Phase separation behavior of poly(ethylene terephthalate)/(trifluoroacetic acid/dichloromethane)/water system for wet phase inversion membrane preparation

Polymeric membrane fabrication by the phase inversion technique requires substantial thermodynamics knowledge of the studied system. The objective of this work is to investigate the phase separation behavior of the poly(ethylene terephthalate) (PET)/[trifluoroacetic acid + dichloromethane (DCM)]/water system by the titulometric method, and evaluate the system characteristics aiming at membrane fabrication by phase inversion technique. The results show that the amount of nonsolvent at the cloud point decreases as the amount of DCM increases in the polymeric solution. The cloud point compositions are well-fitted to the linearized cloud-point curve for all studied systems, confirming that they have the required characteristics of a membrane forming system. The fabrication by wet phase inversion technique provides membranes with porous structure, thin top layer and the addition of DCM in PET casting solutions suppress the macrovoid formation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47263.     

Microporous anisotropic phase inversion membranes from bisphenol A polycarbonate: Effect of additives to the polymer solution

Phase inversion is a very flexible technique to obtain membranes with a large sort of morphologies. Membrane properties can vary greatly depending on the kind of polymer system used. Bisphenol A polycarbonate (PC) could be used as a phase inversion membrane base polymer, and presents very good properties. Nevertheless, very little information on membrane preparation using PC and the phase inversion process can be found in the literature. In this work flat‐sheet microporous membranes were obtained by the phase inversion process using the immersion precipitation technique. A new polymer system was studied, consisting of polycarbonate, N‐methyl‐2‐pyrrolidone as solvent, water as the nonsolvent, and an additive. The influence of some parameters on membrane morphology, such as polymer solution composition, exposition time before immersion into the precipitation bath, and the kind of additive was investigated. Precipitation was followed using light transmission experiments and membrane morphology was observed through Scanning Electron Microscopy (SEM). The viscosity and cloud points of all polymer solutions were also determined. The results were related to the studied synthesis parameters, using the basic principles of membrane formation by the phase inversion technique, looking forward to establishing criteria to control the morphology of flat‐sheet membranes using polycarbonate as the base polymer. The results showed that both additives were able to increase pore interconnectivity and even suppress macrovoid formation. The decrease in the miscibility region of the polymer system and increase in mass transfer resistance are found to be the determining factors during polymer solution precipitation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3085–3096, 2002     

Nanofiltration membranes based on PA6/EVOH with variable composition and morphology

Nanofiltration PA6/EVOH membranes were prepared through a nonsolvent induced phase separation technique. The effects of polymer concentration in the solution and solvent evaporation time on the performance and morphology of the resulting membranes were investigated by cloud point titration, permeation, and scanning electron microscopy (SEM). Experimental cloud point data for various prepared membranes suggested that polymer solutions with higher concentrations of PA6/EVOH need a less content of nonsolvent. SEM observations show that an increase in polymer concentration leads to formation of a thin dense layer on the surface of the membrane thanks to pore size reduction. However, dense top layer of membrane becomes thicker as polymer concentration increases from 15 wt% to 20 wt%. The performance of membranes reveals a decrease with polymer concentration in casting solution. By contrast, Polyamide/Poly(ethylene‐co‐vinyl alcohol) membranes show an optimal performance with various formic acid evaporation times. J. VINYL ADDIT. TECHNOL., 25:E28–E34, 2019. © 2018 Society of Plastics Engineers     

Different parameters controlling the initial solubility of two thermoplastics in epoxy reactive solvents

The influence of different factors on the miscibility of diglycidyl ether of bisphenol A (DGEBA)/thermoplastic blends was studied. DGEBA/poly(ether imide) (PEI) blends exhibited upper critical solution temperature behavior. The addition of a trifunctional epoxy [triglycidyl para‐amino phenol (TGpAP)] increased the miscibility window. The addition of diamines as hardeners could also increase [4,4′‐methylene‐bis(3‐chloro‐2,6‐diethylaniline) (MCDEA)] or decrease (4,4′‐diaminodiphenylsulfone) the miscibility window. DGEBA/poly(ether sulfone) (PES) blends showed lower critical solution temperature behavior. The addition of TGpAP had an effect similar to that for PEI blends, but the presence of MCDEA as a hardener decreased the miscibility of epoxy/PES blends. The modeling of the cloud‐point curves was performed with the Flory–Huggins equation (Flory, P. J. Principles of Polymer Chemistry; Cornell University Press: Ithaca, NY, 1953; p 672) according to the procedure developed by K. Kamide, S. Matsuada, and H. Shirataki (Eur Polym J 1990, 26, 379), with the interaction parameter used as the fitting parameter. A phenomenological model that takes into account the molar mass of DGEBA and the amount of TGpAP is proposed and is found to predict the cloud‐point temperature of any TGpAP/DGEBA/PEI blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1385–1396, 2002     

