Regulation of Mechanical and Barrier Properties of Starch/PBAT Films from Extrusion Perspective: Structural Evolution, Correlation Insights, and Predictive Model Development

Starch/poly(butylene adipate-co-terephthalate) (PBAT) composites are promising biodegradable materials that may be used as sustainable packaging materials in the food and other industries. These composite materials are usually fabricated by using blown-extrusion methods. In this study, the structural evolution of starch/PBAT composites during extrusion was elucidated. Starch underwent a transition from its typical A-type crystalline structure to a predominantly amorphous structure, and then recrystallized into a V6-type crystalline structure in the composite pellets and films. These structural changes were accompanied by hydrogen-bond rearrangement (starch–starch to starch–glycerol), double-helix disintegration, and molecular-weight reduction. Phase separation during film blowing contributed to molecular rearrangements and changes in the crystallization state within the starch and PBAT phases. The relationships between the composition and processing parameters used to form the blown-extrusion films and their final physicochemical properties was established. Correlation analysis revealed the maximum effect size (partial eta-square ≥ 0.9) and pronounced correlation (Mantel’s p ≤ 0.001, r ≥ 0.25) of “starch proportion” with the films’ mechanical and barrier properties, alongside significant interactions among the film-forming parameters (P < 0.05). On this basis, an artificial neural network (3 × 88 × 126 × 15) was constructed to predict the mechanical and barrier properties from these film-forming parameters, with high prediction accuracy (R ≥ 0.9) and generalization ability. These findings enhance the understanding of how extrusion regulates the mechanical and barrier properties of starch/PBAT films, which may help in the industrial production of these sustainable materials.