Assessment and optimization of the stabilization process of mesophase pitch fibers by thermal analyses

The oxidative stabilization process of mesophase pitch fibers was monitored by thermal analyses at several heating rates. Methylnaphthalene-derived mesophase pitch (mNP) fiber showed five exothermic oxidation peaks, three (A, B, C) and two (D, E) of which were ascribed to the formations of oxygen functional groups and oxidation-decompositions of the groups in the stabilization process, respectively. The latter two peaks appeared always at higher temperature, being accompanied by weight loss. The former three peaks reflected the weight gain, with the maximum weight gain just before the peak D. The lower heating rate showed the larger maximum weight gain by oxygen uptake, which is due to the least participation of the oxidation-decomposition into the oxygen-uptaking steps. Slower heating in stabilization endowed higher tensile strength on the resulting graphitized fiber such as 480 kg/mm² at a heating rate as slow as 0.1°C/min. The reactivity of the mesophase pitch fibers and the optimal temperature for the stabilization completion can be easily monitored by the thermal analyses. Among the mesophase pitches available, the thermal analyses proved easily that mNP possessed the highest oxidation reactivity and the largest maximum weight gain in the stabilization.