Preparation of microcellular thermoplastic polyurethane (TPU) foam and its tensile property

Abstract

In this study, the thermoplastic polyurethane (TPU) composed of same type soft and hard segment while different hard segment contents was selected to prepare microcellular TPU foams, using CO2 as the physical blowing agent in a batch foaming process. The TPU with high hard segment content (i.e., 36.1 wt%) exhibited high complex viscosity, low initial CO2 content, and microcrystalline region, while the others (i.e., 32.0 and 26.1 wt%) showed opposite results. The cell structure evolution of TPU foams with the foaming temperature and the foaming time showed that the low hard segment content was benefiting for the expansion ratio, whereas the high hard segment content generated the microcrystalline region acting as the nucleating site to improve the cell density. The tensile behavior of prepared TPU foams was investigated in the cyclic tensile test. It was observed that the hysteresis and residual strain increased with the increasing hard segment content, furtherly exhibited lower value compared to TPU. Moreover, scanning electron microscopy, differential scanning calorimeter, and infrared spectra were used to reveal the microstructure after tensile test. The results indicated that the cell structures had a significant contribution to improve the elasticity, resulting from the protection of cells on the hard domains. POLYM. ENG. SCI., 58:E158–E166, 2018. © 2017 Society of Plastics Engineers