Membrane Substructure Research Articles

Low-cost automated flat-sheet membrane casting: An open-source, advanced manufacturing approach

Novel membrane materials developed in research labs struggle to gain widespread industrial adoption due in part to insufficient reproducibility and unreliable performance data. Open-source hardware approaches, especially 3D printing, enable the democratization of automation within a laboratory setting, and in the context of membranes, can minimize the inherent variability associated with manual methods of membrane casting. In this study, the native hardware and firmware of an inexpensive, conventional 3D printer was extensively modified for the purpose of flat-sheet membrane casting. Replicate poly (ether-ether ketone) (PEEK) membranes were cast with a thickness coefficient of variation of ∼10 % using the modified device. Cast membranes were used to assess the importance of controlling shear rate by characterizing both intra- and inter-film variability. Statistical differences in pure water permeability were observed across tested shear rates, with distinct morphological changes occurring to the membrane substructure. Overall, the technology developed in this study is shown to be an extremely useful approach for improving the process of developing membranes at the bench-scale.

Preparation and characterization of polysulfone/zeolite mixed matrix membranes for removal of low-concentration ammonia from aquaculture wastewater.

Removal of low-concentration ammonia (1-10 ppm) from aquaculture wastewater was investigated via polysulfone (PSf)/zeolite mixed matrix membrane. PSf/zeolite mixed matrix membranes with different weight ratios (90/10, 80/20, 70/30 and 60/40 wt.%) were prepared and characterized. Results indicate that PSf/zeolite (80/20) was the most efficient membrane for removal of low-concentration ammonia. The ammonia elimination by PSf/zeolite (80/20) from aqueous solution for 10, 7, 5, 3 and 1 ppm of ammonia was 100%, 99%, 98.8%, 96% and 95% respectively. The recorded results revealed that pure water flux declined in higher loading of zeolite in the membrane matrix due to surface pore blockage caused by zeolite particles. On the other hand, ammonia elimination from water was decreased in higher contents of zeolite because of formation of cavities and macrovoids in the membrane substructure.

Erythroid-Specific Variant of the Nuclear Exportin Xpo7 Conserved Only in Mammals May Explain Functional Differences Between Mammalian Definitive and Lower Vertebrate (or Primitive) Erythropoiesis

