Origin of Epitaxial Cold Crystallization of Poly(l-lactic acid) on Highly Oriented Polyethylene Substrate

Abstract

Cold crystallization of poly(L-lactic acid) (PLLA) from amorphous state on highly oriented polyethylene (PE) substrate has been studied by electron diffraction and infrared spectroscopy. Both electron diffraction and infrared spectroscopy analyses show that the PLLA in the as-prepared PLLA/PE double layers is in the amorphous state. Annealing of the as-prepared PLLA/PE samples at 130 °C leads to the cold crystallization of PLLA. It is confirmed that the PLLA grown on the oriented PE surface exhibits high orientation with molecular chains aligned perpendicular the chain direction of PE, indicating the occurrence of heteroepitaxy of PLLA on the PE substrate. This provides a first example of perpendicular chain orientation of polymer epitaxy. Moreover, it demonstrates the capability of polymer epitaxy from amorphous state through annealing. Infrared spectroscopy analysis on the as-prepared PLLA/PE double layers shows that the orientation of PLLA molecules in contact with the PE substrate exists already in the amorphous state. It is these oriented PLLA chains in amorphous phase that transform into crystal nuclei during cold crystallization and initiate the oriented overgrowth of PLLA on the PE substrate.

Enhanced Crystallization Rate of Poly(l -lactide) Mediated by a Hydrazide Compound: Nucleating Mechanism Study

“…In the last decade, there have been numerous researches devoted to enhancing the crystallization rate of PLLA, including physical blending with inorganic fillers or a second polymer, epitaxial crystallization on a substrate, as well as applying external extensional and shear flow, etc. Particularly, inorganic fillers have been adopted widely as nucleating agents for PLLA due to their variety resources and strong nucleating ability.…”

Oriented Overgrowths of Poly(l‐Lactide) on Oriented Isotactic Polypropylene: A Sequence of Soft and Hard Epitaxies

“…Oriented overgrowth of a foreign material on oriented crystalline substrates is a process known as epitaxy. It is a simple and versatile way for orienting a wide variety of crystalline materials . Surface‐induced epitaxy is based on favorable crystallographic interactions and defines the crystallographic orientation of the overgrowing polymer.…”

“…. In a recent work, oriented films of PE have been used to orient the biodegradable and biocompatible poly( l ‐lactide) (PLLA) . More precisely, the orientation develops in an amorphous film of PLLA (produced by solvent evaporation) deposited on the PE film upon annealing in the crystallization temperature range of PLLA.…”

Nanohybrid Polymeric Nucleating Agents: In Situ Decorated Carbon Nanotubes and Serial Nucleation Behaviors in a Melt‐Miscible Crystalline/Crystalline Blend

“…Moreover, the mismatches are only 6.9% and 5.9% (less than 10.5%), respectively. Actually, the similar results have been reported in PE/PLLA blends by Yan et al Furthermore, the simultaneous crystallization and the enhancing nucleation of PLLA within the pre‐existed POM spherulites in the PLLA/POM (90/10) blends during the isothermal crystallization (Figure S6, Supporting Information) have been recently observed and the details will be discussed in a future report. These results again indicate that PLLA molecular chains can be epitaxially nucleated on the existing POM lamellae.…”