Crystallization temperature dependence of interference color and morphology in poly(trimethylene terephthalate) spherulite

The relationship between retardation and morphology in highly birefringent poly(trimethylene terephthalate) spherulites was studied from the viewpoint of crystallization temperature dependence. Both the retardation and the morphology relate with the degree of orientation of the molecular chains. Therefore, the degree of orientation of the crystal lamellae was estimated by image processing of transmission electron microscope (TEM) images of the spherulite. It was found that the degree of orientation changed remarkably between the non-banded and the banded morphology and the temperature dependence of the degree of orientation correlated with that of the retardation. Based on the image-processed TEM images, it was recognized that the crystal lamellae formed bundles in the banded spherulite, while few bundled lamellae were observed in the non-banded ones. It is suggested that the formation of bundled lamellae played the significant role for both the magnitude of retardation and determination of the morphology; i.e. whether to form banded spherulites or non-banded ones.