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.
Highlights
Thermoplastic polyurethane (TPU) foams have been recently receiving increasing attention due to their vast range of properties that renders them relevant to several industries
Hossieny et al.[1] have shown that broader hard segments (HSs) domains present in the microstructure of TPU lead to higher nucleation rate. They tried to foam TPUs containing different crystallinity ranges with butane in an autoclave batch foaming process. The interpretation of these results suggests that the HSs can play the role of nucleation sites in a gas-loaded system and promote the cell nucleation rate
The TPU foams were produced by pressure-induced batch foaming, extrusion foaming, and bead foam extrusion
Summary
Thermoplastic polyurethane (TPU) foams have been recently receiving increasing attention due to their vast range of properties that renders them relevant to several industries. TPUs are block copolymer chains with alternating hard segments (HSs) and soft segments (SSs). The presence of HSs and SSs, which are microphase separated at room temperature, leads to the elastomeric nature of TPU.[4] The HSs consist of crystalline rigid segments responsible for thermoplastic behavior, while the extensible SSs contribute to the elastomeric properties. HSs almost always contain diisocyanate units that are connected by short-chain diol molecules known as chain extender. SSs usually consist of long-chain polyethers or polyesters.[5,6,7,8,9]
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