Significantly Improving Oxygen Barrier Propertiesof Polylactide via Constructing Parallel-Aligned Shish-Kebab-LikeCrystals with Well-Interlocked Boundaries.

Recently, some attempts have beenmade to enhance the gas barrierproperties of semicrystalline polymers by precisely controlling thearrangement of their impermeable crystalline lamellae. However, itis still a great challenge to achieve regular arrangement of the lamellaealong the direction perpendicular to the gas diffusion path, especiallyusing conventional polymer processing technologies. This work presentsa novel and simple strategy to dramatically improve oxygen barrierperformance of biobased and biodegradable polylactide (PLA) throughconstructing parallel-aligned shish-kebab-like crystals with well-interlockedboundaries with the aid of a highly active nucleating agent. The nucleatingagent was introduced into PLA by melting compounding and the sheet-likespecimens were fabricated by compression molding. We demonstrate thatthe fibrillar nucleating agent dispersed in PLA melt can serve asshish to induce the change of crystallization habit of PLA from isotopicspherulitic crystals to unique shish-kebab-like crystals and the shearflow in the compression molding can induce the highly ordered alignmentof the nucleating agent fibrils as well as the subsequent shish-kebab-likecrystals along the direction parallel to the sheet surface. More importantly,the growing lamellae are found to interpenetrate and tightly interlockwith each other at the boundary regions of the shish-kebab-like crystalsin the later stage of the crystallization, forming a densely packednanobrick wall structure to prevent gas molecules from permeatingthrough the crystals and thus imparting the PLA sheets with unprecedentedlylow oxygen permeability. This work provides not only a successfulexample of preparing semicrystalline polymer with super gas barrierproperties by tailoring crystal superstructure but also a promisingroute to rapidly fabricate high-performance food packaging materialsvia industrially meaningful melt processing. [ABSTRACT FROM AUTHOR]