INFLUENCE OF HEAT-TREATMENT ON SURFACE-PROPERTIES OF EX-MESOPHASE CARBON-FIBERS

Surface properties of carbon fibres prepared from a mesophase pitch were investigated as a function of their final heat treatment temperature (HTT). A complete surface characterisation of carbon fibre was realized by ESCA, ASA and IGC analysis. The surfaces of the carbon fibres, differing from their bulk radial structure, consist principally of basal planes having a high ability to undergo dispersive interactions. As the HTT varies from carbonization to graphitisation, the graphic crystallinites at the surface orient more and more with their basal planes parallel to fibre surfaces. As a consequence, the number of edge carbon atoms at fibre surfaces decreases with HTT and the number of oxygen atoms bonded to them decreases too. The ability of fibre surfaces to undergo specific interactions is proportional to the number of oxygen atoms at fibre surfaces. Increasing the HTT decreases the acidic rather than basic functional groups on fibre surfaces. The ability of fibre surfaces to undergo dispersive interactions is so important that it can not be neglected in characterization of the adhesion between fibre and matrix.