Hollow fiber microfiltration membranes from poly(ether ether ketone) (PEEK)

A procedure for obtaining high performance large internal diameter (ID; >1 mm) hollow fiber microfiltration membranes from poly(ether ether ketone) (PEEK) is presented. A simple mixture of isomers of diphenylphthalate is a good solvent for employing the thermal‐phase inversion process to obtain PEEK membranes. Obtaining large ID hollow fibers with substantial transmembrane flux requires sufficient melt strength during spinning to prevent excessive draw of the extruding fiber. The use of a second leachable polymer to the blend satisfies the conditions, and polysulphone (PS) is found to provide superior membranes relative to either poly(etherimide) (PEI) or poly(ether sulphone) (PES) as a second polymer. PEEK membranes obtained by this process yield better chemical resistance to a concentrated warm surfactant/oil solution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 175–181, 1999     

Sulfonated poly(ether ether ketone)‐induced porous poly(ether sulfone) blend membranes for the separation of proteins and metal ions

Asymmetric ultrafiltration (UF) membranes were prepared by the blending of poly(ether sulfone) (PES) and sulfonated poly(ether ether ketone) (SPEEK) polymers with N,N′‐dimethylformamide solvent by the phase‐inversion method. SPEEK was selected as the hydrophilic polymer in a blend with different composition of PES and SPEEK. The solution‐cast PES/SPEEK blend membranes were homogeneous for all of the studied compositions from 100/0 to 60/40 wt % in a total of 17.5 wt % polymer and 82.5 wt % solvent. The presence of SPEEK beyond 40 wt % in the casting solution did not form membranes. The prepared membranes were characterized for their UF performances, such as pure water flux, water content, porosity, and membrane hydraulic resistance, and morphology and melting temperature. We estimated that the pure water flux of the PES/SPEEK blend membranes increased from 17.3 to 85.6 L m^?2 h^?1 when the concentration of SPEEK increased from 0 to 40 wt % in the casting solution. The membranes were also characterized their separation performance with proteins and metal‐ion solutions. The results indicate significant improvement in the performance characteristics of the blend membranes with the addition of SPEEK. In particular, the rejection of proteins and metal ions was marginally decreased, whereas the permeate flux was radically improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and performances of poly(phthalazinone ether sulfone ketone) hollow fiber membranes with excellent thermotolerance

The cloud points of PPESK/NMP/H₂O ternary system at different temperatures were measured by titrimetric method. The binodal lines in the ternary phase diagram of the poly(phthalazinone ether sulfone ketone (PPESK) dope system was determined, on the basis of the cloud point experimental data being linearly fitted with the semiempirical linear cloud point correlation. Furthermore, phase separation behavior during the phase inversion of PPESK membrane‐forming system was discussed in terms of the phase diagram. Then, dry–wet spinning technique was employed in manufacturing PPESK hollow fiber membranes by immersion precipitation method. The cross‐section morphologies of hollow fibers were observed by scanning electronic microscopy. Also, the effects of dope solution composition and spinning parameters, including the coagulant composition and the spinning temperature on the separation performances of fibers, were evaluated by permeability measurements. The thermotolerance of the PPESK hollow fiber membranes prepared in the work was examined for the permeation operation at different temperatures and pressure differences. The experimental results showed that pure water flux increases several fold along with the temperature increases from 20 to 80°C at different operation pressures, while the solute rejection only decreases slightly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 878–884, 2006     

Effect of polymer and additive on the structure and property of porous stainless steel hollow fiber

Porous stainless steel hollow fiber has been widely used due to its high mechanical strength, excellent thermal conductivity and good sealing properties compared with other porous supports. We successfully prepared porous stainless steel hollow fibers using polyacrylonitrile (PAN) as polymer via dry-wet spinning followed by sintering through temperature programming method. The PAN concentration had an obvious impact on the structure and property of porous stainless steel hollow fiber even if it would be burned off during sintering. The results showed that the morphology could be tuned by adjusting the concentration of PAN. With increasing PAN concentration in casting solution for spinning, the viscosity was increased dramatically, resulting in much compact structures with high pure water flux (higher than 3×10⁵ L·m^?2·h^?1·Pa^?1). A more dense structure could be obtained by adding additive polyvinylpyrrolidone (PVP) as viscosity enhancer.     

