A STRUCTURAL STUDY ON OXIDATIVE STABILIZATION OF MESOPHASE PITCH FIBERS DERIVED FROM COAL-TAR

The oxidized fiber of coal-tar based mesophase pitch showed the maximum weight gain at a particular oxidation temperature according to the heating rate to the temperature as the balance of oxygen uptake and decomposition of oxygen functional groups. The graphitized fiber showed the maximum tensile properties whenever the oxidized fiber gained the maximum weight, regardless of the heating rates of 0.5-2.0-degrees-C/min. Fourier transform infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy (XPS) indicated the dominant presence of the conjugated carbonyl after oxidation at lower temperatures (below 350-degrees-C). NMR study revealed that these groups could be triggers for oxygen bridges such as ethers and esters and for dehydrogenative coupling to form the larger molecular weight components in successive carbonization at the elevated temperature. In contrast, more carboxylic acids were introduced after oxidation at higher temperatures (above 400-degrees-C) through the cleavage of the hexagonal ring. Such extensive oxidation may reduce the tensile properties of graphitized fibers.