Solvated mesophase pitch-based carbon fibers: thermal-oxidative stabilization of the spun fiber

Potentially low-cost, continuous carbon fiber (CF) was prepared by meltblown spinning of solvated mesophase pitch, followed by drying, oxidation and carbonization. The drying and oxidation stabilization of the spun fiber was investigated by thermal analysis to understand the thermal behavior of the fiber and to improve the mechanical properties of the resulting CFs. The solvents in the spun fiber can be almost completely removed by heating the fiber in the flowing N2 or argon. In contrast, less amounts of solvents were removed as the spun fiber was dried in air because some solvents could be oxidized and/or trapped by the oxidized pitch materials. The separate drying and oxidation processes not only remove solvents effectively, but also promote oxidation stabilization. Thin fiber gains more weight (oxygen uptake) than the thick fiber at the same stabilization conditions. Moisture is easily adsorbed onto the stabilized fibers due to the formation of oxygen-containing groups. The moisture uptake increases proportionally with oxidation time. As compared with simultaneous drying and oxidation in air, the separate drying and oxidation processes provide the prepared CF with a significant improvement in tensile strength and modulus. For larger diameter fibers, the optimum oxidation condition is 350 °C for 30–60 min; for smaller diameter fibers, it is only about 2 min. Due to shorter oxidation time, higher carbon yield is achieved in resulting CFs.