Recycled carbon fibre mats for interlayer toughening of carbon fibre/epoxy composites

Abstract

Exploring routes for the effective use of recycled carbon fibres (rCFs) is critical to close the loop in the life cycle of carbon fibres. This work demonstrated a potential of using rCFs for interlayer toughening of carbon fibre/epoxy composites. Nonwoven mats based on rCFs and commingled rCFs/Polyphenylene-sulfid (PPS) fibres were used to interlay a laminate, aiming to improve the mode-I and mode-II fracture toughness. The experimental results proved significant enhancements in the interlaminar fracture properties upon interleaving, with the rCF/PPS mats exhibiting a more prominent toughening effectiveness than the rCF mats. For example, the maximum increase in mode-I and mode-II fracture initiation energies of the laminates was 51% and 66%, respectively upon interleaving the rCF mats, and 220% and 105%, respectively by adding the rCFs/PPS mats. The fractography analysis proved that the main toughening mechanisms were fibre debonding and pulling-out for the rCF mats and fibre bridging for the commingled rCFs/PPS mats. The differences in the toughening mechanisms resulted in opposite effects of the interlayer/epoxy adhesion to the fracture toughness, i.e. an improved interlayer/epoxy adhesion increased the toughening effectiveness of the rCF mats, but negatively affected the toughening performance of the rCF/PPS mats.