Molecular Industrial Mycology, chap. 6, 129-148, edited by S. Leong and R. Berka, Mercel Dekker 7 - Ward, M., Wu, S., Dauberman J., Weiss, G., Larenas, E., Bower, B., Rey, M., Clarkson, K and Bott R., (1993) In Trichorderma reesei Cellulases And Other Hydrolases, edited by P. Suominen, T. Reinikainen, Foundation for Biotechnical and Industrial Fermentation Research - Finland, 8, 153-158 8 - Saloheimo, A., Henrissat, B. and Pentilla, M., (1993) In Trichorderma reesei Cellulases And Other Hydro lases, edited by P. Suominen, T. Reinikainen, Foundation for Biotechnical and Industrial Fermentation Research - Finland, 8, 139-146 9 .. Evans, E., Wales, D., Bratt, R. and Sagar, B., (1992) J. Gen. Microbiol., 138, 1639-1646 10 - Standart Proposal UNE 57.039 11 - Chidambareswaran, P., Sreenivasan S. and Patil N., (1987) Textile Research Journal, April, 219-222 12 - Ghose, T., (1987) Pure and Applied Chem., 59, 257-268 13 - Nidetzky, B., Steiner W., Hayn, M. and Claeyssens, M., (1993) In Book of Abstracts ofTRICEL 93, A12, June 2-5, Majvik, Finland 14 - Biely, P., Vrsanka M. and Claeyssens, M., (1993) In Trichorderma reesei Cellulases And Other Hydro lases , edited by P. Suominen, T. Reinikainen, Foundation for Biotechnical and Industrial Fermentation Research - Finland, 8, 99-108 15 - Cavaco-Paulo, A. and Almeida, L., (1994) Biocatalysis, 10 353-360 16 - Cavaco-Paulo, Almeida, L., (1994), Paper presented at 204th ACS Meeting - Cell Div., S. Diego, CA. 17 - Ramos, L., Nazhad, M.and Saddler, J., (1993) Enz. Microb. Tee., 15,1-11 18 - Finch, P., (1985) In Cellulose Chemistry and its Applications, edited. by T. P. NeveU, S. H. Zeronian, pp. 312-343, John Wiley & Sons 19 - Sagar, B. F. (1985) In Cellulose and its Derivatives: Chemistry, Biochemistry and Applications, edited by J. F. Kennedy, G. O. Phillips, D. J. Wedlock & P. A. Williams, pp. 199-207, Ellis Horwood
25 Characterisation of paperboard packages designed for liquid containment C J Harrold and J T Guthrie - Polymer Group, Department of Colour Chemistry, University of Leeds, Leeds LS2 9JT, UK
Introduction Many types and forms of polymers are used extensively in today's packaging industry. The need for extended self life along with special packaging criteria, means that the technology required has to change to meet these needs. This is clearly evident in the packaging of liquid products. Liquid producers require packages that are cheap, strong, aesthetically acceptable, and environmentally sound. By using virgin and recycled paperboard in conjunction with advanced multi-layer polymer coatings, these criteria can be met by the packaging company. The main polymers that have been used to fulfil these requirements are: • Poly(propylene) • Poly(ethylene) • Ethylene-vinyl alcohol copolymer These polymers have been adapted, using new coating technology, to produce various types of coatings that give the barrier properties that enable many types of liquids to be contained. These coating formulations are now established for the packaging of low to medium 'aggressive' liquid products. However, the need to pack more 'chemically aggressive' liquids is growing and so new coating technologies will need to be developed by the packaging industries. This paper shows a range of results from various techniques that have been used to characterise three packaging systems. Characterisation of these products is a necessary step for future advancement. The results will show why and how more 'chemically aggressive liquids' escape from these types of cartons.
235
236 Physical and chemical processing of fibre and fibrous products
Experimental The cartons used in this study were manufactured by Field Group, Newcastle. The cartons were made of virgin paperboard manufactured by Enzo-Gutzeit OY, Finland. The paperboard was coated on both sides. The upper surface of the paperboard was coated with 20 grams of poly(ethylene). This surface was used for printed material on the outside of the carton. The lower surface was coated with a co-extrusion of poly(ethylene) and ethylene-vinyl alcohol copolymer. This surface was the barrier to liquid escape on the inside of the carton. The liquids used in this study were: • • • • • • • • •
Mr. Muscle window cleaner Werner & Mertz Frosch Spulmittel Kanzentrat cone. dishwash McBride liquid detergent code:64140 Werner & Mertz Frosch Essigreiniger bath/kitchen cleaner McBride Q-matic liquid detergent code 64239 Vernel fabric conditioner Reckitt & Colman Naison Verte fabric conditioner x 4 German softlan fabric conditioner Comfort fabric conditioner
The carton system and the liquids to be contained therein were characterised using various techniques available to the Colour Chemistry Department at the University of Leeds. The characterisation techniques used were:
•
Scanning Electron Microscopy (S.E.M.) - The Scanning Electron Microscopy used in the Department of Colour Chemistry is a JOEL 820 with x-ray mapping capabilities.
•
Differential Scanning Calorimetry (D.S.C.) - The instrument used was a DuPont 2000 unit. The Program used was:
•
Room temperature to 300°C at a rate of 1DoC per minute. A nitrogen gas purge of 3 D.2dm per minute was used.
•
Wetting Studies - Zisman and Kaelble Manipulations The 'critical surface tension' and the 'solid wetting tension' of the barrier coating surface was measured using the Zisman and Kaelble approaches. With the Kaelble method the contribution of polar and dispersive forces to the surface activity is measured. With the Zisman method the overall surface activity is measured. - Surface Tension Measurement Using a du Nouy tensiometer with a platinum ring the surface tension of the various liquids was measured.
•
Particle Size Analysis - The particle size of the test liquids was measured using a Coulter" multisizer. The experimental procedure used was: • • • •
1g of test liquid in 150g of electrolyte Electrolyte: lsoton 2, azide free, balanced solution Run time of 100 seconds Number difference and number cumulative methods for manipulation of data
Paperboard packages
•
237
Wicking Studies - In this analysis the paperboard was used as a chromatography plate. Samples of the coated paperboard were placed into the various test liquids and the rate of liquid uptake measured.
These techniques were employed to try and gain information on why certain liquids could not be contained in this type of carton system.
Results and Discussion The main technique used to examine the carton system was scanning electron microscopy. This high powered microscopy was used to give information on the micro structure of the coatings and seal areas within the carton. Figure 1 shows an example of a micrograph produced using this technique. Figure 1 shows how the barrier coating has fractured to reveal the cellulosic board underneath. In these areas it is evident that high stresses on the coating system cause failure. \
•\
\
Figure 1
Micrograph of a seal in a carton that has failed to contain Mr Muscle window cleaner
Differential scanning calorimetry was used to examine the thermal charactenstics of the barrier coating used on the inner surface of the cartons. The resulting thermograph can be seen in Figure 3. This thermograph shows temperature bands where the various layers within the barrier coating melt. These temperature are important in the carton sealing procedure. If too Iowa
238 Physical and chemical processing of fibre and fibrous products
temperature is used then polymer melt will not occur and seal areas will not be covered. If too high a temperature is used blistering of the polymer will occur. The temperatures shown in thermographs of the polymer coatings can be related to the temperatures measured in carton sealing. -0.2 -0.4 -0.6
'iii
~
I
-0.8
..
: :::a:
-1
ii:
akAui nment 103°C - Melt for poly(ethylene) Layers 124°C - Melt for ethylene-vinyl alcoholl oly(ethylene) co-extruded region 163°C - Melt for ethylene-vinyl alcohol polymer layer
-1.2 -1.4
+------+ I -----+-------+------+-----+--------f
o Figure 3
50
100
150
200
250
300
Temperature (OC) Thermograph of the co-extruded poly(ethylene)/ethylene-vinyl alcohol barrier coating
Another way of characterising the surface of the barrier coating is through wetting studies. These involve manipulation of measured surface properties to gain a critical value of surface tension for the polymer surface. The two manipulative techniques used were the Zisman plot and the Kaelble plot. The results obtained using these two methods can be seen in Table 1.
Table 1 Summary of Results showing the Critical surface tension, Ye, and the solid wetting tension,
rs, for the barrier coating.
Board
Zisman Critical Surface -1
Kaelble Solid Wetting -1
Tension (mNm ')
Tension (mNm ')
Unheated barrier coating
27.12
28.91
Flamed sealed barrier coating
28.85
32.35
The results in Table 1 clearly show that the barrier coating is 'activated' in the seal areas. That is, the wetting tension is higher so allowing a wider range of liquids to spontaneously wet the surface. This can be seen when we look at the surface tensions of the liquids to be contained, Table 2. Looking at Table 2, the liquids that cannot be contained all have surface tensions lower than Ye and 1s in the flame sealed areas of the barrier coating. Therefore, in these areas, the liquids will spread across the seals. Any defects in the sealed areas will then be open to failure. Another physio-chemical property to be measured was particle size. Table 3 shows the mear particle sizes of several test liquids used in this study.
Paperboard packages 239
Table 2 Surface tensions for a selection of the test liquids Liquid
Mr. Muscle window cleaner Werner & Mertz Frosch Spulmittel Kanzentrat conc. dishwash McBride liquid detergent code:64140 Werner & Mertz Frosch Essigreiniger bath/kitchen cleaner McBride Q-matic liquid detergent code 64239 Vernel fabric conditioner Reckitt & Colman Naison Verte fabric conditioner x 4 German softlan fabric conditioner Comfort fabric conditioner Fail Pass
Surface Tension (mNm- 1) 27.03 30.00 30.04 30.50 34.74 34.83 36.28 39.37 44.19
=Liquid can not be contained =Liquid can be contained
Table 3 Particle Size Results Test Liquids
Mean Particle Size
blm)
Mr.Muscle window cleaner
1.44
Werner & Mertz Frosch Spulmittel Kanzentrat conc. dishwash
1.05
McBride liquid detergent code:64140
1.70
Werner & Mertz Frosch Essigreiniger bath/kitchen cleaner
2.75
McBride Q-matic li_guid detergent code 64239
3.67
Vernel fabric conditioner
9.02
Reckitt & Colman Naison Verte fabric conditioner x 4
4.59
German softlan fabric conditioner
13.37
Comfort fabric conditioner
7.99
Fail Pass
=Liquid can not be contained =Liquid can be contained
From Table 3 we can see that the liquids with a mean particle size below 3 microns fait whereas liquids with a mean particle size above 3 microns pass. This suggests that a liquid containing a high proportion of very small particulates will be difficult to contain. The final characterisation technique used in this study was wicking analysis. This technique examines what happens after the liquid has passed through the defect in the barrier coating. It measures how quickly the liquid passes through the cellulosic board. An example of the results obtained with this technique can be seen in Figure 4. The wicking study showed that the liquids that were difficult to contain were also the liquids that wicked through the cellulosic paperboard quickly.
240 Physical and chemical processing of fibre and fibrous products
0.5
I!
~ c
........Uquid 1
0.4
~Uquid2
-Ir-Uquid3 ..... Uquid4 ..... Uquid5 -'-Uquid6 -+-Uquid7 -Uquid8
~ 0.3 ~
-r
O.2
t:
~
C
0
~-----+-----+-----+------+-----+---------; I
o
50
100
150
200
250
300
Time (Hours)
Figure 4 Results of a Wicking Study carried out on Enso SBS Board
Conclusions This study was carried out with two clear objectives. Firstly, to establish how carton failure occurs and with which types of liquids. Secondly, to investigate how the liquids that fail can be separated from liquids that pass by their physio-chemical nature. The results that have been obtained have shown that: • • • • • •
liquids escape the carton assembly via defects in the barrier coating the defects are caused by fracturing of the barrier coating in the seal areas and by poor polymer flow over the gusset point at the base of the carton the defects are a result of the mechanics of sealing of the carton rather than any inherent faults in the polymers used there is no trend between type of liquid packaged and carton failure the liquids that are most likely to fail have low surface tensions and/or small mean particle size distributions liquids that fail tend to wick through the paperboard quicker than liquids that pass
These observations show that to contain a wider range of liquids the mechanics of sealing the carton must be addressed. Until then it is possible to predict how 'aggressive' a liquid will be towards the carton assembly by measuring it's surface tension, mean particle size, and wicking rate. The results of these three tests can then be compared to results obtained for liquids that are known to pass or fail containment.
References [1] [2] [3] [4] [5] [6] [7] [8]
L.$tepek, Polymers as Materials for Packaging, Ellis Horwood Ltd, 1987. Barrier Polymers and Structures, Various. American Chemical Society, 1990. Reference Manual for the CaULTER® Multisizer, issue F. D.Campbell & J.R.White, Polymer Characterisation, Chapman & Hall, 1989. D.J.Shaw, Introduction to Colloid and Surface Chemistry. 3rd Edition, Butterworths, 1980. C.A.Finch, Poly(Vinyl Alcohol) - Developments. Wiley, 1992. l.H.Sperling, Introduction to Physical Polymer Science. 2nd Edition, Wiley, 1992. Physiochemical Aspects of Polymer Surfaces, Volume 1 & 2. Proceedings of the International Symposium on Physiochemical Aspects of Polymer Surfaces, August 2328, 1981, in New York City, New York. Plenum Press, 1983.
Paperboard packages
[9]
241
L.Mascia, Thermoplastics, Materials Engineering. 2nd Edition, Elsevier Applied Science, 1989.
26 Biochemical investigation of cellulosic and ligneous materials in museum collections M A Robson - Studio, 29 Park Avenue, Birmingham, BI8 5ND, UK
ABSTRACT
Cellulose is the main structural component of plant cell walls. It is recycled relatively quickly which emphasizes both its susceptibility to attack by organisms and the range of organisms able to do so and utilize the breakdown products. It occurs as the major constituent of wood (and thence by processing, to paper and chipboard), and similarly, as plant fibres used in textiles; for example flax and jute are phloem fibres, sisal and manila are leaf fibres and cotton is made up from seed fibres. Cellulose is often chemically modified in the production of derivative forms for particular uses. Such uses are textiles (rayon is regenerated cellulose), packaging films (such as cellophane), photographic film (cellulose nitrate and acetate), and as thickeners, fillers and extenders (eg. carboxymethyl cellulose) in adhesives foods and emulsion paints. Many of these forms of cellulose are susceptible to biological attack. This depends on the presence of suitable environmental conditions for colonization by organisms and also on the physical and chemical form of the cellulose which will vary depending on the type of product being made. Physical break up of cellulose fibres by grinding can increase susceptibility. When paper is manufactured the cellulose is delignified, yielding a more susceptible material. Lignin protects cellulose from microbial attack as shown by the greater resistance of sisal or jute fibres compared to cotton. (1) Enzymes released by organisms can continue to break down materials even when the cells which produced them are removed or no longer alive. 243
244 Physical and chemical processing of fibre and fibrous products
Numerous studies have been reported on the deterioration of works of art due to growth of fungi. Staining of wood does not significantly alter the strength of the wood but does reduce its value. Ethnographic artefacts in anthropological collections are collected because they are part of the description of an evolving race of men whose traditional skills may otherwise be lost. The organic nature of the raw materials used for their manufacture (eg. wood, fibre, leaves, bark, bamboo, rattan etc) are difficult to preserve and are particularly susceptible to deterioration by biological agents. Similarly, are collections of archival material, cellulosic textiles natural history specimens and photographic film. Museums are a special category of buildings, with respect to risk of damage caused by organisms. Good housekeeping and suitable environmental control, which should be the basis of all biodeterioration prevention are of paramount importance in the museum environment and cannot be over emphasised. An ecological approach is relevant to the biodeterioration of collections. Moisture content and nutrients are both important when considering remedial measures or predicting the susceptibility of an artefact to biodeterioration. Regular inspection of collections in storage and on display will safeguard against further biological infestations. INTRODUCTION Collection management of lignocellulosic materials in museums has in the past relied solely on the expertise of both the curator and conservator. Identification of the nature and extent of the conservation of such collections and the special problems and needs that exist, will today forge interdisciplinary alliances between the scientist, technologist, conservator and curator worldwide. Such collections consist of archaeological and historical wood, ethnographic material, natural history specimens, archival and library material and photographic documents and film. Traditional methods and techniques of preservation of cellulosic ethnographic material are time consuming. Infestation eradication is carried out where appropriate, and worm-eaten wood and moth-infested textiles are restored. Fungus-induced stains on archival and library material and natural history specimens are conserved. Periodic checks are carried out in the stores for insect attack, particularly silverfish on tapa or bark cloth, and the larvae of the female furniture beetle on objects made from wood, bamboo, cork, papier machie, cane and rushwork. Damp conditions can induce mildew and mould and will dissolve any binding adhesive in cloth and in any painted decoration.
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DETERIORATION In time, all objects deteriorate because of the materials that are used in their manufacture gradually wear out or break down. Lignocellulosic collections are very susceptible to degradation and by handling. Such collections are altered almost imperceptibly by the environment in which they are kept. The main factors which affect materials are light, temperature, humidity and air pollution. The process of deterioration is inevitable and irreversible and is merely slowed down by controlling the environment. Light will fade dyes or pigments and embrittle fibres. A reduction in light level to 50 lux will help protect against such damage.
RELATIVE HUMIDITY Sensitive organic materials are also susceptible to relative humidity which relates to the amount of moisture in the air. Moisture content varies with temperature. Hot air retains more moisture than cold air. With a lowering of temperature the air dispels water as droplets which may form on cold surfaces. The term "relative humidity" is used as a measure of the moisture content of air. Relative humidity relates to the amount of moisture in a given quantity of air at a certain temperature, to the maximum amount of moisture the air can hold at that temperature. The organic materials in lignocellusosic collections contain a certain amount of water in their structure. This amount alters according to the amount of moisture in the atmosphere. If the air is very dry they will give up moisture, and if damp, they will absorb it. Cellulosic fibres and paper become brittle if the air is dry and wood will crack and warp. When the air is damp, most organic materials swell, although canvas and other textiles made from a twisted thread will shrink and become taut. If the amount of moisture in the air frequently fluctuates, the dimensions of the object will alter. This continuous change puts a strain on the structure of the material and it may start to break up. The strain is greater if there are several different materials combined together in one object as they change directions by different amounts. For example paint will flake off cellulosic fabrics such as canvas because it does not move as much as the canvas which will stretch and shrink with changes of relative humidity. Veneer will lift off wooden furniture because the veneer and the wood of the underlying structure swell and shrink different amounts in different directions. Moisture in the air also encourages mould to grow.
246 Physical and chemical processing of fibre and fibrous products
A steady relative humidity should be maintained between 50 and 60 per cent, preferably 55 per cent. Above 65 per cent, mould will grow; below 45 per cent organic materials become brittle and shrink.
TEMPERATURE The deterioration of a material is caused by chemical reactions taking place in it. If the room temperature is high these reactions will take place much faster. Mould and fungi flourish in warm temperatures and stagnant air. All materials expand and contract with changes of temperature but they do this to different degrees. Thus if different materials are used together in one object, the change in dimension can cause problems. The temperature of a room can affect an object more indirectly by altering the humidity of the air. The temperature should be as constant as possible throughout the day and night.
AIR POLLUTION Air pollution consists of fine dust and gases. Some gases such as sulphur dioxide, nitric oxide and nitrogen dioxide form acids with the moisture in the air which can harm materials such as textiles. Sunlight mixed with car fumes makes ozone which will destroy photographs, degrade textiles and cause some pigments to change colour. Dust not only soils the object but can be acidic. There is also internal pollution generated from materials or objects within the store or display case. For instance rubber flooring and some dyes in textiles give off sulphur compounds which will degrade cellulosic fibres; photocopiers produce ozone which is harmful to photographs; many composite woods such as block board and chipboard give off formaldehyde. (2) It is not easy to control these harmful effects of the environment as air conditioning may be cost-prohibitive. When installed, it will correct the relative humidity, pollution and the temperature but it is expensive to maintain.
DISCUSSION An ecological approach is relevant to the biodeteriation of such collections. Enzymes released by organisms can continue to break down materials even when the cells which produced them are removed or no longer alive.
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Degradation phenomena are being studied, new conservation methods developed and deacidification problems investigated. Chemical intervention with the use of biocidles, insecticides and furnigants for long-term eradication of fungus induced stains and beetle infested wood has highlighted potential dangers both to the operator and the artefact in the long-term. Freeze-drying techniques give promising results as an alternative form of treatment. Laser-stain removal and gamma eradication are being developed within health and safety guidelines. Information, imaging and communication technologies will over the next decade assist museums, libraries, galleries, archives and documentation centres in making their resources user-friendly and readily available to the student and scholar without having to handle the material. Suitable environmental controls, good housekeeping and regular inspections in spring or early summer when the beetle emerge will safeguard the curation of lignocellulosic material in museum collections.
CONCLUSIONS Moisture content and nutrients are both important when considering remedial measures or predicting the susceptibility of an artefact to biodeterioration. Biochemical investigation of lignocellulosic rnaterials in museum collections will provide the knowledge which enables the conservator to use minimal intervention. Such passive conservation is based not on remedial treatment of damage but on environmental inspection and control which will retard the natural life cycle of the destructive organisms and agents. The time spent on such in-house maintenance is well invested. The artefacts will therefore be displayed for a longer period in a more authentic condition.
ACKNOWLEDGEMENT The author wishes to thank the following for their discussion, encouragement and support: David Bailey, Leo Biek, Debbie Bolton, Pat Brown, Andrew Carson, Eileen Collins and Christopher Radbourne, Richard Green and Alan Mitchell, Anne Hudson, Hilde Smith and Pauline Timmins, and to Wendy Firmin, Editorial Critic, Bunny Warren and Cathie Mair, Secretariat, Kevin and Robert Brown, Directors of Advance Office Services, UK for practical assistance and professional advice.
REFERENCES 1.
,.,
Allsopp, D. (1986) Introduction to Biodelerioration, Edward Arnold, London. Plowden, A. and Halahan, F. (1987) Looking after Antiques, Pan Books Ltd, London.
Part 4: Physical and chemical processing of fibre and non fibrous products
27 Polymeric materials derived from the biomass A Gandini - Materiaux Polymeres, Ecole Francaise de Papeterie et des Industries Graphiques (INPG), BP 65, 38402 St. Martin d'Heres, France
INTRODUCTION The incessant production of organic molecules arising from the biological activities of the animal and vegetal realms, commonly called the biomass, forms the very essence of the perpetuation of our species (food) and has contributed to improve the quality of its life (energy, clothing, materials, health care, culture...). These natural compounds synthesized by living organisms cover a wide domain of molecular structures, topologies and sizes and are assembled in an extraordinary variety of supramolecular architectures. The traditional exploitation of these renewable resources are today complemented by recent efforts not only to ameliorate their yield, quality and variety but also the modes of their recovery, refining and transformation. In the specific context of materials, man has taken advantage of: (i) natural polymers e.g. in textile manufacturing, papermaking, the use of leathers and furs, the elaboration of elastomeric products, and of course all the applications of wood; (ii) oligomers and resins e.g. for paints, lacquers, skin tanning, inks, adhesives; and (iii) monomers and other small molecules e.g. as dyes and precursors to polymers and resinous products. Some of these technologies call upon little or no chemical modification of
251
252 Physical and chemical processing of fibre and non fibrous products
the original structures, as with wood, cellulosic fibers, natural rubber, tanning and indeed papermaking in which only lignins are chemically degraded. Others are more radical in that the natural products are submitted to rather drastic transformations in order to manufacture novel polymeric materials. This review deals only with the latter aspect, applied either to the bulk of the product e.g. in the polymerization of a terpene, or just to its surface, e.g. in the compatibilization of cellulosic fibers with a polypropylene matrix. Its scope is moreover limited to recent investigations which have shown that renewable resources can provide polymeric materials with special properties and promising applications. The extraordinary achievements of polymer science and technology in the last few decades are reflected in the multitude of materials available today. These are the result of a very intensive and well-financed research programme based mostly on petrochemistry. The strategic choice made in the aftermath of the second world war to privilege fossil rather than renewable sources for the elaboration of polymers has delayed the progress of the latter alternative for lack of adequate funding and therefore any product arising from the chemical exploitation of the biomass is bound to face an unfair comparison, both technical and economic, with petroleumbased counterparts. It seems thus premature to envisage the industrial production of materials for routine applications, i.e. polymers capable of competing with the standard "plastics", unless particularly simple and economic procedures are found to convert these ubiquitous raw materials produced by photosynthesis into polymers for everyday requirements. On the other hand, there is certainly much scope today for devoting sustained efforts to elaborate macromolecular structures possessing special properties, unique features and/ or potential added value, i.e, to prepare polymers by making good use of those chemical peculiarities of natural substances (or of their derivatives) which are not readily accessible from fossil-based counterparts. The examples discussed below attempt to show that these approaches are feasable and that polymer science can profit from the rational exploitation of monomers, oligomers and polymers derived from the biomass. A more extensive treatment of this topic has been published recently (1) and brought up to date in a series of forthcoming articles (2).
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THE CHEMICAL MODIFICATION OF NATURAL POLYMERS Polysaccharides Cellulose owes its peculiar properties both to the regular and linear enchainment of anhydroglucose units and to the ease with which intermolecular hydrogen bondings can be organized along its polysaccharide chains. The disruption of the macromolecular regularity and/or of those strong interactions by reactions involving the hydroxy groups of the polymer is always accompanied by important changes in the mechanical, thermal and solubility behaviour as clearly illustrated for example by the major difference in the properties of cellulose and its esters and ethers. This type of chemical modification has been practiced for over a century and recent advances are modest in terms of the novelty associated with the ensuing materials, except for the possibility of preparing thermotropic and lyotropic liquid-crystalline polymers (3). Grafting processes induce of course much more important structural changes in polysaccharides. Much attention has been devoted to studying and later optimizing the mechanisms leading to the attachment of synthetic polymer strands onto the backbone of the natural polymer (4). The best results are obtained with free radical initiation, but two problems persist, viz. the relatively low grafting efficiencies and the formation of non-negligible amounts of homopolymer formed concomitantly with the branches. These drawbacks are sufficiently serious to have limited very drastically the number of industrial applications of grafted polysaccharides. Cellulose bearing polyacrylamide grafts shows interesting superabsorbent properties coupled with the additional advantage related to the potential biodegradability of the main chain. A recent study has shown that cellulosic derivatives can be used as basic components for the elaboration of polymer electrolytes (see Schoenenberger, Le Nest and Gandini, this book). In one specific instance cellulose ethers were grafted and crosslinked with polyether chains by condensation reactions involving mono- and di-functional macroisocyanates. The role of the cellulosic backbones in these structures is to improve their film-forming properties in order to allow the manufacture of solid state lithium batteries by continuous casting of the polymer electrolyte between the two electrodes. If on the one hand the bulk transformation of polysaccharides by chemical reaction has not provided many new materials in recent years,
254 Physical and chemical processing of fibre and non fibrous products
the shift of attention towards the modification of the surface of cellulosic fibres in view of their utilization in composite materials has sparked numerous investigations and stimulating results. The number of conferences and ensuing papers devoted to this subject in the last few years (5-7) testify to its vitality. Several reasons justify the use of these natural fibers: (i) their excellent mechanical properties; (ii) their ready availability directly from numerous vegetal species or from papermaking (including recycled fibers) and other biomass refineries; (iii) their variety in terms of morphology, geometry and surface properties, again depending on the source and/or the separation processes used to isolate them; (iv) their renewable character and (v) their low cost in most instances. In specific applications, their low density with respect to glass fibers can also be a considerable advantage. These positive features are unfortunately accompanied by some problems related to the structure of cellulose, namely: (i) its modest temperature resistance which limits the application of these composites to below about 1S0°C and (ii) its hydrophilic character which can induce dimentional instabilities and a long-term drop in mechanical properties. Whereas the former disadvantage has no solution because it is intrinsic to the very chemistry of the polysaccharide chain, the latter can be overcome if the matrix is a very effective barrier to water diffusion. This explains the particular emphasis on research related to the use of polyolefins as the continuous phase in cellulosic composites. As with other more conventional composites, the problem of compatibilization between the cellulosic fibers and the synthetic matrix has been a major issue aimed at optimizing the mechanical properties of these novel materials. As an example, the quality of the interface cellulose/polyolefins can be improved by corona treatment (8) or specific chemical modification (9,10) of the fibers' surface or the matrix. The former process introduces polar groups following free radical activation, the second is based on reactions which can lead to chemical bonding between the two components as with certain surface treatments of glass fibers. Inverse gas chromatography has been particularly useful for the characterization of the cellulosic surfaces. Work in progress on this topic in our laboratory concentrates on two possible means of rendering the fiber/matrix interface more compatible. One approach consists in treating the fibers with alkenyl monomers bearing NCO groups in order to induce their condensation with the superficial OH functions and then suspending
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the modified fibers in the monomer which is to form the matrix so that, during its polymerization, the double bonds fixed on their surface participate in the growth process giving a chemically-bound interface. The other procedure involves preparing copolymers between conventional monomers and comonomers bearing NCO groups and then adding the cellulosic fibers so that their superficial OH groups condense with the NCO functions of the copolymer matrix thus establishing a good interface. Up to 60% fibers can be added in these composites and the gains in mechanical properties in the systems where good adhesion has been insured between matrix and fibers are of about a factor of four in tensile modulus and a factor of two in tensile strength with respect to the values related to the pure polyolefin. Cellulose "whiskers" in the form of rodlike microfibrils obtained from animal sources are also a potential source of very good mechanical reinforcement. Chitin is the most abundant polysaccaharide from animal source found essentially in the shell of marine intervertebrates. Its main structural difference with respect to cellulose, starch and other vegetal polysaccharides is the presence of an N-acetyl side group on each unit. Its deacetylation leads to the formation of chitosan which is its primary amino derivative. The inclusion of these polymers derived from animal sources in the present context is justified by the interest of their use in a chemically modified form in materials (11). Apart from reactions with acids and isocyanates which involve both the OH and NH2 groups of these peculiar polysaccharides, the formation of Schiff bases with mono- and dialdehydes is specific to the presence of the latter functions. Chitin, chitosan and their numerous derivatives have a strong chelating character which makes them particulary interesting in applications such as ion collectors (recovery of traces of metals from solutions) and chromatographic substrates. They are also used as textile additives, dialysis membranes and in medical, surgical and pharmaceutical applications.
Wood The main reasons for the chemical modification of wood, apart from the specific treatments for its preservation against pests, are aimed at its plasticization and at the improvement of its dimensional stability and weathering, viz. the resistance to moisture, light and oxygen. The essence of these modifications (12) is the partial or total destruction of the
256 Physical and chemical processing of fibre and non fibrous products
crystalline character of cellulose, e.g. the destruction of intermacromoleculer hydrogen bonds through the establishment of new moieties having a non-polar or a less pronounced polar character. Of course these processes concern the hydroxy groups and therefore also involve lignins and hemicelluloses. The reagents used for softening the wood structure include organic halides, anhydrides, oxiranes and isocyanates. The replacement of the OH groups gives rise to various new moieties (esters, ethers, urethanes), but more importantly to the inclusion in the macrostructure of aliphatic or aromatic groups of variable size. It follows that depending on the nature and specific structure of the reagent (e.g. aliphatic chain length attached to the reactive group) as well as the amount added with respect to the wood substrate, a whole variety of materials can be obtained ranging in mechanical and thermal properties from semicrystalline to amorphous, from rigid to elastomeric, from waterswelled to hydrophobic, from thermoset to thermoplastic. This last change implies that lignin has been partly depolymerized with the destruction of its three-dimensional topology. Two extreme examples show the range of applications of the materials obtained. The antishrink properties linked to the decrease in water affinity of wood can be greatly improved by partial acetylation which however does not destroy the main supramolecular features of the substrate (13). On the other hand, the esterification of wood with important proportions of long-chain aliphatic anhydrides gets rid of most hydrogen bonding, cellulose cristallynity and the crosslinked character of lignin. These drastic effects, coupled with the plasticizing role of the aliphatic chains produce a softened thermoplastic material which can be cast into films, moulded into objects and expanded to give foams (14).
THE POLYMERIZATION OF NATURAL MACROMONOMERS From the point of view of polymer science, one must distinguish between two major families of oligomeric compounds encountered in the biomass: (i) the structures which bear no reactive sites (e.g, saturated triglycerides) and are therefore inert to further chain growth to give polymeric materials, but which find useful applications as additives (e.g, in printing inks in replacement of mineral oils) or precursors to specific products (e.g. soaps); and (ii) structures which possess one of several moieties which can
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be activated in chain or step polymerization reactions and which can therefore be used as macromonomers alone or in conjunction with more conventional monomers. The most relevant among the latter substances are drying oils, plant resins, hemicelluloses, tannins and lignin fragments (1,2). The applications of drying oils (e.g, linseed oil) and resins (e.g. rosin used as such or after specific chemical modifications) in paints, inks and other coating materials as well as their basic modes of polymerization are well established and represent in fact one of the best examples of the rational exploitation of renewable resources. Hemicelluloses have not found any major application as macromonomers, but must be considered important precursors to polymers via their transformation into furans as discussed in the next section. The "phenolic" macromonomers are examined briefly below. Tannins Tannins are oligomeric flavonoids present in the bark or wood of several trees. The traditional use as tanning agents remains the basic application of these natural products, but their intervention as macromonomers in the formulation of formaldehyde-based resins has been studied and successfully applied (15). The resultig resins can contain up to 65% tannins and display good adhesive properties, particularly adapted to plywood manufacturing. Lignins Lignins accompany cellulose and hemicelluloses in most manifestations of the biomass and are the second most important polymer produced by the biosynthesis. In the composite assembly of wood and plant macrostructures, the cellulosic fibers are the reiforcing element and lignins the crosslinked amorphous matrix. Traditional chemical pulping for papermaking as well as more recent biomass refinery technologies, e.g. organolv and steam explosion, provoke the degradation of lignins in order to solubilize the resulting fragments and isolate the cellulosic fibers. Depending on the vegetal species used and their mode of delignification, these fragments vary considerably in molecular mass and distribution, topology and detailed composition in terms of the relative proportion of characteristic "monomeric" units. It follows that, contrary to cellulose, the term "lignins" comprises a whole family of structures (16) which bear
258 Physical and chemical processing of fibre and non fibrous products
however a common denominator: the presence of "phenylpropane" units, i.e. phenolic moieties with three aliphatic carbon atoms attached at their C-4 position. The other chemical feature common to all lignins is the presence of important proportions of aliphatic hydroxy groups. An attempt at representing an in situ lignin macromolecule is given in 'another paper in this book (see Montanari & Gandini): the oligomers obtained in the various splicing processes can have average DPs typically ranging from 10 to 100 and polydispersity indices going from about 2 all the way to more than 10, not to mention the varied chemical structure of the fragments in terms of functional groups. This lack of uniformity has been the major obstacle to the rational exploitation of lignins for polymeric materials. Thus, any degradation all the way down to "monomeric units" will provide a mixture of phenolic derivatives which would be difficult to use as well-defined chemicals unless economic separating procedures are devised. The use of lignin fragments as macromonomers seems a more reasonable approach, but even then only in formulations where the variety of structures and molecular masses do not affect the essential properties of the materials obtained. Three major strategies have been investigated in this context (1,2): (i) the chemical incorporation of lignins in formaldehyde-type resins in partial substitution of phenolic monomers; (ii) the grafting of lignins with alkenyl monomers; and (iii) the use of lignins in polycondensation reactions. Lignins, particularly those obtained by organosolv processes, participate in the growth of phenolic-type resins although of course steric hyndrance makes them less reactive than monomeric phenols. This incorporation can be improved by methylolation or phenolation (1,15,17). Grafting lignins by radical polymerization of alkenyl monomers is marred in some systems by the retarding role of the phenolic units, but interesting materials have been obtained with polyacrylamide strands (18). The third route to lignin-based polymers consists in exploiting the reactivity of phenolic and aliphatic OH groups borne by all lignins, albeit in different proportions. Polyesters, polyurethanes and polyethers have been obtained in this way as discussed in the paper by Montanari & Gandini in this book and the results obtained both on the reactivity of different lignins and on the properties of the materials indicate that this is the most promising way
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of pursuing research on the valorization of this underprivileged natural product in the realm of materials science. POLYMERIZATION OF MONOMERS FROM THE BIOMASS Some simple structures produced by vegetal activities possess the chemical characteristics required for polyaddition or polycondensation. Other interesting monomers are obtained through the chemical exploitation of natural precursors.
Polyols Glycerol is a by-product of the industrial transformation of fats and oils. It is used in the manufacture of polyesters and polyurethanes. Some monosaccharides like sorbitol are also precursors to polyols for the elaboration of rigid polyurethanes. These crystalline sugars must first be transformed into a viscous liquid by oxipropylation in order to facilitate their rapid mixing with the polyisocyanate comonomers.
Terpenes Many essential oils contain unsaturated hydrocarbons which are dimeric structures of isoprene. These terpenes respond to cationic polymerization and give resinous oligomers which find applications in adhesives (tackifying agents), printing inks, paints and varnishes (1). Recent progress in cationic polymerization has opened the way to living systems, i.e. the possibility of obtaining polymers and copolymers with controlled structure and narrow DP distribution. The application of these criteria to the polymerization of terpenes should provide new materials with a wider range of properties.
