Improving Welding Behavior of ETPU Bead Foams by Surface Modification with Plasticizers

Efficient resource and energy usage are crucial for sustainable industrial production. Particle foams offer excellent mechanical properties, low weight, and design flexibility. Radio frequency (RF) technology is an alternative to steam chest molding, introducing energy directly into the material without steam, resulting in significant energy and water savings. However, the RF process often develops a temperature gradient in the mold, leading to inconsistent part quality. Thus, suitable modifiers for the Expanded Thermoplastic Polyurethane (ETPU) beads were identified to improve weldability. Stearic acid (SA) and tributyl citrate (TBC) were used as modifiers. Dip‐coating the beads in the dissolved modifier (5 wt.‐% SA in Ethanol (EtOH), 10 wt.‐% TBC in EtOH) significantly increased the bead strength between individual beads in the bead‐to‐bead tensile analysis at 100°C, 120°C and 140°C. The modifiers exhibited different effects on the bead surface. While TBC diffuses directly into the beads during the coating process, SA initially accumulates on the surface of the beads as a coating layer. During heating of the bead, SA melts and diffuses into the bead, leading to a plasticizing effect. Parts produced via RF‐process with modified beads allowed processing at a significantly lower temperature window, enabling faster and easier processing.