Exportin 7 (Xpo7) was previously found to be crucial for late murine erythroid nuclear maturation when its knockdown significantly inhibited chromatin condensation and ultimate enucleation in a primary mouse erythroblast culture [1]. Additionally, Xpo7 was found to have an erythroid-specific isoform, transcribed from an erythroid-specific transcription start site (TSS) in the first intron of Xpo7 (named Xpo7-1B in contrast to the ubiquitously expressed variant -1A) [1]. Xpo7-1B differs from Xpo7-1B in 8 amino acid residues in the first exon and 9 residues in the 5th exon, and these differences are not conserved either in lower vertebrates or in primitive mouse erythropoiesis. It is intriguing that both lower vertebrate and primitive mammalian erythroblasts do not enucleate.In order to understand the in vivo function of Xpo7 and determine if these differences in the two isoforms confer differential functions to the proteins or are simply regulatory, we examined the definitive fetal liver erythropoiesis (considered adult "stress erythropoiesis") and adult steady state erythropoiesis of transgenic mouse models lacking either Xpo7-1A, Xpo7-1B, or both. We had previously knocked down Xpo7 in zebrafish using morpholinos (zebrafish only express the Xpo7-1A homologue) and found no effect on adult erythroid differentiation or proliferation. Adult Xpo7-1A knockout (KO) mice are born in normal Mendelian ratios, are not anemic, and express normal Xpo7-1B only in the blood. Closer examination reveals that fetal liver erythroid proliferation is actually higher in Xpo7-1A KO mice than either heterozygous (HET) or wild type (WT) while differentiation is normal. The double KO (Xpo7-1AB KO) appears to be embryonic lethal as only 4 live knockout pups were born out of 71 live births and even these 4 pups appear to be partial chimeras. We characterized the Xpo7-1AB HET mice in more detail and fetal liver erythroblasts of HET mice showed normal proliferation and differentiation compared to WT, and adults showed no differences in red blood cell (RBC) counts, hematocrit or hemoglobin. No complete live Xpo7-1AB KO has been born so we are now evaluating embryos at E3, E9.5, and E14.5. Given the possibility of embryonic lethality, in order to evaluate the erythroid-specific isoform Xpo7-1B, we have crossed a mouse floxed for the Xpo7-1B TSS/1st exon with a tamoxifen-inducible Cre-recombinase mouse. These mice have been given tamoxifen after reaching adulthood and we are currently evaluating their hematopoietic parameters. We have also set up HET-HET timed matings and administered tamoxifen to pregnant females to evaluate fetal liver erythropoiesis in Xpo7-1B HET, WT, and KO embryos.Not only will this work further our understanding of the process of global chromatin condensation during erythropoiesis, data from this in vivo study may reveal differences in erythropoiesis between mammals and lower vertebrates, which may also reflect intrinsic differences in mammalian primitive versus definitive erythropoiesis. Based on our in vitro knockdown studies, we anticipate that the phenotype of the Xpo7-1B KO mice may be similar to congenital dyserythropoietic anemia (CDA), a human disorder involving abnormalities in erythroid progenitor chromatin condensation and nuclear membrane substructure, so examination of these mice may also uncover a novel mechanism for this form of ineffective erythropoiesis.[1] Hattangadi, SM, et al. Blood (2014) 124, 1931-40. DisclosuresNo relevant conflicts of interest to declare.

Tuning substructure and properties of supported asymmetric triblock terpolymer membranes

Asymmetric poly(isoprene-b-styrene-b-4-vinylpyridine) (ISV) block copolymer membranes fabricated via self-assembly and non-solvent induced phase separation (SNIPS) process have drawn significant attention due to the simple processing method and the generation of high-quality isoporous ultrafiltration membranes. With the present study on SNIPS membrane substructure, we systematically varied membrane casting parameters to tune the cross-sectional morphologies of SNIPS membranes while simultaneously preserving top surface structure. Parameters such as polymer concentration, evaporation time, solvent ratio, and coagulation bath temperature were investigated to control transformation of commonly produced sponge-like cross-sectional morphologies into more open and permeable finger-like substructures. Membranes with sponge-like and finger-like substructures were then integrated onto nylon supports for enhanced mechanical properties. Hydraulic permeability tests at various pH conditions gave distinct open-state flux values for SNIPS membranes with different sublayer morphologies, while maintaining pH responsive functionality resulting from the poly(4-vinylpyridine) block.

High efficient removal of lead(II) and nickel(II) from aqueous solution by novel polysulfone/Fe3O4–talc nanocomposite mixed matrix membrane

Novel mixed matrix membranes were prepared from polysulfone (PSf), talc and Fe3O4–talc nanocomposite by phase inversion technique. PSf/Fe3O4–talc membranes showed higher lead and nickel rejections compared to PSf/talc membranes, which reaches to 99.4 and 96.2% for lead and nickel ions, respectively, at feed pH 5 and lower rejections at pH 3.5 and 2. Higher surface area in Fe3O4–talc nanocomposite than talc could be considered as a main reason of higher heavy metals removal in PSf/Fe3O4–talc membranes. The heavy metals removal enhances with the increase in nanocomposite content from 7 to 9 wt.% because higher numbers of vacant sites in membrane morphology were available for adsorption. Heavy metals rejection reduces in higher nanocomposite concentrations (11 and 13 wt.%) due to the formation of macrovoids in membrane substructure. In addition, a reduction in the metal ion rejection was recognized by enhancement in feed solution concentration and applied pressure. This is caused by difficulty for the remaining vacant sites to be filled with the heavy metal ions because of repulsive forces between the adsorbed solute molecules on the surface and solute in bulk phase. The interactions of lead and nickel ions with nanocomposite placed on the membrane top layer were revealed by the scanning electron microscopy with energy dispersive X-rays.

