SUPERCRITICAL-FLUID FRACTIONATION OF A LOW-MOLECULAR HIGH-DENSITY POLYETHYLENE WAX USING CARBON-DIOXIDE, PROPANE, AND PROPANE-MODIFIED CARBON-DIOXIDE

Supercritical fluids can in many instances be advantageous alternatives to traditional liquid solvents in areas of polymer processing. In this study, the use of three different supercritical fluids, carbon dioxide, propane, and 20 vol % propane in CO2 were evaluated for their ability to fractionate a low molecular weight, high-density polyethylene wax into several narrow molecular weight distributions. Supercritical CO2 was found to generate cuts with polydispersities as low as 1.02 but was unable to extract material heavier than about 2000 MW. Supercritical propane demonstrated much greater solvating strength for the parent polymer but was unable to provide the same degree of selectivity as CO2. A 20 vol % mixture of propane in CO2 nearly doubled the overall recovery compared with pure CO2 while not significantly broadening the MWDs of the resulting fractions.