Effects of degree of chemical interaction between carbon fibers and surface sizing on interfacial properties of epoxy composites

Abstract This paper offers a simple approach to increase the interfacial bonding strength of carbon fiber/epoxy composites by optimizing the degree of chemical interaction among functional groups of fiber surface, sizing agent and resin via heat treatments on carbon fibers. 130 °C treatment on CF1 and 150 °C treatment on CF2 results respectively 71.1% and 15.1% improvements on interfacial shear strength (IFSS), as compared with untreated CF1 and CF2 composites. Variations of IFSS for heat treated carbon fibers correspond well to dispersion component to polar component (γ d /γ p ) tendency of desized heat treated fibers. The work of adhesion between heat treated fibers and resin matrix only reveals close correlation with IFSS trend for CF1/epoxy composites, while not applicable for CF2/epoxy composites. With increasing heat treatment temperature, the decreasing γ d /γ p of desized fibers indicates increasing degree of chemical interaction between fibers and surface sizing, which was also proven by the results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. High degree of chemical interaction between fibers and surface sizing is adverse to the interaction between sizing and resin matrix, and thus lower the IFSS.