Search

In this study, to improve the water flux of porous hydrophobic membranes, various water-soluble polymers including neutral, cationic and anionic polymers were adsorbed using 'salting-out' method. The adsorbed hydrophobic membrane surfaces were characterized mainly via the measurements of contact angles and scanning electron microscopy (SEM) images. To enhance the durability of the modified membranes, the water-soluble polymers such poly(vinyl alcohol) (PVA) were crosslinked with glutaraldehyde (GA) and found to be resistant for more than 2 months in vigorously stirred water. The water flux was much more increased when the ionic polymers used as the coating materials rather than the neutral polymer and in this case, about 70% of 0.31 L/m2·h (LMH) to 0.50 LMH was increased when 300 mg/L of polyacrylamide (PAAm) was used as the coating agents. Among the cationic coating polymers such as poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA), poly(acrylic acid-comaleic acid) (PAM) and poly(acrylic acid) (PAA), PSSA_MA was found to be the best in terms of contact angle and water flux. In the case of PSSA_MA, the water flux was enhanced about 80%. The low concentration of the coating solution was better to hydrophilize while the high concentration inclined to block the pores on the membrane surfaces. The best coating condition was found: (1) coating concentration 150 to 300 mg/L, (2) ionic strength 0.15, (3) coating time 20 min.

The sulfonated polyether ether ketone (SPEEK) as a cation exchange polymer and aminated polysulfone (APSf) as an anion exchange membrane (AEM) were synthesized to prepare bipolar membranes (BPMs) through hot pressing. The water splitting electrodialysis (WSED) experiments were conducted to produce acids and bases by using the resulting SPEEK/APSf BPM. For comparative performance evaluation of the commercialized ASTOM membrane and the newly synthesized membranes in our lab, the acid/base production rate and the voltage changes according to the constant current were measured. The acid and base formation rates of the commercialized membrane from ASTOM were 2.3 and 2.7 g/L/h, respectively, whereas the rates of the membranes we developed were 1.0–2.4 and 1.5–2.7 g/L/h, respectively, depending on the amine contents in the AEM. The performance of the synthesized BPM in our lab was equivalent or higher than that of the commercialized membrane from the viewpoint of the acid/base production rates.

폴리페닐렌옥사이드(PPO)와 폴리에테르이미드(PEI)에 대해 각각 설폰화(SPPO) 및 아민화(APEI) 반응이 이루어졌다. SPPO와 APEI의 특성평가를 위하여 FTIR, 열무게분석(TGA), 팽윤도, 이온교환용량(IEC) 및 이온전도도 등에 대한 측정을 하였다. 표면불소화를 실시한 후 표면불소화된 SPPO와 APEI 막과 불소화하지 않은 막과의 차이점을 알아보기 위하여 위에서 실시한 특성평가를 다시 수행하여 비교하였다. SPPO막의 이온교환용량을 고정시킨 후 APEI의 이온교환용량을 변경하면서 전체적으로 3개 유형의 바이폴라막을 제조하였고, 이를 차염소산 발생을 위하여 여러 전류밀도 하에서 저농도 및 고농도 소금용액에 적용하였다. 표면불소화된 막의 차염소산 생성 농도는 APEI의 이온교환용량에 의존하며 80 mA/m 2 에서 차염소산 농도 491-692 ppm의 결과를 얻었으며, 5 mA/m 2 에서 18-28 ppm의 차염소산 농도를 나타내었으며 내구성이 매우 상승된 것을 보여 주었다.

In this study, sulfonated poly(phenylene oxide) (SPPO) and aminated polysulfone (APSf) were synthesized for use as a cation exchange polymer and an anion exchange polymer respectively. The resulting ion exchange capacities of SPPO and APSf of 0.93 and 1.0 respectively were almost equivalent to each other. Then the ion exchange polymers were coated onto the surface of commercial carbon electrodes. Membrane capacitive deionization (MCDI) performance using these coated electrodes was tested under various operating conditions such as adsorption/desorption time, feed flow rate, and feed NaCl concentration and compared with capacitive deionization (CDI) under the same conditions. The experimental results indicate that the effluent concentration during desorption becomes higher with increased adsorption time and a lower feed flow rate. Also it was shown that the introduction of both cation and anion exchange polymers was effective in preventing the “co-ion” effect. With MCDI, a salt removal efficiency of 100% was obtained under the conditions of 5 min/1 min adsorption/desorption time and 23 mL/min feed flow rate, while with CDI the salt removal efficiency was less than 40% under the same conditions. Open image in new window

