Effect of electrolytic oxidation upon the surface chemistry of type A carbon fibres—Part II, analysis of derivatised surface functionalities by XPS, and TOF SIMS

Abstract

Type AU carbon fibres were electrolytically oxidised in aqueous ammonium bicarbonate and were analysed by time-of-flight secondary ion mass spectrometry (TOF SIMS) and, after derivatisation, by X-ray photoelectron spectroscopy (XPS). The reaction of trifluoroacetic anhydride vapour with model polymers and carbon fibre surfaces were examined to enable the surface hydroxyl group concentration [OH]to be determined. The conditions required for the stability of the label is discussed. The [OH]increased in a similar way to the overall oxygen concentration over the range of degree of fibre treatments (DFT) considered. Aqueous barium labelling was also employed to determine the carboxylic acid concentration [COOH], which also followed a similar trend to that of the total oxygen signal. The relative O − and CN − ion signals in the SIMS spectra from samples of differing DFT were also observed to increase in a similar way. These were followed using the normalised peak intensity (NPI) parameter. Epichlorohydrin (ECH) was adsorbed onto the surface to determine the reactivity of the fibres of differing DFT to the epoxy functionality. A polymeric deposit was observed to result from the reaction with ECH, which complicated the analysis and prevented the use of the chlorine concentration as a measure of ECH fixation. Instead, fibre nitrogen signal attenuation was used as a measure of the quantity of material adsorbed; this provided a qualitative assessment of the reactivity of the fibres to the epoxide. The level of ECH fixation increased in line with that of the oxygen functionalities, and is consistent with the assertion that these react with the epoxy group.