Demixing Rate Research Articles

Morphology formation during the nonisothermal thermally‐induced phase separation (TIPS) process

AbstractIn high‐viscosity polymer solutions and blends, temperature variations during the quench process of the thermally‐induced phase separation (TIPS) influence the dynamics and thermodynamics of phase separation. Hence, this study aims to investigate the impact of temperature variations on the morphology formation during the TIPS process. First, the influence of temporal temperature variations on phase separation is investigated by coupling a transient heat conduction model and the Cahn–Hilliard equation, and the results are compared with the isothermal phase separation process. Next, the morphology formation during phase separation is inspected by applying quench from two opposite sides of the sample to the same and different temperatures through coupling the Fourier heat transfer equation and the Cahn–Hilliard equation. The influence of the enthalpy of demixing on the morphology formation and the competition between the heat and mass transfer is also evaluated. It is confirmed that temporal variations of temperature alone have a significant impact on the morphology formation during the TIPS process. In addition, quenching the system to the same and different temperatures both leads to anisotropic morphology formation, which is affected by the quench rate, quench temperature, solution viscosity, and enthalpy of demixing. Upon applying different quench temperatures from opposite sides, two different types of morphologies and droplet sizes were formed as a result of the difference in the cooling rates between the two sides. Employing the enthalpy of demixing during phase separation induced a shallow quench effect on the deep quench side due to the fact that the heat moved toward the lowest temperature in the system, which led to the formation of a distinctive structure.

Development of a method for estimating particles mixing curves in short DEM simulation time

A new method for estimating particles mixing curves by simulating the particles behavior for a short period of time using discrete element method (DEM) was developed. The mixing curve is the time variation of the mixing degree, and can be divided into the following two stages: one is the mixing degree increasing stage, and the other is the mixing degree stagnation stage. The mixing curves could be estimated from time variations of mixing and de-mixing rates by assuming that the stagnation occurs when the mixing and de-mixing are balanced. Assuming the mixing and de-mixing rates are represented by the first-order exponential functions, each rate was estimated by the simulations of particles behavior for a short period of time. The estimated mixing curves agree with experimental ones and the proposed estimation method reduced the calculation time to approximately one-fifth of the conventional one that does not use a method to reduce the mixing time. Therefore, the proposed estimation method could estimate the mixing curve in a short period of time.

Strategy to prepare skin-free and macrovoid-free polysulfone membranes via the NIPS process

The non-solvent induced phase separation (NIPS) process applied to polysulfone (PSf) casting solutions traditionally leads to the formation of membranes decorated with large macrovoids in their cross-section on top of which lies a dense skin offering a significant resistance to flow. Macrovoids, are considered weak points. They are prone to compaction leading to poor filtration performance over time. Here, we used 2-pyrrolidone (2P) to prepare skin-free PSf membranes by NIPS, and studied the effect of water as an additive to help suppress the formation of macrovoids. The surface images showed the presence of multiple pores while the cross-section images exhibited the successful suppression of macrovoids. The latter was attributed to the enhancement of the solution viscosity causing the mass transfer kinetics to be slowed down, consequently affecting the demixing rates. Moreover, the rheological behavior of the casting solutions revealed that high degree of chain entanglement helped mitigate macrovoid formation. Using 2P as the solvent for PSf permitted the retention of interconnected pores from the top surface, due to the high viscosity of the solution which prevented coarsening. The high porosity (>75%) and large pores (>0.3 μm) of the PSf membranes were still maintained. The permeability of membranes was maintained after suppressing the macrovoids but their mechanical attributes were improved. The feasibility of utilizing water to eliminate macrovoid growth was further validated when applied to other PSf/solvent systems which showed similar trends in the SEM images. These results imply that water as a casting solution additive can provide a highly cost-effective and simple strategy to obtain macrovoid-free p olysulfone membranes.

