Single- and double-ring spherulites in poly(nonamethylene terephthalate)

A new mechanism of formation of ring-banded spherulites was discovered, where three different types of spherulites were present in poly(nonamethylene terephthalate) (PNT) cast in thin film forms. The growth and morphological features in three ring-banded spherulites were compared and analyzed using polarized/non-polarized light microscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) and element analysis by energy dispersive spectroscopy (EDS) on surfaces of spherulites. Three types of spherulites (labeled: Type-0, 1, and 2) are possible in PNT when crystallized at wide range of crystallization temperature (Tc); however, only two of the three types can co-exist in PNT at a given Tc. At lower Tc (<55 °C), within Regime-III, the spherulites in PNT are either of Type-0 (appearing ringless in POM) or Type-2 (double-band in POM). When crystallized at temperature of Tc = 55 °C or higher (Regime-II), the morphology is featured with Type-1 (single-ring-banded in POM) spherulites as the majority species that co-exist with Type-2 (double-ring-banded in POM) spherulites as imbedded minority. Origins and morphological differences of the single-band vs. double-band spherulites were compared. The double-band spherulites have much larger inter-ring spacing than do the single-band spherulites. By comparison, the rod-like lamellae in the double-banded spherulites (Type-2) are longer and thicker, and more ordered than those in the single-banded spherulites (Type-1).