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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]

The development of a loose inner-selective polyethersulfone (PES) hollow fiber by one-step spinning process for nanofiltration (NF) has been demonstrated in this study. It is found that the addition of a small amount of sulfonated polysulfone (SPSf) and the use of a specially designed bore fluid made of hydrophilic additives such as polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) are of great importance to fabricate this type of NF membranes. Not only are they able to reduce the pore size but also suppress the formation of finger-like macrovoids. After optimizing both dope solution and spinning conditions, the as-fabricated membrane can have a 70% rejection to PEG 1000 and a pure water permeability (PWP) of 12.8 L m −2 h −1 bar −1 . Its rejection of indigo carmine (MW: 466 gmol −1 ) can reach 96.64%. In addition, it shows good stability in a continuous 76-h operation with good efficiency of dye removal. The newly developed membrane may have great potential in the treatment of textile wastewater. [ABSTRACT FROM AUTHOR]

Curved and structured membrane geometries are known to have the potential to reduce concentration polarization and fouling rates in membrane filtration and membrane contacting applications. However, their production is cumbersome and often comprises various successive processing steps. We present a new direct fabrication process of two new hollow fiber geometries: Curled and meandering hollow fibers. The phenomenon of liquid rope-coiling is adapted to a membrane spinning process resulting in mostly spiralling curly fiber geometries. Parameters influencing geometric properties are evaluated and experimentally obtained structures are presented. Fibers were prepared from a polyethersulfone-based polymer solution in an air gap spinning process. Prepared structured hollow fibers are investigated regarding geometrical measures and pore structures. A comprehensive analysis of the complex interplay between the influencing parameters is suggested. [ABSTRACT FROM AUTHOR]

Abstract: Due to the unique properties of amphiphilic Pluronic block copolymers, they have been blended with other polymers such as PVDF to prepare membranes. Considering the stability issue, the strong pore-forming ability of Pluronic F127, and the mechanical strength of the resultant membranes, Pluronic/LiCl mixed additive consisting of a very low concentration of Pluronic has been used in this study. The effects of spinning conditions on PVDF hollow fiber fabrication have also been studied. It is found that the use of merely 0.2wt% of Pluronic is sufficient to impose significant impacts on the morphology, filtration performance, and mechanical properties of the resultant fibers. Hollow fibers spun using higher coagulant temperature, higher take-up speed, and water as the bore fluid exhibit better mechanical properties and filtration performance. PVDF hollow fiber membranes with PWP of 1180L/m2 hMPa and MWCO of 5kDa were obtained when spun with optimized spinning conditions and using 3wt% of LiCl and 0.2wt% of Pluronic as the mixed additive. The fibers can withstand a pressure of 0.55MPa from the lumen. [Copyright &y& Elsevier]

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: Porous stainless steel hollow fibers have been prepared via the dry–wet spinning process, based on phase inversion of a particle loaded polymer solution, followed by sintering. The morphology of the green fibers combines sponge like structures and macro voids, and is related to the dynamics of the phase inversion process. The morphology can be tuned by changing the spinning conditions and the composition of the spinning mixture. In analogy to their ceramic counterparts the morphology of the stainless steel fibers is preserved during sintering, apart from shrinkage due to densification. At a length scale comparable to the diameter of the steel particles the microstructure and related pore size distribution are more strongly affected by the sintering temperature, as compared to their ceramic counterparts. Sintering the stainless hollow fibers at temperatures>1100°C results in a sharp decrease in nitrogen permeance and an increase in bending strength, due to densification. The strength (∼1GPa) and nitrogen permeance (0.1mmolm−2 Pa−1 s−1 at 21°C) of stainless steel fibers sintered at 1050–1100°C are superior as compared to their ceramic counterparts. The excellent properties of the stainless steel hollow fibers make them suitable as membrane (supports) for applications involving harsh environments. [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: This article describes the research study on exploitation of polymer blending technology and dual-layer hollow fiber spinning process for the fabrication of a novel class of high performance gas separation membranes. The specific functional material employed for this purpose is a polymer blend constructed of the interpenetrated networks of PBI and Matrimid. It is within the scope of this study to unravel the effect of various key parameters on the microstructural evolution, transport properties and separation performance of the developed hollow fiber membranes. The resultant membranes possess desirable morphological and microstructural characteristics, particularly at the outer functional layer, and are free from any delamination at the interface. Analysis of the membranes suggests that both increase in the air-gap distance and application of elongational drawing have promoting effects on the membranes’ permeance. Results also indicate that membranes with H2/CO2 selectivities as high as 11.11 () can be obtained through spinning at sufficiently large air-gap distance. On the other hand, inducing the elongational drawing to the nascent fibers offers membranes with CO2/CH4 selectivities as high as 41.81 (). Therefore, either of these approaches can be employed for desirable tuning of the membrane''s properties to suit the specific application. The variation in outer dope flow rate is identified as another effective technique amenable for tailoring the properties of the hollow fiber membranes. Other findings also show the effectiveness of chemical modification for further enhancing the H2/CO2 separation performance of the membranes. Membranes developed in this research study exhibit a very good resistance toward CO2-induced plasticization and have viable potentials for various gas separation applications including hydrogen purification and natural gas separation. [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]