Preparation of polyvinylchloride membranes from solvent mixture by immersion precipitation

In this study, polyvinylchloride (PVC) membranes were prepared through the immersion precipitation method using a mixture of two solvents (tetrahydrofuran (THF) and dimethyl formamide (DMF)), which had different affinities with the nonsolvent (water). Membranes prepared from PVC/THF/water system showed a sponge‐like structure with isolated pores, which were impermeable to water even at a feed pressure of 20 bars, whereas those prepared from PVC/DMF/water exhibited a porous macrovoid containing morphology with a high water flux. The precipitation time and polymer concentration profiles were calculated by using a simple mathematical model and were in good agreement with the experimental findings on PVC/THF/water and PVC/DMF/water systems. By using a mixture of DMF and THF as solvent and changing the mixed solvent composition, membranes with different morphologies from sponge‐like to macrovoid containing were obtained. The membranes showed no water flux below a DMF concentration of 50 wt % and then became increasingly permeable with increasing DMF content in the casting solution. Measurement of the system cloud points showed a linear change of system thermodynamics with variation of the mixed solvent composition. The obtained results showed that although the system thermodynamics could explain the overall behavior of the system, but the local changes such as change of membrane performance from impermeable to permeable at a certain mixed solvent composition could not be explained by the thermodynamics alone. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40206.     

Interactions in PEG/Aerosil® and PLA/Aerosil® composites described by IGC-determined Flory-Huggins χ 23 parameter

Nonsolvent Induced Phase Separation (NIPS) is among the most well-known methods for membrane fabrication in which the phase separation behavior of the polymer solution is one factor that governs the structure of the membrane ultimately obtained. In this study, phase separation behavior of the polyetherimide (PEI)-casting dope was investigated for different types of coagulants and nonsolvent additives. Cloud point data were obtained by the titration method on the ternary polyetherimide/solvent/coagulant diagram from a limited number of experiments. The whole cloud point curves were then drawn by calculation using the fitting parameters based on the linearized cloud point relation (LCP). In the first part, water, methanol, ethanol, glycerol, and acetic acid were used as the coagulants for the PEI/NMP solution. The cloud point curves obtained for the above coagulants indicated that water has the strongest coagulation power among them. In the second part, methanol, ethanol, glycerol, and acetic acid were used as nonsolvent additives to NMP in different (nonsolvent additive/NMP) mass ratios. The latter (NMP?+?nonsolvent additive) mixtures were then used as the solvents to prepare PEI/(NMP?+?nonsolvent additive) solutions. The cloud point data obtained for the above solutions using water as a coagulant indicated that the cloud point curves shift toward the polymer/solution axis as the (nonsolvent additive/NMP) mass ratio increases.

Effect of Casting Solution on Morphology and Performance of PVDF Microfiltration Membranes

The effects of preparation‐influencing parameters such as polymer concentration, thickness of casting solution, and type of solvent on morphology and performance of poly(vinylidene difluoride) (PVDF) microfiltration membranes for the treatment of emulsified oily wastewater were investigated. Flat‐sheet membranes were prepared from a casting solution of polymer and additive in various solvents by immersing the prepared films in nonsolvent‐containing mixtures of water and 2‐propanol. The membranes were characterized using scanning electron microscopy. Increasing the polymer concentration and membrane thickness significantly affected the pore size, leading to permeate flux decrease. An attempt was made to correlate the effect of the solvent on membrane morphology and performance employing solubility parameters between solvent and nonsolvent).     

