Casting Solution Temperature Research Articles

Preparation of a cyclodextrin metal-organic framework (CD-MOF) membrane for chiral separation

Due to their unique properties, the efficient separation of racemic mixtures remains a great challenge. Recently, membrane separation has been demonstrated as a promising chiral separation technique with the advantages of continuous operation, high throughput, and cost effectiveness. In this work, a cyclodextrin-metal-organic framework (CD-MOF) was prepared and then composited with polyvinylidene fluoride (PVDF) polymer by the phase inversion via immersion precipitation method to form a CD-MOF/PVDF composite membrane for chiral amino acid separation for the first time. The composite membranes prepared under different conditions were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) thermogravimetric analysis (TGA)and differential scanning calorimetry (DSC). The effects of preparation conditions including CD-MOF load, polymer concentration, and casting solution temperature on the hydrophilicity, water flux, bovine serum albumin (BSA) rejection and chiral separation performance of the membrane were investigated. It is found that the composite membrane (V-5%−12) prepared with the CD-MOF load of 5%, polymer concentration of 12%, and casting solution of 70 ℃ shows the best performance with the water flux of 466.4 L/m2∙h, BSA rejection rate of 24.3% and stable 100% separation efficiency for phenylalanine (Phe) enantiomers for 4 h. The interaction energies between the CD-MOF and D-Phe and L-Phe were calculated using the Gaussian 09 program package and the chiral separation mechanism of the composite membrane was proposed at the molecular level. Our work demonstrates great development potentials of the CD-MOF/PVDF composite membrane in the chiral separation of drugs.

Organic solvent-free polyelectrolyte complex membrane preparation: Effect of monomer mixing ratio and casting solution temperature

The organic solvent-free aqueous phase separation (APS) process is a new and sustainable alternative to the conventional nonsolvent-induced phase separation (NIPS) process. However, low water permeability is a primary concern of such APS membranes. Herein, we introduced casting solution temperature and mixing ratio as two key parameters to improve the performance of poly (sodium 4-styrene sulfonate) (PSS) and branched Polyethylenimine (PEI) complex membrane prepared by pH shift-induced APS process. It was found that PSS-PEI monomer mixing ratios of 1:1.65 and 1:1.70 resulted in nanofiltration membranes with pure water permeability (PWP) of ∼4.5 and ∼8 LMHbar−1. The salt retention tests of these membranes showed higher divalent salt retention than monovalent salt following the order of MgCl2 > MgSO4 > Na2SO4 >NaCl. In comparison, PSS-PEI monomer mixing ratios of 1:1.75 and 1:1.80 led to the formation of ultrafiltration membranes with BSA retention of ∼98% and ∼36%, and PWP of ∼40 and ∼199 LMHbar−1, respectively. The variation of casting solution temperature also showed a significant influence on membrane morphology and performance. The increase in temperature from 25 to 60 °C resulted in ultrafiltration membranes with high BSA retention (>90%) and PWP in the range of ∼53–140 LMHbar−1. This sharp increase in PWP was attributed to the combined effect of the thinner skin layer and larger pore size of the membranes. Overall, this work demonstrated that casting solution temperature and monomer mixing ratio could be used as new tuning parameters for high-performance PSS-PEI membrane fabrication with excellent control over membrane structure and performance.

Preparation of PVDF membrane via synergistically vapor and non-solvent-induced phase separation

