Rheological properties of HDPE and LDPE at the low-frequency range under supercritical CO2

Abstract

The effects of temperature, pressure (using helium as the pressurizing medium) and dissolved CO2 concentration on the rheological properties of linear high-density polyethylene (HDPE) and branched-chain low-density polyethylene (LDPE) were carefully investigated using a high-pressure rheometer. The results showed that at low pressure, the rheology of the PEs was sensitive to pressure increase. As the pressure increased to higher values, the rheology leveled off for HDPE and increased for LDPE. Under supercritical CO2, the plasticization of the dissolved gas contributed primarily to the thickening effect of pressure. Furthermore, the loss factors decreased with increasing pressure and increased with increasing CO2 pressure. Lastly, the effect of gas concentration was described by the Fujita-Kishimoto model on the assumption that the coupled effect of pressure and CO2 concentration could be separated.