Furanic monomers and polymers Saccharide structures in the form of monomeric, oligomeric and polymeric pentoses and hexoses can be converted into furanic derivatives by acid-catalyzed dehydration. In particular, virtually all agricultural wastes, e.g. corn cobs, rice hulls, .sugar-cane bagasse, contain sufficient amounts of C5 hemicelluloses to be interesting raw materials for the production of furfural. This heterocyclic aldehyde has been an industrial commodity for over fifty years, but its role as a first-generation synthon is
260 Physical and chemical processing of fibre and non fibrous products
far from being exploited to its full potential. Most of it is converted into furfuryl alcohol and the rest provides a modest range of applications. Yet, research carried out in the last two decades (1,2,19,20) shows that many monomers can be prepared from it through simple and convenient routes and that the polymers and copolymers arising from them are an original family of materials. The mechanistic peculiarities of these polymerizations as well as the properties of the products obtained have been described in specific studies and summarized in appropriate reviews (1,19,20). Only some recent investigations will be briefly discussed here. 5-Methylfurfural, which is always obtained as a side product in the industrial synthesis of furfural, polymerizes by successive condensations between the methyl group and the aldehyde function in a strongly basic medium to give a conjugated macromolecular structure (21):
Nu
(n+l)
~~
~
O/y
n<,
o
o
These strongly coloured polymers, obtained in a simple one-pot synthesis, are stable to atmospheric oxidation, photoactive and display good electronic conductivities after doping. They can be converted into block copolymers, e.g. with polyethylene oxide bearing terminal NH2 groups, to improve its film- or fiber-forming properties and to provide both electronic and ionic conductance capabilities. 2-Furyloxirane is readily prepared from furfural in high yields. Its epoxide function is much more reactive than that of aliphatic and aromatic homologues and can be activated by OH functions from alcohols and even water without any catalytic aid. OH-telechelic polyethers are therefore obtained when water is used to initiate its polymerization:
GO \7 o
H~
•
The use of macrodiols like polyethylene glycols as initiators produces triblock copolymers whereas polymers with side OH groups, e.g.
Polymeric materials
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polyvinylalcohol or cellulose, are grafted directly by 2-furyloxirane. A transfer reaction limits however the length of these polyether chains to oligomeric levels. The other furanic compound which is an excellent source of monomers is 5-hydroxymethylfurfural, obtained from hexoses (fructose is the best precursor) via the same acid-catalyzed dehydration used for the production of furfural. A variety of difunctional structures have been prepared and polymerized, mostly by step reactions, namely polyesters, polyamides, polyurethanes,... (1,2,19,20). Recent investigations in this area include an exhaustive study of furanic polyurethanes (22) including thermoplastic elastomers (22) and polyschiff bases (23). The polyurethanes were synthesized from furanic diols and/ or diisocyanates and comprised structures bearing the heterocycles within the main chain: H H I I
yN
N""'-./O
o~
or as a side group, or both. The structure-properties relationships of these materials were analyzed in detail. Insulating crosslinked foams were also prepared and compared with conventional counterparts. Polyshiff bases were the result of polycondensations between 2,S-furandicarboxyaldehyde and various diamines. Conjugated insoluble polymers with very high cohesive energy were obtained with aromatic diamines, whereas aliphatic homologues gave thermoplastic materials. The other interesting application of furan chemistry is in the modification of polymers bearing furanic rings as pendant moieties, end groups or in the main chain: functionalized oligomers, block and graft copolymers and reversibly crosslinked structures can be implemented through simple procedures thanks to the specific reactivity of the heterocycle (1,2,19,20), e.g. in Diels-Alder cycloadditions and regiospecific electrophilic substitutions at C5. CONCLUSION This succinct survey purported to give a glimpse of the richness of materials which can be obtained from new chemistry applied to renewable resources and to stimulate further investigations in this promising field.
262 Physical and chemical processing of fibre and non fibrous products
REFERENCES 1. 2. 3. 4. 5. 6.
7. 8. 9. 10. 11. 12.
13. 14. 15. 16. 17. 18. 19.
20. 21. 22.
23.
Gandini, A. (1992) "Polymers from Renewable Resources", in Comprehensive Polymer Science, Aggraval, S.L. and Russo, S. (Eds) p. 527, Pergamon Press, Oxford. Gandini, A. and Belgacem, N.M. in Polymeric Materials Encyclopedia, Salamone, C. (Ed), esc Press, in press. Zugenmaier, P., Revol, I.F., Giasson, J, Guo, J.X., Harkness, B., Marchessault, R.H. and Gray, D.G., Ref. 6, pp. 105-122. Hebeish, A. and Guthrie, J.T. (1981) The Chemistry and Technology of Cellulosic Copolymers, Springer-Verlag, Berlin. Pacific Rim Bio-Based Composites Symposium (1992), Plakett D.V. and Dunningham, E.A. (Eds), Rotura, New Zealand. Cellulosics: Chemical, Biochemical and Materials (1993), Kennedy, J.F., Phillips, G.O. and Williams, P.A. (Eds) Ellis Horwood, New York. Rowell, R.M., Laufenberg T.L. and Rowell J.K. (1992) Materials Research Society, Symp. Proc., 266, 47-194. Belgacem, M.N., Bataille, P. and Sapieha, S. (1994) J. Appl. Polym. Sci., 53,379. Raj, R.G. and Kokta, B.V. (1990) ACS Symp. Ser., 489, 99. Felix, J.M. and Gatenholm, P. (1991) J. Appl. Polym. Sci., 42, 609. Skjak-Braek, G., Anthonsen, T. and Sandord, P. (Eds) (1998) Chitin and Chitosan, Elsevier, London. Chemical Modification of Lignocellulosics, (1992) Plakett, D.V. and Dunningham, E.A. (Eds) Rotura, New Zealand. Rowell, R.M. in Wood and Cellulosic Chemistry (1991) Hon, D.N.S. and Shiraishi, N. (Eds), Marcel Dekker, New York, chapter 15. Shiraishi, N. , ref. 13, chapter 18. Pizzi, A. Advanced Wood Adhesives Technology (1994) Marcel Dekker, New York. Lin, S.Y. and Dence, C.W. (1992) Methods in Lignin Chemistry, Springer Verlag, Berlin. Glasser, W.G. and Kelly, S.S. (1988) in Encyclopedia of Polymer Science and Engineering, Mark, H.F., Bikales, N.M., Overberger C.G. and Menges, G. (Eds), Wiley, New York, Vol. 8. p 795. Meister, J.J., Lathia, A. and Chang, F. (1991) J. Polym. Sci. Chern. Ed., 29, 1465. Gandini, A. (1986) in Encyclopedia of Polymer Science and Engineering Mark, H.F., Bikales, N .M., Overberger C.G. and Menges, G. (Eds) Wiley, New York, Vol. 7, p 454. Gandini, A. (1990) ACS Symp. Sere 433, 195. Gandini, A. and Mealares, C. (1994)Trends Polym. Sci., 2, 127. Boufi, S., Belgacem, M.N., Quillerou J. and Gandini, A. (1993) Macromolecules., 26, 6706. Hui, Z. and Gandini, A. (1992) Eur. Polym. J. 28,1461.
28 High performance and highly functional polymeric materials from plant components H Hatakeyama - National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan
Introduction This paper is concerned with the molecular design and properties of saccharides and phenols which are two major plant components in nature. In this paper, attention is paid to (1) hydrogels and liquid crystals formed from polysaccharide electrolytes with water, (2) highperformance polymers derived from lignin degradation products, and (3) biodegradable polyurethanes derived from plant materials. The relationship between the chemical structures and physical properties of natural polymers, their derivatives and synthetic polymers from the above plant components is also discussed in the paper. 1. Hydrogels and liquid crystals formed from polysaccharide electrolytes with water The formation of hydrogels and the liquid crystalline state from waterpolyelectrolyte systems was investigated by differential scanning 263
264 Physical and chemical processing of fibre and non fibrous products
calorimetry (DSC), nuclear magnetic resonance spectroscopy (NMR), small and wide angle X-ray scattering analyses (SAXS and WAXS), polarizing light microscopy (POL), and thermomechanical analysis (TMA).
Lithium, sodium, potassium, magnesium and calcium salts of carboxymethylcellulose (LiCMC, NaCMC, KCMC MgCMC, and CaCMC) were supplied by Daiichi Seiyaku Co. Sodium cellulose sulfate (NaCS) was obtained from Scientific Polymer Products Inc. The Na salt of xanthan gum (NaXan) was obtained from Kelco Co. The Li, K and Ca salts of xanthan gum (LiXan, KXan and CaXan) were prepared by ion exchange at our laboratory. Gellan gum was received from Sanei Chemical Co. Ltd. Sodium alginate (NaAlg) was obtained from Kibun Food Chemifer Co. Ltd. Calcium alginate (CaAlg) was prepared by ion exchange. The chemical structures of the above materials are shown in Table 1. Tablel. Chemical structures of polysaccharide electrolytes Cellulose sulphate
Carboxymethyl cell ulose
Alginic acid
Polymeric materials from plant components
265
The water content (Wc) of each sample was defined by: W c (gIg) = Ww/W s (gIg)
(1)
where W w is the weight of water and W s is the dry weight of the sample. DSC measurements were carried out using a Perkin Elmer model DSCII, a Du Pont model DSC 910 and a Seiko Instruments model DSC 200. Nuclear magnetic relaxation was measured using a Nicolet FT-NMR model NT-200 WB and a Bruker Ff-NMR model MSL 300. Small angle X-ray scattering (SAXS) and wide angle X-ray scattering (W AXS) experiments were performed using a MAC Science Model MXP18 X-ray instrument. Synchrotron orbital radiation (SOR) experiments were carried out at the synchrotron facility of the National Laboratory for High Energy Physics, Tsukuba, Japan. Microscopic observations were made using a polarizing light microscope, Leitz model Orthoplan-Pol. A colour plate (450 nm) was used as a test plate to determine interference colours. The elastic modulus (E') was measured by a needle penetration method using a Seiko Instruments TMA-120. Figure 1 shows representative DSC curves of the water-sodium carboxymethylcellulose (NaCMC) system with W c = 1.26. When the sample was cooled at a rate of 10K/min, two exotherms were found at 268 K and 245 K (Curve I) [IJ. When the sample was reheated at 10 Klmin (Curve II), a step-wise change in the baseline at 190K, a broad exotherm at around 240 K and two endothermic peaks at 265 K and 330 K were observed. The large endothermic peak observed at 265 K was attributed to the melting of ice (T m) as reported previously (1). The small endothermic peak observed at 330 K was attributed to the transition (T*) from the liquid crystalline state to the liquid state. This was supported by observations of the presence of the liquid crystalline phase in the temperature range between T m and T* using a polarizing light microscope. The peak corresponding to T* appeared when Wc was ca. 0.4. The peak temperature (T*) decreased with increasing Wc. When the sample was quenched from 320 K to 150 K (Curve III), the step-wise change in the baseline at 190 K and the exotherm at around 240 K became prominent. The temperature corresponding to the stepwise change in the baseline showed a heating rate dependency. This change also showed enthalpy relaxation by slow cooling or annealing at a temperature slightly lower than the endothermic deviation of the
266 Physical and chemical processing of fibre and non fibrous products
baseline. This transition was therefore attributed to the glass transition (Tg).The exotherm at about 240 K was attributed to cold crystallization (TCt') of the system via which the glassy state was transformed to the crystalline state.
Te
Te*
eo~g
II
------
o
"t:J
..... - ..
c:
W
.-----
III
Tee
Tg
T*
heating
Tm 150
200
250
300
350
Temperature / K
Fig. 1
DSC curves of the water-NaCMC system. We = 1.26; scanning rate 10 K/min; curve I, cooling curve, curves III, heating curves; Tg , glass transition; Tc c , cold crystallization; Tm , melting; P, transition from liquid crystalline phase to isotropic liquid phase; T*c, transition
from isotropic liquid phase to liquid crystalline phase; Tc , crystallization.
Other water-polysaccharide electrolyte systems such as LiCMC, KCMC, MgCMC, CaCMC, NaXan, LiXan, KXan, CaXan, gellan gum and NaAlg showed similar phase transitions, as shown in Fig. 1. Generally speaking, the water-polysaccharide electrolyte systems with divalent cations required more time for the molecular rearrangement than the systems with monovalent cations. Polarizing light micrographs of the water-polysaccharide electrolytes also showed the formation of the higher order structure in the Wc range between 0.5 and 3.0. When we observed the morphology of the sample with a colour sensitive plate, the colour indicated that the molecular axis is aligned in parallel to the glass plate.
Polymeric materials from plant components
267
The above observation showed that various polysaccharide electrolyte -water systems form liquid crystals, when the water content (Wc) of the system ranges from ca. 0.5 to ca. 3 depending on the type of polyelectrolyte [1,2]. The longitudinal relaxation time (T 1) and transverse relaxation time (T2) of 1Hand 23Na of the waterpolyelectrolyte systems were measured as a function of temperature and Wc [1,2] The NMR results suggested that the counter ion is associated with the main chain in the liquid crystalline state, and the increase of free and freezing bound water surrounding hydrophilic groups hinders the regular molecular alignment of polyelectrolyte molecules through the dissociation between the counter ion and the main chain. Formation of hydrogels was observed in the Wc range until 200. In xanthan and gelIan hydrogels the position of the SAXS diffraction peak maximum, d, corresponds to either the average size of the scattering centres in the gel or the mean inter scattering centre distance (the mean mesh size) [3,4]. On annealing for longer periods (>30min.) at the sol state, the average size of the junction zones increases to values greater than in the unannealed state. The following observations are made: (i) the freezing bound water is coordinated to a greater degree with the xanthan and gellan matrix, (ii) the intensity of the SAXS diffraction peak and therefore the concentration of scattering centres increased, and (iii) the elastic modulus increased considerably. These observations are consistent with the hypothesis that d represents the average junction zone size. The sol state in this case cannot be considered to be in an isotropic liquid state, rather it can be said that a high order structure is formed. DSC and TMA analyses have also revealed that the sol state of xanthan and gellan hydrogels is not an isotropic liquid state, but that in fact a high order structure is developed in solution with annealing. This high temperature annealing leads to an increase in the size of the junction zones and elastic modulus of the gels subsequently formed on cooling. 2. High-performance polymers from lignin degradation products High-performance polymers having 4-hydroxyphenyl, guaiacyl and syringyl groups were synthesized from lignin degradation products [5]. Physical properties of the polymers were investigated by DSC, thermogravimetry (TG), NMR, POL, gel permeation chromatography (GPC) and viscosity measurements. The relationship between the chemical structure and physical properties of polymers was investigated.
268 Physical and chemical processing of fibre and non fibrous products
Table 2. Chemical structures of high performance polymers derived from lignin degradation products Polyhydroxystyrene derivatives
(I. IT and m) [I] : R. R'= H [U] : R
= 0013, R' = H ocas
[ID]:
R. R' =
R:
-fCHdn ·
Polyesters with spiro-dioxane rings (N)
-0-
Polyethers with methoxybenzalazine units (V)
Polyesters with methoxybenzalazine units (VI)
Polyacylhydrazones having guaiacyl units with alkylene groups (VI[)
m : 2,4,6 R :
-fCHz7;
or
'0'
Polyesters with syringyl-type biphenyl units ('VI ) R = OCH3' H R' =
-0- .-0 .-tm:1;-
Polymeric materials from plant components
269
Aromatic polyethers with phospine oxide groups (IX)
~R-o-O-o-~~ ~6~
YH3 CH3
R = -C-
(polyether A)
(Polyether B)
Copolyesters with guaiacyl and syringyl groups (X)
lO~0-8~8t ~-LO~0-8-O-8+
~
OCH)
OCR)
m
R = HorOCH 3
min (mol/mol) : 10/0.713,5/5,
n
3n and 0/10
Copolyesters with syringyl groups (XI)
la, b
to-O:1, fH~W)! +~-AJ+O to-O:! -E:~t +~-Ar-~+o t°-O:1, to-oEt +~-M-~+O OCR)
H)CO
OCR)
3
2a, b
3a, b
AT:
a:
0
b:
0-0
Polyhydroxystyrene derivatives, polyethers and polyesters which were synthesized at our laboratory are shown in Table 2. Physical properties of obtained polymers were analyzed according to the methods described previously. Concerning TG measurements, a Seiko TG 220 was used. Poly(4-hydroxystyrene) [I], poly(4-hydroxy-3-methoxystyrene) [II], poly-(4-hydroxy-3,5-dimethoxystyrene) [III] and their acetates were synthesized from 4-hydroxybenzaldehyde, vanillin and syringaldehyde [6]. The molecular weight of the polymers was controlled by changing polymerization conditions: from 6.6 x 103 to 3.7 x 105. The molecular weight distribution was from 2.2 to 4.3. T g'S of styrene derivatives were prominently influenced by the molecular weight and the chemical structure, changing from 320 K to 450K. The introduction of the
270 Physical and chemical processing of fibre and non fibrous products
hydroxyl group to the 4-position of the aromatic ring is noteworthy. Tg values of [I ] and [II] are 10-60 K higher than those of polystyrene and the acetylated samples. On the other hand, if the methoxyl group is introduced to the 3-position of the aromatic ring, adjacent to the hydroxyl group at the 4-position, the T g decreases due to the steric hindrance to hydrogen bonding. It was also found that polyhydroxystyrene derivatives [I], [II] and [III] are biodegradable [6,7]. Polyesters having spirodioxane rings [IV] were synthesized by the reac ti on of 3,9-bis(4-hydoxy-3-methoxyphenyl)-2,4,8, 10-tetraoxaspiro-[5,5] undecane, which was obtained from vanillin and pentaerythritol, with terephthaloyl chloride or sebacoyl chloride [8]. The thermal stability of the obtained polyesters, polyterephthalate (IVterephthalate) (inherent viscosity, llinh = 1.30 dl/ g) and polysebacate (IV -sebacate) (llinh = 0.89 dl/g) having spirodioxane rings, was analyzed by TG. IV-terephthalate started to decompose at 568 K and IV-sebacate at 527K. Although no transition was observed in the DSC curve of IV-terephthalate, a glass transition at 363 K was seen in a DSC curve of IV-sebacate. The X-ray diffractogram of IV-terephthlate showed. a crystalline pattern, while that of IV-sebacate showed an amorphous pattern. The results of the above measurements showed that the rigidity of the spiro-dioxane ring is almost similar to the polyester from disubstitued bis(4-hydroxyphenyl)methane [9]. Polyethers [V] and polyesters [VI] having methoxybenzalazine units with various alkylene groups (C4, C6 and Cs) in the main chain were synthesized from vanillin [10,11]. The condensation reaction of 4,4' alkylenedioxybis(3-methoxybenzaldehyde) with hydrazine monohydrate was applied to the synthesis of polyethers [V] (Mn, 7.4 x 103 for C4, 7.3 x 103 for C6 and 4.1 x 103 for C8 derivatives). Polyesters [VI] (llinh, 0.35 dl/g for C4, 0.38 dl/g for C6 and O.43dl/g for Cg) derivatives were synthesized from 4,4'-dihydroxy-3,3'-dimethoxybenzalazine and dicarboxylic acid chlorides by low temperature solution polycondensation. The thermal stability of [V] and [VI] was studied by TG. The decomposition temperatures (Td'S) of polyethers (574 K for V-C4, 570 K for V-C6 and 571 K for V-Cg) were higher than those of polyesters ( 533 K for VI-C4, 541K for VI-C6 and 539 K for VI-C8). However, T d did not depend on chain length of the alkylene groups in either the polyethers or polyesters. The polyethers crystallized during cooling from the molten state. On the other hand, the polyesters showed cold-crystallization from the glassy state.
Polymeric materials from plant components
271
Polyacylhydrazones [VII] having two guaiacyl units with the alkylene groups in each repeating units were synthesized using vanillin and dibromoalkanes as starting materials [12]. The phase transition and thermal stability of the six polymers synthesized were studied by DSC and TG. Inherent viscosities, T g'S and T d 'S are as shown below. Table 3. Physical properties of syntehsized polyacylhydrazones [VII] -(CH 2) m2 4 6 2
4 6
-R(CH2)4 (CH2)4 (CH 2)4 m-C6I-4 m.-C6I-4 m- C6H4
YJinh, dl/g
0.56 0.60 0.53 0.92 0.95
T g, K 394 358 363 460 450 430
Td, K 609 609 610 622
618 615
The obtained results showed that the aromatic group is more rigid than the alkylene group. Polyesters having syringyl-type bisphenyl units [VIII] were synthesized from 4,4'-dihydroxy-3,3',5,5'-tetramethoxybiphenyl which was synthesized from 2,6-dimethoxy phenol [131. Polyterephthalate with Tlinh = 1.42 dl/g, polyisophthalate with YJihh = 0.73 dl/g and polysebacate with llinh = 0.43 dl/ g were obtained. Their T d'S were 614 K, 618 K and 588 K in nitrogen, respectively. Polyterephthalate did not show any transition until degradation. However, polyisophthalate and polysebacate showed Tg's at 525 K and 365 K. The low Tg for polysebacate may be attributed to the flexibility of the sebacoyl group. Aromatic poly ethers having phosphine oxide groups [IX] were synthesized from bis(4-fluorophenyl)phenyphosphine oxide with bisphenols [14]. The llinh, T g and Td of polyether A and polyether Bare as follows. Table 4. Physical properties of synthesized aromatic polyethers [IX]
Polyether A Polyether B
llinh, dl/g
T g, K
0.63
470 498
0.48
Td in N2~ K 778 808
272 Physical and chemical processing of fibre and non fibrous products
They are highly thermal stable polymers. Copolyester with guaiacyl and syringyl groups [X and XI] were synthesized from guaiacol and 2,6 dimethoxyphenol [15,16]. Their Td'S were at around 630 K and the polyesters with syringyl structures ([Xl with R = OCH3 and [XI,la,b]]) showed the liquid crystalline state at around 570 K [15,16]. As mentioned above, physical properties such as molecular weight, solubility in solvents, crystallinity, relaxation in glassy state and thermal decomposition temperature, could be controlled by the appropriate arrangements of chemical bonds and functional groups such as phenylene group, methoxyl group, and alkylene group. 3. Biodegradable polyurethanes derived from plant materials Polyurethane (PU) is one of the most useful three-dimensional polymers, since PU has unique features: for example, various forms of materials such as sheets, foams, adhesives and paints can be obtained from PU, and their properties can easily be controlled. Accordingly, many attempts to use lignocelluloses as raw materials for PU synthesis have been made, since natural polymers having more than two hydroxyl groups per molecule can be used as polyols for polyurethane preparation if the polyols from natural polymers can be reacted efficiently with isocyanates. Polyurethanes having saccharide and lignin structures in their molecular chains were prepared from various plant resources such as kraft lignin (KL), solvolysis lignin (SL), woodmeal (WM) and molasses (ML) by polymerization with polyethylene glycol (PEG), polypropylene glycol (PPG) and diphenylmethane diisocyanate (MDI) [17-23]. Prior to obtaining polyurethane, it was necessary to dissolve or to suspend lignocelluloses ( KL, SL and WM ), and saccharides (ML) in polyols such as PEG and PPG. The obtained polyol solutions or suspensions were mixed with MDI and plasticizer (PEG or PPG) at room temperature, and precured polyurethanes were prepared. Each of the precured polyurethanes was heat-pressed and a PU sheet was preparecl. In order to prepare PU foam, first the above polyol solution or suspension was mixed with plasticizer, surfactant, and catalyst, and then MDI was added. This mixture was vigorously stirred with a droplet of water which was added as a foaming agent. The chemical
Polymeric materials from plant components
273
n
I
CONH-R~
-R'-NHCO'"
-R'NHCO to+CH2CH2
-O+~O
-NHR'NIICO-].:.......:/
OCB)
-
.....
R'-NHCO-O- C J O O / " ' /
[¢l
OCH
3] n
-R'-NHCO-O
Fig. 2
Schematic chemical structures of poyurethanes from saccharides and lignin.
structure of prepared polyurethanes is dependent on the plant raw materials. The polyurethanes consist of core structures of lignin and saccharides linked by urethane bonding. Figure 2 shows schematic structures of saccharide and lignin with urethane bonding. Glass transition temperature (T g) and degradation temperature (T d) of prepared PUts were mostly dependent on the content of KL, SL, WM and ML. Tg increased with increasing content of phenyl groups from lignins, since phenyl groups act as hard segments in PU networks. However, T d decreased with increasing content of lignin, since the dissociation of urethane bonds between isocyanate groups and phenolic hydroxyl groups occurs at the temperature region lower than the dissociation of urethane bonds between isocyanate and alcoholic groups
274 Physical and chemical processing of fibre and non fibrous products
[23]. Mechanical properties, such as tensile strength and Young's modulus of polyurethane sheets and also compression strength and modulus of polyurethane foams, were highly improved with the addition of plant materials such as KL, SL, WM and ML. The above facts suggest that saccharide and lignin residues act as hard segments in polyurethanes. It was also found that the polyurethanes obtained were biodegradable in soil. The rate of biodegradation was between that of cryptorneria (Cryptomeriajaponica) and beech (Fagus Sieboldi). RE~FER:E:NCES
[1] [2]
[3]
[4] [5]
[6] [7]
[8] [9] [10] [11] [12]
Hatakeyama H., J. National Inst. Materials and Chern. Res., 1994, 1,65. Hatakeyama, H. and Hatakeyama, T., "Mesomorphic Properties of Polyelectrolytes with Water" in "Properties of Ionic Polymers Natural and Synthetic" (Salmen, L. and Htun, M. eds.), STFI Meddelande A-989, 1991, pp.123. Quinn, F. X., Hatakeyama, T., Yoshida, H., Takahashi, M. and Hatakeyama, H., M. Polymer Gels and Networks, 1993, 1, 93. Quinn, F. X., Hatakeyama, T., Takahashi, M. and Hatakeyama, H., Polymer, 1994,35, 1248. Hatakeyama, H., Hirose, S. and Hatakeyama, T., "High Performance Polymers from Lignin Degradation Products" in "Lignin Properties and Materials"(Glasser, W. G. and Sarkanen, S., Eds., ACS Symposium Series 397, ACS, Washington D. C., 1989, pp.205. Hatakeyama, H., Hayashi, E. and Haraguchi, T., Polymer, 1977, 18,759. Haraguchi, T. and Hatakeyama, H., "Biodegradation of LigninRelated Polystyrenes" in "Lignin Biodegradation: Microbiology, Chemistry and Potential Applications" ( Kirk, T. K., Higuchi, T. and Chang, H-M. Eds.), esc Press, Florida, 1980, pp.147. Hirose, S., Hatakeyama, T. and Hatakeyama, H., Sen-i Gakkaishi, 1982,38, T-507. Morgan, P. W., Macromolecules, 1970,3,536. Hirose, S., Hatakeyama, T. and Hatakeyama, H., Kobunshi Ronbunsyu, 1982,39,733. Hirose, S., Hatakeyama, H. and Hatakeyama, T., Sen-i Gakkaishi, 1986,42, T-49. Hirose, S., Hatakeyama, H. and Hatakeyama, T., Sen-i Gakkaishi, 1983,39, T-496.
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[13] Hirose, S., Hatakeyama, H. and Hatakeyama, T., Sen-i Gakkaishi, 1985,41, T-432 (1985). [14] Hirose, S., Nakamura, K., Hatakeyama, T. and Hatakeyama, H., Sen-i Gakkaishi, 1987,43,595. [15] Hirose, S., Hatakeyama, T. and Hatakeyama, H., Sen-i Gakkaishi, 1991,47,388. [16] Acevedo, M., Hirose, S. and Hatakeyama, H., "Morphological and Thermal Properties of Copolyesters Having Mono- and Dimethoxyphenylene Groups", Polymer Preprints, Japan, 1993, 42 (2), 1129. [17] Yoshida, H., Morek, R., Kringstad, K. P. and Hatakeyama, H., J. Appl. Polym. Sci, 1985, 30,2207 [18] Yoshida, H., Morek, R., Kringstad, K. P. and Hatakeyama, H., J. Appl. Polym Sci., 1990,40, 1819. [19] Reimann, A., Morek, R., Yoshida, H., Hatakeyama, H. and Kringstad, K. P., J. Appl. Polym. Sci., 1990,41,39 (1990). [20] Hirose, S., S. Yano, S., Hatakeyama, T. and Hatakeyama, H., "Heat Resistant Polyurethanes from Solvolysis Lignin" in "Lignin Properties and Materials" (Glasser, W. G., and Sarkanen, S., Eds.), ACS Symposium Series 397, American Chemical Society, Washington DC., 1989, pp.382. [21] Yano, S., Hirose, S., Hatakeyama, H., "The Mechanical Properties of Polyurethane from Lignocellulose" in "Wood Processing and Utilization" (Kennedy, J. F., Phillips, G. 0., Williams, P. A., Eds.) Chichester, Ellis Horwood, 1989, pp.263. [22] Nakamura, K., Morek, R., Kringstad, K. P., and Hatakeyama, H., "Compression Properties of Polyurethane Foam Derived From Kraft Lignin" in "Wood Processing and Utilization" (Kennedy, J. F., Phillips, G. 0., and Williams, P. A. Eds.) Chichester, Ellis
Horwood, 1989, pp.263. [23] Hatakeyama, H., Hirose, S., Nakamura, K. and Hatakeyama, T., "New Types of Polyurethanes Derived from Lignocellulose and Saccharides" in "Cellulosics: Chemical, Biochemical and Materials Aspects" (Kennedy, J. F., Phillips, G. O. and Williams, P. A. eds.) Ellis Horwood, London, 1993, pp.525.
29 Preparation and physical properties of biodegradable polyurethanes derived from the lignin-polyester-polyol system S Hirose, K Kobashigawa* and H Hatakeyama - National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan; *Tropical Technology Center Ltd, 5-1 Suzaki, Gushikawa, Okinawa 900, Japan
Abstract Polyurethane (PU) foams could successfully be prepared by the following procedure. A mixture consisting of an ethylene glycol (EO) solution of kraft lignin and polyester-polyol (PCL, diol type polycaprolactone, molecular weight 550) was reacted with diphenylmethane diisocyanate (MDI) in the presence of small amounts of water, tin catalyst and silicone surfactant. Thermal and mechanical properties of PU's were studied by differential scanning calorimetry (DSC) and compression test.. Glass transition temperature increased with the increase of lignin content in PU. Compressive strength (a)/ density (p) and compressive elasticity (E)/p also increased with increasing lignin content. These results suggest that lignin act as a hard segment in PU molecules.
1. Introduction Natural polymers are fundamentally biodegradable, and they are circulated in the ecological system. Synthetic polymers, which contain natural polymers and their degradation products, are considered to be biodegradable. We have studied extensively polyurethanes which were derived from plant components such as cellulose, hemicellulose .and lignin [1-5]. In these studies, polyurethanes (PU's) were prepared using polyethers such as polyethylene glycol and polypropylene glycol as 277
278 Physical and chemical processing of fibre and non fibrous products
polyols. In the present investigation, PUts containing lignin were prepared using a polyester-polyol (diol-type polycaprolactone, PCL). Thermal properties of the obtained PU's were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG). Mechanical properties of PU's were also studied by compression test.
2. Experimental 2.1 Materials Kraft lignin (KL) was obtained from Holmen Pulping Company. Kraft lignin was purified byreprecipitation method using an alkaline solution of lignin and a diluted sulfuric acid solution. The purified KL was dried over phosphorus pentoxide in vacuum at 80°C. KL was dissolved in ethylene glycol (EG). This KL solution was mixed with polycaprolactone (peL, molecular weight 550, Daicel L 205 AL), and small amounts of water, silicon surfactant and dibutyltin dilaurate. The mixture was reacted with diphenylmethane diisocyanate (MDI, Mitsui Toatsu Chemical Industries Ltd., CR 200) under a vigorous stirring at room temperature. After foams were obtained in vessels, the samples were allowed to stand overnight at room temperature and then cured at 120°C for 1 hr in an oven.
2412 Measurements DSC measurements were carried 011t using a Seiko DSC 220. Samples of ca. 7 mg were heated at a rate of 20°C/min in nitrogen. A Seiko TG 220 was used for TG measurements. The measurements were carried out in nitrogen at a heating rate of 10°C/min. Compression tests were performed using a Shimadzu AGS 500B according to a JIS method. 3. Results and Discussion 3.1 Preparation of PU foams Lignin is a solid polymer. Accordingly, lignin must be dissolved in a polyol in order to prepare PU.lt was found that lignin was not soluble in peL. Therefore, as shown in Scheme 1, lignin was at first dissolved in ethylene glycol, and then the solution was mixed with PCL. This mixture was reacted with MDI. Fig. 1 shows the changes of density of PU's against KL content in the KL-EG-PCL system. The values were from 0.05 to 0.2 g/cm 3, indicating that good PU foams having low densities were successfully prepared.
Biodegradable polyurethanes
Kraft Lignin (Kl)
FEG Solution
pel Mixture MOl PU Foam
Scheme 1. Preparation of polyurethane foams.
0.045 ~
r - - - - - - - - - - -.....
0.04
o eo
-- 0.035
o
~
.~
CIJ
~
8
o
0.03
o. 025
...-.-_ _a..-.-_---..j~ 10 20 KL Content / % _
o
____..
30
Fig. 1. Relationship between KL content and density ofPU foam.
279
280 Physical and chemical processing of fibre and non fibrous products
3.2 Physical properties of PUts Fig 2 shows DSC curves of PUts with various KL contents in the EGPC:L-KL system. KL content is indicated for each DSC curve. A marked change in baseline due to glass transition is observed in each DSC curve. Glass transition temperature's(Tg's) were determined by a method reported previously [6]. Fig 3 shows the relationship between Tg and KL content in the polyol system. Tg increases with increasing KL content. It is known that lignin is a cross-linked and highly branched polymer which has rigid phenyl propanes as repeating units. Lignin has also more than two hydroxyl groups i.n a molecule. Therefore, it is considered that lignin reduces the mobility of the main chain of PU molecules. Fig 4 shows the change of Tg against PCL content in the polyol system. PCL has two hydroxyl groups in a molecule and flexible alkylene groups. A,; shown in Fig. 4, Tg decreases with increasing PCL content, suggesting that PCL acts as a soft segment in PU molecules.
t Tg
KL=25%
"'-~
20
0
15
"0 t::
~
~
10
1
5 0
a
20
~
~ ~ 40
80 60 Temperature / °C
100
120
Fig. 2. DSC curves of PU foams having various KL contents.
Biodegradable polyurethanes
60
u o '-.
on 40
~
20
--a
~
o
10 20 KL Content / %
30
Fig. 3. Relationship between Kl content and Tg of PU foam.
35
u
r-----------_
30
o
'-.
on ~ 25
20
-_....Io-_...4.-_--I-_---&._~
o
10
20 30 40 ret. Content / %
50
Fig. 4. Relationship between pel content and Tg of PU foam.
281
282 Physical and chemical processing of fibre and non fibrous products
Mechanical properties of PU foams were also studied by compression tests. Fig. 5 shows the changes of compressive strength (0)1 apparent density (p) and compressive elasticity (E)/p as a function of KL content in the polyol system. alp and E/p increase with increasing KL content. These results agree well with DSC results and suggest that lignin acts as a hard segment in PU molecules.
9
0.2 ~
~
S eo 0.15 ~ -.....
S 8 on
~
-..... ~
~
~
7
c,
--C> 0
-""'6
0.1
0
~
--
0.
0.
'b5
0
0
0
4
0
10 20 KL Content / %
0.05
-..... ~
0 30
Fig. 5. Changes of compressive strength (a)/density (p) and compresiive elasticity (E)/p against KL content of PU foam.
References [1] S. Hirose, S. Yano, T. Hatakeyama and H. Hatakeyama, in ACS Symposium Series 397 (W. G. Glasser and S. Sarkanen eds.), ACS, Washington DC, 1989, p382 [2] H. Yoshida, R. Morek, K. Kringstad and H. Hatakeyama, J. Appl. Polym. Sci., 34, 1187 (1987) [3] K. Nakamura, R. Morek, A. Reiman, K. P. Kringstad and H. Hatakeyama, Polym, Adv. Techno/., 2, 41 (1991) [4] K. Nakamura, T. Hatakeyama and H. Hatakeyama, Polym. Adv. Techno/., 3, 151 (1992) [5] H.Hatakeyama, K. Nakamura, S. Hirose and T. Hatakeyama, in "Cellulosics: Chemical, Biochsmiscal and Materials Aspects" (J. F. Kennedy, P. A. Williams and G. o. Phillips eds.), Ellis Horwood Ltd., Chichester, 1993, Chapter 77 [6] S. Nakamura, M. Todoki, K. Nakamura and H. Kanetsuna, Thermochimica Acta, 163, 136 (1988)
30 Viscoelastic properties of biodegradable polyurethanes derived from coffee grounds K Nakamura,* Y Nishimura,* T Hatakeyama and H Hatakeyama** *Otsuma Women's University, Sanban-cho, Chiyoda-ku, Tokyo 102, Japan; **National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305, Japan
Abstract Polyurethane (PU) films containing coffee grounds (CG) were prepared from coffee residue. CO mixed with either polyethyleneglycol (PEO having two functional groups, Mw=400) or polypropyleneglycol (PPO having three functional groups, Mw=400), was used as a polyol. PU films, prepared by reacting the mixture of CO polyol and catalyst of dibutyltin dilaurate with diphenylmethane diisocyanate (MOl), were obtained by solution casting. Thermal, mechanical and viscoelastic properties of PU films were measured. The glass transition temperature (Tg) and the tensile strength of PU films increased with increasing CG/polyol ratio. From viscoelastic measurements, a main dispersion peak (a) was clearly observed from 40 to 100°C in the case of CO-PEOMDI system and from 50 to 160°C in the case of CO-PPO-MDI system. The two other small dispersion peaks were observed at about -80°C (~) and -130°C (y) in the CG-PEGMDI system and were observed at about -20 "C
(~)
and -100°C (y) in the CO-PPO-
MDI system. The dynamic modulus (E') of the CG-PPG-MDI system was higher than that of the CG-PEG-MDI system since PPG, which is a polymer having three functional groups, forms high density crosslinks of PU networks to a greater degree than PEG. The tan 0 peaks shifted to the higher temperature side with increasing CG content. From these results it was found that CG powder acted as a hard segment in PU and that viscoelastic properties of PU's were controlled by the amounts of CO and polyol. 283
284 Physical and chemical processing of fibre and non fibrous products
Introduction We have developed biodegradable polyurethane (PU) derived from natural polymers, such as cellulose, lignin, wood tar etc [1-3]. PU generally consists of rigid molecules functioning as hard segments and flexible molecules as soft segments. In the above PU's, the major components of plant materials, pyranose rings and phenyl groups, are used as hard segments of PU's. We have also found that the mechanical and thermal properties increased with the introduction of plant component [4-11]. The amount of coffee grounds(CG) produced in the coffee industry is a hundred thousand tons/year in Japan. Coffee grounds have not been used since no application methods were found for effective utilization. Polyurethanes are one of the most useful multi-purpose polymers, since they can be processed in a wide variety of forms such as sheet, foams, paints etc .. PU's have been synthesized using various ester and ether type polyols and isocyanates. Natural polymers which are obtainable from various kinds of plants are suitable candidates for use as raw materials of PU's because plant materials contain hydroxyl groups in their structure. In the reaction to form the urethane linkage between isocyanate and plant materials, the hydroxyl groups in lignocellulose act as reaction sites. From the ecological view point, PU's containing natural polymers are beneficial, since natual polymers are generally recognized as biodegradable polymers. For the purpose of establishing the practical application of puts derived from coffee grounds, in this paper, viscoelastic properties of PU's were measured by a dynamic mechanical analyzer and the effects of CG powder and polyol on the viscoelastic properties of PU are reported.
