The micro-nano construction of metal-free nacre-like interface for polyimide/carbon fiber composite via multi-molecular grafting method

The multi-molecular grafting interface becomes significant for the perfect structure construction of carbon fiber reinforced composite (CFRC), being built in this study between the epoxy-sized carbon fibers (CFs) and polyimide (PI) matrix via the multi-molecular coupling reactions among the epoxy sizing layer, hydroxyl-rich silicide nanomaterial (SiO 2  OH), and disulfide catalyst. They not only endowed the composite with multiple coupling interactions at the PI/CF interface but also promoted the surface-initiated radical curing reactions on both the sizing layer and the surface of SiO 2  OH. As a result, the SiO 2  OH nanofiller within the PI/CF composite constituted the composite interface with a nacre-like structure, exhibiting superior interfacial shear stability and excellent mechanical properties. The interfacial shear strength (IFSS) of the PI/CF composite reached 1.93 times the original thermally cured ones (value of 144.23 MPa), keeping higher flexural strength and modulus of 2000.1 MPa and 191.0 GPa. The nanofilling effect of SiO 2  OH components endowed the CFRC with structural integrity and mechanical failure mechanism based on the whole fracture of the composite rather than the delamination failure among the CF/matrix multilayers.