CAUTION: For the purpose of the Sustainable Composites pages, the materials described are those from natural sources, without prejudice to the results of any future Quantitative Life Cycle Analysis (QLCA) which may (or may not) make the case for these materials being more environmentally-friendly than equivalent systems manufactured from man-made fibres and synthetic resins.  The inclusion of any specific system here is not an endorsement of that product: potential users will need to fully consider each system in the context of their specific technical requirements.

The value of Eco-System Services

PowerPoint presentation (211KB .ppt file)  NB: superseded by the Sustainable Composites presentation.

• Technical publications for bamboo, coir, flax, kenaf and sisal fibres
• Environmental, technical and economic issues
• Glossary of fibre/textile terms
• Suppliers of natural fibres

Natural fibres for the reinforcement of polymer matrix composites are normally the bast fibres (the structural fibres from plant stems) [1-3]. The principal plants used are flax, hemp, jute and kenaf. There is growing interest in the potential of nettle fibres.  A useful source for information on a wide variety of plants is the Crop Index at Purdue University Center for New Crops and Plant Products - crops are listed alphabetically by genus and common name.

This page considers

• flax,
• hemp,
• jute,
• kenaf, and
• nettle bast fibres.

ADAS has recently reviewed and analysed the breeding and regulations of hemp and flax varieties available for growing in the United Kingdom.

References

1. Caroline Baillie, Green Composites: polymer composites and the environment, Woodhead Publishing Limited, Cambridge, 2004. ISBN 1-85573-739-6. UOP Library
2. R R Franck (editor), Bast and other plant fibres, Woodhead Publishing Limited, Cambridge, March 2005.  ISBN 1-85573-684-5. UOP Library
3. AK Mohanty, M Misra and LT Drzal, Natural Fibers, Biopolymers, and Biocomposites, CRC Press/Taylor & Francis Group, Boca Raton FL, 2005.  ISBN 0-8493-1741-X.  UOP Library
4. A Stamboulis, CA Baillie and T Peijs, Effects of environmental conditions on mechanical and physical properties of flax fibers,
   Composites Part A: Applied Science and Manufacturing, 2001, A32(8), 1105-1115.
5. Richard Wool and X Susan Sun, Bio-Based Polymers and Composites, Elsevier, August 2005. ISBN 0-12-763952-7. Overview.
6. NL Hancox, Fibre Composite Hybrid Materials, Elsevier Applied Science, Barking, 1981. ISBN 0-85334-928-2.
7. TJ Reinhart, Engineered Materials Handbook 1: Composites, ASM International, 1987. ISBN 0-87170-279-7.
8. Richard Mark Johnson, Innovations and applications in the usage of miscanthus grass: executive summary, Dissertation submitted in partial fulfilment for the degree of Doctorate of Engineering, Warwick Manufacturing Group - School of Engineering - University of Warwick, September 2006 (reproduced here with the permission of Kerry Kirwan).
9. N Chand, RK Tiwary and PK Rohatgi, Resource structure properties of natural cellulosic fibres - an annotated bibliography, Journal of Materials Science, 1988, 23(2), 381-387.
10. WD Brouwer, Natural Fibre Composites in Structural Components: Alternative Applications for Sisal?, Seminar: Common Fund for Commodities - Alternative Applications for Sisal and Henequen, Food and Agriculture Organization of the UN (FAO) and the Common Fund for Commodities (CFC), Rome, 13 December 2000.
11. RM Rowell, AR Sanadi, DF Caulfield and RE Jacobson, Utilization of Natural Fibers in Plastic Composites: Problems and Opportunities,
    http://www.fpl.fs.fed.us/documnts/pdf1997/rowel97d.pdf, accessed 22 December 2006 at 12:23.
12. C Baley, Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase, Composites Part A: Applied Science and Manufacturing, July 2002, 33(7), 939-948.
13. K Charlet, JP Jernot, M Gomina, J Bréard, C Morvan and C Baley, Proceedings of the 12th European Conference on Composite Materials (ECCM-12), Biarritz - France, August/September 2006.
14. E Bodros and C Baley, Study of the tensile properties of stinging nettle fibres (Urtica dioica), Materials Letters, 15 May 2008, 62(14), 2143-2145.
15. Koichi Goda, MS Sreekala, Alexandre Gomes, Takeshi Kaji, Junji Ohgi, Improvement of plant based natural fibers for toughening green composites - effect of load application during mercerization of ramie fibers, Composites Part A: Applied Science and Manufacturing, December 2006, 37(12), 2213-2220

