Influence of CNTs on the gradient phase structure formed by the layered resin structure used to model the interlaminar region of interleaved FRPs

The interleaved fiber-reinforced polymer composites (FRPs) by carbon nanotubes (CNTs)/thermoplastic polyetherketone-cardo (PEK-C) hybrid interleaves show the potential of comprehensively improving the mechanical properties of composites and have been hotspot. However, the synergistic effect and mechanism of CNTs and TP resin have not been attained. The interlaminar region of interleaved composites is too narrow and complex to be fully analyzed. Therefore, the layered resin structure composed of an interlayer and a matrix (epoxy) layer was prepared to model the interlaminar region in this study. The evolution of gradient structure developed by the layered structure in curing and the influence of presence of CNTs in interlayer were investigated based on morphology characterization. The results showed that epoxy resin gradually diffused into the interlayer, resulting in the concentration gradient and the resultant gradient phase structure. The presence of CNTs in hybrid interlayer hindered the resin diffusion and consequently hindered the formation of dual-phase structure, which was not conducive to the toughness improvement. The inappropriate high temperature was not recommended due to the effect of facilitating diffusion, probably resulting in the formation of excrescent epoxy layer in the interlaminar region and undesired mechanical performance. This study conducted experiments on resin system to simplify the interesting subject and the results will help to develop the synergistic mechanism of TP resin and nanoparticles.