Effect of surface‐modifying macromolecules and membrane morphology on fouling of polyethersulfone ultrafiltration membranes

Polyethersulfone (PES) ultrafiltration (UF) membranes with and without surface‐modifying macromolecules (SMMs) were prepared and characterized in terms of the mean pore size and pore‐size distribution, surface porosity, and pore density. The results demonstrated that both the mean pore size and the molecular weight cutoff (MWCO) of the SMM‐modified membranes are lower than those of the corresponding unmodified ones. Membrane fouling tests with humic acid as the foulant indicated that the permeate flux reduction of the SMM‐modified membranes was much less than that of the unmodified ones. Therefore, fouling was more severe for the unmodified membranes. Moreover, the dry weight of the humic acid deposited on the membrane surface was considerably higher for the unmodified membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3132–3138, 2003     

Surface modification of poly(ether sulfone) ultrafiltration membranes by low‐temperature plasma‐induced graft polymerization

Low‐temperature helium plasma treatment followed by grafting of N‐vinyl‐2‐pyrrolidone (NVP) onto poly(ether sulfone) (PES) ultrafiltration (UF) membranes was used to modify commercial PES membranes. Helium plasma treatment alone and post‐NVP grafting substantially increased the surface hydrophilicity compared with the unmodified virgin PES membranes. The degree of modification was adjusted by plasma treatment time and polymerization conditions (temperature, NVP concentration, and graft density). The NVP‐grafted PES surfaces were characterized by Fourier transform infrared attenuated total reflection spectroscopy and electron spectroscopy for chemical analysis. Plasma treatment roughened the membrane as measured by atomic‐force microscopy. Also, using a filtration protocol to simulate protein fouling and cleaning potential, the surface modified membranes were notably less susceptible to BSA fouling than the virgin PES membrane or a commercial low‐protein binding PES membrane. In addition, the modified membranes were easier to clean and required little caustic to recover permeation flux. The absolute and relative permeation flux values were quite similar for the plasma‐treated and NVP‐grafted membranes and notably higher than the virgin membrane. The main difference being the expected long‐term instability of the plasma treated as compared with the NVP‐grafted membranes. These results provide a foundation for using low‐temperature plasma‐induced grafting on PES with a variety of other molecules, including other hydrophilic monomers besides NVP, charged or hydrophobic molecules, binding domains, and biologically active molecules such as enzymes and ribozymes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1699–1711, 1999     

Fouling control in sugarcane juice ultrafiltration with surface modified polysulfone and polyethersulfone membranes

Commercial 50 and 100 kD polyethersulfone (PES) and polysulfone (PS) ultrafiltration membranes were surface modified by UV photografting of poly(ethylene glycol) methacrylate (PEGMA) monomer. The modified membranes were characterized by the degree of grafting, water flux and molecular weight cutoff (MWCO) rating. The flux and fouling of the modified and unmodified membranes were examined with sugarcane juice and its polysaccharide fraction. Under the conditions of this study, the modified membranes displayed a low degree of grafting (26-36 μg/cm²), which was independent of the UV exposure duration; however, both membrane water flux and MWCO rating were affected by the irradiation time. In the best case, the modified membranes exhibited lower fouling with sugarcane juice; furthermore, the propensity to foul also decreased. More significantly, juice flux recovery was almost complete for successive UF-cleaning cycles.     

Influence of feed concentration and transmembrane pressure on membrane fouling and effect of hydraulic flushing on the performance of ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) is a promising technology developed for treating the wastewater containing metal ions or organic pollutants. One of the greatest problems in MEUF is membrane fouling which is mainly caused by concentration polarization, gel layer or cake formation caused by the deposition of surfactant micelles on the membrane surface and surfactant adsorption in the membrane interior. In this study, surfactant sodium dodecyl sulfate (SDS), which was used in membrane separation as colloidal particles, caused the flux decline. The transmembrane pressure (TMP) and feed concentration of SDS had significant influences on the flux. This paper presented that the lower TMP had a smaller effect on membrane fouling, and when SDS concentration was around the critical micelle concentration (CMC), lower permeate flux and higher additional membrane fouling resistance were obtained. The effects of three kinds of hydraulic flushing methods on membrane permeate flux were investigated, including periodic forward flushing, periodic backwashing and forward flushing followed by backwashing. It was found that when the periodic combined flushing interval was 10 min, forward flushing and backwashing phase times were 150 s and 90 s, respectively, and that combined flushing was more conductive to permeate flux recovery in this study.     

