Preparation and characterization of poly (vinyl chloride)-blend-poly (carbonate) heterogeneous cation exchange membrane: Investigation of solvent type and ratio effects

In this research polyvinylchloride/polycarbonate blend heterogeneous cation exchange membranes were prepared by solution casting technique using cation exchange resin powder as functional groups agent. Tetrahydrofuran (THF) and dimethylformamide (DMF) were utilized as solvents. The effect of solvent type and ratio (THF/DMF mixture) on properties of prepared membranes was studied. SEM and SOM images showed relatively uniform particle distribution and also uniform surface for the membranes. Images showed that at high DMF ratio decrease of polymer conformation with particles surface reduces the compatibility of polymer-particle. The membrane ion exchange capacity and permeability were enhanced initially by increase of DMF ratio up to 5% (v/v) in casting solution and then they began to decrease with more DMF ratio. Results showed that membrane potential, transport number, selectivity and thermal stability all were decreased by DMF ratio increasing. Conversely, membrane water content, specific surface area and roughness showed opposite trends. Membrane electrical resistance initially declined by increase in DMF content up to 15% (v/v) and then it began to increase. The increase of electrolyte concentration also led to decrease in membrane transport number and selectivity. Membrane with (95:5) (v/v) solvent ratio (THF:DMF) exhibited more appropriate performance compared to others.     

Performance evaluation of polyvinylchloride/polyacrylonitrile ultrafiltration blend membrane

Polyvinylchloride (PVC) membranes were modified by blending with polyacrylonitrile (PAN) as a second polymer. The miscibility of PVC/PAN blend was examined using an incompressible regular solution (CRS) model in no need to make a membrane. The results showed that the PVC/PAN blend was immiscible for all compositions at a temperature range of ?25 to 225 °C. Furthermore, the prediction of the phase behavior of a PVC/PAN/DMF ternary system showed that the blend of two polymers was highly incompatible even in their common DMF solvent. However, this incompatibility led to a remarkable increase in the porosity of the blend membrane and pure water flux compared to those for pure PVC membrane. The pure water flux of the PVC membrane (37.9 ± 1.5 L/m² h) increased about 41 and 76% by adding 10 and 20 wt% PAN, respectively. The blend membranes also showed an enhanced flux recovery ratio (FRR) compared to a pure PVC membrane, although the PVC membrane rejection for Bovine serum albumin (BSA) was decreased after blending with PAN. The PVC/PAN (90/10) blend membrane was subjected to hydrolysis with NaOH alkaline solution at three different concentrations and contact times to further enhance its performance. The membrane, which was hydrolyzed with a 0.5 mol/L NaOH solution for 0.5 h, showed a highest pure water flux of 75.6 ± 7.2 L/m² h due to its increased hydrophilicity. This membrane also revealed an improved FRR and better thermal and mechanical properties compared to an unmodified membrane.     

Preparation of high strength ultrafine polyvinyl chloride fibrous membrane and its adsorption of cationic dye

The polyvinyl chloride (PVC) ultrafine fibrous membranes were prepared by electrospinning. After solvent and thermal treatments, the membranes were used for the adsorption of cationic dye. The factors, the solvent ratio, the time of solvent treatment and the temperature of thermal treatment, were studied to enhance the mechanical properties of the membranes. The effects of the initial dye concentration and the solution temperature on the adsorption behaviors of the membranes were investigated. The results indicate that, long and uniform PVC ultrafine fibers were steadily electrospun at the PVC concentration of 10 w/v% in the mixture solvents of THF and DMF. The highest tensile strength of membranes reached 7.87 MPa, whereas the value of untreated counterpart was only 0.67 MPa. The equilibrium sorption capacity Q_e increased with the increases of the initial dye concentration and solution temperature. The equilibrium adsorption of the membranes followed Freundlich isotherm and the adsorption kinetics observed Lagergren’s pseudo-second order equation.     

Study of the solvent effect on miscibility between poly(vinyl chloride) and poly(methyl methacrylate) in the solution state – viscometric measurements

