Viscosity Of Casting Solution Research Articles

Combining dip-coating and rotate-drying to preparation of PDMS on SiC tubular support with macropore for high pervaporation performance

High-performance polydimethylsiloxane (PDMS)/ceramic tubular pervaporation membranes have potential in industrial separation applications, but realizing the preparation of PDMS layer on the ceramic supports with micrometer-scale pore size (0.8 μm or 4.3 μm) for improving performance remains a challenge. We report a strategy (combined dip-coating and rotate-drying, DCRD) to preparation of PDMS on silicon carbide (SiC) tubular support with macropore. Response surface methodology was employed to optimize the dip-coating process, and the influence of friction velocity on tubular composite membranes was investigated. The results indicate that pulling speed, casting solution viscosity, and their interaction have significant effects on the pervaporation performance of PDMS/SiC tubular composite membranes. Moreover, increasing friction velocity results in uneven PDMS layer thickness, which in turn impacts the pervaporation performance of the composite membrane. Furthermore, the rigid structure of SiC restricts the movement of PDMS polymer chains, enabling the composite membrane to maintain stable pervaporation performance at higher isobutanol feed concentrations (3 wt%) or elevated feed temperatures (60 °C). After continuous operation for 200 h, the developed PDMS/SiC tubular composite membrane consistently maintained the total flux of 650 g m−2 h−1 and the separation factor of 39 for isobutanol/water. Eventually, this novel fabrication method offers new insights into the preparation of various other organic-inorganic tubular composite membranes.

Preparation of novel zwitterionic polysulfone ultrafiltration membranes for the dual-enhanced antifouling and antibacterial properties by in-situ one pot crosslinking reaction

Zwitterionic polysulfone (PSf) ultrafiltration membranes were fabricated by non-solvent phase separation (NIPS) method. Herein, a casting solution at 45 °C was developed by using chloromethylated polysulfone (CMPSf), N, N-dimethylacetamide (DMAc) as a solvent, 4-amino-benzenesulfonic acid monosodium salt (ABS) as a cross-linking agent, and Na2CO3 as an acid binder. Simultaneously, the occurrence of the electrophilic substitution reaction between ABS and CMPSf caused the formation of ABS grafting CMPSf (CMPSf-g-ABS). After a specific reaction time, the casting solution was applied to cast membranes, which were subsequently submerged in coagulation bath. A zwitterionic ultrafiltration (ZUF) membrane was obtained using NIPS following the treatment of hydrochloric acid (HCl) solution (1 M mol). Because of the formation of cross-linked CMPSf-g-ABS, the results revealed that the casting solution's viscosity increased sharply from 425.4 mPa s at the initial stage (0 h) to 4810.8 mPa s (22 h). Interestingly, the morphology of the membranes with an asymmetric finger-like structure at 0 h gradually transformed to a gradient sponge-like structure after 22 h. Specifically, the ZUF membrane (M22-H) with the gel fraction of 72.1% procured after the reaction of 22 h demonstrated a low water contact angle (40.17°) and a high pure water permeance (420.4 L m−2 h−1 bar−1). The M22-H also exhibited a high flux recovery rate (FRR) (90.2%), bovine serum albumin (BSA) rejection (>95%), and Escherichia coli (E. coli) antibacterial rate (96.2%). The surface of the ZUF membrane with numerous zwitterionic groups enhances the hydration layer's energy (i region <16 nm) and creates a thick hydration layer (ii region >16 nm), causing a significant improvement in the antifouling performance. This research opens new avenues for preparing zwitterionic functional membranes.

Polyphenylsulfone membrane blended with polyaniline for nanofiltration promising for removing heavy metals (Cd2+/Pb2+) from wastewater

