Effective recovery of perfluoropolyether surfactants from PVDF and PTFE by supercritical carbon dioxide extraction

The extraction of ammonium carboxylate perfluoropolyether surfactants from poly(vinylidenefluoride) (PVDF) and poly(tetrafluoroethylene) (PTFE) was performed with supercritical carbon dioxide. When proper conditions in terms of temperature, pressure and flow rate were used, extraction recoveries higher than 90% were obtained. For PVDF (with a concentration of surfactant of 5% w/w), at low pressure (12 MPa) and 40 °C, more than 100 min are necessary to have a quantitative extraction. On the other hand, at higher pressure (20 MPa) a quantitative recovery was obtained after few minutes. A strong influence of the temperature on the extraction recovery was also found. In the case of PTFE with a very low content of surfactant (600 ppm), high recovery was obtained at 20 MPa, CO2 flow rate 11 g/h, T = 40 °C after 240 min. Our results suggest that extraction with scCO2 can be a process of applicative interest for the removal of this class of stabilizers from fluoropolymers.