Effect of extrusion on the foaming behavior of thermoplastic polyurethane with different hard segments

Although it is known that the extrusion process significantly affects the cell morphology of thermoplastic polyurethane (TPU) foam, its effect on foam shrinkage, which is a critical problem in foam processing, has not yet been studied. Extrusion also significantly influences the thermomechanical properties and foaming behavior of TPUs. In this study, polyether-based TPUs of three different hardness levels were foamed by one-step batch foaming using CO2 as the blowing agent. Although the molecular weight decreased significantly after extrusion, the re-distribution of hard segments in the TPU caused the cell density to increase by 30 to 50 times. In addition, the elongation at break of the TPU solids increased by 40%. The cell size, expansion ratio, cell density, and shrinkage versus saturation temperature (T-sat), and saturation pressure (P-sat) were also studied extensively. The results show that T-sat has a significant effect on expansion ratio and P-sat has more impact on foam shrinkage, while the extrusion processing has little impact on foam shrinkage. In our case, a TPU foam with more than six times expansion and a fine cell structure with limited shrinkage was successfully prepared.

Automated summary

This study investigated the effects of the extrusion process on the cell morphology and foam shrinkage of thermoplastic polyurethane. The results showed an increase in cell density and elongation at break after extrusion, with significant impacts of T-sat and P-sat on foam properties.