Effect of TPU soft segment molecular weight on TPU’s bead foaming behavior

Abstract

The bead foaming behavior of three different thermoplastic polyurethane (TPU) samples with different polyol soft-segment molecular weights was investigated through a lab-scale bead foaming reactor. These TPU samples possessed similar hard-segment content and soft-segment molecular weights of 1000, 2000, and 3500 g/mol. The evolution of the hard-segment crystallization during the isothermal saturation as well as the increased solubility of supercritical CO2 within the soft-segment region are, respectively, determinative parameters on improving the heterogeneous cell nucleation and expansion of the expanded TPU (ETPU) bead foams. The effect of saturation temperature, pressure, and time on the hard-segment crystallization and hence on the foaming behavior of TPU samples were explored. The results showed that the increase in soft-segment molecular weight increased the expansion ratio of the bead foams while the processing parameters differently influenced the hard-segment crystallization and CO2 solubility and hence the foaming behavior of ETPU foams.