Preparation and characterization of silver-modified poly(vinyl alcohol)/polyethyleneimine hybrids as a chemical and biological protective material

Nanohybrid membranes based on the silver (Ag) and a poly(vinyl alcohol)/polyethyleneimine (PVA/PEI) blend were prepared by an in-situ reduction method, in which the silver nitrate, PVA and PEI acted as precursor, linker and polyamine reductant, respectively. The objective of the study was to develop and evaluate permeable membranes (PVA/PEI) impregnated with Ag nanoparticulates that can protect against simulants of chemical and biological warfare agents. The physical properties of the PVA/PEI-Ag hybrids were examined using SEM, TEM, TGA, and UV-vis spectroscopy, the results indicated that the Ag was incorporated in the PVA/PEI matrix after impregnation. The Ag content and surface morphology of the PVA/PEI-Ag hybrids depended on the initial concentration of AgNO₃. The chemical barrier properties against 2-chloroethyl-ethyl sulfide (CEES) were investigated based on static-diffusion method with gas chromatograph (GC). The antibacterial effects of the PVA/PEI-Ag hybrids were assessed by the zone of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and plate-counting methods. The results of this study showed that PVA/PEI-Ag hybrids that act against simulants of chemical and biological weapons while retaining their ability to transmit moisture vapor could be obtained.     

Poly(vinylalcohol)/poly(ethyleneglycol)/poly(ethyleneimine) blend membranes - structure and CO2 facilitated transport

Poly(vinylalcohol) (PVA)/poly(ethyleneimine) (PEI)/poly(ethyleneglycol) (PEG) blend membranes were prepared by solution casting followed by solvent evaporation. The effects of the blend polymer composition on the membrane structure and CO₂/N₂ permeation characteristics were investigated. IR spectroscopy evidenced strong hydrogen bonding interactions between amorphous PVA and PEI, and weaker interactions between PVA and PEG. DSC studies showed that PVA crystallization was partially inhibited by the interactions between amorphous PVA and PEI blend, in which PEG separated into nodules. The CO₂ permeability decreased with an increase in CO₂ partial pressure in feed gas, while the N₂ permeability remained constant. This result indicated that only CO₂ was transported by the facilitated transport mechanism. The CO₂ and N₂ permeabilities increased monotonically with the PEI content in the blend membranes, whereas the ideal selectivity of CO₂ to N₂ transport showed a maximum. When CO₂ is humidified, its permeability through the blend membranes is much higher than that of dry CO₂, but the change in permeability due to the presence of humidity is reversible.     

Integrating 31P DOSY NMR Spectroscopy and Molecular Mechanics as a Powerful Tool for Unraveling the Chemical Structures of Polyoxomolybdate‐Based Amphiphilic Nanohybrids in Aqueous Solution

Novel organic–inorganic hybrids of various sizes were generated by reaction of 1,8‐octanediphosphonic acid (ODP) and (NH₄)₆Mo₇O₂₄ in aqueous solution. The formation of rodlike hybrids with variable numbers of covalently bound ODP and polyoxomolybdate (POM) units can be tuned as a function of increasing (NH₄)₆Mo₇O₂₄ concentration at fixed ODP concentration. The chemical structure of the ODP/POM hybrids was characterized by ¹H, ³¹P, and ⁹⁵Mo NMR spectroscopy. Heteronuclear ³¹P DOSY (diffusion‐ ordered NMR spectroscopy) and molecular mechanics (MM) calculations were applied to determine the size and shape of the nanosized hybrids generated at various ODP/POM ratios. For this purpose, the structures of ODP/POM hybrids with variable numbers of ODP and POM units were optimized by MM and then approximated as cylinder‐shaped objects by using a recently described mathematical algorithm. The thus‐obtained cylinder length and diameter were further used to calculate the expected diffusion coefficients of the ODP/POM hybrids. Comparison of the calculated and experimentally determined diffusion coefficients led to the most probable ODP/POM hybrid length for each sample composition. The ³¹P DOSY results show that the length of the hybrids increases with increasing POM concentration and reaches a maximum corresponding to an average of 8 ODP/7 POM units per chain at a sample composition of 20 mM ODP and 14 mM POM. With excess POM, above the latter concentration, the formation of shorter‐chain hybrids terminated by Mo₇ clusters at one or both ends was evidenced on further increasing the POM concentration. The results demonstrate that the combination of ³¹P DOSY and MM, although virtually unexplored in POM chemistry, is a powerful innovative strategy for the detailed characterization of nanosized organic–inorganic POM‐based hybrids in solution.     

