Pervaporation of ethanol-water mixtures through temperature-sensitive poly(vinyl alcohol-g-N-isopropyacrylamide) membranes

Novel temperature-sensitive membranes have been synthesized by grafting poly(N-isopropyacrylamide) (poly(NIPAAm)) onto a poly(vinyl alcohol) (PVA) backbone using hydrogen peroxide-ferrous ion as initiator. Due to the grafting of poly(NIPAAm), the hydrophilic/hydrophobic balance and the polarity of the pendent groups within the membranes are modified. Significant temperature sensitivity of the grafted membranes is observed close to the LCST of linear poly(NIPAAm) in the pervaporation processes for ethanol-water separation. Both the pervaporation and sorption selectivities for water show a maximum value in the vicinity of 30–32°C for an ethanol content of 75 and 80%. The temperature sensitivity of the grafted membranes also depends on the ethanol concentration. The maxima of pervaporation and sorption selectivities disappear when the ethanol content is lower than 75% because the much larger degree of swelling reduces the size screening effect of the membranes.     

Pervaporation of alcohol-toluene mixtures through polymer blend membranes of poly(acrylic acid) and poly(vinyl alcohol)

Homogeneous membranes were prepared by blending poly(acrylic acid) with poly(vinyl alcohol). These blend membranes were evaluated for the selective separation of alcohols from toluene by pervaporation. The flux and selectivity of the membranes were determined both as a function of the blend composition and of the feed mixture composition. The results showed that a polymer blending method could be very useful to develop new membranes with improved permselectivity. The pervaporation properties could be optimized by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing poly(vinyl alcohol) content for both methanol—toluene and ethanol—toluene liquid mixtures. The alcohols permeated preferentially through all tested blend membranes, and the selectivity values increased with increasing poly(vinyl alcohol) content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The fluxes increased exponentially with increasing alcohol concentration in the feed mixtures, whereas the selectivities decreased for both liquid mixtures.     

Pervaporation separation of water + isopropanol mixtures using novel nanocomposite membranes of poly(vinyl alcohol) and polyaniline

Novel nanocomposite polymeric membranes containing nanosized (30–100 nm) polyaniline (PANI) particles dispersed in poly(vinyl alcohol) (PVA) were prepared and used in the pervaporation separation of water–isopropanol feed mixtures ranging from 10 to 50 mass% of water at 30 °C. Of the three nanocomposite membranes prepared, the membrane containing 40:60 surface atomic concentration ratio of PANI:PVA produced the highest selectivity of 564 compared to a value of 77 observed for the plain PVA membrane. Flux of the nanocomposite membranes was lower than those observed for the plain PVA membrane, but selectivity improved considerably. Membranes were characterized by differential scanning calorimetry, dynamic mechanical thermal analyzer, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The highest selectivity with the lowest flux was observed for 10 mass% water containing feed mixture. Flux increased with increasing amount of water in the feed, but selectivity decreased considerably. These results were attributed to the acid-doped PANI particles in the PVA membrane as a result of change in the micromorphology of the nanocomposite membranes. In addition, molar mass between cross-links and fractional free volume of the membranes are responsible for the varying membrane performance. Temperature effect on permeability was investigated for 10 mass% water containing feed with the membrane containing higher concentration of PANI particles, the presence of which could be responsible for varied effect of water permeation through the membrane. Membranes of this study could remove as much as 98% of water from the feed.     

High-performance membranes for pervaporation II. Crosslinked poly(vinyl alcohol)–poly(acrylic acid) blends

Dense membranes made by crosslinking of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) were prepared and tested in pervaporation and differential permeation of water–alcohol mixtures. Instead of a decrease of permeation flux as generally observed with most crosslinking agents, an increase in the permeability was observed with PAA crosslinked membranes at low PAA contents. The permeation flux increases with PAA contents in the polymer with no selectivity reduction for membranes containing less than 15 wt. % PAA. The membranes show good performances to water–2-propanol and water–ethanol mixtures, i.e. high fluxes and high selectivities to pure water. The membranes were stable and highly permeable to water. The enhancement of the permeability of PVA can be explained by a reduced crystallinity and an improved diffusivity due to the presence of PAA.     

