Graphite Fiber Treatments which Affect Fiber Surface Morphology and Epoxy Bonding Characteristics

Abstract

Means of inducing carbonyl functional groups to high modulus graphite fibers (Thornel 50) are described. One approach involves wet chemical oxidation of the fibers in aqueous sodium iodate solution. Another route to hypothesized augmented carbonyl functionality on graphite fibers proceeds through reaction of the fibers in an aqueous dioxane osmium tetroxide solution. In the latter case, coupling of graphite carbonyl to oxirane epoxy is postulated as occurring through an intermediate stannic chloride complex, Bonding of fibers to matrix is shown to be improved with little to no loss in tensile properties of the fibers. As a result of the specificity of the reactions, the surface characteristics of the graphite fibers are revealed when viewed with high magnification scanning electron microscopy (SEM). Based on such observations, a model of the fiber is diagrammed as a compromise of a fibrillar structure and ordered crystallites with tilt and sub-grain boundaries. Also described is a thermal oxidative, polymeric coating treatment which showed modest success in improving graphite fiber/epoxy matrix bonding. Fractured composites in this phase of study indicated unusual fiber anomalies in the form of rod-like extensions from the internal portion of individual graphite filaments.