Interlaminar fracture toughness behaviour of carbon fibre reinforced polymer with epoxy-dicarboxylic acid vitrimer matrix

Healable and recyclable fibre reinforced vitrimer composites have been developed by taking advantage of the mechanical strength and topological rearrangement via bond exchange reaction. While the tensile properties of vitrimer laminates have been extensively studied, interlaminar properties have yet to be demonstrated. Experiments on mode I interlaminar fracture toughness and flexural characteristics of carbon fibre reinforced polymer (CFRP) composites based on epoxy-dicarboxylic acid vitrimer with various epoxy:acid ratios are presented in this paper. By hand lay-up and hot press, two vitrimer laminates with epoxy:acid ratio of 1:0.5 (off-stoichiometric, C50/CF) and 1:1 (stoichiometric, C100/CF) were successfully fabricated. From the flexural test, both C50/CF and C100/CF reveal marvellous stiffness of ∼60 GPa. Additionally, C50/CF also shows excellent flexural strength of 821 MPa which is in a similar range to conventional anhydride epoxy CFRP composites. In terms of interlaminar fracture properties under mode I loading, vitrimer CFRP composites outperform standard epoxy laminates on mode I fracture energy at initiation and propagation zones. At the initiation stage, fracture energies of C50/CF and C100/CF are two times higher than those of epoxy/CF. Furthermore, the average fracture energies during crack propagation of C50/CF and C100/CF were increased by ∼42% and ∼63%, respectively, when compared to epoxy/CF. The fracture surfaces of vitrimer laminates revealed matrix residue on the fibres, demonstrating that vitrimer and carbon fibres had good interfacial adhesion. These findings revealed a huge potential for further development of vitrimer CFRP composites for advanced applications.