Physical foaming of 25% post-industrial recycled TPU using the supercritical foaming technology

The production of recyclable TPU foams has seen rising interest due to the requirement for a green alternative to chemical foams. While extensive research has been conducted on batch foaming and microcellular injection molding of TPU, the processing of recycled TPU (rTPU) remains largely unexplored. This paper investigated the foaming process of 25% post-industrial recycled TPU using the microcellular method and nitrogen as the physical blowing agent. Rectangular specimens with a thickness of 14 mm and a density of 0.22 g/cm3 were molded. Gas counterpressure was utilized to favor the uniform foaming of the component. Average cell size and cell number analyses were performed, demonstrating that in the core region of the specimen, the recycled TPU foams exhibited similar properties as the foams manufactured using virgin material. In the skin region, rTPU samples showed an improved morphology when compared to the non-recycled foams. The processing temperature of rTPU proved to have a great impact on the properties of the material, with lower temperatures being favorable to avoid excessive degradation.