Secretory vesicle cholesterol: Correlating lipid domain organization and Ca2 + triggered fusion

Membrane organization has received substantial research interest since the degree of ordering in membrane regions is relevant in many biological processes. Here we relate the impact of varying cholesterol concentrations on native secretory vesicle fusion and the lateral domain organization of membrane extracts from these vesicles. Membranes of isolated cortical secretory vesicles were either depleted of cholesterol, had cholesterol loaded to excess of native levels, or were depleted of cholesterol but subsequently reloaded to restore native cholesterol levels. Lipid analyses confirmed cholesterol was the only species significantly altered by these treatments. Treated vesicles were characterized for their ability to undergo fusion. Cholesterol depletion resulted in a decrease of Ca2+ sensitivity and the extent of fusion, while cholesterol loading had no effect on fusion parameters. Membrane extracts were characterized in terms of lipid packing by surface pressure–area isotherms whereas the lateral membrane organization was analyzed by Brewster angle microscopy. While no differences in the isotherms were observed, imaging revealed drastic differences in domain size, shape and frequency between the various conditions. Cholesterol depletion induced larger but fewer domains, suggesting that domain coalescence into larger structures may disrupt the native temporal–spatial organization of the fusion machinery and thus inhibit vesicle docking, priming, and fusion. In contrast, adding excess cholesterol, or rescuing with exogenous cholesterol after sterol depletion, resulted in more but smaller domains. Therefore, cholesterol is an important membrane organizer in the process of Ca2+ triggered vesicular fusion, which can be related to specific physical effects on native membrane substructure.

The Role of Solution and Coagulation Temperatures in Crystalline Structure, Morphology, Roughness, Pore Diameter Distribution, and Separation Properties of Nanoporous Membranes Fabricated Via Phase Inversion

In this study, fabrication of poly(vinylidene fluoride) (PVDF) flat sheet membranes and correlation of membrane morphology, roughness, crystalline structure, and pore diameter distribution as functions of coagulant temperature (TC) and precursor-solution preparation temperature (TS) in the phase inversion (PI) process of PVDF-DMF-H2O mixture with 20%wt of PVDF concentration was investigated. The results demonstrated that membranes have a typical asymmetric structure with a dense skin top layer and a porous substructure. An increasing amount of macrovoids was observed in the membrane substructure when TS is decreased. It was found that at lower TC, the membrane solution precipitated into a uniform morphology composed of spherical crystallites that exhibited the β-form crystal structure. By contrast, when PVDF was precipitated at higher temperatures, the formed membrane became largely in the α-form crystal structure. The pore size was estimated by Barett-Joyner-Halenda (BJH) method, ranging from 15 nm to tenth of hundred nm, depending on TC. The performance of the prepared membranes has been tested by the measure the effects of TC and TS on the separation characteristic of nanoporous PVDF membranes. We observed that the removal of Acid Yellow 23 (AY23) decreases as TS increases and extremely high dye removal efficiency of 99.37% was achieved.

Hydrogen separation from multicomponent gas mixtures containing CO, N2 and CO2 using Matrimid® asymmetric hollow fiber membranes