Effect of adding carbon quantum dots to a NMP solution of cellulose acetate on the formation mechanism of ensuing membrane

BackgroundCarbon quantum dots (CQDs) can improve membrane separation efficiency and significantly contribute to solving global problems. Investigating the influence of adding CQDs on phase separation of cellulose acetate (CA)/ N-methyl-2-pyrrolidone (NMP) solution would provide more understanding of membrane formation. MethodsCA+CQDs membrane was fabricated through non-solvent induced phase separation, using water as coagulant. Kinetic and thermodynamics behavior of polymer solution affected the phase separation mechanism. The thermodynamic behavior was observed in cloud-point curve from the ternary phase diagram of CA/NMP/water, whereas the kinetic was studied by correlating the viscosity of the dope with light transmittance experiment and optical microscope observation. Fourier transform infrared microscope measured the time of phase separation at different depths of the casting plate. Significant findingsAdding CQDs can affect both the kinetics and thermodynamic behavior CA/NMP solution. At the top of the casting plate, phase separation behavior was affected mainly by the formation of pseudo water layer, causing fast demixing rate with more porous structure. In the inner part, phase separation was facilitated by kinetic of the dope. The 1,000 ppm CQDs added CA membrane delivered the highest pure water flux of 731.90 ± 68.27 L·m−2·h−1 (1 bar).

Study on thermo-kinetic modeling of green route synthesized inorganic loading on PVDF membrane for Cr(VI) removal and its optimization

Mathematical modeling of a phase inversion membrane was studied to predict the morphology. The effect of different concentrations of TiO2 nanoparticles on the thermodynamic and kinetic properties of polyvinylidene fluoride (PVDF) membrane casting solutions was investigated. The addition of green synthesized TiO2 increases the viscosity, and a sufficient amount results in the formation of two phases. Thermodynamics enhances the demixing rate, whereas kinetics delays the demixing rate; this trade-off between thermodynamic and kinetic parameter will affect the membrane morphology. A quadratic phase diagram for PVDF/ TiO2/solvent/Water system was drawn experimentally at different concentrations of TiO2 using a new method. Synthesized membranes were characterized by the contact angle, porosity, and permeability. Surface morphologies at different compositions were also examined using High Resolution scanning electron microscope (HRSEM). At TiO2 concentration of 2 wt% in the polymer casting solution, thermodynamics parameter dominates kinetics parameter; thus, maximum porosity with enhanced permeability was achieved experimentally. The importance of thermo-kinetic parameters was further assessed using response surface optimization. The study suggested an optimum value of 2.165% of weight% TiO2 at 5.125 pH giving excellent agreement to the experimental data.

A novel homogenous in-situ generated ferrihydrite nanoparticles/polyethersulfone composite membrane for removal of lead from water: Development, characterization, performance and mechanism

• Homogenous ferrihydrite NPs/PES composite membranes were firstly prepared by in-situ generation. • The membrane exhibited high adsorption, good selectivity and superior reusability for Pb removal. • The adsorption of Pb by M9 mainly occurred via the cation exchange between Pb 2+ and H + . • HA enhanced Pb removal in filtration via adsorption and size exclusion mechanisms. • The prepared membrane shows great potential for the removal of heavy metals from water. Nanocomposite adsorptive membranes with nanosorbents incorporated have become a promising material for the treatment of heavy metal-containing water, but their practical applications have been limited by the aggregation of nanosorbents in the membrane matrix. In this study, a homogenous in-situ generated ferrihydrite nanoparticles (NPs)/polyethersulfone (PES) adsorptive membrane was prepared for the removal of lead from water for the first time. The XRD, TEM and XPS results showed that ferrihydrite particles with the size smaller than 10 nm were successfully introduced into the composite membrane. The SEM-EDS result indicated a homogenous distribution of the in-situ generated ferrihydrite NPs in PES membrane. With more generated NPs, the membrane structure varied from a larger finger-like macro-void structure (i.e. M3, M6) to a suppressed finger-liker macro-void structure, due to the contributions of viscosity hindrance and thermodynamic enhancement to the demixing rate. Besides, the surface hydrophilicity and water flux increased gradually. The membrane M9 was stable for treating lead-contaminated water at pH above 3.0, with the optimal adsorption pH at 5.5. Furthermore, the M9 displayed the highest adsorption capacity of Pb 2+ of 64.77 mg/g, high selectivity toward Pb 2+ , and excellent reusability without significant loss of adsorption of Pb 2+ . In filtration process, the M9 can effectively remove Pb 2+ mainly by adsorption via cation exchange between Pb 2+ and H + in the presence of ferrihydrite NPs in membrane. More importantly, the presence of humic acid can significantly enhance Pb 2+ removal by M9 via adsorption and size exclusion mechanisms (caused by either chelation with HA or barrier effect caused by HA filter cake). Therefore, the present nanocomposite adsorptive membrane can be used as a promising material for treatment of heavy metal-containing water.

