Construction of Multi‐Level Crosslinking Network in Boric Acid Modified Poly(Vinyl Alcohol) System and Its Effect on Structure and Properties of the Biaxially Stretched Films

Poly(vinyl alcohol) (PVA) is a commercial polymer with one of the lowest oxygen transmission rates, demonstrating considerable application potential in high‐barrier packaging. However, its poor thermal processability severely limits its practical use. Based on molecular complexation technology for thermal processing of PVA developed in our research group, a small amount of boric acid (BA) was further introduced to form both crosslinking and hydrogen bonding in the system while preserving the excellent thermal processability and biaxial stretchability of PVA. In this way, high‐performance modified PVA (G‐PVA/BA) films were successfully fabricated via melt extrusion and biaxial stretching, leading to a significant enhancement in mechanical properties and barrier performance. With BA addition of only 0.10 wt.%, the biaxially stretched film exhibited an elongation at break of 434% and a tensile strength of 95 MPa, primarily attributing to the notable increase in crystallinity induced by orientation. The well‐ordered crystal structure also provided a robust physical barrier, resulting in the low oxygen permeability coefficient of 1.117 × 10 −18 cm 3 ·cm/(cm 2 ·s·Pa) at 23°C and 50% RH. This high‐strength, high‐barrier PVA film has broad application prospects in fields such as food, tobacco, electronics, and textile packaging.