This study reported polyaniline (PANi), an emerging multifunctional nanomaterial, for fabricating the polyphenylsulfone (PPSF)–PANi nanocomposite membrane for nanofiltration (NF) to remove heavy metals (Cd2+/Pb2+) from wastewater. PANi was synthesized via oxidative polymerization of an aniline monomer at a low concentration (≤0.1 M). Furthermore, the nanostructure of PANi was determined using transmission electron microscopy. The membrane structure and characteristic properties were studied in terms of surface and cross-section morphologies, topography, hydrophilicity, and surface charge using scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) measurement, and zeta potential measurement, respectively. Thermal and mechanical properties and casting solution viscosity were also studied. The SEM results demonstrated that PANi inclusion helped to construct a typical asymmetric membrane with a pore size of ∼1 nm. Additionally, it enhanced the surface properties, which was indicated by a more considerable hydrophilicity (CA ≤ 52) and a shift in the zeta potential from −40 to −10 mV. Increasing the PANi concentration from 0.25 to 0.50 wt% aided the heavy metal rejection by the nanocomposite membrane, affording an increase of the Cd2+/Pb2+ rejection. However, the Cd2+/Pb2+ rejection decreased when the PANi concentration was 1.0 wt%. The optimized PPSF–PANi nanocomposite membrane at 0.50-wt% PANi exhibited a water permeability of 1.8 LMH/bar and high rejections of 99% and 95% toward Pb2+ and Cd2+, respectively. Tensile strength and TGA tests also revealed the role of PANi as a positive reinforcement on the mechanical and thermal properties of the membrane.

Fabrication of Polyacrylonitrile UF Membranes by VIPS Method with Acetone as Co-Solvent.

For the first time, a systematic study was carried out of the replacement of the low-volatility solvents N-methyl-2-pyrrolidone (NMP) or dimethylsulfoxide (DMSO) with the high-volatility solvent acetone in the casting solution of polyacrylonitrile (PAN). The effect of acetone’s presence in the casting solution on the performance of ultrafiltration membranes fabricated via vapor-induced phase separation (VIPS) was investigated. It was possible to replace 40% of NMP and 50% of DMSO with acetone, which resulted in the reduction of the casting solution viscosity from 70.6 down to 41.3 Pa∙s (20% PAN, NMP), and from 68.3 down to 20.6 Pa∙s (20% PAN, DMSO). It was found that 20 min of exposure to water vapor (relative humidity—85%) was sufficient to govern the phase separation, which was mainly induced by the water vapor. Regardless of the casting solution composition (15 or 20% PAN; DMSO or NMP), all membranes formed via VIPS possessed a sponge-like porous structure. The addition of acetone to the casting solution allowed the reduction of the transport pore size from 35–48 down to 8.5–25.6, depending on the casting solution composition. By varying the acetone content at constant polymer concentration, it was possible to decrease the molecular weight cut-off (MWCO) from 69 to 10 kg/mol. Membranes prepared from 20% PAN solution in an acetone/DMSO mixture had the lowest MWCO of 10 kg/mol with a water permeance of 5.1 L/(m2·h·bar).

MOF/Polymer Mixed-Matrix Membranes Preparation: Effect of Main Synthesis Parameters on CO2/CH4 Separation Performance.

Design and preparation of mixed-matrix membranes (MMMs) with minimum defects and high performance for desired gas separations is still challenging as it depends on a variety of MMM synthesis parameters. In this study, 6FDA-DAM:DABA based MMMs using MOF-808 as filler were prepared to examine the impact of multiple variables on the preparation process of MMMs, including variation in polymer concentration, filler loading, volume of solution cast per membrane area, solvent type used and solvent evaporation rate, and to identify their impact on the CO2/CH4 separation performance of these membranes. Solvent evaporation rate proved to be the most critical synthesis parameter, directly influencing the performance and visual appearance of the membranes. Although less dominantly influencing the MMM performance, polymer concentration and solution volume also had an important role via control over the casting solution viscosity, particle agglomeration, and particle settling rate. Among all solvents studied, MMMs prepared with chloroform led to the best performance for this polymer-filler system. Chloroform-based MMMs containing 10 and 30 wt.% MOF-808 showed 73% and 62% increase in CO2 permeability, respectively, without a decrease in separation factor compared to unfilled membranes. The results indicate that enhanced gas separation performance of MMMs strongly depends on the cumulative effect of various synthesis parameters rather than individual impact, thus requiring a system-specific design and optimization.

