Comparative study on foaming process of thermoplastic polyester and polyether polyurethane with supercritical CO2 as foaming agent

The aim of this study was the comparison of beads foaming process and synergistic effect of foaming process parameters on melting crystalline characteristics between thermoplastic polyester and polyether polyurethane(TPU) via batch process using supercritical CO2(scCO2) as blowing agent. Method was based on the generation of expandable TPU foam beads (ETPU) prepared by self-designed autoclave foaming apparatus. The surface morphology, cell structure, and crystalline melting characteristics of the ETPU depending on the processing parameters, such as saturation pressure (Pf), saturation temperature (Tf), and saturation time (tf), were investigated. Results demonstrated both ETPU exhibited fine closed cell morphology with polygons structure and would induce the disappearance of multiple endothermic peaks during the foam process. As any of those three process parameters increased, the HS content, high crystalline melting and Er were improved, while with regard to cell structure, Pf demonstrated the opposite effect compared with Tf and tf. Comparing with polyether TPU, polyester TPU possess a larger cell density and a clear bimodal cell structure could be found under certain condition, while beads foaming process had a greater impact on polyether TPU, which had a low density and the appropriate tf is 2h.