Experimental Samples Coffee grounds having 180 microns (80 mesh) particle size after extracting coffee by an industrial process were provided by Ueshima Coffee Co. Ltd. CG was ground using a mill and passed through a screen. The average particle size was 75 microns (200 mesh). The main chemical components of dry CG are hemicellulose (36.2%), cellulose
(19.9%), fat (11.4%), protein (9.7%), lignin (8.7%) and ash (4.1 %). Polypropylene glycol (PPG) and polyethylene glycol (PEG) having average molecular weight (Mw) of 400 and crude diphenylmethane diisocyanate (MDI) were obtained from Mitsui Toatsu Chern. Co. Ltd.
PU Preparation Two PU systems, CO-PEO-MDI and CG-PPG-MDI, were prepared. In order to prepare PU films containing CG, a certain amount of CG having 200 mesh size was
Viscoelastic properties of biodegradable polyurethanes
285
mixed well with either PEG or PPG (Mw=400). The mixture was homogenized. The above polyol mixture was mixed with three drops of catalyst (di-n-butyltin dilaurate) and MDI of the same weight of polyol in tetrahydrofuran (THF). The amounts of THF used was 5 times of the total weights of polyol and MDI. 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 30min in an electric oven. The MDI/polyol ratio, CG content (CG/polyol) were defined as the following equations: MDI/polyol = weight of MDI / weight of polyol (gig) CG/polyol
= weight of CO / weight of polyol (gig)
(1) (2)
Measurements Viscoelastic Properties of PU films Viscoelastic properties of PU films were measured using a dynamic mechanical analyzer (DMA, Seiko Instruments Inc., DMS 200). The sample with 30 mm length and 5 mm width was measured by tensile mode at a heating rate of 1°C/min. Temperature was varied from -150 to 250°C using an apparatus with an automatic temperature controller. Measuring frequencies were 0.5, 1,2,5 and 10 Hz. Thermal Properties Thermal properties of puts were measured by a differential scanning calorimeter (DSC 220C, Seiko Instruments Inc.). A PU sample of about 5 mg was sealed in an aluminium sample vessel. DSC curves were obtained in a temperature ranging from 20 to 200°C at the scanning rate of 10°C/min. The glass transition temperature (Tg) was defined by the method reported previously [12]. Mechanical Properties Tensile properties of PU films were determined using a tensile test machine (TENSILON RTA-500, Orientec Co. Ltd.) at 25°C. The strain rates were 5mm/min. The gauge length was 50mm and thickness and width of PU films were about 0.5 mm and 5mm, respectively. Five test specimens were measured for each sample. Tensile stress at break (<Jb), strain at break (Eb) and Young's modulus (E) were calculated. Results and Discussion Figure 1 shows representative dynamic modulus (E'), dynamic loss modulus (En) and loss tangent (tan b = E"IE') curves of CG-PU films (CG-PEG-MDI) measured at 1 Hz as a function of temperature. E' decreased slowly with the rise in temperature in the
286 Physical and chemical processing of fibre and non fibrous products
glassy region, decreased rapidly in the glass transition region, reached a plateau in the rubbery region and finally decreased due to viscous flow. The E' values of the plateau region increased with increasing CG/polyol ratio. E" and tan 0 showed three peaks corresponding to the variation of tan
o. Each peak was denoted as
a,
13 and y from high
to low temperature. Tan 0 peak of a dispersion shifted from 40 to 120°C with increasing CG/polyol ratio. The local mode relaxation peaks were observed at about -80°C
(13) and
at about -130°C co although the peak intensity was weak. This suggests that the local molecular motion is restricted due to the three dimensional network.
10 10
...----------------,
10 11
...-----------------,
CG-PEG-MDI
CG-PPG-MDI
'----
109
0.5
~_------l_----'-:--...-....---'------------,
~----'----~---~--I
1.0 \--_ _
-l...-_ _- - I . -_ ____'__ _~
0.25
0.4
0.1
-50 50 150 Temperature, "e
Fig.l DMA curves ofPU (CG-PEG-MDI) films having various CG/polyol ratio.
Fig.2 DMA curves of PU (CG-PPG-MDI) films having various CG/polyol ratio.
Viscoelastic properties of biodegradable polyurethanes 287
Figure 2 shows DMA curves ofPU films of the CG-PPG-MDI system measured at 1 Hz as a function of temperature. The slopes of E' curves of the CG-PPG-MDI system in the glassy region were similar to those of the CG-PEG-MDI system. However, the E' value of the CG-PPG-MDI system was higher than that of the CG-PEG-MDI system. This comes from the fact that PPG has three functional groups in a repeating unit. The crosslinking density of PU networks of CG-PPG-MDI is higher than that of CG-PEGMDI prepared using two functional groups of PEG. According to the variation of E' of PU having CG/polyol= 1,
E' decreased gradually
from -150
to 250°C. The
temperature of a peak shifts to the high temperature side with increasing CG/polyol ratio. At the same time, the width of the tan 0 peaks also increased with increasing CG/polyol ratio as shown in Figure 2. Moreover, the shoulder of a peak was observed in the PU's having a large amount of CO content. This peak which was denoted as a' dispersion, kept a constant temperature of 50 °C. This means that the a' peak is independent of the molecular motion of the molecules in the CG component. Figure 3 shows the relationships between peak temperatures of tan 0 peaks of CGPPG-MDI system, CO-PEG-MDI system and CO/polyol ratio. The peak temperature of a dispersion of CG-PPG-MDI system shifts to the higher temperature side with increasing CG/polyol ratio. In contrast, peak temperatures of a',
~
and y dispersions
maintain an almost constant values at 50, -30 and -100 °C, respectively. As shown in Figure 3, peak temperatures of the CG-PEG-MDI system are lower than those of the CG-PPG-MDI system. This is reasonable, if we consider the functionality of PEG and PPG. 200
CG-PU Film
15
o 150 MDI/Polyol=1.2 cU
10
... 100 a; ... ~
Q)
a-
D
E
.! ~
cu Q)
Q.
~
o
cCI)
•
P
-50
:a::
CG-PPG-MDI
0
:::J
C'"
... Q)
LL
CG-PEG-MDI
c-o
0 ----rr---o
e
!! -100 -150
N
a'
50
L-_-L-_--L-_--J.-_~_
o
0.2
0.4
0.6
0.8
____'
1.0
CG/Polyol, gig
Fig.3 The relationship between tan 0 peak temperature and CG/polyol ratio. ... CG-PEG-MDI, - CG-PPG-MDI.
0.3
L - - _ " ' O " ' - _ - - - ' - - _ - - - - ' -_ _" - - - - _ - . . . - _ - - - '
2
2.2
2.4 2.6 2.8 T/1000:/ 1000/K
3
3.2
Fig.4 Arrhenius plots of tan 0 peaks of ex dispersion of PU (CG-PPG-MDI).
288 Physical and chemical processing of fibre and non fibrous products
Figure 4 shows representative Arrhenius plots of tan 0 peaks of ex dispersion of PU's having various CG contents of CG-PPG-MDI system. All plots were linear therefore, it was possible to calculate the activation energy (Llli) of each dispersion from the gradient of the line. In the case of a' dispersion, it was difficult to calculate the dE, because the shoulder temperature could not be read accurately for all the range of frequencies. In the case of the CG-PEG-MDI system, Arrhenius plots of A., ~ and 'Y peaks were obtained and dE was calculated. Figure 5 shows the dE of ex,
pand 'Y dispersions of the CG-PPG-MOl
system plotted
against CG/polyol ratio. dE of ex dispersion changed linearly from 230 to 300 Kl/mol, This fact suggests that ex dispersion is attributed to the main dispersion [13, 14], showing that the molecular chains including hard segments are enhanced together with soft segments. ~E of J3 dispersion also changed linearly from 100 to 250 Kl/mol, This value corresponds to the molecular motion of the rotation of phenyl groups [14-16].
~E
of'Y dispersion was almost constant at 50 Kl/mol, The value of 50 Kl/mol corresponds to the rotation of methyl groups [14].
~E
ofCG-PEG-MDI system was from about 150
P
Kl/mol to 250 Kl/mol for ex dispersion, from about 40 Kl/mol to 70 Kl/mol for dispersion and from about 20 Kl/mol to 40 Kl/mol for 'Y dispersion.
Figure 6 shows the relationship between stress at break (<Jb) and Young's modulus (E) of CG-PU (CG-PPG-MDI) films and the CG/polyol ratio estimated from stress-strain measurements. E increased with increasing CG/polyol ratio, although the value of <Jb increased with increasing CG/polyol ratio until about 0.5 and then decreased. The 350 , . . . - - - - - - - - - - - - - - - .
60
-- ---
2.5
0
300
•
('Q
a..
250
."..."""
0
50
,,;-
•
en In
..,--
E 200
~
(1)
::: 30
~
en
u.i 150
.!!!
100
2.0
u) 't:J 0
CG-PPG-MDI
0"------1.----.....--......10...---...1
o
0.25
0.5
0.75
1
CG/Polyol, gIg
Fig.5 Activation energies (~E) of 0., and "( dispersions of CG-PPG-MDI system.
~
E U)
·0
c
:;,
(1)
t-
r --c~.....L.--G---a._-l
('Q
a..
1.52 :;, 1.0
.~ 20
<J
50
....
""."... ~
C)
::E 40
"0
,,;-
o
0.5>
10 CG-PPG-MDI
O'----...I...--~----'-----'-------'O
o
0.2
0.4 0.6 0.8 CG/Polyol, gIg
1.0
Fig.6 The relationship between stress at break (<Jb) and Young's modulus (E) and CG/poly~1
ratio of CG-PPG-MDI system.
Viscoelastic properties of biodegradable .polyurethanes
289
variation of E values estimated by mechanical measurements carried out at 25 °C also accorded well with that of E' estimated by dynamic measurements. Both results indicate that the CG component functions as a hard segment and that PU samples in the glassy state are hardened with increasing CG content. Figure 7 shows the glass transition
140
temperature (Tg) estimated from DSC heating
120
curves of CG-PPG-MDI and CG-PEG-MDI
100
systems as a function of CG/polyol. The values of Tg increased with increasing CG/polyol ratio and agrees well with the
o
C)
I-
results of Figure 3, although the Tg values estimated from DSC curves were lower than tan () peak temperatures of a. dispersion. In general, it is known that Tg values measured by DSC corresponded to the starting temperature of tan ()peak measured by DMA.
•
80 60
",.
/
40
o / / CG-PEG-MDI o /
20
o -20
/'0
/
/
/
/
0
L . . - - _ - L - _ - - - ' - - _ - - - I_ _o o o L - _.......
o
0.2
0.4
0.6
0.8
1.0
CG/Polyol, gIg Fig.7 The relationship between Tg and CG/polyol ratio.
Conclusions From the above results it is concluded that: (1) PU films having a variety of viscoelastic properties can be derived from coffee grounds by reaction with MDI and polyols. (2) Coffee grounds act as a hard segment in PU's. (3) Glass transition temperature increased with increasing amount of CG. At the same time, the activation energy of a. dispersion increased, suggesting that the molecular chains including the hard segments are enhanced together with the soft segments. (4) Beside a. dispersion, two local mode relaxations, ~ and 'Y, were observed;
~
dispersion is attibuted to the local mode relaxation of the phenyl groups in PU and 'Y dispersion is attributed to the rotation of the methyl groups. (5) Dynamic modulus of CG-PPG-MDI system was higher than that of CG-PEG-MDI system because of the difference of functionality.
References 1. Hirose S., Yano S., Hatakeyama H. and Nakamura K., U. S. Pat., 4, 987, 213 (1991). 2. Hirose S., Hatakeyama H. and Nakamura K., Japanese Pat., 1,791,797 (1993). 3. Hirose S., Yano S. and Hatakeyama H., Japanese Pat., 1, 813, 561
(1994).
290
Physical and chemical processing of fibre and non fibrous products
4. Yoshida H., Morck R., Kringstad K. P. and Hatakeyama H., J. Appl. Polym. Sci., 40, 1819 (1990). 5. Reimann A., Morck R., Yoshida H., Hatakeyama H. and Kringstad K. P., J. Appl. Polym. Sci., 41,39 (1990). 6. Yoshida H., Morek R., Kringstad K. P. and Hatakeyama H., J. Appl. Polym. Sci., 34, 1187 (1987). 7. Hirose S., Yano S., Hatakeyama T. and Hatakeyama H., in "Lignin, Properties and Materials", ACS Symp. Ser., 397, W. G. Glasser and S. Sarkanen, Eds., p.382, American Chemical Society, Washington D.C. (1989). 8. Yano S.,
Hirose S. and
Hatakeyama
H., in
"Wood Processing
and
Utilizat.ion", J. F. Kennedy, G. O. Phillips and P. A.Williams Eds., p.269, Ellis Horwood, Chichester 9. Nakamura
K., Morek
(1989). R., Reimann A. and Hatakeyama
H., in "Wood
Processing and Utilization", J. F. Kennedy, G. O. Phillips and P.A. Williams Eds., P.175, Ellis Horwood, Chichester (1989). 10. Nakamura K., Morck R., Reimann A., Kringstad K. P. and Hatakeyama H., Polym. Adv. Technol., 2, 41 (1991). 11. Nakamura K., Hatakeyama T. and Hatakeyama H., Polym. Adv. Technol., 3, 151 (1992). 12. Nakamura
S., Todoki M., Nakamura
K. and Kanetsuna H.,
Thermo.
Chimica. Acta., 136, 163 (1988). 13. Hatakeyama H., Nakamura K. and Hatakeyama T., Pulp. Paper Mag. Canada,
6, TRIOS (1980). 14. Wada Y., "Kobunshi no Kotai Bussei", "Solid State Properties of polymers", p.69, p.260-271, p.278, p.293, p.298, p.300, Baifukan, Tokyo (1971). 15. Hirose S., Yoshida H., Hatakeyama T. and Hatakeyama H., "Viscoelasticity of Blomaterials", W.G. Glasser and H.Hatakeyama Eds., p.385, American Chern. Soc., Washington, DC (1992). 16. Kamimoto M., Hatakeyama T., Magoshi J., Mitsuhashi F. and Yokokawa H., "Shin Netsu Bunseki no Kiso to Oyo" , "Fundamentals and Applications of Thermal Analysis, New Edition", p.157, Riaraizu-sha, Tokyo (1989).
31 The fractional composition of polysaccharides in alkaline pre-treated and steam pressure treated wheat straw R Sun, J M Lawther and W B Banks* - The BioComposites Centre and *School of Agricultural & Forest Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, Wales
ABSTRACT
Wheat straw, pre-treated with 1.5% sodium hydroxide at 20°C for 6 h, was extracted with 0.250/0 ammonium oxalate for 4 h at 85°C, followed by steam pressure treatment at 120°C/2 bar for 7 h. The residue was then delignified using acidic sodium chlorite solution, followed by treatment with 24% potassium hydroxide with 2% boric acid for 2 h at 20 0 e for determination of hemicellulose and a-cellulose.
The yields were
determined gravimetrically and related to the control sample. Results showed that pretreatment with 1.50/0 sodium hydroxide significantly influenced the solubility of hemicellulose, whilst the steam pressure treatment had a pronounced effect on lignin solubility.
It was also found that xylose was the major sugar constituent in the
hemicellulose fraction and the hydrolysate obtained during NaOH pre-treatment, with
291
292 Physical and chemical processing of fibre and non fibrous products
glucose and galactose as minor components. The content of arabinose was higher in the hydrolysate obtained from the pre-treatment than in the hemicellulose fraction, whereas xylose in hemicellulose was higher than that in the hydrolysate of the pretreatment.
The content of uronic acid in the hydrolysate obtained from the 1.5%
NaOH pre-treatment was higher than in the hemicellulose fraction. The range of molecular weights of both the hemicellulose and "pre-treatment" straw hydrolysate was also examined.
Key words: pre-treatment, wheat straw, steam pressure treatment, lignin, extraction, hemicellulose, pectic substances, sugar, uronic acids, molecular weight.
IN~rRODUCTION
Significant solubilisation of cell walls and hemicellulose has previously been ascribed to the synergistic effect of sodium hydroxide and steam pressure treatment of wheat straw (1). Rai and co-worker (2) have reported that the combined effect of alkali and steam
pressure treatment brought about dramatic changes in chemical composition as well as utilization of cellulose and hemicellulose of rice straw. The present investigation was aimed at determining the effect of sodium hydroxide and steam pressure treatments on the constituents of polysaccharides in wheat straw.
Fractional composition of polysaccharides
293
MATERIALS AND METHODS
Materials
Wheat straw was obtained from Silsoe Research Institute (Silsoe, Bedfordshire) and was ground using a Christie Laboratory mill to a 60-mesh size screen. The ground straw was then dried in a cabinet oven with air circulation for 16 h at 60°C and stored at 5°C until use. All chemicals were of analytical or reagent grade. All experiments were performed in duplicate and weights and yields are given on a dry, untreated, straw weight basis.
1.5% NaOH pre-treatment (figure 1)
The ground wheat straw was firstly pre-treated in air with 1.50/0 sodium hydroxide at 20°C for 6 h. After filtration on a nylon cloth, the residue was recovered, washed three times with water, twice with 960/0 ethanol and once with acetone, then dried in an oven for ) 6 h at 60°C and reweighed. The weight lost was defined as dry matter loss. The disappearances of hemicellulose and lignin were calculated from the control sample, which vias dipped only in distilled water for 6 h at 20°C.
The supernatant was
neutralized with dilute acetic acid and concentrated on a rotary evaporator under reduced pressure at 40°C against water to dry.
The resultant brown hydrolysate
obtained from the pre-treatment was kept in a fridge at O°C until analysis.
294 Physical and chemical processing of fibre and non fibrous products
Extraction of pectic substances
Pectic polysaccharides were extracted from the residue of 1.5% NaOH pre-treated for 4 h at 85°(: using 0.25% ammonium oxalate (AO) according to the method described by Phatak et al (3).
The supernatants were extensively concentrated on a rotary
evaporator under diminished pressure at about 40°C to one-twentieth of their original volume, and then precipitated with 5 volumes of 96% ethanol for 24 h at 20°C. After filtration and drying in an air circulated 'oven for 16 h at 60°C, the resultant pectic substances or pectin fractions were stored in a fridge at DoC until analysis. The residue was rinsed once with water, twice with 96% ethanol and once with ether and then dried in an oven for 16 h at 60°C.
Steam pressure treatment
1.3 g of the residue from the 0.25% AO extraction was treated in a 100 ml capacity
autoclave at 120°C/2 bar for 7 h. The liquid/solid ratio was 25: 1. The reactor was placed in an oil bath which had previously been brought to a sufficiently high temperature so that the contents of the vessel could be heated to the reaction temperature within 5 min. When the desired temperature was reached timing was begun. The reactor was removed and placed into a water bath for rapid cooling at the end of the treatment period. After filtration, _the residue was washed three times with water, dried at 60°C for 16 h, reweighed and then stored at room temperature ready for extraction of polysaccharides.
The liquor from the water steam treatment was
concentrated to dryness on a rotary evaporator under reduced pressure at 40°C. The dried supernate was kept in a fridge at 5°C until analysis of polysaccharides solubilised during the steam pressure treatment process.
Fractional composition of polysaccharides
295
Delignification
Lignin content in wheat straw was determined according to the method described by Bagby et al (4), Collings et al (5) and Asensio et al (6).
The residue from above
procedures (1.0 g) was stirred with water (100 ml) and 100/0 acetic acid (8 ml), and delignified with sodium chlorite (NaCI02, 3.2 g) in flask fitted with a magnetic bar. The mixture was heated for I h at 75°C. More acid (4 ml) and sodium chlorite (1.6 g) were then added and the mixture heated for another hour. After 2 h the residue was filtered out on a nylon cloth and washed with water (three times), 96% ethanol (twice) and ether (once), then dried at 60°C for ]6 h and reweighed. The difference in weight was defined as sodium chlorite lignin.
Isolation of hemicellulose and cellulose
Hemicellulose was isolated from the remaining straw using an aqueous solution of 240;0 potassium hydroxide (0.9 g straw residue/I 00 ml extractant) and 2% boric acid, in air, for 2 h at 20°C. The residue was recovered, washed with water until alkali free and then with 5% acetic acid (once), water (once), ethanol (once) and acetone (once). It was then dried at 60°C for 16 h. The weight lost was taken as hemicellulose. The weight of the residue which remained after the alkaline extraction, corrected for ash content, was termed a-cellulose.
After neutalization with dilute acetic acid, the
supernatant was concentrated to a small volume under reduced pressure at a temperature not exceeding 40°C, and then precipitated with 5 volumes 96% ethanol for 24 h at 20°C. After filtration and drying in an air circulated oven for 16 h at 60°C, the resultant hemicellulose fraction was kept in a fridge at 0 °C until analysis.
296 Physical and chemical processing of fibre and non fibrous products
Neutral sugar, uronic acid, methyl ester and acetyl content analyses
Preliminary identification of the neutral sugars in the hydrolysates of the steam pressure pre-treatment, pectic substances, hemicelJuloses and cellulose was obtained using thinlayer chromatography with ethylacetate-isopropanol-water (60:30: 10) as the solvent system. The visualization of sugars on the thin-layer chromatograms was achieved with 100/0 aqueous ammonium molybdate and heated to 100
0
e for
10 min according to the
method of Egon et al. (7).
The contents of the neutral sugars (arabinose, xylose, mannose, galactose and glucose) in the solubles of steam pressure treatment, pectic polysaccharides, hemicellulose, cellulose and the hydrolysate of pre-treatment were measured by gas chromatography after conversion to corresponding trimethylsilyl (TMS) ether derivatives. Methods are described in our other paper in this volume.
The uronic acids were assayed colorimetrically, as anhydrogalacturonic acid in pectin, or as glucuronic acid in hemicellulose and in the hydrolysates, using 3-phenylphenol color reagent according to the procedure outlined by Blumenkrantz and Asboe-Hanson (8) with a modification by Wedig and co-workers (9).
A Hewlett-Packard Diode
Array 8452A spectrophotometer was used to measure anhydrogalacturonic acid or glucuronic acid at a wavelength of 520 nm.
The value of rhamnose in pectin was determined by the quantitative colorimetric procedure of Gibbons (10) and Dische et al (11) after hydrolysis for 4 h in 2 N trifluoroacetic acid. Methyl ester content was determined according to the method described by Wood and Siddiqui (12). Acetic acid content was estimated using the
Fractional composition of polysaccharides 297
transesterification method outlined by Browing (13), with a small modification from
Whistler and Jeanes' procedure (14).
Measurement of physicochemical properties of pectin and hemicellulose
Viscosity was determined using a Brookfield Synchro-Lectric Viscometer (Model LV). A citrus pectin was used as a reference. Pectin samples (2%,w/v) were prepared in O.IM sodium phosphate buffer, pH 7.0, allowed to hydrate at 4°C for 16 h (15). Viscosity was then estimated (cps) at 25°C.
Optical rotation was measured on a polarimeter (Perkin Elmer, type 108) according to the methods described by McCready et al (16).
Pectin samples (1.00/0, w/v) were
prepared in double distilled water and centrifuged before measurement. A citrus pectin was also used as a reference.
The average molecular weights (M w) of pectin and hemicellulose were determined by gel permeation chromatography (17) on a PL aquagel-OH 50 column (300 x 7.7mm, Polymer Laboratories Ltd)., calibrated with PL pullulan polysaccharide standards (peak average molecular weights 667, 5800, 12200, 23700, 48000, 100000, 186000, and 386000, Polymer Laboratories Ltd). The pump was a Knauer HPLC pump 64., with a flow rate of 0.5 ml/min for measuring pectin and 0.1 ml/min for the hydrolysates and hemicellulose. The eluents were double distilled water for pectin and 0.02 N NaCI in 0.005 M sodium phosphate buffer, pH 7.5 for the hydrolysates and hemicellulose, respectively.
Detection was achieved by a Knauer differential refractometer.
column oven was maintained at 30°C.
The
Pectin samples were dissolved in double
298 Physical and chemical processing of fibre and non fibrous products
distilled water at a concentration of 0.1%. The hydrolysates and hemicellulose were dissolved with 0.02N NaCI in 0.005 M sodium phosphate buffer, pH 7.5.
Gelling of AO extracted pectin samples was tested according to the procedure of Chang et al. (18). Pectin samples were prepared in distilled water at a concentration of
1.00/0 (w/v).
Wheat straw
I Dry at 60°C for 16 h. Dried wheat straw
IPre-treatment with 1.5% NaOH at 20°C for 6 h. Pre-treated wheat straw
I Addition of 0.25% ammonium oxalate at 85°C for 4 h. Depectinated wheat straw ITreatment with pressure steam at 120°C/2 bar for 7 h. Steam pressure treated straw Addition of acetic acid and sodium chlorite to pH 4.2-4.7 for delignification at 75°C for 2 h.
Lignin free sample 24% KOH and 2% boric acid at 20°C for 2 h alkaline extraction of hemicellulose.
Hemicellulose free sample The residue washed with water until alkaline free and 5% acetic acid(once ), water( once), ethanol(once), and acetone( once), then dried at 60°C for 16 h.
Cellulose Figure 1. Scheme for extraction and isolation of polysaccharides from sodium hydroxide pre-treated and steam pressure treated wheat straw
Fractional composition of polysaccharides
299
Nitrobenzene oxidation of lignin in wheat straw, pre-treated wheat straw, and extracted hemicellulose and cellulose
The method. for alkaline nitrobenzene oxidation of lignin remaining attached to/associated with hemicellulosic tractions and cellulose was based on the procedure published by Scalbert and Monties (19) with some modifications.
The method is
described in our other paper in this volume.
RESlJLTS AND DISCUSSION
The fractional composition of sodium hydroxide pre-treated and steam pressure treated wheat straw
Plant cell walls contain three types of structural polysaccharides, namely cellulose, hemicellulose and pectic substances. In wheat straw, cellulose and hemicellulose are the predominant components, comprising about 700/0 of dry mass. The third major cell wall component in straw is lignin, which composes of 14-170/0 (sodium chlorite lignin) of dry straw. The fractional composition of 1.50/0 sodium hydroxide pre-treated and steam pressure treated wheat straw is shown in table 1. The weight loss of dry matter in 1.5% sodium hydroxide pre-treatment (at 20°C for 6 h) process is
28.47%~
about
20% of lignin and 50% of hemicellulose are dissolved during treatment. More details of the neutral sugar composition of soluble hemicellulose in the pre-treatment are given elsewhere (20).
300 Physical and chemical processing of fibre and non fibrous products
Table 1. The fractional composition of sodium hydroxide pre-treated and steam pressure treated wheat straw (0/0 dry weight)
The weight loss of 1.5% NaOH treatment 28.47(containing 3.56 lignin and 16.35 hemicellulose) Pectin
5.34
The weight loss of steam pressure treatment 10.81(containing 3.63 lignin and 5.07 hemicellulose) Lignin Hemicellulose
10.13 11.42
Cellulose
34.07
Ash
3.02
Total
103.26
The composition and physicochemical properties of pectin
The yield of anhydrogalacturonic acid, methoxyl, acetyl and ash contents of pectin extracted with 0.25% ammonium oxalate at 85°C for 4 h from the residue of NaOH pre-treated wheat straw are shown in table 2. A pectin value of 5.34% was obtained. The content of anhydrogalacturonic acid in extracted pectins was 24.52%.
The
methoxy content was low in the sample indicating that wheat straw pectin is a lowmethoxy pectin. The data also showed that ammonium oxalate extracted pectins have acetyl groups present in their structure. The acetyl content of pectin in the extract was about 4.64%. This indicated that pectic substances are only partially acetylated. Based
Fractional composition of polysaccharides
301
on study of sugar beet pectins, Rombouts and Thibault (21) concluded that most of the acetyl groups were associated with galacturonic acid residues rather than with neutral sugars.
In 1982, Chesson and Monro (22) observed that hot water soluble pectins
contained more acetyl groups as well as more neutral sugars than did oxalate soluble pectins. They also assumed that acetyl groups in pectins were primarily associated with galacturonic acid residues. The extracted pectin contained a high amount of ash, which was due to the pre-treatment with mineral hydroxide.
Table 2. The chemical composition(%) and functional properties of pectin extracted with 0.25% ammonium oxalate at 85°C for 4 h(1.5 g wheat straw / 100 ml extractant) from 1.5% NaOH pre-treated(at 20°C for 6 h) wheat straw.
Composition'! and functional propertiesa
0.250/0 ammonium oxalate extraction
Pectin yield
5.34
Anhydrogalacturonic acid
24.52
Methoxy content
4.76
AcetyI content
4.64
Avcrage molecular weight Optical rotation
laln25 °
17000 +70 3.05
Viscosity (cps) Ash (w/w)
15.68
aDate are expressed on a dry basis, and represent the mean of duplicate runs.
'Table 3 shows the neutral sugar composition of pectin extracted with 0.25% ammonium oxalate from NaOH pre-treated wheat straw.
As shown in table 3, the
302 Physical and chemical processing of fibre and non fibrous products
extract was found to be rich in galactose, xylose and arabinose and low in rhamnose and glucose. Undoubtedly, xylose is a good indicator for hemicellulose and glucose for cellulose (23).
It appeared that an amount of hemicellulose was solubilized and
extracted during the 0.25% AD treatment process. Studies of sycamore suspension cell wall by Darvill et al. (24) also showed that the neutral and acidic pectic polysaccharides were covalently attached to the hemicellulose.
Table 3. The composition of neutral sugars (relative %) in pectin extracted with
0.25~/0
ammonium oxalate at 85°C for 4 h ( 1.5 g wheat straw / 100 ml extractant) from 1.5% NaOH pre-treated (at 20°C for 6 h) wheat straw.
Sugars
Content'vrclativc %)
Rhamnose
8.41
Arabinose
24.20
Xylose
18.17
Mannose
NDb
Galactose
37.36
Glucose
11.90
aDate are expressed on dry basis, and are the mean of duplicate analyses. bNot detectable.
The acidic polysaccharide has been identified as a pectin and contained galacturonic acid as the major sugar component with small amounts of galactose, arabinose, rhamnose, and xylose (25, 26). It is also important to point out that the galacturonic acid content of commercially available pectin extracted from citrus, apple peel, and
Fractional composition of polysaccharides
303
sugar beet pulp is remarkably different from the galacturonic acid content of wheat straw pectin isolated by the procedure described here, mainly in the much lower galacturonic acid content of wheat straw pectin.
The average molecular weight of pectin isolated by 0.25% AO peaked at 17, 000. Optical rotation of the pectin (1.0%, w/v) was about +70. The viscosity (2%, w/v) of pectin was determined at 3.05 cps. These values were much lower than those observed in citrus pectin.
The pH, molecular size, degree of methylation, and temperature
significantly affect the viscosity of wheat straw pectin.
However, this low viscosity
property of wheat straw pectin, which is similar to sugar beet pulp pectin, indicates a high potential for application in low-caloric, high fibre beverages (3).
Due to the presence of acetyl groups, low viscosity and low molecular weight, in extracted wheat straw pectin, no gel formation was observed for the extract at 1.00/0 level of addition to water (27). Citrus pectin at 1.00/0 formed a firm gel.
The weight loss and the content of neutral sugars of water soluble material during the steam pressure treatment
The dry weight loss during the steam pressure treatment was 10.81 %; this fraction was found to contain about 21 % of lignin and 15% of hemicellulose. This indicated that the NaOH pre-treatment significantly influenced the solubility of hemicellulose, whereas steam pressure treatment had a great effect on lignin dissolution. Rai and co-worker ( I) observed that sodium hydroxide pre-treatment of wheat straw followed by steam pressure treatment increased the solubilization of cell walls and hemicellulose. content of neutral sugars in the water soluble fraction obtained
The
during the steam
304 Physical and chemical processing of fibre and non fibrous products
pressure treatment is shown in table 4.
Xylose was the major sugar constituent.
Galactose, arabinose and glucose were present in noticeable amounts.
From the
aforementioned data shown in table 4, it is also noteworthy that some portion of hemicellulose was removed during the steam pressure treatment.
Table 4. The content (0/0) of neutral sugars of water soluble material during the steam pressure treatment (120 0 C/2 bar for 7 h)
Neutral sugars''
Content(%)
Arabinose
2.7
Xylose
6.J
Mannose
o.~
Galactose
J.5
Glucose
l.~
aDetermined by hydrolysis with 2 N trifluoroacetic acid at 121 C for 2 h in sealed 0
pressure tube then by gas chromatography after conversion to trimethylsilyl(TMS)
ether derivatives(mean of duplicate analysis).
The neutral sugar composition of hemicellulose and cellulose
The hemicellulose fraction of wheat straw is thought to be composed mainly of {3 1-4 linked D-xylopyranose units with side chains of various lengths containing L-arabinose, D-glucuronic acid or its 4-0-methyl ether, D-galactose and possibly D-glucose (28). The relative sugar composition of hemicellulose, extracted from NaOH pre-treated and steam pressure treated wheat straw, is presented in table 5. Xylose was the major
Fractional composition of polysaccharides
305
constituent and comprised more than 800/0 of the total sugars in hemicellulose. Minor constituents were galactose, glucose and arabinose. Mannose is present only in trace amounts in extracted hemicellulose.
Compared with the relative sugar content of 1.50/0 NaOH pre-treated straw hydrolysate, the hemicellulose containing high content of xylose could be extracted only after treatment with chlorite and subsequent alkaline extraction.
This provides
evidence that hemicelluloses in wheat straw cell wall material were either bound to or shielded by lignin, preventing their extraction prior to delignification (29).
Table 5. The sugar composition(relative 0/0) of hemicellulose and cellulose extracted from sodium hydroxide pre-treated and steam pressure treated wheat straw.
Sugars
Hemicellulose
Cellulose
63
1.2
Xylose
83.3
2.8
Mannose
Traces
Arabinose
Galactose
3.6
Glucose
6.2
Traces 96.0
Table 5 also shows the composition of the neutral sugars in wheat straw cellulose after extraction with 240/0 KOH and 20/0 H3B03 for 2 h at 20°C.
It is evident that
O!-
cellulose is contaminated with hemicelluloses which have not been removed by the previous fractionation procedures. Treatment with 72% H2S04 (2 h, 20°C) and 3% H2S04 (6 h, 100°C) hydrolysed the cellulose and produced a neutral sugar
306
Physical and chemical processing of fibre and non fibrous products
composition(relative %) of arabinose 1.2%, xylose 2.8%, glucose 96.00/0 and trace amounts of galactose.
The resistance to extraction by 240/0 KOH suggests that
hemicellulose is very strongly associated with the cellulose, analogous to the observation that xylans are often associated with lignified tissues.
The content of uronic acids and the range of molecular weights in hemicellulose and the hydrolysate of NaOH pre-treatment
The content of uronic acids in the hemicellulose fraction was very low; 1.00/0, whilst a relatively high content was detected in the hydrolysate of the sodium hydroxide pre-
treatment; 4.4%.
The ranges of the molecular weight of wheat straw hemicellulose extracted using 24% KOII and 2% H3B03 at 20°C for 2 hand 1.5% NaOH pre-treated straw hydrolysate are shown in figure 2. The 1.5% NaOH pre-treated straw hydrolysate gave a molecular weight about 18 000. In contrast, a sharp and symmetric peak of hemicellulose had
apparent low molecular weights, corresponding to 9 500. This result was in agreement with Whistler and co-workers' study (30) in early 1948.
They indicated that weak
alkaline solutions generally solublized hemicellulose B, the more acidic or branched fraction, to a greater extent than hemicellulose hemicellulose.
~
a more linear and less acidic
Therefore, hemicellulose B can be more or less selectively extracted
from wheat straw with very weak alkaline solutions, such as saturated lime water or low percentage sodium hydroxide solution (e. g. 1.5% NaOH pre-treatment). These studies have also shown that the hydrolysate of the pre-treatment with 1.5% NaOH contained more hemicellulose B, which had a relatively high content of uronic acid and high molecular weight, while the hemicellulose extracted with 240/0 KOH and 20/0
Fractional composition of polysaccharides
307
H3B03 at 20°C for 2 h from NaOH pre-treated and steam pressure treated wheat straw contained more hemicellulose A, which had a lower content of uronic acid, and was low molecular weight. In addition, the high molecular weight of the hydrolysates can probably be ascribed to the fact that some soluble lignin-polysaccharide complexes were extracted during the 1.5% NaOH pre-treatment process.
The content of phenolic acids and aldehydes of alkaline nitrobenzene oxidation lignin in wheat straw , pre-treated wheat straw , wheat straw hemicellulose and cellulose.