The effect of polymer surface modification via interfacial polymerization on polymer–protein interaction

Membrane separation is an important processing technology used for separating food ingredients and fractionating value‐added components from food processing byproducts. Long‐term performance of polymeric membranes in food protein processing is impeded by the formation of fouled layers on the membrane surface as a result of protein adsorption onto the membrane surface. Surface modification of synthetic membranes, i.e., changing surface characteristics to reduce protein adsorption permanently, is one of the innovative ways of reducing the fouling of membrane surfaces. In this study, surface modification of flat‐sheet ultrafiltration membrane, polyethersulfone (PES), was investigated in improving the hydrophilicity of PES surfaces, thereby reducing adsorption of the protein caused by hydrophobic–hydrophobic interaction between the protein and the membrane. Hydrophilic polymer grafting through thin‐film composite using interfacial polymerization was employed to improve the hydrophilicity of the commercial PES membranes. Poly(vinyl alcohol), poly(ethylene glycol), and chitosan were chosen as hydrophilic polymers to graft on PES membrane because of their excellent hydrophilic property. Modified PES membranes were characterized by contact angle, FTIR, XPS, and AFM. Contact angles of modified PES membranes were reduced by 25 to 40% of that of the virgin PES membrane. XPS spectrum supported that the PES membranes were successfully modified by interfacial polymerization. Tapping‐mode AFM was used to examine the changes in surface topography of modified PES membranes. The PES membranes modified by interfacial polymerization showed lower roughness (from 1.2 to 2.0 nm) than that of virgin PES membrane (2.1 nm). The results of these instrumental analyses indicated that the PES membranes were successfully enhanced hydrophilically through interfacial polymerization. The protein adsorption on the modified membranes was reduced by 30 to 35% as a result of surface modification of the PES membranes using interfacial polymerization technique. Published 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

氧化铝凝胶改性聚偏氟乙烯超滤膜的制备与表征

为提高聚偏氟乙烯超滤膜的亲水性,采用Al_2O_3凝胶对有机高分子聚偏氟乙烯膜进行改性,制备Al_2O_3凝胶改性聚偏氟乙烯超滤膜,并与非凝胶化无机纳米Al_2O_3颗粒改性进行对比。考察铸膜液中Al_2O_3凝胶加入量对改性聚偏氟乙烯超滤膜性能和结构的影响。采用扫描电镜、X射线能谱、傅里叶红外光谱和超滤实验等对超滤膜结构和性能进行表征,结果表明,Al_2O_3凝胶加入量1.0 g时,改性超滤膜水通量提高5.48倍;扫描电镜表明,改性超滤膜和未改性超滤膜均为典型的非对称结构,改性超滤膜表面孔数目明显增加,断面微观结构未发生改变;红外光谱及能谱分析表明,Al_2O_3凝胶与高分子聚偏氟乙烯之间为物理共混。Al_2O_3凝胶改性聚偏氟乙烯超滤膜,改善了膜表面亲水性,提高水通量,并保持较大截留率。     

The effects of spinning temperature on morphologies and properties of polyethersulfone hollow fiber membranes

Polyethersulfone (PES) hollow fiber membranes were prepared by traditional dry‐wet spinning technique. Scanning electronic microscopy (SEM) was used to characterize membrane morphologies, and the membrane properties were evaluated via bubble point measurements and ultrafiltration experiments. The effects of spinning temperature on the morphologies and properties of PES fibers were investigated in detail. At a high spinning temperature, the obtained membrane structure consisting of a thin skin‐layer and loose sponge‐like sublayer endows PES membrane with not only good permeability, but also high solute rejection. Based on the determination of ternary phase diagrams and light transmittance curves, the relationship of membrane morphologies with thermodynamics and precipitation kinetics of membrane‐forming system was discussed. It was concluded that the morphologies and properties of PES hollow fiber membrane could be conveniently tuned by the adjustment of the spinning temperature and air gap. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and Characterization of pH-Sensitive Polyethersulfone Membranes Blended with Poly(methyl methacrylate-co-maleic anhydride) Copolymer

The current study aims to endow polyethersulfone (PES) hollow fiber membranes (HFMs) with improved pH-sensitivity by blending a random copolymer of poly(methyl methacrylate-co-maleic anhydride) (P(MMA-MA)). It was found that PES membrane modified by random copolymer had more obvious pH-sensitivity than those by alternative copolymer; while low molecular weight copolymer modified PES membrane had no pH-sensitivity. P(MMA-MA) was synthesized by a controlled dosing method via free radical polymerization and characterized by Fourier transform infrared spectroscopy (FTIR) analysis, nuclear magnetic resonance (¹H NMR), elemental analysis, gel permeation chromatography technique (GPC), and differential scanning calorimetry (DSC) measurement. Scanning electron microscopy (SEM) was used to investigate the morphology of the HFMs. The modified HFMs showed excellent pH-sensitivity, pH-reversibility and hysteresis of water flux. Through the ultrafiltration of PEG solution, we investigated the pore size change and the electroviscous effect on the water flux of the modified HFMs. Meanwhile, the modified membranes were stable with respect to the mechanical force (pressure) and exhibited good ability of Cu²⁺ adsorption.     

