Non-woven, recycled carbon fibre composites : development of test methods and assessment of process parameters
The embodied energy of carbon fibre is as high as that of aluminium yet the disposal of composite waste presents a challenge for the circular economy. The sustainable use of carbon fibre could be achieved with its reuse in recycled carbon fibre composites. However, their reinforcement architecture is quite different from that of virgin carbon fibre composites. Recycled carbon fibres are generally discontinuous, chopped, fluffy, and entangled requiring further processing. However, their transformation into non-woven textile fabrics and then to cured laminates, has recently become an efficient, cost-effective technique that makes the whole carbon fibre recycling process viable. The development of new materials is generally followed by rigorous material qualification practices to validate their use in intended applications. It is essential therefore to develop reliable datasets to understand their capabilities and mechanical behaviour. Much of the standardised macro-scale test methods for composite characterisation were developed for continuous, fibre-reinforced composite systems and their applicability to non-woven, recycled carbon fibre composites is a gap in knowledge that needs to be addressed. This research identified and adapted experimental test methods that can objectively quantify key material properties for design purposes. On identification of suitable test protocols, a comprehensive experimental programme encompassing tension, shear, fatigue and environmental durability of particular recycled carbon fibre/epoxy composites was undertaken. The project also assessed the effect of fundamental recycling process variables on moulded composite static and fatigue behaviour. It was found that the reinforcement architecture played a significant role in the mechanical behaviour of recycled carbon fibre composites. Test procedures were adapted or modified with significance given to test geometry, load path and failure characteristics. A specification defining appropriate testing protocols was found to be necessary to generate design allowables for the non-woven recycled carbon fibre/epoxy composites. The overriding outcome of this research was a thorough understanding of the influence of recycling processing parameters on the composite laminate performance. It was found that recycled, non-woven carbon fibre/epoxy composites have good fatigue endurance and environmental durability. The overall outcome of this research provides a rigorous basis for selection approaches of sustainable materials for various potential structural applications in the transportation industry.
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