Preparation and characterization of asymmetric polyethersulfone nanofiltration membranes: The effects of polyvinylpyrrolidone molecular weights and concentrations

In this study, asymmetric flat‐sheet polyethersulfone (PES) nanofiltration (NF) membranes were prepared via immersion precipitation phase inversion with the addition of polyvinylpyrrolidone (PVP). The effects of PVP with the molecular weights (MW) from 17 to 1400 kDa and the concentration from 0 to 3.0 wt % on the morphologies and performances of PES membranes were systematically studied. The prepared membranes were characterized by SEM, AFM, ATR‐FTIR, contact angle, membrane porosity, the water flux, and the rejection measurement. The results indicated that the porosity and the hydrophilicity of PES NF membrane increased with increasing PVP concentration, and the hydrophilicity of PES NF membrane also improved with increasing PVP MW. The enhancements of the porosity and hydrophilicity resulted in the higher water flux of PES NF membrane. The rejection of Bordeaux S (MW 604.48 Da) for the prepared PES membrane was increased to above 90% with the low PVP concentration, but it turned to decrease remarkably when the PVP concentration reached to a critical value which related to PVP MW. It was concluded that the addition of a small amount of PVP could significantly increase the permeability of PES NF membrane and maintain its rejection of Bordeaux S above 90%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43769.     

Effect of Additive Concentration on Cellulose Acetate Blend Membranes-Preparation,Characterization and Application Studies

Abstract

Ultrafiltration techniques have particular advantages for simultaneous purification, concentration, and fractionation of macromolecules. A comparative study is presented on novel ultrafiltration polymeric blend membranes based on cellulose acetate (CA) prepared in the absence and presence of polymeric additives such as polyethylene Glycol 200 (PEG) and polyvinylpyrrolidone (PVP) by phase inversion technique using N,N′-dimethylformamide (DMF) as solvent. Polymer blend composition, additive concentration and casting, and gelation conditions were standardized for the preparation of asymmetric membranes by pore statistics and morphology. These blend membranes were characterized for compaction in ultrafiltration experiments at 414 kPa pressure in order to attain steady state flux and is reached within 4–5 h. The pure water flux was measured at 345 kPa pressure. Membrane hydraulic resistance derived by measuring water flux at various transmembrane pressures and found to be inversely proportional to pure water flux. Water content is estimated by simple drying and weighing procedures and found proportional to pure water flux for all the membranes. The molecular weight cut-offs (MWCOs) of different membranes were determined with proteins of different molecular weights and found to vary from 20 to 69 kDa depending on the PEG 200 and PVP content in the blend in the casting solution. Skin surface porosity of the membranes was analyzed by scanning the samples at various magnifications. The characterized CA, CA/PEG200 and CA/PVP membranes were used for cadmium ion rejection studies at 345 kPa.     

Preparation of Anti-Fouling Polyethersulfone Ultrafiltration Membrane by an External High Voltage Electric Enhancing Method

In this article, a novel method of applying high voltage (1–5 kV) to the conventional immersion precipitation phase inversion process was used to prepare polyethersulfone ultrafiltration membranes when PVP (30 K) was used as an additive. The effects of the external electric field on the structure, surface functional groups, membrane potential, and surface hydrophilicity of the membranes were researched. Bovine serum albumin (BSA) adsorption amounts on the membranes and the separation performances of the membranes were measured. It was found that the external electric field influenced the surface carbonyl groups, surface hydrophilicity, and potential of the membranes. With the increase of the external voltage, the surface hydrophilicity and the membrane potential decreased. It seemed that the external voltage had no influence on the cross-section structure of the membranes, but the surface porosity density slightly reduced when the external voltage increased. In basic BSA solution, the protein adsorption amount on the electric enhanced membranes was distinctly reduced when compared with an un-enhanced membrane, and the rejection was also improved. Consequently, the prepared electric enhanced PES membranes had distinctive anti-fouling properties.     

