Separation of low-molecular-weight fractions of ultrafine polytetrafluoroethylene with supercritical carbon dioxide

The separation of low-molecular-weight fractions of FORUM® ultrafine polytetrafluoroethylene (UPTFE) in supercritical carbon dioxide (SC-CO₂) was studied under static conditions. The experiments were performed over temperature and pressure ranges of 318–383 K and 10–70 MPa, respectively. Over the entire pressure and temperature ranges covered, a behavior typical of solid substance-SC-CO₂ systems was observed: as the pressure and temperature of the solvent increased, so did the concentrations of low-molecular-weight UPTFE fractions in it. The experimental data were interpreted within the framework of three models establishing a relationship between the solubility of a substance with the supercritical fluid density, those proposed by Chrastil, Bartle, and Mendez-Santiago. The experimental data were closely described by the Bartle and Mendez-Santiago models.