Significantly Improving Oxygen Barrier Properties of Polylactide via Constructing Parallel-Aligned Shish-Kebab-Like Crystals with Well-Interlocked Boundaries

Abstract

Recently, some attempts have been made to enhance the gas barrier properties of semicrystalline polymers by precisely controlling the arrangement of their impermeable crystalline lamellae. However, it is still a great challenge to achieve regular arrangement of the lamellae along the direction perpendicular to the gas diffusion path, especially using conventional polymer processing technologies. This work presents a novel and simple strategy to dramatically improve oxygen barrier performance of biobased and biodegradable polylactide (PLA) through constructing parallel-aligned shish-kebab-like crystals with well-interlocked boundaries with the aid of a highly active nucleating agent. The nucleating agent was introduced into PLA by melting compounding and the sheet-like specimens were fabricated by compression molding. We demonstrate that the fibrillar nucleating agent dispersed in PLA melt can serve as shish to induce the change of crystallization habit of PLA from isotopic spherulitic crystals to unique shish-kebab-like crystals and the shear flow in the compression molding can induce the highly ordered alignment of the nucleating agent fibrils as well as the subsequent shish-kebab-like crystals along the direction parallel to the sheet surface. More importantly, the growing lamellae are found to interpenetrate and tightly interlock with each other at the boundary regions of the shish-kebab-like crystals in the later stage of the crystallization, forming a densely packed nanobrick wall structure to prevent gas molecules from permeating through the crystals and thus imparting the PLA sheets with unprecedentedly low oxygen permeability. This work provides not only a successful example of preparing semicrystalline polymer with super gas barrier properties by tailoring crystal superstructure but also a promising route to rapidly fabricate high-performance food packaging materials via industrially meaningful melt processing.

Tailoring the crystallization behavior of poly(L-lactide) with self-assembly-type oxalamide compounds as nucleators: 1. Effect of terminal configuration of the nucleators

“…Thus it is indeed interesting to achieve shish-kebab-like morphology of PLLA crystals free of any flow. A similar phenomenon was recently observed in PLLA/N,N 0 ,N 00 -tricyclohexyl-1,3,5-benzene-tricarboxylamide blends as well [21][22][23]. As discussed that the NA (CY) showed the highest melting temperature (360°C), it could not dissolved completely in the PLLA matrix at 145°C thus the self-organization morphology was not observed notably by POM under the same conditions.…”

“…TMC was proven with high activity which can self-organize in PLLA melt to induce fast crystallization and enhance the mechanical performance of PLLA [21,22]. Consequently, the oxygen permeability coefficient of PLLA was reduced by around 2 orders of magnitude via the addition of TMC and the crystal morphology control [23].…”

Multi-scale analysis of the impact of polylactide morphology on gas barrier properties

“…Much better results were obtained, when the crystalline morphology was designed by arrangements of parallel lamellae perpendicular to the permeation direction. This was achieved with "shish-kebab like" structures by Bai et al [18].…”

“…The values of C p glass Ta and C p liquid Ta were obtained by prolonging the glass and liquid lines to dynamic glass transition temperature after normalization to the MAF content [18]. When the crystallization is not performed to its maximum extent, the MAF splits into intra-and inter-spherulitic amorphous regions and calorimetric measurements can show two separate signatures within the glass transition temperature range [20].…”

Molecular surface area based predictive models for the adsorption and diffusion of disperse dyes in polylactic acid matrix

“…PLA is primarily used in the textile and packaging sectors. The adsorption and diffusion of small molecules in PLA play key roles in textile processing [5,6] and determine the key performance indicators of packaging materials [7,8]. The focus of present work is to investigate the sorption of dye molecules in PLA textile fibers.…”