Chemical modification and adhesion in carbon fiber/epoxy micro‐composites; coupling and surface coverage

Abstract Four compounds were used to improve adhesion between carbon fibers and an epoxy matrix. Triglycidyl isocyanurate (TGIC) and 3‐glycidoxy‐propyl‐triethoxysilane (EPS) contained reactive epoxy groups, while N‐(3‐trimethoxysilane‐propyl)ethylene diamine (AMS) a primary and a secondary amino group. The fourth coupling agent was 4,4' diphenylmethane‐diisocianate (MDI). The interaction of the fiber and the coupling agents was studied by dissolution experiments. Chemical reactions taking place on the surface of the fiber were followed by FTIR spectroscopy. Interfacial shear stress determined by fragmentation was used for the characterization of matrix/fiber adhesion. Beside coupling to the surface, EPS, AMS and MDI formed a polymer layer on the surface, but TGIC also entered into secondary reactions during the treatment. Both the type and the amount of the coupling agent affects strongly interfacial adhesion, which is determined by the thickness and properties of the formed coupling agent layer. The combination of dissolution experiments with the fragmentation test yields valuable information about the processes taking place on the surface of the fiber, facilitate the selection of the best coupling agent, as well as the development of surface treatment technology.