Performances of poly(vinylidene fluoride‐co‐hexafluoropropylene) ultrafiltration membranes modified with poly(vinyl pyrrolidone)

The structure and performance of modified poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVdF‐co‐HFP) ultra‐filtration membranes prepared from casting solutions with different concentrations of poly(vinyl pyrrolidone) (PVP) were investigated in this study. Membrane properties were studied in terms of membrane compaction, pure water flux (PWF), water content (WC), membrane hydraulic resistance ( R _m), protein rejection, molecular weight cut‐off (MWCO), average pore size, and porosity. PWF, WC, and thermal stability of the blend membranes increased whereas the crystalline nature and mechanical strength of the blend membranes decreased when PVP additive concentration was increased. The contact angle (CA) decreased as the PVP concentration increased in the casting solution, which indicates that the hydro‐philicity of the surface increased upon addition of PVP. The average pore size and porosity of the PVdF‐co‐HFP membrane increased to 42.82 Å and 25.12%, respectively, when 7.5 wt% PVP was blended in the casting solution. The MWCO increased from 20 to 45 kDa with an increase in PVP concentration from 0 to 7.5 wt%. The protein separation study revealed that the rejection increased as the protein molecular weight increased. The PVdF‐co‐HFP/PVP blended membrane prepared from a 7.5 wt% PVP solution had a maximum flux recovery ratio of 74.3%, which explains its better antifouling properties as compared to the neat PVdF‐co‐HFP membrane. POLYM. ENG. SCI., 55:2482–2492, 2015. © 2015 Society of Plastics Engineers     

Effect of polyvinylpyrrolidone molecular weights on morphology,oil/water separation,mechanical and thermal properties of polyetherimide/polyvinylpyrrolidone hollow fiber membranes

We prepared polyetherimide (PEI) hollow fiber membranes using polyvinylpyrrolidones (PVP) with different molecular weights (PVP 10,000, PVP 40,000, and PVP 1,300,000) as additives for oil/water separation. Asymmetric hollow fiber membranes were fabricated by wet phase inversion technique from 25 wt % or 30 wt % solids of 20 : 5 : 75 or 20 : 10 : 70 (weight ratio) PEI/PVP/N‐metyl‐2‐pyrrolidone (NMP) solutions and a 95 : 5 NMP/water solution was used as bore fluid to eliminate resistance on the internal surface. Effects of PVP molecular weights on morphology, oil‐surfactant‐water separation characteristics, mechanical, and thermal properties of PEI/PVP hollow fiber membranes were investigated. It was found that an increase in PVP molecular weight and percentage in PEI/PVP dope solution resulted in the membrane morphology change from the finger‐like structure to the spongy structure. Without sodium hypochlorite posttreatment, hollow fiber membranes with higher PVP molecular weights had a higher rejection but with a lower water flux. For oil‐surfactant‐water emulsion systems (1600 ppm surfactant of sodium dodecylbenzenesulfonate and 2500 ppm oil of n‐decane), experimental results illustrated that the rejection rates for surfactant, total organic carbon, and oil were 76.1 ≈ 79.8%, 91.0 ≈ 93.0%, and more than 99%, respectively. Based on the glass transition temperature values, PVP existed in hollow fiber membranes and resulted in the hydrophilicity of membranes. In addition, using NaOCl as a posttreatment agent for membranes showed a significant improvement in membrane permeability for PVP with a molecular weight of 1300 K, whereas the elongation at break of the treated hollow fiber membranes decreased significantly. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2220–2233, 1999     

Performance characterization of cellulose acetate and poly(vinylpyrrolidone) blend membranes

Hydrophilic ultrafiltration membranes have been prepared by blending cellulose acetate (CA) as a matrix polymer with increasing concentrations of poly(vinylpyrrolidone) (PVP) using N,N′‐dimethylformamide as the solvent. It is observed that the presence of PVP beyond 50 wt % in the casting solution did not form membranes. Prepared membranes have been subjected to ultrafiltration characterizations such as compaction, pure water flux, water content, and membrane hydraulic resistance. The results indicate significant changes in the characteristics upon the addition of PVP, which may lead to improved performance. The porosity, pore size, and molecular weight cut‐off of the membranes also increase as the concentration of PVP increases. It is estimated that the pore radius of the CA/PVP membranes increases from 30 to 63 Å, when the concentration of PVP increased from 0 to 50 wt %. This is in agreement with the results obtained from scanning electron microscopic studies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of additives concentration on performance of cellulose acetate and polyethersulfone blend membranes

