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In this study a thermo-sensitive switching membrane was prepared through grafting, using a click reaction, of an N -isopropylacrylamide (NIPAAm) derivative onto an electrospun poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) fibrous membrane (EPFM). The PPO was first electrospun into a fibrous membrane, then brominated and reacted with NaN 3 to generate the azido-terminated EPFMs. A propargyl-terminated poly( N -isopropylacrylamide) (PNIPAAm) was synthesized and grafted onto the azido-terminated EPFMs. The surface roughness of PPO fibers was increased due to the presence of PNIPAAm grafts, such that the thermoresponse of the static water contact angle (SWCA) of PNIPAAm-grafted EPFMs between 25 and 45 °C was significantly greater than that of the same PNIPAAm grafted on a flat surface. Thermo-sensitive affinity of the membrane with water resulted the average pore dimension responded to temperature changes. Taking advantage of this temperature-responsive affinity, we applied the membranes as protein valves that blocked and released an antibody. At 25 °C, the collection efficiency was 90% for antibody concentrations of up to 5 ng/mL. Increasing the temperature to 45 °C caused the collection efficiency to decrease abruptly, to 7.5%, when the antibody concentration was greater than 1.5 ng/mL. Accordingly, this system of PNIPAAm-grafted PPO fibers functioned as a protein valve, allowing the blocking and release of proteins. [ABSTRACT FROM AUTHOR]

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: The silver ionic modification approach and dual-layer hollow fiber spinning technology synergistically lead to the significantly enhanced O2/N2 and CO2/CH4 selectivity of 9.5 and 118, respectively, with an ultrathin dense-selective layer of 1092Å in the pure gas measurement. Even with the presence of competition in sorption sites between two penetrants, the dual-layer hollow fiber membrane developed in this work still reveals the superior CO2/CH4 selectivity of 87.9 in the mixed gas measurement. To our best knowledge, this is the first time for the polyethersulfone (PES) material to achieve so high CO2/CH4 selectivity through the ionic modification. The electrostatic crosslinking, steric hindrance and affinity to some specific gases (e.g. O2 and CO2) induced by the incorporation of ionic groups into the PES matrix may be three dominant factors for the advanced gas separation performance in this work. [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]

Abstract: The relationships between processing conditions and ultimate membrane properties that exist in the spinning of hollow fiber membranes are not fully understood. To address the need for a widely applicable fiber spinning model, the present work builds on the thin filament analysis (TFA) model of the fiber spinning process and predicts the variation of fiber size, velocity, and temperature in the draw zone, including the effects of surface tension. By modeling concentration gradients in the draw zone, this model also predicts both the extent of anisotropy (portion of membrane thickness containing a pore size gradient) and degree of anisotropy (indicative of the pore size range across the membrane thickness). For typical hollow fiber membrane spinning, predicted membrane extent of anisotropy is most sensitive to the diffusion coefficient. The predicted degree of anisotropy is most sensitive to the viscosity activation energy, affected significantly by the diffusion coefficient and spinning temperature, and affected slightly by the air gap length. Trends in the model-predicted and experimental measurements of final fiber outer diameter, ratio of outer to inner diameter (OD/ID), and extent of anisotropy agree. While model sensitivity studies show that surface tension can reduce the rate of fiber elongation, it has little effect on the predicted degree and extent of anisotropy. Furthermore, this analysis allows prediction of counter-intuitive concentration changes associated with temperature dependence of the diluent vapor pressure: for some cases, the degree of anisotropy can increase and then decrease along the draw zone during spinning. Reducing the dependence of vapor pressure on temperature eliminates this phenomenon. [Copyright &y& Elsevier]

Abstract: Poly(vinyl chloride) hollow fiber membranes were prepared by the dry/wet and wet/wet spinning technique at different air gap lengths keeping all other spinning parameters constants. Mean pore size, pore size distribution and mean roughness of both the internal and external surfaces of the hollow fibers were determined by atomic force microscopy. Cross-sectional structure was studied by scanning electron microscopy. Ultrafiltration experiments of pure water and aqueous solutions of different solutes having different molecular weights (bovine serum albumin, polyethylene glycol and polyvinyl pyrrolidone) were carried out. It was found that the inner and outer diameters of the PVC fiber membranes decreased with the increase of the air gap distance due to the gravitational force effect. The hollow fiber membranes prepared without and with air gap distances up to 7cm exhibited a quite symmetric cross-structure consisting of four layers, two small finger-like structure layers at both edges of the hollow fibers and two larger finger-like voids mixed with macrovoids layers in the middle of the cross-section. The outer-middle layer thickness decreased when the air gap distance was increased to 10cm and disappeared from the cross-section of the hollow membranes prepared with higher air gap lengths than 15cm. For all dry/wet spun PVC hollow fibers, the outer pore size and the pure water permeation flux both increased with the increase of the air gap distance. In contrast, the solute separation factor decreased with the air gap distance. This was related to the pore size of the external surface of the PVC hollow fibers. [Copyright &y& Elsevier]