The interface region in glass fibre-reinforced epoxy resin composites: 3. Characterization of fibre surface coatings and the interphase

It is well known that application of a coupling agent to a glass fibre surface will improve fibre-matrix adhesion in composites. However, on a commercial glass fibre the coupling agent forms only a small fraction of the coating, the larger part being a mixture of processing aids whose contribution to composite properties is not well defined. The interfacial region of the composite will therefore be affected not only by the composition of the coating, but also by its distribution on the glass fibre surface and in the composite matrix. We have used a wide range of analytical methods to investigate these coatings, both on the glass fibre surface and in the composite. These techniques included Fourier transform infra-red spectroscopy (FTi.r.), nuclear magnetic resonance spectroscopy (n.m.r.), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (s.i.m.s.), differential scanning calorimetry (d.s.c.), dynamic mechanical analysis (d.m.a.) and contact angle measurements. Information was obtained on the composition of the coatings, their transition temperature and their distribution on the glass fibre surface. Results indicate that the coupling agent on these commercial glass fibres may have already reacted with another component of the fibre coating. The effect of an interphase around the fibre, caused by incomplete dissolution of the coating in the matrix, was determined by d.m.a, and the chemical nature of the interphase was investigated using scanning s.i.m.s.