Effects of Surface Treatment of Carbon Fiber: Tensile Property, Surface Characteristics, and Bonding to Epoxy

In this article, effects of electrochemical oxidation and sizing treatment of PAN-based carbon fibers (CFs) on the tensile properties, surface characteristics, and bonding to epoxy were investigated. As found, the electrochemical oxidation improves the tensile strength of single CF by 16.0%, due to weakening the surface stress concentration and smoothing the surface structure. Further sizing treatment shows a negligible effect on the tensile strength. Both oxidation and sizing treatments significantly improve the wettability and surface energies of CFs by introducing oxygen-containing functional groups. Microbond test was conducted to characterize the interfacial shear strength (IFSS) between a single fiber and an epoxy droplet. The oxidation treatment increases IFSS slightly, which is due to the contradictory effects of the formation of chemical bonds between the resin and CFs, and the reduced mechanical interlocking. Further sizing treatment significantly enhances IFSS from 73.6 to 81.0 MPa, due to the formation of vast chemical bonds. Furthermore, the oxidation and sizing treatment can effectively reduce the degradation of IFSS to the hygrothermal ageing for the CF/epoxy system. (C) 2015 Society of Plastics Engineers