A new technique is introduced for the preparation of composite membranes based on the salting-out effect. The concept of this new technique consists of three parts: (i) polymer precipitation by the salting-out effect, (ii) blocking the pore structure by pressurizing the precipitated polymer particles (polyelectrolyte), and (iii) deposition of opposite charged polyelectrolyte through ionic cross-linking (polyelectrolyte complex). The pore blocked polyelectrolyte has the role of a membrane, and we called this membrane preparation technique by forced fouling induction “precipitated solute pressurization” (PSP). In this study, water-soluble polymers that are all polyelectrolytes were used as coating materials, namely polyethylenimine (PEI), poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA), and poly(vinyl sulfonic acid) (PVSA). The polymer particles formed by the addition of Mg(NO3)2·6H2O were pressurized and flown to the surface of microporous polyvinyledene fluoride (PVDF) to prepare composite membranes under varying conditions of polyelectrolyte concentration, ionic strength of salt, pressure, annealing temperature, etc. The resulting membranes were characterized in terms of the flux and rejection for 100 ppm NaCl at 4 atm to determine their suitability for application in a household water purifier. A combination of PVSA and PEI polyelectrolyte complex produced by the PSP method showed the best performance of flux of 43 LMH and salt rejection rate of 83%, and this performance was maintained without loss of flux or rejection rate in a durability test carried out for 10 days.

The surfaces of the reverse osmosis (RO) membranes prepared by an interfacial polymerization method on the polysulfone supports in our lab were modified by the adsorption of the three hydrophilic polymers, poly(vinyl sulfonic acid) (PVSA), poly(ethylenimine) (PEI) and poly(vinyl alcohol) (PVA). Using the ‘salting-out effect’, these polymers, representative of anionic, cationic and neutral polymers, respectively, were used to investigate which adsorbed polymer is the most resistant to chlorine attack. The surface properties of the adsorbed RO membranes were characterized to confirm the adsorption by using contact angle measurement and scanning electron microscopy (SEM). The performance of chlorine-resistance RO membranes was measured through their evolution, before and after hypochlorite exposures in 3,450 ppm NaOCl solution for desired time points. This was determined in terms of pure water permeability and salt rejection. In order to determine the most dominant factor contributing to chlorine resistance, experiments were carried out under several conditions. The candidate factors included coating time, concentration of coating solution, ionic strength, and salt types. In general, as the coating time and concentration increased, the chlorine resistance increased for any salt used. Among the three materials, PVSA showed the greatest chlorine resistance of ca. 62,000 ppm·h, under the determined conditions, ionic strength (IS)=0.2 Mg and coating time of 60 s. The order of chlorine stabilities for the coating materials was determined to be PVSA, PEI, and PVA. It was found that the chlorine resistance of any polymer-coated membrane is superior to the pristine RO membrane.

In this study, polyvinylamine (PVAm), poly(vinyl sulfonic acid) (PVSA), and poly(styrene sulfonic acid) (PSSA) were physically adsorbed, using the ‘salting-out’ effect, onto hydrophobic membrane surfaces such as polysulfone (PSf), polyvinylidene fluoride (PVDF), and polyethylene (PE), commonly used as ultrafiltration (UF) and microfiltration (MF) membranes. The physical adsorption of such hydrophilic polymers were monitored as a function of concentration, time, type of salt, and ionic strength, and the resulting adsorbed membranes were characterized using a contact angle measurement, a gravimetric analysis, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). In most cases, with increasing the adsorption time, the wettability of surface-modified membranes was significantly improved. Physical adsorption of hydrophilic polymers on hydrophobic membrane surfaces, facilitated by the salt-out effect, was almost achieved within a few minutes. Typically, a contact angle of 47° was observed at ionic strength (IS)=0.1Mg(NO3)2·6H2O and PVAm 2,000 ppm for a PSf membrane. The weight changes by adsorption were varied with adsorption time in the cases of PVSA and PSSA, while the weight change for PVAm approached the equilibrium rapidly after the initial adsorption time. Open image in new window

