Decoupling the contributing factors to material degradation during carbon fibre recycling

The increasing use of carbon fibre-reinforced polymers (CFRP) across aerospace, wind, and automotive sectors is causing an increase in carbon fibre waste. Current recycling methods for CFRPs often lead to reduced material properties of recycled carbon fibre (CF) – a combined effect of various changes to the material introduced by the recycling process. One of these contributing factors is the removal of sizing layer, a common surface treatment for virgin CF, on recycled CFs and the subsequent recycled CFRPs (rCFRPs). This study attempts to de-couple the effect of sizing removal (de-sizing) on the mechanical performance of CFs and their corresponding rCFRPs from the effect of recycling. Original and de-sized virgin CF were analysed through an experimental procedure of manufacturing into composites, recycling, and remanufacturing into rCFRPs. Testing and characterisation were conducted to evaluate tensile and surface properties of fibres as well as flexural properties of composites. We found that de-sizing resulted in reductions in tensile properties of virgin CF, but the combined effect with recycling is not aligned with the degradation experienced by sized CF. The inconclusive result is likely due to the different mechanisms for removing the sizing layer during recycling compared to the de-sizing procedure. Further research is encouraged to analyse pristine un-sized fibres using similar methods and investigate other factors that influence composite properties to provide more insights into the effects of recycling and sizing removal on recycled CF properties.