Asymmetric micro porous membranes have been prepared successfully from blending of cellulose acetate (CA) and polyethersulfone (PES) by the phase inversion method with N, N-dimethylformamide (DMF) as solvent. Two additives were selected in this study, including polyethylene glycol 600 (PEG 600) and polyvinylpyrrolidone (PVP). The effects of concentration of additives on CA/PES blend membrane performance and cross-section morphology were investigated in detail. CA/PES membranes were compared with CA/PES/PEG and CA/PES/PVP membranes in the performance such as pure water flux, membrane resistance, porosity and cross-section morphology. The resulting blend membranes were also carried out the rejection and permeate flux of Egg Albumin (EA) proteins with molecular weight of 45 Da. The membranes thus obtained with an additive concentration of 5 wt% of both PEG and PVP exhibited superior properties than the 80/20% blend composition of CA and PES membranes. The permeate flux of protein was increased from 44 to 134 lm² h with increase in concentrations of both PVP and PEG in 80/20% blend composition of CA and PES membranes. Cross-sectional images from scanning electron microscopy showed larger macropores in the bottom layer of the membranes with increasing additives content. Observations from scanning electron microscopy provided qualitative evidence for the trends obtained for permeability and porosity results.     

Preparation of hydrophilic polysulfone membrane using polyacrylic acid with polyvinyl pyrrolidone

This study examined the consequences of the addition of polyvinyl pyrrolidone (PVP) of different molecular weights with constant molecular weight of polyacrylic acid (PAA) on the morphology and permeation properties of polysulfone (PSF) membranes. The asymmetric polymeric membranes were prepared by phase inversion process using PSF in N‐methyl‐2‐pyrrolidone (NMP) as a solvent. The surface structure and morphology of the prepared membranes were analyzed by field‐emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). The pore number, average pore size and area of pores for all the membranes were determined by permeability method. These ultrafiltration membranes were subjected to characterizations such as measurement of pure water flux (PWF), compaction factor (CF), bovine serum albumin (BSA) rejection for finding the permeability performance, whereas equilibrium water content, contact angle, porosity, hydraulic resistance, and ion exchange capacity (IEC) are measured for evaluating the hydrophilicity. Results demonstrate that the flux performance of the membranes and morphological parameters own a crucial inter‐relationship with the molecular weight of PVP. The membrane pore area and pore number were found to be increased by increasing molecular weight of PVP with constant molecular weight of PAA. A detailed comparative study was done with Chakrabarty et al. (J. Membr. Sci. 2008, 309, 209) and found better in almost all the aspects. All the resulting parameters were compared and concluded with the fact that addition of small amount of PAA in PSF/PVP/NMP casting solution can be better than addition of PVP alone. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41964.     

Effect of PVP Molecular Weights on the Properties of PVDF-TiO2 Composite Membrane for Oily Wastewater Treatment Process

Polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes consisted of TiO₂ and different molecular weight (M_w) of polyvinylpyrrolidone (PVP) (i.e., 10, 24, 40, and 360 kDa) were prepared to treat synthesized oily wastewater. The membrane performances were characterized in terms of pure water flux, permeate flux, and oil rejection while their morphological properties were studied using SEM, AFM, and tensile tester. Results show that the PVDF-TiO₂ composite membrane prepared from PVP40k was the best performing membrane owing to its promising water flux (72.2 L/m².h) coupled with good rejection of oil (94%) when tested with 250 ppm oily solution under submerged condition. It is also found that with increasing PVP M_w, the membrane tended to exhibit higher PVP and protein rejection, greater mechanical strength, smaller porosity, and a smoother surface layer. Regarding the effect of pH, the permeate flux of the PVDF-PVP40k membrane was reported to increase with increasing pH from 4 to 7, followed by decrease when the pH was further increased to 10. Increasing oil concentration in the feed solution was reported to negatively affect the water flux of PVDF-PVP40k membrane, owing to the formation of thicker oil layer on the membrane surface which increased water transport resistance. A simple backflushing process on the other hand could retrieve approximately 60% of the membrane original flux without affecting the oil separation efficiency. Based on the findings, the PVDF-TiO₂ membrane prepared from PVP40k can be potentially considered for oily wastewater treatment process due to its good combination of permeability and selectivity and reasonably high water recovery rate.     

