Surface characterization of carbon fibres and interfacial properties of carbon fibre composites

The surface characteristics of carbon fibres treated by electrochemical oxidation have been determined, and the effect of these properties on the interfacial adhesive strength (interlaminar shear strength (ILSS) and transverse flexural strength) of epoxy-matrix composites investigated. The surface properties of the carbon fibres were dependent on the nature of the electrolyte used during the electrochemical oxidative treatment. Use of a basic electrolyte resulted in an improvement of composite ILSS and transverse flexural strength due to an increase in the number of surface functional groups. On the other hand, using an acid electrolyte resulted in the ILSS increasing with the number of surface functional groups, while the transverse flexural strength decreased for composites in which the carbon fibres had a high surface oxygen content. It is concluded that the weak boundary layer derived from fissures on the surface of carbon fibres treated in an acid electrolyte decreased the transverse flexural strength.