The FTIR spectra of wheat straw and pre-treated wheat straw (figure 3) appeared to be rather similar. However, on closer examination of the spectrum of wheat straw, it can be seen that there is a absorbance at 1720 crrr l.corresponding to ester linkage between cinnamic acids and lignin/polysaccharides in wheat straw cell walls, whereas those of pre-treated wheat straw nearly disappear peak at 1720 em-I. Figure 3 also show the FTIR spectra of hemicellulose (c) and cellulose (d) extracted from pre-treated (6 h, 20°C, 1.5% NaOH) and steam pressure treated (120°C/2 bar, 7 h) wheat straw. The very weak absorbances around 1510 cm- 1 (in hemicellulose) and 1410 cm- 1 (in cellulose) were due to aromatic groups in associated lignin. This figure indicated that the extracted hemicellulose and cellulose still contained some residual lignin.
308 Physical and chemical processing of fibre and non fibrous products
Table 6. The content (%) of phenolic acids and aldehydes of alkaline nitrobenzene oxidation lignin in wheat straw, pre-treated wheat straw and wheat straw hemicellulose and cellulose.
Phenolic acids
Wheat
Pre-treated
straw
straw
Gallic acid
0.21
0.11
Protocatechuic acid
NDb
NO
And aldehydes''
Hemicellulose
Cellulose
0.0042
0.001~
NO
0.0056
p-Hydroxybenzoic acid
0.08
0.047
0.0038
0.0056
p-Hydroxybenzaldehyde
0.28
0.11
0.0060
0.0027
Vanillic acid
0.14
0.051
0.026
0.010
Vanillin
2.34
1.69
0.024
0.012
Syringic acid
0.20
ND
0.01.1
o.())
p-Coumaric acid
0.07
0.010
0.0050
0.020
Syringaldehyde
2.22
1.89
0.0012
0.012
Acetovanillone
0.16
0.083
0.00 10
ND
Ferulic acid
0.25
0.17
0.0012
0.0012
Cinnamic acid
0.05
0.023
0.0033
0.OO3H
0.0030
0.OO~5
0.092
0.11
Unknown Total
6.00
4.18
I
aDetermined by HPLC after alkaline nitrobenzene oxidation at 170°C for 2.5 h in steel autoclaves. bNot detectable.
Fractional composition of polysaccharides
-- a
--+-b
Q) (/)
c: o c, (/)
e (5
'0 Q) a;
o
......-
o----===:lI::=-=---------..-=-:~----------..,.:;:;::::o
6.4
7.6
7.0
8.5
8.2
8.8
9.4
9.1
V(Elution, ml)
Figure 2. The GPC range of the molecular weight of 1.5% NaOH hydrolysates (a) and hemicellulose (b) extracted from NaOH pre-treated and stearn pressure treated wheat
straw. Microns 2.6
2.8
3.0
3.5
-S..O
4..5
5.0
3500
6.0
7.0
1500
8
10
15 20
1000
500
Wavenumber
Figure 3. FTIR spectra of wheat straw (a), pre-treated (1.5% NaOH, 20°C, 6 h) wheat straw (b), hemicellulose (c) and cellulose (d) extracted from 1.5% NaOH pre-treated and steam pressure treated (120° C/2bar, 7 h) wheat straw.
309
310
Physical and chemical processing of fibre and non fibrous products
The phenolic composition of wheat straw, pre-treated wheat straw, hemicellulose and cellulose extracted from 1.5% NaOH pre-treated and steam pressure treated wheat straw is summarised in table 6. The total phenolic contents in wheat straw, 1.5% NaOH pre-treated wheat straw, and extracted hemicellulose and cellulose were 6.00, 4.18, 0.092, and 0.11 %~ respectively.
The major components were found to be
vanillin and syringaldehyde in both wheat straw and 1.50/0 NaOH pre-treated wheat straw.
Hemicellulosic fraction showed higher contents of gallic acid,
p-
hydroxybenzaldehyde, vanillic acid and vanillin than that in cellulose. Protocatechuic acid was not detected in hemicellulose, whereas it appeared at a level of about 0.0056% in cellulose.
A<:KNOWLEDGEMENTS
The authors acknowledge the
financial support for the research from LINK
Collaborative Programme in Crops for Industrial Use. We gratefully thank Dr. James Bolton, Director of The BioComposites Centre, for the award of a research studentship to Runcang Sun. We also grateful to Gwynn Lloyd Jones, Andy McLauchlin and Sara Hughes for their valuable suggestions and constructive discussion.
Fractional composition of polysaccharides
REFERENCES
1. S. N. Rai and V. D. Mudgal, Biological Wastes 24, 105 (1988).
2. S. N. Rai and V. D. Mudgal, Indian 1. Anim. Nutr. 4, 5 (1987). 3. L. Phatak, K. C. Chang, and G. Brown, 1. Food Sci. 53(3),830 (1988). 4. M. O. Bagby, G. H. Nelson, E. G. Helman, and T. F. Clark, Tappi 54 (11), 1876 (1971).
5. G. F. Collings, M. T. Yokoyama, and W. G. Bergen, 1. Dairy Sci. 61, 1156(1978). 6. Amparo Asensio and Eliseo Seoane, 1. Natural Products 50(5),811(1987).
7. H. R. Bolliger, M. Brenner, H. Ganshirt, H. K. Mangold, H. Seiler, Egon Stahl,and D. Waldi, "Thin-layer Chromatography," (Ed.) Egon Stahl, Academic Press, New York, 461(1965). 8. N. Blumenkrantz and G. Asboe-Hanson, Anal. Biochem. 54,484 (1973).
9. Cindy L. Wedig, Edwin H. Jaster, and Kenneth 1. Moore, J. Agric Food Chern. 35,214 (1987). 10. M. N. Gibbons, Analyst (London) 80, 268 (1955). II. Zacharias Dische and Landrum B.Shettles, J. BioI. Chern. 175, 595 (1948).
]2. 0.1. Wood and I. R. Siddiqui, Analytical Biochemistry 39,418 (1971). 13. B. L. Browing, "Methods of Wood Chemistry," Academic Press, New York, 629 (1967). 14. R. L. Whistler and A. Jeans, Ind. Eng. Chern. Anal., Ed., 15,317 (1943). 15. S. A. Andon, Food Technol. 41(1),74 (1987).
]6. R. M. McCready, A. D. Shepherd, H. A. Swenson, Roberta F. Erlandsen, and W. D. Maclay, Analytical Chemistry 23(7),9 (1951). 17. Frank Will and Helmut Dietrich, Carbohydrate Polymers 18, 109 (1992).
311
312 Physical and chemical processing of fibre and non fibrous products
18. K. C. Chang and A. Miyamoto, 1. Food Sci. 57(6), 1435 (1992). 19. A. Scalbert and B. Monties, Holzforschung 40,249 (1986). 20. Runcang Sun, J. Mark Lawther and W. B. Banks, (Accepted for publication) Influence of Alkali Pre-treatment to the Wheat Straw Cell Wall Components, Industrial Crops and products.
21. Rombouts F M and Thibault J F, In: Chemistry and Function ofPectins(ACS Symposium Series 310), (Ed.) Fishman M Land Jen J J, American Chemical Society, Washington, DC, 49 (1986).
22. Chesson A and Monro J
~
1. Sci. Food Agric. 33,852 (1982).
23. M. McNeil, A. G. Darvill, C. Fry, and P. Albersheim, A Rev. Biochem. 625 (1984). 24. A. Darvill, M. McNeil, P. Albersheirn, and D. P. Delmer, " The Biochemistry of Plants," (Ed.) P. K. Stumpfand E. E. Conn, 1:91. Academic Press, New York, (1980).
25. V. Zitko and C.T. Bishop, Can. 1. Chern. 43,3206 (1965). 26. S. Riaz and M. Uddin, Pak. J. Sci. Ind. Res. 15, 167 (1972). 27. P. E. Christensen, Food Res. 19,163 (1954). 28. R. W. Bailely, "Chemistry and Biochemistry of Herbagel," Academic Press, London, 157 (1973).
29. Eva-Maria Dusterhoft, Alfons G. 1. Voragen, and Ferdinand M. Engels, J. Sci. Food Agric. 55,411 (1991).
30. R. L. Whistler, 1. Bachrach, and D. R. Bowman, Arch. Biochem. 19, 25 (1948).
32 Effects of extraction conditions and alkali type on the yield and neutral sugar composition of wheat straw hemicellulose J M Lawther, R Sun and W B Banks* - The BioComposites Centre and *School of Agricultural & Forest Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, Wales
ABSTRACT
The utilization of various alkaline regimes for the optimal extraction and isolation of hemicellulose and cellulose from wheat straw has been extensively examined. Factors investigated include varying concentrations of one alkali (KOH) and H3B03, varying temperature and time of extraction, varying the nature of the alkali. Calcium Hydroxide, Sodium Hydroxide, Lithium Hydroxide and liquid Ammonia were examined.
For example, a preferred extraction of hemicellulose from holocellulose preparations utilised a solution of 24% KOH / 2% H3B03 at 20°C for 2 h. This produced yields
313
314
Physical and chemical processing of fibre and non fibrous products
for hemicellulose and cellulose of 34.23 and 35.96%, respectively. The neutral sugar composition of the hemicellulose fractions was found to vary slightly with treatment regime. In all of the hydrolysates of hemicellulose preparations, xylose was by far the predominant sugar, comprising around 80% of the material. Minor constituents are arabinose, galactose, glucose and uronic acids. The composition of phenolic acids and aldehydes in extracted wheat straw hemicellulose was also studied.
The average molecular weights of the hemicellulose isolates ranged from 12 000 for the 30% KOH/2% H3B03 (20°C, 2 h) extract to 27 000 for the extract obtained using 5% KOH/2% H3B03 (20°C, 2 h).
Key words: wheat straw, hemicellulose, cellulose, polysaccharides, extraction,
sugars, uronic acid, phenolic acids and aldehydes.
INTRODUCTION
Wheat straw contains large amounts of cell wall polysaccharides and lignin (1, 2, 3). Cellulose, hemicellulose and pectin are the major structural polysaccharides found in the material. Hemicellulose ranks second to cellulose in abundance in the straw and its content changes with growth and maturity (4). Hemicellulose, which is rich in a number of neutral sugars, is a promising source of xylose, the predominant sugar. Xylose accounts for 80% of the total monosaccharides and can be modified to give xylitol, a sugar substitute (5). Hemicellulose, however, is the most complex of the
Wheat straw hemicellulose
315
structural components of the straw and requires careful isolation and detailed characterization (6).
Hemicelluloses are heteropolysaccharides, made up of at least two to four different types of sugar residues depending upon the source (7). For example, the lignified tissues of grasses and straws yield, on alkaline extraction after delignification, hemicelluloses containing D-xylose residues together with 5-10% of L-arabinose residues. In some hemicelluloses D-glucuronic acid residues are also present (8).
Within the context of our continuing studies of the polysaccharides from wheat straw, the hemicellulose in particular is discussed here. Extraction of hemicellulose by potassium or sodium hydroxide has been investigated in some detail, but relatively little is known about the precise nature of fractions extracted using different conditions and different alkalis. The objective of this study was therefore to examine the effects of extraction conditions, e.g. time, concentration, temperature and different alkaline species, on the yield of wheat straw hemicellulose and its neutral sugar composition.
The content of uronic acids in hemicellulose fractions
and the molecular weights of the fractions were also estimated.
MATERIALS AND METHODS
Materials
Wheat straw was obtained from Silsoe Research Institute (Silsoe, Bedfordshire) and was ground using a Christie Laboratory mill to a 6O-mesh size screen. The ground
316 Physical and chemical processing of fibre and non fibrous products
straw was then dried in a cabinet oven with air circulation for 16 h at 60°C and stored at 5°C until use.
All chemicals were of analytical or reagent grade.
All
experiments were conducted in duplicate and all weights and yields are given on a dry weight basis.
Determination of moisture, ash and protein
Moisture was determined by drying ground wheat straw in an air circulated oven at 105°C for 16 h. Ash content was measured by incinerating the sample for 5 h in a muffle furnace at 550°C.
Proteins in wheat straw were measured by a Kjeldahl
procedure (9). A protein conversion factor of 6.25 was used.
Preparation of wheat straw holocellulose (Figure 1)
Dried wheat straw was defatted by refluxing with chloroform for 5 h in a Soxhlet apparatus. After drying, the defatted wheat straw was suspended in O. 1M phosphate buffer, pH 7.5, containing 0.02% sodium azide as bacteriocide.
Proteolysis was
then started by the addition of pronase (trypsin, 2.5 mglg wheat straw).
The
suspension was incubated for 6 h at 40°C with continuous stirring. After filtration and washing with water, ethanol and acetone, the residue was gently boiled in distilled water (30 gil) for 2 h, then filtered and washed. The treatment was repeated for another 2 h with further distilled water (30 gil). The residue was recovered by filtration, extensively washed with water, and dried by solvent exchange through ethanol, acetone, and diethyl ether. Pectic substances were isolated from the protein free straw using 0.25% ammonium oxalate for 4 h at 85°C. After filtration and drying, an 80% solution of ethanol in water (1.5 g strawlloo ml extractant) was
Wheat straw hemicellulose
added to the residue and the mixture boiled gently for 3 h.
317
The residue was
recovered by filtration, washed twice with 80% ethanol and water, dried for 16 h at 60 0 e and reweighed. The weight lost was defined as "80% hot ethanol solubles",
Wheat straw
I Dry at 60°C for 16 h. I Chloroform 5 h in a Soxhlet apparatus for dissolving extrctives.
Dried wheat straw
Dewaxed wheat straw In 0.1 M phosphate buffer, pH 7.5, containing 0.020/0 sodium azide as bactericide. proteolysis was started by adding trysin for 6 h at 40°C. Protein was measured by a Kjeldahl method.
Protein free wheat straw
I Addition of distilled water at boil gently for 2 h + 2 h.
Sample free of hot water solubles
I Addition of 0.25% ammonium oxalate for 4 h at 85°C. I 80% ethanol extraction at boil gently for 3 h.
Depectinated wheat straw
Sample free of 80% ethanol soluble material.
I Addition of acetic acid and sodium chlorite to pH 4.2-4.7 for delignification at 75°C for 2 h. Ligninfree sample
I
Addition of different chemicals to extract hemicellulose.
Hemicellulose free sample The residue washed with water until alkaline free and 50/0 acetic acid (once), water (once), ethanol (once) and acetone (once), then dried at 60°C for 16 h.
Cellulose Figure 1. Scheme for extraction and isolation of hemicellulose from wheat straw.
The 80% ethanol extracted straw sample was delignified according to the method described by Bagby et ale (10), Collings et a1. (11) and Asensio et ale (12).
The
residue (3.00 g) was stirred with water (150 ml) and 10% acetic acid (10 ml), with sodium chlorite (NaCI02, 5.0 g) as the oxidant, in a flask fitted with a magnetic
318 Physical and chemical processing of fibre and non fibrous products
bar. The mixture was heated for 1 h at 75°C, more acid (5 ml) and sodium chlorite (2.5 g) were then added and the mixture heated for another hour.
After 2 h of
oxidation, the residue was filtered out on a nylon cloth and washed with water (three times), 96% ethanol (twice) and ether (once), then dried at 60°C for 16 h and reweighed. The difference in weight was defined as "sodium chlorite lignin". The supernatant was concentrated on a rotary evaporator under reduced pressure at 40° C.
The dried supernatant was kept in a fridge at 5°C until analysis of
"polysaccharides solubilised during delignification" was carried out.
Extraction of hemicellulose from holoceUulose
The optimisation of the yield of hemicellulose from wheat straw holocellulose required the systematic evaluation of a range of alkaline extraction regimes. These are detailed below.
The holocellulose was extracted (1.2 g holocellulose/lOO ml extractant) with:
a) 10% potassium hydroxide and 2% boric acid at 20°C in air for 4 h, 8 h, 12 h, 16 h, 21 h, and 26 h, respectively.
b) 5, 10, 15, 20, 24, and 30% potassium hydroxide and 2% boric acid at 20°C for 2 h, respectively.
c) 24% potassium hydroxide and 2% boric acid for 2 h at 0, 10, 20, 35, and 50°C, respectively.
Wheat straw hemicellulose
319
d) using 24% potassium hydroxide without boric acid and with 1, 2, 5, 8, and 12% boric acid for 2 h at 20°C, respectively.
e) using 15% liquid ammonia, 15% calcium hydroxide, 15% potassium hydroxide, 15% sodium hydroxide and 15% lithium hydroxide, each with 2% boric acid at 20° C for 2 h, respectively.
f) using 1M calcium hydroxide, 1M liquid ammonia, 1M potassium hydroxide, 1M
sodium hydroxide and 1M lithium hydroxide with 0.2 M boric acid for 2 h at 20°C.
After filtration on a nylon cloth, the residues were recovered, washed three times with water, once with 5% aqueous acetic acid, once with distilled water, twice with 96% ethanol and once with ether, then dried in an oven for 16 h at 60°C and reweighed.
The weight lost was defined as hemicellulose.
The weight of the
residue which remained after the alkaline extraction, corrected for ash content, was taken as "cellulose." After neutralization with dilute acetic acid, the supernatant was extensively concentrated on a rotary evaporator under reduced pressure at 40°C, and precipitated with 5 volumes 96% ethanol for 24 h at 20°C.
After filtration and
drying in an air circulated oven for 16 h at 60°C, the resultant white hemicellulose fraction was kept in a fridge at O°C until analysis.
Sugar analysis by gas chromatography(GC)
Hydrolysis of hemicellulose was performed using 2 M trifluoroacetic acid for 2 h at 121°C in sealed pressure tubes (13). Trifluoroacetic acid was removed by vacuum evaporation at 40°C. The dried materials were added to 10 ml of a 4: 1 mixture of
320 Physical and chemical processing of fibre and non fibrous products
ethanol-toluene and evaporated in a rotary evaporator flask under reduced pressure to dryness.
1.5 ml of anhydrous pyridine (stored over KOH) was added and
solutions were transferred to glass vials. Sugars were converted to trimethylsilyl (TMS) ether derivatives by addition of 0.5 ml hexamethyldisilazane and 0.25 ml trimethylchlorosilane, with shaking in vials, for 2 min and analyzed by gas chromatography, using flame ionization detection on a glass column (1.7 m x 2 mm i.d.) packed with 3% OV-17 on 80-100 Suppelcoport. The injector and detector temperatures were 200°C and 250°C respectively, and the oven temperature programmed from 100°C to 190°C at 2°C per min with a 10-min hold at 190°C. Nitrogen was used as a carrier gas, and its flow was maintained at 36 ml/min. Aliquots of hemicellulose were combined with myo-inositol as an internal standard before evaporation to dryness under reduced pressure at 40°C.
For the determination of neutral sugars in cellulose, the cellulose was firstly hydrolyzed with 72% sulphuric acid for 2 h at 20°C. Distilled water was added to decrease the acid concentration to 3%(w/v) and the hydrolysate was boiled for 6 h and filtered immediately.
The filtrate was neutralised with ammonia to pH7.0,
water was removed under low pressure and the sugars extracted from the residue into dry pyridine.
The pyridine was then removed using a rotary evaporator.
Finally, the sugars were determined by gas chromatography after conversion to trimethylsilyl ether derivatives as above.
Identification of sugars in trifluoroacetic acid or sulphuric acid hydrolyzed hemicellulose or cellulose fractions was achieved by comparison of the relative retention times of the TMS derivatives of wheat straw sugars with TMS derivatives of authentic sugars in co-ehromatography (14). After identification, the TMS
Wheat straw hemicellulose
321
derivatives of sugars in hemicellulose and cellulose were quantitated from the peak areas and weight ratio of TMS derivatives of authentic sugars and the internal standard, myo-inositol.
Uronic acid measurement by spectrophotometry
Total uronic acids were assayed colorimetrically as glucuronic acid in hemicellulose using 3-phenylphenol color reagent according to the procedure outlined by Blumenkrantz and Asboe-Hanson (15) with a modification of Wedig and co-workers (16).
A Hewlett-Packard Diode Array 8452A spectrophotometer was used to
measure glucuronic acid at a wavelength of 520 nm.
Trifluoroacetic acid
hydrolysate (0.01 g) was added to 10 ml distilled water. The solution was shaken and sodium tetraborate in concentrated sulfuric acid(4.76 g NaB407 10 H20/L of H2S04; 4.8 ml) was added to of the solution sample (0.8 ml). The mixture was shaken again and the tubes were heated in an oven at 100°C for 5 min.
After
cooling in a water-ice bath, 3-phenylphenol reagent (150 mg of 3-phenylphenol diluted to a 100 ml volume with 0.125 N NaOH; 80 III ) was added. The tubes were shaken and absorbance measurement made at 520 nm. A blank was run for each sample without addition of the reagent to correct for any glucose interfering with absorbency. Because carbohydrates produce a pinkish chromogen with sulfuric acid/tetraborate at 100°C, the absorbance of the blank sample was subtracted from the total absorbance. A standard curve was calculated using values determined for 0.01,0.02,0.04,0.06,0.08 and 0.10 mg/ml solutions of glucuronic acid.
Average molecular weight estimation by gel permeation chromatography (GPC)
322
Physical and chemical processing of fibre and non fibrous products
The hemicellulose (O.lg) was dissolved with 0.02 M NaCI in 0.005 M sodium phosphate buffer, pH 7.5 (100 rnl),
The solution was chromatographed on a PL
aquagel-OH 50 column (300 x 7.7 mm, Polymer Laboratories Ltd), calibrated with PL pullulan polysaccharide standards (peak average molecular weights 667, 5800, 12200.. 23700, 48000, 100000, 186000, and 386000, Polymer Laboratories Ltd) and eluted with 0.02 M NaCI in the same buffer above, 0.1 ml/min. Eluent was monitored with a Knauer differential refractometer.
The column oven was
maintained at 30°C.
Nitrobenzene oxidation of lignin in extracted wheat straw hemicellulose
The method for alkaline nitrobenzene oxidation of lignin remaining attached to/associated with hemicellulosic fractions and cellulose was based on the following procedure. 2 M sodium hydroxide (7 ml) and nitrobenzene (0.4 ml) were added to hemicellulosic fractions (0.15 g) in steel autoclaves.
The autoclaves were then
heated in an oil bath for 2.5 h at 170°C. The solutions were filtered and the filtrates were extracted with chloroform (3
X
30 ml), acidified to pH 1 with 20%
hydrochloric. acid, and extracted again with chloroform (3
X
30 ml),
These last
chloroform extracts were evaporated at 40°C to dryness and resolubilised in methanol (4 ml) containing 3' ,5'-dimethoxy-4'-hydroxyacetophenone as an internal standard.
The lignin oxidation products were then analyzed by high performance
liquid chromatography (HPLC) on a Hichrom H50DS column of dimensions 250 X 4.6 mm. Separations were obtained using a linear gradient of two solvent systems: solvent A (water-methanol-acetic acid 89: 10:1) and solvent B (methanol-water-acetic acid 90:9: 1). A linear gradient was run over 31 min from 0% to 40% B at a flow rate of 1 ml min-I. Products were detected at 280 and 320 nm. Peak areas (280
Wheat straw hemicellulose
nm) were calculated relative to the internal standard.
323
Calibration curves were
established with appropriate mixtures of authentic phenolic acids and aldehydes.
RESULTS AND DISCUSSION
The contents of moisture, ash, protein and lipids, and the fractional yields of polysaccharides and lignin
Moisture, ash, protein and lipid contents in wheat straw were determined as 9.18, 7.93, 1.52 and 1.65% respectively. The yields of water soluble polysaccharides in proteolysis and boiling water extraction were 2.92 % and 4.76% respectively. The contents of pectin, 80% ethanol soluble materials and lignin were 1.52, 1.27 and 14.13 % (sodium chlorite lignin) of dry straw, respectively.
Hemicellulose and
cellulose are predominant components, which comprise more than 70% of the dry straw. The ash content was high, presumably due to soil contamination (17). More details of the neutral sugar composition of water soluble polysaccharides obtained during proteolysis, boiling water extraction and delignification, and in pectin and 80% ethanol soluble materials, are given elsewhere (18, 19).
Effects of the time and temperature of extraction, concentrations of KOH and H3B03, and other alkalis on the yields of hemicellulose and cellulose
The variation of hemicellulose and cellulose yields with extraction time using 10% potassium hydroxide and 2% boric acid at 20°C is shown in figure 2. It can be seen that most hemicellulose was removed in the early part of the extraction procedure:
324 Physical and chemical processing of fibre and non fibrous products
more than 90% of hemicellulose was extracted in the first 4 hours, while less than 10% hemicellulose was removed during a prolonged period up to 22 h.
4Q
.ilk---
...
30
s:
0)
'Ci)
I:_ J
~
e
'U ~ ~ 'U Q)
>=
20
10
0
4
12
16
21
26
Extraction time (h)
Figure 2. The effect of extracting time on the yield of hemicellulose and cellulose extracted using 10% KOH and 2% H3B03 at 20°C.
Figure 3 The effect of KOH concentration on the extraction yield of wheat straw hemicellulose and cellulose at 20°C for 2 h extraction with 2% H3B03.
Wheat straw hemicellulose
325
Figure 3 shows the different yields of hemicelluloses and celluloses, depending on the potassium hydroxide concentration, at 20°C for 2 h extraction with 2% boric acid, plotting the yield versus potassium hydroxide concentration for extraction at 5, 10, 15, 20, 24 and 30%(w/v). As expected, at lower concentrations of KOH, the extracting yield increased steeply with potassium hydroxide concentration until a constant value was reached due to the depletion of remaining hemicellulose in the sample. These values were about 27.79, 32.57, 33.57, 34.21, 34.23 and 34.93 at concentrations of 5, 10, 15, 20, 24 and 30% of KOH, respectively. In contrast to hemicellulose, the yield of cellulose was dramatically decreased at the low concentration of KOH and then dropped slowly to a constant value.
The results
obtained coincided with Wise and co-workers' study (20). They demonstrated that, in general, the yield of hemicellulose obtained depended upon the alkaline strength of the extractant with alkaline solutions above 10% giving only small increases in yield.
The yields of hemicellulose and cellulose extracted using 24% potassium hydroxide with 2 % boric acid for 2 h from wheat straw holocellulose was plotted in figure 4 against the extracting temperatures of 0, 10, 20 35 and 50°C.
The yields of
hemicellulose were 31.01, 33.43, 34.23, 35.85 and 36.54% at the respective temperatures. Thus, hemicellulose has a limited solubility in cold alkaline solutions, but, presumably, warm alkaline solutions may lead to hemicellulose degradation (17) even though the extractability still seems to increase above 50°C extraction for the conditions shown. The yield of cellulose decreased from 39.05 to 33.76% as the temperature increased from 0 to 50°C.
326 Physical and chemical processing of fibre and non fibrous products
50
40
:E
30
C>
"ij) ~
e-
0
20
1= -
~ '"C
Q)
:;:
10
0
I
0
~----_
10
20
.._-_ .. __ ._.-
_
35
Temperature (C)
Figure 4. The effect of extracting temperature on the yield of wheat straw hemicellulose and cellulose with 24% KOH and 2% H3B03 at 20°C for 2 h.
Hemicelluloses can be extracted from holocellulose by alkali but a proportion of them, particularly the glucomannans, are exceedingly resistant to extraction.
The
addition of boric acid or borates to potassium hydroxide increases the dissolving power for glucomannans, mainly due to the formation of borate complexes with hydroxyl groups in cis-position (21, 22). The effect of boric acid concentration on the extraction yield of hemicellulose (20°C for 2 h) with 24% potassium hydroxide is shown in figure 5. Significant effectscan be seen. At the lower concentrations of boric acid, the yield of hemicellulose increased with acid concentration; this was particularly enhanced with the increase in rH3B03] from 1-2%.
Above 5%, the
yield of hemicellulose was observed to decrease, dropping from 35.0% to 33.74% at 12% boric acid. This is partly ascribed to the effective neutralisation of alkali as boric acid concentration increased to significant levels.
The"optimum extraction
concentration" of boric acid is therefore either 2 % or 5 %, depending upon which of
Wheat straw hemicellulose
327
the following criteria are considered most important; consumption of boric acid or total hemicellulose yield.
50
1:L-----J
45
...-s:
40
.2> G)
~
e-
35
"C
~ "C
30
Qi
~ 25
20
5
0
12
Concentration (%)
Figure 5. The effect of H3B03 concentration on the extraction yield of wheat straw hemicellulose and cellulose at 20 0 C for 2 h extraction with 24 % KOH.
Figures 6 and 7 clearly show that the "hemicellulose dissolving power" of various alkalis, at the same concentrations, on the yield of hemicellulose varies widely. The yields of hemicelluloses extracted with 15% of Ca(OH)2, NH3H20, KOH, NaOH, and LiOH at 20°C for 2 h were 5.46, 17.84,33.59,34.80 and 35.08% respectively. In a comparison of the extracting power of 1M solutions of potassium, sodium and lithium hydroxide, an approximately equal effect of all three hydroxides was found. This is in agreement with studies of the extraction of xylans from softwood (21). Depending on the strength of alkalis, sodium hydroxide and lithium hydroxide are more effective than potassium hydroxide for the removal of hemicellulose. However, the preferred hydroxide is still potassium hydroxide, mainly because the potassium acetate formed during the neutralization of the alkali
328
Physical and chemical processing of fibre and non fibrous products
Ca(OH)2
NH3.H20
KOH
NaOH
LiOH
Figure 6. The effect of different alkali on the extraction yield of wheat straw hemicellulose with 15 % of each alkali and 2 % H 3B03 at 20° C for 2 h.
35
30
25
P
s:
20
C)
"i) ~
e
15
"'C
~
10
"'C
Gi
>:
5
0 Ga{OH)2
NH3.H20
KOH
NaOH
LiOH
Figure 7. The effect of different alkali on the extraction yield of wheat straw hemicellulose with 1 M each of alkali and 0.2 M "3B03 solution at 20°C for 2 h.
extract is more soluble in the alcohol used for precipitation than sodium acetate (21). The yields of hemicellulose obtained using calcium hydroxide and liquid ammonia were markedly lower than for the alkali metal hydroxide solutions.
In general,
Wheat straw hemicellulose
329
increase In the concentrations of the various alkalis resulted in increased hemicellulose yields.
The studies have shown that the yield of hemicellulose depends strongly on a number of factors. These include concentration and type of alkali, concentration of boric acid, temperature and time of extraction.
Effects of the time and temperature of extraction, concentrations of KOH and "3B03, and various alkalis on the sugar compositions of hemicellulose
Hemicellulose can be found in many structures and compositions.
The most
abundant in wheat straw are the arabinoxylans, which are heteropolymers of xylose units, linked by {3 (1~) glycosidic bond and arabinose residues linked to the main chain (23).
The relative sugar composition of hemicellulose fractions after
hydrolysis are presented in figures 8-11. The sugar analysis of hydrolysates showed that xylose was an extremely predominant component sugar in wheat straw hemicellulose and that it comprised more than 80% of the total sugars in hemicellulose. On the other hand, as was apparent from the figures, arabinose, galactose and glucose were present as minor sugar constituents of hemicellulose. Mannose was also detected in trace amounts. These results accord with those of Hatfield IS (24), in which he stated that in grasses most of the xylose and arabinose would be found in hemicellulose as pectic polysaccharides are present in relatively small amounts.
As can be seen, no big differences in neutral sugar contents were observed for the extractions at different periods with 10% KOH and 2% H3B03 from wheat straw in
330
Physical and chemical processing of fibre and non fibrous products
figure 8. These suggest that extraction time does not greatly affect the nature of the solubilized polysaccharides.
The yield of xylose was increased from 80.00 to
86.12% with the increase of extraction time from 4 h to 26 h.
The yields of
arabinose, glucose and galactose decreased from 13.18 to 9.23%, 5.00 to 3.33%, and 1.78 to 1.23%, respectively during the same period. These data indicated that arabinose, glucose and galactose were readily dissolved with a short period of extraction, while more xylose needed long period of extraction.
100
80
--
lit---
=
=
---..... +
;
~
12
16
o 4
-------------~
..
21
Gal Glu
----
.
Ara
Xyl
----
--
----~~
26
Extraction time (h)
Figure 8. The effect of extracting time on the sugar composition (relative %) of hemicellulose extracted with 10% KOH and 2% H3B03 at 20°C from wheat straw.
The effect on the neutral sugar composition of the hemicellulose fraction of increasing potassium hydroxide concentration from 5 to 30% is shown in figure 9. Inspection of these figures shows that, in general, the relative amount of xylose present in hemicellulose decreases as the KOH concentration is increased from 530%. Yields of arabinose, glucose and galactose increase accordingly. However, it is interesting to note that a significant dip in the xylose yields curve occurs at a
Wheat straw hemicellulose
331
100
-----.---
80
-
~
_ _ _ _ _ _ _ _ _...- -.---e----
-....
60
c: 0 E
...-
UJ
0
Q.
E
40
---
0 0
Ara Gal Glu Xyl
co
C)
::J
en
.
20
~
o 5
------
.
=1
....
15
10
. ....
-~
24
20
30
Concentration (%)
Figure 9. The effect of KOH concentration on the sugar composition (relative %) of hemicellulose extracted from wheat straw at 20° C with 2 % H3B03.
100
.---
•
•
80
~ ......., c:
Ara
60
Gal
0
E
fn
0 0-
GJu
40
E
Xyl
0 0
tiC) ::J
20
(J)
._--------
-----------
0 0
10
20
35
Temperature (C)
Figure 10. The effect of extracting temperature on the sugar composition (relative %) of hemicellulose extracted with 24% KOH and 2% H3B03 for 2 h from wheat straw.
[KOHl of around 15 %, with an obvious concomitant increase in relative yields of the other sugars. A hemicellulose fraction rich in arabinose, glucose and galactose
332 Physical and chemical processing of fibre and non fibrous products
can hence be isolated using a specific extraction regime, nominally 15% KOH, 2% boric acid at 20°C.
In figure 10, the relative sugar compositions of hemicellulose extracted with 24 % potassium hydroxide and 2 % boric acid for 2 h are plotted against extracting temperature.
It is apparent that the amount of arabinose occurring in extracts
increases significantly as the temperature increases from O°C (5.42 %) to 50°C (11.92%).
100
80
.----
=
=
=
~.
-....
Glu
-+-
Gal
---
Xyl
Ara
0 1--------
o
o
...
...
y
... ~
...
-
-
coricentratidh
(%)
8
12
Figure 11. The effect of H3B03 concentration on the sugar composition (relative %) of hemicellulose extracted with 24% KOH at 20°C from wheat straw.
In figure 11, the relative contents of sugars in the hydrolysates of hemicelluloses extracted with 24 % potassium hydroxide and various concentrations of boric acid at 20°C for 2 h, are plotted as a function of the concentration of boric acid.
As
expected, as the boric acid concentration increased, the content of xylose dropped significantly (88.87 to 79.29%). The contents of arabinose and galactose increased
Wheat straw hemicellulose 333
from 6.03 to 8.28% and 1.43 to 1.97% respectively in the boric acid free and 1% boric acid extraction media. Glucose content was generally noted to increase with boric acid concentration. The relative neutral sugar compositions of hemicellulose extracted by the various alkalis with 2% boric acid at 20°C for 2 h (table 1) was very similar. In all cases xylose was the major component, and arabinose, glucose and galactose the minor components of the hemicelluloses.
The only significant difference between the
hemicellulose fractions was that the content of xylose was relatively low, and that of arabinose high in the calcium hydroxide extracts of hemicellulose compared with other alkali extraction.
The molar ratios of xylose:arabinose:galactose:glucose in
15% Ca(OH)2 and 2% H3B03 extracted hemicellulose were 51:10:1.1:2.4, whilst in 15% Li(OH) and 2% H3B03 extracts the corresponding values were 58:5.2:1.2:2.2, respectively.
These results, e.g. large amount of xylose with
relatively low levels of other neutral sugars, pointed to the presence of mainly xylan or arabinoxylan. In 1993 Fidalgo and co-workers (25) showed that the wheat straw hemicellulose contains an arabinoxylan and that a percentage of arabinose units were linked to lignin. In addition, they also revealed that in the alkali lignin fraction the percentage of arabinose units linked to lignin (as percent of total arabinose) was higher than the percentage of linked xylose. This is in agreement with the findings of Xiao-an et al. (26). There is a certain amount of ester bonding between phenolic components of lignin and xylose, arabinose, and uronic acids in the heteroxylans of hemicellulose (27); the amount of bonding appears to increase with plant maturity (28). Lignin inhibits digestion of hemicellulose by steric hindrance as well as by direct bonding to hemicellulose (6, 29).
Overall, xylose is the most resistant of
chemical constituents of hemicellulose to alkali extraction.
334 Physical and chemical processing of fibre and non fibrous products
Table 1. The sugar composition(relative %) of hemicellulose extracted from wheat straw holocellulose using various alkalis at 20°C for 2 h.
Gal
Glu
77.3
1.9
4.3
14.7
76.8
2.6
6.0
15% NH3 + 2% H3B03
7.4
87.9
1.3
3.3
1M NH3 + 0.2M H3B03
7.4
87.8
1.4
3.4
15% KOH + 2% "3B03
10.4
82.6
2.2
5.0
1M KOH + 0.2M H3B03
10.9
83.6
1.3
3.8
15% NaOH + 2% H3B03
7.5
86.4
2.1
4.0
1M NaOH + 0.2M H3B03
7.0
86.6
2.2
4.3
15% LiOH + 2% "3B03
7.8
87.0
2.2
3.9
1M LiOH + 0.2M "3B03
8.2
87.0
1.4
3.4
Chemical concentration
Ara
Xyl
15% Ca(OH)2 + 2% H3B03
15.6
1M Ca(OH)2 + 0.2M H3B03
Man
Ta
T
a Abbreviation for trace.
