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One of the main objectives of sustainable development as it was defined at the 1992 Earth Summit in Rio de Janeiro is to reconcile economic and social progress without jeopardizing the planet’s natural equilibrium. In other words, over the long term there can be no development if it is not economically efficient, socially equitable and environmentally acceptable. Given these conditions, how can an industry like the composite industry find its place in such a framework without compromising the key advantages of these materials (low weight, functional integration, corrosion resistance, complex shapes, etc.)?
(Published on May-June 2006 – JEC Magazine #25)
BY JOËL LEVEQUE, MANAGER, ATOUTVEILLE
Three lines of development can lead to this objective: - promoting eco-design upstream; - promoting the recycling of technosphere materials; - promoting the use of biosphere materials.
The last two goals are part of the development of what are called “ecomaterials”. These are materials that have a minimum impact on the environment yet offer maximum performance for the desired function.
Against this backdrop, biosphere materials – i.e. materials from renewable and recyclable resources – have emerged onto the industrial landscape. Among these materials, natural fibres represent a significant challenge for the composite industry.
Different types of natural fibre
Natural fibres are classified into three major groups according to origin. Animal fibres either come from animal hair, for example wool fibres; are produced by silkworms; or extracted from bird feathers.
Plant fibres can be divided into sub-classes: 1) wood fibres and 2) crop fibres, which consist of seed fibres such as cotton or kapok; bast fibres such as flax, hemp, jute and ramie; leaf fibres such as sisal; stalk fibres such as bamboo and abaca; or fruit fibres such as coir. Asbestos is the main mineral fibre. While animal fibres consist of proteins, plant fibres are made up of cellulose fibrils (very high tensile strength) embedded in a hemicellulose and lignin matrix.
The main advantages of natural fibres are their high biodegradability, low CO2 emissions, high thermal and sound insulation properties and outstanding specific modulus.
They also have a number of disadvantages including: high moisture absorption, low thermal resistance, highly variable quality and low dimensional stability. On average, natural fibres are less expensive than synthetic fibres, although the price of natural fibres varies widely as a function of type.
Natural fibres can be used in a wide range of applications: - pulp and paper production, - textile products (shoes, clothing, carpets, etc.), - geotextiles (drains, filters, erosion control), - fillers for plastics, concrete and mortars, - insulation products, - profiles and particleboard (furniture, decking), - automotive non-wovens (door panels, dashboards, etc.), - ropes and mulching materials, - filtration (air, water), - absorbing products (animal litter).
For applications in connection with polymer-matrix reinforcement, such as the fillers for plastics or non-woven materials used in the automotive industry, the most attractive fibres are those that fulfil a structural function in Nature.
For example, wool fulfils a heat-insulating function but does not have good mechanical properties, while plant fibres from stalks, leaves and fruit, or fibres from animal secretions, do.
One of the most promising sectors for natural-fibre-reinforced composites is automotive, both for applications and tonnage. This sector is certainly the most technically advanced one, and a source of many applications for non-woven products and compounds, including parcel shelves, boot trim panels, under-the-hood parts, structural parts, Class A parts and dashboards. It accounts for 20% of new applications for flax-based non-woven products, for example. Thermocompression and injection moulding are the two main processing technologies used, but tests have also been carried out with other techniques, such as RTM, SMC and hand lay-up.
Thermocompression usually requires a non-woven mat made entirely or partly from plant fibres, which may or may not be combined with synthetic fibres. During the converting process, the synthetic fibres melt and become a matrix for embedding the plant fibres. The end product is lightweight with good mechanical properties, but only simple shapes can be created. The main automotive applications are for inner vehicle-door elements.
Polypropylene (PP) compounds reinforced with 10-60% plant fibres (hemp or flax, among others) are frequently used with the injection moulding process. Products with complex shapes can be manufactured. The main applications are in structural automotive parts or engineered parts.
So far, PP is the polymer resin used most, although tests have been done with other thermoplastic resins such as polyethylene or nylon, and thermosetting resins such as epoxy, polyester and phenolics.
Natural fibres can also be combined with natural or biodegradable polymers to make 100% bio-based composites. Sometimes these are called bio-composites, although the term relates more to the materials used in the biomedical field. Bio-based polymers can originate from bacteria (produced by micro-organisms following fermentation of natural raw materials such as glucose) or plants (starch, cellulose, or lignin), or be produced through chemical polymerisation of a biological entity (for example, lactic acid can be produced by fermenting beet or potato sugars, but it also can be synthesised chemically).
AtoutVeille is a France-based company which provides technology-watch services in the field of materials made of polymers and composites.
The main field of AtoutVeille’s expertise is to collect and analyze relevant data on raw materials, technologies, machinery or tools used to process these materials.
In the framework of its activity, AtoutVeille plays a key role in the process of innovation for companies (OEMs, subcontractors, moulders) which use or manufacture plastic and composite parts or with companies which want to exploit potentialities of plastics and composites.
Then, AtoutVeille works for several industrial sectors including automotive, aerospace, railway industry, packaging, wind energy, infrastructure, sport and leisure, shipbuilding, amongst others.
fermentation of natural raw materials such as glucose) or plants (starch, cellulose, or lignin), or be produced through chemical polymerisation of a biological entity (for example, lactic acid can be produced by fermenting beet or potato sugars, but it also can be synthesised chemically).
Thus, a broad field of investigation is open to the composite industry for the purpose of integrating these materials – both natural fibres and polymers from renewable sources – and learning more about their potential. There will be some technical and economic obstacles to overcome, and the production chain will certainly need to get together to standardise its offering.
The principal challenge, however, will be learning more about these materials, their properties, their current and potential applications, and their processing requirements.
References: - Perspectives on the performance of natural plant fibres, P. O. Olesen & D. V. Plackett – Natural Fibres Performance Forum, 1999. - Natural fibre reinforcement materials, Scott W. Beckwitt – Composites Fabrication, November/December 2003. - The Eco-Design Handbook, Alastair Fuad-Luke – Thames & Hudson, 2004. - Are natural fibre composites environmentally superior to glass reinforced composites?, S. V. Joshi, L. T. Drzal, A. K. Mohanty & S. Arora – Composites: Part A, 2004. - Use of natural fibres in composites in the German automotive production from 1996 till 2003, Michael Karus – Nova Institut, September 2004. - Fibres naturelles de renfort pour matériaux composites, Christophe Baley – Techniques de l’Ingénieur, 2005. - Etude de marché des nouvelles utilisations des fibres végétales, ADEME/Ernst & Young, December 2005.