Self-assembled polyelectrolyte multilayer membranes with highly improved pervaporation separation of ethanol/water mixtures

Ethanol/water pervaporation through ultrathin polyelectrolyte multilayer membranes is described. The membranes were prepared by the layer-by-layer technique, i.e. by alternating sequential adsorption of cationic and anionic polyelectrolytes on a porous support. The separation capability was optimized by variation of the chemical structure of the polyelectrolytes, by variation of pH and ionic strength of the polyelectrolyte solutions used for membrane preparation and by annealing of the polyelectrolyte membranes. It was found that the separation is mainly affected by the charge density of the polyelectrolytes which is controlled by the chemical structure and the degree of ionisation of the polar groups. Selectivity for water was highest, if polyelectrolytes of high charge density such as polyethyleneimine (PEI), polyvinylamine (PVA) and polyvinylsulfate (PVS) were used and if the pH of the polyelectrolyte solutions was equal to the mean of the pK_a values of the corresponding cationic and anionic polyelectrolyte. Best results were obtained for PVA/PVS and PEI/PVS membranes which are characterized in detail with regard to their separation behavior.     

Polyelectrolyte layer-by-layer self-assembly enhanced by electric field and their multilayer membranes for separating isopropanol–water mixtures

An electric field enhanced method is developed for fabricating layer-by-layer (LbL) self-assembly polyelectrolyte multilayer membranes. Three kinds of electric field enhanced polyelectrolyte multilayer membranes (EPEMs), poly(diallyl dimethylammonium chloride)/poly(styrenesulfonate sodium salt) (PDDA/PSS), poly(diallyldimethylammonium chloride)/poly(acrylic acid sodium salt) (PDDA/PAA) and polyethylenimine/poly(acrylic acid sodium salt) (PEI/PAA), were self-assembled on a reverse osmosis membrane (ROM). The pervaporation performances of EPEMs for separating isopropanol–water mixtures (90/10, w/w) are all superior to those of corresponding normal self-assembled polyelectrolytes membranes (PEMs), and the selectivity increases with PDDA/PSS, PDDA/PAA and PEI/PAA in order. For (PEI/PAA)₄PEI EPEM, the separation factor is 1075 and permeation flux is 4.05 kg m⁻² h⁻¹ at 70 °C. This novel method speeds up the LbL process, which makes it promising for the practical application of the LbL multilayer membrane.     

Aromatic Sulfonium Polyoxomolybdates: Solid‐State Photochromic Materials with Tunable Properties

A new aromatic sulfonium counter‐ion motif for polyoxometalate (POM) clusters with potential for structural and electronic fine‐tuning has been designed. Its two derivatives 4‐hydroxyphenyl dimethylsulfonium triflate (HPDST) and 4‐(allyloxy)phenyl dimethylsulfonium triflate (APDST) exhibit ionic liquid behaviors under ambient conditions. HPDST and APDST are used to develop a series of aromatic sulfonium POM hybrids (HPDS/APDS)_n[XMo₁₂O₄₀] (HPDS and APDS are the cations of HPDST and APDST, respectively; X=P or Si; n=3 or 4), which are tested for photochromic behavior. On exposure to UV light, these POM hybrids undergo color change from yellow to green/blue. The coloration kinetics half lives (t_1/2) are less for APDS‐based hybrids than for HPDS‐based hybrids, suggesting that alkyl substitution on the phenolic group helps to fine‐tune the electron availability on the sulfonium moiety and hence to control the photochromic behavior of the POM hybrids. The t_1/2 values of these hybrids are considerably lower than those of the reported aliphatic sulfonium POM hybrids. We have also demonstrated the application of photoreduced POM hybrids as catalysts for the reduction of 4‐nitrophenol to 4‐aminophenol.     

