Development of multifunctional, toughened carbon fiber-reinforced composites

The substitution of fiber-reinforced composite materials for heavier metallic structures in the design of aircrafts contributes to enhanced fuel economy with reduced emissions. However, the use of these materials is limited by the brittle, insulating polymer adhesive between the load-bearing fibers. Thus, the addition of multifunctional nanoparticles for multiscale reinforcement may hold the key to tailoring the matrix-dominated properties, particularly as the cost of nanoparticles are reduced to industrially relevant levels. In this paper, stacked-cup carbon nanofibers (CNF) and elastomeric triblock copolymers were dispersed in the matrix phase of carbon fiber-reinforced composites based on highperformance epoxy systems. Improvements of ∼22-40% in short beam shear strength were observed with the incorporation of 1 part per hundred resin (phr) CNF. The addition of the soft triblock copolymer enhances tensile strain to failure but also yields a slight degradation in modulus and strength. However, these degradations were offset by the addition of CNFs. The interlaminar fracture toughness increases by ∼25% over the base composite with the addition of 1 phr CNF, yet the addition of triblock copolymer yields no further improvement despite yielding a 50% enhancement over the base composite. Scanning electron microscopy images of fracture surfaces reveals local energy dissipation processes brought about by the nanostructured phases, as well as significant CNF agglomeration which limits their efficacy and leads to stress concentrations, which is confirmed by the lack of enhancement in transverse electrical conductivity. These results show good promise for CNFs as low-cost reinforcement for composites, but they also highlight the importance of attaining good dispersion in order to realize the full potential of the nanoparticles.