The effect of low power plasmas on carbon fibre surfaces: A comparison between low and high modulus PAN based fibres with pitch based carbon fibres

Abstract

A comparison of the effects of a variety of low power (<1W) plasmas (air, NH 3 and N 2) on highly ordered pyrolytic graphite (HOPG), polyacrylonitrile (PAN)-based and pitch based carbon fibres has been studied using X-ray photoelectron spectroscopy. Grazing angle techniques have been used to probe only the first 12–15 Å of the fibre surface. Plasma treatments were carried out in an in situ plasma cell which was attached to a PHI 5400 X-ray photoelectron spectrometer. This enabled the immediate effects of the plasma to be studied before the treated surface was exposed to air. The reactivity towards a particular plasma is shown to be largely dependent on the structure of the fibre surface. Air plasmas are much more reactive to the fibre surface than either nitrogen or ammonia plasma. Hydroxyl and carboxyl groups are detected on PAN based fibres where as only hydroxyl groups were detected on pitch based fibres and HOPG. Both ammonia and nitrogen plasmas were successful in introducing aliphatic and aromatic amines (C-NH 2) together with small number of immines (-CNH). The number of C N groups produced on the higher modulus fibres was undesirably low. Their concentration was increased by biasing the fibres to a negative potential (10–30V) during plasma exposure. Examination of these treated fibre surfaces showed that little, if any, etching of the fibre surface had taken place and hence damage to the fibre was minimal.