Rare Lamellar Assembly Mechanism on Special Spherulites of Poly(ε-caprolactone)-b-polyamide 6-b-Poly(ε-caprolactone)

Abstract

Due to the extremely wide crystallization temperature range of chemically jointed PA6 blocks, three types of spherulitic morphologies were found in poly(ε-caprolactone)-b-polyamide 6-b-poly(ε-caprolactone) (PCL-b-PA6-b-PCL), including conventional ring-banded spherulites, special spherulites with a curve-like morphology, and composite spherulites with the above two characteristics. The formation conditions, internal factors, and the lamellar orientation and assembly of different spherulites have been studied in detail. It was found that the PCL spherulites with a curve-like morphology can form only when PCL and PA6 blocks crystallize simultaneously, whereas the ring-banded spherulites can form regardless of whether PA6 is amorphous or crystallized. The morphological results show that the ring-banded spherulites are composed of lamellae with different orientations along the radial direction, while spherulites with a curve-like morphology are composed of different stacked lamellae (flat-on lamellae and tilted flat-on lamellae) arranged alternately along the tangential direction. The appearance of unusual spherulitic morphology may result from different internal stress induced by chemically jointed PA6 blocks under diverse crystallization conditions.