Fouling reduction of a poly(ether sulfone) hollow‐fiber membrane with a hydrophilic surfactant prepared via non‐solvent‐induced phase separation

Membrane fouling is still a crucial problem, especially in applications for water treatment. When fouling takes place on membrane surfaces, it causes flux decline, leading to an increase in production cost due to increased energy demand. The selection of the right membrane material and a special treatment of the membrane are required to avoid membrane fouling. This article reports the fouling resistance of a poly(ether sulfone) (PES) hollow‐fiber membrane modified with hydrophilic surfactant Tetronic 1307. Experiments on several methods of fouling were carried out to investigate the effect of the addition of nonionic surfactant Tetronic 1307 on membrane fouling. The effectiveness of a chemical agent [sodium hypochlorite (NaClO)] in the reduction of bovine serum albumin (BSA) deposition on the membrane surface was also evaluated. Permeation results showed that the fouling of a PES blend membrane with Tetronic 1307 was lower than that of the original PES membrane in the case of BSA filtration. A treatment with a 100 ppm NaClO solution was capable of removing BSA cake formation and effective at improving the relative permeability. The permeability of a PES blend membrane with Tetronic 1307 was almost 2 times higher than the original permeability when the membrane was treated with a 100 ppm NaClO solution because both BSA and Tetronic 1307 could be decomposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Analysis of deposition mechanism during ultrafiltration of glycerin-rich solutions

Clarification of glycerin-rich solution is one of the potential applications of membrane within the oleochemical industry. However, one of the barriers in successfully utilizing the use of membranes such as ultrafiltration (UF) has been due to the fouling. In this work, flux decline during ultrafiltration of the glycerin-rich solutions was studied by using commercialized polymeric polyethersulphone (PES) membrane. Influence of fatty acids as foulants model (palmitic acid, stearic acid and oleic acid), pH of feed solution (3-10) and molecular weight cut-off (5 kDa, 20 kDa and 25 kDa) were analyzed. All the experiments were performed at constant pressure (2 bar) and temperature (40 °C). The Hermia's model was used to analyze the fouling mechanism during the flux decline which involve cake layer model due to adsorption of solute as well as pore blocking model. All the different types of flux decline kinetics were found to occur during the permeation of glycerin-rich solutions. However, the contribution of resistance due to cake layer formation was small for all the conditions studied. The fouling mechanisms were found to depend on the hydrophobicity of the PES membrane itself as well as the nature of foulants used in the study.     

编织型中空纤维膜污染与浓差极化的试验研究

导致膜污染和浓差极化的主要因素有：悬浮液浓度、颗粒粒径、颗粒表面性质、膜材料以及膜表面的流态等。设计的一组试验证明了上述因素导致膜污染与浓差极化对膜处理的危害性;同时也证明了在中空纤维膜中,Dean涡这种不稳定流能较大程度地降低膜污染与浓差极化,降低的程度取决于Dean涡的优化参数。     

Characterization of Surface Modification of Polyethersulfone Membrane

Surface modification of polyethersulfone (PES) membrane surfaces using UV/ozone pretreatment with subsequent grafting and interfacial polymerization on membrane surface was investigated in order to improve the resistance of membrane surface to protein adsorption. The surface modifications were evaluated in terms of hydrophilicity, chemical composition of the surface and static protein adsorption. In both methods, poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG) and chitosan were chosen as hydrophilic polymers to chemically modify the commercial virgin PES membrane to render it more hydrophilic as these materials have excellent hydrophilic property. Modified PES membranes were characterized by contact angle and XPS. Contact angles of modified PES membranes were reduced by 19 to 58% of that of the virgin PES membrane. PES membrane modified with PEG shows higher wettability than other hydrophilic materials with the highest contact angle reduction shown for UV/ozone pretreated, PEG grafted PES membrane surface. In general, XPS spectra supported that the PES membranes were successfully modified by both grafting with UV/ozone pretreatment and interfacial polymerization methods. The results of the static protein adsorption experiments showed all surface modifications led to reduction in protein adsorption on PES membranes; the highest protein adsorption reduction occurred with membrane modified by UV/ozone pretreatment followed by PES grafting, which corresponded to the highest contact angle reduction. However, there seems to be no clear correlation between contact angle reduction and reduction in protein adsorption in the case that involved chitosan. Nevertheless, membranes modified with chitosan do show higher reduction in protein adsorption than membranes modified with other materials under the same conditions.     