Direct Micropatterning of Phase Separation Membranes Using Hydrogel Soft Lithography

AbstractIn this work a novel method is presented to directly apply microscale patterns on the membrane surface using hydrogel facilitated phase separation (HFPS). The hydrogel mold initiates phase separation spontaneously when it contacts the polymer solution and this guarantees that location of the dense skin layer is on the patterned side. In this fashion, the active surface area of a membrane is larger than the equivalent flat surface and subsequently enhances water flux without changing the membrane surface chemistry. The morphological properties of the HFPS membranes show similarity to the nonsolvent induced phase separation ones; however, a pore enlarging is noticed in the HFPS membranes due to the slow demixing rate of the solvent/nonsolvent in the phase separation process. The permeation results show that the HFPS patterned membrane doubles the pure water permeate flux when compared to the HFPS unpatterned membrane. This increase is attributed to the combined effect of enhanced surface area and a slight increase in the average pore size of the membrane. Moreover, fouling experiments with bovine serum albumin solution show a 78% increment in the flux for the patterned membrane after 100 min of operation, demonstrating the advantage of using microstructured membrane for filtration applications.

In situ-generated yttrium-based nanoparticle/polyethersulfone composite adsorptive membranes: Development, characterization, and membrane formation mechanism

In this study, a series of in situ-generated yttrium-based nanoparticle (NP)/polyethersulfone (PES) composite adsorptive membranes were prepared by the phase inversion method for the first time. The Y(NO3)3·6H2O as precursor, uniformly dispersed at the molecular level in casting solution, reacted with OH− in a coagulation bath and ambient CO2 during the phase inversion process. The Y(CO3)0.5(OH)2 NPs were formed in situ and distributed homogeneously in a PES matrix, which was confirmed by X-ray photoelectron spectroscopy (XPS) and Energy Dispersive X-Ray Spectroscopy (EDS) results. The compatibility of the nanocomposite membranes was improved by an in situ preparation method. With the increase in content of Y-based NPs in composite membranes, the surface hydrophilicity and water permeability first increased from M1 to M2, and then slightly decreased from M3 to M5, which was mainly related to membrane structure. From M1 to M5, the demixing way changed from instantaneous demixing to delayed demixing process as a result of thermodynamic enhancement and viscosity hindrance in the phase inversion process. A higher demixing rate led to a structure with large finger-like macro-voids, i.e., M1, whereas a lower demixing rate caused the suppression of finger-like macro-voids, i.e., M5. More importantly, the adsorption study indicated that the nanocomposite adsorptive membranes were stable in the treatment of fluoride-containing water, with no leakage of Y-based NPs from membrane matrix to solution. It is expected that the in situ preparation technique could be used to produce next-generation nanocomposite adsorptive membranes with improved comprehensive properties for application in water treatment.

Physicochemical properties of β-cyclodextrin solutions and precipitates prepared from injectable vehicles

β-Cyclodextrin (β-CyD) is cyclic oligosaccharide of a glucopyranose, containing a relatively hydrophobic central cavity and hydrophilic outer surface. However, the usefulness of β-CyD is limited owing to its low aqueous solubility whereas we found that its apparent high solubility was evident in some injectable solvents including 2-pyrrolidone (PYR), N-methyl pyrrolidone (NMP) and dimethyl sulfoxide (DMSO). Therefore, in the present study, the physicochemical properties of the 30–60% w/w β-CyD in PYR, NMP and DMSO were investigated such as viscosity, water resistant, matrix formation rate and syringeability. The higher the concentration of β-CyD resulted in the increased viscosity and the higher force and energy of syringeability. β-CyD in PYR gave the highest viscosity which contributed to the lowest syringeability while β-CyD in DMSO exhibited the highest syringeability. The β-CyD in DMSO and NMP exhibited the higher rate of matrix formation. β-CyD in PYR showed the highest water resistant for phase separation while β-CyD in NMP gave the faster de-mixing rate compared to that from PYR. The difference in physicochemical properties of β-CyD dried ppts studied by scanning electron microscope (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) revealed that there was partial complexation of β-CyD with respective solvents. Both solution and precipitate characteristic properties will be useful for using β-CyD in further investigation as matrix material dissolved in the injectable vehicles as the in situ forming gel for periodontitis treatment.