Synthesis and characterization of poly(ether‐block‐amide) membranes for the pervaporation of organic/aqueous mixtures

We made poly(ether‐block‐amide) membranes by casting a solution on a nonsolvent surface. The effects of the solvent ratio (n‐butanol/isopropyl alcohol), temperature, and polymer concentration on the quality of the membranes were studied. The results show that the film quality was enhanced with increasing isopropyl alcohol ratio in the solvent. This behavior was related to the reduction of the solution surface tension and the interfacial tension between the solution and nonsolvent. Uniform films were made at a temperature range of 70–80°C and a polymer concentration of 4–7 wt %. The morphology of the membranes was investigated with scanning electron microscopy. The qualities of the films improved with increasing isopropyl alcohol ratio in the solvent. With these membranes, the pervaporation of ethyl butyrate (ETB)/water and isopropyl alcohol/water mixtures was studied, and high separation performance was achieved. For ETB/water mixtures, with increasing ETB content, both the permeation flux and separation factor increased. However, for isopropyl alcohol/water mixtures, with increasing isopropyl alcohol content, the permeation flux increased, but the separation factor was diminished. Increasing temperature in a limited range resulted in a decreasing separation factor and an increasing permeation flux. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Solubility and phase separation of poly(L,D‐lactide) copolymers

In this study, the solubility and precipitation properties of medical‐grade stereocopolymers were investigated. The solubility of the polymers was tested with eight different organic solvents and four nonsolvents. The solubility of poly(L,D ‐lactide) stereocopolymers was highly dependent on the L /D ratio of the copolymer. The phase‐separation ability was tested by cloud‐point titration with a solvent and a nonsolvent. The solvent was in all cases dichloromethane, and the nonsolvents were n‐hexane, methanol, ethanol, and isopropyl alcohol. The results showed that n‐hexane was the most efficient nonsolvent. Methanol and ethanol showed quite similar precipitation properties. Isopropyl alcohol was the least efficient nonsolvent of those studied. Also, the L /D ratio of the copolymer had an effect on the precipitation properties. The precipitation happened most easily when the L content was high. The molecular weight of the copolymer had only a slight effect on the phase separation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ionically crosslinked poly(acrylic acid) membranes. III. Reverse osmosis results for dry cast membranes

The reverse osmosis properties of ionically crosslinked polyacrylic acid membranes were investigated in terms of the salt separation of a 0.1% NaCl solution and water flux. The membranes were synthesized and crosslinked with the metal ion Al³⁺ via the dry casting technique described in a previous paper. The effect of such variables as the polymer concentration in the casting solution, the ratios of solvents used (DMF/H₂O), the ratio of monomer to the crosslinking agent (AA/Al), the evaporation time and temperature, and the nonsolvent nature and treatment times were studied in some detail. The most important variable was found to be the length and nature of the treatment in the nonsolvents acetone and methanol. In the best series of the membranes that were synthesized, fluxes of more than 3.0 gfd, with salt separations at the 80%–85% level, were obtained.     

Preparation and characterization of PES/CA microporous membranes via reverse thermally induced phase separation process

The blend polyethersulfone (PES)/cellulose acetate (CA) flat‐sheet microporous membranes were prepared by reverse thermally induced phase separation (RTIPS) process. The effects of CA content and coagulation bath temperature on membrane structures and properties were investigated in terms of membrane morphology, water contact angle, permeation performance, and mechanical properties. The cloud point results indicated that the cloud point decreased with the increasing content of CA. When the coagulation bath temperature was lower than the cloud point, the membrane formation process underwent nonsolvent induced phase separation (NIPS) process and dense skin layer and finger‐like structure were formed in membranes. These membranes had lower pure water flux and poor mechanical properties. But when the coagulation bath temperature was higher than the cloud point, the membrane formation process underwent RTIPS process. The porous top surface as well as porous cross‐section of the membranes were formed. Therefore, high pure water flux and good mechanical properties were obtained. The contact angles results indicated that the hydrophilicity of the prepared membranes improved obviously with the addition of CA. When the content of CA was 0.5 wt% and the membrane formation temperature was 323K, the PES/CA microporous membrane which was prepared via the RTIPS process displayed a optimal permeability of the pure water flux of 816 L m^?2 h^?1 and the BSA rejection rate of 49.5%, which showed an increase of 48.9% and 23.6% than that of pure PES membrane, respectively. Moreover, the mechanical strengths of the membranes obtained by RTIPS process were better than those membranes prepared by NIPS process. POLYM. ENG. SCI., 58:180–191, 2018. © 2017 Society of Plastics Engineers     

Trade-off between thermodynamic enhancement and kinetic hindrance during phase inversion in the preparation of polysulfone membranes

