Theoretical phase diagram calculation and membrane morphology evaluation for water/solvent/polyethersulfone systems

Theoretical ternary phase diagrams with very good agreement with experimental cloud point data were constructed for water/N,N-dimethylacetamide (DMAc)/polyethersulfone (PES) and water/N-methyl-2-pyrrolidone (NMP)/polyethersulfone systems. Theoretical phase diagrams were determined based on the extended Flory-Huggins theory of polymer solutions. To construct the theoretical phase diagrams, all binary interaction parameters were determined accurately and thoroughly revisited. Also, the structures of membranes prepared of these systems by phase separation process were investigated. The morphological studies showed that in spite of better miscibility between water and DMAc compared to water and NMP, channel-like structures were observed in membranes prepared of water/NMP/PES systems but tear-like structures with more spongy areas were observed in membranes prepared of water/DMAc/PES system. According to the constructed theoretical ternary phase diagrams of these systems, these unexpected observations were attributed to the higher concentration of polymer in the polymer-rich phase of water/DMAc/PES system, which causes an early vitrification in this system which suppresses the growth of macrovoids.     

Vitrification phenomena in polysulfone/NMP/water system

The vitrification line for the ternary system of polysulfone (PSf)/N‐methyl‐2‐pyrrolidinone (NMP)/water was determined by differential scanning calorimeter (DSC) measurements with varying compositions. Pure PSf showed both α‐ and β‐transition temperatures (T_g,α = 187.5°C, T_g,β = −21.4°C). The T_g,α of PSf decreased with increasing solvent concentration. The T_g,α of PSf decreased linearly with the addition of NMP in the concentration range of 70–90 wt % polymer. The vitrification line was indicated in the phase diagram for the ternary system of PSf/NMP/water at 15 and 60°C. As the temperature is increased, a high polymer concentration was needed to reach the vitrification condition. The vitrification composition of the polymer in the binary system of PSf and NMP was 72.0 wt % at 15°C and 79.8 wt % at 60°C. We also found that the slope of the vitrification line changed with the temperature and that a small amount of water (10–20 wt %) can induce the vitrification of the polymer solution in the PSf/NMP/water system at 15°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 431–438, 1999     

Morphology profiles obtained by reaction‐induced phase separation in epoxy/polysulfone/poly(ether imide) systems

The reaction‐induced phase separation in epoxy/aromatic diamine formulations simultaneously modified with two immiscible thermoplastics (TPs), poly(ether imide) (PEI) and polysulfone (PSF), has been studied. The epoxy monomer was based on the diglycidyl ether of bisphenol A (DGEBA) and the aromatic diamine was 4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) (MCDEA). Phase‐separation conversions are reported for various PSF/PEI proportions for blends containing 10 wt% total TP. On the basis of phase‐separation results, a conversion–composition phase diagram at 200 °C was compiled. This diagram was used to design particular cure cycles in order to generate different morphologies during the phase‐separation process. It was found that, depending on the PSF/PEI ratio employed, a particulate or a morphology characterized by a distribution of irregular PEI‐rich domains dispersed in an epoxy‐rich phase was obtained for initially miscible blends. Scanning electron microscopy (SEM) characterization revealed that the PEI‐rich phase exhibits a phase‐inverted structure and the epoxy‐rich matrix presents a bimodal size distribution of TP‐rich particles. For PSF/PEI ratios near the miscibility limit, slight temperature change result in morphology profiles. Copyright © 2005 Society of Chemical Industry     

Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. I. Phase diagram and mass transfer process

The isothermal phase diagram for poly(vinylidene fluoride)/dimethyl formamide/water system was derived. The binodal and spinodal were calculated based on the Flory–Huggins theory and the calculated binodal was approximately in agreement with the experimental data of the cloud points. The isothermal crystallization line was also obtained according to the theory of melting point depression. Mass transfer of the three components during membrane formation by the precipitation from the vapor phase has been analyzed. During this process, phase separation of the polymer solution is induced by the penetration of water vapor in the solution. The calculated result on the changes of the cast film weights indicated the good agreement with the experimental data. The time‐course of the polymer concentration profile in the film was calculated for various cases of different humidity of the vapor phase and different initial polymer concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 159–170, 1999     