The contents of uronic acids in hemicellulose
The content of uronic acids in hemicellulose fractions extracted using different concentrations of KOH at 20°C, for 2 h with 2% H3B03, are shown in table 2. Although a small component in hemicellulose, significant differences appeared at different concentrations of KOH extractions.
An increase of KOH concentration
from 5 to 24 %, led to a 4% decrease in uronic acid content.
Wheat straw hemicellulose 335
Table 2. The content(%) of uronic acids in wheat straw hemicellulose fractions extracted using different concentration of KOH at 20°C for 2 h with 2% H3B03.
Uronic acids (%)
Concentration of KOH (%) 5
7.2
10
5.8
15
4.2
20
3.9
24
3.1
30
3.1
The average molecular weight of hemicellulose
The GPC determined molecular weights of wheat straw hemicellulose extracted using 5, 15, and 24% KOH, at 20
0
e for 2 h with 2%
H3B03, are shown in figure
12. The mean molecular weights of hemicelluloses extracted using 5%, 15% and 24% KOH with 2% H3B03 at 20 respectively (30).
0
e
for 2 h were 27000, 20000 and 12000,
This result is in approximate agreement with Aspinall and co-
worker's study (8). They illustrated that a molecular weight determination by the isothermal distillation method gave a value of 8000-11800
± 400 (degree of
polymerisation 47-76) for the methylated wheat straw xylan.
Wegener (21)
mentioned that extraction with dilute alkali solutions (e.g. 5% KOH) removed the more soluble xylans and galactoglucomannans while most of the glucomannan can be removed only with higher alkali concentrations of 16 or 24% potassium hydroxide or 17.5 % sodium hydroxide,
which is in accordance with our
experimental results. With the increase of alkali concentration from 5 to 24%, the
336 Physical and chemical processing of fibre and non fibrous products
average molecular weights were decreased. Table 3 shows the average molecular weights (M w) of wheat straw hemicellulose fractions extracted using different concentrations of KOH at 20°C for 2 h with 2% H3B03. Corresponding M w for 5, 10, and 15% KOH extracted straw hemicellulose were 27000,
2ססoo
and
2ססoo
respectively. According to Whistler and co-workers' study (31) in early 1948, weak alkaline solutions generally solubilize hemicellulose B, the more acidic and/or branched portion, to a greater extent than hemicellulose A, which is more linear and less acidic nature.
Therefore, hemicellulose B can be more or less selectively
extracted from plant material with very weak alkaline solutions, such as saturated lime water or a low percentage of potassium hydroxide solution (e. g. 5 %). Forty years later, Wen and co-workers (17) studied the isolation and characterization of hemicellulose from sugar beet pulp and indicated that apparent molecular weights of hemicellulose A and B had two major carbohydrate peaks. molecular weight equal or greater than
15ססoo
daltons.
The first one had a The second major
carbohydrate peak had a molecular weight of 4ססoo daltons. Furthermore, they also mentioned that the elution profiles of hemicellulose B extracted with 5% NaOH were similar to that extracted with 10% NaOH, but the peak area of peak I was larger with 5% NaOH extraction than that for 10% NaOH and there was less tailing of the peak.
Hence,
they concluded that higher concentrations of NaOH caused
fragmentation of hemicellulose B. This result is in agreement with our experimental data, which shows that the average molecular weights of hemicellulose decreased from 27000 to 12000 with increase of extraction concentration of KOH from 5 to
30%, mainly due to the fragmentation at high concentration of KOH. In 1992, in a study of the structural and solution properties of corn cob heteroxylans, Ebringerova and co-workers (32) demonstrated that the molecular weight M w of heteroxylans determined by light scattering ranged up to approximately
35ססoo.
During the same
Wheat straw hemicellulose
337
year, based on the analysis of wheat arabinoxylans from a large-scale isolation, Annison and co-workers (33) concluded that the pentosans had a high degree of polymerization with apparent molecular weights of
50ססoo
Da and 758000 Da.
Table 3. The average molecular weight of wheat straw hemicellulose fractions extracted using different concentration of KOH at 20°C for 2 h with 2% "3B03.
Concentration of KOH (%)
Molecular weight
5
27000
10
20000
15
20000
20
20000
24
12000
30
12000
The neutral sugar composition of cellulose
It is evident that a-cellulose is contaminated with hemicellulose and pectic substances which have not been extracted during the previous fractionation procedures. Treatment with 72% H2S04 (2 h, 20°C) and 3% H2S04 (6 h, 100°C) hydrolysed the "cellulose," producing neutral sugar composition (relative %) of arabinose 2.8, xylose 7.3, galactose 1.1 and glucose 88.8, with trace amounts of mannose. The resistance to extraction by 24% KOH suggests that hemicellulose and pectic substances are very strongly associated with the cellulose, which is similar to xylans and are often associated with lignified tissues.
338 Physical and chemical processing of fibre and non fibrous products
According to the model proposed by Preston (34), hemicellulose and cellulose are closely connected and the cellulose mirofibrils are coated with hemicellulose polymers. Studies of sycamore suspension cell wall by Darvill et al. (35) suggested that the neutral and acidic pectic polysaccharides were covalently attached to the hemicellulose.
In 1986, based on a study of hindrance of hemicellulose and
cellulose hydrolysis by pectic substances using pectinase and cellulase, Shalom (36) confirmed that cellulose and hemicellulose in the' cell wall are sterically masked by the pectic substances. This surrounding effect may sterically hinder hemicellulose and cellulose hydrolysis.
The content of phenolic acids and aldehydes of alkaline nitrobenzene oxidation lignin in extracted wheat straw hemicellulose
The .FTIR spectra of hemicellulosic fractions extracted with 5% KOH and 2% H3B03 (a), 10% KOH and 2% H3B03 (b), and 24% KOH and 2% H3B03 (c) at 20°C for 2 h in figure 13 appeared to be rather similar.
However, on closer
examination of the spectrum of the hemicellulosic fraction (a) extracted with 5% KOH and 2% H3B03 at 20°C for 2 h, it can be seen that there are two weak peaks at 1626 and 1562cm-1, whereas that of fraction (c) extracted with 24% KOH and 2% H3B03 at 20°C for 2 h has a strongly single flattened peak at 1562cm- 1. The absorbance around 1626 em-lis a carbonyl stretching band due to para-substituted ketone or aryl aldehydes.
The small bands at 1330, 1220, 1155 and 84Ocm- 1
indicated syringl, guaiacyl ring breathing with CO stretching, aromatic CH in-plane deformation and aromatic C-H out of plane bending vibrations in wheat straw lignin. This figure indicated that the extracted hemicellulosic fractions still contained some residual lignin.
Wheat straw hemicellulose 339
~a
-'b "'-c 12
Q) U)
c:
o a. U)
e
2
o
"0 Q) 1»1
c
0~~~~££~~~~~=*==±-_---~~~~~4 6.4
7.6
7.0
8.4
8.1
8.7
9.0
9.3
V (Elution vol, ml)
Figure 12. The range of the molecular weight of wheat straw hemicellulose extracted using 50/0 KOH (a), 15% KOH (b) and 24% KOH (c) at 20°C for 2 h with 2% H3B03'
2.6
2.8 I
3.0
3.5
,
4..0
Microns l.5 5.0
6.0
7.0
8
10
(8 ,
(c ]
auen Wsyenumber
Figure 13. FTIR spectra of wheat straw hemicellulose extracted with (a) 5% KOH and 2% H3B03, (b) 10% KOH and 2% H3B03 and (c) 24% KOH and 2% H3B03 at 20°C for 2 h.
15
20
340
Physical and chemical processing of fibre and non fibrous products
The phenolic composition of the hemicellulosic fraction (c) extracted with 24% KGH and 2% H3B03 at 20°C for 2 h is summarised in table 4. The free and bound phenolic contents in the hemicellulosic fraction were 0.15 and 0.59%, respectively. The major components in bound phenolic acids and aldehydes were found to be phydroxybenzoic acid and vanillic acid, while the free phenolic content showed higher content of gallic acid. The characterisation of wheat straw lignin and lignin polysaccharide complexes is currently the subject of detailed further study in our laboratory.
Table 4. The composition of phenolic acids and aldehydes in wheat straw hemicellulose extracted with 24% KGH and 2% H3B03 at 20°C for 2 h.
Phenolic acids and aldehydes
Free a( %)
Gallic acid
0.15
Boundb ( % )
0.029
Protocatechuic acid
0.0082
p-Hydoxybenzoic acid
0.24
p-Hydroxybenzaldehyde
0.00094
0.019
Vanillic acid
0.16
Vanillin
0.085
Syringaldehyde
0.021
Ferulic acid
0.0032
Cinnamic acid
0.026
Total
0.15
0.59
aDetermined by HPLC without alkaline nitrobenzene oxidation. bDetermined by HPLC after alkaline nitrobenzene oxidation at 170°C for 2.5 h in steel autoclaves.
Wheat straw hemicellulose
341
SUMMARY
Various procedures for extracting and isolating hemicellulose and cellulose from wheat straw holocellulose have been examined.
The optimal time for extracting
hemicellulose using 10% KOH and 2%H3B03 at 20°C was found to lie between 21 and 26 h. The suitable concentration of KOH for extracting hemicellulose at 20°C for 2 h was 24% and the temperature was around 20°C if 24% KOH was used in the extraction for 2 h with 2% H3B03. The most favourable concentration of H3B03 in the extractant of 24% KOH at 20°C for 2 h was 5%. potassium,
Aqueous solutions of
sodium and lithium hydroxide are appropriate for isolation of
hemicellulose from wheat straw holocellulose, but the preferred alkali was potassium hydroxide.
The molar ratios of xylose:arabinose:galactose:glucnse in 24% KOH
and 2% H3B03 for 2 h at 20°C extracted hemicellulose were 58:5.6:0.7:2.0 and in that the content of uronic acid was 3.1 %. The average molecular weight Mw of the hemicellulose was about 12000. The total content of phenolic acids and aldehydes in hemicellulose extracted with 24% KOH and 2% H3B03 at 20°C for 2 h was 0.64%.
ACKNOWLEDGEMENTS
The authors acknowledge the financial support for the research from LINK Collaborative Programme in Crops for Industrial Use.
We gratefully thank Dr.
James Bolton, Director of The BioComposites Centre, for the award of a research studentship to Runcang Sun. We are also grateful to Gwynn Lloyd Jones, Andy Mclauchlin, Sue Griffiths and Sara Hughes for their valuable suggestions and constructi ve discussion.
342 Physical and chemical processing of fibre and non fibrous products
REFERENCES
1. Per Aman and Erik Nordkvist, Swedish J. Agric. Res. 13,5(1983). 2. M. G. Jackson, Anim. Feed Sci. Technol. 2, 105(1977). 3. A. Chesson, J. Sci. Food Agric. 32,745(1981). 4. K. C. B. Wilkie, Adv. Carbohydr. Chern. Biochem. 36,215(1979). 5. R. W. Jones, L. H. Krull, C. W. Blessin, andG. E. Inglett, Cereal Chemistry 56(5),441(1979). 6. Cindy L. Wedig, Edwin H. Jaster, and Kenneth J. Moore, J. Agric. Food Chern. 35,214(1987). 7. N. Rukma Reddy, James K. Palmer, and Merle D. Pierson, J. Agric. Food Chem.32, 840(1984). 8. G. O. Aspinall and R. S. Mahomed, Canad, J. Chern. 34, 1731(1954). 9. AOAC Official Methods of Analysis, 14th ed Association of official analytical Chemists, Washington, DC. (1984). 10. M. O. Bagby, G. H. Nelson, E. G. Helman, and T. F. Clark, Tappi 54(11)., 1876(1971). 11. G. F. Collings, M. T. Yokoyama, and W. G. Bergen, J. Dairy Sci. 61, 1156(1978). 12. Amparo Asensio and Eliseo Seoane, J. Natural Products 50(5),811(1987). 13. M. Mansoor Baig, Charles W. Burgin, and James J. Cerda, J. Agric. Food Chern. 30, 768(1982). 14. Mohammad A. Sabir, Frank W. Sosulki, and Neil W. Hamon, J. Agr. Food Chern. 23(1); 16(1975). 15. N. Blumenkrantz and G. Asboe-Hanson, Anal. Biochem. 54,484(1973). 16. Cindy L. Wedig, Edwin H. Jaster, and Kenneth J. Moore, J. Agric. Food
Wheat straw hemicellulose
343
Chern. 35,214(1987).
17. L. F. Wen, K. C. Chang, G. Brown, and D.
o.
Gallaher, J. Food Sci. 53(3),
826(1988). 18. R. C. Sun, J. M. Lawther and W. B. Banks, Extraction, Isolation and Physicochemical Characterization of Weak Acidic Pectic Polysaccharides from Wheat Straw, to be published.
19. R. C. Sun, J. M. Lawther and W. B. Banks, Fractionation and Chacterization of Polysaccharides from Wheat Straw, to be published.
20. L. E. Wise, M. Murphy, and A. A. Dj Addieco, Paper Trade J. 122(2), 35( 1946). 21. Dietrich Fengel Gerd Wegener, "Wood Chemistry, Ultrastructure, Reactions," Academic Press, Walter de Gruyter Berlin, New York, 43(1989).
22. G. Gonzalez, J. Lopez-Santin, G Caminal, and C. Sold, Biotechnology and Bioengineering, Vol. XXVIII, 288( 1986).
23. B. L. Browning, "Methods of Wood Chemistry," Vol. II. Intersci. Publ., New York, London, 566(1967).
24. R. D. Hatfield, Agron J. 81,39(1989). 25. Maria L. Fidalgo, Maria C. Terron, Angel T. Martinez, Aldo E. Gonzalez, Francisco J. Gonzalez-Vila, and Guido C. Galletti, J. Agric. Food Chern. 41, 1621 ( 1993).
26. Xiao-an, L. Zhong-Zheng and T. Die-Sheng, Cellul. Chern. Technol. 23, 559 (1989). 27. F. E. II. Bartton, W. R. Windham, and
o.
S. Himmelsbach, J. Agric. Food
Chern. 30, 1119(1982).
28. R. W. Bailey, In Chemistry and Biochemistry of Herbage, (Ed.) G. W. Butler and R. W. Bailey, Academic Press, New York, 157(1993).
344 Physical and chemical processing of fibre and non fibrous products
29. B. D. E. Gaillard, J. Agric. Sci. 59, 639(1962). 30. Yuliko Fulushi, Osamu Otsuru, and Masaakira Maeda, Carbohydrate Research 182, 313(1988). 31. R. L.Whistler, J. Bachrach, and D. R. Bowman, Arch. Biochem. 19 25(1948). 9
32. A. Ebringerova, Z. Hromadkova, J. Alfoldi, and G.Berth, Carbohydrate Polymers 19, 99(1992). 33. G. Annison, M. Choct, and N. W. ,Carbohydrate Polymers 19, 151 (1992). 34. R. P. Preston, "The Physical Biology of Plant Cell Walls," Chapman and Hall, London(1974). 35. A. Darvill, M. McNeil, P. Albersheim, and D. P. Delmer, "The Biochemistry of Plants," (Ed.) P. K. Stumpf and E. E. Conn, 1:91. Academic Press, New '~ork,
(1980).
36. Noach Ben-Shalom, J. Food Sci. 51(3), 720(1986).
33 Tbermodestruction of cellulose and levoglucosone production G Dobele, G Rossinskaja, B Rone and V Yurkjane - Institute of Wood Chemistry, Latvia, Riga
ABSTRACT The present study is dedicated to the process of the thermal transformation of cellulose under the action of phosphoric acid. The problems of the influence of concentration of phosphoric acid and the temperature of preliminary fixation during the impregnation of cellulose upon the development of the dehydration reactions and the formation of l,6-anhydrides levoglucosan and levoglucosenon have been considered.
INTRODUCTION The modification of cellulose with phosphoric acid ensures the change of the direction of the thermal destruction process, including the catalysis of the dehydration reactions and the change of the anhydroformation mechanism. Up to now, insufficient attention has been paid to the low temperature reactions of dehydration and depolymerization proceeding as a result of changing the conditions of the thermofixation of phosphoric acid in the cellulose matrix.
METHODS OF INVESTIGATION Sulphate index of
cellulose samples (6-cellulose content 98%, crystallinity 0.65) were the object of the
345
346 Physical and chemical processing of fibre and non fibrous products
investigation. Phosphoric acid (1-10% from cellulose) was introduced by the impregnation method. The thermal fixation of the samples was realized in an inert atmosphere in the temperature range 100-200°C (heating rate 5°C/min). Pyrolysis was realized at subsequent temperature 350°C. The cellulose samples and the solid products of thermal treatment were analyzed by thermal analysis, IRand X-ray photoelectronic spectroscopies. The dynamics of the evolving of water was determined by stepwise pyrolytic gas chromatography (SPGC). 1,6-Anhydrosugars were determined by gas-liquid chromatography.
RESULTS AND DISCUSSION The introduction of phosphoric acid to the cellulose macromolecule results in a considerable change of the thermodestruction mechanism of a polymer: the amount of the volatile products of destruction is decreasing, the temperature of the main process of thermodestruction is decreasing, and the water yield is increasing (Table 1). Table 1. Characteristics of the cellulose thermodestruction in the presence of H3P04 (% in terms of oven dry matter)
%
10
Initial
Temperature
Mass
temperature of mass loss °C
of maximal rate of mass loss °C
loss of water up to up to 5l2Jl2JoC 500°C % %
260 200 170 170 160
325 280 270 260 245
91.4 74.3 68.6 68.2 64.8
Yield
14.2 24.0 25.8 28.6 31.9
If, during cellulose pyrolysis, levoglucosan is the major component of resin, and the levoglucosan yield does not exceed 0.6 %, then the pyrolysis of cellulose in the presence of phosphoric acid results in an increase of the levoglucosenon yield (Figs. 1 and 2). According to Shafizadeh [1], the maximum levoglucosan yield (8 ... 12%) has been obtained under conditions of isothermal heating of cellulose at 350°C in the presence of 1.5% phosphoric acid. The maximum formation of levoglucosenon (34%) has been registered
Thermodestruction of cellulose and levoglucosone
under pyrolytic gas chromatography conditions (430°C) upon the introduction of 1% phosphoric acid to the cellulose [2]. Yield, %
36
Fig.l Variations in water and levo-glucosenon yield during eel 1 u los e thermodestruction ( 350°C) . ( 1) levoglucosenon, (2) - water o
~
_ _---'_ _
-...J"---
o
H3P04, %
26
Yield, %
80
.. - - .. "
'-'"
•
3
+ .
16
10
- . -
&
- . . ..
.
~ e· • • . . . • • . • •
••••••••.•.•••••••••••••••••••••
Temperature, C
Fig.2 Variations in anhydrosugars yield during thermodestruction of cellulose. (1)- levoglucosan
(pyrolysis of initial cellulose) , (2)levoglucosenon (pyrolysis of cellulose with 5% H3P04)
In the present work, the influence of thermal fixation and concentration of the phosphoric acid introduced to the cellulose upon the formation of levoglucosenon and levoglucosan during the thermal destruction process has been studied. From
the data shown in
Figs. 1 and
2 and
Table 2 it
347
348 Physical and chemical processing of fibre and non fibrous products
follows that both the main representatives of 1,S-anhydrides - levoglucosan and levoglucosenon are formed during the pyrolysis of the phosphoric acid containing cellulose samples. In this case, their total yield depends on the amount of the acid introduced to a small extent, varying within the range 10.3 ... 11.7%. The levoglucosenon/levoglucosan ratio in the total product, upon the introduction of less then 5% phosphoric acid to the cellulose, remains approximately equal, while at an increase of acid up to 10%~ the levoglucosenon yield increases. "hermofixation, during which the initial reactions of solid interaction in the system are being developed affects both tne total yield of 1,6-anhydrosugars and quantative distribution. The slow heating (up to 100°C) of the samples containing up to 5% acid hampers the formation of levoglucosenon during subsequent pyrolysis, and the ratio on nonhydrated and hydrated anhydrosugars increases up to 9.0 (2.4% acid). However, with the increase in the amount of the acid introduced, the hampering effect is inhibited, and at the acid content 10.7%, the specified ratio is 0.8 already. Table 2. Summary yield of 1,6-anhydrosugars (350°C) (% in terms of oven dry matter of cellulose) Amount of H3P04 introduced
Yield of 1,6 - anhydrosugars, % Temperature of thermofixation
JJ
°C
%
20 2.4 4.8 10.8
100
10.3 10.2 10.5 9.3 11.7 16.1
120
140
160
180
200
7.9 13.8 15.0 15.9 17.4
13.6 23.2 16.4
16.6
22.9 22.1
17.0 13.1
An increase in the thermal fixation temperature up to 140 and 160°C for cellulose samples containing 2.4% acid is accompanied by the drop of the levoglucosan/levoglucosenon ratio down to 2.0 and ~.3) respectively. After thermal fixation up to 200°C, the levoglucosan yield is 12.5%. The influence of thermal fixation with the activation of levoglucosenon formation for samples containing 4.8% phosphoric acid is expressed the most prominently. A sharp increase in the levoglucosenon / levoglucosan ratio up to 12.0 is observed in a thermal fixation temperature range of 140 ... 180°C, which
Thermodestruction of cellulose and levoglucosone
corresponds to a levoglucosenon yield of 21.4%. Further increase in the thermofixation temperature results in a decrease in anhydroformation during pyrolysis. For the maximum formation of levoglucosenon upon the introduction of 10.8% phosphoric acid (yield 19.1%) during the process of the fast pyrolysis of cellulose) a thermofixation of 160°C is sufficient. Hence, it has been established that during a thermofixation of 100-200°C, the interaction reaction in the system cellulose-phosphoric acid with the formation and decay of complexes, presumably of the main type, proceed more perfectly as compared to the impregnation process. In this case, the cellulose depolymerization process is activated, which promotes an increase in the yields of non-hydrated and hydrated anhydrosugars during subsequent pyrolysis: low temperature thermofixation (100°C) at a 2.4% content of phosphoric acid limits the development of the dehydration reactions. The levoglucosan and levoglucosenon yields during pyrolysis make up 9.1 and 1.1) respectively; low-temperature thermofixation (180°C) at a 4.8% content of phosphoric acid in the system provides the maximum development of the dehydration and depolymerization reactions. The levoglucosan and levoglucosenon yields during pyrolysis are 1.8 and 21.4%, respectively. The analysis of the experimental data of cellulose pyrolysis has shown that the impregnation with phosphoric acid inhibits the formation of the volatile products of destruction during the increase of the water fraction in their composition (Table 1) (gas-liquid chromatography results in the accumulation of the C=C and c=o bonds in the intermediate products of destruction (IR-spectroscopy). These results indicate that, during the formation of levoglucosenon, the intra- and intermolecular dehydration reactions are decisive. From the data of X-ray photoelectron spectroscopy of the products of the thermal destruction of cellulose (initial ones with the addition of phosphoric acid) (Table 3), the temperature limits of the existence of bonds in the structure: 20-180°C for hydrogen bonds; 18--350°C for mono-) di-) and triester bonds; 260-450°C for P-O-P bonds of polyphosphate groups; 450°C and more for phosphorus-hydrogen bonds have been established.
REFERENCES 1. Shafizadeh F., Furneaux R.H., Stevenson Carbohydrate Res., 1979, 71, 169. 2. Fung D.P.C. Wood Sci., 1976, 9, 55.
T.T.
349
* **
2740 220
28lJ..0 286.LJ.
286.11 287.1J.
1.440 81J.0 300 200
284.0 285.0
287.3
286.l&.
1050 4.50 112 90
680 1200 270
E""r· •••
eV 285 286.7 288.4.
284.0 285.0
imp/sec
C1.
P0 4
H~P04
H~PO.~
134..3
133.3
-
-
-
13lJ..l
-
-
-
13l!..1
-
-
13£&..5
eV
E.... ,-.....
3.8" H3
for sa.mples conta.1nina- 10. 8% for samples containina- 3.8%
450
350
260* 280**
20
ere
Temp. P'2l:'
20 50
-
-
80
-
-
-
20
-
20
imp/"sec
284.0 285.1 286.4287.4
284.0 285.2 286.5
284.0 285.0 286.2 287.2
eV 285.0 286.6 288.2
E.".r' • • •
C1
ll34 3L!O
2600 832
1120 700 180
800 360 160
1060
-
610 1120
1mp//sec
10. 8%
•••
-
-
133.6 135.5
-
134.1 135.6
-
-
134..2 135.4
-
eV 134.4.
E.... r
H:'3P0 4
Table 3. Characteristic of the RF-spectra of the cellulose sample contain1n~ phosphoric acid. p~ior to and after thermal treatment.
-
63 25
-
-
95 30
-
30
1mp/"sec
-
-
30
12/J.
P2"....
w
Vl
VI
~
0-
o
~ "'1
~
=
=t>
a
t:S
o
t:S 0t:S
~
~
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::::h
~
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34 Star-shaped and crosslinked polyurethanes derived from lignins and oligoether isocyanates S Montanari, B Baradie, J-P Andreolety and A Gandini - Materiaux Polymeres, Ecole Francaise de Papeterie et des Industries Graphiques (INPG), BP65, 38402 8t Martin d'Heres, France
INTRODUCTION Lignins have stimulated considerable interest in recent years as potential additives and/or reagents for the elaboration of novel polymeric materials (1,2). The extraordinary abundance of this natural polymer, second only to cellulose, would obviously justify a more rational exploitation of its potential outside its use as a source of energy in paper mills. However, only relatively minor applications have been found for lignins, mostly in the form of lignosulfonates (2). Lignins obtained from various vegetal sources and biomass refinery processes, like the conventional pulping or the newer organosolv and steam-explosion technologies, can differ considerably in structure and molar masses (1,2), but have a single common qualitative feature in terms of their possible use as a macromonomer, namely the presence of both aliphatic and aromatic hydroxy moieties. All other functional groups, capable in principle of providing chain growth, are either too scarce or unreliable to be of general interest in that context. The overall content of OH groups and the relative abundance of phenolic and alcohol-type structures of course vary from lignin to lignin according to the type of species, but within reasonable limits. These variations in hydroxy population bear therefore little or no consequence on their potential exploitation as sites for condensation reactions which include essentially esterification, etherification and the formation of urethanes. 351
352 Physical and chemical processing of fibre and non fibrous products
Our laboratory has been engaged in research efforts towards a more systematic valorisation of renewable resources for the elaboration of polymeric materials (see other paper by Gandini in this book) and has already investigated the synthesis and characterisation of polyesters derived from lignins (3,4) using acid dichlorides as co-reagents. The present communication describes a study of polyurethanes prepared with oligomeric mono- and di-isocyanates. Lignin-based crosslinked polyurethanes have already been prepared and characterized (1,2), but in order to ensure a good reactivity of the OH groups borne by the natural macromolecules, a chain-extension reaction with an oxirane, e.g. propylene oxide, was deemed necessary before carrying out the actual polycondensation with commercial diisocyanates. Our previous experience with polyesters had shown that this chain-extension reaction was not necessary because we found that the OH functions of unmodified lignins were in fact quite available for esterification under appropriate conditions (3,4). The novelty of the approach described here stems therefore from the application of the same principle, namely the use of lignins as macromonomers for the synthesis of polyurethanes, without any preliminary chemical modification. The other original aspect was the fact that the isocyanates chosen as complementary reagents were new mono- and di-functional macromonomers capable of introducing soft segments in the final polymeric structure. With the former, star-shaped topologies were obtained, whereas the latter produced networks. EXPERIMENTAL Most experiments were carried out with Alcell organosolv lignin (5) obtained by the ethanolic pulping of a mixture of hardwoods, kindly provided by Repap Co. This industrial product was thoroughly characterized after precipitation of its acetone solution in dilute HCI, to eliminate phenolic monomers and oligomers, thorough washing with water, and vacuum drying to constant weight. The elemental analysis gave C 67.0%, H 6.4% and 0 26.6%. The GPC and vapour-pressure osmometry, both in THF, yielded Mn=810, Mw=1930. From the 13CNMR spectrum of acetylated samples the following OH contents per C9 unit were determined: 0.22 primary aliphatic, 0.14 secondary aliphatic and 0.58 phenolic. Other analyses included FTIR spectroscopy which, apart from the typical features expected for all lignins, showed a weak absorption at 1705 crrr! denoting minor amounts of carbonyl moieties and DSC analyses which gave a Tg around 65°C. The lignin model compounds, namely ethanol (EtOH), guaiacol (G), 2,6-dimethoxyphenol (DMP) and 4-hydroxy-3-methoxy-benzyl alcohol
Star-shaped and crosslinked polyurethanes
353
(HMBA), were commercial samples (Aldrich), used as received. The model 2-methoxyethylisocyanate (MOEI), the oligopropylene oxide monoisocyanate (0 PO M, Mn=800) and the oligoethylene oxide diisocyanate (OEOD, Mn=700) were prepared from the corresponding commercial primary amines (Aldrich) by the reaction with bis(trichloromethyl)carbonate and characterized as described elsewhere (6). Apart from that of the Alcell lignin itself (L·OH), the structures of the reagents used in this work are shown below: CH 20H
08
OH
©r
OCH 3
CH 30
OCH3
OCH 3
(DMP)
(G)
OH
(HMBA)
(MOEI)
OCN~CH2TH-°teH3 CH 3
9
(OPOM)
OCN{CH2CH2-0tCH2-NCO 12 (OEOD)
Solvents were dried before use and all other reagents were purchased in their purest available form. Reactions were conducted under magnetic stirring in an inert atmosphere in THF at 20-45°C using dibutyltin dilaurate as catalyst. They were all homogeneous and could be followed by monitoring the evolution of the IR spectrum of the solution, and in particular the decrease in the intensity of the NCO peak at 2250 crrr l , The products were characterized by spectroscopic procedures, GPC, vapour-pressure osmometry and thermal analyses, with particular emphasis on 13C-NMR spectroscopy to examine their fine structural details.
RESULTS AND DISCUSSION Research on the reaction of NCO functions (electrophiles) with both aliphatic and aromatic OR groups (nucleophiles) is very well documented and has provided the basis for the controlled elaboration of polyurethanes. In particular, it is well established that aromatic
354 Physical and chemical processing of fibre and non fibrous products
isocyanates are much more reactive than aliphatic counterparts and, between the two families of hydroxylic compounds, phenols are less reactive (less nucleophilic) than alcohols; moreover, among the latter compounds, primary functions react more readily than secondary ones which are in tum more reactive than tertiary ones mostly because of steric effects. Before studying the reaction of the oligoether isocyanates with lignin, it was decided to establish semiquantitative criteria concerning reactions of model compounds and work progressively towards the actual synthesis of the polymeric materials. The first combinations explored were those involving small molecules simulating both the various lignin OH moieties (EtOH, G, DMPand HMBA) and the NCO function attached to aliphatic oligoether chains (MOEI). Reactions occurred smoothly and went to completion albeit at different rates depending on the reactivity of the various hydroxy groups; with HMBA, the primary aliphatic OH condensed more readily than the phenolic counterparts. All these simple urethanes were fully characterized and no anomaly was detected with respect to the expected sructures. The next step consisted in increasing the size of the monoisocyanate, i.e. going from MOEI to OPOM while keeping the monomeric nature of the lignin models. All monofunctional hydroxy compounds reacted stoichiometrically with the macroisocyanate but at rates which depended on the nature and sterle situation of the OH groups, ethanol giving the fastest condensation and 2,6-dimethoxyphenol the slowest, as expected. With HMBA, the reaction of the aliphatic OH occurred normally and much more readily than that of the phenolic function. This was clearly confirmed by studying the interaction at a molar ratio of unity, i.e. with only half NCO groups available with respect to the total number of OH groups: the product obtained contained essentially the urethane moiety resulting from the condensation of the benzylic (aliphatic) hydroxy functions to the detriment of the phenolic counterparts. The characterization of the product arising from the stoichiometric reaction ([NCO]/[OH]=l) showed that only part of the phenolic OH groups had been condensed and that this interaction had become particularly slow after the condensation of the benzylic functions, so slow that the OPOM had been consumed by the notoriously sluggish self-condensation of NCO moieties. This behaviour can be rationalized in terms of a problem of steric hindrance intervening in addition to the intrinsic difference in reactivity between the two types of OH groups. In other words, on the one hand the primary aliphatic hydroxy functions reacted much more readily than the phenolic ones and thereafter the oligoether chains from the macroisocyanate wrapped around the phenolic ring thus establishing a
Star-shaped and crosslinked polyurethanes
355
steric obstacle to the reaction of the second OH group. To these considerations one must add the possible hydrogen bonding between the donor ether moieties from OPOM and the acidic phenolic OH functions. Having established some basic criteria concerning the reactivity of the typical lignin hydroxy groups towards monofunctional aliphatic isocyanates including linear oligoether structures, we moved to the preparation of star-shaped macromolecular polyurethanes based on OPOM and Alcell lignin. The fact of switching from monomeric models to the unmodified natural macromonomer posed again the basic question of whether steric problems might arise, i.e. of the actual availability of the OH groups towards the condensation reaction with the NCO functions borne by OPOM. The systems investigated differed by a single parameter, namely the initial [NCO]/[OH] ratio which varied from 0.15 to 1 in six steps. The infrared spectra taken as a function of time, showed without any ambiguity that the expected condensations were occurring as indicated by: (i) the progressive decrease, down to the actual disappearance, of the band at 2250 crrr l in the spectrum of the reaction medium indicating the consumption of the isocyanate functions; (ii) the appearance of a carbonyl band at 1740 crrr l (urethane functions) which increased as the reaction advanced; (iii) the progressive shifting of the band around 3430 cm- 1 to lower frequencies, i.e. about 3330 crrr-I because of the consumption of the OH groups and the formation of the corresponding NH functions; (iv) the substantial increase in the relative intensity of the large band around 1100 cm- 1 in the spectrum of the isolated product, caused by the C-O-C moieties from the oligoether chains being progressively appended to the lignin cores; and finally (v) the corresponding increase in the bands between 2800 and 2980 cm- 1 caused by the aliphatic C-H bonds from the oligopropylene oxide chains. A more detailed inspection of the structure of these products was achieved by analysing their quantitative 13C-NMR spectra against those of the starting reagents and of the model urethanes prepared in the first and second phase of this investigation. This closer look confirmed, on the one hand, the validity of the general conclusion reached from the IR study and provided, on the other hand, a way of assessing the relative reactivity of aliphatic and phenolic OH groups. The results obtained in the interaction of HMBA and OPOM were confirmed here in that the condensation occurred mostly on the former moieties as revealed by: (i) the systematic presence of a peak at 155.7 ppm, characteristic of the carbonyl carbon borne by an aliphatic urethane, whose intensity grew as the [NCO]j[OH] ratio was increased; (ii) the very modest, if any, contribution of the peak at 153.6 ppm, arising from the same carbon but in an aromatic urethane, which did not grow with increasing relative amounts of OPOM; (iii) the presence of a peak at 148 ppm, attributed to
356 Physical and chemical processing of fibre and non fibrous products
the C3 (guaiacyl) and C3+C5 (syringyl) carbon atoms at ~-O-4 with respect to free phenolic functions, which showed little change as a function of the initial synthetic conditions; and (iv) the presence of a peak at 157.2 ppm, attributed to the carbon atoms of carbonyl functions in self-condensation products of OPOM, which grew as the [NCO]/[OH] ratio was increased. There seems to be little doubt that in the present context only the aliphatic OH groups display an adequate reactivity towards the oligoether monoisocyanate, for the reasons already invoked in the discussion of the results of the condensation between H MBA and the same macroisocyanate. This conclusion was corroborated by carrying out a reaction in stoichiometric conditions between the model MOEI and the Aleell lignin which gave a product characterized by the presence of both aliphatic and aromatic urethanes (resonances at 156.2 and 154.0 ppm, respectively) and the absence of detectable amounts of free phenolic moieties (no peak at 148 ppm). It remains to be seen whether the loss of reactivity of the phenolic OH groups is merely due to the sheer size effect of the isocyanate macromonomer or to concomitant structural features associated with its chain capable of blocking the reactivity by complexation or hydrogen bonding. Work is in progress to unravel this problem. The star-shaped polyurethanes obtained from the reactions of OPOM and Alcell Iignin were submitted to OPC and vapour pressure osmometry analyses which showed that their molar masses as well as the degree of polydispersity increased with an increasing initial proportion of macroisocyanate: thus Mn and M w went progressively from 810 and 1930, respectively for the unreacted lignin to about 1300 and 7000, respectively for the polyurethanes prepared under stoichiometric conditions. These results, analysed in terms of Ip going from 2.4 to more than 5, appear reasonable if one considers that the number of oligopropylene oxide chains which are attached to lignin is the higher the higher the number of available aliphatic OH groups per lignin molecule. The DSC thermograms of these products displayed glass transition temperatures which decreased as the number of oligoether branches per lignin core was increased as shown in Table 1. It is important to underline that lignins are soluble in polyethers like PEO and PPO so that the present star-shaped structures must be viewed as homogeneous systems down to the intramolecular level. Moreover, the two constituents of these materials have very low molar masses. It follows that one would indeed expect the variation of T g with composition to obey an additivity relationship, as is indeed the case, although the initial drop in Tg with 10% OPOM seems rather brutal. This feature could be attributed to both the introduction of the oligoether branches and the
Star-shaped and crosslinked polyurethanes 357
corresponding disappearance of the OH groups of the lignin, a possibility which is being checked by using model isocyanates. Another interesting change in the properties brought about by the progressive introduction of oligopropylene oxide chains as branches on the lignin core is the evolution of the solubility of the ensuing materials. Table 1 gives the extent of extract in diethyl ether as a function of branching, showing that one can readily solubilize lignins in such poor solvents by this type of chemical modification. Similar changes were found with respect to the hydrophilic character of the star-shaped polyurethanes and this feature bears important implications in terms of possible new uses of lignin-based materials, e.g. in water borne printing inks. [NCO]/[OH] Tg (OC) ~ Et20 sol [NCO]/[OH] Tg (OC) o (lignin) 0.4 5 -58 +64 0.1 0 55 0.8 -75 0.2 -30 -83 OPONH2
% Et20 sol. 75 100 100
Table 1. Properties of star-shaped lignin-OPOM materials. The final phase of this exploratory investigation called upon the reaction of Alcell lignin with the OEOD macrodiisocyanate. These polycondensations led to crosslinked polyurethanes containing however a certain proportion of soluble products arising from the self condensation of OEOD. Here, once again the reaction seems to occur mostly on the aliphatic OH groups of lignin and therefore it is not necesary to increase the proportion of NCO functions above that level to induce the bridging
among lignin macromolecules. Indeed, with [NCO]/[OH] as low as 0.2, we obtained about 50% of gelled material and with a ratio of 0.6, more than 80% of the product had crosslinked. The T g s of these networks after extraction with CH2Cl2 were considerably higher than those of the corresponding star-shaped thermoplastic counterparts: about 40°C for the product obtained with 20% NCO (23°C before extraction), 4°C for that corresponding to 60% NCO (-23°C before extraction) and finally -12°C for the network prepared with 80% NCO (-35°C before extraction). This trend is consistent with the stiffening role of lignin cores holding both ends of the oligoethylene oxide chains. The soluble portion, corresponding to branched structures and to 0 E 0 D selfcondensation products, played the role of plasticizing agent for the crosslinked materials. TGA thermograms indicated that all the lignin-based polyurethanes prepared in this investigation were stable up to about 250°C.
