Effect of sizing on the surface properties of carbon fibres

Abstract

Inverse gas chromatography (IGC) was used in this work to compare the surface properties of carbon fibres covered with two different amounts of an unknown sizing agent with those of fresh and industrially oxidised carbon fibres. Thermogravimetry and elemental analysis provided some clues about the nature of the sizing material. IGC results were analysed in terms of free energies, heats and entropies of adsorption, and surface free energies. Dynamic adsorption of n-alkanes showed that oxidation alone induces a high degree of disorder at the fibre surface, whereas sizing strongly reduces the surface energy of the fibres. Characterisation of the surface chemistry by adsorption of probe molecules with different acid–base character indicated that the oxidative treatment produces both acidic and basic groups, while sizing confers basic properties on the carbon fibre surface.