Interfacial Strengthening of Carbon Fiber/Polypropylene Composites via a Modified Acrylate Nanoemulsion

In order to enhance the interfacial bonding between carbon fibers (CFs) and the polypropylene (PP) resin matrix, the modified acrylate nanoemulsion was prepared by emulsifying modified chlorinated polypropylene (CPP) by phase conversion. The nanoemulsion is safer and environmentally friendly than commercial solvent-based nanoemulsions. The nanoemulsion possesses good stability owing to its regular droplet shape and uniform distribution (droplet size <100 nm, absolute zeta potential >40 mV) and is highly suitable for PP resins. The surface properties of CFs, including chemical composition, morphology, wettability, and interfacial adhesion were systematically investigated. Compared to unsized CFs, the surface roughness of sized CFs was reduced and the surface wettability was improved due to the increased surface oxygen content. As the nanoemulsion was uniformly coated on the CFs, the tensile strength and the interlaminar shear strength (ILSS) of the composite were both enhanced. Specifically, the ILSS of the composite sized with the P3 nanoemulsion has increased by 48.5%, indicating that the composite’s mechanical strength and interfacial bonding significantly improved due to the nanoemulsion. On this basis, a dual physical and chemical interfacial strength mechanism of the nanoemulsion in the composite was proposed, and an effective and feasible method was proposed to solve the weak interfacial bonding between CFs and PP.