Effect of carbon fiber surface chemistry on the interfacial properties of carbon fibers/epoxy resin composites

Polyacrylonitrile-based carbon fibers were electrochemically oxidized under a wide variety of current densities, and then surface changes in the morphological structures and the chemical compositions were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Finally, the effects of carbon fiber surface chemistry on the interfacial properties of carbon fiber reinforced composites were researched. The results showed that surface contaminants generated during the production process were removed and the relative contents of oxygen and nitrogen elements increased by 322% and 432%, respectively, after the electrochemical oxidation. Increases in the O/C and N/C ratios resulted in the increase in the interlaminar shear strength values of composites. However, much higher O/C and N/C ratios led to decline in the interlaminar shear strength values. Carboxyl groups were responsible for strong interactions between carbon fiber surfaces and the epoxy resin. When the current densities were more than 5 A/m(2), the interfacial bonding between carbon fibers and the epoxy resin became weak and the interlaminar shear strength values also decreased.