Polysulfone membranes were prepared via the diffusion-induced phase inversion process from casting solutions consisting of polysulfone, dimethyformamide, and polyvinyl pyrrolidone as a polymeric additive. The effect of PVP added in casting solutions was analyzed by measuring the prepared membranes' morphology and water permeability. Variations in a casting solution's thermodynamic and kinetic properties caused by PVP addition suggest that the thermodynamic variation works in favor of the enhancement of demixing in the casting solution, but the rheological variation induces the opposite trend, or the delay of demixing. When prepared by the immersion coagulation into a water bath, the solidified membranes' structural and functional properties indicate that the coagulation of cast solutions was affected by the trade-offrelationship between thermodynamic enhancement and kinetic hindrance. With a small amount of PVP in the casting solution, the thermodynamic driving force played a major role on solution demixing, inducing the demixing enhancement, corresponding to the acceleration of phase separation due to the PVP's nonsolvent effect. Consequently, the PVP acts as a phase separation enhancer, resulting in both macropore enlargement and permeate flux increase. With more addition of PVP, however, the macropore structure and the water permeability were suppressed rather than enlarged or increased. These phenomena reflect that the demixing of the cast solution was delayed, with the kinetic hindrance offsetting the thermodynamic effect for phase separation enhancement.     

非溶剂对浇铸SPEEK膜性能的影响

首次采用磺化聚醚醚酮/N,N-二甲基甲酰胺(SPEEK/DMF)和非溶剂(四氯乙烯或对二甲苯)组成的铸膜液制备了SPEEK膜.采用交流阻抗法和隔膜扩散法分别考察了膜的质子传导性和透水性能.结果表明,由于在SPEEK/DMF中添加非溶剂,膜的透水率增加了约30％,质子导电率提高了50％左右.非溶剂的加入影响了铸膜液中聚合物的形态、尺寸和团聚情况,从而影响了成膜后膜的性能.本研究提出的控制膜微相结构的新方法将有助于提高SPEEK膜燃料电池性能.     

倒相法制备聚偏氟乙烯多孔膜大孔的研究

利用倒相法制备了聚偏氟乙烯(PVDF)多孔膜,扫描电镜表征了膜的微观结构。研究发现,在w(PVDF)=5 0%～20 0%的铸膜液中,大孔孔隙率及孔径尺寸随着PVDF质量分数的升高而降低;在乙醇与水组成的凝固浴中,膜的大孔孔隙率及孔径尺寸随乙醇体积分数的增加而降低,在φ(ethanol)=50%时大孔结构消失,多孔膜由指状大孔结构转变为海绵状结构。分析了大孔形成机理。     

Liquid-liquid phase separation in polysulfone/solvent/water systems

The cloud point curves for polysulfone (PSf)/solvent/water systems were determined by a titration method. A small amount of water was needed to induce liquid-liquid demixing and the temperature effect was small. From numerical calculations, it was found that the binary interaction parameters for the PSf/solvent/water system enlarges the homogeneous region in the phase diagram with a smaller nonsolvent-polymer interaction parameter χ₁₃, a greater nonsolvent-solvent interaction parameter χ₁₂, and a smaller solvent-polymer interaction parameter χ₂₃ and the effect of polymer molecular weight was negligible except in the range of low molecular weight. The phase diagrams, calculated with constant χ₁₂ that was chosen from the concentration-dependent interaction parameter g₁₂ value of the concentration range, were similar to the results obtained with g₁₂. The slope of the tie lines indicated that demixing of the ternary system occurred at relatively similar nonsolvent concentration in both phases. A value of 2.7 for the water-PSf interaction parameter was obtained by fitting the experimental cloud point curve with the calculated binodal lines. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2643–2653, 1997     

EFFECT OF NONSOLVENT ADDITIVES ON THE PORE SIZE AND THE PORE SIZE DISTRIBUTION OF AROMATIC POLYAMIDE RO MEMBRANES

In this paper discussions are made on the effect of nonsolvent swelling agents on the average pore size and pore size distributions at the surface of polyamide membranes which result from casting solutions involving above nonsolvent swelling agents.

The size of the polymer aggregate in the film casting solution and the size of polymer network pores are correlated to physicochemical data of ions which constitute the electrolytes used as nonsolvent swelling agents. As such ionic properties the charge density and the free energy of transition of ions from polyamide phase to water phase were considered. The validity of the correlation is limited in a range of casting solution composition where the polymer concentration in the casting solution is close to the limiting concentration of polymer at the phase boundary and the molar ratio of the nonsolvent swelling agent to the amide group involved in the polyamide polymer is equal to or slightly more than 0.7.     

