Effects of carbon nanotubes grafted on a carbon fiber surface on their interfacial properties with the matrix in composites

Carbon fibers (CFs) were oxidized by concentrated HNO₃ and then reacted with polyamidoamine dendrimers (PAMAM) with an average molecular weight of 157 to form CF-PAMAM. The CF-PAMAM was further reacted with oxidized carbon nanotubes (CNTs) to form CF-PAMAM-CNTs that were used as the reinforcement for epoxy resin-based composites. The functional groups and structure of the CF-PAMAM-CNTs were examined by XPS, SEM and AFM, and their wettability and the tensile strength were investigated by contact angle measurements and single strand extension respectively. The interfacial shear strength of the composites was measured by a micro-debonding method. Results showed that, compared with CFs, the surface roughness, surface energy and tensile strength of the CF-PAMAM-CNTs were increased by 180%, 300% and 22%, respectively when the CNT content was 15 mass%. The interfacial shear strength of the composite reinforced with CF-PAMAM-CNTs was increased by 178% for the same CNT content, which showed that the grafted nanotubes improved the interfacial properties of the filler with the matrix.