Membrane formation with presence of Lewis acid–base complexes in polymer solution

This work investigated membrane formation using Lewis acid–base complexes in a polymer solution, which consisted of poly(ether sulfone) (PES), Lewis acid–base complexes formed by N‐methyl‐2‐pyrrolidone (NMP, Lewis base), and dicarboxylic or monocarboxylic acids from a homologous series (Lewis acids). The solutions were characterized by viscosity measurements, IR spectroscopy, cloud point determination, and light transmission experiments. The membranes were characterized by scanning electron microscopy and gas permeation tests. The results indicated that the solvent–additive interaction, which is a function of their capacity to form complexes, and the acid chain length directly affect the viscosity and miscibility region. Consequently, these parameters combined with the complex dissociation influence the precipitation velocity of the polymer solutions, which will then affect the membrane transport properties. It is also pointed out that the membranes prepared by using 25 wt % PES at the same acid/NMP molar ratios and with different acids presented permeability coefficients in agreement with the binodal shift obtained in pseudoternary phase diagrams. Furthermore, when these solutions were exposed to the environment for a long period of time, the demixing onset sequence also agreed with the miscibility region for all solutions, except for the adipic acid solution because of its extremely high viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2022–2034, 2002     

Generalized Flory–Huggins model for heat‐of‐mixing and phase‐behavior calculations of polymer–polymer mixtures

An extended and generalized Flory–Huggins model for calculating the heats of mixing and predicting the phase stability and spinodal diagrams of binary polymer–polymer mixtures is presented. In this model, the interaction parameter is considered to be a function of both temperature and composition. It is qualitatively shown that the proposed model can calculate the heats‐of‐mixing curves containing exothermic, endothermic, and S‐shaped or sigmoidal types and predict the spinodals, including the upper and lower critical solution temperatures, and closed‐loop miscibility regions. Using experimental results of analog calorimetry for four polymer mixtures of polystyrene/poly(vinyl chloride) (PS/PVC), polycarbonate (PC)/poly(ethylene adipate) (PEA), polystyrene/poly(vinyl acetate) (PS/PVAc), and ethylene vinyl acetate copolymer (EVA Co)/chlorinated polyethylene (CPE), the capabilities of the proposed functionality for the interaction parameter was studied. It is shown that this function can be used satisfactorily for the heat‐of‐mixing calculations and phase‐behavior predictions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1328–1340, 2000     

Phase separation in polyetherimide/solvent/nonsolvent systems and membrane formation

Phase separation phenomena of polyetherimide (PEI)/solvent/nonsolvent systems were investigated by measuring their precipitation values over the temperature range from 20 to 50°C. The solvents used are N‐methyl‐2‐pyrrolidone (NMP), dimethylacetamide (DMAC), and dimethylformamide (DMF). Nine nonsolvents were employed including water, methanol, ethanol, 1‐propanol, 2‐propanol, acetic acid, propionic acid, ethylene glycol, and diethylene glycol. Based on the measured precipitation values, critical solubility parameters for PEI were calculated, and the partial solubility boundary for PEI was obtained in a two‐dimensional solubility parameter coordinate graph. The relationship between solvent strength and membrane structure was examined using PEI hollow‐fiber membranes prepared from binary polymer solutions containing NMP, DMAC, and DMF as solvents. Water was used both as internal and external coagulants. The cross‐sectional structure and gas permeation properties of these hollow fibers were examined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1789–1796, 1999     

Effect of hypochlorite treatment on performance of hollow fiber membrane prepared from polyethersulfone/N‐methyl‐2‐pyrrolidone/tetronic 1307 solution

