Surface characterization of carbon fibers and interphase phenomena in epoxy-reinforced composites

Abstract

Fourier transform IR attenuated total reflection spectroscopy has been used to characterize the surface of oxidized graphitized carbon fibers. The spectra of the samples oxidized for different times are compared, and the bands at 1720 and 1580 cm −1, arising from the oxidative treatment, are followed as a function of the oxidation time. A theoretical approach, based on exact optical theory, has been utilized to aid in the interpretation of the results, particularly the enhancement of the IR absorbances of the surface species, due to the presence of the graphitic substrate. The influence of the surface species on the curing of an epoxy system has also been monitored by the same technique. A curve-fitting program has been used to deconvolve the overlapped IR bands of the epoxy coating. The integrated intensities of the ester, anhydride, epoxy and carboxylic acid, plotted against the curing time, clearly show the dependence of the cross-linking process on the concentration of the surface species. The surface groups act as a catalyst for cross-linking and there exists an optimal concentration below which an activation of the curing process occurs. Above that concentration, a retardation of the curing process has been detected.