Biaxially Stretched Carbazole‐Modified Polyamide 6 Copolymer Films With Enhanced Barrier, Mechanical, and Optical Properties

ABSTRACT Simultaneously improving toughness, optical transparency, and gas barrier performance remains a key challenge for polyamide 6 (PA6)‐based films. Carbazole‐modified PA6 copolymers were prepared and processed into biaxially stretched films to regulate molecular structure and condensed morphology simultaneously. The rigid planar carbazole units restrict chain mobility and promote denser molecular packing, while biaxial stretching induces molecular orientation and the formation of oriented nanocrystals. As a result, a robust amorphous entanglement network and highly aligned crystalline domains are constructed within the films. This synergistic structural regulation leads to significant improvements in multiple properties. The optimized film (BOH15‐2.5 × 2.5) exhibits a tensile strength of 112.9 MPa and an elongation at break of 159.3%, while maintaining excellent light transmission performance. Moreover, the dense packing structure reduces internal free volume and increases gas diffusion tortuosity, resulting in a decrease in oxygen permeability from 26.7 to 16.2 cm 3 /(m 2 ·24 h·0.1 MPa) compared with neat PA6 film. The results demonstrate that the combination of molecular design and biaxial orientation provides an effective strategy for developing high‐performance PA6 films with balanced mechanical, optical, and barrier properties.