Poly(vinyl alcohol)/poly(methyl methacrylate) blend membranes for pervaporation separation of water + isopropanol and water + 1,4-dioxane mixtures

Pervaporation (PV) separation of water + isopropanol and water + 1,4-dioxane mixtures has been attempted using the blend membranes of poly(vinyl alcohol) (PVA) with 5 wt.% of poly(methyl methacrylate) (PMMA). These results have been compared with the plain PVA membrane. Both plain PVA and PVA/PMMA blend membranes have been crosslinked with glutaraldehyde in an acidic medium. The membranes were characterized by differential scanning calorimetry and universal testing machine. Pervaporation separation experiments have been performed at 30 °C for 10, 15, 20, 30 and 40 wt.% of feed water mixtures containing isopropanol as well as 1,4-dioxane. PVA/PMMA blend membrane has shown a selectivity of 400 for 10 wt.% of water in water + isopropanol feed, while for water + 1,4-dioxane feed mixture, membrane selectivity to water was 104 at 30 °C. For both the feed mixtures, selectivity for the blend membrane was higher than that observed for plain PVA membrane, but flux of the blend membrane was lower than that observed for the plain PVA membrane. Membranes of this study are able to remove as much as 98 wt.% of water from the feed mixtures of water + isopropanol, while 92 wt.% of water was removed from water + 1,4-dioxane feed mixtures at 30 °C. Flux of water increased for both the feed mixtures, while the selectivity decreased at higher feed water concentrations. The same trends were observed at 40 and 50 °C for 10, 15 and 20 wt.% of water mixtures containing isopropanol as well as 1,4-dioxane feed mixtures, which also covered their azeotropic composition ranges. Membrane performance was studied by calculating flux (J_p), selectivity (), pervaporation separation index (PSI) and enrichment factor (β). Permeation flux followed the Arrhenius trend over the range of temperatures investigated. It was found that by introducing a hydrophobic PMMA polymer into a hydrophilic PVA, the selectivity increased dramatically, while flux decreased compared to plain PVA, due to a loss in PVA chain relaxation.     

Crosslinking of poly(vinyl alcohol) using functionalized gold nanoparticles

We report on the preparation of a new class of polymer hydrogels obtained through the chemical crosslinking reaction of poly(vinyl alcohol) (PVA) and functionalized gold nanoparticles. Carboxylic group functionalized gold nanoparticles were synthesized, dispersed in a PVA matrix and allow to react with the hydroxyl groups of PVA at high temperature. FT-IR and swelling experiments carried out on the cross-linked samples confirmed that the crosslinking reaction took place. This is the first time, to our knowledge, that functionalized nanoparticles are used as chemical crosslinking agents.     

Novel nanocomposite pervaporation membranes composed of poly(vinyl alcohol) and chitosan-wrapped carbon nanotube

Novel nanocomposite membranes (PVA–CNT(CS)) were prepared by incorporating chitosan-wrapped multiwalled carbon nanotube (MWNT) into poly(vinyl alcohol) (PVA). To further explore the intrinsic correlation between pervaporation performance and free volume characteristics, molecular dynamics simulation was first introduced to qualitatively analyze the contribution of carbon nanotube incorporation on improving free volume characteristics of the nanocomposite membranes. Secondly, the pervaporation performance of PVA–CNT(CS) nanocomposite membranes was investigated using permeation flux and separation factor as evaluating parameters. For benzene/cyclohexane (50/50, w/w) mixtures at 323 K, permeation flux and separation factor of pure PVA membrane are only 20.3 g/(m² h) and 9.6, respectively, while the corresponding values of PVA–CNT(CS) (CNT content: 1%) nanocomposite membrane are 65.9 g/(m² h) and 53.4. In order to explain the simultaneous increase of permeation flux and separation factor, as well as to check the calculation reliability of molecular dynamics simulation, positron annihilation lifetime spectroscopy (PALS) analysis was employed.     

CE of poly(amidoamine) succinamic acid dendrimers using a poly(vinyl alcohol)-coated capillary

Various generations (G1-G8) of negatively charged poly(amidoamine) (PAMAM) succinamic acid dendrimers (PAMAM-SAH) were analyzed by CE using a poly(vinyl alcohol)-coated capillary. Due to its excellent stability and osmotic flow-shielding effect, highly reproducible migration times were achieved for all generations of dendrimer (e.g., RSD for the migration times of G5 dendrimer was 0.6%). We also observed a reverse trend in migration times for the PAMAM-SAH dendrimers (i.e., higher generations migrated faster than lower generation dendrimers) compared to amine-terminated PAMAM dendrimers reported in the literature. This reversal in migration times was attributed to the difference in counterion binding around these negatively charged dendrimers. This reverse trend allowed a generational separation for lower generation (G1-G3) dendrimers. However, a sufficient resolution for the migration peaks of higher generations (G4-G5) in a mixture could not be achieved. This could be due to their nearly identical charge/mass ratio and dense molecular conformations. In addition, we show that dye-functionalized PAMAM-SAH dendrimers can also be analyzed with high reproducibility using this method.     

