Effects of Heat Treatment Atmosphere and Temperature on the Properties of Carbon Fibers

In this study, carbon fibers were heat-treated in a nitrogen and oxygen atmosphere according to temperature to elucidate the mechanism of chemical state changes and oxygen functional group changes on the carbon fiber surface by analyzing the mechanical and chemical properties of carbon fibers. Carbon fibers before and after heat treatment were analyzed using FE-SEM (Field Emission Scanning), UTM (Universal Tensile Testers), XPS (X-ray Photoelectron Spectroscopy), and surface-free energy. In the nitrogen atmosphere, which is an inert gas, the tensile strength was equivalent to that of the virgin up to 500 degrees C but decreased to 71% with respect to the virgin at 1000 degrees C. Furthermore, as the temperature increased from room temperature to 1000 degrees C, the oxygen functional group and the polar free energy gradually decreased compared with the virgin. On the other hand, in the oxygen atmosphere, which is an active gas, the tensile properties were not significantly different from those of the virgin up to 300 degrees C but gradually decreased at 500 degrees C. Above 600 degrees C, the carbon fibers deteriorated, and measurement was impossible. The oxygen functional group decreased at 300 degrees C, but above 300 degrees C, among the oxygen functional groups, the hydroxyl group and the carbonyl group increased. Furthermore, the lactone group formed and rapidly increased compared with the virgin, and the polar free energy increased as the temperature increased.