Immersion Precipitation Process Research Articles

Influence of Clay Content in Membrane Morphology of Polymer Polyamide 6.6/Montmorillonite Clay

Membranes can be defined as a barrier that separates two phases and is widely applied in industrial separation processes. The development of membrane separation processes (PSM) has the major advantage of phase change without separation of components, besides selectivity and simplicity of operation. The addition of mineral fillers in polymers is intended for the cost reduction and increase in rigidity of the materials. When these loads have sizes of nanometric dimensions, this system is called nanocomposites, which exhibit improved properties compared to the pure polymers or conventional composites. Microporous membranes were obtained from polyamide 6.6 nanocomposites of varying amounts of regional montmorillonite clay through the immersion-precipitation process. In general, the membranes showed a filter skin, which contains very small pores and a porous layer, with variations in microstructure, detected by scanning electron microscopy (SEM).

Preparation and characterization of ZrO2/PES hybrid ultrafiltration membrane with uniform ZrO2 nanoparticles

In current or next-generation reuse systems, the development of new classes of antifouling membranes is needed before viable membrane-based approaches for wastewater reclamation can be achieved. In this study, ZrO2/PES hybrid ultrafiltration membranes with uniform ZrO2 nanoparticles were prepared by combining an ion-exchange process with a traditional immersion precipitation process. Hydrous ZrO2 sol was synthesized by addition of anion-exchange resin in N,N-dimethylformamide solvent containing zirconyl chloride. Homogeneous ZrO2/PES casting solution was then obtained by dissolving PES polymer in the ZrO2 sol. The existence and dispersion states of ZrO2 nanoparticles in the resultant membrane matrix were examined by X-ray photoelectron spectrometer, thermogravimetric analysis, scanning electron microscope and transmission electron microscope. The results indicate that the ZrO2 nanoparticles were well dispersed throughout the PES matrix and the diameter of the formed nanoparticles was about 5–10nm. The hydrophilicity of the membranes was determined by measuring the contact angles. The antifouling property was determined by antifouling experiments and atomic force microscopy. The results confirm that the existence of ZrO2 nanoparticles improves the hydrophilicity and reduces protein adsorption of membranes.

Thermodynamic modeling of polyamide-6 (PA-6)/cellulose acetate (CA) blend membrane prepared via casting technique

Abstract Thermodynamic behavior of a ternary system with one low molecular weight component, formic acid (FA) as the solvent, water (non-solvent), and two high molecular weight polymers [polyamide-6 (PA-6) and cellulose acetate (CA)] was investigated using an extended modified Flory-Huggins model. Where, all chemicals were purchased from Leuna Werke AG (Germany). The model was solved by MATLAB SIMULINK software manufactured in the USA. The predicted results from the model explained that the miscibility of the two blend polymers, PA-6 and CA, completed over all compositions at room temperature, and the minimum point where the miscibility of the two polymers completed was in the composition of 0.2 volume fraction of PA-6 at Gibbs free energy change on mixing (ΔGm) of -1.74015 kJ/mole. The critical temperature (Tc) for superiority properties of the polymer blend solution are in the range between the upper critical saturation temperature (UCST) 323K and the lower critical saturation temperature (LCST) 338K. The diffusion model on the solution of the immersion precipitation process in the coagulation bath indicates that the solvent volume fractions increase with time, while the polymer solution volume fraction decreases, due to solvent removal from the polymer solution and membrane formation. According to the mathematical model, it was found that the annealing temperature can affect the densification of the membrane top layer. However, the heat treatment process leads to a decrease in thickness of the membrane bottom layer, as a result of reduced and distributed membrane pores.

Effect of DS on the Structure and Charged Properties of SPSf/PVDF Blend Membranes via Immersion Precipitation Process

Membrane technology is been widely used in drinking water treatment in order to meet the stringent water quality standards. Among the membrane processes, hydrophilic and charged modification of Ultrafiltration(UF) membranes with high filtration efficiency and antifouling properties are being paid more attention. In this work, sulfonated polysulfone (SPSf) with different degree of sulfonation(DS) was used as the modifier to improve the hydrophilic and charged properties of PVDF blend membranes. FTIR and SEM were used to investigate the chemical structure, polymorphism and morphology of the membranes. The charged and hydrophilic properties of the membranes were investigated by zeta potential analyzer and water contact angle instrument. It was found that, for all the investigated cases, the sulfonic acid groups of SPSf could migrate onto the surface of the membranes by surface segregation, which made SPSf/PVDF blend membranes have good charged and hydrophilic properties. DS of polysulfone(PSf) also affected the morphology of the membranes, a tendency toward regular granular structure, larger average pore size and porosity with the addition of SPSf in the membranes was observed. These phenomena all suggested that SPSf/PVDF blend membranes might have a potential application in the drinking water treatment.