358 Physical and chemical processing of fibre and non fibrous products
CONCLUSION As in our previous study on lignin-based polyesters (3,4), we again showed in this work that one can prepare star-shaped (A) and crosslinked (B) polyurethanes based on lignin and polyethers as shown below, without any preliminary modification of the natural macromonomer. However, contrary to polyesterifications (3,4) the present systems displayed a very pronounced difference in reactivity between the aliphatic and the phenolic OH groups of lignin. Work is in progress to gain a deeper insight into this issue and to extend the scope of this general topic to other materials in order to find novel applications for lignins.
(A)
REFERENCES 1. Glasser, W.G. and Kelley, S.S. (1987) in Encyclopedia of Polymer Science and Engineering, Wiley, N.Y., vo1.8, p. 795. 2. Gandini, A. (1992) in Comprehensive Polymer Science, Aggraval, S.L. and Russo, S. (Eds), Pergamon Press, Oxford, p. 527. 3. Guo, Z.X. and Gandini, A. (1991) Europ. Polym. J. 27,1177. 4. Guo, Z.X., Gandini, A. and PIa, F. (1992) Polym. Int. 27,17. 5. Pye, E.K. and Lora, J.H. (1991) Tappi J. 74(3), 113. 6. Callens, S., Le Nest, J.F., Gandini, A. and Armand M. (1991) Polym. Bull. 25, 443.
Part 5: Applications of cellulose, cellulose derivatives, lignin and cellulose-related enzymes
35 The alkaline degradation of cellulose relating to the longterm storage of radionuclides in cement J Shimizu,* J F Kennedy,* L L Lloyd** and W Hasamudin* *Birmingham Carbohydrate and Protein Technology Group, Research Laboratory for the Chemistry of Bioactive Carbohydrate and Proteins, School of Chemistry, The University of Birmingham, Birmingham B15 2TT, UK; **Chembiotech Ltd, University of Birmingham Research Park, Birmingham B15 2SQ, UK
ABSTRACT The pathways of alkaline hydrolysis of cellulose as a function of different exposures to alkali and the influence of the hydrolysates on the europium adsorption on calcite were investigated relating to the longterm storage of radionuclides in cement. Several non-volatile organic acids derived from alkali-treated cellulose were identified as the corresponding trimethylsilyl derivatives by using GC /GC-MS. Hydrolysates of cellulose in 0.1 M and 0.05 M NaOH solutions were different from those in saturated Ca(OH)2 solution. Alkaline hydrolysates of cellulose reduced the absorption of europium on calcite. INTRODUCTION Plans by various countries taking seriously the longterm (>100 years) storage of medium to low level radionuclide waste are being focused on encapsulation of the total waste in metal drums, and incarceration of the drums in cement below ground level [1][2]. Since much of the waste and cement is likely to have a cellulose carrier (pulp, paper, tissue and cotton), concern has been expressed about the possible leaking of the radionuclides by transport in the ground water to water supply sources, because degradation products [3][4][5] of cellulose in alkaline solution such as in the cement, by virtue of being small molecular-weight ionic compounds, could 361
362 Applications
form water soluble salts with radionuclides and possibly enhance [6] this transport dramatically. Accordingly a study of which products could be expected from the anaerobic alkaline degradation of cellulose is being undertaken. This paper describes possible alkaline degradation pathways together with liquid chromatography and GC-MS of the products as a function of different exposures to alkali. EXPERIMENTAL
Alkaline hydrolysis of cellulose Cellulose powder (25 g) (20 urn, Aldrich) was added to 0.05M NaOH, O.lM NaOH and saturated Ca(OH)2 solutions (250 ml). Each sample was then stored at room temperature for periods of 21 to 201 days under anaerobic condition. After degradation, the centrifuged hydrolysate supernatant solutions were neutralised with 1M HCI (c.a. 7-10 drops) and freeze-dried. Gas liquid chromatography of alkaline hydrolysates of cellulose Trimethylsilylation (TMS) was achieved by the following method [7]: 5 mg of freeze dried hydrolysate was added to 0.5 ml pyridine (Aldrich) containing 0.3% (w Iv) lithium perchlorate (LiCI04.3H20) (Aldrich) and the solution maintained at 400C for 2 hr. Trimethylsilylation was then carried out by the addition of 200 fll hexamethyldisylazane (Aldrich). and 100 JlI trimethylsilyl chloride (Aldrich). After a further 10 minutes at 400C the sample (2 J.11 injection) was subjected to gas phase chromatography on a Carlo Erba Instrument GC 8000 series with the following column specification: Alltech Econocap SE-30, 0.54 mm 1.0., 15 m length, film thickness 1.2 microns. Nitrogen, at a flow rate governed by a pressure of 10 kPa, was used as carrier gas, and a temperature program was used for the column (600C to 2200C with the rate of 10oC/min and then maintained at 220 0C for another 10 minutes). The elution profiles were obtained using a flame ionisation detection system. D-Glucitol was used as an external standard to evaluate elution positions for each peak. The same sample was then subjected to GC/MS by employing a Shimadzu Gas Chromatograph GC-14A for gas liquid chromatography and a Kratos Analytical MS 80 for mass spectrometry. Gel permeation chromatography of alkaline hydrolysates of cellulose Alkaline hydrolysates of cellulose were analysed using BioGel P2 gel permeation chromatography (Bio-Rad Laboratories). The water jacketed column (55 x 1.3 em) of the packing was equilibrated and maintained at 60 °C, and 0.1 M NaCI solution was used as the mobile phase (11 ml/hr). The
Radionuclides in cement
363
freeze-dried solid, dissolved in distilled water (100 mg/ml), was centrifuged at 10,000 g for 10 min at 10 °C to yield a water soluble fraction an aliquot (150 JlI) of which was injected into the BioGel P2 GPC column. Column eluents were continuously monitored using a spectrophotometer (Cecil CE-472) at 360 nm to monitor coloured fractions and using an automated L-cysteinesulphuric acid assay [8] at 420 nm with a heating bath and a colorimeter to monitor sugars. Europium adsorption test Sample solutions including alkaline hydrolystes of cellulose, isosaccharinate, methyl ~-D-glucopyranoside and a neutral cellulose oligosaccharides were added to 0.1 M NaOH solutions (20 ml) in centrifuge tubes, together with Ig/l CaC03 in 0.1 M NaOH. The solutions were spiked with 1 ml of a europium-152 in 0.1 M NaOH. The tubes were shaken overnight. Next day, they were centrifuged for 30 min at 50,OOOg. The supernatant was assayed for europium-152 in a gamma-counter (NaIdetector). From the difference in activity before and after adsorption, the distribution factor Kd could be calculated. The distribution factor is defined as: Ka = Ell -152 adsorbed (cpm I g) Eu -152 in solution (cpm / ml)
(mIl g)
The Kd values were compared with the Kd values for the systems where no degradation products were present. This Kd further denoted as Kd". The ratio Kd": Kd is the factor (reduction factor RF) by which the adsorption is reduced by adding a ligand. The relationship between the reduction factor and the ligand concentration (L) is given by:
where K* is the stability constant of the ML complex and [L] is the free (uncomplexed) ligand concentration. RESULT and DISCUSSION Gas liquid chromatogram of alkaline hydrolysates of cellulose Table 1 shows the identification of the degradation products from the alkaline degradation of cellulose after storage for 21 days. Relative retention times of the TMS derivatives were determined with the derivative of D-
364 Applications
glucitol as the reference. Identification of the mass spectra data were based on the published data [3][9][10] Glucometasaccharinic, isosaccharinic, 2-deoxytetronic and lactic acids were detected in the hydrolysates of degraded cellulose (day 21) in the three different conditions (0.1 M NaOH, 0.05 M NaOH and saturated Ca(OH)2). Since the degradations were conducted at ambient temperature, the number of products formed was not as many as the cellulose treated in higher concentration of alkali and extreme temperature [3]. Table 1 Products identified from the alkaline hydrolysate of cellulose under various alkaline conditions after day 21 Product Identified Alkaline Degradation Condition RTa Saturated 0.1 M 0.05M Ca(OH)2 NaOH NaOH 3-deoxy-arabino-hexonic 0.96 X X Xb (glucometasaccharinic) 3-deoxy-2-C-hydroxymethyl-D-threopentonic (~-D-isosaccharinic ) 3-deoxy-2-C-hydroxymethylD-erythro-pentonic (a- D-isosaccharinic) 3-deoxy-D-arabino-hexono-l,4-lactone 3-deoxy-D-ribo-hexono-l,4-1actone 3-deoxy-erythro-pentonic 2-deoxy-erythro-pentonic 3-deoxytetronic 2-deoxytetronic glycolic 2-deoxyglyceric 3-deoxyglyceric (lactic)
0.95
X
X
X
0.95
X
X
X
0.78 X 0.78 X 0.84 X 0.83 0.68 X 0.69 X X 0.45 X 0.41 X 0.43 X X a: GC retention time of TMS derivatives to D-glucitol derivative b: detected
X X
X
X
Gel permeation chromatography of alkaline hydrolysates of cellulose Figures 1, 2 and 3 show chromatograms of alkaline hydrolysates of cellulose exposed to 0.1 M NaOH, 0.05 M NaOH and saturated Ca(OH)2 solution respectively. According to the cysteine-sulphuric acid assay, Figures 1 and 2 show three major peaks. Based on studies by using standard materials (glucose, neutral and acidic oligosaccharides, sodium isosaccharinate, sodium gluconate, acetate, formate), first, second and third peaks corespond to high molecular weight peak (higher than 1800), intermediate molecular weight peak or acidic molecules including organic acids smaller than
Radionuclides in cement
Figure 1 P2 gel permeation chromatogram of alkaline hydrolysate of cellulose exposed to O.IM NaOH for 21 days
365
IMW acidic molecules
HMW
- - cysteine-sulphuric acid assay
monosaccharide
------ absorbance at 360 nm
I'""..
~ !~'
:
o
123 Elution time (hr)
.
r
4
Figure 2 P2 gel permeation chromatogram of alkaline hydrolysate of cellulose exposed to 0.05 M NaOH for 21 days - - cysteine-sulphuric acid assay ------ absorbance at 360 nm
/"'-_
o Figure 3 P2 gel permeation chromatogram of alkaline hydrolysate of cellulose exposed to saturated Ca(OH~for 21 days
..... _--_ ..'
1 2 3 Elution time (hr)
4
- - cysteine-sulphuric acid assay ------ absorbance at 360 nm
,
o
-
.
123 Elution time (hr)
4
366 Applications
monosaccharides (e.g. acetate, formate), neutral oligosaccharides and monosaccharides, respectively. In addition, possible neutral oligosaccharides also eluted between the second peak and the third one. According to the spectrophotometer monitor at 360 nm, coloured materials eluted in the high molecular weight and the intermediate molecular weight or acidic molecules position. The chromatogram (Figure 3) of the hydrolysate of cellulose in saturated Ca(OH)2 solution is different from those in both NaOH solutions: there is a relatively small monosaccharide peak, a trace amount of coloured materials and no high molecluar weight peak. This suggests the mechanism of alkaline hydrolysis of cellulose depends in part on the type of alkali. Europium adsorption test Figure 4 shows the results of the europium adsorption tests. Alkaline hydrolysates of cellulose exposed to 0.1 M NaOH solution for 201 days, stored in form of a non-neutralised and neutralised solution and freezedried solid, have a large effect on the adsorption of europium on calcite (CaC0 3). Figure 4. Europium Absorption Test
1200 1:ceUulose hydrolysate 2:cellulose hydrolysate, neutralised 3:ceUulose hydrolysate, freeze-dried 4:isosaccharinic acid 0.001 M 5:methyl· ~-D-glucopyranoside O.OOIM 6:ceUulose oligosaccharides (lOmglml)
1000
...
S
~
800
~u
600
=
i
~
.,= Q
400
~ Q
{12
..c < 200
0 1
2
3
4
5
6
However, isosaccharinic acid (a representative degradation product of alkaline hydrolysis of cellulose), methyl ~-D-glucopyranoside and alkaline hydrolysates of cellulose exposed to saturated Ca(OH)2 (data not shown) did not reduce the adsorption of europium on calcite (CaC03). However, cellooligosaccharides prepared by hydrolysing cellulose with trifloroacetic acid also reduced the adsorption of europium on calcite (CaC03). This result
Radionuclides in cement
367
may suggest that neutral hydrolysates such as cellooligosaccharides rather than acidic hydorolysates such as isosaccharinic acid are involved in the adsorption inhibition of europium on calcite. CONCLUSIONS
Several non-volatile organic acids derived from alkali-treated cellulose were identified using GC /GC-MS. Hydrolysates of cellulose in both NaOH solutions were different from those in saturated Ca(OH)2. Oligosabhccharides were possibly derived from cellulose in alkaline solutions. Alkaline hydrolysates of cellulose only in NaOH solutions have reduced the absorption of europium on CaC03 and it is noteworthy that neutral oligosaccharide could also reduce the absorption of europium on CaC03. The products of alkaline hydrolysate of cellulose (possibly neutral hydrolysates) specific to exposure to NaOH solutions must therefore be resposible for this efffect. The formation of various types of organic acids as identified in this study is expected to playa significant role in transporting the radionuclides from the storage compartment to the water course. This phenomenon might cause serious pollution problem by the radioactive material. ACKNOWLEDGEMENT
Authors thank Paul Scherrer Institut, Villigen PSI, Switzerland and Nationale Genossenschaft fur die Lagerung radioaktiver Abfalle, Wettingen, Switzerland for their europium absorption tests. REFERENCES
[1] [2]
[3] [4]
[5]
[6]
Nuclear Energy Agency, Excavation Response in Geological Repositories for Radioactive Waste, OEeD, Paris (1987) 11 Roy R., Radioactive Waste Disposal, The Waste Package (vol. 1), Pergamon Press Inc., New York (1982) 52 Johansson M. H. and Samuelson 0., Endwise degradation of hydrolysis in bicarbonate.], App. Poly. Sci (1978)., 22, 615 Alen R., Niemela K.and Sjostrom E., Gas-liquid chromatographic separation of hydroxy monocarboxlic acids dicarboxylic acids on a fused-silica capillary column, J. Chrornatogr. (1984), 301, 273 G. N. Richards and H. H. Sephton, The Alkaline Degradation of Polysaccharides Part 1 Soluble Products of the Action of Sodium Hydroxide on Cellulose J. Chern. Soc. ,(1957), 4492 M. Dozol, W. Krischer, P. Pottier and R. Simon (editors),"Leaching of Low and Medium Level Waste Packages Under Disposal 'Conditions" Graham & Trotman Ltd., London (1985) 15
368 Applications
Kennedy J. F., Selective detection ~nd quantitaive determination of the pentoses Chromatographia (1970)3, 316 [8] Kennedy J. F., Stevenson D. L., and White C. A., The behaviour and Starch-Related Oligosaccharides Series on Gel permeation Chromatography as a Function of Molecular Shapes, Starch/Starke (1988), 40 Nr.10,S. 396 [9] Petersson G., Mass spectrometry of aldonic and deoxyaldonic as trimethyl deivatives, Tetrahedron (1970) 26, 3413 [10] Niemela K. and Sjostrom E., Non-Oxidative and Oxidative Alkaline degradation of Pectic Acid, Carb. Res, (1985), 144, 93-99
[7J
36 The use of cellulose and cellulose derivatives in immobilised systems for the removal of colour from textile effluents N Willmott," J T Guthrie," G Nelson] and B Burdett] - *The Department of Colour Chemistry and Dyeing, The University of Leeds, Leeds, LS2 9JT and tThe British Textile Technology Group, 856 Wilmslow Road, Didsbury, Manchester M20 2RB, UK
ABSTRACT A strategy is outlined for the removal of reactive dye colour from textile wastewaters using bacteria, capable of dye degradation, attached to environmentally-acceptable cellulose copolymeric supports. A mixed population of bacteria have been isolated from dyehouse effluent and tested on ten different reactive azo dyes. All of the tests resulted in the removal of the original colour and the production of unidentified, colourless or differently coloured, species within the time-scale provided. Immobilisation of these bacterial colonies onto characterised cellulosic supports, as a route to enhance their dye degrading activity, is described.
INTRODUCTION Increasing public expectation of the quality of water in rivers and estuaries in the U.K. has led to complaints concerning the discharge of coloured effluent to our watercourses. Faced with new legislation, to be introduced on the 1st of January 1996 [1], and a lack of proven and economically feasible technologies for treating coloured effluents, some sectors of the dyeing and fmishing industry are under threat. Reactive dyes are very important commercially for the dyeing and printing of cellulosic fibres. They are characterised by brilliant shades, excellent wet-fastness and good stability to attack by light and chemicals. Thousands of tons of such organic dyes are wasted every year during manufacture and application [2].Losses of dye from reactive dyebaths can be as high as 50%, resulting in highly coloured, alkaline wastewater containing unreacted dye, hydrolysed dye and salt. At present, there is no commercially
369
370 Applications
available process for the complete removal of reactive dyes from a coloured, textile effluent. Most reactive dyestuffs are recalcitrant to the biodegradation processes currently used in sewage treatment works and their adsorption onto conventional biomass (bioelimination) is low. Approximately 90% of the reactive dyes in textile effluents passes through the receiving sewage treatment works into the adjoining watercourse [3]. For this investigation, a U.K. knitwear dyehouse supplied fresh samples of industrial textile effluent, containing mostly aqueous solutions of reactive dyes. The colour strength of the effluent that this company discharges and its use of large depths of shade often renders coagulation and flocculation treatment methods uneconomical. The aim of this work was to enhance the treatment capabilities of existing biological systems. Previous workers have found azo dye-assimilating bacteria in the sewer soils from dyehouses [4-9]. In this study, a mixed population of bacteria was isolated from textile effluent. This mixed population leads to the degradation of several reactive azo dyes under test conditions. All, or part, of the culture will be immobilised by entrapment, by encapsulation and by covalent linkage to a modified cellulosic support which should in principle stabilise, and perhaps enhance, the dye-degrading activity of the bacteria. It should also make the regeneration and recovery of the active culture from biological reactors much simpler. There are many different examples of immobilised biological species that exhibit biological activity. These include enzymes, antibodies, enzyme inhibitors, antigens and peptide hormones [10]. In recent years, whole cells have been immobilised, particularly for use as industrial catalysts. It is preferable that the immobilised cells are active but unable to proliferate. Novel cellulosic foams, cellulose wood pulp (both natural and chemically modified) and straw can be used as the biological supports for immobilisation. Ine extensions of the current study', regenerated cellulosic foams will be based on the Tencel system. These are prepared by the dispersion of a metal carbonate, or other metal salt, into a solution of cellulose in N-methylmorpholine N-oxide. On immersion in an acidic medium, the cellulosic component precipitates and carbon dioxide is released. The metal ions and the N-methylmorpholine N-oxide are extracted from the foams by washing. The nature of the process provides an even distribution of pores throughout the structure. This is important as the physical form of the biosupport must enable efficient transport of the dyestuffs and the dyestuff metabolites. Graft copolymerisation provides a general method for the modification of the chemical and physical properties of cellulose supports via the covalent linkage of side chains to the polymeric backbone [11]. The following points of interest with respect to the support are the subject of current study :
1. The 2. The 3. The 4. The 5. The 6. The 7. The
dyeability with reactive dyes. adsorption and absorption capabilities. hydrophilic/hydrophobic character. stabilisation of the microbial culture. physical and chemical form. thermal and chemical stability. biodegradability.
Removal of colour from textile effluents
371
8. The stability in continuous liquid media.
EXPERIMENTAL Materials
The reactive dyes used are shown in Table 1. Reactive Red 1 and Reactive Orange 1 were synthesised according to standard methods and purified by salting out from solution using sodium thiocyanate. The structure and purity of the two dyes was confirmed by FTIR spectroscopy and capillary electrophoresis. The bacterial culture used in this work was isolated from a textile effluent sample, using a streak plate technique and maintained on agar-soy broth slants at 3°C. The Agar no.2 and Tryptone Soy Broth were obtained from Lab M, Topley House, Wash Lane, Bury, England. All other chemicals (analar grade) were supplied by Aldrich Chemicals Co.(Gillingham,U.K.), BDH Ltd. (Poole, Dorset,U.K.), Vickers Laboratories Ltd. (Burleyin-Wharfedale, Nr.Leeds,U.K.) and Fluka Chemicals Ltd. (Gillingham, Dorset).
Colour Index Name Reactive Red 1 Reactive Orange 1 Reactive Red 120 Reactive Blue 217 Reactive Yellow 111 Reactive Yellow 125 Reactive Red 195 Reactive Yellow 145 Reactive Blue 221 Reactive Blue 222
Table 1 - Reactive dyes used in this study Dye Manufacturer Commercial Name laboratory synthesised laboratory synthesised ICI, Blakeley, U.K. Procion Red HE-3B LJ.Specialities,Wigan,U.K. Kayacelon React Dark Blue C-NR Drimarene Brilliant Yellow K-2GLK Sandoz, Leeds, U.K. Sandoz, Leeds, U.K. Drimarene Golden Yellow K-2R LJ .Specialities,Wigan,U.K. Sumifix Supra Red 3BF 150% LJ .Specialities,Wigan,U.K. Sumifix SupraYellow 3RF 150% LJ.Specialities,Wigan,U.K. Sumifix Supra Blue BRF 150 % L.J .Specialities,Wigan,U.K. Sumifix Supra Navy BF 150%
Analysis of industrial textile efnuent
The colour, turbidity, odour and pH of fresh effluent samples obtained from a knitwear dyehouse were monitored over a five week period. The conditions used in order to provide an effective analysis of the industrial textile effluent are shown in Table 2. Table 2 - Conditions used in the study of textile effluent samples Temperature / °C Volume / em" Air Supply A 20* none(sealed sample bottle) 1000 B 20 none(sealed glass jar) 180 C 20 limited(air gap in jar) 80 D 20 unlimited(open glass jar) 80 3-5# E none(sealed glass jar) 180 * sample on laboratory bench at room temperature (subject to night time variation) # sample stored in refridgerator
372 Applications
It is inevitable that the exact chemical composition of a textile effluent is undefined because of the number of different processes occurring within a dyehouse. Very few textile fmishing companies segregate liquid discharges. The varying nature of industrial textile effluent must therefore be a consideration in this work. The effluent samples used in this work contained mainly brown, black and navy blue reactive dyes in unknown concentrations. Each sample of effluent was assessed visually on a daily basis and the absorption spectrum of the filtered effluent was measured at various intervals using an SP8-400 PyeUnicham UV-visible spectrophotometer.
Bjodea=radatjon of reactive dyes A mixed population of bacteria was isolated from one of the effluent samples and stored on agar slants. The culture was tested on ten structurally different reactive azo dyes. Two of the dyes were synthesised and purified in the laboratory. The rest were unpurified commercial samples. The bacteria were grown anaerobically on agar plates containing 3 O.25g/dm3 of reactive dye and 30g/dm of Tryptone Soy Broth (a complex nutrient source). The plates were incubated at 30°C for 24 hours. Colour changes occurring in the plates during the test period may be the result of the protonation of the dye chromophore rather than the breakdown of the dye structure. This was tested by the addition of a few drops of citric acid and of hydrochloric acid separately to the top of the dyed agar. Purified Reactive Red 1 (Figure 1) was also tested under aerobic conditions on agar-soy broth plates. Both static and shaking broth cultures were also used with no air supply, with a limited air supply and with an unlimited air supply. Each of the samples was incubated at 30°C for 24 hours. The concentration of Reactive Red 1 in the plates was O.25g/dm3 and the concentration in the broth cultures was 1.4g/dm3 . Figure 1 - Reactive Red 1
Cl
OH I
~ Na OS 3
N--( N N-=(CI
NH--{
SO Na 3
RESULTS AND DISCUSSION Analysis of Industrial Textile Emuent A loss of colour was observed in all of the effluent samples during the timescale provided. The rate and extent of discoloration, greatest in test B, appeared to be dependent upon the conditions used. Limiting the supply of air to the samples resulted in a greater loss of
Removal of colour from textile effluents
373
colour over a shorter time period, particularly when the effluent was stored at room temperature. The extent of discoloration decreased in the order: Test B, Test A, Test C, Test D, Test E for the range of testing conditions (Table 2) A-E. Removal of colour from the effluent was quantified by the decrease in the absorbance values of the sample across a range of wavelengths in the visible region of the spectrum. The rate of the disappearance of colour was greatest during the first seven days of the study. After this, the absorbance values (in the visible region) remained relatively constant. As the colour strength of the effluent samples fell, the rate of discoloration sharply decreased, suggesting that the production of the dye-degrading species was dependent upon the concentration of the biodegradable substrate present. Complete decolouration of the samples did not occur in the timescale provided. Discoloration of the samples was accompanied by the production of a strong sulphurous smell. There was also a reduction in the pH of the effluent (which seemed to be proportional to the extent of discoloration) and an increase in the turbidity of the solutions. The pH of the original effluent sample, which was very slightly turbid, was 8.7. Smaller volumes of the textile effluent exhibited a greater degree of discoloration than did the larger volumes. Discoloration may be due to the action of a biological species present in the textile effluent. A microorganism, or group of microorganisms, operating most effectively under anaerobic conditions, may degrade the dyes to produce differently coloured species. The growth of the microbial colony must be favoured by the warm laboratory temperatures, the exclusion of oxygen and the abundant supply of nutrients (including the reactive dyes) in the fresh effluent. An increase in the size of the microbial population through metabolism of these nutrients would diminish the concentration of nutrients and decrease the rate of growth. Hence, the rate of discoloration of the effluent would decrease with time.
Biodegradation of Reactiye Dyes The mixed population of bacteria removed the original colour from all of the agar plates incubated under anaerobic conditions. The colour loss was not due to protonation. Unidentified, colourless or differently coloured species, were produced during the timescale provided. Discoloration occurred in discrete zones underneath and around the bacterial growth. In some cases the zonal clearance of colour was quite dramatic, as shown in Plate 1. This may suggest that an extracellular biodegradation mechanism is not in operation. However, an extracellular process would be limited by the diffusion of the dyedegrading species through the bacterial cell wall and through the agar medium. Further investigation is required in this area. Under aerobic conditions, discoloration of Reactive Red 1 occurred in the zones around the bacterial growth as with the anaerobic plates. A pale yellow species was produced. The area of the clearance zone was smaller than when anaerobic conditions were used. There was a characteristic change in the hue of the broth cultures depending upon the air supply.This occurred with both the static and the shaken broth cultures. The original solutions were a deep red colour. When filtered, at the end of the incubation time,
374 Applications
the samples with no air supply were bright yellow, the samples with a limited air supply were moss green, and the samples left open to the air were orange-brown. The different colours may be explained by the reactive dye being broken down by a different degradation pathway, or by a varying extent, according to the amount of air available to the system.
Plate 1 - Plate containing 0.25g/dm 3 of Sumifix Supra Blue BRF 150%, 2% Agar no. 2 3 and 30g/dm of Tryptone Soy Broth. The plate was incubated under anaerobic conditions at 30°C for 24 hours.
CONCLUSIONS AND FURTHER WORK A mixed population of bacteria has been isolated and shown to cause the discoloration of ten different reactive azo dyes. The extent of discoloration is greatest when the bacteria are incubated under anaerobic conditions at 30°C for 24 hours. Separation and identification of the mixed bacterial population is the subject of further study. The dye-degrading activity of the immobilised system will be evaluated. Model reactive dyebath effluents of known chemical composition will be used to test the effectiveness of the immobilised treatment system. Real industrial textile effluents will then be used. Capillary electrophoresis will be used to identify the dye degradation by-products. Spectra of the effluent samples will be compared to those of authentic samples of the expected reactive dye metabolites.
Removal of colour from textile effluents
375
REFERENCES [1] Skelly,K., An Industry Approach - Management of Colour in Effluent, DEMOS seminar, Brighouse, U.K., (June 1994). [2] Anliker, R., Colour Chemistry and the Environment, Rev.Prog. Col., 8, (1977), 61-62. [3] Pierce, J., Colour in Textile Effluent - the Origins of the Problem, l.S.D.C., 110, (April 1994),131-133. [4] Idaka, E. and Ogawa, T., l.S.D.C., (March 1978), 91-94. [5] Ogawa, T., Yatome, C. and Idaka, E., Biodegradation of p-Aminoazobenzene by Continuous Cultivation of Pseudomonas pseudomallei 13NA, l.S.D.C., 97, (October 1981),435-437. [6] Ogawa, T., Yatome, C., Idaka, E. and Kamiya, H., Biodegradation of Azo Acid Dyes by Continuous Cultivation of Pseudomonas Cepacia 13NA, l.S.D. C., 102, (1986), 12-14. [7] Yatome, C., Ogawa, T., Koga, D. and Idaka, Biodegradability of Azo and Triphenylmethane Dyes by Pseudomonas pseudomallei 13NA, l.S.D. C., 97, (1981), 166-169. [8] Yatome, C., Ogawa, T., Itoh, K., Sugiyama, A. and Idaka, E., Degradation of azo dyes by cell-free extract from Aeromonas hydrophila var. 24B, l.S.D. C., 103, (nov 1987), 395-398. [9] Yatome, C., Ogawa, T., Hishida, H. and Taguchi, T., Degradation of azo dyes by cellextract from Pseudomonas stutzeri, l.S.D. C., 106, (Sept 1990), 280-283. [10] Burck, S.D., Polymer, 16, (1975), 409. [11] Gil, M. H. M., Immobilisation of Proteins, Enzymes and Cells onto Graft Copolymeric Substrates, PhD Thesis(University ofLeeds), (1983). ACKNOWLEDGEMENTS This work is being funded by the Department of Trade and Industry, London, U.K., the Engineering and Physical Sciences Research Council, and the British Textile Technology Group, East Didsbury, Manchester, U.K. The project is part of the Postgraduate Training Partnership Scheme.
37 New polymer electrolytes based on modified polysaccharides C Schoenenberger, J F Le Nest and A Gandini - Materiaux Polymeres, Ecole Francaise de Papeterie et des Industries Graphiques (INPG), BP 65, 38402 St. Martin d'Heres, France
INTRODUCTION Polymer electrolytes have attracted much attention in recent years because of their potential applications in solid state batteries, sensors, electrochromic devices and supercapacitors. materials (1).
A recent review summarizes the main issues concerning these By definition an electrolyte must contain ionic species, usually in
considerable amounts, and allow their transport towards the corresponding electrodes. The replacement of traditional liquid electrolytes by polymeric counterparts requires structures which can dissolve the ions (good solvating properties) and displaying a high segmental mobility (low glass transition temperatures). Polyethers (preferably polyethylene oxide) have been found to respond adequately to these imperatives in conjunction with various salts, mostly lithium salts of strong acids. In order to optimize the performances of these systems, various generations of materials have been developed. Thus, following the tests on high molecular-weight linear polymers, it became necessary to minimize the crystallisation of the polyether chains and the creep of the electrolyte film by preparing crosslinked structures bearing short polyether chains between branching points. In fact the crystalline regions are non-conductive and therefore an obstacle to ionic transport and linear macromolecules flow when heated. Furthermore, these networks were later modified in order to limit the conductivity to the cationic species by fixing the anions to the polymer chains 377
378 Applications
through covalent bonds. In fact, for applications like batteries, the best results are achieved with Li/Li" as an energy storage couple without the intervention of electrode phenomena related to the anion which tend to decrease the current density. Numerous investigations related to the above synthetic aspects, but also to the full mechanical, electrochemical and thermal characterization aimed at understanding the mechanisms related to ionic transport were carried out in our laboratory and this provided sound fundamental criteria for the optimization of functional properties. In order to prepare viable devices with these electrolytes it is also essential to be able to cast them into films as thin as possible. This was our next challenge which was tackled by introducing into the basic polyether network structure an additional backbone consisting of polysaccharide chains, well known for their film-forming properties. The grafting and crosslinking reactions used to join the polysaccharide chains to the polyether strands were based on the formation of urethane links between the OH groups of the former and the NCO end-groups of especially-prepared oligothers with or without the intervention of an alternative crosslinking by the condensation among pendant Si(OEt)3 moieties in the presence of moisture. The present paper describes a study within this novel approach to polymer electrolytes (2).
EXPERIMENTAL The cellulosic derivative chosen for preparing neutral networks was a commercial hydroxyethylcellulose (HEC) which had a DP of 300 and 2.7 ethylene oxide units per anhydroglucose ring. The oligopropylene oxide monoisocyanate (OPOM, Mn=8oo) and the oligoethylene oxide diisocyanate (OEOD, Mn=7oo) were prepared following the synthetic procedure developed in our laboratory (3). 2-Methoxyethylisocyanate (MOEI), used as a model for the oligoether isocyanates, was prepared by the reaction of 2-methoxyethylamine with bis(trichloromethyl)carbonate according to the same procedure. The product was purified by distillation and successfully characterized by IR and NMR spectroscopy. 3-isocyanatopropyltriethoxysilane was used as purchased. The catalysts dibutyltin dilaurate and triethylamine were high-grade commercial products used without further treatment. The only appropriate reaction solvent for HEC was N,N-dimethylacetamide (DMAc) which was purified and dried before use. The HEC-based networks crosslinked by the urethane moieties were prepared at room temperature by mixing the cellulose derivative with OPOM and OEOD in
New polymer electrolytes
379
DMAc in the presence of catalytic amounts of dibutyltin dilaurate. The reaction mixture was poured into a sylilated glass mould in order to cast a membrane 0.5 mm thick. After the crosslinking had been completed, the membranes were submitted to a Soxhlet extraction with CC14 and thoroughly vacuum dried. The general structure of these networks is shown below. Their specific structure depended of course on the relative amounts of HEC and oligomeric mono- and di-isocyanate. Thus, both the crosslink density and the relative proportion of crosslinks and grafts could be varied.
oII
H~'8o;-\ I
O_C-N
0
0-
"" OH
OH
, \,
o
The networks based on alkoxysilane hydrolytic condensations were prepared by treating HEC first with a mixture of OPOM and 3-isocyanatopropyl triethoxysilane following the same procedure as above. To the resulting grafted polymer triethylamine was added and the solution poured into the mould. Crosslinking by a sol-gel mechanism in the presence of moisture gave the general structure shown below. Again, the specific topology of the networks could be varied as a function of the relative proportions of the reagents involved in this two-phases polycondensation.
380
Applications
The addition of LiCI04 or LiN(CF3S02)2 was carried out by soaking the membranes into a concentrated solution of the relevant salt in acetonitrile and letting the ionic species diffuse into the networks. The
ionomeric
networks
were
prepared
from
commercial
ethylhydroxyethylcellulose (EHEC) with a DP of 80, a DS with respect to ethylation of 2.7 (i.e. a small proportion of residual available OH groups) and an average number of ethylene oxide unit of ca. 1.5 per anhydroglucose ring.
This was first
treated with a stoichiometric amount of chlorosulfonylisocyanate in acetone at 5° under rigorously dried conditions and then with an excess of solid Li 2C03: .,.
EHECell-QH + OCN-SO:lO --...
Li 2C0 3
EHECell-<>trN-s~a --...
o
9
EHECell-QCN-SO:JLi+
g
This EHEC sulfonate with Li+ counterions was precipitated in water, thoroughly vacuum dried and used as a polyelectrolytic additive in place of lithium salts in the preparation of membranes based on HEC, as described above. All the materials obtained were characterized by FTIR spectroscopy, DSC, dynamic mechanical properties, ionic conductivity and cyclic voltammetry.
RESULTS AND DISCUSSION The kinetics of the condensation reaction between HEC and MOEI, OPOM and OEOD were studied by monitoring the decrease in the absorbance of the NCO peak around 2200 crrr las a function of time. All reactions went to completion and showed a second-order behaviour. Table 1 gives some typical values of the second-order rate constant for the three combinations.
The monomeric model isocyanate was
New polymer electrolytes
381
Table 1. Influence of the extent of substitution of the HEC hydroxy groups by OPOM and OEOD on the Tg and the second-order rate constant
OPOM
OEOD
lO5·k2
Tg
%[NCO)/[OH]
%[NCO)/[OH]
l.mol.s!
