Thermal Analysis of Thermally Reversible Gels Made of a Bio-based, Biodegradable Polymer

摘要

A combination of standard differential scanning calorimetry (DSC) and modulated temperature DSC (MDSC) was used to analyze the thermal properties of a series of thermal-reversible gels made of a solution of dimethylformamide (DMF) and bio-based, biodegradable poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx). Thermal analysis of the gel system was performed to determine if physical gelation of PHBHx is due to crystallite formation or phase separation alone. MDSC heat/cool results indicate that concentration of the polymer solution in addition to the 3-hydroxyhexanoate (3HHx) content of the polymer play major roles in the position and intensity of the heating endotherms and cooling exotherms. It was found that increasing the concentration of polymer did not greatly affect the onset and peak temperatures of the endotherms, but increased the exotherms, whereas increasing the 3HHx content of the polymer would decrease these temperatures. This indicates that gelation temperature is governed by 3HHx content more so than polymer concentration. Because the lower 3HHx content polymers are more crystalline, these results would suggest that gelation of these solutions may be due to formation of crystalline domains. Additionally, the linear trend of melting enthalpy as a function of cooling rate indicates crystal presence in the gel system. MDSC results revealed exotherms overlapped with the melting endotherms, suggesting recrystallization as the system approached dissolution.