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Materials


Fig. 3. Door bolsters in the Ford Escape use kenaf fibre.


like flax. Flax fibres have similar mechanical properties to established materials: their Young’s modulus is comparable with that of glass fibre, while their elongation at break approaches that of carbon fibre. Also, their density (at 1,45g/cm3


) is lower than any


conventional fibre. The panels would be produced by pressing together


a pre-impregnated fibre material with thermoplastic sheets. The partners aim to develop a resin that cures within 15 minutes.


Wood in the car


Automotive giant Ford is testing a cellulose fibre-based plastic called Thrive - from Canadian wood products supplier Weyerhaeuser - for stiffness, durability and temperature resistance. As well as cutting carbon footprint, Ford discovered


other advantages of the material: it created parts that were 10 per cent lighter - and could be made 20-40 per cent faster - than those using traditional glass fibres.


“Using composites with cellulose fibres makes sense,”


said Ellen Lee, plastics research technical expert at Ford. “Their excellent thermal stability allows us to extend the range of potential automotive applications for natural fibre materials. With increased use of these renewably sourced materials, we can reduce the


environmental footprint of our products while accruing a variety of benefits across our entire supply chain.” This material is only one example of natural fibre


reinforcement used in Ford cars: the Flex uses wheat straw filler in its plastic bins; door bolsters in the Escape use kenaf fibre; and the Focus Electric uses a wood fibre-based material in its doors. Weyerhaeuser says that Thrive will initially be used


in household goods and automotive parts, but also has potential for office furniture, kitchenware, small and large consumer appliances and other industrial goods. It is available in as a masterbatch for custom compounders, or as ready-to-mould thermoplastic pellets for moulders. “Thrive composites are low mass, yet demonstrate


excellent tensile strength and flexural properties,” said Don Atkinson, vice president of marketing and new products for Weyerhaeuser’s cellulose fibres business. “They can improve moulding cycle times by up to 40 per cent.” He added that the compounds also caused less wear


and tear on processing equipment compared with those containing glass fibres. The compounds are available as cellulose blended


with polypropylene (PP), with both high and low melt flow indices. Because cellulose fibres are compatible with many polymers, Weyerhaeuser plans to expand their use beyond PP. ●


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