Insights into the Foaming Mechanism of Micro-Nanocellular PBAT Foams Regulating by Crystallization Behaviors

Biodegradable poly(butylene adipate-co-terephthalate) (PBAT) is attracting much more attention in the field of porous materials for its superior properties, while the poor cell structures of PBAT foams limit their application. In this work, density functional theory was employed to assist in studying the foaming mechanism of PBAT. Predicted results implied that the crystallized PBAT chains were more conducive to the adsorption of CO₂ molecules, providing a higher supersaturation density for bubble nucleation. The bubble induced by crystallized chains displayed much smaller critical sizes and much larger bubble number densities than those nucleated around amorphous chains. Based on the theoretical values, PBAT foaming experiments at different temperatures were performed by controlling their crystallization behaviors, where the supercritical CO₂ was selected as the foaming agent. PBAT foams with bimodal cell structures were obtained, where the structures gradually disappeared with increasing foaming temperature. In these foams, the average size of small cells could reach 600 nm, and their average cell density was larger than 10¹² cells/cm³. In addition, the PBAT-70 foam presented the best cyclic compressive property, and the PBAT-79 foam exhibited the best thermal insulation property. Generally, the high-performance PBAT foams were facilitated successfully, where the preparing mechanism and properties of the foams were discussed systematically. This study provides some ideas for the preparation and application of PBAT foams.