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A new family of high-performance natural fibre reinforcements have been developed using a novel ‘twistless’ yarn technology. These sustainable materials have been designed to overcome the limitations of existing natural fibre products and have been launched commercially.
DR BRENDON WEAGER, TECHNICAL MANAGER, COMPOSITES EVOLUTION LTD.(Published on February-March 2010 – JEC Magazine #55)
There is currently a dramatic surge in interest in environmentally sound materials and technologies in virtually every industrial sector and global region and composites derived from natural, renewable resources have a significant role to play. Natural fibres such as hemp, flax and wood are already used in the automotive industry to reduce weight, cost and environmental impact. In fact, on a stiffness-for-weight basis, natural fibres can have equal or superior properties to glass fibres.
The natural fibres currently used in composites tend to be short and randomly oriented, which means the composite mechanical properties are relatively low and the applications are limited to nonstructural parts. It is well-known that fibres provide the highest strength and stiffness when they are continuous and aligned in the direction of applied load. Natural fibres are naturally discontinuous and conventional spun yarns tend to be highly twisted which leads to fibre misalignment and poor wet-out.
An exciting recent advancement has been a new family of aligned natural fibre reinforcements developed by a UK-based consortium, which has overcome these issues by using novel ‘twistless’ yarns. The Combine project, co-funded by the UK Technology Strategy Board, was initiated to develop higher performance natural fibrereinforced composites suitable for use in structural or semistructural applications. Following successful development, the materials have been launched commercially with the name Biotex and are available in flax, commingled flax/PP and commingled flax/PLA versions.
Biotex high-performance natural composites: - Flax, commingled flax/PP and commingled flax/PLA- Yarns, fabrics and pre-consolidated sheets- “Twistless” yarn technology- Sustainability, performance and processability
Hemp and flax fibres were selected because they have good mechanical properties and can be grown in European climates. The fibres have been improved by developing the agronomy, retting (where bacteria loosen the fibres in the crop stem) and fibre extraction processes, and investigating treatments to improve the fibre-matrix bonding. The work initially focussed on thermoplastic matrix polymers including polypropylene (PP) and polylactic acid (PLA), a biopolymer from corn starch. In particular, the effects of polymer viscosity and compatibilising additives on consolidation and fibre-matrix bonding were studied.
Natural fibre yarns have been developed using novel ‘twistless’ spinning techniques thereby producing continuous reinforcements with straight fibres, good mechanical properties and good wet-out and impregnation. Woven fabrics were produced from the yarns in a range of weave styles designed to minimise crimp and maximise drape (Figure 1). Yarns and fabrics were produced from flax and hemp to be suitable for reinforcing thermosetting resins such as unsaturated polyester (UP), epoxy or bioresins. In addition, novel commingled yarns and fabrics containing blends of natural fibres (flax or hemp) and thermoplastics (PP or PLA) have been developed for rapid moulding of thermoplastic biocomposites - the thermoplastic melts on heating to form the matrix of the composite.
Processing & performance
The new high-performance natural fibre reinforcements have been evaluated in a range of standard composite processes. The flax fabrics were readily processed by hand lay-up and vacuum infusion, whilst the commingled natural fibre-thermoplastic materials were successfully processed by vacuum consolidation and hot press moulding (Figure 2). For the commingled thermoplastic materials, the optimum fibre content was 40% by volume, the best processing temperature was 190°C and pressures of 1-50bar were suitable. The laminates were subjected to a range of tests including tensile, flexural and impact and typical results are in Table 1.
Table 1: Typical properties for the new natural fibre composites
40 vol%woven flax/PLA
40 vol%woven flax/PP
33 vol%woven flax/UP
Tensile strength (MPa)
The recyclability of the novel biocomposites has also been studied. Flax/PLA laminates were shredded, regranulated, injection moulded and tensile tested and this cycle was performed 5 times. The strength of the recycled material reduced by 10% with each round of recycling but the modulus was unaffected. Flax/PLA is also biodegradable and compostable in the correct conditions.
A range of prototype components (Figure 3) have been developed from the new high performance biocomposite materials including a marine headliner panel from Fairline Boats and two interior automotive parts from Jaguar and Land Rover. Biotex flax/PP fabric was selected by Jaguar and Land Rover due to its combination of good mechanical properties and environmental credentials.
Prototype door modules from both Land Rover Defender and Jaguar XF models were manufactured and their performance compared to current production parts. The biocomposite Defender Front Door Module was approximately 60% lighter than the current steel part at the same stiffness, while the Jaguar XF Rear Door Module was 35% lighter than the current glass filled PP component for the same thickness. Detailed component evaluation is underway.
Following successful development, the materials have been launched commercially as Biotex, backed up by 130 years of experience in spinning and weaving natural textiles and decades of experience in composite materials, processing and applications. The unique twistless technology used in these materials provides a combination of sustainability, performance and processability not previously seen in composites. For the first time, natural fibre composites can provide high levels of performance and the ease of processing normally associated with glass reinforced materials. There are currently three material options - flax, commingled flax/PP and commingled flax/PLA – and the formats available include yarns, woven fabrics and preconsolidated sheets. The materials are already receiving significant interest from a host of sectors including automotive, construction, marine, sports and consumer goods.
These materials were developed during the Combine project, which was co-funded by the UK Technology Strategy Board's Collaborative Research and Development programme (contract no. TP/5/SUS/6/I/H0284C). The contributions of the project partners NetComposites, Queen Mary University of London, Springdale Natural Products, Tilsatec, John L. Brierley, Sam Weller & Sons, Millfield Composites and Fairline Boats are gratefully acknowledged.