Solubility and interfacial tension of thermoplastic polyurethane melt in supercritical carbon dioxide and nitrogen

- Mixtures of TPU with supercritical CO2 and N2 were investigated.
- S-L EOS scaling parameters of TPU, CO2 and N2 were determined.
- Increasing pressure at a constant temperature enhances the solubility for both SCFs.
- The solubility of CO2 is four times greater than the one of N2 in the TPU melt.

Various industries, such as automotive and leisure, show a great interest in foaming thermoplastic polyurethane (TPU) with physical blowing agents. Hence, this study aims to investigate the effects of absorption of carbon dioxide and nitrogen by melt TPU on solubility and interfacial tension. Using a pressure-volume-temperature apparatus for high pressure and temperature combined with a magnetic suspension balance, the solubility of carbon dioxide and nitrogen in thermoplastic polyurethane melt was measured at temperatures from 190 °C to 220 °C and at pressures to 25 MPa. The solubility of both supercritical fluids (SCF) in the TPU melt was then compared with semiempirical data and theoretical values calculated from the Sanchez-Lacombe equations of state (S-L EOS). The surface tension of the TPU/SCF interface was measured using the axisymmetric drop shape analysis profile. It was observed that the dependency of interfacial tension on temperature at high pressures decreases because of a reduction in SCF solubility at high temperatures. The relationship between the interfacial tension and the density difference of polymer-supercritical fluid was also examined using the generalized Macleod's equation.

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