Transport properties of PVA/PEI/PEG composite membranes: sorption and permeation characterizations

Poly(vinylalcohol)/poly(ethyleneglycol)/poly(ethyleneimine) blend membranes were prepared by solution casting followed by solvent evaporation. The chemical structure of the prepared membranes was analyzed by FTIR and DSC. The sorption behavior as well as the permeabilities of the membranes for pure CO₂ and N₂ were investigated. The results show that the PVA/PEI/PEG membranes possess a higher permeability of CO₂ and a lower permeability of N₂. The membrane displays a CO₂ permeability of 27 Barrer, and a N₂ permeability of 3 Barrer at 25°C and 1 bar. CO₂ sorption behavior of the composite membrane, which can be classified as a dual-mode sorption model, and N₂ sorption behavior of the copolymeric membrane is in agreement with the Fickian diffusion model.      

Novel polyelectrolyte complexes between N-carboxyethylchitosan and synthetic polyelectrolytes

Novel polyelectrolyte complexes (PEC) between the polyampholyte N-carboxyethylchitosan (CECh) and polyacid or polybase have been prepared. The complex formation between CECh and poly(2-acryloylamido-2-methylpropanesulfonic acid) (PAMPS), poly(acrylic acid) (PAA) or poly(ethylene imine) (PEI) has been studied. The complex CECh/PAMPS is formed in the pH range from 1.2 to 6.0. The complex CECh/PAA is formed in the range 4.8-6.0 and CECh/PEI—from pH 5.4 to 7.0. The stoichiometry of the complexes depends on the pH value of the medium. In case of CECh/PAMPS and CECh/PAA the maximum quantity of complex is formed in excess of CECh and in the case of CECh/PEI—in excess of PEI. It has been shown that PEC formation between CECh and PAMPS improves the haemocompatibility of CECh.     

Functional membranes prepared by layer‐by‐layer assembly and its metal ions adsorption property

PVDF/(PEI‐C/PAA)_n functional membranes were prepared by layer‐by‐layer (LbL) assembly, and their heavy metal ions adsorption capability was investigated. The changes in the chemical compositions of membrane surfaces were determined by X‐ray photoelectron spectroscopy (XPS). XPS results show that the surface of the PVDF membrane can be alternatively functionalized by PEI‐C and PAA. The membrane surface hydrophilicity was evaluated through water contact angle measurement. Contact angle results show that the surface hydrophilicity of the membrane surface depends on the outermost deposited layer. Morphological changes of membrane surfaces were observed by scanning electron microscopy (SEM). The water fluxes for these membranes were elevated after modification. The performances of the PVDF/(PEI‐C/PAA)_n membranes on the adsorption of copper ions (Cu²⁺) from aqueous solutions were investigated by inductively coupled plasma (ICP). The results indicate that the PVDF/(PEI‐C/PAA)_n functional membranes show high copper ions adsorption ability. Copyright © 2010 John Wiley & Sons, Ltd.     

Facilitated transport of CO2 through polyethylenimine/poly(vinyl alcohol) blend membrane

Polyethylenimine (PEI)/poly(vinyl alcohol) (PVA) blend membranes were prepared for the facilitated transport of CO₂. The polymeric carrier PEI was retained in the blend membrane by the entanglement with PVA chains. The CO₂ permeance decreased with an increase in CO₂ partial pressure in feed gas, whereas the N₂ permeance was nearly constant. This result clearly showed that only CO₂ was transported by the facilitated transport mechanism. The CO₂ and N₂ permeabilities increased monotonically with the PEI weight percent in the blend membrane, whereas the selectivity of CO₂ over N₂ showed a maximum. The selectivity increased remarkably with increasing heat-treatment temperature of the membrane. The highest selectivity obtained reached more than 230 when the CO₂ partial pressure was 0.065 atm. The prepared membrane was stable.     

Effect of introduction of heterocyclic moieties into polymer backbone on gas transport properties of fluorinated poly(ether imide) membranes

