Enhanced interfacial and mechanical properties of high-modulus carbon fiber composites: Establishing modulus intermediate layer between fiber and matrix based on tailored-modulus epoxy

Tailored-modulus epoxy matrix was designed on basis of surface analysis of high-modulus carbon fibers (HMCF), and the effects of modulus intermediate layer on interfacial and mechanical properties of HMCF composites were investigated. Narrow grooves and active functional groups were detected on HMCF surface. The modulus of epoxy was tuned by stiff organic molecular structure of cycloaliphatic epoxy (CE) and amide acid (AA). Modulus intermediate layer was established along with modulus gap shrinkage and interphase extension between HMCF and high-modulus epoxy, causing remarkable improvements in interfacial properties of composites. Schematic model of interphase reinforcing mechanism was proposed, and modulus intermediate layer with a platform in the composites with high modulus epoxy matrix could facilitate the shift in stress concentration and suppress initiation and propagation of cracks, which resulted in improved mechanical properties of HMCF composites by enhancement of interfacial bonding and stress transfer capability between fiber and matrix.