In this manuscript, in order to reduce methanol permeability and, at the same time, to increase proton conductivity THS-PSA containing silica compound, responsible for methanol permeability reduction, and sulfonic acid, responsible for proton conductivity enhancement, was applied onto PVA/PSSA-MA membranes. And in order to improve durability, the resulting membranes, PVA/PSSAMA/THS-PSA, were exposed to 500ppm F2 gas at varying reaction times. The surface-fluorinated membranes were characterized through the measurement of contact angles, thermo-gravimetric analysis, and X-ray photoelec- tron spectroscopy to observe the physico-chemical changes. For the evaluation of the electro-chemical changes in the resulting membranes, its water contents, ion exchange capacity, proton conductivity, and methanol permeability were measured and then compared with the commercial membrane, Nafion 115. Finally, the membran electrode assembly(MEA) was prepared and the cell voltage against the current density was measured. As fluorination time increased, the contents of F2 increased up to maximum 4.3% and to depth of 50 nm. At 60 min of fluorination, the proton conductivity was 0.036 S/cm, larger than Nafion 115 at 0.024 S/cm, and the methanol permeability was 9.26E-08 cm 2 /s, less than Nafion 115 at 1.17E-06 cm 2 /s.

This study focuses on the investigation of the possibility of the crosslinked poly (vinyl alcohol) membranes with both poly (acrylic acid-co-maleic acid) (PAM) and 3-(trihydroxysilyl)-1-propane-sulfonic acid (THS-PSA) for the direct methanol fuel cell application. In order to characterize the prepared membranes, the water content, the thermal gravimetric analysis, the ion exchange capacity, the ion conductivity and the methanol permeability measurements were carried out and then compared with the existing Nafion 115 membrane. The ion exchange capacity of the resulting membranes showed 1.6~1.8 meq./g membrane which was improved than Nafion 115, 0.91 meq./g membrane. In the case of the proton conductivity, the THS-PSA introduced membranes gave more excellent than Nafion 115, . On the other hand, the methanol permeability was increased more than Nafion 115 for all the range of THA-PSA concentration.

Surface fluorination effectively reduced the water absorption of crosslinked polyvinyl alcohol (PVA)/poly(styrene sulfonic acid- co -maleic acid) (PSSA_MA) membranes. The crosslinked PVA membranes were prepared using PSSA_MA as a crosslinking agent as well as a donor of the hydrophilic group (–SO 3 H and/or –COOH). Surface treatment by gaseous fluorine treatment disrupted the C–OH bonds and generated C–F and C–F 2 groups at the membrane surface where atomic percent of fluorine increased up to 5.4%. The membranes with highly hydrophobic fluorinated surface exhibited improved proton conductivity and methanol permeability at a relatively low water uptake.

A series of sulfonated polystyrene-b-poly(ethylene-r-butylene)-b-polystyrene (S-SEBS) membranes with high water permeability and thermo-mechanical stability were prepared to estimate the membrane utility for heating/ ventilation/air conditioner (HVAC) system. The sulfonation degrees of membranes were controlled by the contents of sulfonating reagent (acetyl sulfate) added. Proton conductivity and water permeation properties of the membranes increased with increasing sulfonation degree. And gas permeation properties were measured to investigate effect of sulfonation of the membranes on permeation properties. Membrane stability with increasing sulfonation degree was also studied.

In the present study, crosslinked poly(vinyl alcohol) (PVA) membranes were prepared at different temperatures using poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA) (PVA:PSSA_MA = 1:9). The hybrid membranes were prepared by varying the TEOS content between 5 and 30 wt%. The PSSA_MA was used both as a crosslinking agent and the hydrophilic group donor (-SO3H and/or -COOH). The proton conductivity increased with up to 20 wt% TEOS, but decreased above this level, although the water content decreased with increasing TEOS content. This result suggests that the silica doped into the membrane improved the formation of proton-conduction pathways due to the absorption of molecular water. The PVA/PSSA_MA/Silica containing TEOS 20% showed both high proton conductivity (0.026 S/cm at 90°C) and low methanol permeability (5.55×10-7 cm2/s).

Sulfonation of polyetheretherketones (PEEK) was carried out in order to fabricate commercial perfluorosulfonic acid membrane alternatives, which were characterized in terms of their ion exchange capacity, ionic conductivity, water swelling, methanol crossover and electrochemical performance in their direct application as a methanol fuel cell. A high ion exchange capacity, 1.88, was achieved with a sulfonation reaction time of 8 h, with a significantly low methanol crossover low compared to that of Nafion. However, the morphological stability was found to deteriorate for membranes with sulfonation reaction times exceeding 8 h. Electrochemical cell tests suggested that the fabrication parameters of the membrane electrode assembly based on the sulfonated PEEK membranes should be optimized with respect to the physicochemical properties of the newly prepared membranes.