Ionic liquid doped polybenzimidazole membranes for high temperature Proton Exchange Membrane fuel cell applications

In this work we propose the use of the ionic liquid 1-H-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([h-mim] Ntf2) as conductive filler in a tailor-made porous, polymeric polybenzimidazole (PBI) support as proton conductive membrane for high temperature (>100 °C) fuel cell applications. PBI is chosen because of its excellent thermal and mechanical stability, while the choice for the ionic liquid is based on its high proton conductivity, low water sorption, thermal stability and low viscosity.The morphology of the porous PBI support is especially tailored for this application using a delayed immersion precipitation process. The macrovoid free porous structure has a volume porosity of 65% and a pore size of approximately 0.5 μm.Pores filling with ionic liquid by direct immersion of the PBI support into molten ionic liquid at 50 °C introduced the membrane proton conductivity. After impregnation the proton conductivity of this PBI/IL membrane reached a value of 1.86 mS cm−1 at 190 °C. Fuel cell performance of these membranes clearly exceeds that of Nafion 117 at temperatures above 90 °C. A power density of 0.039 W cm−2 is obtained at the intended operation temperature of 150 °C, which proofs that the developed PBI/IL membrane can be considered as a serious candidate for high temperature fuel cell applications.

Improved surface property of PVDF membrane with amphiphilic zwitterionic copolymer as membrane additive

An attempt to improve hydrophilicity and anti-fouling properties of PVDF membranes, a novel amphiphilic zwitterionic copolymer poly(vinylidene fluoride)-graft-poly(sulfobetaine methacrylate) (PVDF-g-PSBMA) was firstly synthesized by atom transfer radical polymerization (ATRP) and used as amphiphilic copolymer additive in the preparation of PVDF membranes. The PVDF-g-PSBMA/PVDF blend membranes were prepared by immersion precipitation process. Fourier transform infrared attenuated reflection spectroscopy (FTIR–ATR) and X-ray photoelectronic spectroscopy (XPS) measurements confirmed that PSBMA brushes from amphiphilic additives were preferentially segregated to membrane–coagulant interface during membrane formation. The morphology of membranes was characterized by scanning electron microscopy (SEM). Water contact angle measurements showed that the surface hydrophilicity of PVDF membranes was improved significantly with the increasing of amphiphilic copolymer PVDF-g-PSBMA in cast solution. Protein static adsorption experiment and dynamic fouling resistance experiment revealed that the surface enrichment of PSBMA brush endowed PVDF blend membrane great improvement of surface anti-fouling ability.

Performance Improvement of Polysulfone Ultrafiltration Membrane Using Well-Dispersed Polyaniline–Poly(vinylpyrrolidone) Nanocomposite as the Additive

Well-dispersed polyaniline–poly(vinylpyrrolidone) (PANI–PVP) nanocomposite was synthesized through dispersion polymerization and then used as a novel additive to prepare a polysulfone (PSf)/PANI–PVP nanocomposite membrane via immersion precipitation process. During membrane formation, a portion of PVP acted as a pore-forming agent while another PANI–PVP nanocomposite, combined by hydrogen bonds between carbonyl groups of PVP and N-hydrogen groups of PANI, acted as a hydrophilic modification agent. The addition of PANI–PVP nanocomposite increased membrane surface pore size, porosity, and hydrophilicity. Pure water fluxes of PSf/PANI–PVP nanocomposite membranes were 1.8–3.5 times that of PSf membrane with a slight change of bovine serum albumin (BSA) rejection. The membrane antifouling property was examined by the cross-flow ultafiltration using BSA solution as the model system. The results of flux decline behavior and flux recovery ratio showed that PSf/PANI–PVP nanocomposite membranes had an excellent ant...

Asymmetric membranes with interpenetrating proton-conducting morphology made by a combination of immersion precipitation and photopolymerization

► Asymmetric membranes with interpenetrating proton-conducting morphology prepared. ► Immersion precipitation combined with photopolymerization and crosslinking. ► Higher conductivity and better methanol barrier compared to Nafion achieved. A new method for the preparation of asymmetric membranes with an interpenetrating proton-conducting morphology, which consists of cross-linked sulfonic acid functionalized ionomers embedded within a matrix of a thermally-resistant, glassy polymer is presented. This method combines a traditional immersion precipitation process for making membranes with photopolymerization and crosslinking of functional monomers included in the casting solution. The resulting membranes have an integral top skin layer with fine proton-conducting channels on top of a coarser proton-conducting support. In-plane conductivities of some of these membranes measured at ambient temperature were significantly higher than the conductivity of Nafion membranes, while having improved methanol barrier properties. An increase in functionality and molecular weight of crosslinking agents, as well as a selection of materials to promote delayed, rather than instantaneous liquid–liquid demixing were associated with significant improvements in membrane conductivity. Based on the results, a potential use of such membranes in direct methanol fuel cells looks promising.

