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

Abstract

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 µm and density of 202 kg/m3 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/m3 and a minimum cell size equal to 46 µm. 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/m3 and the lowest cell size is 55 µm.

Green Synthesis of Biobased Soft Foams by the Aza-Michael Reaction

“…Nevertheless, the ratio A h / A c showed a lower interconnection when 0.1 equiv of PMHS is used compared to 0.5 equiv. Compared to PU flexible foams, the obtained foams with 0.5 equivalent of blowing agent showed similar characteristics in terms of pore size and distribution. − Moreover the density was also similar to that of PU foams . However, the foam using 0.1 equiv of PMHS showed a lower cell size.…”

“…60−62 Moreover the density was also similar to that of PU foams. 63 However, the foam using 0.1 equiv of PMHS showed a lower cell size. For all the foams, the density was highly reduced with the use of blowing agent (Table 3).…”

Progress in the development of bead foams – A review

“…Today two different production methods are used 31 : a discontinuous suspension and a continuous foam extrusion process. 32 The suspension process is a batch foaming process, where TPU pellets were impregnated with a blowing agent (n-butane 30,33 or carbon dioxide [34][35][36] ) under high pressure. Depressurizing of the systems leads to expansion.…”

Microcellular foam of styrene–isobutylene–styrene copolymer withN2using polypropylene as a crystallization nucleating and shrinkage reducing agent

“…Their results show that the foams produced by batch foaming had a higher cell density and a smaller cell size than foam extrusion and bead foaming. 12 Qu and his coworkers investigated batch foaming of a blend of polystyrene and TPU. They reported that the solubility of CO 2 and the rheological properties were enhanced by blending PS with TPU, and a bimodal cellular structure was formed by blending TPU with PS as a dispersed domain.…”

“…Shabani and coworkers conducted batch foaming, foam extrusion, and bead foam of TPU and compared the cell structures of the resulting foams. Their results show that the foams produced by batch foaming had a higher cell density and a smaller cell size than foam extrusion and bead foaming 12 . Qu and his coworkers investigated batch foaming of a blend of polystyrene and TPU.…”