Influence of Heat Treatment on Amorphous Structure and Mechanical Properties of Isosorbide-Based Bio-Polycarbonate

In the present study, we evaluated the influence of heat treatment on the amorphous structure and mechanical properties of isosorbide-derived bio-based polycarbonate (Bio-PC) to enhance its functionality. We compared the physical and mechanical properties of Bio-PC with those of petroleum-based polycarbonate (Petro-PC) to elucidate the mechanisms of structural changes caused by heat treatment. Dynamic viscoelasticity analysis of the Bio-PC revealed increases in both the tanδ and E′′ values within a temperature range below the glass-transition temperature (Tg) of each heat-treated sample. Each heat-treated PC sample exhibited the enthalpy relaxation phenomenon around the Tg, which is typical of amorphous polymers. There was a decrease in the free volume of the polymer chains owing to the heat treatment, which increased the apparent activation energy of main-chain relaxation, enthalpy relaxation, and density. Moreover, these changes of the amorphous structure led to an increase in tensile yield stress and a decrease in toughness. These results were caused by an increase in, and uniformity of, the intermolecular interaction of the main chains due to the decrease in free volume. In addition, these physical and mechanical properties were influenced by heat-treatment temperature and had a maximum/minimum at an optimal temperature difference Tg − Ta.