Effects of pluronic F127 on the polymorphism and thermoresponsive properties of PVDF blend membranes via immersion precipitation process

AbstractAmphiphilic copolymer Pluronic F127 was used as macromolecular additive to investigate the polymorphism and thermoresponsive properties of poly(vinylidene fluoride) (PVDF) membranes. Fourier transform infrared spectrometer (FTIR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) were conducted to characterize the polymorphism and morphology of PVDF/F127 blend membranes. FTIR results indicated that F127 existed stably in the blend membranes, and lower F127 concentration in the cast solution was in favor of the formation of α‐crystal phase, but higher F127 concentration could promote the formation of β‐ and γ‐crystal phase in PVDF membranes. The results of XRD also confirmed these phenomena. With the increase of F127 in the cast solutions, a more sponge‐like structure appeared at the bottom surface of the membranes as investigated by SEM. PVDF/F127 blend membranes also exhibited good thermoresponsive properties. The water flux of the membranes increased distinctly with the increase of the experimental temperature, decreased with the decrease of the temperature, and the increasing and decreasing curves were almost overlapped. Contact angle measurement and permeation experiment indicated that the blend membranes had good hydrophilicity and fouling resistance. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Performance improvement of polysulfone ultrafiltration membrane using PANiEB as both pore forming agent and hydrophilic modifier

Emeraldine base polyaniline (PANiEB), which is mostly soluble in N-methyl-2-pyrrolidone (NMP) and slightly soluble in water, was used as the additive to prepare polysulfone (PSf)/PANiEB membrane via immersion precipitation process. The behavior of PANiEB during membrane formation and the effect of PANiEB addition on membrane structure and performance were investigated. During membrane formation, a portion of PANiEB, located near the surface of the casting film, could diffuse out of the casting film along with NMP into the coagulation bath and act as pore forming agent. The other portion of PANiEB could remain in the prepared membrane and act as hydrophilic modifier. All the PSf/PANiEB membranes had higher porosity, larger surface pore size, more vertically interconnected finger-like pores and less macrovoids than PSf membrane. PSf/PANiEB membranes exhibited stable pure water flux during membrane compaction at 0.30 MPa TMP and slower pure water flux decline at 0.5 MPa TMP than PSf/polyvinylpyrrolidone (PVP) membranes. Pure water fluxes of PSf/PANiEB membranes were 1.7–2.8 times that of PSf membrane while rejection property including bovine serum albumin, egg albumin and trypsin rejections changed slightly. BSA ultrafiltration experiment showed that PSf/PANiEB membranes had higher flux and better antifouling property than PSf membrane.

Studies on the Relationship between Morphology and Water Flux of PVDF/PU Blend Membranes

Polyvinylidene fluoride/polyurethane (PVDF/PU) blend membranes were made via immersion precipitation process, the surface morphologies and the micro-porous structures of the blend membranes were analyzed using scanning electronic microscope (SEM) and fractal theory, the water flux change with the operation pressure of the blend membranes was investigated, and the relationship between blend membrane morphology and water flux was discussed. The results showed that, the water flux of the resulting blend membranes was increased, and the contribution of different structures to water flux was in the following order: cross-section finger-shaped porous defects > cross-section through holes > blend membrane surface pores. In addition, water flux of the blend membranes was also related to the deformability of PU.

In situ preparation of Al-containing PVDF ultrafiltration membrane via sol–gel process

Recently, inorganic nanoparticles blended within polymeric membranes have shown improved antifouling performance in wastewater treatment. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface. In this study, a new method for in situ preparation of Al-containing PVDF ultrafiltration membranes to improve the dispersion of nanoparticles is reported. The strategy of this method is to combine sol–gel process with traditional immersion precipitation process. Al sol was synthesized by the addition of anionic exchange resin in N,N-dimethylformamide (DMF) solvent containing aluminum chloride. Homogeneous Al-containing PVDF casting solution was then obtained by dissolving PVDF polymer in the Al sol. The membrane formation mechanism was investigated by precipitation kinetics and morphology. Results indicate that the addition of Al species can accelerate phase inversion of casting solution. Scanning electron microscopic images show that a typical transition from sponge-like structure to finger-like structure occurred with increasing Al species content. The existence and dispersion states of Al species in the resultant membrane matrix were further examined by transmission electron microscope and X-ray photoelectron spectrometer. The results indicate the Al species nanoparticles were well dispersed throughout PVDF matrix. Dynamic BSA fouling resistance experiments demonstrate the Al-containing PVDF membranes possess improved separation performances over the pure PVDF membranes.

