Improving Mechanical Properties of Carbon Fiber Composites Using Ionic Liquid-Modified Carbon Nanotube/Polyimide Sizing Agent

To resolve the critical issues of insufficient interfacial adhesion and susceptibility to brittle fracture in carbon fiber/epoxy (CF/EP) composites, an interfacial reinforcement interlayer was constructed within the interfacial region of the composites. This involved the design of a "rigid-flexible" synergistic reinforcement structure. Specifically, carbon nanotubes were modified with ionic liquids. The resulting modified rigid nanofillers, combined with flexible polyimide, were then firmly bonded to the carbon fiber surface. The construction of this interface layer effectively alleviated stress concentration at the interface and promoted stress transfer from the fibers to the matrix. The results indicated that the tensile strength of CF-ICPI3 increased by 30.02% compared with pristine carbon fibers. Furthermore, relative to pristine composites, CF-ICPI3/EP composites exhibited remarkable improvements in flexural strength, interlaminar shear strength, and storage modulus, with enhancements of 85.52%, 45.26%, and 130.70%, respectively. Additionally, the coefficient of thermal expansion of CF-ICPI3/EP composites decreased by 32.30%. Notably, scanning electron microscopy observations after interlaminar fracture revealed that the failure mode of the composites shifted from interfacial debonding to cohesive failure. In summary, the entire modification process described in this paper is simple to operate and cost-effective. It provides a novel strategy for the application of carbon fiber composites.