EFFECT OF POLAR COMPONENTS ON THE PHYSICOCHEMICAL PROPERTIES OF COAL-TAR

The influence of polar compounds like phenols and pyridine-type bases on the morphology and glass transition of coal tar is investigated. A coal tar sample is separated into various fractions which thereafter are recombined progressively in order to reconstitute the starting sample. At each step, the glass transition temperature and activation energy of the relaxation process of the glassy fractions are determined by d.s.c. The amount and morphology of solid particles present in the tar fractions are determined by means of optical microscopy and image analysis. The presence of phenol tends to increase the size of the relaxation unit, which suggests the occurrence of hydrogen bonds between aromatic units of various sizes. In contrast, bases have an opposite effect to phenols. The presence of phenol tends to decrease the mean size of insoluble particles whereas bases increase it. It is concluded that the simultaneous presence of phenols and bases leads to an overall stabilization effect of the coal tar at ambient temperature.