Preparation of an efficient nanofiltration membrane based on blending of polysulfone and polysulfone-g-butylacrylate prepared by ATRP

Polysulfone is one of the most common used polymers for preparation of nanofiltration membranes. These membranes are highly susceptible to fouling problems because of their surface hydrophobic nature. In this paper a new approach for modification of polysulfone to overcome the fouling problems was introduced. The modification was carried out via blending of polysulfone with a modified grafted polysulfone using atom transfer radical polymerization (ATRP) method. The modified grafted polysulfone was synthesized via ATRP grafting of n-butylacrylate from chloromethylated polysulfone. The graft copolymers were characterized by FT-IR, NMR, DSG and TGA techniques. Furthermore, surface morphology and performance of the corresponding membrane were studied in detail using SEM and pure water flux and salt rejection experiments, respectively. The results indicated that the prepared modified polysulfone membranes have high surface hydrophilicity and therefore better fouling resistance and very good water permeability.     

Investigation of structure‐performance properties of a special type of polysulfone blended membranes

Membranes require superior mechanical strength due to applied harsh conditions. The mechanical properties of membranes decrease with increasing hydrophilicity of its elements. In this study, mechanical properties were investigated for two special blended membranes which were made by blending polysulfone with (polysulfone‐g‐poly (n‐butylacrylate) and polysulfone‐g‐poly (tert‐butylacrylate) as components. All of the prepared membranes were characterized by differential scanning calorimeter, thermal gravimetric analysis, field emission scanning electron microscope, and atomic electron microscope and were investigated in terms of pure water flux, water contact angle, molecular weight cut off, and morphology. It was found that water contact angle decreased from 73.6° which belongs to neat membrane decreased to 46° for blended membranes containing higher amounts of copolymers; however, the pure water flux increased with increasing copolymer content considerably compared with the neat membrane. Also, molecular weight cut off increased aggressively. Furthermore, mechanical properties including tensile strength, Young modulus, and elongation at break were measured and compared with the neat polysulfone membrane. Results showed that the tensile strength and modulus decreased with an increase in the copolymers content, despite the increase in the elongation at break. The effect of applied pressure on the membrane structure and also bursting strength were studied, and it has been proved that not only the structure of the membranes but also their performance is strongly affected by the composition of the membranes.     

Studies on cellulose acetate-carboxylated polysulfone blend ultrafiltration membranes--Part I

Hydrophilic polysulfone ultrafiltration (UF) membranes were prepared from blends of cellulose acetate with carboxylated polysulfone of 0.14 degree of carboxylation. The effects of blend polymer composition on compaction, pure water flux, water content and membrane hydraulic resistance (R_m), have been investigated to evaluate the performance of the membranes. The performance of the blend membranes of various blend polymer compositions were compared with that of membranes prepared from pure cellulose acetate and blends of cellulose acetate and pure polysulfone. The hydrophilic cellulose acetate-carboxylated polysulfone blend UF membranes showed better performance compared to membranes prepared from pure cellulose acetate and blends of cellulose acetate and pure polysulfone.     

Effect of the polarity of additional solvent on membrane formation in polysulfone/N-methyl-2-pyrrolidone/water ternary system

Asymmetric polysulfone membranes were prepared by wet phase inversion method with different demixing rate of casting solutions. The influent factor of demixing rate was focused on the polarity of additive in the polysulfone/N-methyl-2-pyrrolidone/water ternary system. With increasing the polarity of alcohols in the casting solution, the decrease in skin layer thickness was observed and then a poor separation performance of membranes can be obtained. It was found that the polar additive caused the rapidly demixing of casting solution in coagulation bath and formed porous asymmetric membranes with defective skin layer. In the other case, chloroform was used as the non-polar additive in casting solution. With increasing the mount of chloroform in the casting solution, the increase in skin layer thickness was observed and then lead to a good separation performance of these membranes. It was found that of the non-polar additive delays the demixing rate of casting solution in this ternary system. The separation performance of these asymmetric membranes were characterized by the measurement of dehydration of ethanol/water mixture by pervaporation and observed the morphology by scanning electron microscopy. It was found that the separation performance of asymmetric polysulfone membrane strongly depends on the polarity of adding solvent in polysulfone/N-methyl-2-pyrrolidone/water ternary system.     

