Effect of oxygen plasma treatment on mechanical properties of vapor grown carbon fiber nanocomposites

The changes in mechanical properties of vapor grown carbon fibers (VGCF)/epoxy nanocomposites, such as storage modulus, fracture toughness, and Izod impact strength, are investigated in this study. The dependence of these mechanical properties on the content of VGCF and adhesion at the interface between VGCF and anhydride-cured epoxy matrix are discussed. Three VGCF with and without oxygen plasma treatment for surface modifications were used in this investigation. To fabricate nanocomposites, the VGCF were sonicated in acetone for two hours. The dispersion of the VGCF was investigated by scanning electron microscopy (SEM), and SEM micrographs showed an excellent dispersion of VGCF in epoxy matrix. Compact tension (CT) specimens were used for fracture testing. The fracture toughness increased with increasing VGCF content and reached the plateau values. The fracture toughness of plasma treated VGCF/epoxy nanocomposites showed lower value than that of untreated VGCF/epoxy nanocomposites. It was because of strong adhesion at the VGCF/epoxy interface, which did not allow dissipation of energy. The Izod impact strength decreased with oxygen plasma treatment, due to better adhesion at VGCF/epoxy interface. Different morphologies of the fracture and impact failure surfaces, highly dependent on the oxygen plasma treatment of dispersed VGCF, were observed using field emission SEM.