Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 1. Comparison between H2SO4 and NaOH solutions

Anodic oxidation of high modulus coal tar pitch-based carbon fibre in alkaline and sulfuric solutions was investigated. X-ray photoelectron spectroscopy (XPS) analysis was used to evaluate the oxygen concentration (O_1S/C_1S) and surface functional groups (---OH, C=O and COOH). The interfacial shear strength between the epoxy matrix and carbon fibre was measured by a fragmentation test. The results showed that the oxygen concentration on fibre surfaces increased rapidly as electrical charge increased, in both alkaline and acidic solution. The best bonding between epoxy matrix and carbon fibre was achieved in alkaline solution. The Raman spectra of carbon fibre oxidized in alkaline and sulfuric solutions suggested that the weak adhesive strength between the epoxy resin and oxidized carbon fibre in sulfuric solution was due to the existence of an oxidized graphite layer, which might easily come off the surface.