Modification of polysulfones by click chemistry: Amphiphilic graft copolymers and their protein adsorption and cell adhesion properties

Well‐defined amphiphilic graft copolymer with hydrophobic polysulfone (PSU) backbone and hydrophilic poly(acrylic acid) (PAA) side chains were synthesized and characterized. For this purpose, commercially available PSU was converted to azido‐functionalized polymer (PSU‐N₃) by successive chloromethylation and azidation processes. Independently, poly(tert‐butyl acrylate) (PtBA) with an alkyne‐end‐group is obtained by using suitable initiator in atom transfer radical polymerization (ATRP). Then, this polymer was successfully grafted onto PSU‐N₃ by click chemistry to yield polysulfone‐graft‐poly(tert‐butyl acrylate), (PSU‐g‐PtBA). Finally, amphiphilic polysulfone‐graft‐poly(acrylic acid), (PSU‐g‐PAA), membranes were obtained by hydrolyzing precursor the PSU‐g‐PtBA membranes in trifluoroacetic acid. The final polymer and intermediates at various stages were characterized by ¹H NMR, FTIR, GPC, and SEM analyses. Protein adsorption and eukaryotic and prokaryotic cell adhesion on PSU‐g‐PAA were studied and compared to those of PSU‐g‐PtBA and unmodified PSU. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

PSF-g-P(PEGMA)的合成及其共混超滤膜的制备与性能研究

以氯甲基化双酚A型聚砜(PSF-CH2Cl)为大分子引发剂,通过原子转移自由基聚合(ATRP)法合成了以聚砜(PSF)为疏水主链、聚(聚乙二醇单甲醚甲基丙烯酸酯)[P(PEGMA)]为亲水侧链的梳状两亲性共聚物PSF-g-P(PEGMA).FT-IR和1H-NMR的表征结果证实了两亲性共聚物的生成.将PSF-g-P(PEGMA)与PSF进行共混,通过浸没沉淀法制备了共混超滤膜.研究发现,引入5 wt%的PSF-g-P(PEGMA),共混膜的孔隙率和平均孔径分别从65.9%和0.08μm提高到81.9%和0.18μm;将共混膜于90℃热水中浸泡24 h后,膜表面O/S从14.63提高到17.16;共混膜的亲水性和抗牛血清蛋白(BSA)吸附性能显著提升.     

Preparation, characterization and effect of annealing on performance of cellulose acetate/sulfonated polysulfone and cellulose acetate/epoxy resin blend ultrafiltration membranes

Polymeric membranes based on cellulose acetate (CA)--sulfonated polysulfone blends at three different polymer compositions were prepared by solution blending and phase inversion technique, characterized and subjected to annealing at 70, 80 and 90 °C. The permeate water flux, separation of bovine serum albumin and its flux by the blend membranes before and after thermal treatment, have been compared and discussed. Similarly, CA and epoxy resin (diglycidyl ether of bisphenol-A) were blended in various compositions, in the presence and in the absence of polyethyleneglycol 600 as non-solvent additive, using N,N^′-dimethylformamide as solvent, and used for preparing ultraflltration membranes by phase inversion technique. The polymer blend composition, additive concentration, casting and gelation conditions were optimized. Blend membranes were characterized in terms of compaction, pure water flux, water content and membrane resistance. The effects of polymer blend composition and additive concentration on the above parameters were determined and the results are discussed.     

