Strengthening Interface Transition Layer of Carbon Fiber/Epoxy Composites with CNTs and Its Effect on Interfacial Performance

The sizing treatments were used to introduce carbon nanotubes (CNTs) to carbon fiber (CF) surfaces for fabrication of CF/CNTs/epoxy multi-scale composites. Comparing with the base composites without CNTs, interlaminar shear strength (ILSS) and flexural strength of the modified composites were increased by 13.54% and 12.88%, respectively. Force modulation atomic force microscope and linear scanning system of scanning electron microscope were carried out to analyze the microstructure of composite interface. The results indicate that a transition layer reinforced by CNTs is constructed between fiber and epoxy (EP) matrix, which has certain thickness and exhibits gradient distribution of modulus and carbon element content. The composites containing CNTs are sonicated before curing to disperse CNTs in the surrounding resin. As a result, the interface transition layer is weakened and the ILSS and flexural strength of prepared composites decrease by 7.33% and 5.34%, respectively. Therefore, the significant role of the interface transition layer in improving the interfacial performance of composites is evidenced again at another perspective