Preparation of blend polyethersulfone/cellulose acetate/polyethylene glycol asymmetric membranes for oil–water separation

Blend PES/CA hydrophilic membranes were prepared via a phase-inversion process for oil–water separation. PEG-400 was introduced into the polymer solution in order to enhance phase-inversion and produce high permeability membranes. A gas permeation test was conducted to estimate mean pore size and surface porosity of the membranes. The membranes were characterized in terms of morphology, overall porosity, water contact angle, water flux and hydraulic resistance. A cross-flow separation system was used to evaluate oil–water separation performance of the membranes. From FESEM examination, the prepared PES/CA membrane presented thinner outer skin layer, higher surface porosity with larger pore sizes. The outer surface water contact angle of the prepared membrane significantly decreased when CA was added into the polymer solution. The higher water flux of the PES/CA membrane was related to the higher hydrophilicity and larger pore sizes of the membrane. From oil–water separation test, the PES/CA membrane showed stable oil rejection of 88 % and water flux of 27 l/m² s after 150 min of the operation. In conclusion, by controlling fabrication parameters a developed membrane structure with high hydrophilicity, high surface porosity and low resistance can be achieved to improve oil rejection and water productivity.     

Effect study of hexagonal mesoporous silica/polyaniline nanocomposite on the structural properties of polysulfone membranes and its heavy metal removal efficiency

New mixed matrix membranes of polysulfone were synthesized by different content of hexagonal mesoporous silica coated by polyaniline and used for nickel and lead ion removal. The membranes were characterized by FESEM, XRD, BET, TGA, and FTIR, and zeta potential measurements. The results showed that PANi/HMS particles enhanced the membrane porosity and permeability. These effects were explained according to an increase of the membrane hydrophilicity due to the formation of new functional groups during membrane casting. The results showed that metal ion rejection was performed by a filtration–adsorption mechanism, resulting in fixation of metal ions on the active sites of membranes.     

聚苯乙烯磺酸钠掺杂正渗透膜的制备及其性能

通过两步无皂乳液聚合法,改变第二步对苯乙烯磺酸钠的加入量,制备表面携带磺酸根基团量不同的纳米粒子（PSS）,并将其应用于正渗透（FO）膜的制备。采用红外光谱仪（FTIR）和光电子能谱仪（XPS）表征粒子组成,通过扫描电子显微镜（SEM）表征膜的表面和断面形貌,测定膜孔隙率和亲水性,考察表面磺酸根量不同的聚合物粒子对膜结构性能的影响。结果表明,PSS的引入能提高膜的孔隙率,改善膜的亲水性,且随着粒子表面携带的磺酸根基团量增多,膜的孔隙率与亲水性也随之提高。这是因为PSS粒子可以支撑内部孔道,且表面携带的亲水基团-SO3Na可以提高膜的亲水性,影响活性层的形成。所制备的FO膜性能也得到相应改善,水通量达到了61.1L/(m²·h),为纯聚砜膜的2.8倍,盐截留率达到93.2%,J_s/J_v值仅为0.31g/L,性能得到极大提升。     

Effects of solubility parameter differences among PEG,PVP and CA on the preparation of ultrafiltration membranes: Impacts of solvents and additives on morphology,permeability and fouling performances

The effects of two different hydrophilic additives and two solvents on the membrane morphological structure,permeability property and anti-fouling performances of cellulose acetate (CA) ultrafiltration membranes were investigated.During the phase-inversion process,cellulose acetate was selected as a membrane forming polymer;polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as additives;acetone (Ac):N,N-Dimethylacetamide (DMAc) andN,N-Dimethylformamide (DMF) were used as solvents;and deionized (DI) water was used in the coagulation bath.All the prepared membranes were characterized in terms of hydraulic permeability (Pm),membrane resistance,average pore radius,and hydrophilicity.The top surface and crosssectional view of the prepared membranes were also observed by using field emission scanning electron microscopy.Membrane fouling and rejection experimentations were done using a stirred batch-cell filtration set-up.The experimental studies of fouling/rinsing cycles,rejection,and permeate fluxes were used to investigate the effect of PEG and PVP additives and effect of the two solvents on the fabricated membranes using bovine serum albumin (BSA) as a model protein.     