In this work, the solvent effect on the miscibility between poly(vinyl chloride) (PVC) and poly(methyl methacrylate) (PMMA) in ternary polymer solutions was examined by the viscometric method. In these systems, we could understand that the used solvents, tetrahydrofuran (THF) or N,N‐dimethylformamide (DMF), mainly affect the interaction between PVC and PMMA, while prompting various miscible properties. In PVC/PMMA/THF solution, THF is a near θ‐solvent and a poor solvent for PVC and PMMA, respectively. The mixing of the tighter PMMA coils and more extended PVC coils in THF may cause the sea–island heterogeneous structure below the weight fraction of PMMA in the polymer mixture w_PMMA = 0.7, resulting in immiscible PVC/PMMA mixtures. At w_PMMA ≥ 0.7, the PVC/PMMA mixtures are relatively miscible, giving homogeneous polymer solutions. It means that the miscibility between PVC and PMMA depends on the composition of polymer mixture. However, due to the similar affinity of DMF to PVC and PMMA, PVC/PMMA/DMF solutions exhibit high miscibility between PVC and PMMA at about w_PMMA = 0.5. © 2000 Society of Chemical Industry     

Influence of Solvent–Evaporation Effect on the Structure and Properties of PVDF-g-PNIPAAm Membranes

Temperature-sensitive poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide)(PVDF-g-PNIPAAm) copolymer was synthesized and its flat membranes were prepared through phase inversion method with mixture of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) as solvent in water coagulation bath. The effects of “open time” (solvent–evaporation time) on the structure and performance of membranes were investigated by X-ray photoelectron spectroscopy, field-emission scanning electronic microscopy, contact angle, filtration experiments and static protein adsorption. It was found that the increasing “open time” endowed the membrane with more pores on the surface, higher flux and better hydrophilicity, provided the membrane with lower protein adsorption. Thus, the copolymer membranes showed a good antiprotein fouling.     

Effects of mixed solvents and PVDF types on performances of PVDF microporous membranes

Polyvinylidene fluoride (PVDF) microporous flat membranes were cast with different kinds of PVDFs and four mixed solvents [trimethyl phosphate (TMP)–N,N‐dimethylacetamide (DMAc), triethyl phosphate (TEP)–DMAc, tricresyl phosphate (TCP)–DMAc, and tri‐n‐butyl phosphate (TBP)–DMAc]. The effects of different commercial PVDFs (Solef® 1015, FR 904, Kynar 761, Kynar 741, Kynar 2801) on membrane morphologies and membrane performances of PVDF/TEP–DMAc/PEG200 system were investigated. The membrane morphologies were examined by scanning electron microscopy (SEM). The membrane performances in terms of pure water flux, rejection, porosity, and mean pore radius were measured. The membrane had the high flux of 143.0 ± 0.9 L m^?2 h^?1 when the content of TMP in the TMP–DMAc mixed solvent reached 60 wt %, which was 2.89 times that of the membrane cast with DMAc as single solvent and was 3.36 times that of the membrane cast with TMP as single solvent. Using mixed solvent with different solvent solubility parameters, different morphologies of PVDF microporous membranes were obtained. TMP–DMAc mixed solvent and TEP–DMAc mixed solvent indicated the stronger solvent power to PVDF due to the lower solubility parameter difference of 1.45 MPa^1/2 and the prepared membranes showed the faster precipitation rate and the higher flux. The less macrovoids of the membrane prepared with TEP (60 wt %)–DMAc (40 wt %) as mixed solvent contributed to the higher elongation ratio of 96.61% ± 0.41%. Therefore, using TEP(60 wt %)–DMAc (40 wt %) as mixed solvent, the casting solution had the better solvent power to PVDF, and the membrane possessed the excellent mechanical property. The microporous membranes prepared from casting solutions with different commercial PVDFs exhibited similar morphology, but the water flux increased with the increment of polymer solution viscosity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of poly(vinyl pyrrolidone) concentration and coagulation bath temperature on the morphology,permeability, and thermal stability of asymmetric cellulose acetate membranes

Cellulose acetate (CA) is widely used in membrane processes. In this study, CA (weight‐average molecular weight = 52,000) was mixed with poly(vinyl pyrrolidone) (PVP; weight‐average molecular weight = 15,000) as an additive in 1‐methyl‐2‐pyrrolidone as a solvent. The phase‐inversion method was used for the preparation of flat‐sheet membranes. The effects of PVP concentration and coagulation bath temperature (CBT) on the morphology, pure water permeation flux, and thermal stability of the prepared membranes were studied and are discussed in this article. The solute rejection of the developed CA membranes was quantified with an insulin protein solution. The results showed that an increase in the CBT levels from 0 to 23°C along with an increase in the PVP concentration in the cast film from 0 to 1.5 wt % resulted in an increase in the macrovoid formation in the membrane sublayer, an increase in the pure water flux (PWF), and a decrease in insulin rejection. Further increases in the PVP concentration from 1.5 to 3, 6, and 9 wt % resulted in gradual suppression of the macrovoid formation, a decrease in PWF, and an increase in insulin rejection. Higher PVP concentrations and lower CBT levels also appeared to result in higher glass‐transition temperatures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of the coagulation‐bath temperature on the phase‐separation process of poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) solutions and membrane structures

A poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) copolymer was synthesized, and flat‐sheet membranes were prepared via the phase‐inversion method with N,N‐dimethylformamide (DMF) as the solvent and water as the coagulation bath. The effects of the coagulation‐bath temperature on poly(vinylidene fluoride) (PVDF)/DMF/water and PVDF‐g‐PNIPAAm/DMF/water ternary systems were studied with phase diagrams. The results showed that the phase‐separation process could be due to the hydrophilicity/hydrophobicity of poly(N‐isopropylacrylamide) at low temperatures, and the phase‐separation process was attributed to crystallization at high temperatures. The structures and properties of the membranes prepared at different coagulation‐bath temperatures were researched with scanning electron microscopy, porosity measurements, and flux measurements of pure water. The PVDF‐g‐PNIPAAm membranes, prepared at different temperatures, formed fingerlike pores and showed higher water flux and porosity than PVDF membranes. In particular, a membrane prepared at 30°C had the largest fingerlike pores and greatest porosity. The water flux of a membrane prepared in a 25°C coagulation bath showed a sharp increase with the temperature increasing to about 30°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of surface properties of polysulfone support on the performance of thin film composite polyamide reverse osmosis membranes

In this work, influence of initial conditions and surface characteristics of porous support layer on structure and performance of a thin film composite (TFC) polyamide reverse osmosis (RO) membrane was investigated. The phase inversion method was used for casting of polysulfone (PSf) supports and interfacial polymerization was used for coating of polyamide layer over the substrates. The effect of PSf concentrations that varied between 16 wt % and 21 wt %, and kind of the solvent (DMF and NMP) used for preparation of initial casting solution were investigated on the properties of the final RO membranes. SEM imaging, surface porosity, mean pore radius, and pure water flux analysis were applied for characterization of the supports. The substrate of the membrane, which synthesized with 18 wt % of PSf showed the most porosity and the synthesized RO membrane had the lowest salt rejection. In case of the solvents, the membranes synthesized with DMF presented better separation performance that can be attributed to their lower thickness and sponge‐like structure. The best composition of support for TFC RO membranes reached 16 wt % PSf in DMF solvent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44444.     

Electrospinning of polycarbonate urethane biomaterials

Polycarbonate urethane (PCU) nano-fibers were fabricated via electrospinning using N,N- dimethylformamide (DMF) and tetrahydrofuran (THF) as the mixed solvent. The effect of volume ratios of DMF and THF in the mixed solvent on the fiber structures was investigated. The results show that nano-fibers with a narrow diameter distribution and a few defects were obtained when mixed solvent with the appropriate volume ratio of DMF and THF as 1∶1. When the proportion of DMF was more than 75% in the mixed solvent, it was easy to form many beaded fibers. The applied voltage in the electrospinning process has a significant influence on the morphology of fibers. When the electric voltage was set between 22 and 32 kV, the average diameters of the fibers were found between 420 and 570 nm. Scanning electron microscopy (SEM) images showed that fiber diameter and structural morphology of the electrospun PCU membranes are a function of the polymer solution concentration. When the concentration of PCU solution was 6.0 wt-%, a beaded-fiber microstructure was obtained. With increasing the concentration of PCU solutions above 6.0 wt-%, beaded fiber decreased and finally disappeared. However, when the PCU concentration was over 14.0 wt-%, the average diameter of fibers became large, closed to 2 μm, because of the high solution viscosity. The average diameter of nanofibers increased linearly with increasing the volume flow rate of the PCU solution (10.0 wt-%) when the applied voltage was 24 kV. The results show that the morphology of PCU fibers could be controlled by electrospinning parameters, such as solution concentration, electric voltage and flow rate.     

Preparation of PVC/PVP composite polymer membranes via phase inversion process for water treatment purposes

In this work, new composite membranes were successfully prepared via phase inversion technique using polyvinyl chloride(PVC) and polyvinylpyrrolidone(PVP) as polymers and tetrahydrofuran(THF) and N-methyl-2-pyrrolidone(NMP) as solvents. The prepared membranes have been characterized by scanning electron microscope(SEM), and fourier transforms infrared spectroscopy(FTIR). The scanning electron microscope results prove that the prepared membranes are smooth and their pores are distributed throughout the whole surface and bulk body of the membrane without any visible cracks. The stress–strain mechanical test showed an excellent mechanical behavior enhanced by the presence of PVP in the prepared membranes. The membranes performance results showed that the salt rejection reached 98% with a high flux. This, in turn, makes the prepared membranes can be applied for sea and brackish water treatment through membrane distillation technology.     

