Effect of Biaxial Orientation on Gas Permeability and Remarkably Enhanced Toughness of Poly(Butylene Succinate)-based Films.

Simultaneously biaxial stretching was applied to poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA), and their blends to investigate the effect of biaxial orientation (BO) on gas permeability and mechanical strength, compared to their thin films. The BO process with a high draw ratio of 4 × 4 and a rapid rate of 300 mm/s effectively induced the formation of both perfect α-PBS crystals and small PBS crystal-like aggregates. The distinctive crystallization behaviors of PBS and PBSA, coupled with various film stretching processes, played crucial roles in crystal formation and orientation, resulting in distinct properties of the oriented films. The lattice plane (021) of α-PBS crystal predominantly formed with isotropic orientation through the BO process, while the (110) planes displayed isotropic formation along orthotropic orientation of the crystal c-axis. Conversely, uniaxial cast film extrusion favored preferential alignment of both (020) and (110) diffraction planes along the meridian direction. The perfect α-PBS crystals from PBS homopolymer played a critical role in enhancing gas barrier performance, while the specific orientation of crystalline phase and PBS fringed-micelle crystals proved insufficient in reducing gas diffusivity within the films. Furthermore, the limited crystallization capability of PBSA copolymer disrupted the densely packed structures of α-PBS crystalline phase, resulting in increased d-spacing with higher PBSA content in the PBS/PBSA blend. Remarkably, the simultaneous BO process enabled balanced tensile properties along both the machine and transverse directions of the PBS, PBSA, and PBS/PBSA films, with a substantial enhancement (3 to 4-fold increase) in puncture toughness for BO films compared to thin films. [ABSTRACT FROM AUTHOR]