In Situ Growth of CoS Nanosheets on Carbon Fiber Surfaces to Enhance the Interfacial Properties of Carbon Fiber/Norbornene Polyimide Composites

This study presents a novel method for altering the surface properties of carbon fiber (CF) to improve the bonding strength at its interface with norbornene–polyimide (PI-NA) resin. Cobaltous sulfide (CoS) nanosheets were successfully synthesized on the CF surface using a solvothermal method combined with a chemical sulfidation process. The modification increased the specific surface area and surface roughness of the CFs, enhancing the interfacial mechanical lock-in effect between the fibers and the resin. This facilitated effective load transfer between the resin and the fibers, thereby significantly improving the interfacial strength of CF-reinforced polymers (CFRPs). The experimental findings showed that after solvothermal treatment with a precursor solution of 0.006 g/mL for 4.5 h, vertical CoS nanosheets were successfully grown on the CF surface. The interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of the modified CF reached 60.03 MPa and 83.27 MPa, respectively, representing increases of 19.49% and 27.01% compared to untreated fiber composites. This research demonstrates that this method is simple to apply and promising in terms of industrial scalability.