Multilayer poly(vinyl alcohol)-adsorbed coating on poly(dimethylsiloxane) microfluidic chips for biopolymer separation

A poly(dimethylsiloxane) (PDMS) microfluidic chip surface was modified by multilayer-adsorbed and heat-immobilized poly(vinyl alcohol) (PVA) after oxygen plasma treatment. The reflection absorption infrared spectrum (RAIRS) showed that 88% hydrolyzed PVA adsorbed more strongly than 100% hydrolyzed one on the oxygen plasma-pretreated PDMS surface, and they all had little adsorption on original PDMS surface. Repeating the coating procedure three times was found to produce the most robust and effective coating. PVA coating converted the original PDMS surface from a hydrophobic one into a hydrophilic surface, and suppressed electroosmotic flow (EOF) in the range of pH 3-11. More than 1,000,000 plates/m and baseline resolution were obtained for separation of fluorescently labeled basic proteins (lysozyme, ribonuclease B). Fluorescently labeled acidic proteins (bovine serum albumin, beta-lactoglobulin) and fragments of dsDNA phiX174 RF/HaeIII were also separated satisfactorily in the three-layer 88% PVA-coated PDMS microchip. Good separation of basic proteins was obtained for about 70 consecutive runs.     

聚乙烯醇/纳米纤维素复合膜的渗透汽化性能及结构表征

将聚乙烯醇/纳米纤维素(PVA/NCC)复合膜应用于乙醇-水混合溶液的渗透汽化脱水过程,探讨了纳米纤维素对膜的溶胀性能、机械性能和渗透汽化性能的影响; 利用原子力显微镜(AFM)探测了纳米纤维素的形貌特征; 采用傅里叶变换红外光谱仪(FTIR)、扫描电镜(SEM)、差示扫描量热仪(DSC)和热重分析仪(TGA)对膜结构...     

聚丙烯酰胺/蒙脱土纳米复合物-聚乙烯醇共混膜的制备及其渗透汽化性能

用原位聚合法制备聚丙烯酰胺/蒙脱土(PAM/MMT)纳米复合材料, 通过透射电镜研究了蒙脱土在聚丙烯酰胺基体中的形貌和分布. 结果表明, 蒙脱土以片层结构分布在聚合物基体中. 用超声波分散聚乙烯醇和聚丙烯酰胺-蒙脱土共混铸膜液制得共混膜, 用红外吸收光谱和扫描电镜研究了两者的相互作用和形貌. 考察了共混膜在异丙醇-水混合溶液中的溶胀吸附性能及共混比和蒙脱土含量对膜分离性能的影响, 结果显示, 聚乙烯醇膜中添加适量的蒙脱土纳米粒子可以大大改善膜的分离选择性.     

High-performances membranes for pervaporation I. Poly(vinyl alcohol)–poly(N-vinyl pyrrolidone) blends

Dense membranes were prepared from poly(vinyl alcohol)–poly(N-vinyl pyrrolidone) (PVA–PVP) blends of different compositions and studied in swelling and dehydration by pervaporation of three organic solvents contaminated by 5 wt% water. The swelling generally increases with the PVP content. No extraction occurs in water–tetrahydrofuran (THF) and water–methyl ethyl ketone (MEK) mixtures. In ethanol containing 10 wt% of water, there is no extraction for blends containing less than 40 wt% PVP and an increasing extraction beyond this PVP content. The pervaporation flux of the water–ethanol mixture increases drastically at the same threshold whereas the water permselectivity falls to a low level. The values of the diffusion and permeability coefficients determined from transient permeation of the test water–ethanol mixture exhibit a similar sudden increase at the same PVP content threshold. This singular behavior of the blend membranes is interpreted by a strong affinity of the PVP component to ethanol, combined with a disappearance of crystallites in the blend at this threshold. Consequently the amorphous membrane can swell freely according to the affinity of the PVP component, leading to the observed behavior.     

