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-based carbon fibres are interpreted in terms of surface composition, chemistry, and free energy. High-energy resolution X-ray photoelectron spectroscopy has been used to investigate changes in surface chemistry. Data for low modulus oxidised fibres indicate marked increases in surface oxygen compared to untreated fibres. This is shown to be due to increases 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 reactive surface. The changes observed for low-modulus materials are consistent with a less ordered structure, with a higher degree of exposed basal plane edge area than the high-modulus fibre surfaces.