CC
10 25 50 75
0 0 0 0 0 10 20 40 60 40 10 30 10 30
49 44
-70 -74 -72 -74 -74 / -40 -50 -48 -66
100
0 0 0
0 20 25
25 50 50
22 21 31
-67 26 -69
7 10-3
6 10-3
-;'~
5 10- 3
bO
f-4
4 10-3
3 10-3
2 10-3 ~"'--'-.....Io...-I-"""""-~~~...&..o.....Io-~--'--"---"~-"""",""-"-"",,,,,--,-~~
0 2 3 4 5
6
[LiCIO 4 ] / mol.r t
Fig. 1 : Evolution of the inverse of Tg with salt concentration for a network prepared with OPOM and OEon ([NCO]/[OH]=O,8). The concentration relates to the polyether chains only.
382
Applications
considerably more reactive than the oligomeric counterparts probably because of steric hindrance with the latter. The reaction between HEC and a mixture of OPOM and OEOD gave a rate constant in the same range as with each individual macroisocyanate. Considering that one is dealing here with aliphatic isocyanates, i.e. with rather sluggish reagents, the results were satisfactory in terms of insuring the consumption of all the NCO groups by the OH function of HEC within a lapse of time of about 24 hours. Table 1 also reports a number of Tg values for various grafted and crosslinked HEC. Interestingly, the fact of appending oligopropylene oxide strands to HEC results in a constant Tg very close to that of the oligomer itself, independent of the grafting density, indicating that there is no interaction between the two polymeric structures which appear to be totally incompatible. The DSC tracings confirmed this situation in that the ~Cp associated with the glass transition was directly proportional to the extent of oligopropyleneoxide grafts. Unfortunately, the Tg of the starting HEC could not be determined because of the spread of this transition over an excessive temperature range, but values around 1300 have been reported for this polymer. Any physico-chemical affinity between the HEC chains and the oligopropylene grafts would have therefore resulted in a variable single Tg, decreasing with increasing grafting density. Crosslinked HEC/OEOD systems gave Tg values close to -50 0 when the proportion of reacted OH was high. This is again the value of oligoethylene oxide unperturbed by the.HEC 'chains except for the fact that they block the two ends of the oligomers. In other words, there is no detectable affinity between these two structures. Mixed topologies with grafts and interchain bridges gave Tgs between -50 and 0 -70 (Table 1), viz. very adequate values in terms of the use of these materials as polymer electrolytes (1). Networks prepared by the sol-gel technique gave Tgs in the same temperature domain. Addition of the lithium salts to these different networks provoked an increase in Tg (Fig. 1) with a linear relation between Tg-l and Li+ concentration with respect to the polyether chains only, as already encountered with simpler polyether-type structures (1). Thus, the polysaccharide chains do not intervene in the solvation of the cations, as observed previously in terms of the non-participation of polydimethylsiloxane chains in polyether-based networks prepared from them (4). Finally, networks containing lithium EHEC sulfonate gave a single Tg around -40°. The study of the dynamic mechanical properties of these elastomeric networks gave curves in which the elastic modulus dropped from 109 to about 106 Pa at the
New polymer electrolytes
glass transition, as shown in the example of Fig. 2.
383
The classical free-volume
treatment of the data through master curves provided very satisfactory values for the Cl(Tg) and C2(Tg) constants in the WLF equation, viz. 10 and 60 K respectively, in excellent agreement with similar values obtained previously with numerous other polyether-based networks (4). The ionic conductivity of these new polymeric electrolytes was measured as a function of temperature, LiCI04
concentration and network topology.
The best
values obtained in this investigation were about 3 10-4 Scm-I at 60° for a ratio [ether oxygen]/[Li+]=20, which is close to the optimum conductivities displayed by polyethylene oxide-based networks with the same salt. Fig. 3 shows Arrhenius-type plots for different salt concentrations. The typical non-linearity stems from the wellknown feature attributing the ionic mobility to segmental motions, i.e. a free volume behaviour, and not to activated jumps. In other words, one is dealing again here with the WLF law and indeed the corresponding treatment of the conductivity data according to that equation provided Cl(Tg) and C2(Tg) values of 14 and 50 K respectively, viz. practically the same values as those obtained from viscoelasticity. The mechanism of ionic transport in these systems is therefore of the same nature as that occurring in polyether-based networks without polysaccharide moieties (1,4), namely the cations and the mobile anions are subject to the intrinsic segmental motion of the polymer host. Moreover, the present results indicate that only the oligoethylene oxide bridges and the oligopropylene oxide grafts are responsible for these movements, since the polysaccharide chains show a negligible affinity for the ionic species. The cyclic voltammetry tests were conducted in the potential range of -0.5 to 3.5 V in a lithium cell. No electrochemical instability was detected at 90° for these systems. Apart from the various characterizations carried out on membranes about 0.5 mm thick, the film-forming aptitudes of these materials were tested and it was found that thicknesses ten times lower could be obtained with good mechanical properties. This is not a lower limit intrinsic to the structures studied, but rather the minimum obtained with very simple processing techniques. In conclusion, this novel family of polymer electrolytes based on cellulose derivatives displays all the positive features inherent to amorphous polyether networks with the added advantage of good film-forming properties. pursued and extended to other polysaccharides such as chitosan.
This study is being
384
Applications
Fig. 2 : Variation of the elastic modulus as a function of temperature at 5 Hz for a saltless network (HEC-OEOD, [NCO]/[OH]=O.4)
9
"~
0..
.5 UJ '-"
bO
8
..9
-20
-40
0
Tr
20
40
60
Fig. 3 : Arrhenius-type plot of the ionic conductivity of an HEC-OPOM-OEOD network ([NCOV[OH]=O.8) containing increasing amounts of LiClO4 .
.-
-3 -4
's ~
-5
•
O/Li=24
tj
•
O/Li=17
'6:0-6
•
O/Li=20
•
O/Li=lO
•
O/Li=5
CI)
.s .9
-7
-8 2.5
~~....1-.-011-""'--'--~~~"--"-_ _"-""'---"--
--"
3.5
REFERENCES 1.1£ Nest, J.F., Gandini, A. and Schoenenberger C. (1994) Trends Polym. Sci. 2,432. 2. Le Nest, J.F., Gandini, A., Xu, L. and Schoenenberger, C. (1993) Polym. Adv. Technol. 4, 92.
3. Callens, S., Le Nest, J.F., Gandini, A. and Armand, M. (1991) Polym. Bull. 25, 443. 4. Le Nest, J.F., Gandini, A. and Cheradame H. (1988) Br. Polym. J. 20, 253.
38 Thermal and FT IR studies of Tencel-gco-Bema and Tencel-g-co-Hema carbanilates M A Kazaure,* J T Guthrie and B B Dambatta* - *Department of Chemistry, Bayero University, PMB 3011; Kano, Nigeria; Department of Colour Chemistry and Dyeing, University of Leeds LS2 9JT, UK
ABSTRACT Tencel has been grafted with 2-hydroxyethyl methacrylate (HEMA) using the Ce(IV) technique for different. HEMA concentrations. The resultant copolymers were converted to their corresponding carbanilates. The structural compositions as well as the thermal behaviour were studied using FT-IR and DSC respectively. Results obtained showed that grafting occurred and there there is evidence of polymer-polymer compatibility.
INTRODUCTION The Ce(IV) initiation method was used to prepare copolymers of Tencel and HEMA using various concentration of the vinyl monomer with the view to producing products with low graft "add-on" having possible industrial utility. The introduction of Tencel by Courtauids pIc in the 90's into the fibre market and its subsequent proven capability of being an environmentally friendly regenerated cellulosic fabric, has necessitated research into the physical and chemical properties of the fabric. Graft copolymerisation reactions have been used to improve some of the physico-chemical properties of Tencel. As a result of the inherent insolubility of the copolymers formed, product characterisation requires that copolymers be converted to some derivative equivalent in order to obtain materials capable of solution characterisation. The method reported by Guthrie and Tune [1] was that of carbanilation. We now
385
386
Applications
report a study dealing with the structural composition as well as the thermal stability of selected copolymers and their corresponding carbanilates using FT-IR and thermal analytical techniques.
EXPERIMENTAL The Tencel was supplied by Courtaulds plc, Derby UK. HEMA, Cerium (IV) ammonium nitrate (CAN) and phenyl isocyanate (Aldrich Chemical Co.) were all used as received without any further purification. Pyridine was purified according to the method described by Ralph and Gilkerson [2]. The grafting reactions were conducted following the method reported by Hebeish at al [3]. Four different concentrations of the monomer were used based on the ratio of 1:1,1:2,1:3, and 1:4 (weight by weight) of Tencel:monomer concentration. Reactions were conducted over 3 hours at 60°C in the presence of O.IM CAN. A control was set up. After grafting, samples were thoroughly washed with methanol and Soxhlet extracted for 24 hours in methanol to remove homopolymer. Copolymers were dried under reduced pressure at 40°C and thus % graft add-on values were calculated. The resultant copolymers were subsequently carbanilated following the method outlined by Guthrie [4].
DSC DSC was conducted using a Du Pont Thermal Analyser 2000. Thus, the required amount of sample was placed into an aluminium pan with an empty pan on the reference platform. The apparatus was purged with nitrogen at a flow rate of 3.3 x 10-6 rrr' S-I. The heating range was between 25°C to 500°C at a rate of 10°C per minute. Restults were recorded as DSC thermograms.
FT-IR STUDIES A Perkin-Elmer 1740 FT-IR spectrophotometer was used in this study. Two different routes were followed for the fibrous materials: diffuse reflectance (DR) and attenuated total reflectance (ATR). In ATR, IR-radiation is made to enter a prism of a high refractive index, IR transmitting material, the radiation being totally internally reflected. At the same time Prism produces an evan escent wave which can interact with the sample in contact with the prism to produce a spectrum. In the DR mode, radiation from the spectrophotometer is focused onto the sample and reflected energy is collected and recorded as the spectrum. ATR produces a very short path length in the sample for (the IR light. This makes the technique ideal for highly absorbing materials such ~ fibres. The FT-IR spectra of the powdery carbanilates were acquired using the KBR technique.
Tencel-g-co-Hema
387
RESULTS Attenuated total reflectance spectroscopy and diffuse reflectance spectroscopy are versatile and powerful techniques, ideal for rapid quantitative and qualitative analyses as sample preparation is relatively simple to perform. The techniques are well suited for providing information about the surface properties or about the bulky nature of a material. We have conducted an investigation of the surface properties of Tencel, Tencel-g-co-HEMA and the corresponding carbanilates. Spectral data obtained from these techniques are summarised in Tables 1, 2, and 3 respectively. Assignments have been made although we suggest that overall interpretation should be carried out with caution.
Table 1
DR-IR absorption assignments (em") for Tencel, Tencel-g-co-HEMA (TgcH) (at different ratios of HEMA) and poly HEMA (PHEMA).
Groups stretching
Tencel
O-H (H bonded)
35673249
O-H (free OH)
3604
TgcH TgcH TgcH TgcH PHEM
(1:1) (1:2) (1:3) (1:4) A
3588- 3581- 3543- 3578- 3441 3258 3256 3225 3206 3604
-
1280
1279
1278
1279
1273
1180
1178
1178 1174
1157
C=O (ester)
1733
1736 1728
1733
1728
C-H (methylene)
2917 2949 2914 2928 2949
C-O-C (ester) C-O-C (ether)
1135
Tencel and Tencel-c-co-HEMA have common O-H stretching vibrations at regions above 3200 em" corresponding to hydrogen bonded substances and suggest that not all the -OH groups available for grafting have been grafted. This is of no great surprise as it has already been reported [4] that only a small proportion of OH groups on cellulosic materials are available for grafting. The presence of a small but sharp peak at 3630 em" for Tencel, however, indicates that it contains freer -OH functionality which is absent in the spectra of copolymers. The spectra of all the Tencel-g-co HEMA samples differ from that of Tencel by the methacrylate vibration
388
Applications
Table 2
ATR FT-IR absorption frequencies for Tencel, Tencel-g-co-HEMA (TgcH) at different ratio of HEMA and poly HEMA (PHEMA).
Groups stretching
Tencel
O-H (H bonded)
36873260
3687- 3686- 3687- 3687- 3441 3333 3333 3333 3333 1260 1259 1259 1259 1273
C-O-C (ester) C-O-C (ether)
TgcH TgcH TgcH TgcH PHEM
(1:1) (1:2) (1:3) (1:4) A
1157
1155 1155 1155 1155 1157
C=O (ester)
1714 1715 1714 1714 1728
C-H (methylene)
2920 2924 2923 2923 2949
depicted in the C-H vibration band (methylene), C-O-C vibration band (ester and ether) at 2922 em", 1252 em", 1150 em" and 1708 em" respectively for TgcH (1:1) which is invariably superimposable on all other copolymers. This is an indication that grafting has occurred and that not all OR groups have been utilised for grafting. The picture presented is in agreement with already calculated % graft add-on. The presence of C=O stretching vibration band at 1703 em" for all copolymers indicates and further confirms the mechanism and action of Ce(IV) on Tencel i.e, the formation of free radical to initiate copolymerisation, and aldehyde group formation on either position 2 or 4 of the anhydroglucose unit. The ATR method tends to show that Tencel and it copolymers all contain free OH groups, a result of a shift in the OH stretching vibration band to 3600 em" absorption region. Considering the partially crystalline nature of all cellulosic materials, this seems normal for Tencel. However, for the copolymers, it may be attributed to a free -OH vibration band corresponding to the ungrafted OR groups as well as the OH group on HEMA. The spectra of the carbanilate are almost indistinguishable and superimposable on each other as shown in Table 3. The main difference, however, occurs in the 1:3 and 1:4 ratio where the -CH-stretching band for the methylene unit is shifted to 3035 em:' probably as a result of higher HEMA content. The spectra of Tencel-g-co-HEMA and that of the corresponding carbanilate differ by the N-H bond stretching vibration bands between 3326 em" to 3387 em" and 3134 em" shown by all the carbanilates. Also, the OH stretching exhibited by Tencel and its copolymers
Tencel-g-co-Hema 389
Table 3
FT-IR absorption frequencies of Tencel-g-co-HEMA carbanilates (TgcHC), Poly HEMA carbanilate (PHEMAC) and Tencel tricarbanilate (TTC).
TgcHC TgcHC TgcHC TgcHC
Groups stretching
(1:1) (1:2)
TTC
(1:3) (1:4)
PHEMA C
3387 3327 3327
3326 3328
N -H stretch
3140 3140 3134 3134
3136 3135
C=O (ester)
1724
1728
1729
1730
C=C (Aromatic ring)
1536 1531
1554 1552
1537
1554
C-H (methylene)
2957 2957 3035 3035
2928 2928
C-O-C (ester or ether)
1221
1222
N-H (H bonded)
1729 1711
1220 1233
1233
is not found in the carbanilates (PHEMAC inclusive). carbanilation if not over carbanilation.
Table 4
1233
This could be a sign of
Thermal behaviour of Tencel(T), Tencel-g-co-HEMA(TgcH), Tencel tricarbanilate(TTC).
Sample%
Grafting
Temperature of endotherm (OC)
T
o
86, 346
TgcH
34.07
87, 353
TTC
o
230, 298, 354
and
390 Applications
Table 5
Thermal behaviour of Tencen-g-co-HEMA at different grafting levels
Sample
% grafting
Temperature of endotherm peak (OC)
TgcH(I:I)
34.07
87, 354
TgcH(I:2)
53.96
84,217, 357
TgcH(1:3)
66.32
84, 356
TgcH(l :4)
69.21
87,357
Table 6
Thermal behaviour of Tencel-g-co-HEMA carbanilates at different grafting levels
Sample
% grafting
Temperature of endotherm peak (OC)
TgcHC(I:I)
34.07
61,283, 349
TgcHC(I:2)
53.96
296, 352
TgcHC(I:3)
66.32
247, 358
TgcHC(I:4)
69.21
247, 359
PHEMAC
241,408
Results of the DSC analysis of Tencel (T), Tencel-g-co-HEMA (TgcH), Tencel-g-coHEMA carbanilates (TgcHC), and Tencel tricarbanilate are shown in Tables 4, 5 and 6. All peaks below 100°C correspond to the H20 peaks. This is as a result of the hygroscopic nature of cellulosic maerials (Tencel inclusive). Table 4 shows that Tencel melts at 346°C and this melt temperature increases to 354 °C with introduction of HEMA. The single peak could be an indication of polymer-polymer compatibility. Thermograrns of Teneel tricarbanilates portray the absence of water and show 3 peaks with the main peak at 298°C equivalent to the carbanilate melting behaviour. The small peak at 230°C could be due to carbanilation but no satisfactory explanation could be given for the other peak at 354°C other than the possible contamination by copolymeric species during measurements. From Table 5, we see that an increase in the Tencel:HEMA ratio does not have any significant influence on the melting behaviour of the copolymer. Rather, what is evident is the presence of
Tencel-g-co-Hema
391
the melting behaviour of the copolymer. Rather, what is evident is the presence of polymer-polymer compatibility portrayed by the single broad peak for all the four different ratios under investigation. The unusual peak at 217°C could probably be due to the formation of Tencel-CAN complex during copolymerisation. The thermograms for Tencel-g-co-HEMA carbanilates showed two basic endothermic peaks which correspond to the carbanilate and the copolymeric melting behaviour. Here also, the melting behaviour is generally independent of the amount of graft addon. Poly HEMA carbanilate showed two peaks with one similar to the carbanilate melting behaviour and the other at 408°C corresponding to the melting of PHEMA.
REFERENCES [1]
J.T. Guthrie, P.D. Tune; J. Polym. Sci. part A Polym. Chern. (1991), 13021312.
[2]
Ralph, E.D., W.A. Gilkerson, J. Chern. Soc. (1964) 86,4783.
[3]
Hebeish, A.M.1. Khalil, E. Alfy; J. Polym. Sci. Polym. 3137-3143.
[4]
J.T. Guthrie, PhD Thesis, University of Salford, (1971).
[5]
J.T. Guthrie, A. Hebeish; The chemistry and technology of cellulosic copolymers, Springer-Verlag, Heidelberg, (1981).
Chern. 19 (1981),
Acknowledgements: The authors wish to acknowledge the help given to M.A. Kazaure by the Bayero University Research Committee and Department of Colour Chemistry of the University of Leeds.
39 ESR as a method for monitoring lignins activity during the interaction with monomer and oligomer silicon containing compounds T Dizhbite, G Telysheva and G Shulga - Latvian State Institute of Wood Chemistry 27 Dzerbenes Str, Riga, Latvia, LV-I006
ABSTRACT
ESR was employed to study the interaction of lignins with silicon-organic compounds. The comparison of the ESR spectra of the co-reagents and products of interaction of lignosulphonates (LS) with the water-soluble oligomer sodium alumomethyl siloxanolate (SAHS) has demonstrated different characters of their interaction in acid and alkaline media. The observation of the behaviour of the lignin radicals as spin probes in a wide temperature range (77-448 K) made it possible to reveal a considerable decrease in the rigidity of the lignin matrix as a result of lignin silylation with monomeric silicon-organic compounds (hexamethylsilazane, phenylaminomethyl-(methyl)-diethoxysi lane).
393
394 Applications
I liTRODUCTI 011 The presence of conjugated systems in the structure of lignin in situ and the development of polyconjugated blocks upon the isolation of lignin during different wood processing ensure the stability of free radicals and make it possible to apply the high-sensitive method ESR for monitoring the lignin changes during the interaction with various co-reagents [1,2]. . The present work demonstrated the application of ESR for investigation of the interaction of lignins with siliconorganic compounds: sodium alumomethyl siloxanolate (SAHS), hexamethylsilazane (HHDS) and phenylaminomethyl(methyl)-diethoxysilane (AH-2).
EXPERIMBNTAL ISH
SPECTRA. The ESR spectra were recorded on a Radiometer RE-1306. The concentration of paramagnetic centers was measured using diphenylpicrylhydrazyl (N8t 5.63*10~1e spin) as a standard. A line in the ESR spectrum of Hn2 + in magnesium oxide served as a secondary standard. The absorption areas were determined by the double integration of the ESR spectra. The error of determining the concentrations of paramagnetic centers and the relative concentration error were 20% and 5%, respectively [3]. An average error of determining the line width was 0.02 mT.
=
THERMAL ARALYSIS. Thermal analysis was made using a derivatograph "HOH" under self-atmosphere conditions, the range of temperatures 20 ... 500°C, the rate of heating 10°C/min~ the standard - aluminium oxide. IR SPECTRA. IR spectra were determined using an IR-20 spectrometer within the range of frequencies 3700 - 450 om- 1 . The samples were pressed with KBr into pellets.
RESULTS AND DISCUSSION. The comparison of the ESR spectra both of co-reagents and products of interaction of lignosulphonates (LS) with SAHS has manifested the different characters of their interactions in acid and alkaline media. It has been shown that this difference is conditioned by the change of the co-reagents structure in media with different activity. In alkaline medium~ the SAHS aqueous solution is optically transparent and does not exhibit any paramagnetic properties. At the same time, in neutral and acid media, the UV-spectrum of SAHS has a specific set of absorption bands and its ESR-spectrum (pH 4.2) is a singlet line with a g-factor of 2.002, 5.5 mT wide. In
ESR as a method for monitoring lignins activity 395 this case. the concentration (Fig. la, Curve 1).
of
PMC
is
1020
spin/g
The ESR-spectra of the modified products in alkaline medium (Fig.lb, Curves 2 ... 4) are practically identical as regards their characteristics (g-factor, the width and form of the singlet line) and the ESR-spectrum of the initial lignosulphonate (Fig.lb, Curve 2). The differences manifest themselves only in rather a higher PMC content in modified samples which is probably caused by the stabilization of a part of the radicalsintermediates appearing during the LS self-oxidation process which are usually observed in alkaline medium [3]. This is obviously connected with the fact that the paramagnetic characteristics of the LS modified in alkaline media do not practically change with the increase in the modificator amount. On the contrary, six equidistant lines with a width equal to the g-factor 2.002 appear in the ESR-spectra of the LS products modified in acid medium (Fig.la, Curves 3 .. 5), in addition to the initial singlet line (Fig. la, Curve 2). The appearance of a sextet is caused by the formation of the new PMC whose uncoupled electron is delocalized on the aluminium atom (1=5/2) of the modificator [4] to a considerable extent. The newly formed PMC are stable for more than two months.
b
2
3
s
Fig.l ESR - spectra of SAHS (1) and LS initial (2) and modified in the acid (a) and alkaline (b) media at Ilass ratio LS/SAMS 1.0:0.1 (3); 1.0:0.5 (4); 1.0:1.0 (5)
396 Applications
It may be suggested that in acid medium, the donoracceptor interaction between aluminium in the SAHS molecule and the lignosulphonate donor groups results in a considerable rearrangement of electron density, both of the donor and acceptor, and is accompanied by the formation of stable paramagnetic centers. A visible increase in the concentration of the PHC yielding a six-linear spectrum of ESR at the transition of the LS/SAH5 mass ratio from 1.0:0.1 to 1.0:0.5 (29*10~1e and 20*10 A18 spin/g respectively) and the retaining of the PHC concentration at the same level (2a*10~1e spin/g) during further increase in the SAHS part shows that the appearance of new stable PHC is possible only up to specific LS/SAHS mass ratios, i.e. is limited by the presence of active centers in the LS molecule. The comparison of the IR-spectra of the initial LS, SAHS and the products of their interaction at different pH values has shown a considerable increase in adsorption in the ranges 590 ... 600 cm- 1 and 1030 ... 1050 cm- 1 (a new peak) characteristic for valent fluctuations of the Si-O bond in the 5i-0-C and 5i-0-5i groups for the products obtained in acid medium. The Si-O-C groups formed are probably rather stable in acid medium, are hydrolyzed in alkaline medium to a great extent [5], and therefore, they practically do not manifest themselves in the IR-spectra. The structural features detected by ESR and IR spectroscopic methods explain the difference of thermooxidative stability of L5 treated with 5AHS in media with different acidity. The thermal analysis data show that modification changes the character of LS thermodestruction significantly. In this case, the variations for acid and alkaline media are ambiguous. In both cases, a temperature shift of the beginning of LS thermal disintegration approximately by 40°C tOWards higher values is observed, i.e. the thermooxidation stability of modified LS is higher, as compared with the initial ones. However, the temperature corresponding the maximum mass loss rate increases from 250 to 299 0C only for the LS modification products in acid medium. No changes are observed for alkaline medium at a low consumption of the modifier, while at LS/5AHS ratios of 1.0:0.5 and 1.0:1.0 the maximum mass loss temperature even decreases.
ESR as a method for monitoring lignins activity
397
The mass loss at 50eoC indicates that the modification of LS in acid medium results in a considerable increase in thermooxidative stability already at a SAHS consumption of 10% from the LS mass. In this case, the absolute mass loss decreases by 16%, as compared with the initial LS. Further 5- and 10-fold increase in the SAHS consumption (from 10 up to 50 and 100% in terms of LS) results in an additional decrease in the absolute value of mass losses 1e and 19%. In fact. up to 500°C. the LS modified in alkaline medium lose the mass equal to the sum of the mass losses of the initial LS and SAHS registered for this temperature. Besides the presence of the stable paramagnetic centers of conjugated systems the ESR spectra of lignins is also conditioned by the presence of the free radicals stabilized by the lignin matrix [3]. In general the heating of the lignin samples in the range of the temperature approximating to the temperature of glass transition causes the decay of the free radicals stabilized by matrix rigidity. Therefore the change of the amount of PHC during the heating under the above mentioned conditions may give the information about state of lignin matrix after modification. This method was employed for characterization of lignin sylilated by HMDS. The heating of the modified lignin was accompanied by enhancing of PMC amount at observed decreasing of the matrix rigidity (data of thermomechanical investigation). This manifests that formation of the free radicals prevails their decay. Formed free radicals could participate in the process of further transformation of modified lignin [6]. The free radicals formed at low-temperature radiolysis of lignin can be used as a spin probe. In the case of investigation of modification of lignin with AH-2 this method allowed to establish the difference in the structure of the products obtained in various conditions [7].
Accelerations of the free radicals death of lignin modified at 200°C indicates on increasing in its structure the microregion content with enhanced molecular mobility (Fig.2). The conclusions made based on the ESR data were confirmed by other physico-chemical methods.
398 Applications
[R]/[Ro]
Fig.2 Temperature dependence of free radicals relative concentration in irradiated (at 19BaC) the lignin samples, previously modified with AH-2 at 130°C (1) and 200°C (2). O-------------I""----....a.------a._ _
...a.-...J
-100
-100
-50
0
50
100
temperature, C
SUMMARY
The application of the ESR method to the investigation of the interaction of lignin with different silicon-organic compounds has allowed to determine the specifity of the processes, taking place with the participation of free radicals and to investigate the microstructure of modified lignins using spin probe.
LITERATURE 1. Sarkanen K.V., Formation, Structure
Ludwig C.H., Lignins. Occurence, and Reactions, New-York, 1971, 916
p.
2. Westermark U., Samuelsson B. and Lundquist K. Proceedings "Seventh International Symposium on Wood and Pulping Chemistry", Vol.l, 1993, p.93. 3. Zarubin H.Ya., Wood Chemistry, 1984, N 5, p.3-19 4. Pshezecki S.Ya., Kotov A.I., Hilinchyk V.I., ESR of Free Radicals in the Radiation Chemistry, H., 1972., 485 p.
5. Telysheva G.M., Lebedeva G.N., Sergeeva V.N., Wood Chemistry., 1983., N 1., p.94-101. 6. Telysheva G.M., Pankova P., Cellulose Chemistry and Technology, 1989, N 6, p.701-721. 7. Telysheva G.M., Pankova P., Sergeeva V.N., Wood Chemistry, 1985; N 4, p.87-91.
40 The regularities of lignosulphonate behavior on different interfaces and its alteration by purposeful modification G Telysheva, T Dizhbite, E Paegle and A Kizima - Latvian State Institute of Wood Chemistry, LV-I006 27 Dzerbenes Str, Riga, Latvian Republic
ABSTRACT
The adsorption behavior of lignosulphonates (L5) and of modified L5 (MLS) with water soluble silicon-containing compounds were investigated within a wide pH range (i11) .
The general
regularities of MLS adsQrption on a solid surface were established to be analogous to those of L5, however MLS differed by enhanced values of maximum adsorption, owing to hydrophobic aspects of MLS molecule and insertion of new active centers.
The participation of macromolecular associates in adsorption has been shown experimentally. The multilayer nature of L5 and HLS adsorption is confirmed by the good agreement between the adsorption isotherms obtained experimentally with those calculated on the basis of the Aranovitch model of adsorption [1], which takes into account the lateral interaction of adsorbate molecules.
399
400 Applications The enhancement of dispersion activity of HLS compared with that of LS has been found owing to an increase in adsorption on kaolin and surface activity.
INTRODUCTION Lignosulphonates (LS) - polydisperse polyelectrolytes, the basic units of which consist of the C6 C3 structure, contain anionic groups of three types, namely: sulfonate, phenolic hydroxyl and carboxyl groups. Uncharged L5 molecules are coiled. The alteration of the degree of dissociation of the L5 ionogenic groups leads to changes in the macromolecule net electric charge and molecule size and conformation. The effective degree of LS dissociation is almost zero at pH 1, about 20% at pH 11 [2].ln the course of 5 and up to 80% at pH dissociation of ionogenic groups, the LS molecule extends due to the electrostatic repulsion between the neighbouring groups. Nowadays, LS are used as surfactants for many industrial applications. In order to optimize the performance of these polymers, numerous scientific investigations have been made to comprehend how different internal and external factors influence the L8 behaviour on different interfaces.
The present
work, is
background for
aimed
at the
purposeful alteration
development of of the
the
efficiency
of the LS activity on different interfaces modification with oligomeric water soluble containing compounds.
by the silicon
MATERIAL AND METHODS The initial sodium lignosulphonate contained 1.23 mequiv/g of sulphonate groups with pKa 1.6 and 1.08 mquiv/g of phenolic hydroxyl groups with pKa = 11. The solution pH was adjusted with sulfuric acid or sodium hydroxide, but the ionic strength was maintained constant. The modifier - sodium oligoheterosyloxanolate (OHS) - contained AI, with 5i/Al ratio of 3.
=
The surface tension (0) of the solutions was measured at 20°C by the Wilhelmy method, using a platinum plate and bidistilled water. The thickness of the monolayer (14 A) was taken from [3]. The formation and characteristics of the associates in solution were monitored by light-scattering on a multiparameter flow cytofluorimeter EPIC.
Lignosulphonate behavior on different interfaces 401
The value of LS adsorption on kaolin was calculated on the basis of the change of the surface tension of L5 solution. The calibration curve was obtained at pH 8.9 the equilibrium pH value of the kaolin - water system. The
rheological
determined
properties
of
suspensions
using a
viscosimeter Rheotest-2, The measuring system was a cone K-1 - plate.
type
were
RV2.
RESULTS AND DISCUSSION The surface tension (0) of initial L8 and modified L5 water solution clearly depends upon the water pha§e pH (Fig.l). Modification provides the decreasing of 0 over all the pH range, although the profiles of the concentration relations are similar, and the range of the maximal 0 depression occurs in acid media for both samples. 80 Sigma·JO.....3. N/m 70
60 50 40
~~
30 '--_ _
o
.. _
__ .. _ . ---A-_--'
- - - - t l . . - -_ _- - - - "
0.4
0.8
1.2
Concentration. %
----
1
-+-
2
3
--e-
4
Fig.l Concentration dependence of surface tension of aqueous solution of: (1) MLS, pH=5.0; (2) MLS, pH=8.9; (3) L5, pH=8.9; (4) L5, pH=4.5. The depression of 0 is determined, to a great extent, by the introduction of hydrophobic blocks to the L5 molecule. The shielding of the charge and blocking of the L3 ionogenic groups as a result of modification affects the molecules conformation on the interface. This can be observed when comparing the average values of the areas occupied by the molecules of the initial and modified L5.
402 Applications
From the plots of Gibbs isotherms it has been established that the values of the average areas occupied by the molecules of the initial L5 increase 3 times when the medium pH increases from 1 to 11. After modification, the pH of L5 changes from 4.5 to 8. It is supposed that at such pH, the molecule of the L5 under study occupies an area of approximately 160 1 2 on the interface, while the extrapolated area for the modified LS did not exceed 140 A2. The study of the L8 and HLS solutions prior to and after their adsorption on kaolin by light-scattering has shown that the associates formed participate in the formation of adsorption layers. For both L5 and HLS, the effective concentration of the associates in solution decreases considerably after the adsorption on kaolin, mainly at the expense off the decrease in the amount of the largest associates (Fig.2). 100 Relative iDlen8it
80
60 40 20
o
1
5
10
1
5
10
Partiole size. mkm (101 seale)
Particle size. mlcm (101 scale)
1
2
Fig.2. Particle size distribution histograms for the 0.3% L8 solution before (1) and after adsorption (2). The modification of L8 results in an increase in adsorption on kaolin. This is connected not only with hydrophobization, but also with the formation of positively charged centers in the LS molecule, since it is known that the edges of the kaolin crystallites have a negative charge. The re-arrangement of experimental isotherms in the co-ordinates of different adsorption models has shown that the Langmuir model is not suitable. Different grid models (BET, Anderson, Hjutig, Aranoyich) have been checked. It has been shown that the isotherms are linear within the most wide range in the co-ordinates of Aranovich's equation [1] which has the
Lignosulphonate behavior on different interfaces 403
variable parameter "z" taking into account the interaction among the adsorption molecules. The maximum constant of regression (0.9987) for the Aranovich model for the adsorbent/adsorbate systems under study may be achieved using the coordination number 11. The high coordination number confirms the previous suggestion concerning the formation of a film - a liquid layer of adsorbed molecules on the surface of solids [4]. All the models under study indicate a multilayer character of L5 and MLS adsorption on kaolin. The enthalpy and absolute Gibbs energy values in the case of MLS adsorption are considerably higher than in the case of L5. They are for MLS UHo 14.5 kJ/mol, UGo -2.2 kJ/mol and for L5 UHo 12.7 kJ/mol, UGo -0.3 kJ/mol. This indicates a high energetic advantage of ML5 surface layer formation. The maxim on the curves of the dependence of the mole heat capacity of the adsorption layer as a function of relative L5 concentration, calculated according the Aranovich model (Fig.3), perhaps, reflects the end of the formation of the adsorption layer and the beginning of filling a new layer, which is accompanied by the change of the system organization and rearrangement of the molecules in adsorption layers.
=
=
=
1 Heat ca.pacit.y, reI.units
=
200 Yield stress, Pa
0.6
150
.
100
...... ~ .....
0.8
0." i'
50
_
.
0.2
o o
Io.-_....L-.-_--a-_..-.&-_---&_---J
0.2
0.4
0.6
C/Cs -1
--+-2
0.8
Ot.--.----'----...I.-------"
o
0.05
0.1
Concentration, -1
0.15 ~
-+-2
Fig.3 (left) Variation of L5 heat capacity during the adsorption processes of L5 (1) and MLS (2) on the kaolin surface, the Aranovich model. Fig.4 (right) Dependence of the relative yield stress of kaolin suspension on L5 (1) and MLS (2) concentration. The comparison of the state of the maxima on these curves shows that the formation of a monolayer in the case of ML5 ends at concentrations lower than in the case of L5.
404 Applications
The sum of such factors as adsorption on kaolin and surface activity determines the enhancement of the dispersion activity of HLS as compared with the initial L5. This is obvious from the graphical dependence of the relation of the yield stress at a definite L5 concentration with the yield stress at a zero L8 concentration against L5 concentration in kaolin suspension (Fig.4). At a 0.1% concentration of HLS in solution, the kaolin suspension approaches complete deflocculation. SUMMARY
The general regularities of L5 and MLS adsorption behaviour are similar at the different interfaces. The participation of macromolecular associates in adsorption as well as multilayer nature of adsorption have been confirmed experimentally. The calculated thermodynamic parameters of adsorption have shown an energetic advantage of surface layer formation by MLS against L5. The enhanced surface activity and dispersion activity of MLS is explained by introduction of hydrophobic blocks and new positively charged centers as well as blocking of LS ionogenic groups.
REFERENCES 1. Aranovich G.L. J. of Phys. Chem., 1989, v.63, N9, p.2529 - 2533 (Russia). 2. Kontturi A.K., Kontturi K. J. Colloid Interface Sci., 1988, v.124, N1, p:328. 3. Fors K., Fremer K.E. Int. Symp. on Wood and Pulp. Chem. Stockholm, 1981, v.4, p.29-38. 4. Afanas'ev N.I., Telysheva G.M., Makarevich N.l., Khrol Y.S. Wood Chemistry, 1990, N2, p.85-92 (Latvia).
41 Some physiochemical properties of xylanolytic enzymes produced by Aspergillus fumigatus IMI 255091 L A Hamilton] and D A J Wase* - tChemical Technology Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, Tennessee, 37891-6194, USA; *Environmental Biotechnology Division, School of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham, B12 2TT, UK
ABSTRACT The xylanolytic enzymes xylanase and f3-o-xylosidase from Aspergillus jumigatus IMI 255091 have temperature optima of 70°C and pH optima lying over a broad range between 4.0 and 7.0. Thermal stability of these enzymes and stability at various pH values suggest that several isoenzymes may exist such that among them there is a range of highly active enzymes which are highly tolerant of elevated temperatures and retain their activities over a broad range of pH values. The specificities of the enzymes for their respective assay substrates were determined: the KM values for xylanase and f3-oxylosidase were 11.7 mg mL- 1 and 0.1 mmol L-1 respectively. Vmax values for xylanase and f3-xylosidase were 0.4 and 0.3 mmol minI mL- I.