Preparation of high‐performance zeolite NaA membranes in clear solution by adding SiO2 into Al2O3 hollow‐fiber precursor

Zeolite NaA membranes were prepared in a clear synthesis solution without the aid of nanoseeds. To improve the properties of the membranes formed in a clear solution, alumina hollow fibers were fabricated by adding silica powder to the conventional spinning slurry, resulting in hollow fibers with a mullite phase. Prior to the membrane synthesis, the hollow fibers were pretreated by dipping in an aged synthesis solution diluted with isopropanol. Dense zeolite NaA membranes on mullite‐containing alumina hollow fibers were successfully obtained at 100°C for 2 h without the aid of nanoseeds. The membranes have a good pervaporation performance with a high flux of 10.8 kg m^?2 h^?1 and a separation factor of over 10,000. The abundant mullite‐phase hydroxyl groups on the support surface promote the nucleation and growth of zeolite crystals on the support, resulting in dense membranes. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2679–2688, 2018     

Correlation of the polymer hydrophilicity and membrane fabrication process on the properties of asymmetric membranes in a vapor‐induced phase‐inversion process

In this study, we sought a better understanding of how the hydrophilicity of a polymer affects the morphology and performance of membranes. Three types of polymer with different hydrophilicity solution systems were considered: poly(aryl ether ketone) bearing a hydroxyl group (PEK–OH‐100) with N,N ‐dimethylformamide (DMF); poly(aryl ether ketone) bearing a 50% fraction hydroxyl group with DMF, and cardo poly(aryl ether ketone) with DMF. These systems were used to investigate the evolution of the morphology and variation in performance versus a change in the hydrophilicity of the polymer. In addition, the fundamental thermodynamic influence of the solution systems on the phase‐inversion process was investigated by cloud‐point measurement and Hansen solubility parameter theory to determine the role of polymer hydrophilicity on the stability of the polymer solution in humid surroundings. The performance of the membranes was tested via testing of the pure water flux, porosity, and rejection of bovine serum albumin (BSA) with respect to variations in the polymer hydrophilicity, evaporation time, relative humidity, and molecular weight of the polymer. The resulting optimal membrane exhibited a flux of 329.3 L m^?2 h^?1 and a 99.3% rejection of BSA at a relative humidity of 90% and an evaporation time of 3 s. The hydrophilic PEK–OH‐100 membranes have promising applications in protein separation and the porous support of reverse‐osmosis membranes and so on. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44701.     

Preparation and characterization of poly(vinyl chloride)/polystyrene/poly(ethylene glycol) hollow‐fiber ultrafiltration membranes

Hollow‐fiber ultrafiltration (UF) membranes were prepared from blends of poly(vinyl chloride) (PVC) and polystyrene (PS) with a dry/wet phase inversion method. Poly(ethylene glycol) (PEG) and N,N‐dimethylacetamide were used as the additive and solvent, respectively. The effects of the PEG concentration in the dope solution as an additive on the cross sections and inner and outer surface morphologies, permeability, and separation performance of the hollow fibers were examined. The mean pore size, pore size distribution, and mean roughness of both the inner and outer surfaces of the produced hollow fibers were determined by atomic force microscopy. Also, the mechanical properties of the hollow‐fiber membranes were investigated. UF experiments were conducted with aqueous solutions of poly(vinyl pyrrolidone) (PVP; K‐90, M_w = 360 kDa). From the results, we found that the PVC/PS hollow‐fiber membranes had two layers with a fingerlike structure. These two layers were changed from a wide and long to a thin and short morphology with increasing PEG concentration. A novel and until now undescribed shape of the nodules in the outer surfaces, which was denoted as a sea‐waves shape, was observed. The outer and inner pore sizes both increased with increasing PEG concentration. The water permeation flux of the hollow fibers increased from 104 to 367 L m^?2 h^?1 bar^?1) at higher PEG concentrations. The PVP rejection reached the highest value at a PEG concentration of 4 wt %, whereas at higher values (from 4 to 9 wt %), the rejection decreased. The same trend was found also for the tensile stress at break, Young's modulus, and elongation at break of the hollow fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 989‐1004, 2013     

Einsatz von perowskitischen Hohlfasermembranen in einem Mikrowellenplasma

For the first time the combination of a separation process with a plasma process was successfully tested. In this case, a mixed‐conducting perovskite membrane separates the oxygen. At 1 kW a permeation of 2.24 mL min^?1cm^?2 could be achieved. Corresponding perovskite membranes have been manufactured as hollow fibers with a very good CO₂ stability. The hollow fibers showed a constant permeation over more than 200 h. Furthermore, a spinning process with a sulphur‐free polymer binder has been established.     

