Steam-chest molding of expanded thermoplastic polyurethane bead foams and their mechanical properties

•A novel expanded bead foam described as ETPU was molded through a steam-chest molding process.•The ETPU bonded effectively, the corresponding products had a smooth surface, and good tensile and compressive properties.•A bonding mechanism was proposed.

The steam-chest molding process can be used to prepare molded bead foams, including expandable polystyrene (EPS), expanded polyethylene (EPE), expanded polypropylene (EPP), and expanded polylactide (EPLA) with complex three-dimensional shapes. A new thermoplastic elastomer bead foam, which is described as expanded thermoplastic polyurethane (ETPU), now exists. Notably, it has an excellent soft touch quality and is ductile. It has also generated widespread interest in both the academic and industrial communities. In this study, three types of ETPU foams with various sample sizes were steam-chest molded. We concentrated on the preparation of the molded ETPU (METPU), which was followed by a mechanical test. Our morphological observations showed that the ETPU bead foams' interfaces had effectively bonded. A high tensile strength of 1.80 MPa and an elongation at break of 360.1% were reached in the METPU sample with a density of 0.35 g/cm3. A 200-fold cyclic compression measurement verified that the compressed METPU sample could recover more than 95% both in stress and modulus, after 6 days of relaxation. This suggested the presence of excellent interbead bonding in the ETPU bead foams. Based on the differential scanning calorimetry (DSC) results, we proposed that a formation mechanism for interbead bonding during the ETPU steam-molding process existed.

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