The application of hollow fiber membranes for the separation of industrial gas mixtures relies on the correct characterization of the permeation of the involved gaseous components through the hollow fiber membranes. Thus, this study is focused on the characterization of the permeation through Matrimid® hollow fiber membranes of four gas mixtures containing H2 (H2/N2, H2/CO, H2/CO2), and the quaternary gas mixture H2/N2/CO/CO2, working at a constant temperature of 303 K and pressures up to 10 bar. The main differences and similarities in the gas permeation properties of hollow fibers with respect to flat membranes, as well as in the permeation of gas mixtures with respect to pure gases, are discussed. Our results suggest that for mixtures containing H2 and CO2 hollow fiber membranes perform better than flat membranes given that a lower depression in the permeability of H2 has been observed. At 2.3 bar feed pressure, ideal selectivity values obtained for H2/N2, H2/CO and H2/CO2 gas pairs were 74.4, 42.6 and 5 respectively, with a H2 permeance of 50.2×10−8 m3(STP) m−2 s−1 kPa−1. The specific behavior observed in the permeation through hollow fiber has been explained by a combination of different phenomena such as hollow fiber membrane substructure resistance, CO2 induced plasticization and competitive sorption effects between the components of the gaseous mixtures.

Lipid Bilayer Membrane Shape Remodeling by Lipid-Modified Ras Proteins

Ras proteins are small GTP-hydrohydrolyzing enzymes that operate as molecular switches in signal transduction pathways and are present in a mutant, activated state in many human tumors. It has been shown that the lipid-modified C-terminus drive lateral segregation of Ras proteins into membrane sub-structure on the plasma membrane. Such transient and dynamic molecular assembly, so-call nanocluster, is emerging as a crucial mechanism by which cells achieve high-fidelity signal transmission. However, little is known about the underlying force driving the formation of nanoclusters on the plasma membrane and their influence on the membrane structure. To investigate the interaction between nanocluster and the membrane, we carried out extensive semi-atomistic molecular dynamics simulations of the C-terminal membrane-targeting motif of H-ras (tH) in a phase separated lipid bilayer composed of 2000 DPPC, DliPC and cholesterol molecules. We found out that at ambient temperature approximately 30–40% of tH molecules assemble into clusters of 4-9 proteins, and preferentially localize at the interface between the liquid-order and liquid-disorder phases of the membrane. In the nanoclusters, tH backbones preferably exhibits an extended conformation and align linearly at the phase interface. With such molecular-level organization, tH molecule act as a linactant at the interface and reduce line tension of the anchor-containing monolayer and induces shape transition of the overall membrane due to the tendency of the system to minimize the free energy. The resultant geometry of the membrane is determined by the different elastic bending modulus of different phases as well as the phase boundary line tension, which is strongly affected by the localization of the nanoclusters. Our findings were explained based on the domain-induced budding model and shed light on the interaction between membrane-bounded proteins and membrane domains, such as lipid rafts.

A Molecular Dynamics Study of Ras Clustering in Membrane Domains

Ras proteins are small GTP-hydrohydrolyzing enzymes that function as conformational switches controlling cell proliferation, differentiation, and development. Ras nanolcustering on the plasma membrane and segregation of the clusters into specific membrane substructure driven by competing effects from the lipidated C-terminus and the globular catalytic domain, has attracted much interest in recent years. In this work, we study the clustering behavior of the full length H-ras protein in a model membrane using coarse-grained Molecular Dynamics (MD) simulations. Our model membrane is a phase-separted bilayer comprised of 3840 DPPC, 2304 DLiPC and 1536 cholesterol molecules. Initial results from the simulations suggest that the same fundamental forces that drive clustering of the minimal H-ras membrane anchor also underlie the clustering behavior of the whole protein. However, steric effects in the full-length protein modulate the size and distribution of its clusters, as well as the elastic properties of the bilayer. The results provide previously unavailable molecular insight into the nanoscale organization of lipidated proteins on the plasma membrane.