Flax (Linum usitatissimum L.) fibres

• Crop Rotation
• Seed and seeding practices
• Fertilizer Practices
• Growth and development
• Diagnostic Guide
• Weed Control
• Field Insect Pests
• Diseases
• Environmental Disorders
• Harvesting
• Varieties
• Flax straw and fibre
• Acknowledgements

The life cycle of the plant consists of a 45 to 60 day vegetative period, a 15 to 25 day flowering period and a maturation period of 30 to 40 days and is illustrated in Turner [F3] and the following images from Turner are accessible below via the respective links from the FCC website [F2].  There are 12 distinct growth stages in the flax plant:

The typical production cycle for flax fibres [F3] is:

• Drilling (planting) the seed: this usually occurs between the end of February and early April in Belgium, France and the Netherlands or in early April in Northern Ireland (NI). For flax in NI, the suggested levels of fertiliser are 20 kg N/ha, 20 kg P2O5/ha and 80 kg K2O/ha.
• Weed control: it is essential to minimise weeds to avoid contamination of the scutched flax fibres.
• Plant growth: as described in the previous paragraph.
• Dessication: glyphosate is typically applied 10-14 days after full flower, at about mid-July in NI.
• Harvest: by either combining or pulling, in August/September.
• Rippling: the removal of flax seed capsules by drawing pulled stems through a coarse steel comb.
• Retting is defined for flax as the “subjection of crop or deseeded straw to chemical or biological treatment to make the fibre bundles more easily separable from the woody part of the stem. Flax is described as water-retted, dew-retted or chemically–retted, etc., according to the process employed” [Textile Institute,1975]. Enzymes (e.g. pectinase digests pectin binder) may be used to assist the retting process, but termination of the retting process may be a problem and failure to achieve this can result in reduced fibre properties.  Pre-harvest retting of flax with glyphosate [F4] applied at the mid-point of flowering depends on uniform desiccation of the entire stem and is difficult to achieve during a dry season. As in dew-retting, stand-retting of the desiccated flax in the field relies on microorganisms and is dependent on the vagaries of the weather. Shekhar Sharma et al [F4] have presented and discussed the role of microbial enzymes, screening of flax cultivars, fibre quality and upgrading of coarse fibres in this context.
• Degumming is a term used in the context of bast fibres for textile applications (but is rare in the context of reinforcement fibres). Liu et al [F5] state that the fibre is extracted by degumming the plant stem using biological, chemical, or biochemical methods but also that existing degumming methods (whether biological, chemical, or biochemical) have their limits in refining fibre as they make the fibre finer and softer at the cost of reducing fibre tenacity and length (both of the latter parameters would be detrimental to the effectiveness of a reinforcement). Bing and Laijiu [F6] state in comparison to fibre obtained by conventional chemical degumming process, those degummed by bio-enzymatic process possess smoother surfaces, better softness, high strength, excellent spinning ability, and could produce high quality fibre for textile industry. However, they also state that systematic research concerning the bio-degumming mechanism at the molecule scale is not yet found in the literature”
• Decortication is the mechanical removal of non-fibrous material from retted stalks or from ribbons or strips of stem or leaf fibres to extract the bast fibres. For flax, the process is usually referred to as “scutching”. This is usually achieved by a manual operation, hammer mill, inclined plane/fluted rollers, steam explosion or willower.  Harwood et al [F7] have described a novel environmentally-friendly and cost-effective method using shock waves generated by high-voltage pulsed electrical discharges (HVPED) on fibres immersed in water.
• Hackling is the combing the line flax in order to remove short fibres, parallelise the remaining long (line) fibres and also remove any extraneous matter (shive).
• Carding is defined as “the disentanglement of fibres by working them between two closely spaced, relatively moving surfaces clothed with pointed wire, pins, spikes or saw teeth” [Farnfield and Alvey].  The product of this process is known as sliver.
• Spinning is the "drafting [decreasing the mass per unit length] and twisting of natural (or man-made) fibres".  The product of this process is known as yarn or filaments.  In the bast- and leaf-fibre industries, the terms ‘wet spinning’ and ‘dry spinning’ refer to the spinning of fibres in the wet state, and in the dry state respectively”.