Polyethersulfone-polyvinylpyrrolidone composite membranes:Effects of polyvinylpyrrolidone content and polydopamine coating on membrane morphology,structure and performances

Hydrophilic modification is a promising method to inhibit fouling formation on ultrafiltration membrane.In this work,different mass concentrations (1％-16％) of hydrophilic polyvinylpyrrolidone were incorpo-rated into polyethersulfone (PES) membranes fabricated by none-solvent induced phase separation.Then,polydopamine (PDA) coating on the surface of prepared membrane was carried out at pH 8.5.The mor-phology and structure,surface hydrophilicity,permeation flux,BSA rejection,antifouling and stability performances of PES and PDA/PES modified membranes were investigated in detail.The results indicated that PDA was successfully attached onto the membranes.Membrane hydrophilicity was evaluated by water contact angle measurement.The contact angles of modified membranes reduced remarkably,sug-gesting that the membrane hydrophilicities were significantly increased.The results of filtration tests,which were done by dead-end filtration of bovine serum albumin solution,showed that the properties of permeability and fouling resistance were obviously improved by PDA modification.When polyvinylpyrrolidone mass content reached 10％,flux recovery ratio of modified membrane was up to 91.23％,and its BSA rejection were over 70％.The results of stability tests showed that the modified mem-branes had good mechanical stability and chemical stability.This facile fabrication procedure and out-standing performances suggested that the modified membranes had a potential in treating fouling.     

Ultrafiltration of Coagulation-Pretreated Serratia marcescens Fermentation Broth: Flux Characteristics and Prodigiosin Recovery

The dead-end ultrafiltration (UF) of coagulation-pretreated fermentation broth of Serratia marcescens SMΔR for prodigiosin recovery was studied. Experiments were performed using different types (regenerated cellulose, YM; polyethersulfone, PES) and molecular weight cut-offs (MWCOs, 1–10 kDa) of the membranes, feed concentrations of prodigiosin (300–1000 mg/L), applied pressures (68.9–206.8 kPa), and stirring speeds (200–400 rpm). With the same MWCO, the YM membrane had a higher retention of prodigiosin and a lower flux than the PES membrane. A two-fold concentration of prodigiosin was observed in the retentate using a 1-kDa YM membrane compared to the concentration in the permeate using a 10-kDa YM membrane. In addition, the extent of membrane fouling was quantitatively analyzed in terms of the modified fouling index. Flux decline in the present batch UF process was mainly due to cake layer formation and partly due to pore blocking. A two-stage UF process was proposed for this purpose, with 81% recovery yield and four-fold concentration.     

Concentration Polarization and Fouling during Ultrafiltration of Colloidal Suspensions and Hydrophobic Solutes

Abstract

Flux reductions experienced during ultrafiltration are due either to concentration polarization or fouling. It is usually difficult to distinguish between these two phenomena, but by using a turbulence-promoting module it is possible to determine the reversibility of a flux reduction, and thus distinguish between concentration polarization and fouling. By using a turbulence-promoting module, it is also possible to distinguish between different cases of fouling. In this paper, fouling caused by the deposition of material at the surface of the membrane is illustrated by results from tests with a silica sol, and fouling due to interactions in the membrane matrix is illustrated by results from ultrafiltration of a low-molecular organic solute.     

Adsorption behavior of β-lactoglobulin onto polyethersulfone membrane surface

The adsorption of whey protein onto polyethersulfone (PES) membrane was investigated by static adsorption experiments to understand fouling mechanism and optimize the process condition to minimize the membrane fouling. Adsorption isotherm was applied to calculate the isotherm parameters such as adsorption capacity (K_F) and surface heterogeneity (1/n). The K_F values increased about 3.7 times at pH 3.0, 1.5 times at pH 5.2, and 2.3 times at pH 9.0 compared to that at pH 7.0. The hydrophobic interaction by dissociation of dimer structure of β-lactoglobulin to monomer structure at acidic and alkaline conditions showed the greatly increasing of the amount of protein adsorption by the protein and membrane interaction which might form the strong and rigid protein layer on the polymeric membrane surface. The addition of salt reduced the protein adsorption on PES membrane because of the interactions between charged protein molecules and salt ions.     

