Mesophase development in coal-tar pitch modified with various polymers

Abstract

The effect of 10% addition of various polymers to coal-tar pitch on its conversion into mesophase during isothermal treatment at 450 °C has been studied using polarized light optical microscopy. The additives appear to modify to a different extent the kinetics of the conversion and morphology of the developed mesophase. A common effect is an acceleration of mesophase unit growth in the early stage of transformation, the influence decreasing from polystyrene to cumarone–indene resin, and, at the advanced stage, an increase of proportion of areas of isotropic appearance in the optical texture. The addition of poly(vinyl chloride) leads to non homogeneous texture of mesophase pitch due to early separation of particulate matter and growth of mesophase in a way typical of pitch matrix which is free from quinoline insolubles. Poly(ethylene glycol) and unsaturated polyester resin tend to hinder the ability of mesophase to coalescence giving products of enhanced proportion of spherical mesophase. The cumarone–indene resin is the only additive that distinctly increases residue yield but does not affect its optical texture. Based on the results the behaviour of polymers within pitch matrix under carbonization conditions and possible interactions of polymer degradation products with pitch constituents are discussed.