Influence of recycled carbon fibre yarn structures on the mechanical properties of unidirectional thermoset composites

Yarns from recycled carbon fibre (rCF) and thermoplastic fibres have shown potential in achieving high mechanical properties in thermoplastic composites. As the thermoplastic fibre component of the yarn melted during the composite manufacturing to form the matrix of the composite, the rCF content of the yarn is equivalent to the rCF content of thermoplastic composites (typically 45-55% by volume). However, in order to use such yarns for thermoset composites from rCF, the yarn must be impregnated with a liquid thermoset resin. To ensure good mechanical properties in thermoset composites, the rCF content in the yarns must be as high as possible. Due to the smooth surface and lack of fibre-to-fibre cohesion, producing yarn or slivers from rCF alone through carding and drawing is highly challenging. As a result, the use of rCF yarns in thermoset composites remains underexplored. This research addresses the knowledge gap by examining the influence of rCF yarn structures on tensile and impact properties of composites. Two yarns were developed using friction and wrap spinning techniques, where a core of rCF is wrapped with thermoplastic filaments or fibres (<10 wt%) to achieve an rCF content of >90 wt%. The developed yarns were impregnated with epoxy resin using the resin transfer moulding technique to produce unidirectional composites. The investigations show that while the compactness, hairiness and processability of the yarn are significantly affected by differences in yarn structure, the tensile and impact properties of the composites remain comparable.