Freezing and glass transition phenomena in polymer-diluent mixtures

Abstract

The freezing and glass transition phenomena in a binary system of polystyrene-benzene and in a multicomponent system (known as kraft black liquor) containing ionic species and polymeric lignin derivatives have been examined using differential scanning calorimetry. The experimental observations indicate that in these binary and multicomponent systems there exist a particular concentration (∼50%) at which the phenomenon occurring changes from freezing to glass transition. Using the existing theories of freezing and glass transition, the significance of this particular concentration where the change-over occurs and its dependence on the polymer-solvent interaction parameter and other characteristics of the components have been examined. Depending on the particular values used the change-over concentration for the polystyrene-benzene system has been predicted to be in the concentration range of 50–70% polymer, which is in accord with experimental observations. Comparisons of the freezing behaviour of the kraft black liquor with that of other aqueous solutions indicate that the overall effect on the freezing point results from the combined influence of the polymeric and ionic constituents of the solute.