Structure Design and Properties of Porous PVDF Membranes Based on Ionic Liquid

Ionic liquid was used as the pore-forming additive to design the structure and properties of PVDF membranes. The crystal structure, morphology and the wettability of the membranes was investigated by Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle measurement. The results of FTIR and XRD suggested that ionic liquid could make α crystal phase in pure PVDF membrane totally transformed into β crystal phase via immersion precipitation process. SEM results also indicated that ionic liquid was a good pore-forming additive, which was in favor of the formation of the pore structure in the membranes. Contact angle results showed that the surface hydrophobic of PVDF membrane increased with the addition of ionic liquid in the casting solution. These results suggested that ionic liquid may be found its further application in the preparation of piezo-electric PVDF films with β crystal phase, and oil/water separation membranes.

Exploring the Thermodynamic Aspects of Structure Formation During Wet-Spinning of Polyacrylonitrile Fibres

Wet-spun polyacrylonitrile fibres are the main precursor for high strength carbon fibres. The properties of carbon fibres strongly depend on the structure of the precursor fibre. Polyacrylonitrile fibres were spun from solutions with varying solvent/nonsolvent content and different draw ratios. Wet-spinning is an immersion precipitation process, thus thermodynamic affinity of spinning dope to the coagulation medium was considered as the driving force of phase-separation, while viscosity of the solution accounted for the resistive force against phase separation and growth of the nucleated voids. Thermodynamic affinity was estimated by modifying Ruaan’s theory and viscosity of the solution was assessed on-line by measuring flow rate and back pressure at the spinneret. Hence, the parameter X (thermodynamic affinity/viscosity) was introduced to predict the porous morphology of the fibres. Generally, an increase in X led to fibres with higher porosity. A combination of electron scanning microscopy (SEM), porosimetry and thermoporometry was applied to fully characterize microstructure of fibres. Based on image analysis of SEM micrographs and data obtained from thermoporometry and porosimetry fractions of dense polymer ligament, micrometer size voids (macrovoids) and nanometer size voids (nanovoids) were estimated. Increasing polymer content or nonsolvent content in the spinning dope caused an increase in the solution viscosity and resulted in fibres with lower porosity. Imposing drawing on the as-spun fibres further decreased the porosity. Drawing also shifted the size distribution of nanovoids toward smaller values.

Characterization of temperature-sensitive membranes prepared from poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) copolymers obtained by atom transfer radical polymerization

In this paper, poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) (PVDF-g-PNIPAAm) copolymers were synthesized directly via grafting temperature-sensitive material NIPAAm on PVDF by atom transfer radical polymerization (ATRP). The chemical structure of the graft copolymers was characterized by Fourier transform infrared (FTIR) and 1H-NMR spectroscopy. The temperature-sensitive membranes were prepared from the PVDF-g-PNIPAAm copolymers by the immersion precipitation process of the phase inversion method. The chemical composition and pore structure of the PVDF-g-PNIPAAm membranes were studied by X-ray photoelectron spectroscopy (XPS) and an automatic mercury porosimeter, respectively. The effects of temperature on pure water flux and bovine serum albumen (BSA) rejection ratio of the membranes were also investigated. The results showed that the grafted PNIPAAm chains tended to enrich on the surfaces of the membranes or the membrane pores during the membrane-forming process. Pore diameter and porosity of the copolymer membranes were larger than those of the pristine PVDF membranes. Also, the PVDF-g-PNIPAAm membranes could exhibit temperature-sensitive performance in water flux and BSA rejection measurements.

