Anodic surface oxidation for pitch-based carbon fibers and the interfacialbond strengths in epoxy matrices

In order to investigate the mechanism of anodic surface oxidation, pitch-ba sed high-modulus carbon fibers with different surface crystal sizes have be en oxidized in 0.1 M NH4HCO3, and their differential double-layer capacity, C-d, and polarization resistance, R-p, in a buffer solution were measured by the coulostatic method. X-ray photoelectron spectroscopy and laser Raman spectroscopy were also employed to characterize the surfaces. The interfac ial bond strengths in epoxy matrices were evaluated from the interlaminar s hear strength (ILSS) or interfacial shear strength (IFSS). It was found tha t the values measured by the coulostatic method could be used for monitorin g the effect of the anodic surface oxidation because there was a good corre lation between C-d and ILSS. From those characterizations, we have proposed that the mechanism of anodic oxidation of pitch-based carbon fibers is sel ective oxidation and the appearance of prismatic surfaces in the crevices, without a change in the surface crystal sizes. Since the prismatic surfaces have many sites that are chemically active with respect to epoxy resin, ev en after the fibers have been deoxidized, pitch-based carbon fibers show st rong adhesion to epoxy resin, (C) 2000 Elsevier Science Ltd. All rights res erved.