Poly(vinylidene fluoride) (PVDF) ultrafiltration (UF) membrane was prepared by vapor and non-solvent-induced phase separation (VNIPS) process, and the relationships between preparation conditions, phase separation behaviors and membrane structures were discussed. The phase diagram was generated by cloud point titration, the effects of environmental relative humidity, air exposure time and casting solution temperature on the structure and performance of the resulted membrane were investigated. The addition of polyvinylpyrrolidone (PVP) additives to the casting solution made the system thermodynamically unstable and led the turbidity curve shift toward the solvent/non-solvent axis. The experimental results showed that both average pore size and porosity increased with higher relative humidity. When the relative humidity increased from 35 to 85%, the mean pore size increased from 35 to 70 nm. The effect of exposure time on membrane structure was related to the air environment. It was found that under low temperature and low humidity conditions, exposure time had little effect on membrane structure. When the relative humidity was 75%, the mean pore size and distribution increased with the exposure time extension from 1.0 to 30 s. The mean pore size of the membrane could be reduced by reducing the relative humidity. When the temperature of the casting solution increased, the membrane pore size reached maximum at 80 °C, and the spherulite on the surface of the membrane decreased. The spherulite morphology almost disappeared when the temperature of the casting solution reached 120 °C. In addition, with the increase in the casting solution temperature, large pores appeared in the sub-layer of the membrane, which gradually widened the pore distribution, leading to the decrease in the tensile strength. The preparation condition was optimized as low temperature of casting solution, low humidity and low temperature of the environment. The fabrication process showed the potential for scaling-up production of the PVDF UF membrane by the VNIPS technique.

Nanoporous polyethersulfone membranes prepared by mixed solvent phase separation method for protein separation

Nanoporous polyethersulfone (PES) membranes with high surface porosity and uniform pore size distribution were prepared by combining the phase separation in NMP/nonane mixed solvent system with the traditional nonsolvent induced phase inversion process. The effects of PES concentration, nonane concentration, evaporation time, casting solution temperature, and varied mixed solvent systems on the porous PES membrane surface morphology were thoroughly investigated and optimized. The optimized nanoporous PES membrane showed a high surface porosity with a uniform pore size of 20 nm, rendering an exceptional molecular weight cut-off of as low as 100 k Dalton. In addition, the membrane exhibited a significant molecular size exclusion with water permeance of 121 LMH bar−1, bovine serum albumin (BSA) protein rejection of 60.1%, and γ-globulin protein rejection of 99.5% at 0.5 bar, respectively, demonstrating the potential of the as-prepared nanoporous PES membrane for application in protein separation.

Metal-organic framework/zeolite nanocrystal/polyvinylidene fluoride composite ultrafiltration membranes with flux/antifouling advantages

In this study, hydrophilic zirconium 1,4-dicarboxybenzene (UiO-66) and chromium (III) terephthalate (MIL-101) metal-organic frameworks (MOFs) and faujasite (FAU) zeolite nanocrystals were synthesized successfully and incorporated into polyvinylidene fluoride (PVDF) matrix as nanofillers to fabricate mixed matrix membranes (MMMs) via non-solvent induced phase separation (NIPS) process. The effects of casting solution temperature and casting speed as two important factors in membrane fabrication via phase inversion method on performance and structure of the neat PVDF membrane were investigated. Then, various contents of the synthesized nanofillers were loaded into the PVDF matrix and the effects of the synthesized nanofillers on hydrophilicity, pure water flux (PWF), morphology and antifouling properties of the fabricated MMMs were explored. Antifouling studies were also performed using Bovine serum albumin (BSA). The obtained results demonstrated that incorporation of the synthesized nanofillers into the PVDF membrane has positive effect on performance and structure of the fabricated MMMs and the MMM containing 0.1 wt% MIL-101 showed the best performance with water flux of 360 LMH, BSA rejection of 100%, irreversible fouling of 22.2% and flux recovery ratio of 77.7%. This work highlighted the potential application of the MOFs as effective nanofillers for MMM fabrication.