Morphological changes in asymmetric PES membranes by addition of polyurethanes: A thermodynamic and experimental study

The effect of adding two types of polyurethane (PU) namely: polyether urethane (ETPU) and polyester urethane (ESPU), on polyether sulfone (PES) blend membrane is investigated. The morphology of the prepared membranes is studied by phase diagram. For this purpose, Hansen solubility parameters are calculated by Van Krevelen and Hoy methods, and the ternary and quaternary phase diagrams for the prepared membranes are produced using Flory Huggins theory. The membranes are prepared by phase inversion method. Different tests such as permeability, water contact angle, FTIR and SEM images are carried out to determine the membranes' characteristics. The results indicate that porosity and gas permeability of PES blend membranes increase by addition of PU as an additive. The PES/ETPU blend membrane has higher permeability and porosity in comparison with the PES/ESPU due to higher compatibility of the polymers and lower de-mixing rate between solvent and non-solvent in PES/ESPU membrane. It should be mentioned that by increasing the additive concentration, viscosity increases and high viscosity acts as a barrier to mass transfer between the solvent and non-solvent. Therefore, the delayed de-mixing rate reduces pore size and permeability.

Influence of additives on the morphology of PVDF membranes based on phase diagram: Thermodynamic and experimental study

ABSTRACTIn the present study, the morphology of asymmetric poly(vinylidene fluoride) blend membranes which were prepared by the phase inversion method is rationalized by comparing two non‐dimensional number represent thermodynamic and kinetic properties of the prepared membrane. These two parameters change phase diagram and demixing rate between solvent and nonsolvent. TiO2 nanoparticles and polyvinylpyrrolidone were used as additives. Hansen solubility parameters of the components are calculated by Van Krevelen method. Furthermore, kinetic and thermodynamic properties of the prepared solutions are determined by drawing phase diagrams and controlling mass transfer rate during precipitation of casting solution. Besides, to further analyze different tests encompass; permeability, rejection, porosity, pore size determination, contact angle, and field emission scanning electron microscopy images were carried out. It is shown, additives as pore former induced higher permeability and porosity, however, at higher concentration of additives high viscosity obstacle mass transfer and sponge‐like morphology is obtained. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46225.

Solid Oxide Cell Degradation Operated in Fuel Cell and Electrolysis Modes: A Comparative Study on Ni Agglomeration and LSCF Destabilization

A set of long-term tests have been carried out in fuel cell and electrolysis modes on typical Ni-YSZ//YSZ//LSCF-CGO cells. In similar operating conditions, the degradation rates were found to be higher in electrolysis than in fuel cell operation. To explain such results, both Ni agglomeration and LSCF destabilization have been investigated by coupling advanced post-test characterizations and modelling. Thanks to 3D electrode reconstructions, it has been found that Ni coarsening upon operation is not sensitive to the polarization, even if the agglomeration explains a significant part of the cell degradation. At the contrary, post-test analyses have revealed that Sr diffusion and formation of SrZrO3 at YSZ/CGO interface occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode. Therefore, the higher degradation rates measured in electrolysis mode could be related to the higher rate of LSCF demixing.

Effects of DC electric field on phase equilibrium and partitioning of ionic liquid-based aqueous two-phase systems

The liquid–liquid equilibrium and partitioning of ionic liquid-based aqueous two phase systems (ILATPS) including [Bmim]Cl-K2HPO4 ATPS, [Bmim]BF4-NaH2PO4 ATPS and [Bmim]BF4-Na3C6H5O7 ATPS in a DC electric field were extensively studied. The demixing rates of three ILATPSs with different tie-line lengths (TLL) were measured at different DC voltage levels with normal polarity (NP) or reverse polarity (RP), respectively, and the partitioning of ILs and model proteins (including lysozyme and bovine serum albumin) were investigated simultaneously. [Bmim]Cl-K2HPO4 ATPS had higher overall salt concentrations (>15wt%) and lower overall IL concentrations (<20wt%) compared with [Bmin]BF4-based ATPSs, which led to faster two phase separation rates and higher efficiency of electrokinetic demixing mainly due to the salting-out effect. The effects of TLL and DC voltage on the dispersing and gathering of IL molecules in the three ILATPS collectively gave the electrokinetic promotion (accelerate ILATPS demixing rate) and electrokinetic inhibition (decelerate ILATPS demixing rate) for the ILATPS demixing. In [Bmim]BF4-NaH2PO4 ATPS, the highest promotion demixing were at TLL=55, 90V (RP), while the highest inhibition demixing were at TLL=64, 150V (RP). The movement and type of organic cations or inorganic anions of IL molecules played an important role in IL partitioning in the three ILATPSs, which generally caused the partition coefficient of IL to decrease in NP and increase in RP to different degrees. There were two different protein partitioning characteristics in the three ILATPS that most model proteins distributed in the IL-rich phase in [Bmim]Cl-K2HPO4 ATPS due to the salting-out effect and distributed in the salt-rich phase in [Bmim]BF4-based ATPS due to hydrophobic repulsion. For the model protein partitioning in the electric field, the DC voltage and electric polarity had no significant effect on the protein partitioning trend.

