Crosslinked Poly Vinyl Alcohol Membranes Research Articles

Low-cost and durable polyvinyl alcohol modified polyethylene separator for vanadium redox flow battery

Porous separators are considered a viable alternative to the high cost Nafion membrane for vanadium redox flow battery (VRFB) commercialization. However, the porous separators suffer from high vanadium ion crossover due to the presence of large micron size pores, which leads to decay in capacity of the VRFB system. To tackle the same, a composite separator is synthesized wherein a cross-linked polyvinyl alcohol (PVA) layer is coated on to the porous polyethylene silica separator (PE separator) to mitigate the vanadium ion crossover rate and employed in the VRFB application. Scanning electron microscopy (SEM) analysis confirmed the successful coating of the PVA film on to the PE separator. Synthesized PE-PVA separator showed a significant decrease in the vanadium ion crossover by 31.44 times compared to the pristine PE separator. Consequently, the self-discharge time increases by 8 and 1.66 times compared to the pristine PE separator and the Nafion117 membrane, respectively. VRFB cell equipped with the synthesized separator showed better capacity retention with a capacity fade rate of 0.2 % Ah·cycle−1 than the Nafion117 membrane (0.5 % Ah·cycle−1). In-situ and ex-situ oxidative stability of the separator is explored in detail and a degradation mechanism of the cross-linked PVA membrane is proposed accordingly. The synthesized single side coated PE-PVA´ separator exhibits higher coulombic efficiency of 99 % and comparable energy efficiency of 71 % at a current density of 120 mA·cm−2 and demonstrated excellent lifetime durability tested up to 1600 charge-discharge cycles at 80 mA·cm−2.

Effect of Crosslinking Conditions on the Transport of Protons and Methanol in Crosslinked Polyvinyl Alcohol Membranes Containing the Phosphoric Acid Group.

In this investigation, we systematically explored the intricate relationship between the structural attributes of polyvinyl alcohol (PVA) membranes and their multifaceted properties relevant to fuel cell applications, encompassing diverse crosslinking conditions. Employing the solution casting technique, we fabricated crosslinked PVA membranes by utilizing phosphoric acid (PA) as the crosslinking agent, modulating the crosslinking temperature across a range of values. This comprehensive approach aimed to optimize the selection of crosslinking parameters for the advancement of crosslinked polymer materials tailored for fuel cell contexts. A series of meticulously tailored crosslinked PVA membranes were synthesized, each varying in PBTCA content (5-30 wt.%) to establish a systematic framework for elucidating chemical interactions, morphological transformations, and physicochemical attributes pertinent to fuel cell utilization. The manipulation of crosslinking agent concentration and crosslinking temperature engendered a discernible impact on the crosslinking degree, leading to a concomitant reduction in crystallinity. Time-resolved attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was harnessed to evaluate the dynamics of liquid water adsorption and ionomer swelling kinetics within the array of fabricated PVA films. Notably, the diffusion of water within the PVA membranes adhered faithfully to Fick's law, with discernible sensitivity to the crosslinking conditions being implemented. Within the evaluated membranes, proton conductivities exhibited a span of between 10-3 and 10-2 S/cm, while methanol permeabilities ranged from 10-8 to 10-7 cm2/s. A remarkable revelation surfaced during the course of this study, as it became evident that the structural attributes and properties of the PVA films, under the influence of distinct crosslinking conditions, underwent coherent modifications. These changes were intrinsically linked to alterations in crosslinking degree and crystallinity, reinforcing the interdependence of these parameters in shaping the characteristics of PVA films intended for diverse fuel cell applications.

Strategies to overcome the limitations of cross-linked hydrophilic PVA membranes; carboxy methyl cellulose blending for epichlorohydrin-isopropanol-water pervaporation dehydration

Sodium carboxyl methyl cellulous (NaCMC)/Polyvinyl alcohol (PVA) coated Alumina hollow fiber (AHF) membrane was developed and applied to dehydration of ECH-IPA-water ternary feed mixture. CMC40 membrane, including 40 wt% of NaCMC showed the highest flux of 0.416 kg/m2h and a separation factor of 898 due to optimized packing density between PVA and the NaCMC polymer chain and relatively higher hydrophilic nature for PV separation to ECH-IPA-water ternary feed. After that, CMC40-coated AHF membrane was prepared according to the number of CMC40 coating and baking temperature. With an increase in baking temperature to 170 °C, the separation factor was significantly improved, while the flux decreased slightly. Moreover, NaCMC40-AHF showed robust properties with stable performance in the 50-h long-term PV test.

Pervaporation Polyvinyl Alcohol Membranes Modified with Zr-Based Metal Organic Frameworks for Isopropanol Dehydration.