INTRODUCTION Vegetative plant materials are, in general, made up of three main lignocellulosic components: cellulose, hemicellulose and lignin. The relative fractions of these components can vary widely, depending on many variables, such as the source of the lignocellulosic, and the season and the time ofyear; similarly, the proportions of various constituents of each of these three materials can also vary. Nevertheless, in the majority of cases, o-xylan has been noted as an important constituent of the hemicellulose fraction. As a result, most investigations of the enzymatic degradation of this polymer have focussed on xylanase and f3-o-xylosidase enzymes. As o-xylan is branched, other enzymes such as a-L-arabinosidase and a-o-g1ucuronidase are also present to remove 405
406 Applications
substituent side-chains. However, in general terms, the degradation of o-xylan can be said to be dependent on the hydrolytic action ofxylanase and p-o-xylosidase [1, 2]. Aspergillusfumigatus IMI 255091 has previously been shown to produce xylanase and
p-o-xylosidase as well as a range of other xylanolytic enzymes [3, 4]. There has been considerable interest in such hemiceUulolytic enzymes, and their potential application in the sugar, alcohol, paper, pulp, feed-processing and food industries [5], and the activity of these enzymes produced by A. fumigatus is particularly high under normal assay conditions. However, the conditions under which activity is optimal are not clear. The purpose of this study was therefore to determine the physicochemical conditions at which greatest activity occurs. MATERIALS AND METHODS
Culture broths containing xylanase and p-o-xylosidase activities were obtained from shake-flask fermentations of A. fumigatus IMI 255091 using hay as lignocellulosic substrate. The liquid medium was as described previously by Hamilton and Wase [6]. Enzyme-containing broths were preparedby filtration ofthe culture broth from day 7 of the fermentation. The resulting broth was stored at 4°C with no detrimental effects to enzymic activity [7] and used for subsequent analyses.
XYLANASEACTIVITY This assay is based on hydrolysis of xylan to reducing sugars. The birchwood xylan used as substrate was prepared in the following manner. A 10 mg mL- 1 suspension of xylan in 50 mmol L-1 citrate buffer, pH 5.0, was autoclavedfor 10 minutes at 121°C, 15 psig, furnishing a fully dissolved solutionofxylan, ready for hydrolysis by xylanase. To 1.0 mL diluted enzyme, 1.0 mL xylan was added, mixed and incubated at 50°C. The reaction was stopped at various time intervals over a period of 15 minutes. The concentration of reducing sugars released was determined by the method described by Sumner and Graham [8]. Activity was expressed as mmols of xylose residues released per minute per mL ofenzyme(IU mL- 1 ).
P-D-XYWSIDASE ACTIVITY p-n-xylosidase activity was assayed by measuring the release of 4-nitrophenol from the substrate, 4-nitrophenyl p-o-xylopyranoside (pNPX). To 0.1 mL enzyme broth, 0.9 mL PNPX (1.0 mmol mL-1 in 50 mmol L-1 citrate buffer, pH 5.0) was added, mixed and incubated at 50°C. The reaction was stopped at various times by adding 1 mL sodium carbonate (2 mol L-1) . Activity was expressed as mmol of 4-nitrophenol released per mL of enzyme per minute (IU mL- 1 ).
EXPERIMENTAL pH and temperature optima The two substrates were hydrolysed at pH 3.0, 4.0, 5.0, 6.0, 7.0 and 8.0 using 0.05 mol mL-1 citrate buffer (pH 3.0-pH 6.0) and 0.05 mol mL-1 sodium phosphate buffer (pH 7.0-pH 8.0). Enzyme activitywas determined as previously described [9]. The optimum
Physiochemical properties of xylanolytic enzymes
407
hydrolysis temperature for each of the substrates was established by hydrolysing it at the following temperatures: 30°C, 40°C, 50°C, 60°C, 70°C and 80°C.
Temperature stability Glass vials containing the enzyme broths were incubated at 30°C, 50°C and 70°C. At various time intervals (0, 5, 10, 20, 30 minutes, 1, 2, 4, 8, 24 and 48 hours) aliquots of enzyme broth (0.6 mL ) were removed and xylanase and f3-o-xylosidase activities were determined as previously described [9].
Stability at various pH values Glass vials containing enzyme broths, adjusted to pH 3.0, 5.0 and 7.0 using the buffers described above, were incubated at 30°C. At various time intervals (0, 5, 10, 20, 30 minutes, 1, 2, 4, 8, 24 and 48 hours) aliquots of enzyme broth (0.6 mL) were removed and xylanase and f3-o-xylosidase activities were determined as previously described [9].
Determination of K M and VDIU The constants of Michaelis-Menten (KM and Vmax) were determined from plots of the Lineweaver-Burk type and confirmed using plots of the Eadie-Hofstee type. KM is the concentration of substrate when the rate of reaction is half its maximum rate; Vmax is the maximum reaction rate of substrate hydrolysis [6]. RESULTS AND DISCUSSION
Temperature and pH optima Typical bell shaped curves (not shown here) resulted for both xylanase and f3-nxylosidase enzymes (see Table 1 for temperature optima). Xylanase was active over a broad range of temperatures having at 30°C approximately 50% of the activity measured at 70°C, the optimum. In contrast, at 30°C, J3-o-xylosidase activity was unmeasurably low, but activity at 70°C was optimal for this enzyme, too. It is interesting to note that optimum activity at 70°C markedly exceeds that of 30°C, the normal temperature for cultivation of A. fumigatus. Indeed optima as high as this suggest that enzymes produced by this strain of A. fumigatus are extremely thermotolerant and as such may be suitable for use in the saccharification of lignocellulosics, although there are further factors such as pH and stability still to be considered. It has been shown previously that the cellulase complex of A. fumigatus has pH optima well to the acid side of neutrality [9]. This also seems to the case with f3-D-xylosidase, in which optimum activity occurs when the pH is 4.5 (see Table 1). However, the optimum pH for xylanase is not so clearly defined (see Table 1). Maximum activity was achieved when hydrolysis of birchwood xylan was carried out over a large range of pH values (from pH 4.0 to pH 7.0). Royer and Nakas [10] similarly showed that Trichoderma longibrachiatum xylanase activity was optimal between pH 4.8 and pH 5.8 and Hrmova et ale [11] also showed that xylanases from Aspergillus terreus and Aspergillus niger were highly active between pH 7.1 and pH 8.0. In contrast, the extracellular xylanase and f3-o-xylosidase of the hemicellulase complex of Aureobasidium pullulans had pH optima that were
408 Applications
different from the corresponding optima for A., fumigatus. To confuse matters further, Myburgh et al. [1] showed that xylanase activity from A. pullulans was optimal when the pH was 4.0 and that it was (3-o-xylosidase that possessed high activity over a broad range of pH (between 4.0 and 7.0). Overall, then, it is impossible to be specific in the case of hemicellulases, and tests must be used to establish optima for the particular microbial strain in question.
Table 1: Temperature and pH optima for xylanase and p-o-xylosidase enzymes produced by A. fumigatus IMI 255091.
Enzyme
Temperature Optimum
pH Optimum
Xylanase
70°C
4.0-7.0
J3-o-xylosidase
70°C
4.5
Thermal and pH Stability It has been mentioned that the xylanase and J3-o-xylosidase enzymes produced by A. fumigatus are highly active at elevated temperatures. At these temperatures, initial conversion rates may be at their highest but thermal denaturation of the enzyme may result in a process in which overall product yields are poor. Enzymes with enhanced stabilities are therefore highly advantageous. Considerable stability of the hemicellulase complex of A. fumigatus is demonstrated in Table 2. There was little loss of activity at 30°C. At 50°C, rapid loss of activity occurred initially, but 50% of the activity was retained, even after 48 hours (e.g. see Figure 1). In contrast, substantial deactivation of the enzymes occurred during incubation at 70°C. However, xylanase activity remained significant, with 20% of the original activity retained.
Table 2: Thermal stability ofxylanase and p-o-xylosidase at various hydrolysis temperatures over 48 hours. Temperature
% Activity Remaining After 48 Hours
Xylanase
p-o-Xylosidase
30°C
80
100
50°C
50
50
70°C
20
0
Figure 1 demonstrates how enzyme activity initially declined during the first few hours of incubation, and then levelled out to a constant value. This is also true for the cellulase enzyme complex produced by this strain of A. fumigatus, and was discussed previously by Wase et. al. [9]. Stewart and Heptinstall [12] showed the presence of isoenzymes for A. fumigatus IMI 246651 and so it would be reasonable to suggest that
Physiochemical properties of xylanolytic enzymes 409
the same is true for Ai fumigatus IMI 255091. That is, isoenzymes may exist such that amongst them there is a range of highly active to semi-active enzymes, some of which are highly tolerant of elevated temperatures. ~
~
~
C
• ...-4
120 100
>
80
<>
60
• ...-4 ~
(I)
40
• ...-4
~ .......
~
20 0
0
0
10
20
30
40
50
Time (h) Figure 1: Thermal stability of xylanase (II, 30°C; . , 50°C; 0, 70°C). In each case, activity fell sharply during the initial few hours. However, after at most 5h exposure to the test temperature, the residual activity was constant for the remainder of the two-day period, suggesting initial dissimilation of unstable isoenzymes. Similar stability profiles resulted when either xylanase or 13-n-xylosidase was incubated at various pH values (see Figures 2 and 3). Thus, 13-n-xylosidase (Figure 2) retained 100% of its original activity at pH 5.0. Either side of this pH value there was initial deactivation; thus effects of incubation at pH 3.0 and pH 7.0 were essentially equal. Within a short time, activity approximately halved, then remained at this level. Although xylanase (Figure 3) was active over a broad range of pH values, the activity of the enzyme decreased almost immediately with time. Most activity was retained (ca. 60%) during incubation at pH 5.0 whereas most was lost at pH 3.0 (ca. 70%). ~
~
~
C
• ...-4
120 100
>
80
<>
60
• ...-4 ~
(I)
40
• ...-4
~ .......
~
20 0
0
10
20
30
40
50
Time (h) Figure 2: p-n-xylosidase stability at various pH values (II pH 3; . , pH 5; 0, pH 7).
410 Applications
120 ~--------------. 100 80 60 40
20
O------------.. . . .--..A.---.-....--.... o 50 40 20 30 10 Time (h) Figure 3: Stability ofxylanase at various pH values (II, pH 3;., pH 5; C, pH 7). Myburgh et ale [1] studied the stability of xylanase and p-o-xylosidase from Aureobasidium pullulans NRRL Y 2311-1. between pH 4.0 and pH 8.0. They found that 100% ofthe xylanase activity was retained after 5 hours at pH 5.0. At pH values of 4.0 and 6.0 activity dropped to 700A. in the first 5 hours. At pH values higher than pH 6.0 the activity dropped in two stages. After 5 hours incubation the activity had dropped to 25% of the original activity then to zero when incubated up to 24 hours. The authors attributed this phenomenon to the presence of multiple forms of xylanase, each with a different stability from the others. The results obtained for A. jumigatus show a similar trend in that activity reaches a constant level also indicating the presence of multiple forms of xylanase. Like xylanase, A. jumigatus p-o-xylosidase retained activity even after 48 hours at pH 5.0. Similarly, the enzyme from Aureobasidium pullulans also retained maximum activity after 24 hours incubation at its optimum pH of 4.0 [1]. Although Myburgh et ale [1] did not study the effects of pH stability on p-o-xylosidase activity below pH 4.0, one suspects that the same trend would result. That is, with A. fumigatus J3-oxylosidase, optimum stability is at pH 5.0. At pH values greater than or lower than pH 5.0 the enzyme becomes less stable losing approximately the same amount of activity.
Substrate specificities of Iylanase and p-D-xylosidase Xylanase enzymes may be assayed using xylans from various sources. During this investigation it was decided to use birchwood xylan since it contains 90% xylose residues. The synthetic substrate, PNPX appears to be the substrate of choice in the literature. The Michaelis-Menten constants observed for xylanase and J3-n-xylosidase are summarised in Table 3.
Physiochemical properties of xylanolytic enzymes
411
The general variability of xylans and assay conditions for determining xylanase activity makes direct comparisons with xylanase enzymes from other sources difficult. However, the specificity of xylanase and J3-o-xylosidase appears to be measured in terms of which substrates are hydrolysed by separated and purified forms of xylanase and p-o-xylosidase. Problems also arise because of the broad specificity of one enzyme for several substrates. For example, Ozcan et ale [13] observed that the xylanase enzyme produced by the yeast Pichia stipitis was also able to hydrolyse PNPX. The rate at which PNPX was hydrolysed by xylanase was extremely slow compared with 13o-xylosidase. Table 3: The Michaelis-Menten constants for the hydrolytic action ofhemicellulases produced by A. jumigatus. Enzyme
KMmgmL- 1
Vmu nunol mL- 1 min- 1
Xylanase
11.69
0.42
(3-Xylosidase
0.10
0.34
GENERAL DISCUSSION Recently, xylanases and other hemicellulases have received increased attention due to their possible application in paper manufacturing. Xylanase pretreatment of paper pulps has been shown to aid the bleaching process, while preserving the cellulose fraction. Trials using these enzymes for prebleaching are currently being carried out [14, 15]. Enzymes that exhibit high temperature optima and stability and are active over neutral to alkaline pH values would clearly be highly desirable for such a process. For the xylanase and fl-o-xylosidase activities of A. fumigatus to be suitable for such a process in the paper pulp industry, they need to be potent and stable for long periods of time at 50°C and neutral pH. Our investigations have indeed shown that this is so. ACKNOWLEDGMENT Lesley A. Hamilton thanks S.E.R.C. (Science and Engineering Research Council) for a research studentship for this work.
REFERENCES [1] Myburgh J., Prior B.A. and Kilian S.G. Process Biochem., (1991), 26, 343-348. [2] Puis J. and Poutenan K. In "Enzyme systems for lignocellulose degradation". Ed. M.P. Coughlan. Elsevier Science Ltd., London, UK. (1989), Pp. 151-165. [3] Kim S.W. Ph.D. Thesis, (1989). University of Birmingham, Birmingham, UK. [4] Wase D.A.J. and Raymahasay S. In "Cellulose and its derivatives -chemistry, biochemistry and applications". Eds. J.F. Kennedy, G.O. Phillips, D.J. Wedlock and P.A. Williams. Ellis-Horwood, Chichester, UK. (1985), Ch. 49. [5] Gomes, J., Purkarthiofer, H. M., Kapplomiller, J.,Sinner, M. and Steiner, W. Appl. Microbiol. Biotechnol. (1993), 39, 700-707.
412 Applications
[6] Hamilton L.A. and Wase D.A.J. Process Biochem., (1991), 26, 287-292. [7] Holland T.M. Ph.D. Thesis, (1989). University ofBirmingham, Birmingham, UK. [8] Sumner J.B. and Graham V.A. J. Bioi. Chem., (1925), 65, 393-395. [9] Wase D.A.J., Hamilton L.A., Holland T.M., Kim S.W. and McManamey W.J. In "Cellulosics: materials for selective separations and other technologies". Eds. J.F. Kennedy, G.O. Phillips and P.A. Wtlliams. Ellis-Horwood, Chichester, UK. (1993), Ch. 30. [10] Royer J.C. and Nakas J.P. Enzyme Microbial Technol., (1989), 11, 405-410. [11] Hrmova M., Biely P. and Vrsanska M. Enzyme Microbial Technol., (1989), 11, 610-616. [12] Stewart J.C. and HeptinstaJl J. Methods in Enzymology, (1988), 160, 33-39. [13] Ozcan S., Kotter P. and Ciriacy M. Appl. Microbiol. Biotechnol., (1991), 36, 190195. [14] Grant R. Pulp Paper Int., (1991),33, 61-63 [15] Khasin A., Alchanati I. and Shoham Y. Appl. Environ. Microbiol., (1993), 59(6), 1725-1730.
42 Endoglucanase, !3-D-glucosidase and xylanase induction in Dichomitus squalens (Karst) Reid E Resende, M Carolino and N Teixeira Rodeia - Departamento de Biologia Vegetal, Bloeo C2, ~ piso, Faeuldade de Ciencias da Universidade de Lisboa, Campo Grande, 1700 Lisboa, Portugal
ABSTRACT The amount of endoglucanase, B-D-glucosidase and xylanase produced by the fungus D. squalens were found to be dependent on the source of carbon and on the presence of the Tween 80 in the growth medium. Growth on cotton cellulose enhanced the production of endoglucanase, B-D-glucosidase and xylanase in the culture filtrates relative to the other sources of carbon (Avicel cellulose, carboxymethylcellulose = CMC, paper mill sludge, sawdust of Pinus sp).The endoglucanase induced by CMC exhibits 760/0 of residual activity after 2 h at 80 oC, maintaining about 1000/0 activity after 1 h at 50 oC, pH 5.0; it has a half-life of 17 min at 70 oC, pH 5.0. This enzyme shows optimal pH activity at pH 5.0 and pH stability between 4.0 and 6.36 where it exhibits a residual activity of more than
76%.The B-D-glucosidase component was isolated by chromatography on DEAE Sephadex A-50.
INTRODUCTION Cellulases and xylanases are produced by a variety of fungi and bacteria. These enzymes hydrolyse glycosidic bonds in cellulose and xylan, two of the most abundant polysaccharides in nature. Both enzymes have potential applications in the bioconversion of lignocellulose to useful products.The purpose of the present study was to examine the effect of carboxymethylcellulose, sawdust of Pinus sp., Avicel cellulose, paper mill sludge, cotton cellulose, Tween 80 and hemicellulose - rich substrates on the production of cellulases and xylanases by Dichomitus squalens .
MATERIAL AND METHODS MATERIALS
Dichomitus squalens
(n~
571) belongs to the Mycology Center's culture collection of
413
414 Applications
the Faculty of Sciences of Lisbon. It was isolated from a stump of Pinus sp. The fungus has been maintained by sub-culture on potato dextrose agar. MElHODS
Cultivation methods 250 ml Erlenmeyers containing 100 ml of a basal liquid medium, Norkrans & Hammarstrorn (1963), enriched with biotin 5 ug 1-1 and thiamine 100)lg 1-1 and supplemented with different carbon source (Avicel cellulose - 1%; cotton fibre 2.76%; CMC - 1%; paper mill sludge - 1.5%; sawdust of pinus tree - 1.5%) were inoculated with mycelium discs and incubated at 28 0C. The effect of a surfactant on the production of cellulases or xylanases was evaluated adding 0.1 % of Tween 80 to each half series flasks containing cotton as carbon source.
Enzyme assays Endoglucanase and xylanase activities were assayed using the method of Wood & Bhat (1988). B-D-glucosidase activity was assayed using the method of Wood (1968). Protein is estimated using the method of Lowry et ale (1951) or by absorbance at 280 nm. Units of activity are expressed, in the case of endoglucanase, as the release of 1 umole of reducing sugar (glucose equivalent) per minute. In the case of B-Dglucosidase as the release of 1 umole of o-nitrophenol per minute and in the case of xylanase activity as the release of 1 umole of reducing sugar (xylose equivalent) per minute. Temperature and pH optima - the effect of pH, temperature and the half-life at 70 0C and pH 5.0 of the endoglucanase activity and stability were evaluated by the method of Parr (1983).
Enzyme purification All operations were performed at room temperature.The extracellular extract was concentrated in an ultrafiltration apparatus under nitrogen pressure (ultrafilters cut-off of PM-5 or PM-IO KDa membrane in an Amicon cell -50ml- under a constant pressure of 25 - 30 psi ). When the concentrated enzyme solution from the ultrafiltration step was chromatographed on DEAE - Sephadex A-50 column, endoglucanase and 'B-D-glucosidase activities were adsorbed on the column. These were eluted with a linear gradient composed of 0.1 M sodium acetate buffer, pH 4.0 and 1M NaCI in the same buffer.
RESULTS In Figure 1 where are represented B-D-glucosidase, endoglucanase and xylanase activities and the substrates utilized ( cotton fibre, Avicel cellulose, sludge of paper mill and sawdust of Pinus sp.) it is evident that cotton was the best inducer substrate for D .squalens produce all enzymes and in contrast the sawdust of pinus tree was the worst inducer substrate. In the same Figure we can observe the enzyme quantities produced with the time of culture. In Figure 2 we can observe that the surfactant Tween 80 promotes an higher liberation of all enzymes on the 5th week and in some cases with an increase higher than 100 %. In Figure 3 we represent the effect of temperature on the endoglucanase induced by CMC and it has a higher activity at 60 0 C although it was more stable at 50 0 C
Physiochemical properties of xylanolytic enzymes 415
E
.. 400
'0
E
C200
Cot. Avl. Slu. Sew.
Col.
=cotton fibre;
Avi.
Cot. Avl. Slu. Sew.
Cot. Avl. Slu. Sew.
= Aviccl cellulose; Slu.= sludge of paper min; Saw. =sawdust
Fig.I - Effect of cotton fibre, Avicel cellulose, sludge of paper mill and sawdust of pine tree on the (l-glucosidase, endoglucanase and xylanase enzyme activities.
i
..
1
n.,lucoeld •••
C
i
-. 'i
.. ..
X,'_nee•
I
i
I
1
TI",.
c•••".)
I
I
TIfft.
.
Wilh Tween RO (0)
t
(•••".,
1
TI", • • • • • • •,
Without Tween 80 (.)
Fig. 2.- Effect of the surfactant Tween RO on the production of endoglucanase 13glucosidase and xylanase enzymes from D.squlliells with cotton as carbon source.
(results not shown). We can conclude that this enzyme has a half-life of 17 min at 700C and pH 5.0. We also studied the effect of pH on the endoglucanase of the D.squalens induced by CMC and we can observe that the optimum pH level for activity was of S.O and for stability was 5.7 ( Fig. 4). When the enzyme was kept for I8h at pH values from 4.0 up to 6.36 the residual activity was higher than 76%. However pH below 4.0 or higher than 7.0 a rapid deactivation of the enzyme was promoted ( Fig. 4). In Figure 5, we can verify that the endoglucanase has a half-life of 17 minutes at 70 0 C and at pH 5.0. In Figure 6 we represent the separation of the enzymes using DEAE Sephadex A-50 and we can conclude that Sephadex permits a better separation
416
Applications
Therefore with Sephadex the B-D-glucosidase is separated from the endoglucanase being eluted the first enzyme between fraction 17 and 22 and the endoglucanase between fraction 26 and fraction 44, when CMC was the substrate inducer. Although when the cotton was the substrate they were separated one endoglucanase and one BD-glucosidase with inverse molecular weight from those present in CMC.
120
100
60 Enz. Act. (%) 40 ;----_r-----.-----r-...--__-
O-t------,r----r-~-__r_-~------.
20
40
60
80
3
4
5
_ 7
6
pH
Temp.(OC)
Fig. 3 - Effect of the temperature on the endoglucanase activity from D.squalens induced by CMC .
Fig. 4 - Effect of pH on the acuvity and the stability of one endoglucanase from D.squalens induced by CMC. 30
2,2
__ 1,8
.(,J
<
~ ......., oil
j
1,4
1
. , . - . - - - - r -_ _-
,Ol~
5
15
25
__
35
----r-~
45
Pre-Inc.nnln.)
Fig. 5 - Kinetic ot thermal inactivation of one endoglucanase from D .squalens induced byCMC.
o
10
20
30
40
Nr of Fraction
Fig. 6 - Elution pattern of cellulolytic enzymes on DEAE Sephadex A-50 column chromatography. Fractions of 3 ml were collected.
Physiochemical properties of xylanolytic enzymes
417
DISCUSSION In this work, we have examined the effect that lignocellulosic or cellulosic-rich substrates have on the production of cellulases or xylanases from D .squalens . Growth on cotton cellulose enhanced the production of endoglucanase, (3-Dglucosidase and xylanase in the culture filtrates relative to the other sources of carbon i.e. Avicel cellulose, carboxymethylcellulose - CMC, paper mill sludge and sawdust of Pinus sp. (Fig.l). Studies of regulation of xylanases and cellulases in fungi are often complicated by a simultaneous production of these enzymes and sometimes also by substrate cross - specificity of cellulases and xylanases. Thus, it is not surprising, when grown on cellulose (Avicel), cellulases are produced together with xylanases, moreover as it is reported practically all cellulase-producing microorganisms also produce xylanases and vice-versa. The addition of the surfactant Tween 80 to the culture medium containing cotton as carbon source, promoted an higher liberation of the endoglucanase, B-D-glucosidase and xylanase enzymes (Fig.2) . The optimal temperature and pH for endoglucanase activity for the hydrolysis of CMC are 50 65 0C and pH 5.0, respectively (Figs 3 and 4 ).The enzyme is stable between pH 4.0 and 6.36 at room temperature for 18 h where it exhibits a residual activity of more than 76% (Fig. 4). The endoglucanases induced by CMC exhibit 760/0 of residual activity after 2 h at 80 oC, maintaining about 1000/0 activi ty after 1 h at 50 oC, pH 5.0; it has a half-life of 17 min at 70 0C, pH 5.0 (where endoglucanase activity presented half of its activity) (Fig. 5) . The B-D-glucosidase and endoglucanase components in the extracellular extract were isolated by chromatography on DEAE Sephadex A-50 (Fig. 6) .
ACKNOWLEDGEMENTS This research was financed with a grant from JNICT and had financial help from INIC and the Faculty of Sciences of Lisbon, enabling us to participate in Cellucon 93 Conference, Lund, Sweden, 20-24 June 1993.
REFERENCES Lowry, O.H.; Rosebrough, N.J.; Farr, A.L. & Randall, AJ. (1951). Protein measurement with the Folin phenol reagent. Journal Biological Chemistry. 193: 265275. Norkrans, B. & Harnmarstom, A. (1963). Studies on growth of Rhizina undulata Fr. and its production of cellulose and pectin decomposing enzymes. Physiologia Plantarum 16 (1): 1 - 10. Parr, R.S. (1983). Some kinetic properties of the B - 0 - glucosidase (cellobiase) in a commercial cellulase product from Penicillium [uniculosum and its relevance in the hydrolysis of cellulose. Enzyme Microbiology Technology,S: 457 - 462. Wood, R.K.S. (1968). Cellulolytic enzyme system of Trichoderma koningii. Separation of components attacking native cotton. Biochemistry Journal, 109: 217 227. Wood,T. & Bhat, M. (1988). Methods for measuring cellulase activities. In: Methods in Enzymology 160 (A) : 87 - 112. Wood, A.W.; Kellogg, T.S. (eds). Academic Press, Inc. London.
Index Carboxylic acid groups 179 Carboxylmethylcellulose 263, 265 Catalytic action 198 Cell-wall thickness 113 Cellobiohydrolase (CBH) 227-234 Cellobiohydrolase 198 Cellobiose 198 Cellulase treatment 227-234 Cellulase synergism 227-234 Cellulase general model 227 Cellulase 194, 197, 198,204 Cellulases on textiles 227 Cellulonic materials, biochemical investigation 243-247 Cellulose tricarbanilates 153, 154 Cellulose dissolving pulps 157 Cellulose 174-176, 197-204, 323-329, 345-350 Cellulose pulp 37 Cellulose degradation 361-367 Cellulose copolymers 370 Cellulose derivatives 378-384 Cellulose ethers 377, 379 Cellulose, chemical modification 253 Cellulosic networks 378-384 Celsol 197, 204 Cement 361-367 Chemical oxygen demand 143, 146 Cemical pulping 177-179 Chemical composition of temperate hardwoods 114-116 Chemical composition of temperate softwoods 114-116 Chemical composition of tropical hardwoods 112-116
Acetylation of wood 184 Acetylation using acetic anhydride 183 Acid hydrolysis 202 Adsorption 399-405 Agricultural residues 37 Air pollution 246 Alkaline degradation 361-367 Aluminium 192 Aminoalkyl dyes 223 Angiosperm 25 Anisotropy 216 Approximate chemical analysis 46 Aspect ratio 170 Aspergillus niger 199, 200, 204 Aspergillus fumigatus 405-412 Avicel cellulose 413-417 Bagasse 38 Bamboo 40 Barley straw 31, 133 Bending properties of cotton fabrics 228, 232, 233 Biobleaching 143-145 Biochemical oxygen demand 144 Biochemical investigation 243-247 Biodegradable 268, 274, 277 Biodegradation 284 Biosupports 370 Biotransformation 197, 199 Birch, pulping properties of 119-125 Black liquor 143-146 Blackcurrant 25 Bleaching 64, 127, 133 Bond strength development 217 Bonding reactivity 218
Chemimechanical pulping 175-179 Cadoxen 152-157 Carbanilates 388-391 Carbon fixation 19
Chitin, chitosan 255 CMC-carboxymethylcellulose 413-417 Coffee grounds 284 419
420
Index
Composites 166 Compression wood 178 Conjugated furanic polymers 261 Copolymerisation 388-391 Copper 119-125 Cotton reducing power 228, 231, 232 Cotton crystallinity 228, 232 Cotton stalks 100 Cotton linters 44 Cross-linking 178, 179, 289 Crosslink 136 Crosslinked polyurethanes 357-358 Crystallinity 77 Cuprammonium 151, 152 Cupriethylene diamine 151, 152 Decortication 43 Degradation of cellulose 361-367 Degradation 198, 199 Degree of polymerization 151-157 Dehydration 345, 350 Dehydroferulic acid 31 Delignification 81, 84, 133, 177-179 Density profile 215 Depolymerisation 101 Derivatisation 388-391 Desilication 41 Deterioration 245 Dichomitus squalens 413-417 Differential Scanning Calorimetry (DSC) 236, 237 Dimensional stability 183, 185 Dimers 31 Dioxane 35 Diphenylmethane diisocyanate 269 Dispersion activity 399-405 Donnan equilibrium 179 DPw 151-155 DRIFT 29, 133 Drop test 185 DSC 264, 267, 388-391
Enzyme activities 227-234 Enzyme 197-204 Enzyme purification 413-417 ESCA analysis 65, 78 ESR 393-398 Ethanol pulping 99 Etiolated 35 Eucalyptus oil 55, 56 Extensibility 203 Extraction 101 Fabric strength 228, 232, 233 Ferulic acid 31 Fiber length 112 Fibre separation 218 Fibre modification 218 Fibre orientation 218 Fibre supplies 13-24 Fibre 191, 197-204 Fibre orientation 213 Fibre networks 213 Fibre, aspect ratio 170 Film-forming properties 378 Flax 138 Flax, pulping properties of 119-125 Flexibility ratio 113 Fluidized bed reactor 143-146 Forage rape 138 Forest products, world consumption 13, 14 Forest resources 3-5 Fourier transform infrared spectroscopy (FT-IR) 319 Fourier transform infrared spectroscopy 339, 340 Frankincense 57, 58 FT-IR 388-391 FfIR-Raman spectroscopy 65,66 Furanic monomers 259 Furanic polymers 259 Furfural, monomers and polymers from 259
Endoglucanase (EG) 227-234
Endoglucanase 198, 413--417
Galactan 27
Environmental Scanning Electron Microscopy (ESEM) of cellulase treated cotton fibres 227-234
Gas permeability 215, 218 Gas chromatography 319-321 Gellan 265, 267
Index
Glass transition 265 Glass transition temperature 175-177 Glucomannan 27 Glucose 198 I3-D-Glucosidase 198,413-417 Glucuronoxylan 27 Graft copolymerisation 388-391 Graft copolymers 388-391 Gramineae 32
Grass, pulping properties of 119-125 Guaiacyl 266 Gum arabic 50-52 Gums 49-59 Half-life activity 413-417 Hardwood 25, 199-204 Hardwoods, chemical composition of 114-116 Heat and moisture transfer 216 Hemicellulase properties 405-412 Hemicellulase stability 405-412 Hemicellulose 202, 295, 303-304, 316, 317,323-329 Hemicelluloses 174-177 Hemp, pulping properties of 119-125 High temperature corking 75 High performance liquid chromatography (HPLC) 299, 318, 322, 323, 340 High-performance polymers 266 Hot pressing 214 HOURI-FU 43 Hydroferulic acid 31 Hydrogels 263, 267 Hydrolysis 198-203 Hydrophobicity 183 Hydroxymethylfurfural, monomers and polymers from, 259 4-Hydroxyphenyl 266 Hygro-thermo-viscoelasticity 216 Hygroscopicity 216
421
Ionic conductance 377, 383 Iron 119-125 Kaelble 236, 238 Kappa number 116-118 Kenaf 45 Kenya 37 Kenya, plant derived gums in 49-59 Kinetics 81, 84 Lace 44 Laminate 191 Laser light scattering 151-155 Levogluconsenon 345-350 Levoglucosan 345-350 Libriform fibre 26 Ligneous materials, biochemical investigation 243-247 Lignin 28, 81, 82, 175-179, 202, 278, 295,317,318,339,393-398 Lignin-carbohydrate complexes 177 Lignins, as macromonomers 257, 351-358 Lignosulphonates 393-398, 399-405 Linumsitatissimum 34
Liquid state 264 Liquid crystal 263-267 Liquid crystalline state 264 Longterm productivity 9, 10 Lumen width 113 Magnetic orientation 218 Manganese 119-125 Mannan 28 Mean chain length of oligosaccharides 228, 230, 231 Mechanical pulping 177-179 Mechanical properties 288 Methoxyl groups 178 Microfibrillar orientation 163 Microfibrils 174, 175 Micropores 202
Immobilisation 143-145, 370
Microtetraspora flexuosa 127
Impregnation 101
Middle lamella 177
Intercellular bonding 166 Internal Property Distribution Control (IPDC) 215
Mineral concentration 119-125 Molecular weight 297, 298, 322 Morphological properties 112-114
422
Index
Morphology 174-176 Museum collections 243-247 Myrrh 57,58 Nitrobenzene oxidation 322, 323 Nitrogen 119-125 NMR29 Non-wood plant fibres 37 Non-wood species, pulping properties of 119-125 Oligomeric isocyanates 378, 379 Oxone 133 Packaging 191 Paper properties 66-80 Particle board 168, 205-212 Particle size 236, 239 Pectic substances 294, 301-304 Performance indices 214 Peroxymonosulphate 133 Phanerochaete chrysosporium 143-149 Phenolic hydroxyl groups 179 Phenolic acids and aldehydes 299, 340 Phenolic resin 205-212 Phosphoric acid 345-350 Photochemical 32 Phthalic anhydride 205-212 Physical properties 280-282 Pina 43 Pine oil 52-55 Pine 184 Pineapple leaves 43 Plant derived, gums and resins 49-59 Plant fibres, property enhancement 161-172 Plant fibres 213 Plantation forestry 6, 7 Polyhydroxystyrene 266 Poly(methyl methacrylate) bonded boards 169-171 Polyacylhydrazone 267
Polymer electrolytes 377-384 Polymeric materials 251-262 Polypropylene glycol 269 Polysaccharides electrolytes 263, 266 Polyester-polyol 278 Polyurethane 268, 274, 277, 283 Polyurethanes from lignins 258 Polyurethanes from furanic monomers 262 Polyurethanes 352-358 Pre-treatment 293 Preparation 279 Primary wall I77 Protein 177 Pulp industry 37 Pulping yield 116-118 Pulping properties 119-125 Pulping process 116-118 Pulping 81, 82, 202 Pulping, steam explosion 63-80 Pulpzyme 33 Quaternary cellulosic fibres 221 Radionuclide damage 361-367 Ray parenchyma 26 Reactive cellulose fibres 221 Reactive azo dyes 369, 371 Reactive dye effluent 370-373 Reactive dye biodegradation 370-373 Reactivity of lignin OH groups 351-358 Recovery 191 Recycled materials 22 Recycling 191 Reeds 42 Relative humidity 245 Renewable resources 251-262 Resins 49-59 Revenue analysis 47 Rheology 216 Ribes nigrum 25 Roll angle 185
Polyester 267, 270 Polyesters from lignins 258 Polyether networks 377-384 Polyethylene glycol 269
Saccharinic acids 361-367 Sawdust 413-417 SAXS 264, 267
Index 423
Scandinavian pine 183 Scanning Electron Microscopy (SEM) 236, 237 Scanning Electron Microscopy (SEM)-of cellulase treated cotton fibres 227-234 Secondary wall 177 Shape Optimal Design (SOD) 214 Silicon 119-125 Silicon-containing compounds 399-405 Silicon-organic compounds 393-398 Sisal 42 Sludge of paper mill 413-417 Small angle X-ray scattering 264 Soda process 82 Softening 175-177 Softwood 199-204 Softwoods, chemical composition of 114-116 Spatial properties distribution 213 Spinning 197-204 Spirodioxane ring 266 Star-shaped copolymers 354-357 Steam pressure treatment 294, 301-304 Steam explosion pulping 63-80 Steam injection 219 Straw, pulping properties of 119-125 Sugar 296,314-316,319-321 Supermolecular structure 197, 199, 202 Surface tension 236, 239, 399-405 Sustainability 8 Swamp 42 Swelling 179-180 Synchrotron orbital radiation 265 Synergistic 198 Syringyl 266 Tall fescue 100 Tannins 257 Tensile strength 163, 170, 203
Thermal conductivity 218 Thermodestruction 345-347 TPD-Tons/day 46 Tracheid 26 Trametes versicolor 148 Translation properties 216 Triazine 222 Trichoderma reesei cellulases 227-234 Trichoderma reesei 199, 200, 204 Truxillic acid 32 Tween 80 413-417 Uronic acid 296,316,321 Vinylsulphone 223 Viscoelastic properties 286 Viscoelasticity 382, 383 Viscosity tests 151, 152 Viscosity and fluidity of CED solutions of cellulose 228, 231, 232 Viscosity/DP interconversion 151-155 Water repellence 183 Water sensitivity 168 Water resistance 205-212 WAXS 264 Wettability analysis 185 Wheat straw 39,81,82, 100,315,316 White-rot fungi 144 Wicking 236, 240 Wide angle X-ray scattering 264 Wood fibre board 167 Wood modification 205-212 Wood supplies 13-24 Wood polymer distribution 174-176 Wood 174,175 Wood based composites 166 Wood, performance of 162 X-ray diffraction patterns 79 Xanthan 265, 267 Xanthate 197 Xylan 174, 179
Tensile modulus 183, 184
Xylanase 33, 127,405-412,413-417
Tension wood 27 Terpenes 259 Thermal properties 289
f3-D- Xylosidase 405-412 Zisman manipulations 236, 238