Glass transition and enthalpy relaxation process in coal tar pitches

Abstract

Coal tar pitches generally have very complex chemical compositions and structures. Their physico-chemical properties depend on the mutual molecular interactions of their various components. In order to characterize these materials further the properties related to their glass transition behaviour have been investigated. As for polymeric materials, enthalpy relaxation can provide useful information on the interactions occurring in a glassy-type structure. Glass transition characteristics have been determined by means of differential scanning calorimetry. The kinetics of enthalpy relaxation have been analysed with the model developed by Moynihan et al. Mean molecular size and molecular size distribution have been determined for a coal tar and different types of pitches. The glass transition characteristics have been compared in some cases to results obtained by other techniques. It is shown that the investigation of tars and pitches by means of their glass transition properties leads to a good description of their structure and changes occurring during thermal treatment.