Composite banded core and non-banded shell transition patterns in stereocomplexed poly(lactide acid) induced by strongly interacting poly(p-vinyl phenol)

Abstract

Banded cores and non-banded shells with transitional patterns in stereocomplexed poly(lactic acid) sc-PLA (PLLA : PDLA = 1 : 1) interacting with amorphous poly(p-vinyl phenol) (PVPh) (20–30 wt%) were investigated by using polarized optical (POM), atomic force (AFM), and scanning electron microscopy (SEM). The central core of the spherulites is ring-banded, which transitions into non-banded patterns on the outer peripheral in sc-PLA/PVPh blends crystallized at T_c = 160–180 °C. This composite crystal morphology is distinctly different from that of the neat sc-PLA, which is a Maltese-cross without any ring patterns in spherulites. The bands in the core region are also dramatically different from those bands with birefringence contrasts observed in classical ring-bands. The bands in the core show only crystal topology and no birefringence difference. Both regions of ring-banded and non-banded crystals are composed of edge-on lamellae, but the central-core lamellae undergo periodical waving up and down. The specific stage-wise and preferential interactions between PVPh and sc-PLA and glass substrate, which simultaneously occur during amorphous PVPh rejection and growth processes, were evaluated as some plausible kinetic reasons for the special composite crystal morphology of sc-PLA complex induced by blending with PVPh.