聚乙烯醇／壳聚糖共混膜优先透醇性能的研究

聚乙烯醇／壳聚糖共混膜优先透醇性能的研究王新平，沈之荃，张富尧，林荣轩（浙江大学高分子系，化学系，杭州，３１００２７）关键词渗透蒸发，聚乙烯醇／壳聚糖共混物膜，乙醇水溶液本文首次报道利用亲水性的聚乙烯醇和壳聚糖制得具有很高的乙醇优先透过选择性的透醇型...     

Physically crosslinked poly(vinyl alcohol)-hydroxyethyl starch blend hydrogel membranes: Synthesis and characterization for biomedical applications

Poly(vinyl alcohol), PVA is a polymer of great importance because of its many appealing characteristics specifically for various pharmaceutical and biomedical applications. Physically crosslinked hydrogel membranes composed of different amounts of hydroxyethyl starch (HES) in (PVA) and ampicillin were prepared by applying freeze–thawing method. This freezing–thawing cycle was repeated for three consecutive cycles. Physicochemical properties of PVA–HES membrane gel such as gel fraction, swelling, morphology, elongation, tensile strength, and protein adsorption were investigated. Introducing HES into freeze–thawed PVA structure affected crystal size distribution of PVA; and hence physicochemical properties and morphological structure have been affected. Increased HES concentration decreased the gel fraction %, maximum strength and break elongation. Indeed it resulted into a significant incrementing of the swelling ability, amount of protein adsorption, broader pore size, and pore distribution of membrane morphological structure. Furthermore, an increase in HES concentration resulted in better and still lower thermal stability compared to virgin PVA and freeze–thawed PVA. The maximum weight loss of PVA–HES hydrogel membranes ranged between 18% and 60% according to HES content, after two days of degradation in phosphate buffer saline (PBS), which indicates they are biodegradable. Thus, PVA–HES hydrogel membranes containing ampicillin could be a novel approach for biomedical application e.g. wound dressing purposes.     

Structure and coordination properties of facilitated olefin transport membranes consisting of crosslinked poly(vinyl alcohol) and silver hexafluoroantimonate

The high selectivity of solid‐state crosslinked poly(vinyl alcohol) (CPVA) membranes containing silver hexafluoroantimonate (AgSbF₆), with respect to olefin/paraffin mixtures, was previously reported. The structure and coordination properties of CPVA/AgSbF₆ complexes were investigated in this study with wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), and theoretical ab initio calculations, and they were compared with those of poly(vinyl alcohol) (PVA)/AgSbF₆ complexes. Contrary to expectations, the measurements of the intersegmental d‐spacings and glass‐transition temperatures indicated that the chain mobility in the PVA/AgSbF₆ membranes was lower than that in the CPVA/AgSbF₆ membranes. The different extents of transient crosslinking in the two systems were attributed mostly to their different coordination structures; silver ions in PVA/AgSbF₆ were coordinated with hydroxyl oxygens located near the polymer main chains, whereas those in CPVA/AgSbF₆ were coordinated with aldehyde oxygens located far from the main chains. According to WAXS spectra, AgSbF₆ was completely dissolved in both PVA and CPVA, and this disrupted the crystallinity of the polymers. However, our DSC study showed that the silver ions dissolved in both polymer matrices recrystallized into silver oxide at elevated temperatures. The binding energy of Ag3d_5/2, as determined from XPS spectra, shifted to lower values with the addition of increasing amounts of the polymer matrix, indicating the increasing coordination of silver ions with polymer chains. The presence of various oxygen species with and without coordination to silver ions was confirmed from O1s XPS spectra of CPVA membranes containing silver ions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 621–628, 2004     

Preparation of electrospun chitosan/poly(vinyl alcohol) membranes

Electrospinning of chitosan from its solutions in 2% aqueous acetic acid was studied by adding poly(vinyl alcohol) (PVA) as a “guest” polymer. Properties of the chitosan/PVA solutions including viscosity, conductivity, and surface tension were measured, and effects of the polymer concentration, chitosan/PVA mass ratio and processing parameters (applied voltage, flow rate, capillary-to-collector distance) on the electrospinnability of chitosan/PVA were investigated. Analyses of scanning electron micrographs and transmission electron micrographs suggested that the chitosan/PVA ultrafine fibers were often obtained along with beads, and chitosan was located in the elctrospun fibers as well as in the beads. Uniform chitosan/PVA fibers with an average diameter of 99 ± 21 nm could be prepared from a 7% chitosan/PVA solution in 40:60 mass ratio. Results of Fourier transform infrared spectroscopy and X-ray diffraction demonstrated that there were possible hydrogen bonds between chitosan and PVA molecules, which could weaken the strong interaction in chitosan itself and facilitate chitosan/PVA electrospinnability. The electrospun chitosan/PVA membranes showed higher water uptake and would have potential applications in wound dressings.     