A similar route is followed for the other bast fibres. Subsequent treatments [Textile Institute, 1975] of natural fibre textiles may include:

• acetylation: defined as the "process of introducing an acetyl radical into an organic molecule" and the term "is used to describe the process of combining cellulose with acetic acid".
• bleaching: defined as the "procedure, other than by scouring only, of improving the whiteness of textile material by decolorizing it from the grey state, with or without the removal of natural colouring and/or extraneous substances. Note: removal of colour from dyed or printed textiles is usually called 'stripping'".
• grafting is the incorporation of monomers (e.g. cyanoethylation: reaction with acrylonitrile) or oligomers (short chain polymers) by chemical reaction at the fibre surface.
• mercerisation: defined as the "treatment of cellulosic textiles in yarn or fabric form with a concentrated solution of caustic alkali [soda], whereby the fibres are swollen, the strength and dye affinity of the materials are increased, and their handle is modified. The process takes its name from its discoverer, John Mercer (1844)".
• scouring (solvent treatment): defined as the "treatment of textile materials in aqueous or other solvents in order to remove natural fats, waxes, proteins and other constituents, as well as dirt, oil, and other impurities".

In the context of the reinforcement of composites by natural fibres, there has been increasing interest in grafting short polymer (oligomer) chains onto the fibre to increase the compatibility of the fibre and the matrix.

At the end of life, there is potential for controlled degradation of cellulose fibres by composting or other methods.

In 1941, flax fibres (and hemp) were used in resin matrix composites for the bodywork of a Henry Ford car [F1].  Flax is amongst the natural fibres now finding use in thermoplastic matrix composite panels for internal structures (door panels, parcel shelves and boot linings) in the car industry.

References

F1. Anna Lewington, Plants for People, Eden Project Books/Transworld Publisher, London, 2003. ISBN 1-903-91908-8.
F2. Flax Council of Canada
F3. John Anthony Turner “Linseed Law: A handbook for growers and advisers”, BASF (UK) Limited, Hadleigh - Suffolk, June 1987.  ISBN 0-9502752-2-0.
F4. HSS Sharma, PC Mercer and AE Brown, Review of recent research on the retting of flax in Northern Ireland, International Biodeterioration, 1989, 25(5), 327-342.
F5. Liu et al, Mechanical modification of degummed jute fibre for high value textile end uses, Industrial Crops and Products, January 2010, 31(1), 43-47.
F6. Bing and Laijiu, Bio-degumming process on jute fiber for textile, Journal of Biotechnology, October 2008, 136(Supplement 1), S474
F7. R Harwood, V Nusenbaum and J Harwood, Cottonisation of flax, International Conference on Flax and Other Bast Plants (Fiber Foundations - Transportation, Clothing and Shelter in the Bioeconomy),
      Saskatoon (Saskatchewan), CANADA, 21-23 July 2008, Paper ID number 22, pages 118-128. ISBN-13: 978-0-9809664-0-4.

Background material includes, for example:

• Alister D Muir and Neil D Westcott, Flax: The genus Linum, CRC Press, Boca Raton FL, 2003. ISBN 0-4153-0807-0. UOP Library
• J Salmon-Minotte and RR Franck, Chapter 3: Flax, In RR Franck, Bast and other Plant Fibres, Woodhead Publishing, Cambridge, 2005.  ISBN 1-85573-684-5. UOP Library
• HS Shekhar Sharma and CF van Sumere, The biology and processing of flax, M Publications, Belfast, c1992. ISBN 0-9519963-0-4. UOP Library
• Flax (Linen)
• Interactive European Network for Industrial Crops and their Applications: flax and linseed.

