Novel PVDF-HFP membranes tailored by supercritical drying ..

The work is based on the drying of PVDF-HFP gels with a procedure assisted by supercritical CO2 to obtain nano-sized porous membranes at high quality/low cost ratio. Poly(vinylidene fluoride) (PVDF) as homopolymer or copolymer with hexafluoropropylene (PVDF-HFP) is a very interesting material largely used in catalytic membrane reactors, chemical and biomedical applications and various filtration processes. For this reason, many studies have been performed concerning the formation of porous PVDF-HFP structures by means of traditional phase inversion or gels drying methods. The classic gels drying presents some problems. These problems can be avoided using supercritical CO2, which preserves the polymeric network of gels during the drying and aerogels formation. Moreover, this new approach appears advantageous with respect to conventional phase inversion methods, due to the reduced-solvent manufacturing process. PVDF-HFP gels have been prepared from polymer/acetone solutions adding ethanol; then, the solutions have been cooled at -20°C for 30 min. Series of supercritical drying experiments have been performed at 35°C, 200 bar and at various polymer concentrations (from 5 to 12% w/w). Effects of the tailoring conditions on the membrane structural parameters have been evaluated by SEM analysis. In all cases, the membranes exhibit interconnected structures with nano-sized pores and highly porous surfaces.