Novel approaches to study the crystal assembly in banded spherulites of poly(trimethylene terephthalate)

Abstract

Poly(trimethylene terephthalate) (PTT), with large, well-defined, and strongly birefringent spherulites upon crystallization, has been chosen as a model to study the correlation between the interior lamellae assembly and the top surface banding structures. Approaches to investigate the bulk interior of the banded spherulites are needed to shed new light on the crystallization mechanism of polymers. Two etching methods (with two different etchants: methylamine and permanganate) were applied to two identical samples to enhance the contrast of crystal arrangements in three-dimensional perspectives. Methylamine, under mild conditions, was found to etch out lamellae bundles on ridges and leave discrete crevice-separated circumferential crystal layers. On the other hand, the oxidizing potassium permanganate was found to dissolve the circumferential crystal layers between the successive bands, exposing circular patterns. These two etching results mutually support the discontinuity of radial growth of PTT spherulites, providing valuable hints as to the actual crystal assembly of PTT.