Modulating impact resistance of flax epoxy composites with thermoplastic interfacial toughening

The application of natural flax fibre/epoxy composites is growing in the automotive sector due to their good stiffness and damping properties. However, the impact damage resistance of flax/epoxy composites is limited due to the brittle nature of both epoxy and flax fibres and strong fibre/matrix adhesion. Here, biobased thermoplastic cellulose acetate (CA) is deployed as a fibre treatment to alter the damage development of flax/epoxy composites subjected to low-velocity impact. The perforation threshold energy and the perforation energy of unmodified cross-ply composites increased respectively by 66% and 42% with CA-treated flax fibres. The CA-modification modestly decreased the transverse tensile strength and in-plane tensile shear strength of the composites. However, it altered the brittle nature of flax/epoxy laminates in quasi-static tests into ductile failure with clearly increased fibre-matrix debonding.