Crosslinked poly(vinyl alcohol) (PVA) membranes were prepared at various crosslinking temperatures using poly(acrylic acid-co-maleic acid) (PAM) containing different PAM contents. The thermal properties of these PVA/PAM membranes prepared at various reaction temperatures were characterized using differential scanning calorimetry (DSC). The proton conductivity and methanol permeability of PVA/PAM membranes were then investigated as PAM content was varied from 3 to 13 wt%. It was found that the proton and methanol transport were dependent on PAM content in their function both as crosslinking agent and as donor of hydrophilic -COOH groups. Both these properties decreased monotonously with increasing PAM concentration. The proton conductivities of these PVA/PAM membranes were in the range from 10−3 to 10−2S/cm and the methanol permeabilities from 10−7 to 10−6cm2/sec. In addition, the effect of operating temperature up to 80 °C on ion conductivity was examined for three selected membranes: 7, 9 and 11 wt% PAM membranes. Ion conductivity increased with increasing operating temperature and showed and S/cm at 80 °C, respectively. The effects of crosslinking and ionomer group concentration were also examined in terms of water content, ion exchange capacity (IEC), and fixed ion concentration. In addition, the number of water molecules per ionomer site was calculated using both water contents and IEC values. With overall consideration for all the properties measured in this study, 7∼9 wt% PAM membrane prepared at 140 °C exhibited the best performance. These characteristics of PVA/PAM membranes are desirable in applications related to the direct methanol fuel cell (DMFC).

Poly(vinyl alcohol) (PVA) membranes crosslinked with poly(acrylic acid-co-maleic acid) (PAM) were prepared to investigate the effect of aging on their morphology by swelling them for up to 7 days. PAM was used both as a crosslinking agent and as a donor of the hydrophilic -COOH group. A 30 wt% weight loss of the dry membrane was observed in the swelling test after 6 days. The surface of the membrane was dramatically changed after the swelling test. The surface roughness of the PVA/PAM membrane was increased, as determined by atomic force microscopy (AFM). The swelling loosened the polymer structure, due to the release of the unreacted polymer and the decomposition of the ester bond, thereby resulting in an increase in the free volume capable of containing water molecules. The water molecules present in the form of free water were determined by differential scanning calorimetry (DSC). The fraction of free water increased with increasing swelling time. The swelling of the membrane may provide space for the transport of protons and increase the mobility of the protonic charge carriers. The proton conductivity of the membranes measured atT=30 and 50 °C was in the range of 10−3 to 10−2 S/cm, and slightly increased with increasing swelling time and temperature.

Sulfonated polysulfone (SPSU) ionomer membranes were prepared via a solution sulfonation method using mixtures of chlorosulfonic acid (HSO 3 Cl) and chlorotrimethylsilane ((CH 3 ) 3 SiCl) as sulfonating agent. Ion exchange capacities (IECs) of SPSU ionomer membranes were controlled by varying the amount of HSO 3 Cl. In the present study, we investigated the thermal transition behavior of SPSU membranes annealed at different temperatures (60 and 150 °C) below glass transition temperature ( T g ) of SPSU ionomer membranes, and also studied the annealing effect on the proton conductivity and methanol transport through these ionomer membranes. The changes in T g (°C), ion exchange capacity (IEC, mmol/g), water uptake content (%), proton conductivity (S/cm), and methanol permeability (cm 2 /s) were reported and discussed. The heat-treatment of SPSU membranes at higher temperature led to the increase in T g and simultaneously the decrease in water uptake, proton conductivity and methanol permeability. Here, it was found that the annealing below T g accelerated the equilibrium process and physical aging of SPSU ionomer membranes and subsequently induced more compact chain packing structure, which eventually affected the proton and methanol transport through these ionomer membranes.

Cross-linked poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA)/silica hybrid membranes were prepared to evaluate the possibility of use as a proton exchange membrane for direct methanol fuel cell (DMFC). A chemical cross-linking agent having sulfonic acid group (–SO3H) was used to increase proton conductivity, and simultaneously to prevent methanol transport through the cross-linked membranes. In addition, silica particles were dispersed into polymer matrices via sol–gel reaction under acidic conditions, expecting the barrier to the methanol transport. The proton and the methanol transport were investigated in terms of PVA/PAA compositions and cross-linker (sulfosuccinic acid, SSA) concentration. It was found that the compositions of PVA/PAA and the cross-linker concentration affected the transport properties of the membranes. Particularly, the concentration of cross-linker markedly affected the proton and the methanol transport because SSA was used not only as a chemical cross-linker but also as a donor of fixed anionic group (–SO3−H+). The proton conductivities of the hybrid membrane were in the range of 10−3–10−2 S/cm, and the methanol permeabilities ranged between 10−8 and 10−7 cm2/s. Noticeably, the methanol permeabilities were reduced by cross-linking between PVA, PAA and SSA chains without a large sacrifice of proton conductivity. Moreover, the silica particles embedded in the cross-linked polymer membranes acted as a reducing material for fraction of free water as well as a methanol barrier to hinder pathway from penetrating methanol molecules.

