Doping of carbon fiber into polybenzimidazole matrix and mechanical properties of structural carbon fiber-doped polybenzimidazole composites

Carbon fibers (CF) were oxidized and reduced to introduce -OH, -COOH, and -NH2, on which polybenzimidazole (PBI) was in situ polymerized. The CF reinforced PBI composites (CF/PBI) were characterized by H-1 nuclear magnetic resonance spectroscopy and thermal gravimetric analysis. The effect of oxidation and/or reduction of the CF on the chemical states of typical elements such as C, N, and O were investigated by means of X-ray photoelectron spectroscopy. The PBI and CF/PBI powders were hot-press sintered in a vacuum oven to generate structural samples, and the mechanical properties of the structural samples were evaluated using a mechanical properties testing machine. Besides, a scanning electron microscope was used to observe the microscopic features of the structural samples. It was found that -COOH, C-OH, and -NO2 could be introduced onto the surfaces of the CF using H2O2 and H2SO4/HNO3 as the oxidizing agents, while the -NO2 on the surface of the CIF could be reduced to -NH2 by SnCl2.2H(2)O/HCl. This would make it feasible for PBI to be grafted to the surface of CF via in situ polymerization. Hence the mechanical properties of the structural CF/PBI were significantly improved. (C) 2008 Elsevier Ltd. All rights reserved.