Preparation of isotropic pitch precursors for general purpose carbon fibers (GPCF) by air blowing—II. Air blowing of coal tar, hydrogenated coal tar, and petroleum pitches

Abstract

Three representative isotropic pitches, coal tar pitch NP80, its hydrogenated NHP and petroleum pitch A60, were air blown at 330°C in order to study comparatively their oxidation reactivities in the preparation of isotropic pitch precursors with a high softening point. They showed different oxidation behaviors during air blowing. Coal tar pitch with a low softening point of 80°C showed the most rapid rise of softening point but suffered the smallest pitch yield. Air-blown coal tar pitches, NP80-1 and NHP-1, exhibited a higher degree of aromatic condensation and larger QI content than the petroleum one even when their softening points were around 280°C. The structure characterization of the parent and air-blown pitches by FT-IR, FD-mass and solution 1H-, 13C-NMR suggests the mechanism of air blowing to raise the softening point. Unexpectedly slow rises in softening points of hydrogenated coal tar and petroleum pitches appear to be ascribed to their alkyl and naphthenic groups, which may terminate the chain reaction of oxidation.