Novel PVDF-HFP membranes tailored by supercritical drying process
Sustainable process-product development & green chemistry
SCF as Solvent Substitutes (T1-8P)
Keywords: PVDF-HFP, Membranes, Supercritical, Nanostructure.
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. In particular, the surface tension of solvent to be eliminated can cause the collapse of the gel polymeric structure, leading to a partially non-porous structures. This problem 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 FE-SEM, AFM, DSC and IR analysis. Contact angle measurements have been performed in order to evaluate changes in the surface properties. Also, pore size, porosity and transport properties have been estimated for all membranes. In all cases, the membranes exhibit interconnected structures with nano-sized pores and highly porous surfaces. These PVDF-HFP membranes can lead to an interesting class of nano-structured films resistant to harsh environments, which can find application in different separation processes that can be useful for chemical and pharmaceutical industry.
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