Advanced FO membranes from newly synthesized CAP polymer for wastewater reclamation through an integrated FO‐MD hybrid system

A new cellulose acetate propionate (CAP) polymer has been synthesized and used to prepare high‐performance forward osmosis (FO) membranes. With an almost equal degree of substitution of acetyl and propionyl groups, the CAP‐based dense membranes show more balanced physicochemical properties than conventional cellulose acetate (CA)‐based membranes for FO applications. The former have a lower equilibrium water content (6.6 wt. %), a lower salt diffusivity (1.6×10¹⁴ m² s^?1) and a much lower salt partition coefficient (0.013) compared with the latter. The as‐prepared and annealed CAP‐based hollow fibers have a rough surface with an average pore radius of 0.31 nm and a molecular weight cut off of 226 Da. At a transmembrane pressure of 1 bar, the dual‐layer CAP‐CA hollow fibers show a pure water permeability of 0.80 L m^?2 h^?1 bar^?1 (LMH/bar) and a rejection of 75.5% to NaCl. The CAP‐CA hollow fibers were first tested for their FO performance using 2.0 M NaCl draw solution and deionized water feed. An impressive water flux of 17.5 L m^?2 h^?1 (LMH) and a reverse salt flux of 2.5 g m^?2 h^?1 (gMH) were achieved with the draw solution running against the active CAP layer in the FO tests. The very low reverse salt flux is mainly resulting from the low salt diffusivity and salt partition coefficient of the CAP material. In a hybrid system combining FO and membrane distillation for wastewater reclamation, the newly developed hollow fibers show very encouraging results, that is, water production rate being 13–13.7 LMH, with a MgCl₂ draw solution of only 0.5 M and an operating temperature of 343 K due to the incorporation of bulky propionyl groups with balanced physiochemical properties. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1245–1254, 2013     

Fabrication of 6FDA‐durene polyimide asymmetric hollow fibers for gas separation

We have developed defect‐free asymmetric hexafluoro propane diandydride (6FDA) durene polyimide (6FDA‐durene) hollow fibers with a selectivity of 4.2 for O₂/N₂ and a permeance of 33.1 ×10^?6 cm³ (STP)/cm²‐s‐cmHg for O_2. These fibers were spun from a high viscosity in situ imidization dope consisting of 14.7% 6FDA‐durene in a NMP solvent and the inherent viscosities (IV) of this 6FDA‐durene polymer was 0.84 dL/g. Low IV dopes cannot produce defect‐free hollow fibers, indicating a 6FDA‐durene spinning dope with a viscosity in the region of chain entanglement seems to be essential to yield hollow fibers with minimum defects. The effects of spinning parameters such as shear rates within a spinneret and bore fluids as well as air gap on gas separation performance were investigated. Experimental data demonstrate that hollow fibers spun with NMP/H₂O as the bore liquid have higher permeances and selectivities than those spun with glycerol as the bore liquid because the former has a relatively looser inner skin structure than the latter. In addition, the selectivity of hollow fibers spun with NMP/H₂O as the bore liquid changes moderately with shear rate, while the selectivity of hollow fibers spun with glycerol are less sensitive to the change of shear rate. These distinct behaviors are mainly attributed to the different morphologies generated by different bore fluids. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2166–2173, 2001     

Engineering design of outer‐selective tribore hollow fiber membranes for forward osmosis and oil‐water separation