Hemp (Cannabis sativa L.) fibres

Hemp is an annual plant native to central Asia and known to have been grown in China over 4500 years ago [H1].  It probably reached central Europe in the Iron Age (circa 400 BC) and there is evidence of growth in the UK by the Anglo-Saxons (800-1000 AD).  It does not require fertiliser, herbicides or pesticides to grow well (and hence is potentially of great interest in the context of sustainability).  In suitable warm conditions, it can grow to 4 metres in just 12 weeks.

In 1941, hemp fibres (and flax) were used in resin matrix composites for the bodywork of a Henry Ford car which was able to withstand ten-times the impact on an equivalent metal panel [H1].  Hemp is amongst the natural fibres now finding use in thermoplastic matrix composites for internal structures (door panels, parcel shelves and boot linings) in the car industry.

H1. Anna Lewington, Plants for People, Eden Project Books/Transworld Publisher, London, 2003. ISBN 1-903-91908-8.

Background material includes, for example:

• Physical, Chemical and Pulping Characteristics of Hemp
• Michael Karus: European hemp industry 2001: cultivation, processing, and product lines
• Marianne Leupin: New processing with hemp
• Bo Madsen: Properties of Plant Fibre Yarn Polymer Composites - An Experimental Study, PhD thesis, Technical University of Denmark, Report BYG·DTU R-082, 2004. ISSN 1601-2917. ISBN 87-7877-145-5
• J Sponner, L Toth, S Cziger and RR Franck, Chapter 4: Hemp, In RR Franck, Bast and other Plant Fibres, Woodhead Publishing, Cambridge, 2005.  ISBN 1-85573-684-5. UOP Library

Jute (Corchorus capsularis. L. - white jute or C. olitorius L. - Tossa jute) fibres

Jute is the second most common natural fibre (after cotton) cultivated in the world.  It is an annual plant that flourishes in monsoon climates and grows to 2.5-4.5 m [J1].  It is primarily grown in Bangladesh, Brazil, China, India and Indonesia.  Jute-based thermoplastic matrix composites find a substantial market in the German automotive door-panel industry (growing from 4000 tons in 1996 to over 21000 tons in 1999 and rising) [J1].

J1. Anna Lewington, Plants for People, Eden Project Books/Transworld Publisher, London, 2003. ISBN 1-903-91908-8.

Background material includes, for example:

• The Golden Fibre
• Biotechnology in jute fibre processing
• KB Krishnan, I Doraiswamy and KP Chellamani, Chapter 2: Jute, In RR Franck, Bast and other Plant Fibres, Woodhead Publishing, Cambridge, 2005.  ISBN 1-85573-684-5.  UOP Library

Kenaf (Hibiscus cannabinus L.) fibres

Kenaf is a fibre plant native to east-central Africa, and a common wild plant of tropical and subtropical Africa and Asia.  It has been grown for several thousand years for food and fibre.  The plant has a unique combination of long bast with short core fibres in place of the hollow core.  Strong interest is being shown in this plant in Malaysia as it is fast growing and hence can yield two crops/year in the local climate.

Background material includes, for example:

• T Nishino, Chapter 4: Natural fibre sources, in C Baillie, Green Composites: Polymer Composites and the Environment, Woodhead Publishing, Cambridge, 2004, pp 49-80.  ISBN 1-85573-739-6.  UOP Library
• PJ LeMahieu, ES Oplinger and DH Putnam: Alternative Field Crops Manual: Kenaf, April 1991.
• Charles S Taylor: Kenaf: an emerging new crop industry, 1993 (in New Crops, 1993).
• Daniel E Kugler: Kenaf commercialisation: 1986-1995 (in Progress in New Crops, 1996).
• T Sellers, GD Miller, MJ Fuller, JG Broder and RR Loper: Lignocellulosic-Based Composites Made of Core From Kenaf, An Annual Agricultural Crop

Nettle (Urtica dioica) fibres

Nettles yield ~ 8-10 tonnes fibre/acre [N1] and are far stronger than cotton but finer than other bast fibres such as hemp.  They are a much more environmentally friendly fibre crop than cotton, which requires more irrigation and agrochemical input.

