THE CHEMICAL ENVIRONMENT OF NITROGEN IN THE SURFACE OF CARBON-FIBERS

The electrolytic oxidation of Type AU carbon fibres in an ammonium bicarbonate electrolyte was used as a model for the surface treatment of commercially available Type AS fibres. XPS and ToF SIMS of a range of fibre treatment levels was used to obtain information on the chemical changes at the fibre surface resulting from this treatment. The chemical state of the nitrogen determined by XPS to be present on the surface of Type AU fibre was identified as a protonated amine from the N1s peak position. Nitrogen was introduced into the surface of the Type AU fibre as a result of the electrolytic oxidation process. From a combination of XPS and ToF SIMS it it postulated that this was present as either an aromatic imide or urethane. On the basis of this information and composite strength measurements by other authors it is postulated that the chemical contribution to the increase in fibre-epoxy bond strength was provided solely by the introduced oxygen functionalities. It is proposed that chemical reaction of the protonated amine present on the untreated fibres with the epoxy resin was responsible for the high ILSS of untreated Type A fibre-epoxy composites relative to fibres with no surface nitrogen such as Type I.