Fabrication of Polyvinyl Alcohol‐Based Packaging Film With Hydrophobic Surface and High Mechanical Strength

ABSTRACT Despite extensive research on alternatives to petroleum‐based materials, developing polyvinyl alcohol (PVA)‐based films that simultaneously exhibit high hydrophobicity and mechanical robustness remains a persistent challenge. In this study, we propose a straightforward surface modification strategy to fabricate PVA‐based packaging film with enhanced mechanical strength in a watery environment. The approach employs imidazole‐blocked hexamethylene diisocyanate (BHDI) in ethyl laurate, a food‐grade, non‐toxic solvent that swells PVA film without dissolving it. Unlike conventional crosslinking strategies that rely on toxic aldehydes or strong organic solvents, this method enables uniform, controlled surface crosslinking via thermally activated deblocking. The regenerated isocyanate then reacts with surface hydroxyl groups through nucleophilic addition without compromising processing safety. The resulting crosslinked PVA‐BHDI films displayed a water contact angle (WCA) of 102° at room temperature. The PVA‐BHDI 5 film demonstrated a tensile strength of 80.1 ± 0.33 MPa under dry condition. The film retained a tensile strength of 36.2 ± 0.20 MPa after 24 h immersion in water at ambient temperature, similar to that of polyethylene (PE) in its dry state. Remarkably, the films maintained their hydrophobicity and structural integrity, showing no signs of dissolution or fracture even after 4 h of immersion in 95°C hot water. In addition, the crosslinked films showed improved moisture barrier and UV‐blocking capabilities. This study presents the first demonstration of a safe, solvent‐assisted, surface‐targeted BHDI crosslinking system for PVA, enabling high hydrophobicity, wet‐state mechanical strength, and thermal water resistance for potential use as plastic bags and packaging.