Thermal analysis of the multiple melting behavior of poly(butylene succinate-co-adipate)

The melting behavior of poly(butylene succinate-co-adipate) (PBSA) isothermally crystallized from the melt was investigated by differential scanning calorimetry. Triple, double, or single melting endotherms were observed in subsequent heating scan for the samples isothermally crystallized at different temperatures. These endothermic peaks were labeled as I, II, and III for low-, middle-, and high-temperature melting endotherms, respectively. The independence of endotherm III to the crystallization temperature, the existence of an exothermic crystallization peak just below the endotherm III, and the heating rate dependence of endotherm III indicated that endotherm III was due to the remelting of recrystallized lamellar during a heating scan. The influence of crystallization time on the melting behavior of PBSA showed that endotherms II and III developed prior to endotherm I; endotherm III developed rather simultaneously with endotherm II. Further investigation showed that the peak temperature of endotherm I increased linearly with the logarithm of the crystallization time. It suggested that endotherm II was attributed to the melting of the primary lamellae, while endotherm I was due to the melting of secondary lamellae.