Polyphenylsulfone/zinc ion‐exchanged zeolite Y nanofiltration mixed matrix membrane for water desalination

AbstractIn the present study, zinc ion‐exchanged zeolite Y (ZnY) was incorporated as a dispersed phase into polyphenylsulfone (PPSU) polymer matrix to prepare PPSU/ZnY porous mixed matrix membranes (MMMs) with enhanced separation properties. Various MMMs with different ZnY contents (0, 0.25, 0.5, 0.75, 1, 1.5, and 3 wt.%) were fabricated using phase inversion method. The morphologies of prepared membranes were characterized by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. Fourier transform infrared (FTIR) and X‐ray diffraction (XRD) were used to investigate the chemical structures and microstructural properties, respectively. Differential scanning calorimetry (DSC) analysis and tensile test were done to investigate thermomechanical properties of the membranes. Density and dynamic viscosity of membrane casting solutions as well as porosity, mean pore size, contact angle and water content of the prepared membranes were determined to investigate how these parameters affect the morphology of the membranes. Finally, separation performance of the membrane samples was investigated by determining water flux, salt (CuSO4) rejection, and anti‐fouling properties. SEM results showed an increase in top layer pore volumes with the incorporation of ZnY nanoparticles, which offer a higher water flux. AFM images indicated the higher surface roughness for an MMM compared to the pure PPSU membrane. FTIR spectroscopy confirmed the presence of all PPSU and ZnY functional groups in the MMM and showed no existence of chemical bonds at the polymer‐particle interface. XRD patterns exhibited a decrease in the degree of crystallinity by addition ZnY nanoparticles into PPSU matrix. DSC and tensile tests confirmed the XRD analysis and show lower Tg and tensile stress for an MMM compared to the pure PPSU membrane. Porosity measurements showed that the membrane porosity improved by decreasing the polymer concentration in the casting solutions and by incorporation of ZnY nanoparticles. The contact angle measurement indicated that the values decrease upon loading of ZnY nanoparticles. Finally, an enhanced pure water flux of 4.315 L m−2 h−1 bar−1 and a salt rejection of 75%, respectively as compared to 3.591 L m−2 h−1 bar−1 and 81% for pure PPSU membrane, were observed for the MMM with 1 wt.% of ZnY filler.

A Biofouling Resistant Zwitterionic Polysulfone Membrane Prepared by a Dual-Bath Procedure.

This study introduces a zwitterionic material to modify polysulfone (PSf) membranes formed by a dual bath procedure, in view of reducing their fouling propensity. The zwitterionic copolymer, derived from a random polymer of styrene and 4-vinylpyrridine and referred to as zP(S-r-4VP), was incorporated to the PSf solution without any supplementary pore-forming additive to study the effect of the sole copolymer on membrane-structuring, chemical, and arising properties. XPS and mapping FT-IR provided evidence of the modification. Macrovoids appeared and then disappeared as the copolymer content increased in the range 1–4 wt%. The copolymer has hydrophilic units and its addition increases the casting solution viscosity. Both effects play an opposite role on transfers, and so on the growth of macrovoids. Biofouling tests demonstrated the efficiency of the copolymer to mitigate biofouling with a reduction in bacterial and blood cell attachment by more than 85%. Filtration tests revealed that the permeability increased by a twofold factor, the flux recovery ratio was augmented from 40% to 63% after water/BSA cycles, and irreversible fouling was reduced by 1/3. Although improvements are needed, these zwitterionic PSf membranes could be used in biomedical applications where resistance to biofouling by cells is a requirement.

Fabrication of ultrafiltration membranes from non-toxic solvent dimethylsulfoxide: Benchmarking of commercially available acrylonitrile co-polymers

