MORPHOLOGY OF BANDED SPHERULITES IN POLY(EPSILON-CAPROLACTONE) POLY(STYRENE-RAN-ACRYLONITRILE) BLENDS/

The occurrence of banded spherulites in blends of poly(epsilon-caprola ctone) with poly(styrene-ran-acrylonitrile) is studied by means of opt ical-, scanning electron-, environmental scanning electron-, and atomi c force-microscopy as well as small-angle X-ray scattering. The measur ements reveal that lamellae are confined in fibrils that bend periodic ally from the center of spherulites in a radial direction. The fibrils show also a regular spacing in the lateral direction. Single bent lam ellae can be observed by atomic force microscopy after permanganic etc hing. The enrichment of amorphous material near to the growth front of the spherulites can be directly observed by polarized light microscop y after temperature jump experiments. The excluded amorphous material on the surface of the growing spherulites has the shape of droplets. T his might be the main reason for the initiation of the bending process because the result is a non-uniform stress distribution acting on the growing lamellae at the interface between spherulites and the surroun ding melt. The amorphous material of the blends can be found in three areas as observed by small-angle X-ray scattering experiments and micr oscopical methods: i) between the lamellae, ii) excluded from the inte rlamellar region but within the spherulite, and iii) for high contents of non-crystallizable material, it can be excluded from the spherulit e. The banding periodicity of spherulites as a function of the crystal lization temperature can be described in terms of two models, based ei ther i) on the inherent twisting of lamellae perpendicular to the axis of a screw dislocation or ii) on the dependence of the diffusion of a morphous material away from the growth front of lamellae and the tempe rature dependence of the rate of crystallization Both models fail at v ery low supercoolings near to temperatures where the banding disappear s completely.