Effects of phase inversion and composition of casting solution on morphology and gas permeance of polyethersulfone/polyimide blend membranes

AbstractIn this study, the preparation of high flux gas separation flat sheet membranes based on polyethersulfone (PES) and polyimide (PI) Matrimid 5218 blends was investigated. The process of dry/wet phase inversion with three different compositions of PES/PI (80/20, 50/50 and 20/80 wt%) in N, N‐dimethylacetamide (DMAc) or tetrahydrofuran (THF) were employed. The utilization of these solvents has not been reported. Scanning electron microscopy (SEM) was used to investigate the morphological characteristics and the structure of asymmetric membranes. The results indicate that the blend ratio of the polymers plays a vital role in membrane structure and capability. The prepared membranes possessed a typical asymmetric structure with a dense skin layer and a porous substructure. Macrovoids were observed in the membrane substructure with high PES concentration (80 wt%). The effect of PES/PI membrane surface coating with polydimethylsiloxane rubber solution on gas permeance and selectivity was investigated. After coating, the modified membranes exhibited O2 permeances from 3 to 36 gas particulate unit (GPU). However, the membrane selectivity for O2/N2 was decreased from 18 to 5 at room temperature. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 31: 298–309, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20253

Purpose of recently detected inhibitory domain of the Helicobacter pylori protein CagA

Helicobacter pylori infection is the most common bacterial infection worldwide and is strongly associated with gastric oncogenesis. Recently, we discovered that the H. pylori protein CagA, a risk factor for carcinogenesis, consists of two distinct membrane-targeting domains. The C-terminal membrane-binding domain induces host cell responses associated with a high oncogenic potential. The N-terminal membrane-targeting domain, however, localizes to a different membrane substructure at the site of newly formed cell-cell contacts thereby diminishing the effects of C-terminal signaling motifs on host cell physiology. This inhibitory function may allow H. pylori to establish a colonization niche in the host by maintaining the host epithelial architecture and thus decreasing the oncogenic potential as a side effect. From a bacterial standpoint, however, its main purpose maybe is to translocate the CagA protein via the type IV secretion apparatus into host epithelial cells.

Novel polyphenylsulfone membrane for potential use in solvent nanofiltration

In this work, the preparation of nanofiltration flat sheet membranes based on polyphenylsulfone (PPSU) was investigated. A synthesis method based on phase inversion with three different compositions of PPSU (17 wt.%, 21 wt.% and 25 wt.%) in dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP) and a mixture of dimethylformamide (DMF) and NMP was employed. Scanning electron microscopy (SEM) was used to investigate the morphological characteristics and the structure of the membranes, which were found to have a typical asymmetric structure with a dense skin top layer and a porous substructure. The pore size was estimated by measuring the permeation rate of N 2 when different pressures are applied, ranging from 15 nm to 40 nm, depending on the manufacturing method. An increasing amount of macro-voids was observed in the membrane substructure when the polymer concentration is decreased. The performance of the prepared membranes has been tested by the measure of methanol permeability and the rejection of a dissolved dye (Rose Bengal). The methanol permeability decreases with increasing polymer concentration while the rejection of Rose Bengal (RB) increases. In addition, the impact of ethyl acetate, n-hexane, toluene, diethyl ether, iso-propanol and acetone on the membranes was investigated by measuring the flux of methanol and rejection of RB before and after solvent exposure. The membranes were visually stable in most of the solvents except acetone and toluene. The performance of the membranes changed dramatically for ethyl acetate and diethyl ether while iso-propanol had a minor effect and complete stability was observed with n-hexane.

Overcoming mass‐transfer limitations in partial hydrogenation of soybean oil using metal‐decorated polymeric membranes

AbstractThe conventional soybean oil hydrogenation process (metal catalyst on solid support particles slurried in oil, H2 bubbled through the oil) is compared with metal‐decorated integral‐asymmetric polyetherimide (PEI) membranes, as far as changes in temperature and pressure are concerned. Using metal‐decorated polymeric membranes, H2 is supplied to the catalytic sites by permeation from the membrane substructure. As opposed to the slurry process, metal‐decorated membranes show only slightly increased trans fatty acid (TFA) formation when the temperature is raised (50–90°C) to accelerate the process. This is likely due to the efficient and to some extent self‐regulating H2 supply directly to the catalytic sites on the membrane skin. The hydrogenation rate and TFA formation of the metal‐decorated membrane process show a minor dependence on pressure. © 2010 American Institute of Chemical Engineers AIChE J, 2011

