Annular Multi-Shelled Spherulites in Interiors of Bulk-Form Poly(nonamethylene terephthalate)

Morphology of crystallized spherulites in poly(nonamethylene terephthalate) (PNT) in bulk forms, instead of thin-film forms, was investigated using scanning electron microscopy (SEM), polarized-optical microscopy (POM), and transmission electron microscopy (TEM). Ring textures were found to exist on the fractured surfaces or microtomed films from bulk PNT samples. By further SEM and TEM examinations, the fracture surfaces and microtomed films from the interior of the bulk display similar ring-banded patterns as those in thin films cast on glass slides. Although the cast PNT thin films in two-dimensional growth are known to display both Type-1 ring bands as majority and Type-2 ring bands as minority, this study further shows that the interior of PNT bulk exhibits mainly Type-1 (single rings with narrower spacing than Type-2) ring bands, and Type-2 spherulites exist sporadically in three-dimensional forms. From these analyses on the ring bands in the interiors of bulk-form PNT crystallized at several specific temperatures, it can be proposed that the growth of spherulites in three dimensions is layer-bylayer, packing into a multi-shells structure in three-dimensional ring-banded spheres.