Supercritical carbon dioxide foamed thermoplastic polyester elastomer with poly(lactic acid) blending: shrinkage reduction and expansion ratio improvement

Abstract

Thermoplastic polyester elastomer (TPEE) microcellular foam materials prepared using supercritical carbon dioxide (scCO₂) as a physical blowing agent suffer from poor dimensional stability, which significantly limits their applications across various fields. This study thoroughly investigates the prevalent issues of high shrinkage and low expansion ratio in the scCO₂ foaming process of TPEE. By introducing poly(lactic acid) (PLA), a rigid material with moderate compatibility, into TPEE through blend modification, we markedly improved the shrinkage behavior of foamed TPEE while enhancing its expansion ratio. The experiments successfully produced TPEE/PLA20 microcellular foams with a stable expansion ratio of 19 times. Compared to pure TPEE, the shrinkage rate decreased from 77.3 to 19.0%. Due to its moderate compatibility, PLA was uniformly dispersed within the TPEE matrix as a dispersed phase, which refined the cell structure through heterogeneous nucleation and reduced cell walls strain. Additionally, rigid PLA micro/nanoparticles acted as stress concentration points, promoting the formation of an open-cell structure by causing cell walls rupture, thereby accelerating gas diffusion. More importantly, high glass transition temperature (T_g) PLA nanoparticles are stretched and embedded in the cell walls during the foaming process, and the heterogeneous nucleation effect of PLA enhances the crystallinity of TPEE. These two factors together increase the rigidity of the cell walls. The synergistic effects of these factors enabled the TPEE/PLA microcellular foam materials to effectively resist shrinkage caused by the pressure differential between the inside and outside of the cells and molecular chain relaxation.

Graphical Abstract