Outer‐selective thin‐film composite (TFC) hollow fiber membranes offer advantages like less fiber blockage in the feed stream and high packing density for industrial applications. However, outer‐selective TFC hollow fiber membranes are rarely commercially available due to the lack of effective ways to remove residual reactants from fiber's outer surface during interfacial polymerization and form a defect‐free polyamide film. A new simplified method to fabricate outer‐selective TFC membranes on tribore hollow fiber substrates is reported. Mechanically robust tribore hollow fiber substrates containing three circular‐sector channels were first prepared by spinning a P84/ethylene glycol mixed dope solution with delayed demixing at the fiber lumen. The thin wall tribore hollow fibers have a large pure water permeability up to 300 L m^?2 h^?1 bar^?1. Outer‐selective TFC tribore hollow fiber membranes were then fabricated by interfacial polymerization with the aid of vacuum sucking to ensure the TFC layer well‐attached to the substrate. Under forward osmosis studies, the TFC tribore hollow fiber membrane exhibits a good water flux and a small flux difference between active‐to‐draw (i.e., the active layer facing the draw solution) and active‐to‐feed (i.e., the active layer facing the feed solution) modes due to the small internal concentration polarization. A hyperbranched polyglycerol was further grafted on top of the newly developed TFC tribore hollow fiber membranes for oily wastewater treatment. The membrane displays low fouling propensity and can fully recover its water flux after a simple 20‐min water wash at 0.5 bar from its lumen side, which makes the membrane preferentially suitable for oil‐water separation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4491–4501, 2015     

Effect of different PVDF and additives on the properties of hollow fiber membranes contactors for CO2 separation

In the present work, different poly(vinil fluoride) (PVDF) were selected for preparing membranes, based on the fact that they are able to form polymer solutions with different viscosities. This characteristic can affect spinning, as well as, mass transfer between the polymer solution and precipitation bath; therefore, each PVDF solution can differently affect membrane formation. The effect of different additives in the polymer solutions was also investigated. Flat sheet and hollow fiber membranes were characterized by Scanning Electron Microscopy analysis, contact angle, gas permeation, porosity, and membrane gas–liquid contactor tests, aiming carbon dioxide removal. The hollow fibers prepared by the polymer which formed a less viscous solution (named PVDF-I) had a faster light transmittance decay, which started around 150 s before the more viscous solution (PVDF-II). Hollow fibers obtained using PVDF-I and propionic acid, in the polymer solution, presented the best gas–liquid contactor performance. CO₂ removal increased from 21 to 35.1%, for PVDF-II and PVDF-I, respectively, using aqueous diethanolamine solution, as absorbent liquid. In conclusion, even though PVDF-I and PVDF-II membranes were obtained by using the same spinning conditions and experimental methodology, the difference between the polymers properties certainly affected the final membrane morphology and transport properties.     

Effect of polyethylene glycol molecular weights and concentrations on polyethersulfone hollow fiber ultrafiltration membranes

Polyethersulfone (PES) hollow‐fiber membranes were fabricated using poly(ethyleneglycol) (PEG) with different molecular weights (MW = PEG200, PEG600, PEG2000, PEG6000, and PEG10000) and poly(vinyl pyrrolidone) PVP40000 as additives and N‐methyl‐2‐pyrrolidone (NMP) as a solvent. Asymmetric hollow‐fiber membranes were spun by a wet phase‐inversion method from 25 wt % solids of 20 : 5 : 75 (weight ratio) PES/PEG/NMP or 18 : 7 : 75 of PES/(PEG600 + PVP40000)/NMP solutions, whereas both the bore fluid and the external coagulant were water. Effects of PEG molecular weights and PEG600 concentrations in the dope solution on separation properties, morphology, and mechanical properties of PES hollow‐fiber membranes were investigated. The membrane structures of PES hollow‐fiber membranes including cross section, external surface, and internal surface were characterized by scanning electron microscopy and the mechanical properties of PES hollow‐fiber membranes were discussed. Bovine serum albumin (BSA, MW 67,000), chicken egg albumin (CEA, MW 45,000), and lysozyme (MW 14,400) were used for the measurement of rejection. It was found that with an increase of PEG molecular weights from 200 to 10,000 in the dope solution, membrane structures were changed from double‐layer fingerlike structure to voids in the shape of spheres or ellipsoids; moreover, there were crack phenomena on the internal surfaces and external surfaces of PES hollow‐fiber membranes, pure water permeation fluxes increased from 22.0 to 64.0 L m^?2 h^?1 bar^?1, rejections of three protein for PES/PEG hollow‐fiber membranes were not significant, and changes in mechanical properties were decreased. Besides, with a decrease of PEG600 concentrations in the dope solution, permeation flux and elongation at break decreased, whereas the addition of PVP40000 in the dope solution resulted in more smooth surfaces (internal or external) of PES/(PEG600 + PVP40000) hollow‐fiber membranes than those of PES/PEG hollow‐fiber membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3398–3407, 2004     

