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

Biodegradable poly(butylene adipate-<i>co</i>-terephthalate)\n(PBAT) is attracting much more attention in the field of porous materials\nfor its superior properties, while the poor cell structures of PBAT\nfoams limit their application. In this work, density functional theory\nwas employed to assist in studying the foaming mechanism of PBAT.\nPredicted results implied that the crystallized PBAT chains were more\nconducive to the adsorption of CO<sub>2</sub> molecules, providing\na higher supersaturation density for bubble nucleation. The bubble\ninduced by crystallized chains displayed much smaller critical sizes\nand much larger bubble number densities than those nucleated around\namorphous chains. Based on the theoretical values, PBAT foaming experiments\nat different temperatures were performed by controlling their crystallization\nbehaviors, where the supercritical CO<sub>2</sub> was selected as\nthe foaming agent. PBAT foams with bimodal cell structures were obtained,\nwhere the structures gradually disappeared with increasing foaming\ntemperature. In these foams, the average size of small cells could\nreach 600 nm, and their average cell density was larger than 10<sup>12</sup> cells/cm<sup>3</sup>. In addition, the PBAT-70 foam presented\nthe best cyclic compressive property, and the PBAT-79 foam exhibited\nthe best thermal insulation property. Generally, the high-performance\nPBAT foams were facilitated successfully, where the preparing mechanism\nand properties of the foams were discussed systematically. This study\nprovides some ideas for the preparation and application of PBAT foams.