Hydrogels of starch-g-(<Emphasis Type="Italic">tert</Emphasis>-butylacrylate) and starch-g-(<Emphasis Type="Italic">n</Emphasis>-butylacrylate) copolymers

The synthesis, characterization, and hydrogel properties of starch-g-(tert-butylacrylate) and starch-g-(n-butylacrylate) copolymers were studied. The optimum conditions for the grafting process of tert-butylacrylate into 1.0 g of starch were as follows: [tert-butylacrylate] = 0.04 mol/L, [CAN] = 9.0 × 10⁻⁴ mol/L, temperature = 20 °C in 100 mL solution, whereas the results using n-butylacrylate monomer were as follows: [n-butylacrylate] = 0.04 mol/L, [CAN] = 4.0 × 10⁻³ mol/L, temperature = 30 °C in 100 mL solution. The grafting evidences of monomers into starch were done through TG and its derivative DTG for thermal changes and mass losses, scanning electron microscope (SEM) for morphological changes, powder X-ray for crystallinity measurements and FTIR for functional group changes. Acid hydrolysis method was used efficiently to allow the calculations of the viscosity average molecular weight (M _v) of the grafted chains on starch and consequently the real percent of grafting efficiency (i.e. %GY). The capability of starch-g-(n-BAC) hydrogel to absorb water were found 10 times more than starch-g-(tert-BAC) hydrogel, which were clarified through the X-ray and SEM results.     

Effect of PEG additive on membrane formation by phase inversion

This study investigates the effect of PEG additive as a pore-former on the structure formation of membranes and their permeation properties connected with the changes of thermodynamic and kinetic properties in phase inversion process. The membranes were prepared by using polysulfone (PSf)/N-methyl-2-pyrrolidone (NMP)/poly(ethylene glycol) (PEG) casting solution and water coagulant. The resulting membranes prepared by changing the molecular weight of PEG additive and the ratio of PEG to NMP were characterized by scanning electron microscope observations, measurements of water flux and PEG rejection. The thermodynamic and kinetic properties of membrane-forming system were studied through coagulation value, light transmittance and viscosity. The correlations between the final membrane structure/permeation properties and thermodynamic/kinetic properties of membrane forming system are discussed extensively.     

Effect of gelation conditions on gas separation performance for asymmetric polysulfone membranes

Asymmetric gas separation membranes were prepared by the phase inversion technique under different gelation conditions from polysulfone/N,N-dimethylacetamide (DMAc) solutions. The dual bath method was employed to control the skin layer properties: the cast film was immersed in 2-propanol bath and water bath in sequence. The membranes were characterized by the permeance of oxygen and nitrogen gases and the observation with scanning electron microscopy (SEM). A thin layer of silicone rubber (PDMS) was laminated on the surface of each asymmetric polysulfone membrane to eliminate the effect of defects in the skin layer. The oxygen permeance was inversely proportional to the square root of immersion time in the first (2-propanol) bath. The skin layer thickness determined by SEM observation increased with an increase in the immersion time in the first bath. For a given immersion time, the oxygen permeance decreased with an increase in the polymer concentration in the casting solution. Selectivity of oxygen over nitrogen also depended both on the immersion time in the first bath and the polymer concentration.     

Crosslinked chitosan composite membrane for the pervaporation dehydration of alcohol mixtures and enhancement of structural stability of chitosan/polysulfone composite membranes

Chitosan composite membranes having a microporous polysulfone substrate were prepared and tested for the pervaporation dehydration of aqueous isopropanol mixtures. When the composite membrane experienced excessive swelling at the feed mixture of high water content, the composite membranes were found to be segregated in structure due to the opposite characteristics to water of chitosan and polysulfone. Efforts to enhance the structural stability under various pervaporation operational conditions were made. The polysulfone substrate was immersed into hydrophilic binding polymer solutions such as polyvinyl alcohol, polyacrylic acid, and hydroxyethylcellulose before the casting of chitosan layer to increase the affinity between the thin chitosan layer and porous polysulfone layer which resulted in increased geometrical stability of the chitosan/polysulfone composite membranes. The chitosan layer was crosslinked with glutaraldehyde and H₂SO₄ in acetone solution to control the permselectivity.     

