Scalable Gas Barriers Enabled by in Situ Curing of Natural Branched Polyester Oligomers in Poly(butylene adipate- <i>co</i> -terephthalate) Membranes

Poly(butylene adipate-co-terephthalate) (PBAT) is a promising biodegradable polymer for packaging applications; however, its inherently poor gas barrier performance (7.46 cm3·cm/(cm2·s·0.1 MPa)) severely limits practical use. Herein, we report a scalable and additive-efficient strategy to enhance the gas barrier properties of PBAT by incorporating a natural branched polyester oligomer, shellac, via in situ thermal self-curing. Owing to the excellent compatibility between shellac and PBAT, shellac can be homogeneously dispersed within the PBAT matrix during melt processing. Upon thermal treatment, shellac undergoes controlled self-cross-linking, forming densely packed nanoscale particles in situ without altering the crystallinity of PBAT. These cured nanoparticles act as impermeable barriers, significantly increasing the tortuosity of gas diffusion pathways. As a result, the optimized PBAT/shellac composite film exhibits markedly reduced oxygen, carbon dioxide, and water vapor permeability, with the oxygen permeability decreased to 1.22 cm3·cm/(cm2·s·0.1 MPa). Furthermore, the enhanced barrier performance translates into superior food preservation capability, as demonstrated by the prolonged freshness of macadamia nuts and ground coffee during storage. This work provides a green and effective route for designing high-barrier biodegradable PBAT-based packaging materials through the in situ self-curing of natural oligomers.