Superior Ductile and Barrier PLA/PGA Films by an In Situ Constructing Transversely Isotropic Network and Well-Ordered Crystalline Nanolayers

Simultaneously achieving excellent toughness, transparency, and gas barrier properties is still a challenge for poly(lactic acid) (PLA) films. In this work, we address an effective and scalable strategy based on biaxial stretching to make superior ductile, transparent, and high-barrier PLA films by incorporating polyglycolic acid (PGA) and constructing a transversely isotropic structure in the PLA matrix with numerous nanocrystals and a nanolayer PGA barrier phase. The transversely isotropic structure endowed PLA/PGA films with a robust chain entanglement network, which prevents the formation of densely distributed cohesional entanglement and the physical aging of PLA, allowing the molecular chains of PLA to move sufficiently to exhibit excellent toughness. Consequently, the tensile strength of the PLA/PGA film increased from 67 to 157 MPa while maintaining a high elongation at break (>100%), high transparency (>85%), and high durability, demonstrating excellent comprehensive physical and mechanical properties. Importantly, the in situ constructed nanolayer barrier phase greatly prolongs the diffusion path of gas molecules in the PLA/PGA films, and consequently the oxygen permeability coefficient (P_O2) of the PLA/PGA film decreased by almost two orders of magnitude, i.e., from 1.66 × 10^–14 to 7.10 × 10^–16 cm³·cm/cm²·s·Pa, compared to that of neat PLA, and three orders of magnitude lower than that of the polyethylene film. Therefore, this work contributes a deeper understanding of the structure–property relationship of biaxially oriented PLA-based films and may enable their application in the high-barrier green packaging field.