Isothermal melt crystallization kinetics, melting behavior, and spherulitic morphology of novel biobased poly(hexylene oxalate)

Abstract

The isothermal melt crystallization kinetics, melting behavior, and spherulitic morphology of poly(hexylene oxalate) (PHO), a novel semicrystalline polyester derived from biobased resources, were investigated in detail with differential scanning calorimetry and polarizing optical microscopy in a wide crystallization temperature (T_c) range. The isothermal melt crystallization kinetics of PHO was well described by the Avrami equation in the investigated T_c range. With increasing T_c, the crystallization rate of PHO was reduced; however, the crystallization mechanism remained unchanged. Double melting endotherms were observed for PHO, which was explained by the melting, recrystallization, and remelting mechanism. Through the Hoffman–Weeks equation, the equilibrium melting point of PHO was determined to be 86.6 °C. Depending on T_c, PHO exhibited different spherulitic morphologies. Banded spherulites were observed in a wide range of T_c; moreover, the band spacing increased with increasing T_c. The spherulitic growth rates of the PHO spherulites decreased with increasing T_c; furthermore, the PHO spherulites exhibited a crystallization regime transition from regime II to regime III at about 50 °C, according to the secondary nucleation theory.