Dynamic modification of poly(methyl methacrylate) chips using poly(vinyl alcohol) for glycosaminoglycan disaccharide isomer separation

We describe a microchip electrophoresis (MCE) method for the assay of unsaturated disaccharides of chondroitin sulfates, dermatan sulfates, and hyaluronic acid (HA). Poly(vinyl alcohol) (PVA) could be irreversibly adsorbed onto poly(methyl methacrylate) (PMMA) substrates and this approach was applicable for dynamic coating. The characteristics of the PMMA surface with PVA coating were evaluated in terms of the wettability, EOF, and adsorption of 2-aminoacridone (AMAC)-labeled disaccharide. The water contact angle decreased from 73 degrees on a pristine PMMA surface to 37.5 degrees on a PVA-coated surface, indicating that the PVA coating increased hydrophilicity. EOF was reduced approximately twofold and was relatively stable. Scanning electron microscopy and fluorescence microscopy images showed that adsorption of AMAC-labeled disaccharides was dramatically suppressed. Using the PVA coating, baseline separation of two pairs of glycosaminoglycan (GAG) disaccharide isomers, DeltaDi-diS(B)/DeltaDi-diS(D) and DeltaDi-0S/DeltaDi-HA, was achieved in Tris-borate buffer within 130 s by MCE.     

Preparation of poly(vinyl alcohol) hydrogels with radiation grafted citric and succinic acid groups

Ternary mixtures of PVA/Citric acid (CA)/water and PVA/Succinic acid (SA)/water were gamma irradiated to various doses in air at ambient temperature. Gelation % vs dose curves were constructed and swelling behavior of gels with maximum conversions was studied. In maximum gelled systems 80% of CA used in the feed composition was retained in the gel structure whereas this was only 20% for SA. The volume of swelling of ionic PVA gels increased from 230% to 530% for PVA/CA systems when pH was increased from 2.6 to 7.5. Less significant increase in swelling was observed for PVA/SA gels, from 250% to 330% in the same pH interval. The incorporation of SA and CA groups onto PVA networks improved remarkably the affinity of these structures for Co²⁺ and Ni²⁺ ion uptake.     

Preparation and pervaporation properties of crosslinked hyperbranched poly(amine-ester) membranes

Crosslinked hyperbranched poly(amine-ester) (HPAE) membranes were prepared by crosslinking its terminal hydroxyl groups with glutaraldehyde (GA). The crosslinked HPAE membranes showed high reactivity and good hydrophilicity. The crosslinking degree was investigated by Fourier transformation infrared spectra (FT-IR). Atom force microscope (AFM) and scanning electron microscope (SEM) reveals that the crosslinked HPAE films have smooth surfaces, dense and homogenous matrices. The swelling degree of the membrane was higher in water than that in isopropanol. From the permeation of pure water through the HPAE membrane, the effect of hydroxyl/aldehyde group ratio on the permeation flux and separation factor was investigated. The results indicated that the permeation flux increase was accompanied with the separation factor decrease if the water concentration increased in the feed solution.     

Enhancing the antifouling property of polyethersulfone ultrafiltration membranes through surface adsorption-crosslinking of poly(vinyl alcohol)

An adsorption-crosslinking process of poly(vinyl alcohol) (PVA) was introduced to modify the surface of polyethersulfone (PES) ultrafiltration membranes for enhancement of their antifouling property. XPS and water contact angle measurement confirmed the obvious enhancement of surface hydrophilicity. Ultrafiltration results showed that the spreading of PVA chains over the hydrophobic membrane surface caused substantial but acceptable decrease on membrane flux. The fouling type analysis indicated that PVA adsorption effectively improved the antifouling property of PES membranes. With a PVA concentration of 0.5 wt% and three cycles of alternative adsorption-crosslinking, the total and irreversible fouling ratio of modified membranes were 0.38 and 0.22, respectively, much lower than those of control PES membrane (0.61 and 0.47), and the flux recovery ratio was increased accordingly. The long-term ultrafiltration experiment demonstrated the improvement of recycling property and the reliability of adsorption-crosslinking process.