Optimization of Aggregated Structure of Biaxially Oriented Polyamide Composite Films With High Gas‐Barrier Performance

ABSTRACT Biaxially oriented polyamide (BOPA) films exhibit high water absorption (~9 wt%) due to their intrinsic polar amide groups, which results in deterioration of mechanical properties and dimensional stability in humid environments. In this study, composite BOPA films with their controls were constructed by introducing PA66 with symmetric amide groups and nanoscale inorganic fillers. Specifically, the 5 wt% PA66 with high crystallization temperature exerts a heterogeneous nucleation during melt compounding, whereas 1.00 wt% layered organically modified montmorillonite (OMMT) extends the penetration paths of water molecules, thus decreasing their hygroscopicity to 2.5%. Moreover, the extension of PA chains and the regular arrangement of hydrogen bonds are inhibited via the rapid quenching during the melt‐casting process, and the biaxial stretching significantly enhances the α‐crystal crystallinity of BOPA films from the metastable γ ‐crystal of cast films through molecular orientation. Based on the synergistic mechanism of “melting‐stretching crystallization”, the optimized BOPA films are developed with low oxygen permeability (14.38 mL m −2 day −1 ) and low linear tearing deviation (< 3.5%). Therefore, these findings provide a new understanding for the low‐hygroscopic modification of the BOPA films with trace functional fillers, contributing to the high gas‐barrier properties.