Preparation, characterisation, and desalination performance study of cellulose acetate membranes with MIL-53(Fe) additive

This study describes the preparation and characterisation of MIL-53(Fe) and its effect on the performance of forward osmosis (FO) membranes. The cellulose acetate (CA)/MIL-53(Fe) hybrid membranes were fabricated using the method of phase inversion by dispersing MIL-53(Fe) in a CA casting solution. To improve the selectivity and permeability performance of FO membranes, the effects of MIL-53(Fe) content, casting solution temperature, coagulation bath temperature, and annealing temperature were studied. Results from scanning electron microscopy, membrane porosity, atomic force microscopy, and water contact angle tests of all the membranes show that the structural properties of the CA/MIL-53(Fe) hybrid membranes were optimised. The results of the FO performance tests, including the values of water flux and reverse salt flux, indicate improvement in the selectivity and permeability properties of the CA/MIL-53(Fe) hybrid membranes. Under the conditions of deionised water as the feed solution and 1 M NaCl solution as the draw solution, the water flux and reverse salt flux of the CA/MIL-53(Fe) hybrid membranes reached 34.9 L/(m2·h) and 2.02 g/(m2·h), respectively, in comparison with CA membranes. This study demonstrates that MIL-53(Fe) can improve the desalination performance and structural properties of FO membranes.

Investigation of parameters affecting the flux of microfiltration poly(vinylidenefluoride) membranes for particulate removal

AbstractThe effects of membrane preparation conditions on characteristics of poly(vinylidenefluoride) (PVDF) microfiltration membranes dissolved in dimethylacetamide (DMAc) were studied. Influence of the casting thickness, coagulation bath temperature, evaporation time, and casting solution temperature on membrane performance and morphology was investigated. The flat‐sheet membranes prepared by immersion precipitation technique were characterized using scanning electron microscopy (SEM). Membrane performance was evaluated by estimation of flux and rejection using blue indigo dye suspension as the feed. The results showed that by increasing the casting thickness, flux was initially improved due to the formation of more macrovoids. However, a further thickness increment leads to lower flux due to establishment of higher resistance against the water flow. Effect of the coagulation bath temperature and evaporation time on membrane morphology was particularly correlated to the temperature difference between the coagulation bath and the casting solution. For similar temperature of casting solution and coagulation bath, higher flux was observed for shorter evaporation time. However, higher flux was obtained for longer evaporation time when the temperature of casting solution and coagulation bath was dissimilar. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 31: 29–40, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20232

Preparation of Polyethersulfone Ultrafiltration Tubur Membranes with Superior Properties

Phase inversion via immersion precipitation was employed for PES tubular membrane preparation and using N,N-dimethylacetamide(DMAc) as solvent, PEG-400 as main constant additive. Through the experimental study we obtain a preparation process of PES tubular membrane with superior properties. Ethanol caused an increment in the flux at low coagulation bath temperature relative to the non-ethanol. And the low temperature of coagulation bath also improve membrane’s rejection and its influence was most important. Other conditions included that the casting solution temperature must not be too high (15? was best) and the membrane don’t be exposed to atmosphere in long time. The prepared membrane under this condition shows excellent performance on flux and retention. Test results show that the flux can be up to 160 L·m-2h-1 and the rejection can reach more than 97% (for ovalbvmin) under this condition. The flux was increased clearly compare to non-ethanol and high temperature.

Preparation, characterization and performance of phenolphthalein polyethersulfone ultrafiltration hollow fiber membranes

Phenolphthalein polyethersulfone (PES-C) is potentially an excellent candidate as a membrane. This assumption is based upon its mechanical and thermal properties. Here we report the manufacture of hollow-fiber membranes using the PES-C using a dry-wet spinning technique. The influence of different hollow-fiber contact forming conditions including solvent, composition of PES-C temperature, internal quench medium extrusion pressure and winding-up velocity on the structure and properties of prepared membranes were investigated. The content of PES-C in the spinning solution affects the properties of the membranes prepared, including porosity, average pore diameter and water flux. These decrease with increasing content of PES-C. Water flux of membrane increases with casting solution temperature. When the temperature reaches 40°C, water flux is maximum while retention reaches a minimum. Furthermore, water flux increases with increasing internal quench medium extrusion pressure, while inner and outer diameters increases and wall thickness decreases with increasing internal quench medium extrusion pressure. The inner and outer diameters of hollow membrane decreases with increasing winding-up velocity, the outer diameter decreases more than the inner diameter, which leads to a decrease of membrane wall thickness.