The effects of incorporation of heterocyclic moieties into fluorinated poly(ether imide) membranes on their gas transport properties were investigated. Four novel fluorinated poly(ether imide) (PEI) membranes were prepared from four different bis(ether amine)s namely, 4,4-bis[3′-trifluromethyl-4′(4′′-aminobenzoxy)bezyl]biphenyl (BAQP); 1,4-bis[3′-trifluromethyl-4′(4′′-aminobenzoxy)bezyl] benzene (BATP); 2,6-bis[3′-trifluromethyl-4′(4′′-aminobenzoxy)bezyl]pyridine (BAPy) and 2,5-bis[3′-trifluromethyl-4′(4′′-aminobenzoxy)bezyl]thiophene (BATh), and a fluorinated dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane (6FDA) as a common dianhydride. Gas transport properties of these membranes were measured to investigate the effect of chemical structure on gas permeation and diffusion processes over four different gases (e.g., CH₄, N₂, O₂ and CO₂) at different temperatures (e.g., 35, 45 and 55 °C) at an applied pressure of 3.5 bar. It has been found that at 35 °C the permselectivities of BAPy and BATh based polymeric membranes (6.4 and 6.6, respectively) toward O₂ relative to N₂ are higher in comparison to BAQP and BATP (5.5 and 5.3, respectively) containing PEI membranes. The permeability coefficient of CO₂ for BAPy and BATh (51.92 and 45.31, respectively at 35 °C) based PEI membranes were observed to be much higher than BAQP and BATP based membranes (36.61 and 33.51, respectively at 35 °C) with comparable selectivity values of CO₂ relative to CH₄. All these membranes exhibit higher CO₂/CH₄ selectivity than those of common glassy polymers e.g., cellulose acetate, polysulfone and polycarbonate. The order of permeability of these gases was found as CO₂ > O₂ > N₂ > CH₄. The temperature dependency of permeation and diffusion processes enables to calculate the activation energies of the permeation and diffusion processes for these four different gases through four PEI membranes.     

Synthesis of Ultrastable Ag Nanoplates/Polyethylenimine–Reduced Graphene Oxide and Its Application as a Versatile Electrochemical Sensor

Investigations on Ag nanostructures/reduced graphene oxide composites have been frequently reported, yet the morphology control of those loaded Ag nanocrystals is still challenging. We herein develop a facile method to grow triangular Ag nanoplates (AgP) on polyethylenimine‐modified reduced graphene oxide (AgP/PEI‐rGO). The AgP/PEI‐rGO hybrids show unexpected high stability against chloride ions (Cl^?) and hydrogen peroxide (H₂O₂), which is possibly due to the strong interaction between surface Ag atoms with the amine groups of PEI. In the chronoamperometry measurements for detecting H₂O₂, N₂H₄, and NaNO₂, the AgP/PEI‐rGO hybrid shows very wide linear ranges (usually 10^?6–10^?2 mol L^?1 for H₂O₂, N₂H₄, and NaNO₂) and low detection limits (down to ≈1×10^?7 mol L^?1), which demonstrate the promising electrochemical sensor applications of these metal/graphene hybrids with well‐defined morphologies and facets. In addition, this strategy could be extended to the deposition of other noble metals on rGO with controlled morphologies.     

Development of Functional Composite Cu(II)-Polyoxometalate/PLA with Antimicrobial Properties

Novel composite self-disinfecting films of polylactic acid (PLA) filled with nanosized particles of double sodium–copper(II) paratungstate B Na₂Cu₃(CuOH)₂[W₁₂O₄₀(OH)₂]·32H₂O (POM) were developed. The solvent casting (POM/PLA film) and solvent-free melt extrusion methods (Extr. POM/PLA film) were applied for film preparation. The copper (II) ion release to water from both types of the films after 10 days at different temperatures demonstrated that the PLA matrix acts as a diffusion barrier, and the resulting concentration of released copper in water at room temperature remained low, at 0.79% for POM/PLA film and 0.51% for Extr. POM/PLA film. The POM-containing films reveals a significant inhibitory effect against E. coli ATCC 25922 in the agar diffusion test. The numbers of CFUs in washes of the films after incubation for 24 h were found to be 3.6 log CFU mL^–1 (POM/PLA film) and 4.1 log CFU mL^–1 (Extr. POM/PLA film). The films combine the antibacterial properties of POM and a bio-based polymer matrix, which makes them a prospective coating material for applications in hospital indoor environments. Excellent thermal stability of POM gives a technological advantage for industrial manufacturing to allow the processing of novel composite material in the solvent free (molten) state.     

New multifunctional materials obtained by the intercalation of anionic dyes into layered zinc hydroxide nitrate followed by dispersion into poly(vinyl alcohol) (PVA)

Different anionic blue and orange dyes have been immobilized on a zinc hydroxide nitrate (Zn₅(OH)₈(NO₃)₂nH₂O — Zn–OH–NO₃) by anion exchange with interlayer and/or outer surface nitrate ions of the layered matrix. Orange G (OG) was totally intercalated, orange II (OII) was partially intercalated, while Niagara blue 3B (NB) and Evans blue (EV) were only adsorbed at the outer surface. Several composite films of poly(vinyl alcohol) — PVA were prepared by casting through the dispersion of the hybrid material (Zn–OH–OG) into a PVA aqueous solution and evaporation of water in a vacuum oven. The obtained composite films were transparent, colored, and capable of absorbing UV radiation. Improved mechanical properties were also obtained in relation to the nonfilled PVA films. These results demonstrate the onset of a new range of potential applications for layered hydroxide salts in the preparation of polymer composite multifunctional materials.     

