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Abstract: Fibre reinforced composites have excellent specific properties and are widely sought after by engineers seeking to reduce mass. However, end of life disposal is a significant problem and so research into more sustainable natural fibre composites is extremely topical. This paper examines the applicability of natural fibre composites for high performance structural applications. Woven flax and regenerated cellulose (Cordenka) textiles were pre-impregnated with commercially available epoxy resins and consolidated into test laminates in an autoclave to determine their static (compressive, tensile, flexural) and dynamic (energy absorption) properties. The range of compressive strengths was 77.5–299.6MPa. Tensile strengths ranged from 63 to 92.6MPa and interlaminar shear strength (ILSS) from 10.7 to 23.3MPa. Specific energy absorption (SEA) varied between 21.2–34.2kJ/kg. Biotex flax combined with MTM49 resin matched the SEA of T300 carbon fibre using the same resin system and layup. This work has demonstrated that natural fibre composites have significant scope for use in structural applications but additional work is required on fibre to matrix bonding in order to maximise their properties whilst remaining an environmentally credible option. [Copyright &y& Elsevier]

Abstract: This study was designed to ascertain if the addition of lignin to hemp-epoxy composites was beneficial to their mechanical properties. Composites were made using a VARTM method with a two-part epoxy resin and a non-woven hemp fibre mat. Lignin was added to the resin before infusion at concentrations varying between 0 and 10% w/w. Samples were then tested according to the relevant ISO standards. There was an increase in impact properties of the fabricated composites with the energy absorbed by the composite containing 5% w/w lignin being 145% higher than the composite with no lignin added. Both flexural and tensile modulus showed an increase when lignin was added up to 2.5% w/w, although there was a drop in both when the lignin was increased to 5% w/w, attributed to poor mixing and infusion due to the increased viscosity of the resin. In all cases, the addition of lignin increased the structural properties of the composites to some degree when compared with composites with no additional lignin. [Copyright &y& Elsevier]

Abstract: Natural fibre composites represent an environmentally sustainable alternative to conventional glass and carbon fibre composites. Fibres derived from plants are renewable and have low levels of embodied energy compared to synthetic fibres. They are also low cost, low density, have high specific properties, are non-abrasive and less harmful during handling. In motorsport the front and rear impact structures are required to act as both load-bearing members and energy absorption devices. The requirement to absorb large amounts of energy means that the specific energy absorption (SEA) of the material is critical to maintaining a low mass. This work focuses on the potential for natural fibres to replace synthetic fibres for future environmentally friendly energy absorption structures. Conical test specimens of jute, flax and hemp were manufactured using vacuum assisted resin transfer moulding (VARTM) and subjected to impact testing. The natural fibre cones exhibited high values of SEA: unwoven hemp 54.3J/g, woven flax 48.5J/g and woven jute 32.6J/g. The SEA was influenced primarily by fibre volume fraction (Vf) where a high Vf leads to high SEA. Significant variability in SEA resulted from the variation in fibre strength and Vf as a result of the VARTM manufacturing process. Natural fibre composites have the potential to be widely applied as low cost, sustainable energy absorption structures. [Copyright &y& Elsevier]

Abstract: This paper compares the mechanical properties of virgin and recycled woven carbon fibre prepreg and goes on to assess the potential for recycled carbon fibre reinforced plastic (rCFRP) to be used in high performance energy absorption structures. Three sets of material were examined: fresh containing virgin fibres and resin, aged which was an out of life but otherwise identical roll and recycled which contained recycled fibre and new resin. The compressive strength and modulus of rCFRP were approximately 94% of the values for fresh material. This correlated directly with the results from impact testing where rCFRP conical impact structures were found to have a specific energy absorption of 32.7kJ/kg versus 34.8kJ/kg for fresh material. The tensile and flexural strength of rCFRP were 65% of the value for fresh material. Tensile and flexural moduli of rCFRP were within 90% of fresh material and ILSS of rCFRP was 75% that of fresh. Overall rCFRP has been proved to remain a highly satisfactory engineering material. This is a significant finding as it proves that carbon fibre can be recycled and reused in high performance applications. This has significant implications for use of carbon fibre in the automotive industry where End of Life Vehicle (ELV) legislation requires 85% of materials to be recyclable. This work opens the door to significantly expanded use of carbon fibre in the automotive industry. Of equal significance is the finding that the mechanical properties of fresh and aged carbon fibre were all within ±6% of one another. This highlights an opportunity to understand resin system life in more detail in order to prevent the creation of composite waste at source. [Copyright &y& Elsevier]