Metal-organic frameworks (MOFs) are perceptive modifiers for the creation of mixed matrix membranes to improve the pervaporation performance of polymeric membranes. In this study, novel membranes based on polyvinyl alcohol (PVA) modified with Zr-MOFs (MIL-140A, MIL-140A-AcOH, and MIL-140A-AcOH-EDTA) particles were developed for enhanced pervaporation dehydration of isopropanol. Two membrane types (substrateless–freestanding; and formed on polyacrylonitrile support-composite) were prepared. The additional cross-linking of membranes with glutaraldehyde was carried out to circumvent membrane stability in pervaporation dehydration of diluted solutions. The synthesized Zr-MOFs were characterized by scanning electron microscopy, X-ray powder diffraction analysis, and specific surface area measurement. The structure and physicochemical properties of the developed membranes were investigated by Fourier-transform infrared spectroscopy, scanning electron and atomic force microscopies, thermogravimetric analysis, swelling experiments, and contact angle measurements. The PVA and PVA/Zr-MOFs membranes were evaluated in pervaporation dehydration of isopropanol in a wide concentration range. It was found that the composite cross-linked PVA membrane with 10 wt% MIL-140A had optimal pervaporation performance in the isopropanol dehydration (12–100 wt% water) at 22 °C: 0.15–1.33 kg/(m2h) permeation flux, 99.9 wt% water in the permeate, and is promising for the use in the industrial dehydration of alcohols.

Microwave-induced ultrafast crosslinking of Poly (vinyl alcohol) blended with nanoparticles as wave absorber for pervaporation desalination

Although pervaporation (PV) membranes based on crosslinked polyvinyl alcohol (PVA) exhibit high desalination performance, the thermal crosslinking process often takes several hours. Here, we report a microwave assisted method to reduce the crosslinking duration. Moreover, to the PVA crosslinking system, a MOF particle, UIO-66, was added to increase the microwave absorbing efficiency and improve the desalination property. As a result, the PVA crosslinking time decreased to 2 min and the water flux increased by 67% compared with the plain crosslinked PVA membrane.

Swelling-Resistant, Crosslinked Polyvinyl Alcohol Membranes with High ZIF-8 Nanofiller Loadings as Effective Solid Electrolytes for Alkaline Fuel Cells.

The present work investigates the direct mixing of aqueous zeolitic imidazolate framework-8 (ZIF-8) suspension into a polyvinyl alcohol (PVA) and crosslinked with glutaraldehyde (GA) to form swelling-resistant, mechanically robust and conductivity retentive composite membranes. This drying-free nanofiller incorporation method enhances the homogeneous ZIF-8 distributions in the PVA/ZIF-8/GA composites to overcome the nanofiller aggregation problem in the mixed matrix membranes. Various ZIF-8 concentrations (25.4, 40.5 and 45.4 wt.%) are used to study the suitability of the resulting GA-crosslinked composites for direct alkaline methanol fuel cell (DAMFC). Surface morphological analysis confirmed homogeneous ZIF-8 particle distribution in the GA-crosslinked composites with a defect- and crack-free structure. The increased ionic conductivity (21% higher than the ZIF-free base material) and suppressed alcohol permeability (94% lower from the base material) of PVA/40.5%ZIF-8/GA resulted in the highest selectivity among the prepared composites. In addition, the GA-crosslinked composites’ selectivity increased to 1.5–2 times that of those without crosslink. Moreover, the ZIF-8 nanofillers improved the mechanical strength and alkaline stability of the composites. This was due to the negligible volume swelling ratio (<1.4%) of high (>40%) ZIF-8-loaded composites. After 168 h of alkaline treatment, the PVA/40.5%ZIF-8/GA composite had almost negligible ionic conductivity loss (0.19%) compared with the initial material. The maximum power density (Pmax) of PVA/40.5%ZIF-8/GA composite was 190.5 mW cm−2 at 60 °C, an increase of 181% from the PVA/GA membrane. Moreover, the Pmax of PVA/40.5%ZIF-8/GA was 10% higher than that without GA crosslinking. These swelling-resistant and stable solid electrolytes are promising in alkaline fuel cell applications.

A Study on Synthesis of Chemical Crosslinked Polyvinyl Alcohol-Based Alkaline Membrane for the Use in Low-Temperature Alkaline Direct Ethanol Fuel Cell

In this paper, an economical and simple procedure was adopted for the fabrication of chemically crosslinked polyvinyl alcohol (PVA)-based KOH-doped alkaline membrane for the use in an alkaline direct ethanol fuel cell (ADEFC). The membrane parameters, namely, water uptake, KOH uptake, and ionic conductivity were systematically evaluated. The ionic conductivity of the synthesized membrane was in the order of 9 × 10−3 S/cm. The performance of the synthesized alkaline membrane is evaluated in a single ADEFC. Commercial Pt–Ru (30 wt %: 15 wt %)/C and Pt (40 wt %)/high surface area carbon (CHSA) from Alfa Aesar, Haverhill, MA, were used for anode and cathode, respectively. The performance of the membrane was further evaluated in a single cell using different grades of membranes containing different glutaraldehyde (GA) concentration, anode and cathode electrocatalyst loading, ethanol concentration, and KOH concentration. The maximum open circuit voltage (OCV) of 0.73 V was obtained at a temperature of 35 °C for anode feed containing 2 M ethanol and 1 M KOH for the membrane crosslinked with 2.5 wt % glutaraldehyde doped with 6 M KOH. The maximum power density of 4.15 mW/cm2 at a current density of 20.69 mA/cm2 was obtained for the same condition. The optimum electrocatalyst loading was 1 mg/cm2 of Pt-Ru/C at the anode and 1 mg/cm2 of Pt/CHSA at the cathode. The performance of KOH-doped chemically crosslinked PVA membrane was comparable with the published literature.

