Thermal Properties and Crystallization Behavior of Curdlan Acetate Propionate Mixed Esters

Curdlan, a β-1,3-glucan polysaccharide, produced by microorganisms, was used as a raw material to synthesize a completely substituted Curdlan mixed ester, Curdlan acetate propionate (CDAcPr). The degree of propionylation was changed (0.4–2.8), and the resulting thermal and crystal properties were analyzed using DSC and wide-angle X-ray diffraction (WAXD). Results showed that CDAcPr had a single Tg at all degrees of propionylation, indicating that the acyl groups were randomly distributed in its molecular chains rather than a physical blend of homoesters. Further, unlike typical mixed esters, CDAcPr also showed melting points ranging from 293 to 231 °C, with several samples showing multiple melting peaks. WAXD results suggested that CDAcPr underwent cocrystallization observed in certain copolymers, exhibiting isodimorphism. The crystal structure and melting point of CDAcPr could be controlled by changing the degree of propionylation. Such structural control greatly expanded the possibilities of biomass-based plastics derived from polysaccharides.