In order to improve the interaction between the reinforcement and the matrix binder, fibre surface modification with micro-organisms is proposed. Enzymatic hydrolysis of surface macro-molecules in aramid fibres leads to the formation of carboxyl groups. If an aqueous solution containing polyvinyl alcohol is the nutrient for the micro-organisms, hydrolysis is followed by the grafting of alcohol molecules onto the fibre surface through etherification. The fibre strength does not deteriorate, but the morphology and the chemical nature of the surface undergo alterations. As a result, wetting by molten thermoplastics is improved. The three-fibre method was used to investigate the adhesion between poly-p-amidobenzimidazole fibres (unmodified and modified) and thermoplastic matrices (polysulphone and polycarbonate). The biochemical treatment almost doubled the bond strength. Examination of the modified fibres, separated from the matrices, by scanning electron microscopy indicated the presence of a diffuse interphase between the fibre and the matrix. In the case of untreated fibres, the adhesional contact failed through interfacial shear; however, with modified fibres both were observed: interfacial shear and cohesive failure in the fibre. Thus, biochemical modification seems to be a simple method for fibre treatment to promote the compatibility of fibres and matrices, and to increase the composite strength.
