Interfacial tension of linear and branched PP in supercritical carbon dioxide

In this study, sessile drops are imaged in a high-pressure and high-temperature view chamber to determine the density and interfacial tension of linear polypropylene (LPP) and branched polypropylene (BPP) melts in supercritical carbon dioxide (CO2). The pressure–volume–temperature (PVT) data of polyprophylene (PP)–CO2 is investigated by monitoring the swelling changes of the polymer melt in supercritical CO2. The density difference between the polymer/CO2 mixture and the CO2 is determined by combining the swelling results with the CO2 solubility information in the polymer melt. Both the Sanchez–Lacombe (SL) and the Simha–Somcynsky (SS) equations-of-state (EOS) are applied to predict the density of the PP–CO2 mixture, which is then compared to the density data obtained experimentally. The dependence of interfacial tension on the temperature and pressure of PP in supercritical CO2 is investigated at temperatures from 180 °C to 220 °C and pressures up to 31 MPa. Effects of long-chain branching on the density and interfacial tension of PP–CO2 mixtures are discussed.