Polyethersulfone (PES) hollow fiber membrane was prepared by blending with nonionic surfactant Tetronic 1307 to improve its hydrophilicity. The membranes were posttreated by hypochlorite solution of 10, 100, 500, and 2000 ppm. The effect of hypochlorite treatment on the performance of PES membrane was investigated. Experimental results showed that the water permeability of treated membrane was two to three times higher than that of untreated membrane in case of blend membrane prepared from PES/N‐methyl‐2‐pyrrolidone (NMP)/Tetronic 1307 solution. On the other hand, hypochlorite treatment has no effect on water permeability of the membrane prepared from PES/NMP solution. Elemental analysis and ATR–FTIR measurement results indicated that hypochlorite treatment led to decomposition and leaching out of Tetronic 1307 component from the membrane. The change of membrane surface structure by the hypochlorite treatment was confirmed by atomic force microscopy measurement. The hypochlorite treatment brought about no significant impact on the mechanical property of the membranes. This indicated that the hypochlorite treatment of PES membrane prepared with surfactant was a useful way to improve the water permeability without the decrease of membrane strength. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polysulfone/poly(ether sulfone) blended membranes for CO2 separation

Polymer blending as a modification technique is a useful approach for augmenting the gas‐separation and permeation properties of polymeric membranes. Polysulfone (PSF)/poly(ether sulfone) (PES) blend membranes with different blend ratios were synthesized by conventional solution casting and solvent evaporation technique. The synthesized membranes were characterized for miscibility, morphology, thermal stability, and spectral properties by differential scanning calorimetry (DSC), field emission scanning electron microscopy, thermogravimetric analysis, and Fourier transform infrared (FTIR) spectroscopy, respectively. The permeation of pure CO₂ and CH₄ gases was recorded at a feed pressure of 2–10 bar. The polymer blends were miscible in all of the compositions, as shown by DSC analysis, and molecular interaction between the two polymers was observed by FTIR analysis. The thermal stability of the blend membranes was found to be an additive property and a function of the blend composition. The morphology of the blend membranes was dense and homogeneous with no phase separation. Gas‐permeability studies revealed that the ideal selectivity was improved by 65% with the addition of the PES polymer in the PSF matrix. The synthesized PSF/PES blend membranes provided an optimized performance with a good combination of permeability, selectivity and thermal stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42946.     

Preparation and performances of poly(phthalazinone ether sulfone ketone) hollow fiber membranes with excellent thermotolerance

The cloud points of PPESK/NMP/H₂O ternary system at different temperatures were measured by titrimetric method. The binodal lines in the ternary phase diagram of the poly(phthalazinone ether sulfone ketone (PPESK) dope system was determined, on the basis of the cloud point experimental data being linearly fitted with the semiempirical linear cloud point correlation. Furthermore, phase separation behavior during the phase inversion of PPESK membrane‐forming system was discussed in terms of the phase diagram. Then, dry–wet spinning technique was employed in manufacturing PPESK hollow fiber membranes by immersion precipitation method. The cross‐section morphologies of hollow fibers were observed by scanning electronic microscopy. Also, the effects of dope solution composition and spinning parameters, including the coagulant composition and the spinning temperature on the separation performances of fibers, were evaluated by permeability measurements. The thermotolerance of the PPESK hollow fiber membranes prepared in the work was examined for the permeation operation at different temperatures and pressure differences. The experimental results showed that pure water flux increases several fold along with the temperature increases from 20 to 80°C at different operation pressures, while the solute rejection only decreases slightly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 878–884, 2006     

PMMA‐modified divinylester/styrene resins: Phase diagrams and morphologies

Binary and ternary experimental cloud‐point curves (CPCs) for systems formulated with a low molar mass synthesized divinylester (DVE) resin, styrene (St), and poly(methyl methacrylate) (PMMA) were determined. The CPCs results were analyzed with the Flory–Huggins (F‐H) thermodynamic model taking into account the polydispersity of the DVE and PMMA components, to calculate the different binary interaction parameters and their temperature dependences. The St‐DVE system is miscible in all the composition range and down to the crystallization temperature of the St; therefore, the interaction parameter expression reported for a higher molar mass DVE was adapted. The interaction parameters obtained were used to calculate the phase diagrams of the St‐PMMA and the DVE‐PMMA binary systems and that of the St‐DVE‐PMMA ternary system at three different temperatures. Quasiternary phase diagrams show liquid–liquid partial miscibility of the St‐PMMA and DVE‐PMMA pairs. At room temperature, the St‐DVE‐PMMA system is miscible at all compositions. Final morphologies of PMMA‐modified cured St‐DVE materials were generated by polymerization‐induced phase separation (PIPS) mechanism from initial homogeneous mixtures. SEM and TEM micrographs were obtained to analyze the generated final morphologies, which showed a direct correlation with the initial miscibility of the system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4539–4549, 2006     

