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Abstract: The charged poly(vinyl butyral) (PVB) hollow fiber ultrafiltration membranes were fabricated with perfluorosulfonic acid (PFSA) as additive by wet spinning method. Evolution of the precipitation kinetics, morphologies, permeation performances, electrokinetics and mechanical properties of the as-spun PVB membranes were investigated with the PFSA content and bore fluid. The results illustrate that the PVB/PFSA/N-methyl-2-pyrrolidone (NMP) dopes experience an instantaneous demixing mechanism and the precipitation rate increases with the addition of PFSA. The fibers fabricated with 50wt% ethanol aqueous solution as bore liquid have an asymmetrical double finger-like structure; nevertheless, the fibers fabricated with 90wt% NMP aqueous solution as bore liquid form a single finger-like structure. The PVB membranes containing more PFSA content and with 90wt% NMP aqueous solution as bore fluid have higher hydraulic permeability (J w ) than the fibers containing lower PFSA content and with 50wt% ethanol aqueous solution as bore fluid. The highest J w value 78.9LM−2 H−1 bar−1 is obtained for the PVB membrane with a MWCO of 50.1kDa. Streaming potential measurements verify that the apparent zeta potential (ζ app) of the PVB membranes fabricated with 50wt% ethanol aqueous solution as bore liquid ranges from −4.88mV to −11.28mV as PFSA content increases from 1wt% to 3wt%. The break strain and Young’s modulus values of the resultant fibers increase when the PFSA content increases regardless of the bore fluid. [Copyright &y& Elsevier]

Abstract: Hollow fiber membranes are the most applicable form of membranes in laboratory and industrial scale with their large surface to volume ratios. Hollow fiber membranes usually are fabricated by dry–wet solution spinning, where a polymer solution is co-extruded through an annular region with a bore fluid and the nascent hollow fiber passes through an air gap and then enters a liquid coagulation bath. The spinneret dimension, dope and bore fluid flow rates, air gap length, bore fluid and dope compositions and their physical properties, coagulant composition and condition, shear stress within a spinneret, the ratio of dope to bore fluid volumetric flow rate, and the take-up-to-initial velocity ratio (draw ratio) are the primary factors that determine the final hollow fiber morphology and separation properties. All of the aforementioned parameters are not independent and some of them are functions of others. The objective of this paper is to elucidate the interdependence between some of the above parameters. For this purpose, dope and bore fluid axial velocity in the air gap was assumed as a function of the axial distance from the spinneret outlet, z, and radial velocity as a function of the radial distance from the center of the hollow fiber, r, and z. Dimensionless equations of motion and continuity were then simplified and solved simultaneously based on preceding assumptions. It was found from the analysis that the dimensionless axial velocity of dope was a function of the Reynolds number, Capillary number and Stokes number indicating that the axial velocity acceleration in the air gap is determined by viscous, capillary, and gravity force gradients. It was also concluded that the optimum value of the ratio of bore liquid flow rate to dope flow rate is equal to 0.8 of the ratio of the cross-sectional area of the bore fluid to that of the dope at the spinneret outlet. [Copyright &y& Elsevier]