Organic–inorganic hybrids based on poly(vinyl alcohol) (PVA)/SiO 2 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 SO 3 H 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 cm 2 /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.

In the present study, crosslinked poly(vinyl alcohol) (PVA) membranes were prepared using sulfosuccinic acid (SSA) at different crosslinking temperatures. The crosslinked PVA membranes were also synthesized by varying the amount of SSA (5–30 wt.%) in order to achieve desirable proton conductive properties for fuel cell applications. The crosslinked PVA membranes were characterized using an FT-IR spectroscopy, a thermogravimetric analysis (TGA), and a differential scanning calorimetry (DSC). Ion exchange capacities (IECs) of the crosslinked PVA membranes were in the range of 0.5–2.24 mmol/g. The water content was in the range of 10–80%, depending on the amount of SSA containing sulfonic acid group. The proton conductivities and the methanol permeabilities through the membranes were investigated in terms of various crosslinking conditions. Especially, it was found that the SSA used in this study played a decisive role in proton conduction (SO3−H+) and at the same time acted as a barrier for methanol transport. The proton conductivities and the methanol permeabilities of all the membranes were in the range of 10−3 to 10−2 S/cm and 10−7 to 10−6 cm2/s in the temperature range of 25–50 °C, respectively, depending on the crosslinking conditions.

Organic–inorganic hybrid membranes of poly(vinylidene fluoride)-cohexafluoropropylene (PVDF-HFP) and silica composites containing sulfonic acid groups were prepared via in situ polymerization of tetraethoxysilane (TEOS) and sulfosuccinic acid (SSA) using the sol-gel process. The membranes containing more sulfonic acid groups showed a higher vapor sorption and greater swelling behavior. The bound and free water content of the membrane is proportional to the SSA concentration. However, the hybrid membranes without SSA do not have free water. The ion conductivity of the membranes is proportional to the SSA concentration. Silica content in the hybrid membrane without SSA had great effect on their mechanical properties. Tensile modulus and yield stress increased and yield strain and elongation at break decreased with increased silica content. However, in the case of the hybrid membrane containing SSA modulus, yield stress decreased and yield strain and elongation at break increased with increased silica content due to the weak interactions between the hydrophobic polymer chain and the hydrophilic group of SSA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 209–218, 2004

Sulfonated polysulfone (SPS) membranes were prepared, and the gas-transport properties of the resulting ionic polymers were examined. Gas-transport measurements were made on dense films of these polymers with a continuous flow technique. The sulfonation of polysulfone and the metal-cation exchange of SPS were confirmed with Fourier transform infrared spectroscopy and electron spectroscopy for chemical analysis. The SPS membranes exchanged with the monovalent metal ions showed higher permeability coefficients than the SPS membranes exchanged with the multivalent metal ions, whereas the selectivities of all the metal-cation-exchanged sulfonated polysulfone (MeSPS) membranes for O2/N2 and CO2/N2 gas pairs were higher than those of SPS membranes. When the MeSPS membranes with metal cations of similar ionic radii were compared, the ideal selectivities of O2/N2 and CO2/N2 through MeSPS with divalent cations were higher than those through MeSPS with monovalent cations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2611–2617, 2002

Poly(vinyl alcohol)/sulfosuccinic acid (PVA/SSA) membranes in the hydrogen form were converted to monovalent metal ion forms Li+, Na+, and K+. The effect of exchange with metal ions was investigated by measuring the swelling of water–ethanol (10/90) mixtures at 30 °C and by the pervaporative dehydration performance test for aqueous ethanol solutions with various ethanol concentrations at 30, 40, and 50 °C. In addition, electron spectroscopy for chemical analysis (ESCA) analysis was carried out to study the quantity of metal ions in membranes. From the ESCA analysis, the lithium ion quantity in the resulting membranes is greater than that of any other metal ions in question because of the easy diffusion of a smaller metal ion into the membrane matrix. The swelling ratio was in the following order: PVA/SSA-Li+ > PVA/SSA-Na+ > PVA/SSA-K+ membranes. For pervaporation, the PVA/SSA-Na+ membrane showed the lowest flux and highest separation factor for all aqueous ethanol solutions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1867–1873, 2002