Poly(vinylidene fluoride) membranes by phase inversion: the role the casting and coagulation conditions play in their morphology, crystalline structure and properties

Flat membranes with controlled morphology, pore dimensions, mechanical properties and crystal structure were prepared by wet and dry wet phase inversion from polyvinylidene fluoride (PVDF). The effects of several parameters such as precipitation temperature, composition of the polymer solution (concentration, type of solvent), exposure time before immersion in the coagulation bath, type of coagulant on the sequence and the extent of the two phase separation processes, i.e. liquid–liquid and liquid–solid demixing (crystallization), were studied. Using solvent/nonsolvent pairs with different mutual affinity (DMA/water, DMA/C1–C8 alcohols), different morphologies were obtained. High casting solution temperature plays important role to increase the rate of the liquid–liquid demixing on the crystallization, i.e. the type of crystallites formed (α-type) also by using a soft coagulation bath. Exposure time before immersion favours the first type of phase separation and therefore once again crystallites of α type were observed. At room temperature, using C1–C8 alcohols as nonsolvents, the presence of crystallites of α type can be related to molar volume of the coagulant.

Study on preparation of heterogeneous polysulfone affinity filter membrane and its sorption properties for Hg2+

AbstractHigh quality heterogeneous polysulfone affinity flat filter membranes having chelating groups were prepared by phase separation by the use of blends of chelating resin and polysulfone as membrane materials, N,N‐dimethylacetamide as the solvent, and water as the extraction solvent. The effects of blending ratio, chelating resin grain size, and temperature of casting solution on the structure of affinity membranes were investigated. The sorption process of an affinity filter membrane for Hg2+, adsorbed under various chelating conditions such as chelating resin grain size, pH value, and the concentration of the metallic ion solution, was also studied. The results revealed that the greatest chelating capacity of an affinity filter membrane for Hg2+ was 1050 μg/cm2 per membrane under appropriate conditions, and the sorption isotherms of Hg2+could be expressed by the Freundlich sorption model. Dynamic chelating experiments indicated that the Hg2+ could be extracted with the affinity filter membrane and reextracted under acidic conditions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 908–915, 2003

Acrylonitrile-maleic anhydride copolymer membrane (I): effects of casting conditions

The effects of casting conditions, including casting solution (composition and temperature) and coagulation conditions (pre-evaporation time, temperature and concentration of coagulation bath) on the structure and performance of acrylonitrile–maleic anhydride copolymer membrane have been investigated. The results showed that the water flux decreased gradually while the rejection of bovine serum albumin (BSA) decreased as the concentration of copolymer increased. When the total solid concentration was kept unchanged, the water flux increased with additive polyvinylpyrrolidone (PVP), the rejection did not decrease until the ratio of PVP/copolymer was 60%. When the content of copolymer in the casting solution was kept constant, the water flux decreased rapidly while the rejection increased a little (compared with the case of no additive) as the ratio of PVP/copolymer increased. As to the temperature of casting solution, the water flux had a maximum at 45 °C and the rejection had a maximum and a minimum at 45 and 55 °C, respectively. The water flux had a maximum value when the pre-evaporation time was 40 sec. The rejection of BSA was almost unchanged when the pre-evaporation time was less than 40 sec. and then decreased and reached a minimum value at 60 sec. As the temperature of coagulation bath increased, the water flux reached a maximum at 35 °C while the rejection increased uniformly. With increasing the concentration of DMSO in the coagulation bath, the water flux decreased gradually and got to a minimum at 50 wt% as the concentration of dimethylsulfoxide in the coagulation bath increased, but no apparent effect on the rejection was observed. Copyright © 2000 John Wiley & Sons, Ltd.