Structure Formation of Integral Asymmetric Composite Membranes of Polystyrene‐block‐Poly(2‐vinylpyridine) on a Nonwoven

The formation of an integral asymmetric membrane composed of a cylinder‐forming polystyrene‐block‐poly(2‐vinylpyridine) on a nonwoven by using solvent casting followed by solvent/nonsolvent exchange (phase inversion) is reported for the first time. The influence of parameters such as solvent composition, evaporation time of the solution‐cast block copolymer film before phase inversion, and immersion bath temperature is demonstrated. The optimized membranes are characterized in terms of stimuli‐responsive water flux properties. The morphologies of the membranes as well as of the bulk of the block copolymer are imaged by scanning force microscopy, scanning electron microscopy, and transmission electron microscopy.

     

Phase behavior and mechanism of formation of protofiber morphology of solution spun poly(acrylonitrile) copolymers in DMF‐water system

Phase diagrams of a series of copolymers of acrylonitrile (AN) and acrylic acid (AAc) were constructed using linearized cloud point correlation. The miscibility region in the phase diagram was found to increase with the increase in AAc content of the copolymers. For various compositions, χ₁₃ (polymer–water interaction parameter) values were estimated by sorption experiment. As the hydrophilic nature of the polymer increased with the increase in the content of acrylic acid, the χ₁₃ interaction parameter was found to decrease from poly(acrylonitrile) homopolymer to its copolymer with 50 mol % acrylic acid (AA50B). The polymer–solvent interaction parameters (χ₂₃) and composition at the critical points for all the polymers were determined by fitting the theoretical bimodal curves to the experimental cloud point curves using Kenji Kamide equations. The polymer composition at the critical point was found to increase by 400% with increasing AAc content. The polymers were solution spun in DMF‐water coagulation bath at 30°C and their protofiber structures were investigated under scanning electron microscopy. The observed morphological differences in protofibers were explained on the changes brought about in the phase separation behavior of the polymer–solvent–nonsolvent systems. The copolymers with higher acrylic acid content could be solution spun into void free homogeneous fibers even at conditions that produced void‐filled inhomogeneous fibers in poly(acrylonitrile) and its copolymers with lower AAc content. The experiments demonstrate the important role of thermodynamics in deciding the protofiber morphology during coagulation process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Liquid–liquid phase separation in polysulfone/polyethersulfone/N‐methyl‐2‐ pyrrolidone/water quaternary system

To construct a phase diagram of the polysulfone (PSF)/polyethersulfone (PES)/N‐methyl‐2‐pyrrolidone (NMP)/water quaternary system, cloud point measurements were carried out by a titration method. The miscible region in the PSF/PES/NMP/water quaternary system was narrow compared to the PSF/NMP/water and PES/NMP/water ternary systems. The binary interaction parameters between PSF and PES were estimated by water sorption experiments. The calculated phase diagram based on the Flory–Huggins theory fit the experimental cloud points well. In addition to the usual polymer–liquid phase separation, polymer–polymer phase separation, which resulted in a PSF‐rich phase and a PES‐rich phase, was observed with the addition of a small amount of nonsolvent. The boundary separating these two modes of phase separation could be well described and predicted from the calculated phase diagrams with the estimated binary interaction parameters of the components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2113–2123, 1999     

Pure component recovery from polyamide 6/6 6 mixtures by selective dissolution and reprecipitation

A selective dissolution/reprecipitation technique was applied for the effective recovery of Polyamide 6 (PA 6) and Polyamide 6 6 (PA 6 6) from their mixtures. The proposed process comprises mainly selective polyamide dissolution in an appropriate solvent at a specific temperature, reprecipitation of the polymer from the solution by addition of a nonsolvent, washing, and drying. A model mixture of virgin PA 6 and PA 6 6 pellets was initially tried, whereas in a following stage the selective dissolution technique was applied for the recovery of a PA‐copolymer layer from a three‐layered bottle end product also containing HDPE and EVA. End‐group analysis, dilute solution viscometry, and differential scanning calorimetry were used to assess the molecular weight preservation and crystallizability of the recycled polyamides. The recycled materials demonstrated excellent retention of the properties studied, although in the copolymer case, due to hydrolysis, a molecular weight decrease was detected, accompanied with a slight compositional shift, favoring the PA6 6 presence in the final product. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1924–1930, 2002