Pore-filling concept was applied to prepare high permselective composite membranes for CO2 separation. The membrane is composed of two polymeric materials: a porous substrate and filling polymers that fills the pore of the substrate. In this study, asymmetric polyacrylonitrile (PAN) membrane was used for a substrate and methoxy poly(ethylene glycol) acrylate (MePEGA, Mw=454) was used for a photoinitiated graft polymer. The analysis of graft membrane by Fourier transform infrared and attenuated total reflection (FT-IR, FT-IR/ATR), electron spectroscopy for chemical analysis (ESCA) and field emission scanning electron microphotography (FE-SEM) revealed that the graft polymer filled the pores of the substrate. High CO2/N2 permselectivity was shown by this pore-filling membrane: carbon dioxide permeation flux, J CO 2 =5.65 GPU (10−6 cm3(STP)/cm2 s cmHg) and selectivity of CO2 over N2, JCO2/JN2=32.4 at 30°C, measured by the time-lag method. The high permselectivity of the present pore-filling membrane is attributed to the high solubility selectivity due to the affinity of CO2 to PEO segment.

Currently, polyamide reverse osmosis membranes are highly effective for desalination, industrial process water, and home drinking water. However, they have poor resistance to strong oxidants especially chlorine due to chain cleavage of aromatic polyamide. In general, aromatic polyamide RO membranes are essentially random copolymers consisting of the linear and crosslinked structures. The amide ring is sensitive to attack by chlorine because it is an electron-rich region. Therefore, the activated carbon or sulfite addition processes are essential to remove the chlorine in the separation processes. Many research groups have studied to improve the chlorine-resistance RO membrane having hydrophilic groups (− SO 3 H and − COOH) or nitro groups (− NO 2 ) such as electron acceptors. In this study, thin film composite polyamide RO membranes were prepared by interfacial polymerization method including cross-linking agents having hydroxyl groups to improve the chlorine-resistance. The chlorine-resistance of polyamide RO membrane was influenced by the thermal cross-linking conditions (temperature and time) and cross-linking density of polyamide membranes.

Poly(vinyl alcohol)(PVA)/poly(acrylic acid)(PAA) and PVA/sulfosuccinic acid (SSA) membrane performances have been studied for the pervaporation separation of methyl tert-butyl ether (MTBE)/methanol (MeOH) mixtures with varying operating temperatures, amount of cross-linking agents, and feed compositions. Typically, the separation factor, about 4000, and the permeation rate, 10.1 g/m2/h, were obtained with PVA/PAA = 85/15 membrane for MTBE/MeOH = 80/20 mixtures at 50°C. For PVA/PAA membranes, it could be considered that the flux is affected by the structural changes of the membranes due to the cross-linking and the free carboxylic acid group also took an important role in the separation characteristics through the hydrogen bonding with PVA and the feed components leading to the increase of flux. The latter membrane of the 5% SSA membrane shows the highest separation factor of 2095 with the flux of 12.79 g/m2/h for MTBE/MeOH = 80/20 mixtures at 30°C. Besides the swelling measurements were carried out for pure MTBE and MeOH, and MTBE/MeOH = 90/10, 80/20 mixtures using PVA/SSA membranes with varying SSA compositions. It has been recognized that there are two factors, the membrane network and the hydrogen bonding in the swelling measurements of PVA/SSA membranes. These two factors act interdependently on the membrane swelling. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1699–1707, 2000

A new microencapsulation was established in which small microcapsules with a hydrophilic polymeric wall could be fabricated, capsulizing the water-soluble content. The new microencapsulation is based on an emulsion interfacial reaction technique that combines the characteristics of an interfacial reaction and conventional emulsion processes. In this technique, hydrophilic polymers [poly(vinyl alcohol) and chitosan] were used as the wall material of the microcapsules. The microencapsulation process was composed mainly of the following steps: preparation of a water/oil (w/o) emulsion 1 containing hydrophilic polymers and a water-soluble core material and w/o emulsion 2 containing a water-soluble crosslinking agent and catalyst; the formation of microcapsules by mixing emulsion 1 and emulsion 2; and washing and drying the formed microcapsules. In the new technique an insoluble polymer film was formed easily by the fast crosslinking reaction on the surface of tiny emulsified polymer solution particles in contact with the emulsified crosslinking agent solution particles under mixing with high speed agitation. Thereby, small stable microcapsules were formed. The emphasis in this study was on the establishment of the microencapsulation process by which microcapsules were formed and controlled. The microencapsulation was characterized by analysis of the size distribution of microcapsules fabricated with process conditions. The clarification of the effect of the preparation conditions was also made on the morphology and diameter of the microcapsules. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1645–1655, 2000

