Abstract
In this work, Rhodiasolv® PolarClean was employed as a more sustainable solvent for the preparation of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) flat sheet membranes via phase inversion technique by coupling vapour induced phase separation (VIPS) and non-solvent induced phase separation (NIPS) processes. Preliminary calculations based on Hansen solubility parameters well predicted the solubilization of the polymer in the selected solvent. The effect of exposure time on humidity and the influence of polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) and sulfonated polyether sulfone (S-PES) on membrane properties and performance, were evaluated. Three different coagulation bath compositions were also explored. The obtained membranes, prepared using a more sustainable approach, were compared with those produced with the traditional toxic solvent N-methyl-2-pyrrolidone (NMP) and characterised in terms of morphology, porosity, wettability, pore size, surface roughness and mechanical resistance. The potential influence of the new solvent on the crystallinity of PVDF-HFP-based membranes was also evaluated by infrared spectroscopy. The adjustment of the parameters investigated allowed tuning of the membrane pore size in the microfiltration (MF) and ultrafiltration (UF) range resulting in membranes with various morphologies. From the water permeability and rejection tests, performed with methylene blue dye, the prepared membranes showed their potentiality to be used in MF and UF applications.
Highlights
Introduction published maps and institutional affilPolymeric membranes are used in a plethora of applications involving separation processes, spanning from gas separation and water treatment to haemodialysis
The fluoropolymer PVDF-HFP was employed for the first time for the preparation of membranes by the vapour induced phase separation (VIPS)/non-solvent induced phase separation (NIPS) technique using PolarClean as a green solvent
The use of PVDF-HFP allowed us to operate at a milder dope solution temperatures (80 ◦ C)
Summary
Polymeric membranes are used in a plethora of applications involving separation processes, spanning from gas separation and water treatment to haemodialysis. Their lower material and fabrication cost, ease of processability and flexibility, together with the possibility of producing a wide variety of pore sizes, make them the preferred choice in many fields of interest [1]. Among the various techniques employed for the preparation of polymeric membranes, phase inversion is the most widely used both in industry and academia [2] It consists of dissolving a polymer in a suitable solvent and inducing the phase inversion applying external forces (non-solvent induced precipitation, vapour induced precipitation, thermally induced precipitation) or internal forces (evaporation induced phase separation) [3]. N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and N-methyl-2-pyrrolidone (NMP) are dipolar iations
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