Effect of the rheology of poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) dope solutions on the formation of microporous hollow fibers used as membrane contactors

The effects of the shear rate on the permeation flux and molecular weight cutoff (MWCO) of the membranes made by Batch III-2L.5T dope solution (2 wt.% LiCl and 0.5% Tween 80 as the additive) presented a V shape curve; while for the polymer dope of Batch V-2P9G (2 wt.% PVP and 9 wt.% glycerol as the additive), the effect of the shear rate on the resultant membranes showed a different pattern: increasing the shear rate resulted in smaller MWCOs, enhanced water permeation flux and higher elongation strength. These behaviors have been discussed thoroughly based on the shear-induced macromolecular chain orientation and close packing, variation of the porosity with the shear rate and shear-thinning rheological property of the dope solution under a high shear stress.