CO2-philic chain extenders: Engineering interfacial activation for optimized cellular morphogenesis in biodegradable polymer foams

Abstract

With the growing global emphasis on environmental protection, supercritical CO₂ foaming technology for biodegradable materials such as polylactic acid (PLA), poly(butylene adipate-co-terephthalate) (PBAT), poly (butylene succinate) (PBS) and their blends has emerged as a research and application hotspot. However, the low melt strength and poor compatibility of these polymers often lead to low nucleation efficiency, cell wall rupture and coalescence, exhibiting inferior foaming performance. In this work, aiming to enhance the foamability of PLA and PLA/PBAT blends, a fluorinated chain extender, F-CE (GMA-co-DFHA-co-MMA), was designed and synthesized. Through the reactive melt blending, F-CE effectively enhanced the melt strength of PLA and interfacial adhesion between PLA and PBAT, leading to a significant improvement in foaming performance. Additionally, the fluorine groups in DFHA demonstrated high affinity for CO₂, providing additional heterogeneous nucleation sites for bubble formation, thereby increasing both foam expansion ratio and cell density. Notably, the F-CE/PLA foam exhibited a cell diameter of ∼13.8 μm with an exceptionally high expansion ratio of ∼35. As a contrast, pristine PLA foam shows an expansion ratio of ∼30, but with large cell diameter (∼118 μm). Although PLA foam containing CE without fluorine (CE/PLA foam) exhibits small cells with an average cell diameter of ∼13.6 μm, the expansion ratio is low (∼23). In addition, F-CE also exhibits superior performance in improving the foamability of PLA/PBAT blends. This work presents a chain extender specifically engineered for foaming applications, which functions as a highly efficient foaming additive to holistically enhance the foaming performance of polymers.