In recent years, increased attention is given to sustainability and environmental safety of existing processes and materials. The membrane separation is considered as attractive alternative to conventional separation processes due to its greater energy efficiency and smaller carbon footprint. However, most organic solvents used for the production of polymeric membranes (DMF, DMAA, NMP), are hazardous and toxic; thus, non-toxic solvents like dimethylsulfoxide (DMSO) are considered nowadays as a perspective alternative to this solvents. The systematic study of the application of DMSO as “green” solvent for the fabrication of ultrafiltration membranes from the commercial polymer was carried out. Acrylonitrile homopolymer and six co-polymers of various composition and molecular weight were screened. It was revealed that the viscosity of the polymeric solution plays a major role in the resulting morphology and the performance of the membranes obtained. Regardless of the polymer origin and solvent nature, the studied membranes possessed finger-like porous structure if the viscosity of casting solution was lower than 42 Pa∙s, and the sponge-like porous structure at the viscosity greater than 78 Pa∙s. Analysis of the filtration data revealed that the replacement of traditional solvent DMF by non-toxic DMSO allowed obtaining the membranes with better overall performance in terms of pure water flux and rejection. The use of DMSO allowed to decrease the concentration of poly(acrylonitrile-co-itaconic acid) from 15 to 12 wt% in the spinning solution to achieve the same viscosity; and the resulting hollow fiber membrane demonstrated higher water flux and rejection compared to the one prepared from DMF.

Effect of Solution Viscosity on the Precipitation of PSaMA in Aqueous Phase Separation-Based Membrane Formation.

Aqueous phase separation (APS) is a recently developed sustainable alternative to the conventional organic solvent based nonsolvent-induced phase separation (NIPS) method to prepare polymeric membranes. In APS, polyelectrolytes are precipitated from aqueous solutions through pH or salinity switches. Although APS differs from NIPS in the polymer and solvents, they share many tuning parameters. In this work, we investigate the APS-based preparation of membranes from poly(styrene-alt-maleic acid) (PSaMA) with a focus on acid concentration in the coagulation bath, and polymer and additive concentration in the casting solution. Nanofiltration membranes are prepared using significantly lower concentrations of acid: 0.3 M HCl compared to the 2 M of either acetic or phosphoric acid used in previous works. It is shown that higher polymer concentrations can be used to prevent defect formation in the top layer. In addition, acetic acid concentration also strongly affects casting solution viscosity and thus can be used to control membrane structure, where lower acetic acid concentrations can prevent the formation of macrovoids in the support structure. The prepared nanofiltration membranes exhibit a very low molecular weight cutoff (210 ± 40 dalton), making these sustainable membranes very relevant for the removal of contaminants of emerging concern. Understanding how the parameters described here affect membrane preparation and performance is essential to optimizing membranes prepared with APS towards this important application.

Constructing Microstructures of Chlorinated Polyvinyl Chloride Microporous Membranes by Non-solvent Induced Phase Separation for High Permeate Flux and Rejection Performance

To obtain the excellent permeate flux, rejection performance and mechanical properties, the chlorinated polyvinyl chloride (CPVC) porous membrane was fabricated on the polyethylene terephthalate (PET) non-woven fabric by non-solvent induced phase separation (NIPS), using Tween80 (polyoxyethylene sorbitan monooleate) as a hydrophilic surfactant to regulate the microstructure of the membrane. Porous skin layer and sub-layer were achieved when 3 wt.% Tween80 was added with a small amount of deionized water as additive, and internal layer consisted of various finger-like holes. The forming mechanism of microstructures was investigated according to the effects of Tween80 molecular chain structure on the viscosity and surface tension of casting solution. Significantly, the modified membranes obviously exhibited higher pure water flux, which was increased by 257 % compared with the pristine membrane. The rejection to ink suspension was over 99 %. Furthermore, the antifouling performance of modified membrane was also greatly improved on account of the above microstructure and more hydrophilic surface. This study provides a new idea for the construction of membrane microstructure and the hydrophilic modification.

High-Performance Hemodialysis Membrane: Influence of Polyethylene Glycol and Polyvinylpyrrolidone in the Polyethersulfone Membrane