Merilä [N2] has reported elastic moduli and strengths for nettle fibre composites as follows:

Lewington [N3] states that "during the Second World War ... Britain's Ministry of Aircraft Production experimented with the use of a very strong, high-grade paper made from nettle fibre for reinforcing plastic aircraft panels as well as gear wheels and other machine parts".

N1. http://jacksonsrow.topcities.com/tikun_olam/nettle.html
N2. Ann-Jeanette Merilä, Stinging nettle fibres as reinforcement in thermoset matrices, MSc Engineering/Materials Technology, Luleå University of Technology, 2000.
N3. Anna Lewington, Plants for People, Eden Project Books/Transworld Publisher, London, 2003. ISBN 1-903-91908-8. UOP Library
N4. J Dreyer and G Edom, Chapter 9.5: Nettle, In RR Franck, Bast and other Plant Fibres, Woodhead Publishing, Cambridge, 2005.  ISBN 1-85573-684-5. UOP Library

ANIMAL FIBRES

• Charu Vepari and DL Kaplan, Silk as a biomaterial, Progress in Polymer Science, August-September 2007, 32(8-9), 991-1007.
• Thomas Scheibel, Spider silks: recombinant synthesis, assembly, spinning, and engineering of synthetic proteins, Microbial Cell Factories 2004, 3:14.
• Oxford Silk Group

Further reading

1. RR Franck - Bast and other plant fibres, Woodhead, Cambridge, 2005. ISBN 1-85573-684-5.
2. AK Mohanty, M Misra and LT Drzal - Natural fibers, biopolymers, and biocomposites, Taylor & Francis, Boca Raton FL, 2005. ISBN 0-84931-741-x.
3. AD Muir and ND Westcott - Flax: the genus linum, Routledge, London, 2003. ISBN 0-415-30807-0.
4. K Pickering, Properties and performance of natural-fibre composites, Woodhead Publishing, Cambridge, 2008. ISBN-13: 978 1 84569 267 4.
5. HSS Sharma and CF van Sumere - The biology and processing of flax, M Publications, Belfast, 1992. ISBN 0-951996-30-4.
6. JA Turner - Linseed law: a handbook for growers and advisers, BASF, Hadleigh, 1987. ISBN 0-950275-22-0.
7. SV Joshi, LT Drzal, AK Mohanty and S Arora - Are natural fiber composites environmentally superior to glass fiber reinforced composites?, Composites Part A: Applied Science and Manufacturing, 2004, 35(3), 371-376.
8. A Stamboulis, CA Baillie and T Peijs, Effects of environmental conditions on mechanical and physical properties of flax fibers, Composites Part A: Applied Science and Manufacturing, August 2001, 32(8), 1105-1115.
9. Peter Zugenmaier - Conformation and packing of various crystalline cellulose fibers, Progress in Polymer Science, 2001, 26(9), 1341-1417.
10. Yan Li, Yiu-Wing Mai and Lin Ye - Sisal fibre and its composites: a review of recent developments, Composites Science and Technology, 2000, 60(11), 2037-2055.
11. J Schurz, A bright future for cellulose, Progress in Polymer Science, 1999, 24(4), 481-483.
12. AK Bledzki and J Gassan, Composites reinforced with cellulose based fibers, Progress in Polymer Science, 1999, 24(2), 221-274.
13. HSS Sharma, PC Mercer and AE Brown, A review of recent research on the retting of flax in Northern Ireland, International Biodeterioration, 1989, 25(5), 327-342.
14. John Summerscales, Nilmini Dissanayake, Wayne Hall and Amandeep Virk, Characterisation of Bast Fibres and their Composites: a review, in submission for journal publication. Restricted: Download 658KB .pdf file

Other resources

• Paul Knox, Plant Cell Walls, Paul Knox Cell Wall Lab, 2003-2009