AN INVESTIGATION OF CARBON-FIBER SURFACE-CHEMISTRY AND REACTIVITY BASED ON XPS AND SURFACE FREE-ENERGY

The surface effects of anodic oxidation on high and low modulus PAN-ba sed carbon fibres are interpreted in terms of surface composition, che mistry, and free energy. High-energy resolution X-ray photoelectron sp ectroscopy has been used to investigate changes in surface chemistry. Data for low modulus oxidised fibres indicate marked increases in surf ace oxygen compared to untreated fibres. This is shown to be due to in creases in surface C-O-, C=O, and COOH. An increase in carbon-nitrogen bonding is also detectable. These changes in chemistry are reflected in an increase in the polar contribution (gamma(s)(p)) to the surface free energy of the fibre. For high-modulus fibre surfaces, the effects of oxidation are less marked, indicating a more graphitic, less react ive surface. The changes observed for low-modulus materials are consis tent with a less ordered structure, with a higher degree of exposed ba sal plane edge area than the high-modulus fibre surfaces.