Preparation and characterization of a polyimide coating on the surface of carbon fibers

Organic, solvent-free polyamic acid sizing was coated onto T300 grade carbon fibers (3k) to prepare a polyimide (PI) coating having a high thermal stability and oxidative resistance. The surface of PI-coated carbon fibers was characterized by FTIR and SEM. The mechanical strength of the carbon fibers, thermal stability and oxidative resistance of the coating were also investigated. Results indicate that a continuous and uniform PI coating is formed on the surface of the carbon fibers. Compared to a carbon fiber coating with epoxy, the PI coating produces excellent thermal stability with onset decomposition and a 5% weight-loss temperatures of 567 and 619 ℃, respectively. The tensile strength of PI-coated carbon fibers after thermal oxidation in air at 400 ℃ for 1 h has only a slight decrease of 6%, which is significantly lower than the decrease of 22% for epoxy-coated fibers.