The effects of a co-solvent on fabrication of cellulose acetate membranes from solutions in 1-ethyl-3-methylimidazolium acetate

Ionic liquids have been considered green solvents for membrane fabrication. However, the high viscosity of their polymer solutions hinders the formation of membranes with strong mechanical properties. In this study, acetone was explored as a co-solvent with the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) to dissolve cellulose acetate. The effects of acetone on the thermodynamic and kinetic aspects of the polymer solutions were studied and the physicochemical properties and separation capability of their resultant membranes were analyzed. The Hansen solubility parameters of [EMIM]OAc were measured by the software HSPiP and these data demonstrated that acetone was a suitable co-solvent to increase the solubility of cellulose acetate. The Gibbs free energy of mixing ΔGm was estimated to determine the proper composition of the polymer solution with better solubility. The study of the kinetics of phase separation showed that the demixing rate of the CA polymer solution in acetone and [EMIM]OAc was higher than that for solutions in [EMIM]OAc only. The membranes prepared from the former solution had higher water permeance and better mechanical stability than those prepared from the later solution. Adding acetone as a co-solvent opened the opportunity of fabricating membranes with higher polymer concentrations for higher separation capability and better mechanical properties.

Modification of polysulfone hollow fiber ultrafiltration membranes using hyperbranched polyesters with different molecular weights

A series of hyperbranched polyesters (HBPEs) using trimethylolpropane (TMP) as a core were synthesized via an esterification reaction, and the molecular weights of these HBPEs were 1600, 2260, 3370, and 5170 g/mol, respectively. Then, these HBPEs were added into dope solutions to prepare PSf hollow fiber membranes via a wet-spinning method. When the HBPE molecule weight increased from 1600 to 5170 g/mol, the initial viscosities of the PSf–HBPE–PEG400–DMAc dope solutions increased, and the shear-thinning phenomenon of these dope solutions became increasingly obvious. When these dope solutions were immersed into the deionized water, the demixing rate increased with an increase in the HBPE molecule weight at first and then decreased; this results in the increase of membrane porosity and the coexistence of finger-like and sponge-like structures. With the addition of HBPE, the start pure water contact angle and the mean effective pore size of the membranes decreased, and the Jw increased. For the mechanical properties of the membranes, the breaking strength and the elongation of the membranes also increased. Copyright © 2015 John Wiley & Sons, Ltd.

Comparison study of the effect of blending method on PVDF/PPTA blend membrane structure and performance

A novel hydrophilic poly (vinylidene fluoride)/poly (<i>p</i>-phenylene terephthalamide) (PVDF/PPTA) blend membrane was prepared by <i>in situ</i> polycondensation of <i>p</i>-phenylene diamine (PPD) and terephthaloyl chloride (TPC) in PVDF solution with subsequent nonsolvent induced phase separation (NIPS) process. For comparison, conventional solution blend membrane was prepared directly by adding PVDF powder into PPTA polycondensation solution. Blend membranes were characterized by means of viscometry, X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM). The effects of different blending methods on membrane performance including water contact angle (WCA), mechanical strength, anti-fouling and anti-compression properties were investigated and compared. Stronger interactions between PVDF and PPTA in <i>in situ</i> blend membranes were verified by viscosity and XPS analysis. The incorporation of PPTA accelerated the demixing rate and caused the formation of a more porous structure in blend membranes. <i>In situ</i> blend membranes exhibited better hydrophilicity and higher tensile strength. The optimal values of WCA and tensile strength were 65° and 34.1 MPa, which were reduced by 26.1% and increased by 26.3% compared with pure PVDF membrane. Additionally, antifouling properties of <i>in situ</i> blend membranes were greatly improved than pure PVDF membrane with an increasing of flux recovery ratio by 25%. Excellent anti-compression properties were obtained in <i>in situ</i> blend membranes with a stable pore morphology. The correlations among membrane formation mechanism, structure and performance were also discussed.