Biofouling potentials of microporous polysulfone membranes containing a sulfonated polyether-ethersulfone/polyethersulfone block copolymer: correlation of membrane surface properties with bacterial attachment

Multivariate methods were used to identify relationships between bacterial attachment (biofouling potential), water transport, and the surface properties of nine modified polysulfone (MPS) membranes comprising blends of polysulfone (PS) with a sulfonated polyether-ethersulfone/polyethersulfone block copolymer. The topology of the microporous MPS membranes, including surface roughness, surface height, pore size and pore geometry were determined by atomic force microscopy (AFM) and digital image analysis. Other measurements included relative surface hydrophobicity by captive bubble contact angle, surface charge (i.e., degree of sulfonation) by uranyl cation binding, wt% solids, porosity, membrane thickness, water flux, and the affinity of membranes for a hydrophilic Flavobacterium and hydrophobic Mycobacterium species. The mycobacteria attached best to the MPS membranes, but the attachment of both organisms was inversely correlated with the mean aspect ratio of pores, suggesting that irregular or elliptic pores discouraged attachment. Multivariate regression analyses identified the pore mean aspect ratio, mean surface height, PS content, and the n-methylpyrrolidone+propionic acid (NMP–PA) solvent concentration as influential factors in Mycobacterium attachment, whereas membrane thickness, surface roughness, pore mean aspect ratio, porosity, and the mean pore area/image area ratio influenced Flavobacterium attachment. Cluster analyses revealed that Mycobacterium attachment was associated with hydrophobic determinants of the MPS membranes, including PS content, wt% solids, and air bubble contact angle. In contrast, Flavobacterium attachment was primarily associated with membrane thickness and charge (i.e., uranyl cation binding or degree of sulfonation). Membrane flux was inversely correlated with surface hydrophobicity and PS content, but (in contrast to cell attachment) positively correlated with most pore geometry parameters including the mean aspect ratio, suggesting that pore geometry can be optimized to minimize cell attachment and maximize water transport. Other variables influencing water flux included the NMP–PA solvent concentration and membrane roughness. The results should facilitate the design of novel microporous PS membranes having reduced biofouling potentials and greater water fluxes.     

Polymer micelles from tadpole-shaped amphiphilic block-graft copolymers prepared by “Grafting-through” ATRP

A series of tadpole-shaped block-graft amphiphilic copolymers, i.e., block copolymers consisting of a cylindrical hydrophilic brush block and a coiled hydrophobic block were synthesized using “grafting-through” atom transfer radical polymerization. A tadpole-shaped block-graft copolymer from polystyrene bromide and a methacryloyl-terminated poly(tert-butyl acrylate) was prepared first. Then, hydrolysis of the poly(tert-butyl acrylate) side chains to polyacrylic acid side chains provided tadpole-shaped block-graft amphiphilic copolymers, which formed pH responsive micelles in water, the latter being confirmed by dynamic light scattering and atomic force microscopy.     

Photochemically prepared polysulfone/poly(ethylene glycol) amphiphilic networks and their biomolecule adsorption properties

Polysulfone/poly(ethylene glycol) amphiphilic networks were prepared via in situ photo-induced free radical crosslinking polymerization. First, the hydrophobic polysulfone diacrylate (PSU-DA) oligomer was synthesized by condensation polymerization and subsequent esterification processes. Then, the obtained oligomer was co-crosslinked with the hydrophilic poly(ethylene glycol) diacrylate (PEG-DA) or poly(ethylene glycol) methyl ether acrylate (PEG-MA) at different feed ratios. In the case of PEG-MA, the resulting network possessed dangling pendant hydrophilic chains on the crosslinked surface. The structure and the morphology of the membranes were characterized by attenuated total reflection infrared spectroscopy (ATR-IR) and scanning electron microscopy (SEM). The enhancement of surface hydrophilicity was investigated by water contact angle measurements. The biomolecule adsorption properties of these networks were also studied. The biomolecules easily adsorbed on the surface of the hydrophobic polysulfone networks whereas dangling hydrophilic chains on the surface prevented the adsorption of the biomolecules.     