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     

Development of a mathematical model for studying bioethanol–water separation using hydrophilic polyetherimide membrane

An essentially predictive mathematical model was developed to simulate pervaporation process. The group contribution method UNIFAC was used for calculating the upstream activity coefficients. The diffusion coefficient in the membrane was predicted using free‐volume theory. Free‐volume parameters were determined with viscosity and temperature data, and the binary interaction solvent–polymer parameter was calculated by a group‐contribution lattice‐fluid equation of state (GCLF‐EOS). A simulator named PERVAP was developed applying the mathematical model. Pervaporation process was simulated for separating bioethanol–water through polyetherimide membrane. The simulated results were validated using experimental data of bioethanol/water separation through polyetherimide membrane. The model presented a satisfactory performance compared to experimental data. Related to the simulation of the studied separation, a 99% molar enriched bioethanol stream was obtained with a recovery of 94%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of the addition of the surfactant Tetronic 1307 on poly(ether sulfone) porous hollow-fiber membrane formation

Poly(ether sulfone) (PES) hollow-fiber membrane was prepared via a nonsolvent-induced phase-separation method, and the effect of the addition of the surfactant Tetronic 1307 on the membrane performance and characteristics was investigated. The phase diagram of the PES/N-methyl-2-pyrrolidone (NMP)/water system was clarified. When the polymer solution involved Tetronic 1307, the amount of water required to induce the phase separation decreased, which indicated that Tetronic 1307 was one kind of nonsolvent. The kinetics of phase separation for the PES/NMP/Tetronic 1307 system were studied by light-scattering measurements. With the addition of Tetronic 1307, delayed phase separation was observed, and the structure growth rate decreased. Scanning electron microscopy images for all of the membranes showed the formation of fingerlike macrovoids through the cross section. Membrane surface morphologies were measured by atomic force microscopy. The obtained results indicated that membrane with 7 wt % Tetronic 1307 had higher roughness parameters than original membrane without the addition of surfactant. Ultrafiltration experiment results showed that the addition of Tetronic 1307 brought about an increase in water permeability and decreased the rejection of dextran with a molecular weight of about 10,000. The contact angles of water on the membrane outer surface decreased with the addition of Tetronic 1307. This mean the membrane surface became more hydrophilic. Thus, the addition of Tetronic 1307 was useful for improving the water permeability and for obtaining a hydrophilic membrane surface. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Lower critical solution temperature of linear PNIPA obtained from a Yukawa potential of polymer chains

The lower critical solution temperature (LCST) behavior of a linear poly(N‐isopropylacrylamide) (PNIPA) in water is thought to result from the polymer–polymer attractive interaction. This polymer–polymer attraction is modeled by a temperature‐dependent Yukawa attractive potential, with Yukawa parameters determined by fitting the theoretical phase diagram for a pure Yukawa fluid to the experimental lower consolute boundary for a PNIPA–water solution. The predicted coexistence curve for the PNIPA–water mixtures in the temperature‐polymer volume fraction plane is reasonably close to the experimental cloud point data for the PNIPA–water system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1971–1976, 2000     

Influence of attapulgites on cure‐reaction‐induced phase separation in epoxy/poly(ether sulfone) blends

