Synergistic interlaminar strengthening of unidirectional carbon fiber-reinforced composites using carbon nanofiber-modified sizing on the surface of PET interleaves

Abstract

A unidirectional carbon fiber-reinforced composite with excellent interlaminar fracture toughness (ILFT) was fabricated, analyzed, and evaluated. The composites were formed by inserting polyethylene-terephthalate (PET)-based thermoplastic veils between prepregs to enhance the ILFT. Carbon nanofiber (CNF)-modified coupling agents were spray-deposited onto the PET veil surface to minimize the reductions in the tensile strength and modulus of the composites caused by the use of thermoplastic veils and maximize the enhancements in the ILFT. The microfibers of the PET veils endowed the composites with delamination resistance, whereas the coupling agents and CNFs coated on the PET surface induced chemical bonding and mechanical interlocking with the epoxy matrix, respectively. Therefore, multiscale reinforcement mechanisms, including these mechanical and chemical interactions, generated a synergistic effect on the mechanical properties of the composites. Reductions in the tensile strength and modulus of the composites decreased by up to 104.7% and 100.8%, respectively, following the application of the CNF/coupling agent-modified PET interleaves, and their Mode-Ⅰ and Mode-Ⅱ ILFT values increased by up to 105.3% and 610.9%, respectively, compared with those of neat composites.