A Comparative Study on the Melt Crystallization of Biodegradable Poly(butylene succinate-co-terephthalate) and Poly(butylene adipate-co-terephthalate) Copolyesters

As an important biodegradable and partially biobased copolyester, poly(butylene succinate-<i>co</i>-terephthalate) (PBST) possesses comparable thermal and mechanical properties and superior gas barrier performance when compared with poly(butylene adipate-<i>co</i>-terephthalate) (PBAT), but it was found to display poorer melt processability during pelletizing and injection molding. To make clear its melt crystallization behavior under rapid cooling, PBST₄₈ and PBST₄₄ were synthesized, and their melt crystallization was investigated comparatively with PBAT₄₈. PBST₄₈ showed a PBAT₄₈-comparable melt crystallization performance at a cooling rate of 10 °C/min or at isothermal conditions, but it showed a melt crystallization ability at a cooling rate of 40 °C/min which was clearly poorer. PBST₄₄, which has the same mass composition as PBAT₄₈, completely lost its melt crystallization ability under the rapid cooling. The weaker chain mobility of PBST, resulting from its shorter succinate moiety, is responsible for its inferior melt crystallization ability and processability. In comparison with PBAT₄₈, PBST₄₈ displayed higher tensile modulus, and both PBST₄₈ and PBST₄₄ showed higher light transmittance. The findings in this study deepen the understanding of PBST's properties and will be of guiding significance for improving PBST's processability and application development.