Precipitation kinetics, morphologies, and properties of poly(vinyl butyral) hollow fiber ultrafiltration membranes with respect to polyvinylpyrrolidone molecular weight

• PVP Mw influences the precipitation kinetics of PVB/PVP/NMP dopes.
• PVP Mw impacts the morphology and properties of PVB membranes.
• PVB membrane with PVP of lower Mw has a higher hydraulic permeability.
• PVB membrane with PVP of higher Mw has better mechanical properties.

The poly(vinyl butyral) (PVB) hollow fiber ultrafiltration membranes were prepared using three polyvinylpyrrolidones (PVPs) with different molecular weight (Mw) as additives by wet spinning method. Effects of PVP Mw on the coagulation process, morphologies and properties of the as-spun PVB membranes were researched with PVP Mw and bore liquid. The results illustrate that the PVB/PVP/N-methyl-2-pyrrolidone (NMP) dopes have an instantaneous demixing mechanism and the demixing rate declines with the rise of PVP Mw. The fibers fabricated with both two bore liquids have an asymmetrical single finger-like structure. Nevertheless, the fibers fabricated with 90 wt.% NMP aqueous solution as bore liquid form slightly longer single finger-like macrovoids and larger pores in the inner surfaces. The PVB membranes containing PVP with lower Mw and with 90 wt.% NMP aqueous solution as bore liquid have higher hydraulic permeability (Jw) than those containing PVP with higher Mw and with 50 wt.% ethanol aqueous solution as bore liquid. The highest Jw value 135.1 L M−2 H−1 bar−1 is obtained for the PVB membrane with a MWCO of 111.7 kDa. The break strain, elongation ratio and Young’s modulus values of the fabricated fibers increase when the PVP Mw increases. The fibers with 90 wt.% NMP aqueous solution as bore liquid have lower mechanical properties than those with 50 wt.% ethanol aqueous solution as bore liquid.

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