Microporous poly(vinylidene fluoride) hollow fiber membranes fabricated with PolarClean as water-sol

Methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv^Ⓡ PolarClean) as a water-soluble green solvent was used for the first time to prepare poly(vinylidine fluoride) (PVDF) hollow fiber membranes. Due to the solubility of PolarClean in water, a combination of thermally induced phase separation and non-solvent induced phase separation was observed during the membrane formation. The effects of additives such as poly(vinyl pyrrolidone) (PVP) with different molecular weights (10k, 55k, 360k and 1300k) and glycerol (5 wt% and 15 wt%) were studied at different quenching bath temperatures (5, 15 and 25 °C). The properties of the hollow fiber membranes, such as their morphology, roughness, mechanical properties, overall porosity, water permeability, polymorphism in the skin layer and polymorphism in the bulk of the membrane structure were investigated as well. A phase diagram for the PVDF/PolarClean system showed the PVDF crystallization temperature around 53 °C. PolarClean along with additives induces porous structure and the formation of β-polymorphs in the membranes, resulting in high water permeability.