Thin-Film-Composite Gas Separation Membranes: On the Dynamics of Thin Film Formation Mechanism On Porous Substrates

Abstract

A wide range of gas separations of interest in energy applications are carried out using membranes. Growing attention has been paid to the technology of making thin-film-composites(TFCs) membranes. Understanding the polymer solution and substrate property is key to successfully preparing TFCs membranes. This paper reports on some fundamental issues of coating hollow fibers with polymer from solution by dip coating. Polymeric porous hollow fibers with varying porosities and permeances were coated with polymer solutions of different viscosities in a continuous process. In addition, the fibers were coated dry and by presoaking in the coating solvent. It was found that the thickness of the coating on the low permeance/porosity/wet and dry fibers could be approximated by the Deryaguin model (h/R = 1.33 (Ca) ^0.67). For dry fibers, as the fiber porosity increased, the measured coating thickness was significantly underestimated by the Deryaguin equation. It is believed that the pores in the fiber allow rapid capillary suction of the solvent into the fiber walls and the bore, thus increasing the solution viscosity near the fiber wall, resulting in an increase in the coating thickness. Significant differences in the rate of solvent uptake were observed in these fibers by wicking experiments on a microbalance to support the above hypothesis.     

Hollow Fiber Ultrafiltration Membranes from Poly(Vinyl Chloride): Preparation,Morphologies, and Properties

Hollow fiber poly(vinyl chloride) membranes were prepared by using the dry/wet spinning method. Cross-section, internal, and external surfaces of the hollow fibers structure were studied by SEM. The pore size and pore size distribution of the hollow fibers were measured by a PMI capillary flow porometer. UF experiments of pure water and aqueous solution of PVP K-90 were carried out. The effect of the PVC concentration on the hollow fibers mechanical properties was also investigated. It was found that the PVC fibers cross-sectional structure was affected by the polymer concentration in the dope solution. In particular, reduction of macrovoids size was observed when increasing PVC concentration from 15 to 19 wt%. The pore size distribution of the PVC hollow fibers was controlled by adjusting the PVC concentration. Indeed, an increase of PVC concentration up to 19 wt% leads to fibers with sharp pore size distribution (the 99% of pores is about 0.15 µm).The pure water permeation flux decreased from 162 to 128 (l/m² · h · bar), while the solute separation performance increased from 82 to 97.5%, when increasing the PVC concentration. The elongation at break, the tensile strength, and the Young's modulus of the PVC hollow fibers were improved with PVC concentration in dope solution.     

Mechanical,swelling and adsorptive properties of dry–wet spun chitosan hollow fibers crosslinked with glutaraldehyde

Chitosan (CS) hollow fiber (HF) membranes were successfully prepared according to the dry–wet spinning technique. A post-treatment with glutaraldehyde (GA) aqueous solution was carried out to perform the cross-linking reaction. The effect of GA concentration in the range 50–1000 mg l^?1 on the swelling, mechanical and adsorptive properties was investigated. The morphology and chemical structure of the fibers were examined by means of SEM and FTIR. The degree of swelling and adsorption capacity decreased as the GA concentration increased. CS hollow fibers swelled the most in acidic solution as compared with distilled water and saline solution. The adsorption capacity of CS HFs increased while decreasing of initial pH from 7.5 to 3.5. Desorption experiments showed that CS HFs were reusable as adsorbent. Mechanical properties were strongly affected by GA post-treatment: tensile strength and elastic modulus increased at low GA concentration (50 mg l^?1), to sharply decrease when concentration was ?500 mg l^?1. Breaking elongation decreased with increasing GA concentration.     

Investigation on the effect of spinning conditions on the properties of hollow fiber membrane for hemodialysis application

