POLYDIMETHYLSILOXANE COATED CARBON-FIBERS FOR THE PRODUCTION OF CARBON-FIBER REINFORCED CARBON

HT-fibres (Grafil XAS12K) were coated with thin layers of polydimethylsiloxane in order to prevent or diminish the adhesion of the phenolic resin to the fibre surfaces. The physical and chemical changes of the polydimethylsiloxane layer at various stages of curing and thermal treatment were studied using contact angle measurements, scanning electron microscopy, infrared spectroscopy, and ESCA. It is shown by the various methods that the adhesion can, in fact, be prevented up to 600-degrees-C or 700-degrees-C. Beyond this temperature the polydimethylsiloxane layer is decomposed to silica, which effects a very strong adhesion of the carbonized matrix. This is reflected by an interlaminar shear strength that is 60% higher than that of composites with non-coated fibres.