Molecular weight, casting conditions and the mechanical strength of acrylonitrile-maleic anhydride copolymer membrane

The effects of molecular weight and casting conditions on the separation performance of acrylonitrile–maleic anhydride copolymer membrane have been discussed , and their effects on the mechanical property of the membrane investigated. The casting conditions included concentration of casting solution, pre-evaporation time, and temperatures of casting solution and coagulation bath. The breaking strength increased with an increase in molecular weight and concentration of casting solution. There was a minimum value of breaking strength when the pre-evaporation time was 40 sec and a maximum value when the temperature of casting solution was 40 °C or the temperature of the coagulation bath was 35 °C. Though the breaking strength of an acrylonitrile–maleic anhydride copolymer membrane can be improved by selecting casting conditions, it is more efficient to increase the molecular weight of the copolymer. The breaking strength of a copolymer membrane with an Mw of 3.4 × 105 was 309 N/cm2. Copyright © 1999 John Wiley & Sons, Ltd.

PVC as a sensor membrane material: influence of solvent casting variables.

Unplasticized polyvinyl chloride (PVC) has proved an especially difficult membrane material to form reproducibly. In its fabrication for sensor use, variable temperature solvent casting has been assessed and related to function as external membranes of a classical dual membrane amperometric oxidase electrode. The thermal history of the casting solution was shown to have an effect on both thickness and the permeability. With increasing temperature of the cast solution (4-37 degrees C) membrane thicknesses increased (5-30 microm). Amperometric responses to catechol and hydrogen peroxide decreased with increasing casting solution temperature whereas responses to ascorbate remained unchanged. These properties are tentatively attributed to the formation of discrete layers through differential changes in the rate of solvent evaporation. Scanning electron microscopy revealed distinct microstructure zones supporting this proposition and attesting to the need to factor in environmental temperature during casting.

Studies on syntheses and permeabilities of special polymer membranes. X. Effects of conditions of membrane preparation on permeation characteristics of cellulose acetate membranes in separation of aqueous polymer solutions

AbstractThe effects of casting solvents, dissolution temperature of casting solution, and pH and temperature of gelation solution, etc. on the permeation characteristics of cellulose acetate membranes in the separation of polymers from their aqueous solutions were investigated, using aqueous solutions of poly(ethylene glycol) and poly(vinyl alcohol) as feed. The permeation characteristics were influenced significantly by the conditions of membrane preparation and of the permeation. It was found that a concentration polarization at the membrane surface occurred with poly(vinyl alcohol) molecules, but it was very small with poly(ethylene glycol). The above results were discussed in detail from points of view of structure of the resulting membranes and the interactions between the solvent, the solute in the feed and the cellulose acetate molecules.

An approach to the development of cellulose acetate ultrafiltration membranes

The film-casting solution consisted of a mixture of cellulose acetate, acetone, and aqueous magnesium perchlorate [Mg(ClO4)2:H2O = 1:8.5], designated as polymer P, solvent S, and nonsolvent N, respectively. Using the composition P:S:N = 17: 69.2: 13.8 as reference, films were obtained from 19 different casting solutions in which the weight ratios S/P, N/S, and N/P were varied in different directions. The casting solution temperature was 0°C, and solvent evaporation period during film formation was minimum in most cases. The effects of variations of casting solution temperature and solvent evaporation period were also briefly studied. Reverse osmosis experiments with resulting membranes were carried out at 100 psig using 200 ppm NaCl–H2O as the feed solution. Decrease in S/P, increase in N/S, and increase in N/P in the casting solution, decrease in temperature of the casting solution, and increase in solvent evaporation period tend to increase the size of pores on the surface of resulting membranes in the ascast condition. Increase in S/P in the casting solution, and increase in the temperature of the casting solution tend to increase the effective number of pores on the membrane surface. These results offer definitive physicochemical criteria in terms on solution structure–evaporation rate concept for developing useful cellulose acetate ultrafiltration membranes.