Self-assembly of amphiphilic di and triblock copolymers of styrene and quaternized 5-(N,N-diethylamino) isoprene in selective solvents

Self-association of highly asymmetric block copolymers of styrene and quaternized 5-(N,N-diethylamino)isoprene was studied. After quaternization with dimethyl sulfate, the di and triblock copolymers consisted of a long block of polystyrene (PS) with a short poly[5-(N,N,N-diethylmethylammonium)isoprene][methyl sulfate](PAI) block at one or both chain ends, respectively. The aggregates were prepared by first dissolving the copolymers in an organic solvent and then adding water to induce the segregation of the PS chains. Pure DMF, THF or dioxane was used as the organic solvent, as well as DMF/THF mixtures. The critical water content (cwc) and the morphologies were studied as a function of the common solvent, initial copolymer concentration and architecture (di or triblock) by static light scattering and by Transmission Electron Microscopy (TEM), respectively. It was found that both, the cwc and the morphologies of the aggregates are most strongly affected by the nature of the common solvent. Some unexpected behaviors were found for the triblock copolymer. Morphologies of a triblock copolymer in various mixtures of DMF and THF, quenched at determined water contents, were investigated in order to study the degree of morphological control that can be achieved solely as function of the organic solvent composition. Multiple morphologies have been found including equilibrium morphologies and kinetically trapped ones. Finally, the stability of primary micelles prepared in DMF was studied by DLS, upon dilution with DMF and water, and a possible mechanism for the destabilization of the aggregates is proposed.     

溶剂对水处理用PVDF微孔膜结构性能影响

利用N,N-二甲基甲酰胺(DMF)、N,N-二甲基乙酰胺(DMAc)、磷酸三乙酯(TEP)和二甲基亚砜(DMSO)4种溶剂制备PVDF微孔膜,考察溶剂对成膜性能的影响,除了测试膜结构、孔隙率、清水通量等常规指标外,增加膜污染速率指标,研究4种溶剂成膜在实际膜-生物反应器(MBR)内的运行情况,得到4种溶剂成膜结构不同,具有贯穿性指状孔的DMSO溶剂成膜具有最高的孔隙率,高清水通量,并在MBR内表现出最低的污染速率,最适于制备水处理用的PVDF膜;具有海绵状孔的TEP溶剂成膜具有最高的清水通量,高的孔隙率,在MBR内污染速率较低;DMF、DMAc溶剂成膜结构类似,具有不贯穿的指状孔,孔隙率及清水通量均较低,膜污染速率高,不适于水处理MBR用膜。     

Effects of coagulation bath temperature and polyvinylpyrrolidone content on flat sheet asymmetric polyethersulfone membranes

In this study, effects of coagulation bath temperature (CBT) and polyvinylpyrrolidone (PVP K15) concentration as a pore former hydrophilic additive on morphology and performance of asymmetric polyethersulfone (PES) membranes were investigated. The membranes were prepared from a PES/ethanol/NMP system via phase inversion induced by immersion precipitation in a water coagulation bath. The morphology of prepared membranes was studied by scanning electron microscopy (SEM), contact angle measurements, and mechanical property measurements. Permeation performance of the prepared membranes was studied by separation experiments using pure water and bovine serum albumin (BSA) solution as feed. The obtained results indicate that addition of PVP in the casting solution enhances pure water permeation flux and BSA solution permeation flux while reducing protein rejection. Increasing CBT results in macrovoid formation in the membrane structure and increases the membrane permeability and decreases the protein rejection. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Effects of processing parameters on morphology of electrospun polystyrene nanofibers

This study focused on the preparation of electrospun polystyrene (PS) nanofibers. PS solutions were prepared in single (dimethylformamide; DMF, dimethylacetamide; DMAc or tetrahydrofuran; THF) and mixed solvent (DMF/THF and DMAc/THF) systems with and without tetrabutylammonium bromide (TBAB) salt. The effects of PS concentration, solvent system, the addition of salt, appearance and diameter of PS fibers were examined. The average diameter of the as-spun fibers increased upon increasing PS concentration. The morphology of the fibers significantly depended on the properties of the solvents. The obtained fibers were smooth without any beads and their diameters were affected by the amount of THF in the solvent and PS concentration. The beads in the fibers disappeared and the fiber diameter significantly decreased after the addition of TBAB. The smallest diameter and the narrowest diameter distribution of PS nanofibers (376±36 nm) were obtained from 15% PS solution in DMAc with 0.025% w/v TBAB.     

