Production of PVDF-HFP nanostructured membranes for water purification by supercritical phase inversion

In this work, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membranes for water purification were produced by supercritical phase inversion using a mixture of supercritical CO2 (SC-CO2) and ethanol as non-solvent. Different polymer concentrations (from 10 to 20% w/w) and ethanol amount by volume (from 1 to 50% v/v) with respect to SC-CO2 flow rate, were tested in order to study their influence on membranes morphology, surface area and porosity; supercritical processing was performed at a pressure of 200 bar and a temperature of 45 °C. Membranes characterized by a cellular morphology with a nanoporous substructure and/or by an homogeneous nanoporous morphology were obtained, changing the starting polymer concentration and the ethanol amount during the process. In particular, increasing the amount of ethanol from 1 to 50% v/v, an increase of membranes porosity and surface areas was obtained, and the membranes morphology changed from microporous with nanoporous cell walls to completely nanoporous, due to an increase of the non-solvent power that improved the in-situ gelification mechanism during the supercritical phase separation.