Growth of molecular orientation during post‐process annealing of poly(lactic acid) containing a fibrous nucleating agent

Abstract

AbstractPoly(lactic acid) (PLA) is known to exhibit slow crystallization. Therefore, post‐process annealing is often performed, at which structure change is inevitable. In this paper, the structure development during annealing of PLA containing N,N′‐ethylenebis(12‐hydroxystearamide) (EBHS) is studied using extruded strands. First, EBHS, which acts as a nucleating agent, is dissolved in molten PLA, and then segregates with a fibrous shape during cooling. Next, the PLA containing EBHS is extruded, which causes EBHS fibers in the strand to orientate with the flow direction. When the strand is annealed at 100°C, amorphous PLA chains initially lose their orientation. Then, the chain orientation in the PLA strand develops because of transcrystallization from the surface of EBHS fibers that are aligned with the flow direction. As a result, the Hermans orientation function increases from 1.8 × 10−3 (before annealing) to 6.0 × 10−3 (after annealing). Moreover, the annealed PLA/EBHS strand shows less shrinkage (0.80 ± 0.19%) than the annealed PLA strand (2.04 ± 0.27%). The promotion of PLA chain orientation induced by the presence of aligned EBHS fibers can be used to control the structure and dimensional change of PLA products during annealing.