Role of Marangoni Instability in Fabrication of Axially and Internally Grooved Hollow Fiber Membranes

Hollow fiber membranes (HFMs) are extensively used in different industrial applications. Under some controlled fabrication conditions, axially aligned grooves can be formed on the HFM inner surface during typical immersion precipitation-based phase inversion fabrication processes. Such grooved HFMs are found to be promising for nerve repair and regeneration. The axially aligned grooves appearing on the inner surface of the membrane are considered as hydrodynamic instability patterns. During the immersion precipitation process, a transfer of solvent takes place across the interface between a polymer solution and a nonsolvent. This solvent transfer induces gradients of interfacial tension that are considered to be the driving mechanism for Marangoni instability. The onset of the stationary instability is studied by means of a linear instability theory, and the critical and maximum wavenumbers are determined and discussed in terms of the dimensionless groups characterizing the system: viscosity ratio, diffusivity ratio, Schmidt number, crispation number, adsorption number, Marangoni number, and the polymer bulk concentration. A good agreement is found between the predicted wavelength of the most dangerous wave and the experimental groove width. Consequently, solutal Marangoni instability can explain the groove formation mechanism in HFM fabrication.

Ranking the key parameters of immersion precipitation process and modeling the resultant membrane structural evolution

AbstractKey parameters coupling with the instantaneous nucleation concept (ie, the Big Bang analogy) was used to model immersion precipitation process. The merits of the acquired model were verified via comparing its predictions with experimental results of two well‐prepared and characterized cellulose acetate (CA) and polyacrylonitrile (PAN) membranes. A morphology predictable map, ΔPη−1 versus ϕ1, was constructed, where ΔP, η and ϕ1 are osmotic pressure difference between nonsolvent and dope solution, dope viscosity and intruded nonsolvent volume fraction into the dope, respectively. The phase separation map, ΔPη−1 (proportional with apparent system diffusivity with the unit of time−1) versus ϕ1 showed three regimes which, at least qualitatively, depicted the correct morphological evolution trends of the studied systems. Phase separation in regime one of CA membrane with the longest delayed time or lowest ΔPη−1, led to bead‐like morphology. CA membrane with the shortest elapsed time or highest ΔPη−1, separated to finger‐like morphology in regime three. Finally, phase separation in the intermediate regime of CA membrane, ended up to sponge‐like morphology. Phase separation time scales of the PAN membranes versus intruded nonsolvent into the dope solution were located in finger‐like region of the CA membrane, which its downward transition lowered the fingers population. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Polymorphism in porous poly(vinylidene fluoride) membranes formed via immersion precipitation process

Porous poly(vinylidene fluoride) (PVDF) membranes were prepared via immersion precipitation process from PVDF/dimethyl sulfoxide (DMSO)/water system. By manipulating precipitation temperature and PVDF concentration in casting solution, the polymorphism in the formed porous membranes was studied. Membrane morphologies were observed by field emission scanning electron microscopy (FESEM) and thermal behaviors of membranes were examined by differential scanning calorimetry (DSC). Wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) were employed to analyze the crystalline structures of the overall membranes and the surface layers. It was found that, for all the investigated cases, PVDF mainly crystallized into the α form crystalline structure in the overall membrane, while the α and β phases coexisted in the surface layers. The total crystallinity of the membrane and the β/α phase ratio in the surface layers increased simultaneously while raising PVDF concentration in casting solution or reducing precipitation temperature.

Morphologic analysis of porous polyamide 6,6 membranes prepared by phase inversion

Porous polyamide membranes have been commercialized for many years and in nowadays widely used in fine separation processes often manufactured by the immersion precipitation process. This process for the membrane preparation involves precipitation of an incipient casting dope metastable. In this paper the morphology of polyamide 6,6 membranes prepared by phase inversion from ternary system (water/chloridric acid/polyamide 6,6) was investigated. Depending upon the precipitation conditions membranes the morphologics and hydraulic properties that reflect the compartment of membranes. The MP10 and MP15 membranes had been characterized in the FT-IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The formation of the dense layer can be observed in the scanning electronic micrographs (SEM). It can be observed that approximately 60% of the distribution of the pores were found in the band between 7 and 6nm (mesoporous system). It can be concluded that the gotten membrane is mixing, therefore presents a dense part and this membranes was a promising candidate for nanofiltration (NF) and osmosis reversal (OR) process.

Study on the interfacial micro-voids of poly(vinylidene difluoride)/polyurethane blend membrane

The poly(vinylidene difluoride)/polyurethane (PVDF/PU) blend membrane was prepared using the method of immersion-precipitation process. The influence of the miscibility of the two polymers on the formation of the interfacial micro-voids (IFMs) of the blend membranes was analyzed by the theory of thermodynamics and discussed with DMA, DSC and SEM. The effect of working pressure on the pure water flux (PWF) of the IFMs was also studied using membrane instrument. Results show that the IFMs are formed due to the miscibility of PVDF and PU. The existence of IFMs attributes much to the PWF of the PVDF/PU blend membrane, and the PWF of the IFMs is related not only to the miscibility of PVDF and PU but also to the deformation of IFMs under working pressure.