Superior Ductile\nand Barrier PLA/PGA Films by In Situ\nConstructing a Transversely Isotropic Network and Well-Ordered Crystalline\nNanolayers

Simultaneously achieving excellent toughness, transparency,\nand\ngas barrier properties is still a challenge for poly(lactic acid)\n(PLA) films. In this work, we address an effective and scalable strategy\nbased on biaxial stretching to make superior ductile, transparent,\nand high-barrier PLA films by incorporating polyglycolic acid (PGA)\nand constructing a transversely isotropic structure in the PLA matrix\nwith numerous nanocrystals and a nanolayer PGA barrier phase. The\ntransversely isotropic structure endowed PLA/PGA films with a robust\nchain entanglement network, which prevents the formation of densely\ndistributed cohesional entanglement and the physical aging of PLA,\nallowing the molecular chains of PLA to move sufficiently to exhibit\nexcellent toughness. Consequently, the tensile strength of the PLA/PGA\nfilm increased from 67 to 157 MPa while maintaining a high elongation\nat break (>100%), high transparency (>85%), and high durability,\ndemonstrating\nexcellent comprehensive physical and mechanical properties. Importantly,\nthe <i>in situ</i> constructed nanolayer barrier phase greatly\nprolongs the diffusion path of gas molecules in the PLA/PGA films,\nand consequently the oxygen permeability coefficient (<i>P</i><sub>O<sub><b>2</b></sub></sub>) of the PLA/PGA film decreased\nby almost two orders of magnitude, i.e., from 1.66 × 10<sup>–14</sup> to 7.10 × 10<sup>–16</sup> cm<sup>3</sup>·cm/cm<sup>2</sup>·s·Pa, compared to that of neat PLA, and three orders\nof magnitude lower than that of the polyethylene film. Therefore,\nthis work contributes a deeper understanding of the structure–property\nrelationship of biaxially oriented PLA-based films and may enable\ntheir application in the high-barrier green packaging field.