Surface repair of carbon fiber via direct fluorination and its advanced composites

Abstract

Surface defect and insufficient interfacial combination become non-negligible issues for limiting mechanical strength of carbon fiber and their composites. Utilizing long-term radical among sizing agent induced by direct fluorination, it is found that fluorinated sizing agent on carbon fiber could be naturally grafted onto fiber surface as in-situ contacting, which highly improved its tensile strength over 10%. Utilizing the nucleophilic substitution reaction between C-F bonds and amine-cured epoxy resin, fluorinated carbon fiber surface formed controlled covalent bonding in resin-based composite interface. Molecular Dynamics (MD) and mechanical experiments simultaneously revealed the optimized stress transfer was mainly contributed by covalent-interface provided synchronous deformation and resulted stress response, thus the interlaminar shear strength (ILSS), flexural strength and modulus of fluorinated carbon fiber reinforced composites respectively increased by 32.8%, 10.0% and 38.5% at maximum. Besides, due to the covalent interface highly reduced its free volume, composite saturated water uptake decreased to 0.63% thus its mechanical retention after hygrothermal aging reached 92.7%, and the interfacial thermal resistance also decreased to obtain much better heat disspation capacity than before. Therefore, direct fluorination provided a large-scaled route for manufacturing advanced carbon fiber and its composites towards potential challenges in future application.