XPS study of sizing removal from carbon fibers

X‐ray photoelectron spectroscopy (XPS) was used to investigate the effectiveness of the techniques commonly used to remove polyvinyl alcohol (PVA) sizing from graphitized carbon fibers. Unsized samples of P55 and P100 mesophase‐pitch fibers were used as standards for comparison and the oxygen‐to‐carbon ratio on the fiber surfaces was the primary criterion for judging the degree of sizing removal. No significant change in fiber sizing was found to result from either ‘burn‐off’ in air or soaking in boiling water. Characterization of as‐received sized fiber revealed that the PVA surface undergoes major changes in composition as a result of normal ageing processes. The unsized fibers were found to have extremely low levels of adsorbed oxygen and no detectable hydrocarbons after extended exposure to air. Direct comparison with cleavage surfaces of Ticonderoga graphite showed that unsized pitch fiber surfaces are chemically indistinguishable from the basal plane of graphite, with a very low defect density which decreases with increasing fiber modulus. The implications for carbon‐fiber‐reinforced composite technology are discussed.