Enhancing the performance of TFC nanofiltration membranes by adding organic acids in polysulfone support layer

Throughout this study, the effect of certain organic acids, methacrylic acid, lactic acid and tartaric acid, doped in polysulfone (PSF) casting solution onto the performance of nanofiltration (NF) membranes was investigated. Different NF membranes have been prepared from m-phenylenediamine and trimesoylchloride onto the top surface of the acid-modified PSF membranes through regulating the concentration and contact time of the conventional interfacial polymerization process. The study of scanning electron microscopy (SEM) was used to investigate the influence of acids on the morphology of membranes and cross-sectional structures. The functional groups, hydroxyl and carboxylic acid, of the acids have resulted in a significant increase in membrane thickness, porosity and hydrophilicity, with a decrease in macrovoid capacity of the PSF layer. The acid-modified PSF/TFC membranes showed higher rejection of salt, with an increment in water flux compared to the neat membrane. Water flux and salt rejection (R_s %) of the control membrane was 7.6 L/m² h and 65.4%, whereas polysulfone/methacrylic acid (PSF/MAAc), polysulfone/tartaric acid (PSF/TAc), and polysulfone/lactic acid (PSF/LAc) were 16.8, 18.5, and 20.2 L/m² h and 88, 88.2 and 94.1%, respectively. Efficiency of prepared NF membranes under various inlet pressures and specific salts was investigated with selectivity and salt rejection. The salt rejection of a mixed salt solution was found to meet the order of R_s % CaSO₄ ≥ R_s % Na₂SO₄ ˃ R_s % MgSO₄ ˃ R_s MgCl₂ ˃ Rs % NaCl.     

Polyethylene/poly(styrene-co-divinylbenzene) sodium sulphonate membranes : Part 1. Synthesis and properties

Transport properties of cation-exchange membranes have been studied. The self-diffusion coefficients of sodium and chloride ions, the transport numbers of sodium ions and water, and the conductivities were measured in 0.1 M sodium chloride at 25°C. The concentration potentials were determined in the system 0.05/0.15 M sodium chloride.The membranes were prepared by sulphonation of oriented polyethylene (PE) film modified with 30 wt % of styrene—divinylbenzene copolymer (poly(St-co-DVB)). The copolymer was introduced by interpolymerization of the monomers within the film without its dissolution. A sequence of membranes having similar ion-exchange capacity but differing in water content was then obtained from sheets of normal PE/poly(St-co-DVB)SO₃Na membranes by expanding them by heating in water followed by a thermal treatment in air.The deviations of the measured transport properties from the behaviour of homogeneous membranes and the analysis of the Kedem—Katchalsky relationships for composite membranes have led to the conclusion that in PE/poly(St-co-DVB)SO₃Na membranes a structure prevails with a series arrangement of layers with different properties.     

Polymerization of vinyl monomers via MAO activated iron(II) dichloro complexes bearing bis(imino)pyridine-, quinolinaldimine- and thiophenaldimine-based tridentate nitrogen ligands

A series of iron(II) complexes (4a-d, 10, and 11) bearing 2,6-bis[(imino)ethyl]pyridine-(3a-d), quinolinaldimine-(8) and thiophenaldimine-(9) based ligands were disclosed as active complexes for the polymerization of tert-butylacrylate (t-BA). After activation with methyl aluminoxane (MAO), the complexes showed moderate to high polymerization activities and produced high molar mass polymers. In addition, the catalyst system 4d/MAO was examined for the polymerization of methyl methacrylate (MMA) and n-vinylcarbazole (NVC). The influence of MAO/Cat. molar ratio, polymerization time, and monomer concentration on the polymerization reaction of methyl methacrylate was explored.In the polymerization of tert-butylacrylate with 2,6-bis[(imino)ethyl]pyridine iron(II)-based catalysts, bulky terminal aliphatic substituents have a favorable influence on the polymerization activity compared to the aromatic ones. This catalyst system was also more active than the quinolinaldimine-, (10) and thiophenaldimine-, (11) based catalysts.     

