Effect of Physical Structure of Thermoplastic Polyurethane on the Supercritical CO2 Foaming

The effect of macroscopic structures such as pellet size, shape, and orientation on the structure development in the formation of a thermoplastic polyurethane (TPU) foam by supercritical CO2 foaming was studied. If the same amount of supercritical CO2 diffused into the polymer, it was found that pellets having a relatively large volume and surface area show the decreasing of cell density and increasing of cell size, consequently, an increase in the expansion ratio of foaming was obtained. The chain orientation resulted in the increase in cell density and decrease in cell size, thereby the foam expansion ratio was reduced. This was understood that the chain orientation might prevent the diffusion of supercritical CO2 and promotes nucleation at the same time.