Using crosslinked polyvinyl alcohol polymer membrane as a separator in the microbial fuel cell

Separator between anode and cathode is an essential part of the microbial fuel cell (MFC) and its property could significantly influence the system performance. In this study we used polyvinyl alcohol (PVA) polymer membrane crosslinked with sulfosuccinic acid (SSA) as a new separator for the MFC. The highest power density of 759±4mW·m−2 was obtained when MFC using the PVA membrane crosslinked with 15% of SSA due to its desirable proton conductivity (5.16±10−2 S·cm−1). The power density significantly increased to 1106±30 mW·m−2 with a separator-electrode-assembly configuration, which was comparable with glass fiber (1170±46 mW·m−2). The coulombic efficiencies of the MFCs with crosslinked PVA membranes ranged from 36.3% to 45.7% at a fix external resistance of 1000 Ω. The crosslinked PVA membrane could be a promising alternative to separator materials for constructing practical MFC system.

Preparation and modification of poly (vinyl) alcohol membrane: Effect of crosslinking time towards its morphology

This paper is concerned with the crosslinking of poly (vinyl) alcohol (PVA) using glutaraldehyde as the crosslinking agent. PVA is highly hydrophilic and has excellent film-forming and chemical resistance properties. Chemical crosslinking is the most common approach for stabilizing PVA membranes, which makes it less swollen in the water. Asymmetric PVA membranes were prepared by the immersion–precipitation technique and were further crosslinked with glutaraldehyde. Then, the effects of the crosslinking time on the pore size distribution were examined by porometer. Also, the porosity of the crosslinked PVA membranes was observed via the SEM images and the functional groups that exist in the membrane were determined using Fourier-transform infrared spectroscopy (FTIR). Ultimately, the pure water permeate flux of the crosslinked membrane is done to observe the permeability of produced membrane.

Surface fluorinated poly(vinyl alcohol)/poly(styrene sulfonic acid- co-maleic acid) membrane for polymer electrolyte membrane fuel cells

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 3H 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.

Dehydration of 1,4-dioxane by pervaporation using filled and crosslinked polyvinyl alcohol membrane

Polyvinyl alcohol (PVOH) membrane, was modified both physically and chemically by incorporation of inorganic filler, sodium aluminosilicate and chemical crosslinking with maleic acid and glutaraldehyde. The change of morphology and crystallinity of PVOH by this physical and chemical modification was studied by FTIR, DSC, TGA, SEM and XRD. These membranes were evaluated in terms of its potential for dehydration of dioxane by preferential sorption and permeation using pervaporation (PV) technique. These membranes were cast in the laboratory by solution casting from the polymer and other additives. The performance of the unfilled (containing no filler) glutaraldehyde (GA) crosslinked PVOH-1 and maleic acid (MA) crosslinked PVOH-2 membranes were compared with filled (containing aluminosilicate filler) but GA crosslinked PVOH-3 and filled but MA crosslinked PVOH-4 membranes. The filled membranes were found to show higher flux and water selectivity. Among all the four used membranes, the MA crosslinked filled PVOH-4 membrane was found to show best results in terms of both water selectivity and flux.

Synthesis of Chemically Modified Polyvinyl Alcohol Membranes for Dehydration of Dioxane by Pervaporation

Polyvinyl alcohol (PVOH) has been chemically modified by polymerizing hydroxyethylmethacrylate (HEMA) in aqueous solution of PVOH and finally crosslinking PVOH with glutaraldehyde to produce a semi-interpenetrating network (SIPN) membrane. Accordingly, three such SIPNs i.e., SIPNI, SIPNII, and SIPNIII were synthesized with different weight ratio of PVOH: HEMA i.e., 1:0.25 (SIPNI), 1:0.50 (SIPNII) and 1:0.75 (SIPNIII). These SIPN membranes were used for pervaporative dehydration of dioxane. PVOH without any chemical modification but crosslinked with the same amount of glutaraldehyde has also been used for this study for comparison. All the SIPN membranes were also characterized with various conventional methods like mechanical properties, DSC and TGA. Water permeability and water selectivity of the IPN membranes were found to be much higher than those of the crosslinked PVOH membrane which was not chemically modified. The permeability of the membranes were also found to increase with increase in the HEMA content in PVOH matrix.