Thermoplastic polyurethane foams: From autoclave batch foaming to bead foam extrusion

Two ester-based and one ether-based thermoplastic polyurethane grades have been used to produce thermoplastic polyurethane foams. The foaming process comprised pressure-induced batch foaming, foam extrusion, and bead foam extrusion by using an underwater granulator. Foam density and morphological properties, such as cell size, cell size distribution, and cell density, were measured through different analytical methods. Through autoclave batch foaming a minimum cell size of 10 mu m and density of 202 kg/m(3) is obtained, which is lower than the densities previously reported in the literature for thermoplastic polyurethane. Extrusion foaming however could not achieve the same range of foam expansion given that the lowest density achieved is 635 kg/m(3) and a minimum cell size equal to 46 mu m. The production of thermoplastic polyurethane bead foams is also reported for the first time. The minimum density of the obtained foamed beads is 306 kg/m(3) and the lowest cell size is 55 mu m.

Automated summary

In this study, thermoplastic polyurethane foams were produced using different grades of polyurethane, and various foaming methods were employed to achieve different foam densities and morphological properties. Pressure-induced batch foaming resulted in lower density and minimum cell size, while extrusion foaming had a narrower range of foam expansion.