Modification of coal-tar pitch by air-blowing — I. Variation of pitch composition and properties

Abstract

Pitch oxidation by air-blowing has been studied as a possible method to modify pitch properties for composite preparation. Two commercial coal-tar pitches, an impregnating pitch and a binder pitch, were air-blown at temperatures between 250–300 °C, for 18 and 14 h, respectively, to produce pitches of similar softening point ranging from 148 to 223 °C. Parent and treated pitches were characterized by elemental analysis, FTIR, thermal analysis (TMA, TGA, and DTA), solubility in toluene and quinoline, XPS, X-ray diffraction, and optical microscopy. Additionally, parent pitches were also characterized by extrography. Pyrolysis products of parent and treated pitches, obtained at 450 °C, were characterized by optical microscopy to monitor the influence of air-blowing on mesophase formation. Results show that pitch modification by air-blowing produces a significant increase in carbon yield, without restricting the fluidity necessary to pitch for impregnation. During air-blowing, the reactions of dehydrogenative polymerization and crossing-linking of oligomers occur.