Ultrafiltration membranes obtained by poly(acrylonitrile) grafted onto poly(vinylchloride)

Acrylonitrile (AN) has been grafted onto Polyvinylchloride (PVC) dissolved in Dimethylformamide (DMF) by means of gamma rays from a Co⁶⁰ source. The grafting yield has been studied as a function of irradiation dose and initial AN/PVC ratio in the solution.

The ratio PAN/PVC has been evaluated both in the grafted copolymer and its fractions by infrared spectroscopy. Ultrafiltration membranes have been prepared from the grafted PVC and its fractions, using the phase inversion technique.

The UF performances have been studied as a function of PAN grafted %.

The results show that both water flux and rejection increase with the grafting. Electron microscopy has also been employed to investigate the membrane structure.     

Studies on the electrospun submicron fibers of SIS and its mechanical properties

The submicron fibers were prepared via electrospinning the styrene–isoprene–styrene (SIS) triblock copolymer from a pure solvent of tetrahydrofuran (THF) and a mixed solvent of THF and N, N‐dimethylformamide (DMF). The addition of DMF to THF resulted in a beneficial effect on the fiber formation and the electrospinnability. The obtained results revealed that the fibers were only formed in a narrow solution concentration range of 8–15 wt %; the morphology, diameter, structure, and mechanical performance of as‐spun fibers from PS and SIS solutions were affected by the composition weight ratio and the solution properties; and those from the solution at the intermediate concentration of 10 wt % exhibited a maximum tensile strength and strain at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Investigation of the effect of tetrahydrofuran and acetone as cosolvents in acrylonitrile–butadiene–styrene–based nanofiltration membranes

In this study, novel nanofiltration membranes were prepared with acrylonitrile–butadiene–styrene (ABS)–poly(ethylene glycol)–N,N ‐dimethylacetamide–[tetrahydrofuran (THF)–acetone] as a cosolvent. All of the membranes were prepared by the phase‐inversion method and a casting solution technique. The effects of the cosolvent concentration in the casting solution and the evaporation time before the immersion/precipitation step on the membrane performance and properties were investigated. The prepared membranes were characterized through their permeation flux, salt rejection, and phase‐inversion time values. The salt rejection was increased from 53% for the bare ABS membrane to 73% for the membrane prepared with 40 wt % THF as a cosolvent. The water flux was decreased from 4345 to 1121 cc m^?2 h^?1 with the addition of THF to the casting solution. The addition of acetone to the casting solution improved the water flux from 4345 to 5607 cc m^?2 h^?1 and reduced the salt rejection from 53 to 36%. The evaporation time of THF and acetone led to similar effects on flux and rejection. However, with evaporation time, membranes prepared with acetone were denser than those prepared with THF; this was due to the lower boiling point and higher boiling rate of acetone at the same temperatures. This resulted in greater effects on the ABS performance and structure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44993.     

Solvent-resistant polymeric microfiltration membranes based on oxidized electrospun poly(arylene sulfide sulfone) nanofibers

Polymeric membranes have been widely used in the separation of aqueous system, but there were few studies on the organic solvent-resistant microfiltration (MF) membranes. In this study, organic solvent-resistant oxidized poly(arylene sulfide sulfone)-6 (O-PASS-6) nanofibrous MF membrane with high water flux was prepared through electrospun technology, cold-press, and oxidation treatment. The O-PASS-6 nanofibrous MF membrane was made from the interwoven electrospun uniformly 295 nm nanofibers, and the mean pore size was 0.44 μm. The morphology, chemical structure, and aggregation structure of O-PASS-6 nanofibrous MF membrane were characterized systematically by the scanning electron microscope, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. Investigations on the weight loss, swelling ratio, and microstructure change all revealed that the O-PASS-6 membrane had superior stability in strong polar solvents, such as 1,3-dimethyl-2-imidazolidinone (DMI), dimethylformamide (DMF), and tetrahydrofuran (THF). MF performance results showed that the pure water flux of O-PASS-6 nanofibrous membrane was up to 753.34 L·m⁻²·h⁻¹, and the rejection ratio was 99.9% to 0.2 μm particles. More importantly, after treated by aggressive solvents, the membranes still possessed good MF performance: the water flux was 770.08, 775.66, and 766.36 L·m⁻²·h⁻¹ when soaked in DMI, DMF, and THF for 7 days, respectively, and high rejection ratio also maintained (>99%) for both particles investigated. The O-PASS-6 membrane with good solvent resistance proved to be a promising candidate as a prefiltration membrane to eliminate submicron particles in both sewage and aggressive solvents. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48506.