Polyethersulfone (PES) hollow fiber membranes were fabricated via the dry‐wet phase inversion spinning technique, aiming to produce an asymmetric, micro porous ultrafiltration hollow‐fiber specifically for hemodialysis membrane. The objective of this study is to investigate the effect of spinning conditions on the morphological and permeation properties of the fabricated membrane. Among the parameters that were studied in this work are air gap distance, dope extrusion rate, bore fluid flow rate, and the take‐up speed. The contact angle was measured to determine the hydrophilicity of the fibers. Membrane with sufficient hydrophilicity properties is desired for hemodialysis application to avoid fouling and increase its biocompatibility. The influences of the hollow fiber's morphology (i.e., diameter and wall thickness) on the performance of the membranes were evaluated by pure water flux and BSA rejection. The experimental results showed that the dope extrusion rate to bore fluid flow rate ratio should be maintained at 1:1 ratio to produce a perfectly rounded asymmetric hollow fiber membrane. Moreover, the flux of the hollow fiber spun at higher air gap distance had better flux than the one spun at lower air gap distance. Furthermore, spinning asymmetric hollow fiber membranes at high air gap distance helps to produce a thin and porous skin layer, leading to a better flux but a relatively low percentage of rejection for BSA separation. Findings from this study would serve as primary data which will be a useful guide for fabricating a high performance hemodialysis hollow fiber membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43633.     

Preparation of poly(ether sulfone) nanofibers by gas‐jet/electrospinning

Poly(ether sulfone) (PES) nanofibers were prepared by the gas‐jet/electrospinning of its solutions in N,N‐dimethylformamide (DMF). The gas used in this gas‐jet/electrospinning process was nitrogen. The morphology of the PES nanofibers was investigated with scanning electron microscopy. The process parameters studied in this work included the concentration of the polymer solution, the applied voltage, the tip–collector distance (TCD), the inner diameter of the needle, and the gas flow rate. It was found from experimental results that the average diameter of the electrospun PES fibers depended strongly on these process parameters. A decrease in the polymer concentration in the spinning solutions resulted in the formation of nanofibers with a smaller diameter. The use of an 18 wt % polymer solution yielded PES nanofibers with an average diameter of about 80 nm. However, a morphology of mixed bead fibers was formed when the concentration of PES in DMF was below 20 wt % during gas‐jet/electrospinning. Uniform PES nanofibers with an average diameter of about 200 nm were prepared by this electrospinning with the following optimal process parameters: the concentration of PES in DMF was 25 wt %, the applied voltage was 28.8 kV, the gas flow was 10.0 L/min, the inner diameter of the needle was 0.24 mm, the TCD was 20 cm, and the flow rate was 6.0 mL/h. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Positively charged hollow‐fiber composite nanofiltration membrane prepared by quaternization crosslinking

Poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by interfacial polymerization to develop a positively charged dense network structure. According to this mechanism, a positively charged hollow‐fiber composite nanofiltration (NF) membrane was prepared by quaternization to achieve a crosslinked PDMAEMA gel layer on the outer surface of polysulfone hollow‐fiber ultrafiltration (UF) membranes with a PDMAEMA aqueous solution as a coating solution and p‐xylylene dichloride as an agent. The preparation conditions, including the PDMAEMA concentration, content of additive in the coating solution, catalyzer, alkali, crosslinking temperature, and hollow‐fiber substrate membrane, were studied. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the structure of the membranes. This membrane had a rejection to inorganic salts in aqueous solution. The rejection of MgSO₄ (2 g/L aqueous solution at 0.7 MPa and 25°C) was above 98%, and the flux was about 19.5 L m^?2 h^?1. Moreover, the composite NF membranes showed good stability in the water‐phase filtration process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermo-responsive mixed-matrix hollow fiber membranes

Up to date, preparation of thermo-responsive mixed-matrix membranes (MMM) has only be described as small scale flat membranes or multi-step processes for hollow fiber membranes. In this work, the development of thermo-responsive MMM hollow fibers composed of polyethersulfone as membrane polymer and poly(N-isopropylacrylamide) (PNIPAM) microgel particles via the wet spinning process is presented. PNIPAM particles are synthesized with (NP-S, z_{avg 20°C} = 105 nm) and without (NP-L, z_{avg 20°C} = 250 nm) sodium dodecyl sulfate and their thermo-responsive behavior is characterized by dynamic light scattering. Particle size (NP-S, NP-L), particle content (10%, 15%) and the extrusion pressure in the wet spinning process (1.0–3.0 bar) are investigated as experimental parameters. Reversible thermo-responsive behavior of the hollow fibers is demonstrated by water permeability measurements at different temperatures (20 and 50°C). The largest switching factors (R) are observed for the hollow fibers containing NP-L. For 15% NP-L and 1 bar extrusion pressure, water permeances between 0.5 and 6.0 L m⁻² h⁻¹ bar⁻¹ are observed, corresponding to R = 12 and a dextran (500 kDa) rejection of 91% at 25°C.