Enhanced cyclic compression properties of aliphatic thermoplastic polyurethane foams with bimodal cell structure fabricated with supercritical carbon dioxide

In this paper, aliphatic thermoplastic polyurethane (TPU) foams with bimodal cell structure were successfully prepared by regulating crystallinity during the saturation process via a simple one-step depressurization foaming method using supercritical carbon dioxide (scCO2) as the physical foaming agent. Taking advantage of the strong crystallization capacity of aliphatic TPU, the crystallinity of aliphatic TPU matrix was controlled effectively by changing the isothermal crystallization time (ti) and temperature (Ti). With the increase of ti or the decrease of Ti, the crystallinity increased and cell structure changed from unimodal to bimodal. In addition, results of cyclic compression test showed that TPU foams with bimodal cell structure exhibited better resilience and compressive properties. Importantly, the relationship among crystallization behavior, cell structure and cyclic compression properties was discussed, and the mechanism of bimodal cell structure for better resilience and compressive properties was analyzed systematically. This work is expected to provide meaningful guidance for the preparation of aliphatic TPU foam with bimodal cell structure and the study of its cyclic compression performance.