Wrinkled thermoplastic polyamide elastomer foams with enhanced mechanical properties fabricated by dynamic supercritical <scp> CO ₂ </scp> foaming

Abstract Wrinkled foams (WF), distinguished by their numerous cell wall wrinkles, exhibit superior impact resistance compared to conventional foams (CF), making them ideal for applications such as sports protection and packaging. Despite their potential, the mechanisms behind wrinkle formation remain underexplored, limiting production and process optimization. In this study, we use a custom supercritical foaming reactor with a sapphire glass viewing window to investigate the differences between wrinkled and conventional thermoplastic polyamide elastomer foams. Our findings suggest that “excessive expansion‐shrinkage” is crucial for wrinkle development. Molecular dynamics simulations reveal that molecular chains align with the flow field of dynamic CO 2 , which increases the intramolecular stress. The release of intramolecular stress triggers wrinkle formation, driven by thermodynamic instability. Furthermore, comparisons of the impact resistance and compression performance between WF and CF show that wrinkled structures alter the deformation behavior under force. The wrinkles facilitate increased collision, squeezing, and friction between cell walls, thus dissipating energy as heat and creating “micro‐air units” that enhance cushioning capability. These distinctive characteristics make WF a promising material for high‐performance applications in cushioning and energy absorption, such as in sports protection and packaging. Highlights Wrinkled polyamide foams are fabricated by dynamic scCO 2 foaming. Chain stretching and shrinkage under scCO 2 flow are verified by MD simulation. Excessive expansion‐shrinkage foaming behavior causes the wrinkled structure. Wrinkled structure greatly increases the impact absorption ability.