Study of the mechanical properties of thermoplastic polyurethane (TPU) recycled from end-of-life ski-boots and techno-economic analysis (TEA) of the mechanical recycling processes

A novel process for the mechanical recycling of thermoplastic polyurethane (TPU) parts of end-of-life ski-boots was developed with the aim to produce new ski-boots with a fully circular approach. A detailed study on the effects of the use of the boot and of the recycling processes on the properties of the recycled TPU was reported. Chemical and thermal analyses showed a slight degradation of the TPU polymer due to the use of the boots, which however did not affect the mechanical properties of the material. Multiple recycling processes were conducted and the TPU recovered from virgin boots exhibited a loss of the tensile strength (from 44 to 26 MPa) and of elongation at break (from 1046% to 840%) values after three consecutive recycling steps, while the TPU recovered from used boots exhibited similar mechanical losses already after two recycling steps. The simulation of aging by water/thermal cycles showed a plasticization effect (Young Modulus decreased of 16%) by immersion in water, followed by cold temperatures, while an opposite trend (Young Modulus increase of 13%) was observed for the aging treatments performed at 75 °C for 100 h. The Techno-Economic Analysis of the proposed recycling process showed that the recycling processes are scalable, but the recycling of at least 30000 ski-boots is needed to be economically profitable.