Improved Mode II delamination fracture toughness of composite materials by selective placement of protein-surface treated CNT

Abstract The recently invented SP1 protein treated CNT are utilized in this study together with the concept of selective application of nanoreinforcement to critical sections in composite structures – studied here for Mode II interlaminar fracture toughness and interlaminar shear strength of woven carbon fiber/epoxy laminates. Specifically, a treated carbon nanotube-reinforced epoxy leaf is inserted at the midplane of the laminates and the fracture properties are measured by end-notched-flexure and 3-point bend tests. It is shown that addition of a small amount of treated carbon nanotubes at the midplane of the composite results in an 85% improvement in the interlaminar fracture toughness, without deteriorating the interlaminar shear strength. This is taken as a strong indication of the unique properties of the protein-treated CNT and as strong support for the concept of selective placement of nanoreinforcement in critical sections with high stress concentrations instead of their wasteful dispersion throughout the structure. The study reveals that the unique contribution of the SP1 protein stems from its ability to bind simultaneously to the CNT and carbon fibers and to the epoxy matrix.