Boosting mechanical properties of carbon fibers by gas-liquid dual-effect approach

The tensile strength and tensile modulus of existing carbon fibers (CFs) are 3 %–5 % of the theoretical values, which greatly limits the performance of CFs when used alone or as a reinforcing material. To increase the chemical reaction activity and roughness of the surface of CFs based on the enhancement of their mechanical properties, a comprehensive treatment of CFs was carried out by the gas-liquid dual-effect method. CFs were oxidized at high temperatures after immersion treatment using cobalt nitrate solution, and the effects of cobalt nitrate solution concentration, oxidation time, and calcination temperature on the surface morphology, functional groups, structural defects, and mechanical properties of CFs were investigated by the controlled-variable method. The results showed that when the concentration of cobalt nitrate solution was 0.2 molL-1, the calcination temperature was 200 °C, and the oxidation time was 4 h, the modification effect was the best. At this time, the tensile strength of CF is 6104.50 MPa, which is 40.35 % higher than that of the pure CF, and the tensile modulus is 378.56 GPa, which is 13.27 % higher than that of the pure CF, with a significant enhancement effect. It can offer feasible ideas for further research and development of CF composites, and provide an effective way to promote the industrialization of modified CFs for application. Carbon fibers modified with cobalt nitrate solution were synthesized using gas-liquid dual-effect method, and their mechanical properties were greatly improved. Mainly due to the introduction of cobalt oxide and oxygen-containing functional groups on the surface of carbon fibers, it enhanced the chemical activity and roughness of the carbon fiber surface. [Display omitted] •Modified carbon fibers were successfully synthesized using a gas-liquid dual-effect method.•The tensile strength and tensile modulus of modified carbon fibers have been greatly improved.•The introduction of cobalt oxide improves the surface activity and roughness of carbon fibers.