How Micro/Nanoarchitecture Facilitates Anti-Wetting: An Elegant Hierarchical Design on the Termite Wing

The termite is an insect which is a weak flier, has a large wing area in relation to its body mass, and many species typically fly during rain or storm periods. Water droplets placed on these insects' wings will spontaneously roll off the surface. Here we show how the intricate hierarchical array design of these insect wings achieves anti-wetting properties with water bodies of various sizes by reducing contact area and thus adhesion. To repel large droplets, the termite uses an array of hairs with a specially designed nanoarchitecture, which we demonstrate is critical for this function. By coating single hairs with a polymer of varying thicknesses (with a similar hydrophobicity to insect cuticle), we demonstrate that hairs of the same chemistry and with the complete nanoarchitecture show the greatest resistance to penetrating water bodies. The wings also consist of an underlying non-wetting membrane substructure comprising an array of star-shaped microstructures which minimize interaction with micro-sized droplets of water. The sophisticated micro/nanostructured hierarchy on the termite wing membrane not only results in non-wetting at different length scales but also demonstrates a design for weight and material minimization while achieving this state. Elucidating the function of such structures has implications for understanding insect biology and the evolution of wings.

Characterization of asymmetric membranes of cellulose acetate from biomass: Newspaper and mango seed

Asymmetric membranes may be used in a broad range of applications such as reverse osmosis, hemodialysis and separation of organic mixtures. In this paper, asymmetric membranes were produced using cellulose acetate (CA) from biomass: newspaper and mango seed. The degree of substitution of CA was 2.65 ± 0.07. Different formulations were used to prepare the CA membranes: CA/dichloromethane/water with and without magnesium perchlorate. The asymmetry of the membranes was characterized by scanning electron microscopy (SEM). Membranes produced with magnesium perchlorate presented higher water vapor flux than those produced without this salt. This difference is due to pore formation in the membrane skin when using magnesium perchlorate. Membrane substructure showed to be a determining factor in ion diffusion experiments. The coefficient of ion diffusion for the membrane of cellulose acetate from mango seed was 1.82 × 10 −8 cm 2 s −1 while for the membrane of cellulose acetate from newspaper was 7.43 × 10 −8 cm 2 s −1 which similar to the value reported in the literature for commercial CA (8.46 × 10 −8 cm 2 s −1).

Comparison of the performance of two different regenerated cellulose ultrafiltration membranes at high filtration pressure

The hydrophilicity of a regenerated cellulose (RC) ultrafiltration (UF) membrane C 30FM is a great advantage in pulp and paper mill filtration applications. However, a better knowledge on its performance stability at high pressure could increase its area of application, for instance in the sugar industry. Thus, in this study, the C 30FM was tested at different pressures from 100 to 1200 kPa in the filtration of reverse osmosis (RO) treated water, polyethylene glycol (PEG) solution and spent sulphite liquor (SSL) used in the sugar industry. In addition, the same experiments were performed with another RC UF membrane, C2, which is from another manufacturer and has its cut-off value in the same range as the C 30FM. The performances of the membranes were compared by evaluating the stabilities of membrane structure, flux and observed PEG retention. The results showed crucial differences in the compaction of the C 30FM and the C2 owing to their differences in membrane substructure. The C 30FM was more compacted than the C2 but the compaction decreased the pure water fluxes (measured at 100 kPa) of both of the membranes. The compaction did not significantly affect the observed PEG retentions of the membranes at 100 kPa. Despite the compaction both of the tested membranes were, according to the results, applicable for the filtration of SSL in the pressure range 550–750 kPa.

