Process for production of expanded thermoplastic elastomer

A process for production of pellets of expanded thermoplastic polyurethane, the pellets having a bulk density in a range from 80 g/l to 140 g/l, said process comprising the steps of:

• (a) adding monomers and/or oligomers used for producing the thermoplastic elastomer with or without further starting materials into a first stage of a polymer-processing machine,
• (b) mixing the monomers and/or oligomers and also the optionally added further starting materials and reacting the monomers and/or oligomers to give a polymer melt in the first stage of the polymer-processing machine,
• (c) immediately or directly passing the polymer melt into a second stage of the polymer-processing machine and adding a physical blowing agent with or without further starting materials to obtain a polymer melt comprising a blowing agent, wherein the blowing agent comprises 50 wt % to 100 wt % carbon dioxide and 0 wt % to 50 wt % nitrogen and no further blowing agent,
• (d) molding the polymer melt comprising a blowing agent into pellets of expanded thermoplastic polyurethane in a system for producing a pellet material which follows the second stage wherein the first stage of the polymer-processing machine and the second stage of the polymer-processing machine are parts of one machine.