C-Perpendicular Orientation of Poly(ʟ-lactide) Films.

Paola Rizzo,Christophe Daniel,Gaetano Guerra,Lucia Baldino,Baku Nagendra

doi:10.3390/polym13101572

Abstract

Poly(ʟ-lactide) (PLLA) films, even of high thickness, exhibiting co-crystalline and crystalline α phases with their chain axes preferentially perpendicular to the film plane (c⊥ orientation) have been obtained. This c⊥ orientation, unprecedented for PLLA films, can be achieved by the crystallization of amorphous films as induced by low-temperature sorption of molecules being suitable as guests of PLLA co-crystalline forms, such as N,N-dimethylformamide, cyclopentanone or 1,3-dioxolane. This kind of orientation is shown and quantified by two-dimensional wide-angle X-ray diffraction (2D-WAXD) patterns, as taken with the X-ray beam parallel to the film plane (EDGE patterns), which present all the hk0 arcs centered on the meridian. PLLA α-form films, as obtained by low-temperature guest-induced crystallization, also exhibit high transparency, being not far from those of the starting amorphous films.

Highlights

Co-crystallization of polymers with suitable guest molecules can lead, without any stretching procedure, to films with high degrees of crystal phase orientation
We show that suitable procedures for guest-induced crystallization on amorphous PLLA films can lead to an unprecedented co-crystalline and crystalline phase orientation with chain axes being preferentially perpendicular to the film plane (c-perpendicular orientation or more shortly c⊥ orientation) [2,3,4,5]
It is well known that PLLA is able to form host–guest co-crystalline forms with suitable guest molecules like cyclopentanone, tetrahydrofuran, 1,3-dioxolane, γ-butyrolactone and N,N-dimethylformamide (DMF), [18,22,23,24,25] and some crystalline structures have been proposed [18,22]

Summary

Introduction

Co-crystallization of polymers with suitable guest molecules can lead, without any stretching procedure, to films (even of high thickness) with high degrees of crystal phase orientation. Planar and uniplanar orientations, i.e., the preferential orientations of a crystal axis or a crystal plane with respect to the film plane, can be achieved [1,2,3,4,5,6,7,8,9,10,11] Both planar and uniplanar orientations have been obtained for two commercial polymers: syndiotactic polystyrene (s-PS) [1,2,3,4,5,6,7] and poly(2,6-dimethyl-1,4-phenylene ether) (PPO) [8,9] for their co-crystalline forms and for the corresponding nanoporouscrystalline phases, as produced by guest removal [10]. A uniplanar orientation with acplanes of crystallites being preferentially parallel to the film plane (defined as a-parallel, c-parallel, shortly a||c||) has been recently observed [18]

Methods

Results

Conclusion