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

The electrolytic oxidation of Type AU carbon fibres in an ammonium bic arbonate 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 chemic al state of the nitrogen determined by XPS to be present on the surfac e of Type AU fibre was identified as a protonated amine from the N1s p eak position. Nitrogen was introduced into the surface of the Type AU fibre as a result of the electrolytic oxidation process. From a combin ation of XPS and ToF SIMS it it postulated that this was present as ei ther an aromatic imide or urethane. On the basis of this information a nd composite strength measurements by other authors it is postulated t hat the chemical contribution to the increase in fibre-epoxy bond stre ngth 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 wi th no surface nitrogen such as Type I.