Fabrication and Characterization of Nanocomposite Flexible Membranes of PVA and Fe3O4

Composite polymer membranes of poly(vinyl alcohol) (PVA) and iron oxide (Fe₃O₄) nanoparticles were produced in this work. X-ray diffraction measurements demonstrated the formation of Fe₃O₄ nanoparticles of cubic structures. The nanoparticles were synthesized by a coprecipitation technique and added to PVA solutions with different concentrations. The solutions were then used to generate flexible membranes by a solution casting method. The size and shape of the nanoparticles were investigated using scanning electron microscopy (SEM). The average size of the nanoparticles was 20±9 nm. Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) were utilized to investigate the structure of the membranes, as well as their vibration modes. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated the thermal stability of the membranes and the crystallinity degree. Electrical characteristics of the thin membranes were examined using impedance spectroscopy as a function of the nanoparticles’ concentrations and temperatures. The resistivity of the fabricated flexible membranes was possible to adjust by controlled doping with suitable concentrations of nanoparticles. The activation energy decreased with the nanoparticles’ concentrations due to the increase in charge carriers’ concentrations. Therefore, the fabricated membranes may be applied for practical applications that involve the recycling of nanoparticles for multiple application cycles.     

Direct borohydride fuel cell performance using hydroxide-conducting polymeric nanocomposite electrolytes

Solid electrolyte membranes based on alkali-doped polyvinyl alcohol (PVA) and PVA/carbon nanotubes (PVA/CNTs) are used in direct borohydride fuel cells (DBFCs). As 0.05 wt % of CNT is incorporated into the PVA matrix, the polymer crystallinity is decreased from 42.4% to 38.0% and the fractional free volume increases from 2.48% to 3.53%. The KOH-doped PVA/CNT exhibits the highest ionic conductivity of 0.0805 S cm⁻¹, because of the increased polymer free volume (which promotes vehicular OH⁻ transport) and the presence of CNT (which serves as the conducting microchannels). Sodium borohydride (NaBH₄) in NaOH solution and potassium borohydride (KBH₄) in KOH mixture are fed into the cells. The power density of the KBH₄-based DBFC is almost twice that of the NaBH₄-based DBFC (184 vs. 92 mW cm⁻²) due to less KBH₄ permeability through the films, higher conductivity of the KOH-doped PVA composites than those in the sodium counterpart, and probably higher electro-catalytic kinetics. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1779–1789, 2013     

Poly(ethylene imine) hybrids containing polyhedral oligomeric silsesquioxanes: Preparation, structure and properties

Both octaglycidyletherpropyl polyhedral oligomeric silsesquioxane and hepta(3,3,3-trifluoropropyl)glycidyletherpropyl polyhedral oligomeric silsesquioxane were synthesized via the hydrosilylation reactions between octahydrosilsesquioxane [and/or hepta(3,3,3-trifluoropropyl)hydrosilsesquioxane] and allyl glycidyl ether. The polyhedral oligomeric silsesquioxane (POSS) macromers were characterized by means of Fourier transform infrared and nuclear magnetic resonance spectroscopy. The inter-component macromolecular reactions between the POSS macromers and poly(ethylene imine) (PEI) were employed to prepare the POSS-containing organic-inorganic PEI hybrids. The inclusion of octaglycidyletherpropyl POSS into PEI results in the formation of the organic-inorganic hybrid networks whereas the introducing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS to PEI affords the linear POSS-grafted PEI copolymers. Differential scanning calorimetry and thermogravimetric analysis show that the POSS-containing PEI hybrids displayed increased glass transition temperatures (T_g’s) and enhanced thermal stability compared to the plain PEI. These PEI hybrid composites can be significantly swollen with water without dissolving, suggesting the formation of hydrogels. The PEI hydrogels containing octaglycidyletherpropyl POSS is in reality the chemically-crosslinked hydrogels whereas the those containing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS displayed the behavior of physical hydrogels. The formation of physical hydrogels is ascribed to the microphase-separated morphology in the hybrids. In addition, the hybrids containing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS exhibited the typical amphiphilicity as evidenced by the increase in surface hydrophobilicity.     