the preparation of high-performance hemodialysis membrane, the effect of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and also the simultaneous effect of both additives in the polyethersulfone (PES) membrane were investigated. Viscosity measurements demonstrated that PVP has better compatibility with PES, owing to the amorphous nature, closer glassy transition temperature (Tg), and solubility parameters rather than PEG (semi-crystalline and low Tg). This could lead to enhancement in the solution viscosity. SEM results revealed that membranes morphology was dependent upon casting solution viscosity and with increasing viscosity; the formation of macro-voids suppressed and achieving to a membrane with a smaller mean pore size would be possible. The results of the AFM study demonstrated that, with the addition of PVP, membranes with smooth surface were achieved. In contrast, the PEG addition led to a rougher membrane surface. The results verified that PEG had a tangible effect on the permeability of membrane rather than PVP or blend of PVP and PEG, which is owing to its impressive pore-forming role. The maximum pure water permeability (PWP) was achieved for MV4 (24.9 L/m2.h.bar), MG2 (44.8 L/m2.h.bar), MVG2 (25.2 L/m2.h.bar), and MVG3 (25.1 L/m2.h.bar). Rejection test showed that MV3, MV4, MG3, MG4, MVG2, and MVG3 had the best performance in terms of urea removal and maintaining other components, especially bovine serum albumin (BSA). In-vitro cytotoxicity demonstrated the biocompatibility of MV2, MG3, and MVG3 as representative of all membranes. The lactate dehydrogenase (LDH) test confirmed that PVP has a tangible effect on the reduction of platelet adhesion on the membrane surface.

Effect of Temperature Exposition of Casting Solution on Properties of Polysulfone Hollow Fiber Membranes

It was shown for the first time that the conditions of thermal treatment of the casting solution significantly affect the morphology and transport properties of porous, flat, and hollow fiber polysulfone (PSf) membranes. It is ascertained that the main solution components that are subjected to thermo-oxidative destruction are the pore-forming agent polyethylene glycol (PEG) and solvent N-methyl-2-pyrrolidone (NMP). It is proved that hydroxyl groups of PEG actively react in the process of the casting solution thermo-oxidative destruction. It is shown that despite the chemical conversion taking place in the casting solution, their stability towards coagulation virtually does not change. The differences in the membrane morphology associated with the increase of thermal treatment time at 120 °C are not connected to the thermodynamic properties of the casting solutions, but with the kinetics of the phase separation. It is revealed that the change of morphology and transport properties of membranes is connected with the increase of the casting solution viscosity. The rise of solution viscosity resulted in the slowdown of the phase separation and formation of a more densely packed membrane structure with less pronounced macropores. It is determined experimentally that with the increase of casting solution thermal treatment time, the membrane selective layer thickness increases. This leads to the decrease of gas permeance and the rise of the He/CO2 selectivity for flat and hollow fiber membranes. In the case of hollow fibers, the fall of gas permeance is also connected with the appearance of the sponge-like layer at the outer surface of membranes. The increase of selectivity and decline of permeance indicates the reduction of selective layer pore size and its densification, which agrees well with the calculation results of the average membrane density. The results obtained are relevant to any polymeric casting solution containing NMP and/or PEG and treated at temperatures above 60 °C.

New frontiers in sustainable membrane preparation: Cyrene™ as green bioderived solvent

In this work, Cyrene™ was employed for the first time as solvent for polyethersulfone (PES) and poly(vinylidene fluoride) (PVDF) membrane preparation via phase inversion. The two selected polymers are among the most required materials in the industrial membrane field. PES and PVDF membranes were prepared by coupling Vapour Induced- and Non-solvent Induced Phase Separation (VIPS and NIPS, respectively) with the aim to study the influence of the adopted operational conditions on the final membrane structure and properties. By changing the exposure time to fixed atmospheric relative humidity (55%) and temperature (25 °C) in the range between 0 and 5 min, membranes with different features, pore size and pure water permeability (PWP) could be tailored. The experimental data were discussed with respect to the casting solution viscosity, ternary phase diagram, membrane morphology, thickness, porosity, contact angle, pore size and PWP. In the case of PVDF, additional differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) analysis were performed for evaluating the polymorphism and crystallinity change of the material, which influences the membrane properties too. By working in complete absence of additives and at room temperature, the combinations PES/Cyrene™ and PVDF/Cyrene™ allowed to develop a new sustainable approach of producing membranes for potential application in water treatment.