The influence of attapulgites (ATTs) on cure‐reaction‐induced phase separation in diglycidyl ether of bisphenol A/poly(ether sulfone) (PES) blends has been studied with scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy, time‐resolved light scattering, and dynamic mechanical analysis at different ATT and PES concentrations. The SEM results show that the incorporation of a small amount of ATT into the blends can change the final phase morphology markedly and affect the secondary phase separation. The TEM results show that ATT particles are pinned down by the interfacial tension at the phase interfaces, and this slows the interfacial motion. In addition, the incorporation of a small amount of ATT particles can improve the modulus because of the increased interfacial interaction of the PES‐rich and epoxy‐rich phases. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermodynamic study of a water–dimethylformamide–polyacrylonitrile ternary system

Experimental cloud‐point data were obtained by cloud‐point titration. The phase diagram for a ternary system of water–dimethylformamide–polyacrylonitrile was determined by numerical calculation on the basis of the extended Flory–Huggins theory and was found to agree well with the cloud‐point data. To construct the theoretical phase diagram, three binary interaction parameters were obtained with different methods. The ternary phase diagram was used to investigate the mechanism of fiber formation. The skin–core structure and fingerlike pores in polyacrylonitrile fiber may be effectively eliminated if the composition of the spinning solution is properly chosen, and consequently, homogeneous polyacrylonitrile fiber with a bicontinuous structure and good mechanical properties can be obtained through the spinning process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

State diagram of phase transition temperatures and solvent‐induced recovery behavior of shape‐memory polymer

In this study we analyzed the phase and state transitions of shape‐memory polymers (SMPs)/solvent mixtures using the Flory–Huggins (FH) theory by extension of Vrentas and the Couchman–Karasz theory for glass transition, as well as Clausius–Clapeyron relation for melting transition. Using scaling relations of model parameters, we have obtained a theoretical prediction of state diagrams of the phase transition temperature and solvent‐induced recovery in SMPs. The inductive decrease in transition temperature is identified as the driving force for the solvent‐induced shape‐memory effect in SMPs Consequently, the thermodynamics of the polymer solution and the relaxation theory were employed to characterize the dependencies of shape recovery time on the FH parameter and the ratio of the molar volume of solute to solvent. With the estimated model parameters, we constructed the state diagram for SMP, which provides a powerful tool for design and analysis of phase transition temperatures and solvent‐induced recovery. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Phase separation and crystallization behavior in extruded polypropylene/ethylene–propylene rubber blends

Liquid–liquid (L–L) phase separation and its effects on crystallization in polypropylene (PP)/ethylene–propylene rubber (EPR) blends obtained by melt extrusion were investigated by time‐resolved light scattering (TRLS) and optical microscopy. L–L phase separation via spinodal decomposition (SD) was confirmed by TRLS data. After L–L phase separation at 250°C for various durations, blend samples were subjected to a temperature drop to 130°C for isothermal crystallization, and the effects of L–L phase separation on crystallization were investigated. Memory of the L–L phase separation via SD remained for crystallization. The crystallization rate decreased with increasing L–L phase‐separated time at 250°C. Slow crystallization for the long L–L phase‐separated time could be ascribed to decreasing chain mobility of PP with a decrease in the EPR component in the PP‐rich region. The propylene‐rich EPR exhibited good affinity with PP, leading to a slow growth of a concentration fluctuation during annealing. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 695–700, 2001     

On the one‐phase state of aqueous protein‐uncharged polymer systems: Casein‐guar gum system

Although the majority of biopolymers are incompatible in water, systems containing casein molecules and a neutral polysaccharide (guar gum galactomannan) showed phase separation only at an ionic strength above 0.09–0.2. Static light scattering, circular dichroism spectroscopy, velocity sedimentation, viscosimetry, phase analysis in different solvents, and Rosenberg's method were used to estimate the effect of polymer–solvent and polymer–polymer interactions on the phase state of casein‐guar aqueous systems. Different solvent conditions were used to try to clarify the nature (electrostatic or nonelectrostatic) of the interaction between the two macromolecular species. Data obtained show that the dominant mechanism controlling the single‐phase state at low ionic strength (below 0.01) involves the formation of water‐soluble weak interpolymer complexes, which may be destroyed by increasing ionic strength. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 471–482, 1999