The removal of trace chlorinated hydrocarbons from water has been performed through poly(dimethylsiloxane), which had been fabricated by addition crosslinking reaction. The membrane had a more hydrophobic characteristic than that fabricated by a condensation reaction because it has no polar groups in the polymeric chain, such as hydroxyl and chlorine groups. This study concentrated on the comparison of the permeation behaviors of homologous series of chloromethanes aqueous solutions with that of a chloroethane solution. It was suggested that when the hydrophobic characteristics of a membrane system is greater, water molecules in the membrane tend to exist in the form of clusters; thereby, the permeating size of water component increases, resulting in suppressing water permeation and increasing the enrichment factor for the organic component. The permeation behaviors at various temperatures and membrane thicknesses were indirectly interpreted in terms of the effect of concentration polarization and the effect of interactions of organic–membrane, and water–organic-absorbing membrane. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 601–611, 1999

For the purposes of the water-selective membrane material development for pervaporation separation, we crosslinked poly(vinyl alcohol) (PVA) with sulfur-succinic acid (SSA), which contains —SO3OH, by heat treatment and investigated the effect of the crosslinking density on the separation of water–alcohol mixtures by pervaporation technique. The crosslinking reaction between PVA and SSA was characterized through Fourier transform infrared spectroscopy and differential scanning calorimetry tests by varying the amount of the crosslinking agent, the reaction temperature, and the swelling measurements of each pure component. The separation performance of the water–methanol mixture is not good due to the existence of sulfonic acid, hydrophilic group, in the crosslinking agent. However, for the water–ethanol mixture, the flux of 0.291 kg/m2h and the separation factor of 171 were obtained at 70°C when PVA-crosslinked membrane containing 7 wt % SSA was used. The same membrane also showed flux of 0.206 kg/m2h and a separation factor of 1969 at the same operating temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1717–1723, 1998

The pervaporation separation and the swelling behavior of acetic acid-water mixtures were investigated at 30, 40, and 50°C using the crosslinked poly(vinyl alcohol) (PVA) membranes with varying the poly(acrylic acid) (PAA) contents and the acetic acid concentration in the feed mixture. Typically, for the pervaporation separation of 90 wt % acetic acid in the feed, the PVA/PAA = 75/25 membrane gives the separation factor of 795 and the flux of 5.6 g/m2 h at 30°C, respectively. The swelling degree decreases as the PAA content in the membrane decreases to 20 wt % of PAA due to the increase of the crosslinking portion in the membrane and increases beyond this PAA content. The swelling degrees show fairly high at the operating temperatures and the total range of the liquid mixtures in question. The overall activation energy of permeation was also calculated using an Arrhenius type relationship. From this study, it could be concluded that the diffusion step is dominant over the sorption step. © 1997 John Wiley & Sons, Inc.

The pervaporation separation of methanol–water (M/W) mixtures was carried out using crosslinked poly(vinyl alcohol) (PVA) membranes with the low molecular weight of poly(acrylic acid) (PAA) as the crossinking agent. The PVA/PAA ratio in the crosslinked membrane was 90/10, 85/15, and 80/20 by weight. The operating temperatures were 50, 60, and 70°C, and the compositions of methanol–water mixtures to be separated were 70/30, 80/20, 90/10, and 95/5 (M/W) solutions. In all cases, the PVA/PAA = 80/20 membrane showed the best results. For M/W = 90/10 solution, the separation factor, αw/m = 465, and the permeation rate, 0.109 kg/m2h, at 70°C were obtained using the PVA/PAA = 80/20 menbrane. The permeation rate and the separation factor for M/W = 95/5 solution showed 0.033 kg/m2h and αw/m = 2650, respectively, when PVA/PAA = 80/20 membrane was used. © 1996 John Wiley & Sons, Inc.