Pervaporation dehydration of ethylene glycol with chitosan–poly(vinyl alcohol) blend membranes: Effect of CS–PVA blending ratios

Chitosan–poly(vinyl alcohol), CS–PVA, blended membranes were prepared by solution casting of varying proportions of CS and PVA. The blend membranes were then crosslinked interfacially with trimesoyl chloride (TMC)/hexane. The physiochemical properties of the blend membranes were determined using Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), tensile test and contact angle measurements. Results from ATR-FTIR show that TMC has crosslinked the blend membranes successfully, and results of XRD and DSC show a corresponding decrease in crystallinity and increase in melting point, respectively. The crosslinked CS–PVA blend membranes also show improved mechanical strength but lower flexibility in tensile testing as compared to uncrosslinked membranes. Contact angle results show that crosslinking has decreased the surface hydrophilicity of the blend membranes. The blend membrane properties, including contact angle, melting point and tensile strength, change with a variation in the blending ratio. They appear to reach a maximum when the CS content is at 75 wt%. In general, the crosslinked blend membranes show excellent stability during the pervaporation (PV) dehydration of ethylene glycol–water mixtures (10–90 wt% EG) at different temperatures (25–70 °C). At 70 °C, for 90 wt% EG in the feed mixture, the crosslinked blend membrane with 75 wt% CS shows the highest total flux of 0.46 kg/(m² h) and best selectivity of 986. The blending ratio of 75 wt% CS is recommended as the optimized ratio in the preparation of CS–PVA blend membranes for pervaporation dehydration of ethylene glycol.     

Preparation and characterization of crosslinked PVA/SiO2 hybrid membranes containing sulfonic acid groups for direct methanol fuel cell applications

Organic–inorganic hybrids based on poly(vinyl alcohol) (PVA)/SiO₂ hybrid membranes containing sulfonic acid groups were prepared using the sol–gel process under acidic conditions. The PVA/sulfosuccinic acid (SSA)/silica hybrid membranes were fabricated from different SSA contents. The proton conductivity and methanol permeability of the hybrid membranes were studied with changing SSA content from 5 to 25 wt.%. It was found that the proton conductivity and the methanol permeability were dependent on the SSA content both as a crosslinking agent, and as a donor of the hydrophilic SO₃H group. Up to an SSA content of about 20 wt.%, both of these properties decrease, and above this SSA content, they begin to increase with increasing SSA content. The proton conductivities of the PVA/SSA/silica membranes were in the range of 10⁻³ to 10⁻² S/cm, and the methanol permeabilities ranged between 10⁻⁸ and 10⁻⁷ cm²/s. The presence of silica particles in the organic polymer matrix, which reduce the free water ratio of the membranes, results in hybrids with markedly reduced methanol permeabilities. These characteristics of the PVA/SSA/silica hybrid membranes are desirable for future applications related to direct methanol fuel cells.     

Polyetherimide/polyvinylpyrrolidone vapor permeation membranes. Physical and chemical characterization

Integrally skinned capillary tube membranes were prepared by the wet-phase inversion method. A series of polyetherimide (PEI, Ultem 1000) membranes were prepared with varying amounts of polyvinylpyrrolidone (PVP) in the casting solution. The surfaces of the membranes were analyzed by electron spectroscopy for chemical analysis (ESCA). It was found that the molecular structure of PEI, both with and without PVP, changes considerably during membrane preparation. The ESCA results indicated that the amount of PEI nitrogen remaining fully imidized at the surface varied in the range 63–86%. The PVP/PEI mass ratio at the membrane surface was found to increase linearly from 0 to 0.10 as the ratio was increased from 0 to 0.43 in the casting solution. The PVP/PEI mass ratio in the membrane bulk was determined by thermogravimetric analysis (TGA) to reach a maximum of 0.067. Vapor permeation experiments were done with a water/n-propanol mixture. The addition of PVP increased the membrane selectivity (α=P_A/P_B, A=water, B=1-propanol) from 76 to 810, while the permeance for water remained relatively constant at 1.3×10⁻⁶ mol/m² s Pa.