Improvement of porous cellulose acetate reverse osmosis membranes by change of casting conditions

AbstractThe effects of temperature of casting solution in the range −10° to 15°C, that of casting atmosphere in the range 10° to 30°C, relative humidity of casting atmosphere in the range 35% to 75%, and solvent evaporation period in the range 0.5 to 3 min were studied on shrinkage temperatures, solute separations, and product rates of Loeb‐Sourirajan‐type cellulose acetate membranes in reverse osmosis experiments. The composition of casting solution used was as follows: cellulose acetate, 17; acetone, 69.2; magnesium perchlorate, 1.45; and water, 12.35 wt‐%. Best performance was obtained with membranes cast under the following conditions: temperature of casting solution, 10°C; temperature of casting atmosphere, 30°C; relative humidity of casting atmosphere, 65%; and solvent evaporation period, 1 min. For a 90% level of solute separation, the productivities of the above type of membranes were 22.9, 61.4, and 64.5 gallons/day‐ft2 at 250, 600, and 1500 psig using 3500 ppm NaCl–H2O, 5000 ppm NaCl–H2O, and 28395 ppm NaCl–H2O feed solutions, respectively. In all cases, the feed flow rates corresponded to a mass transfer coefficient of 45 × 10−4 cm/sec on the high‐pressure side of the membrane. The general specifications of the above type of membranes are given for the operating pressures of 250, 600, and 1500 psig. The effects of the above casting condition variables on the surface pore structure during film formation are discussed.

Studies on the development of improved reverse osmosis membranes from cellulose acetate–acetone–formamide casting solutions

AbstractImproved membranes from cellulose acetate–acetone–formamide casting solutions have been prepared for low‐pressure reverse osmosis applications. The film‐casting details for one such type of membranes (Batch 400) are as follows. Casting solution composition: cellulose acetate (E‐398‐3), 17 wt‐%, acetone, 56 wt‐%, formamide, 27 wt‐%; temperature of casting solution, 24°C; temperature of casting atmosphere, 24°C; casting atmosphere, ambient air in contact with 30 wt‐% acetone in aqueous solution; solvent evaporation period, 30 sec; gelation medium, ice‐cold water. Using aqueous feed solutions containing 3500 ppm of NaCl, the product rates obtained with the above membranes at 95, 90, and 60% levels of solute separation were 15.9, 22.1, and 58.7 gallons/(day ft2), respectively, at 250 psig under feed flow conditions corresponding to a mass transfer coefficient of 45 × 10−4 cm/sec on the high‐pressure side of the membrane. The effects of casting solution composition, presence of acetone in the casting atmosphere, evaporation period, evaporation rate constant, and the remoteness of casting solution composition from the corresponding phase boundary composition on membrane performance and shrinkage temperature profile were found to be similar to those reported earlier for membranes obtained from cellulose acetate–acetone–aqueous magnesium perchlorate casting solutions. The results illustrate the practical utility of the approach based on the solution structure–evaporation rate concept for creating more productive reverse osmosis membranes.

Effect of casting conditions on the performance of porous cellulose acetate membranes in reverse osmosis

AbstractSeveral sets of porous cellulose acetate membranes were made using the same casting solution composition and gelation conditions but varying the casting solution temperature and solvent evaporation conditions. The films were tested in reverse osmosis experiments at 250 psig using aqueous feed solutions containing 3500 ppm NaCl. The results show that the product rate obtained at a given level of solute separation is independent of evaporation time in the range tested and, for a given casting solution composition, the temperature of the casting solution and conditions of solvent evaporation during film formation together constitute an important interconnected variable governing the porous structure of the resulting membranes. These results offer a new approach to the problem of developing more productive reverse osmosis membranes and have led to a new class of porous cellulose acetate membranes capable of giving product rates 100% to 150% higher than those of the best membranes reported, at any given level of solute separation under the experimental conditions used. These results are of practical importance in low‐pressure reverse osmosis applications.