Microcellular Thermoplastic Polyurethane (TPU) with Multimodal Cell Structure Fabricated Based on Pressure Swing Strategy and Its Compressive Mechanical Properties

The production of soft thermoplastic polyurethane (TPU) foam typically faces challenges such as low production efficiency and inherent shrinkage characteristics. In addressing these issues, this study combines the pressure swing strategy with a N2/CO2 mixed foaming strategy, and based on the mixed gas state equation and cubic antishrinkage model, this study systematically investigates their influence on the production process of TPU foam. The results indicate that the pressure swing strategy significantly reduces the saturation time and achieves a TPU foam with a multimodal cell structure. By adjusting parameters such as the CO2/N2 ratio and residual pressure, the pressure swing strategy can flexibly regulate the cell size (20.41–312.42 μm) and expansion ratio (2.59–7.17). Compared to TPU foam with a uniform cell structure, TPU foam with a multimodal cell structure exhibits superior resilience (energy loss coefficient of ∼21% and compression modulus of ∼0.63 MPa) and fatigue resistance (maximum stress of ∼0.21 MPa and compression strength of ∼0.02 MPa). This work is of significant importance for enhancing the performance of elastomeric foams and improving the efficiency of the production process.