Ring-banded spherulites in polylactide and its blends

Abstract

In this paper the influence of different aspects of crystallization process on the formation of ring-banded spherulites and the transition between banded and non-banded structures in polylactide was analyzed. Based on the measurements using the differential scanning calorimetry (DSC) and polarized optical microscopy (POM), it was found that the banding phenomenon of spherulites in polylactide and its blends with triethyl citrate (TEC) exclusively depends on the degree of supercooling (ΔT). In the work, for the first time, the equilibrium melting point (Tm0) of polylactide was correlated with the isothermal crystallization temperature (Tic) in the context of banded spherulites formation. To determine the Tm0 of polylactide blends, due to the possibility of modifier migration towards the sample surface, a correction of the methodology was proposed. It has been shown that ΔT necessary to initiate the growth of spherulites with a ring pattern in polylactide ranges from 46 to 56 °C. The inclusion of TEC into polylactide matrix shifts the Tic range in which banded spherulites appear towards lower values, but does not change the required value of supercooling degree. A direct correlation between the band space of the ring-banded spherulites and the degree of supercooling was also demonstrated.