Removal of phenol and phosphoric acid from wastewater by microfiltration carbon membranes

Microfiltration carbon membranes were developed to cope with the wastewater containing phenol and phosphoric acid. The structure of carbon membranes was characterized by scanning electron microscope, x-ray diffraction, bubble pressure method and specific surface area analysis. The separation efficiency of carbon membranes was investigated by varying the operation factors, including feed concentration, running time, and pressure. Results have shown that the carbon membranes are abundant in porous structure with the porosity of 42%, along with a narrow pore size distribution centering at 0.18?µm. Within the scope of the study, the highest removal rates reach to 81.9% for phenol and 55.3% for phosphoric acid from wastewater, respectively.     

用于处理染料废水的PVDF/TPU共混中空纤维膜的制备

采用相转化法制备PVDF／TPU共混中空纤维膜,以PVP为添加剂可以改善成膜性能。通过水通量超滤实验、牛血清白蛋白截留实验、扫描电子显微镜表征膜的表面与截面结构分析得出铸膜液中纤维膜的质量分数为16％,m（PVDF）：m（11Pu）为80：20,添加5％PVP时制备的膜的综合性能最佳。对不同的溶液包括BSA、PVPK30、PEG10000、染料活性艳蓝KN-R进行截留实验分析膜过滤性能。在pH范围为1—14时,膜的水通量及截留率均无明显变化,说明PVDF／TPU共混中空纤维膜具有良好的抗酸、碱性。用清水冲洗10min后,膜污染的恢复率即可达到86．5％,膜的抗污染性能良好。     

In situ crosslinking of hyperbranched polyglycerol in casting solutions and its effect on the structure and properties of porous PVDF membranes

Porous membranes were prepared via phase inversion process from casting solutions composed of poly(vinylidene fluoride), hyperbranched polyglycerol (HPG), and N,N‐dimethylacetamide. To seek a stable presence of HPG in the resulting membranes, it was crosslinked in the casting solutions using 4,4′‐oxydiphthalic anhydride as the crosslinking agent. The membranes were characterized in terms of morphology, surface and bulk chemical compositions, water contact angle, porosity, water flux, and bovine serum albumin (BSA) adsorption experiments. The effects of HPG content and crosslinking degree on the membrane structure and properties were investigated. The increasing of crosslinking degree resulted in a significant improvement in HPG stability in the membrane matrix, and a remarkable enrichment of the crosslinked HPG at the separation surface was observed when the membrane was shaken in water at a relatively high temperature (60°C). This enrichment led to a decrease in the value of water contact angle and an improvement in fouling‐resistance. To optimize the membrane performance, a small amount of poly(vinylpyrrolidone) (PVP) was used as an additive, and it was found that the addition of PVP led to a considerable increase in water flux. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

用于反渗透复合膜的海绵状结构支撑膜制备研究

通过调节铸膜液中聚砜浓度和非溶剂含量,浸没沉淀法制备海绵状结构的支撑膜,并在支撑膜上界面聚合制备聚酰胺反渗透复合膜。分别对支撑膜及反渗透复合膜的结构和性能进行表征,考察聚砜浓度对支撑膜结构和性能的影响,以及不同结构支撑膜对反渗透复合膜结构和性能的影响。结果显示,随着聚砜浓度的增加,支撑膜表面孔径和孔隙率下降,断面结构变致密,耐压性增强。在不同支撑膜上制备的反渗透复合膜具有不同的通量和脱盐率。综合考虑支撑膜及反渗透复合膜的性能,以聚砜浓度为15%制备的海绵状结构支撑膜更适于作为制备反渗透复合膜的支撑层。     

Preparation of poly(vinyl chloride) (PVC) ultrafiltration membranes from PVC/additive/solvent and application of UF membranes as substrate for fabrication of reverse osmosis membranes