Ionic liquid induced surface exclusion and anomalous first-order phase transition in Laponite dispersions

Spontaneous liquid–liquid phase separation occurring in Laponite dispersions of ionic liquid (IL) solutions was observed at room temperature driven by surface exclusion of clay platelets at the water–air interface. The water–air interface dependent demixing behavior followed anomalous first-order phase transition kinetics described by a partition reaction CSK↔S+C with a demixing partition coefficient K=[S]/[C] where the initial homogeneous dispersion [CS] phase separated into a Laponite-poor [S] and Laponite-rich [C] state. The colloidal aggregates were found to be fractal structures with a mass fractal dimension 1.35<df<1.75. The demixing process could be described by a droplet splitting model. The settling dynamics was induced by ionic liquids due to their charge specific interaction with clay platelets, and the surface exclusion of clay particles at the liquid–air interface governed the rate of demixing. Interestingly, the time-constant of first-order dynamics was found to be invariant of IL concentration.

Modification of polysulfone hollow fiber ultrafiltration membranes using hyperbranched polyesters with different molecular weights

A series of hyperbranched polyesters (HBPEs) using trimethylolpropane (TMP) as a core were synthesized via an esterification reaction, and the molecular weights of these HBPEs were 1600, 2260, 3370, and 5170 g/mol, respectively. Then, these HBPEs were added into dope solutions to prepare PSf hollow fiber membranes via a wet‐spinning method. When the HBPE molecule weight increased from 1600 to 5170 g/mol, the initial viscosities of the PSf–HBPE–PEG400–DMAc dope solutions increased, and the shear‐thinning phenomenon of these dope solutions became increasingly obvious. When these dope solutions were immersed into the deionized water, the demixing rate increased with an increase in the HBPE molecule weight at first and then decreased; this results in the increase of membrane porosity and the coexistence of finger‐like and sponge‐like structures. With the addition of HBPE, the start pure water contact angle and the mean effective pore size of the membranes decreased, and the Jw increased. For the mechanical properties of the membranes, the breaking strength and the elongation of the membranes also increased. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Impact of casting conditions on PVDF/nanoclay nanocomposite membrane properties

In order to optimize the properties of PVDF/nanoclay nanocomposite membrane, the impact of casting conditions on membrane properties including PVDF crystalline phase, membrane morphology, mechanical strength and nanoclay retention were investigated. Nanoclays with hydrophilic modifiers tended to form membranes with larger macrovoids and higher beta-phase, and nanocomposite membranes with Nanomer® I.30E, which has a simple single alkyl group on the ammonium ion as organic modifier, had the highest nanoclay retention. Long air exposure time prior to immersion had a negative impact on nanoclay retention while adding sodium chloride to the quench bath helped retain nanoclay. Despite the slight changes, nanoparticle retentions varied from 32% to 48% for all membranes tested relative to the respective original concentration in the dope. Mechanical strength of the membranes was associated with membrane morphology, which was controlled by various casting conditions. Increases in air retention time, decreases in quench bath temperature and casting at high humidity increased the demixing rate which resulted in membranes with large macrovoids and poor mechanical properties including low tensile strength, ductility and stiffness. To form good membrane structure, polymer concentration and molecular weight of PVDF has to be high enough to provide the necessary viscosity in the dope. Casting conditions should be chosen carefully not only to retain more nanoclay for economic reasons but also for the morphology and mechanical strength needed for the required applications.

Fabrication and characterization of hydroxylated and carboxylated multiwalled carbon nanotube/polyethersulfone (PES) nanocomposite hollow fiber membranes

Pilot scale studies were performed to investigate how CNTs might affect hollow fiber membrane (HF) resistance to stress. Further, this research explored how the addition of CNTs into membrane solutions affected trends associated with changes in conventional HF spinning parameters. Nanocomposite polymer solutions were formed by adding functionalized multiwalled carbon nanotubes (MWCNTs) (0.2wt.%, 0.4wt.% and 0.8wt.%) and PES. Membranes were fabricated under three different air residence times (1.875s, 0.935s, and 0s) by changing either the air gap (15cm or 0cm) or the fiber take-up speed (0.16m/s or 0.08m/s). Subsequently, HF membranes were characterized according to their porosity, permeability, contact angle, and tensile strength. As expected, stress resistance and Young's Modulus increased up to 125% and 118% for certain membranes containing CNTs, respectively. Shorter air residence times caused significant porosity increases and large permeability decreases in the membranes containing CNTs. Finally, the effect of the de-mixing rate was more pronounced in nanocomposite membranes, while the effect of take-up speed was more pronounced in pristine membranes. This study establishes the potential for CNTs to improve the mechanical properties of HF membranes, and serves as the first demonstration of industrial-scale production of CNT-polymer HF membranes.