The effect of fibre surface treatments during CFRP production on the tensile strength of recycled carbon fibres

Carbon fibre reinforced polymers (CFRPs) are not widely recycled at the end-to-life stage due to challenges associated with the quality of recycled fibres. In the pyrolysis recycling approach, carbon fibres experience reduction in the fibre tensile strength due to oxidative degradation. The variation in CFRPs further leads to inconsistent quality of recycled carbon fibres. The different fibre surface treatments could be part of this complication. It is unclear whether fibre surface treatments would alter the thermal behaviours of CFRP during recycling and lead to different quality of recycled carbon fibres. This study investigates the effects of electrochemical oxidation in ammonium bicarbonate ((NH4)HCO3) bath and fibre sizing with epoxy resin 834 on the quality of recycled carbon fibres. Lab-scale recycling trials were carried out on four types of CFRPs with different fibre surface treatments. The results show that both treatments have limited effects on the thermal characteristics of CFRP during the pyrolysis recycling processes. Recycled carbon fibres from CFRP with these fibre surface treatments experienced a 5.1% - 12.8% reduction in tensile strength compared to the virgin fibres. This study shows that fibre electrochemical oxidation in ammonium bicarbonate and sizing with epoxy 834 during CFRP production have a minor impact on the tensile strength of recycled carbon fibres.