Optimizing separation performance and interfacial adhesion of PDMS/PVDF composite membranes for butanol recovery from aqueous solution

Bio-butanol is an important aspect for development of renewable energy. Currently, it remains challenging for developing highly permeable and selective composite membranes to efficiently recover butanol produced in biomass fermentation process. In this work, we fabricated polydimethylsiloxane (PDMS) into thin and defect-free composite membranes by using porous PVDF as the substrate. The formation of PDMS membrane layer was finely controlled by optimizing the substrate pore size and casting solution viscosity. In particular, the interfacial adhesion between PDMS active layer and PVDF substrate layer, which is critical for practical application of composite membrane, was probed by using in-situ nano-indentation/scratch technique for the first time. The transport properties of the prepared PDMS/PVDF composite membranes were studied by pervaporation recovery of n-butanol from aqueous solution with different feed concentrations or temperatures. The results indicated that the PDMS membrane layer with a carefully tuned thickness of ∼11 μm offered high total flux of 2210 g/m2h and excellent separation factor of 46 (1 wt% butanol/water at 70 °C), as well as strong interfacial adhesion for the PDMS/PVDF composite membrane. The separation performance is superior to the reported membranes, showing great potential for application in bio-butanol separation.

Janus graphene oxide nanosheet: A promising additive for enhancement of polymeric membranes performance prepared via phase inversion

Although polymeric membranes find important role in water and waste water treatment in recent years, their fouling is still an important problem. Application of hydrophilic nanoparticles (NPs) is one of the proposed methods for reducing fouling of membranes but their dispersion and stability in hydrophobic polymer matrix is challenging. In this study Janus functionalization of the NPs was introduced as a promising technique toward achieving this goal. Polysulfone (PSf) membranes containing various concentrations of graphene oxide (GO) nanosheets and Janus graphene oxide (Janus GO) nanosheets (as additives) were fabricated via phase inversion. The synthesized nanosheets were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and dynamic light scattering (DLS). The prepared membranes also were then characterized by scanning electron microscopy (SEM), contact angle (CA), water uptake, porosity, mean pore size and casting solution viscosity. The membrane performance was also tested by determining pure water flux (PWF), bovine serum albumin (BSA) separation, flux reduction by fouling and flux recovery. CA reduced from 85° to 68° and PWF increased from 23.15 L/m2 h to 230.61 L/m2 h for PSF and Janus GO nanosheets containing membrane, respectively. Also investigation of antifouling performance of membranes revealed that membrane with the 1 wt.% of Janus GO nanosheets had higher water flux recovery ratio (FRR) and lower irreversible fouling (Rir) of 84% and 16%, respectively. These improvements were attributed to the better dispersion and stability of Janus GO nanosheets in the prepared mixed matrix membranes.

Investigation of UF membranes fouling and potentials as pre-treatment step in desalination and surface water applications

The surface fouling of UF membranes used upstream as pre-treatment stage is critical for the long-term stability of the subsequent treatment stage (NF/RO membranes). In this paper, an attempt was made to probe and compare the potential of versatile UF membranes structures in terms of flux decline and selectivity, for more convenient pretreatment membranes selection. The role of polyethersulfone (PES) host polymer concentration, on the morphology and surface characteristics of asymmetric flat sheet ultrafiltration (UF) membranes, has been comprehensively investigated. Distinctly, as the casting solution viscosity decrease, a higher pore size, pore size distribution and pure water flux was observed along with lower mechanical properties and wider cross-section morphologies. However, this impact was trivial on water contact angle, surface roughness parameters and charge negativity of the membrane. To further assess the potential performance of the hand-made fabricated membranes, they were systematically evaluated against three organic model foulants with dissimilar origins; humic acid (HA) – as natural organic matters (NOM), sodium alginate (NaAlg) – as polysaccharide, and bovine serum albumin (BSA) – as protein, under different initial feed concentration and pH chemistry. A disparate fouling behavior was observed depending on the membrane characteristics and the organic model foulant used. Depending on the UF membrane cut-off used, lower MWCO membranes, PES22 (6 kDa) and PES20 (10 kDa) exhibited a negligible relative flux decline while extremely low relative flux patterns were observed in the filtration with the 100 kDa membrane (PES16), as a result of one or more pore blocking mechanisms observed.