Membrane thickness and preparation temperature as key parameters for controlling the macrovoid structure of chiral activated membranes (CAM)

A macrovoid structure is formed in polysulfone (PSf) polymeric membranes prepared by the immersion technique using N-dimethylformamide (DMF)/water as a solvent/non-solvent pair. It is actually important controlling the macrovoid formation process, because macrovoids can cause unwanted mechanical failure during high-pressure applications. In order to control the formation of these structures, the influence of different parameters like membrane thickness, solvent additives (isopropyl myristate, IPM or N-hexadecyl-l-hydroxypriline, HHP), temperature of the coagulation bath, and solvent/non-solvent pair has been studied for chiral activated membranes. With the same purpose, corresponding membranes where physically characterized by scanning electron microscopy (SEM) measurements of their cross-section images. Those SEM images have been treated by the software IFME^®, which provides the parameters of asymmetry and irregularity of the membranes. The surface of the membranes has been analyzed by atomic force microscopy (AFM) and brightness analysis in order to calculate their roughness. A comparison of the same PSf membranes, but prepared by evaporation precipitation, or by using chloroform/methanol as solvent/non-solvent pair during the immersion precipitation step, has been also checked. That paper helps us to understand and predict which will be the best conditions to prepare the optimum membranes.     

P(AA-AMPS)–PVA/polysulfone composite hollow fiber membranes for propylene dehumidification

A series of composite hollow fiber membranes, poly(acrylic acid-co-2-acrylamido-2-methyl-1-propane sulfonic acid) (P(AA-AMPS))–poly(vinyl alcohol) (PVA) membranes as skin layers and polysulfone (PS) hollow fiber membranes as support layers, were prepared for dehumidification of propylene gas. The chemical and physical structures, including inter-components interaction, crystallinity, glass transition temperature and free volume of the membranes, were systematically characterized. Through the sorption experiments, it was found that the membrane exhibited a preferential sorption toward water, and initially the water sorption increased remarkably with P(AA-AMPS) content increasing, afterwards reached the zenith, then decreased rapidly. Dehumidification performance showed that the membrane containing 50 wt.% P(AA-AMPS) exhibited the highest permeance of 363 GPU and an infinite separation factor for 0.5 wt.% water in feed at 298 K. Permeance decreased considerably with increasing operating temperature, but increased considerably with increasing water content.     

Application of polysulfone (PSf)– and polyether ether ketone (PEEK)–tungstophosphoric acid (TPA) composite membranes for water electrolysis

The ion exchange membrane using polysulfone (PSf) and polyether ether ketone (PEEK) as a basic material was prepared to apply in the polymer electrolyte membrane electrolysis (PEME). The sulfonated block copolymer of PSf and poly(phenylene sulfide sulfone) (SPSf-co-PPSS) and the sulfonated PEEK (SPEEK) were blended with tungstophosphoric acid (TPA) to avoid water swelling at elevated temperatures led to decrease in mechanical strength. These prepared ion exchange membranes showed some interesting characteristics including physicochemical stabilities, mechanical and membrane properties.The prepared ion exchange membrane was utilized to prepare the membrane electrode assembly (MEA). MEA consisted of Pt/PEM/Pt was prepared by equilibrium and non-equilibrium impregnation–reduction (I–R) methods. The prepared MEA by non-equilibrium I–R method was used in the PEME unit cell. The cell voltages of the MEA using SPSf-co-PPSS/TPA and SPEEK/TPA membranes were 1.83 V and 1.90 V at 1 A/cm² and 80 °C, with platinum loadings of 1.12 and 1.01 mg/cm², respectively.