Supercritical CO2 foaming and mechanical properties of thermoplastic polyurethane based on molecular structure

The molecular structures of thermoplastic polyurethane (TPU) affect its microphase separation and foaming behavior. Three aliphatic TPUs were studied to investigate the influence of their molecular structures on their crystallization behavior, shear rheological properties, mechanical properties, and foaming behavior. The experimental results indicated that the branched structure and hard segment content affected the crystallization behavior of TPU. Lower crystallinity decreased the foaming initiation temperature, whereas higher crystallinity enhanced the stability of cell structure. The branched structure and hard segment domains functioned as heterogeneous nucleation sites, leading to increased cell density and reduced cell size in microcellular TPU. Microcellular TPU with a high molecular weight and branched structure exhibited superior tensile strength and elongation at break, i.e., the tensile strength and elongation at break of TPU1 with a density of 0.25 g/cm3 reached 10.82 MPa and 373 %, respectively. This study demonstrated the regulation of microcellular TPU by analyzing its molecular structures.