Preparation of poly(L-lactic acid) membrane from solvent mixture via immersion precipitation

ABSTRACTPoly (L-lactic acid) (PLLA) membranes were fabricated through immersion precipitation method. 1, 4-dioxane (DX), N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethyl-acetamide (DMAc), and DX/NMP, DX/DMF and DX/DMAc were used as solvents severally. With a focus on the PLLA/DX/NMP/H2O system, the effect of solvent mixture on PLLA membrane was investigated by altering the ratio of DX/NMP. Various membrane morphologies were obtained, which were further correlated by mean of solubility parameter and viscosity of casting solution. It was found that the membrane cast with DX/NMP (1/1) exhibited ideal structure and better performance compared with membranes cast with same concentration of PLLA.

Solvent stable nanoporous poly (ethylene-co-vinyl alcohol) barrier membranes for liquid-liquid extraction of lithium from a salt lake brine

Loss of organic extraction in membrane extraction process could be avoided by using an ion permeable, solvent stable barrier membrane. Development of solvent stable materials has been a key issue for liquid-liquid membrane extraction. A new type of solvent resistant membrane, prepared from block copolymer poly (ethylene-co-vinyl alcohol) (EVAL) via immersion precipitation, is introduced as the barrier in membrane extraction of lithium from a real salt lake brine. The influence of EVAL concentration on the casting solution viscosity and the membrane properties was investigated. The membranes were characterized by scanning electron microscopy (SEM), water uptake, pure water flux, mechanical strength, and Li+ diffusion flux. Membrane phase separation was conducted at a temperature below the crystallization temperature of the polymer to ensure suitable membrane structure. The membrane prepared from 30wt% EVAL content showed a Li+ flux of 2.7×10−8molcm−2s−1 at a Li+ feed concentration of 0.1mol/L in a diffusion test. Using a tributylphosphate (TBP)/kerosene extractant, the lithium flux in a membrane extraction showed a linear relationship with the feed lithium concentration. In addition, long term stability tests showed a stable lithium extraction flux for about 1037h. These results indicate that EVAL material is a promising stabilizing barrier membrane in liquid-liquid extraction of lithium.

The effect of casting solution composition on surface structure and performance of poly(vinylidene fluoride)/multi-walled carbon nanotubes (PVDF/MWCNTs) hybrid membranes prepared via vapor induced phase separation

Abstract In this work, the poly(vinylidene fluoride)/multi-walled carbon nanotubes (PVDF/MWCNTs) hybrid membranes were obtained through vapor induced phase separation (VIPS). In addition, the effects of solution composition on crystal behavior, elemental composite, morphology and hydrophilicity of membranes surface and the viscosity of casting solution were analyzed. The results of field emission scanning electron microscopy and X-ray photoelectron spectroscopy showed that the rough porous surface could be built in all hybrid membranes due to the slower double diffusion mechanism of the VIPS process, which also provided enough time for MWCNTs to move to the surface and be enriched there, to ensure the lowest surface free energy. Furthermore, other analysis displayed that both adding tiny amounts of MWCNTs and a low concentration of PVDF were favorable to the growth and aggregation of PVDF, which were put down to the adverse effect of hydrophobic MWCNTs on the thermodynamic compatibility of polar casting solution, the less nucleation points and the good fluidity with lower concentration of polymer. Then, the diameter of PVDF spherical particles and the membrane surface roughness increased, whereas the hydrophilicity of membrane surface declined effectively.

Influence of nanoparticle processing and additives on PES casting solution viscosity and cast membrane characteristics

Abstract Nanoparticle stabilizer type, casting solution additives, and nanoparticle processing by centrifugal or magnetic separation were varied, and specific membrane characteristics were evaluated. Specifically, membrane casting solution viscosity, cast membrane thickness, pure water flux, and internal morphology were evaluated. While the addition of the additives ethanol and polyvinylpyrrolidone to a polyethersulfone-dimethylacetamide solution causes an expected increase in viscosity, the addition of nanoparticles can cause an increase or decrease in viscosity depending on the ligand stabilizer used during nanoparticle synthesis and casting solution additive concentration. Viscosity can also be affected by nanoparticle separation method, but again, changes are also dependent on casting solution composition. Varying changes in membrane thickness are observed and can be correlated to viscosity. Pure water flux decreases for all samples when nanoparticles are added, but the extent of the change is affected by casting solution composition. Internal morphology can partially explain the decrease in flux for nanoparticle-embedded membranes.