Ultrafiltration (UF) membranes were prepared from poly(vinyl chloride) (PVC) as main polymer, poly(vinyl pyrrolidone) (PVP) as additive, and 1‐methyl‐2‐pyrrolidone (NMP) as solvent using Design Expert software for designing the experiments. The membranes were characterized by SEM, contact angle measurement, and atomic force microscopy. The performance of UF membranes was evaluated by pure water flux (PWF) and blue indigo dye particle rejection. In addition, the molecular weight cutoff of UF membranes was determined by poly(ethylene glycol) (PEG) rejection. The UF membranes were used as substrates for fabrication of polyamide thin film composite (TFC) reverse osmosis (RO) membranes. The results showed that the model had high reliability for prediction of PWF of UF membranes. Also, increment in PVC concentration caused reduction of PWF. Moreover, at constant PVC concentration and if the concentrations of PVC was lower than 10 wt %, the PWF reduced by increasing the concentration of PVP. However, at PVC concentration higher than 11 wt %, increment in PVP concentration showed increment and reduction of PWF. The PEG rejection results showed that the prepared membranes had UF membranes properties. Finally, the NaCl rejection tests of RO membranes by PVC as substrates indicated that the performance of RO membranes were lower than commercial membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46267.     

Fabrication of novel polyethersulfone based nanofiltration membrane by embedding polyaniline-co-graphene oxide nanoplates

Mixed matrix polyethersulfone (PES) based nanofiltration membrane was prepared through phase inversion method by using of polyvinylpyrrolidone (PVP) as pore former and N, N dimethylacetamide (DMAc) as solvent. Polyaniline-co-graphene oxide nanoplates (PANI/GO) were utilized as additive in membrane fabrication. The PANI/GO nanoplates were prepared by polymerization of aniline in the presence of graphene oxide nanoplates. FTIR analysis, scanning electron microscopy (SEM), scanning optical microscopy (SOM), 3D images surface analysis, water contact angle, water content tests, tensile strength tests, porosity tests, salt rejection and flux tests were used in membrane characterization. FT-IR results verified formation of PANI on graphene oxide nanoplates. SOM images showed uniform particles distribution for the mixed matrix membranes. SEM images also showed formation of wide pores for the modified membranes. Water flux showed constant trend nearly by use of PANI/GO in the casting solution. Opposite trend was found for the membrane surface hydrophilicity. Salt rejection was enhanced sharply by utilizing of PANI/GO. The membrane’s tensile strength was improved by increase of PANI/GO concentration. The water content was increased initially by use of PANI/GO nanoplates up to 0.05%wt into the casting solution and then decreased. Membrane porosity was also enhanced by using of PANI/GO nanoplates. Modified membrane containing 0.5%wt PANI/GO nanoplates showed more appropriate antifouling characteristic compared to others.     

Fabrication and performance of a polyethersulfone nanofiltration membrane impregnated with a mesoporous silica–poly(1‐VInylpyrrolidone) nanocomposite

Fouling is a serious problem in the membrane formation process. Adding hydrophilic polymers or inorganic particles into the membrane is an effective way for improving the antifouling performance. However, most of the water‐soluble polymeric additives leach out during the phase inversion process, and the inorganic particles are prone to agglomerate in the membrane, which decreases the antifouling property of the membrane. In this study, poly(1‐vinylpyrrolidone) (PVP) was grafted onto mesoporous silica (MS) nanoparticle surface, and polyethersulfone (PES)/MS–PVP nanocomposite membranes were fabricated by the phase inversion method. MS–PVP dispersed well on the membrane surface, and the hydrophilicity of the PES/MS–PVP membranes increased with increasing content of MS–PVP. PES/MS–PVP membranes exhibited higher water flux than that of the bare PES membrane without any loss in NaCl rejection, and water flux of 25 L/m²h could be achieved by the membrane containing 3% of MS–PVP, which is almost 1.5 times as high as that of bare PES membrane at 0.6 MPa. The protein adsorption onto the membrane surface declined significantly from 49 to 25 mg/cm² when the MS–PVP loading increased from 0% to 3%. POLYM. COMPOS., 38:908–917, 2017. © 2015 Society of Plastics Engineers