Tuning the Gas Permeability of PBAT Composite Films Through Maleic Anhydride—Induced In Situ Aggregation of Shellac During Thermal Curing

This study developed a bio‐based PBAT composite film with enhanced barrier performance through maleic anhydride (MA)‐induced in situ thermal curing and aggregation of shellac. MA promoted esterification and crosslinking of shellac during melt processing, generating dense microdomains within the PBAT matrix that reduced free volume and increased gas diffusion tortuosity. Structural analyses confirmed the successful incorporation of MA into the shellac network and the formation of a compact interfacial structure. The barrier properties of the films were strongly dependent on both MA dosage and curing temperature. At a shellac:MA ratio of 1:2, the composite film showed the lowest oxygen permeability and water vapor transmission rate, reaching 1.49 cm 3 ·cm/(cm 2 ·s·0.1 MPa) and 0.2403 g·mm/(d·m 2 ), respectively. Further optimization of the curing temperature to 170°C reduced these values to 1.24 cm 3 ·cm/(cm 2 ·s·0.1 MPa) and 0.2323 g·mm/(d·m 2 ). In food preservation tests, the optimized film effectively delayed quality deterioration of macadamia nuts and coffee powder, outperforming neat PBAT and in some cases even polyethylene film. These results demonstrate that MA‐induced in situ aggregation of shellac is an effective strategy for fabricating sustainable PBAT packaging films with excellent oxygen and moisture barrier properties for food preservation.