Influence of membrane morphology on pore activation in membrane emulsification

The low throughput of the disperse phase is one of the issues in cross-flow membrane emulsification. This is apparent in the low percentage of pores at which droplets are formed (few active pores). To determine the effect of membrane morphology on pore activation, we developed and experimentally validated a model that describes the flow phenomena in and under a membrane with uniform pores (microsieve). In this model the membrane is divided into two parts: the toplayer and the membrane substructure. The model was validated with a larger-scale physical analogon. It predicts a linear increase of the number of active pores with increasing transmembrane pressure, while the pressure difference over the active pores is independent of the transmembrane pressure as long as not all pores are active. Although the resistance of the microsieve substructure was found to be four times lower than the resistance of a single pore, the resistance of the membrane substructure had a large effect on the activation of pores. Hence, the number of active pores can be increased by increasing the ratio of flow resistance in the pores and the flow resistance in the membrane substructure. Preliminary experiments show that the gradual increase in active pores at a ceramic membrane surface can be explained in the same way.

Post-testicular development of a novel membrane substructure within the equatorial segment of ram, bull, boar, and goat spermatozoa as viewed by atomic force microscopy

Atomic force microscopy has been used to investigate changes in the plasma membrane overlying the head region of mammalian spermatozoa (bull, boar, ram, goat, stallion, mouse, and monkey) during post-testicular development, after ejaculation, and after exocytosis of the acrosomal vesicle. On ejaculated ram, bull, boar, and goat spermatozoa the postacrosomal plasma membrane has a more irregular surface than that covering the acrosome. The equatorial segment, by contrast, is relatively smooth except for an unusual semicircular substructure within it that has a coarse uneven appearance. This substructure (referred to as the equatorial subsegment) is situated adjacent to the boundary between the postacrosomal region and the equatorial segment itself and seems to be confined to the order Artiodactyla as it has not been observed on stallion, mouse, or monkey spermatozoa. The equatorial subsegment develops during epididymal maturation, and following induction of the acrosome reaction with Ca 2+ ionophore A23187, its topography changes from a finely ridged appearance to that resembling truncated papillae. A monoclonal antibody to the equatorial subsegment binds only to permeabilized spermatozoa, suggesting that the subsegment is related to the underlying perinuclear theca that surrounds the sperm nucleus. A role for the equatorial subsegment in mediating fusion with the oolemma at fertilization is discussed.

High flux polyethersulfone–polyimide blend hollow fiber membranes for gas separation

In this work, the preparation of gas separation hollow fibers based on polyethersulfone Sumikaexcel (PES) and polyimide Matrimid 5218 (PI) blends, for three different compositions (i.e. PES/PI: 80/20, 50/50 and 20/80 wt.%), is reported. The dry/wet spinning process has been applied to prepare asymmetric hollow fibers by using blends of two different polymers with a common solvent. Dope viscosity measurements were performed to locate the blend concentrations where significant chain entanglement occurs. Cloud point measurements were carried out to estimate the tolerance of both pure components and blends in water. Scanning electron microscopy (SEM) was used to investigate the morphological characteristics and the structure of asymmetric hollow fibers. The permeation rates of CO 2 and N 2 were measured by the variable pressure method. In all cases, hollow fibers exhibit a typical asymmetric structure with a dense skin layer and a finely porous substructure. Macrovoids in the membrane substructure were observed only for the fibers spun at high PES concentration (80 wt.%). After coating with a silicone rubber solution, the developed hollow fibers exhibit a CO 2 permeance varying from 31 to 60 gas permeation units (GPU) and a CO 2/N 2 selectivity varying from 40 to 35, at room temperature. The thickness of the skin layer, which corresponds to these permeation rates, varies from 0.1 to 0.15 μm. The effect of air-gap distance on hollow fibers structure and permeation performance is examined. The aforementioned permeation properties, establish PES/PI hollow fibers as excellent candidates membranes for the separation of gaseous mixtures in industrial level.