Effects of poly(propylene carbonate) on poly(butylene adipate-co-terephthalate) microcellular foams: Improved expansion and reduced shrinkage

Microcellular foams made from poly (butylene adipate-co-terephthalate) (PBAT) using supercritical carbon dioxide (scCO(2)) as a physical foaming agent have exhibited high shrinkage and low expansion ratios, limiting their potential applications. Previous studies have indicated that while PBAT exhibits foaming capabilities, its maximum expansion ratio typically does not exceed 20, and it is characterized by a high shrinkage ratio, which limits its application in high-performance foams. In contrast, this study presented an 80PBAT/20PPC microcellular foam that has achieved a stable expansion ratio of 38.9 and a substantial reduction in shrinkage ratio to 9.4% from the 89.5% observed in pure PBAT. This advancement is attributed to the blending of PBAT with poly(propylene carbonate) (PPC), a polymer with moderate compatibility. PPC was uniformly dispersed within the PBAT matrix in micro/nano particle form, which inhibited crystallization and leveraged its unique molecular structure to enhance CO2 solubility, thereby increasing the expansion ratio and refining the cell structure. Additionally, PPC particles acted as stress concentrators, promoting cell wall rupture and forming an open-cell structure. Furthermore, the higher glass transition temperature (T-g) of PPC further enhanced the stiffness of the cell walls. These synergistic effects enabled PBAT/PPC microcellular foams to effectively resist shrinkage caused by internal-external pressure differentials.