The application of the pervaporation process in biotechnology is rapidly growing. A two stage pervaporation process could be applied to the downstream processing of ethanol fermentation. In this paper, the second stage process—a water-selective process—was investigated in detail using the crosslinked poly(vinyl alcohol) membranes with the low molecular weight of poly(acrylic acid) as the crosslinking agent. The ratio of poly(vinyl alcohol) and poly(acrylic acid) in the membrane was 90/10, 85/15, and 80/20 by weight. The prepared membranes were tested to separate the various compositions of the water–ethanol mixtures, specially 50/50 solution at 60°C and 30/70, 20/80, 10/90, and 4.4/95.6 solutions at 60, 70, and 75°C. For water: ethanol = 50 : 50 solution, the separation factor αw/e = 260 at 75°C was obtained by using a PVA/PAA = 80/20 membrane. The permeation rate and the separation factor at the azeotropic point of a water–ethanol mixture showed 30 g/m2/h and 5800 at 75°C, respectively, when a PVA/PAA = 80/20 membranes was used. © 1995 John Wiley & Sons, Inc.

For the purpose of the water-selective membrane material development for pervaporation separation, poly(vinyl alcohol) (PVA) was crosslinked with a low molecular weight of poly(acrylic acid) (PAA). The crosslinking reactions between PVA and PAA were characterized through IR spectroscopy, differential scanning calorimetry (DSC), and tensile tests when varying the reaction conditions, that is, time, temperature, amounts of cross-linking agents, PAA. It was found that the crosslinking reaction was fast: in other words, that the reaction mainly occurred at the initial step of each reaction condition. The best reaction conditions for preparing the crosslinked PVA membranes were found to be: reaction time not over 1 h, reaction temperature in the range of 150-180 C. PAA contents of 15-20 wt% were found satisfactory with respect to the application areas.

Novel ionically cross-linked blended membranes of nylon 6 and poly(acrylic acid) (PAA) were studied for the pervaporation separation of the binary organic mixture of pentane and methanol. Membranes of composition 25 wt % PAA were used after cross-linking. The experimental data obtained from the pervaporation runs were compared with the theoretical values of the individual permeabilities for binary mixtures predicted by the modified Fels and Huang model. This new model is based on an extension of the free volume theory and the introduction of Flory–Huggins thermodynamics for the calculations of the binary interaction parameters and the diffusion coefficients. The calculated values of permeabilities obtained from this modified model were reasonably close to the experimental values.

In the present study, crosslinked poly(vinyl alcohol) (PVA) membranes were prepared using poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA) (PVA:PSSA_MA = 1:7). The PSSA_MA was used both as a crosslinking agent and as a donor of the hydrophilic group (–SO3H and/or –COOH). The hybrid membranes were prepared by modified clay such as Clay Na+, Clay 30B, and Clay 15A. The thermal, water uptake, proton and methanol transport properties of the hybrid membrane were found to be sensitive to the clay type and content. The hybrid membrane with Clay 30B shows higher proton conductivity than other hybrid membranes due to hydroxyethyl group. The membrane with Clay 15A showed the lowest methanol permeability due to lower specific gravity than other clay. Compared to the membrane without modified, the PVA/PSSA_MA/Clay 15A containing 4 wt% of Clay 15A showed both high proton conductivity (0.023 S/cm) and low methanol permeability (2.19 × 10−7 cm2/s).

Crosslinked poly(vinyl alcohol) (PVA) membranes were prepared at various crosslinking temperatures using poly(acrylic acid-co-maleic acid) (PAM) containing different PAM contents. The thermal properties of these PVA/PAM membranes prepared at various reaction temperatures were characterized using differential scanning calorimetry (DSC). The proton conductivity and methanol permeability of PVA/PAM membranes were then investigated as PAM content was varied from 3 to 13 wt%. It was found that the proton and methanol transport were dependent on PAM content in their function both as crosslinking agent and as donor of hydrophilic -COOH groups. Both these properties decreased monotonously with increasing PAM concentration. The proton conductivities of these PVA/PAM membranes were in the range from 10−3 to 10−2S/cm and the methanol permeabilities from 10−7 to 10−6cm2/sec. In addition, the effect of operating temperature up to 80 °C on ion conductivity was examined for three selected membranes: 7, 9 and 11 wt% PAM membranes. Ion conductivity increased with increasing operating temperature and showed and S/cm at 80 °C, respectively. The effects of crosslinking and ionomer group concentration were also examined in terms of water content, ion exchange capacity (IEC), and fixed ion concentration. In addition, the number of water molecules per ionomer site was calculated using both water contents and IEC values. With overall consideration for all the properties measured in this study, 7∼9 wt% PAM membrane prepared at 140 °C exhibited the best performance. These characteristics of PVA/PAM membranes are desirable in applications related to the direct methanol fuel cell (DMFC).

Polymerisation anionique de la pyrrolidone-2, a 40°C, en presence de CO 2 /KOH et CO 2 /KOH/18-crown ether