Influence on fracture toughness arising from controlled morphology of multiphase toughened epoxy resins in the presence of fibre reinforcement

Numerous studies found in the literature focus on enhancing the fracture toughness of thermosetting polymers by incorporating various toughening agents. The resulting gains in fracture toughness are mostly attributed to an expansion in the volume of the plastic deformation zone ahead of the propagating crack and the modified resin blends are subsequently introduced as matrices for fibre reinforced composite materials. It is often assumed that improvements in fracture toughness of the polymer matrix are directly transferred to the resulting fibre reinforced composites. This paper shows that this is not necessarily the case. The present study is focused on the fracture behaviour and phase morphology of the continuous carbon fibre reinforced polymer composites (CFRPs) based on resin systems modified by including carbon nanotubes and a phase separating thermoplastic (TP) toughener. It is shown that the presence of fibre reinforcement influences the phase distribution in TP modified epoxies, where the toughening potential of the deformable TP phase is curtailed. Incorporating high aspect-ratio CNTs is an effective means to control and enhance the uniformity of the multiphase morphology, hence further improving the interlaminar properties of CFRPs. This is shown to be due to the interference of the CNTs in the kinetics of the reaction induced phase separation by affecting the polymer diffusion rate.