A Study on Concentration Polarization in Ultrafiltration

Abstract

A finite-difference solution of coupled transport equations for momentum and solute continuity is presented to model the concentration polarization in a tubular ultrafiltration (UF) system. The model includes the effects of solute osmotic pressure and solute rejection at the membrane surface, axial pressure drop and resistance of the gel layer. This provides a fundamental understanding of the dynamics of various operating parameters on concentration polarization and transmembrane flux. Simulation results are presented for a wide range of operating variables to show their effects on local variation of solute concentration and transmembrane flux. The numerical results were also compared with previously published experimental data, which shows that a concentration polarization model based on constant membrane permeability (usually obtained from pure water flux data) grossly overestimates the flux behavior. If the effect of gel polarization is included, the model can predict the actual permeate flux very closely. Thus, in modeling ultrafiltration, one needs to be careful in using the appropriate membrane permeability terms. The commonly used intrinsic membrane permeability which is usually a constant, may not describe the true flux behavior in ultrafiltration. Actually the nature of the feed, solute-surface interaction and gel layer formation control the effective permeability, which varies axially along the membrane length.     

Synthesis of a novel sulfonated poly(amide‐imide) and its application in preparation of ultrafiltration PES membranes as a modifier

Sulfonated poly(amide‐imide) (SPAI) copolymer was synthesized, characterized, and blended into poly(ether sulfone) (PES)/dimethylacetamide casting solutions to prepare ultrafiltration membranes. Different weight ratios of the copolymer (0–10 wt %) were mixed in the PES casting solution. The analyses of contact angle and attenuated total reflection‐Fourier transform infrared spectra were used to study hydrophilicity and physicochemical properties of the membrane surface, respectively. The membranes were further characterized by scanning electron microscopy images, ultrafiltration performance, and fouling analyses. The outcomes showed that addition of the SPAI in the PES matrix improved considerably the membranes hydrophilicity. Moreover, with increasing SPAI concentration, the porosity, flux recovery ratio, and pure water permeability of the modified membranes were improved. The pure water flux was increased from 3.6 to 12.4 kg/m² h by increasing 2 wt % SPAI. The antifouling property of the modified PES membranes against bovine serum albumin, tested by a dead‐end filtration setup revealed that bovine serum albumin rejection of the obtained membrane was also enhanced and the antifouling properties of the blending membranes were improved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46477.     

XPS study of dimethylolurea polymers and hollow fibers modified by these polymers. II. XPS study of hollow fibers modified by dimethylolurea polymers

Polysulfone ultrafiltration hollow fibres are modified on the surface with polymers obtained by polycondensation of dimethylolurea (DMU). Depending upon the reaction conditions, polymers on the surface present a gel or a film form. In the first case the membranes are called “gel-supported” and in the second case “coated”. Modified and unmodified polysulfone membranes were analysed by XPS spectroscopy. The modifications observed on a modified membrane were studied by reference to the previous article dealing with XPS analysis of gel and film DMU polymers. The study showed that gel-supported membranes are modified by a polymer of a gel-type chemical structure whereas coated membranes are modified by a polymer of film-type chemical structure. The nature of the support, polysulfone, does not affect the final form of the polymer. © 1994 John Wiley & Sons, Inc.     

An improved method for surface modification of porous water purification membranes

The surfaces of polysulfone and polyethersulfone ultrafiltration membranes were coated with polydopamine, yielding hydrophilic membranes that, under constant transmembrane pressure fouling conditions, have previously shown enhanced flux relative to unmodified membranes. When evaluated under constant permeate flux fouling, however, modified membranes exhibited higher transmembrane pressures than their unmodified analogs. This increased transmembrane pressure in the coated membranes was ascribed to the decrease in membrane permeance resulting from applying the polydopamine coating. The membrane permeance could be tuned by varying polydopamine deposition time and, even at the shortest deposition times studied here, a few minutes, a substantial increase in membrane hydrophilicity could be achieved. Therefore, polydopamine was deposited on a membrane of relatively high permeance until the pure water permeance of the modified membrane matched that of a membrane having lower native permeance, permitting a comparison of the fouling performance of a modified and unmodified membrane with the same pure water permeance. This approach was repeated, using a single, high permeance membrane as the base membrane for modification, to produce a family of modified membranes having the same initial pure water permeances as lower permeance, unmodified membranes. When unmodified and modified membranes of the same initial permeance were compared at constant flux fouling conditions, the modified membranes consistently exhibited lower transmembrane pressures and similar organic rejections to the unmodified membranes. Because many porous water purification membranes are operated at constant flux in industrial settings, an interesting methodology for membrane surface modification may be to surface-modify a membrane of high permeance until the desired permeance is achieved, rather than by surface modification of a membrane that natively has the desired water transport characteristics, since the surface modification procedures almost invariably lead to lower pure water permeance.