Reactive interfacial design enables oxygen–moisture transport regulation in PLA/cotton-stalk films for food preservation

Effective food preservation using biodegradable films depends on the balanced regulation of oxygen and moisture transport rather than the isolated optimization of a single barrier parameter. Here, cotton stalk (CS), an agricultural residue, was incorporated into polylactic acid (PLA) matrices, with PLA-g-MAH used as a reactive compatibilizer to tailor the PLA/CS interface. FTIR and XPS analyses indicated changes in the local chemical environment of hydroxyl-, ester-, and carboxyl-related groups at the PLA/CS phase boundary, supporting possible interfacial reactions and secondary interactions. SEM and three-dimensional surface profilometry demonstrated that the film containing 6% PLA-g-MAH exhibited the most compact fracture morphology and the lowest surface roughness. This configuration minimized both the oxygen transmission coefficient and water vapor transmission rate, indicating that targeted interfacial regulation suppressed defect-driven molecular diffusion pathways. In contrast, excessive PLA-g-MAH induced local phase heterogeneity that partially reopened transport channels. In food storage tests, the optimized film reduced banana weight loss, slowed visible color deterioration, and lowered total viable counts in fresh pork without requiring migratory antimicrobial additives. These findings support a passive preservation strategy in which agricultural-residue-based PLA films modulate oxygen and moisture transport through interfacial design.