Fabrication of Thermoplastic Polyurethane Foams with Wrinkled Pores and Superior Energy Absorption Properties by CO2 Foaming and Fast Chilling

Precise control and delicate manipulation of pore morphology are challenges for supercritical CO2 (scCO(2)) foaming of polymer foams to boost their performances and extend their applications. Herein, a simple two-step scCO(2) foaming and fast chilling method is proposed to fabricate thermoplastic polyurethane (TPU) foams with unique wrinkly structures inside the pores by introducing a fast cooling procedure in an ice water bath right after the foaming process. The combined effects of the increase of TPU surface tension and the decrease of CO2 pressure inside the pores induce intense intermolecular stress on the pore walls, which trigger the formation of micro-sized wrinkles on the pore walls. The wavelength of the wrinkly structure can be reduced from 2.8 to 1.1 mu m by raising the foaming temperature, which is associated with the wrinkled structure changing from hexagon to labyrinth. Compared with conventional foams, wrinkled foams possess superior compressive modulus, strength, and energy absorption performance, and wrinkled foams with wrinkles display better energy absorption. This study provides a facile approach to produce wrinkled foams with controllable morphology and gives insights into the remarkable compressive performance of the wrinkled foams, which make them promising materials for energy absorption applications.