Preparation of poly(vinyl alcohol) grafted with acrylic acid/styrene binary monomers for selective permeation of heavy metals

A study was made to modify water‐soluble poly(vinyl alcohol) (PVA) by grafting acrylic acid and styrene (AAc/Sty) comonomers using gamma rays as an initiator. The factors that affect the preparation process and grafting yield were studied and more economical grafts under the most favorable reaction conditions were obtained. It was found that the high degree of grafting in such systems was obtained in the presence of an ethanol–water mixture in which water plays a significant role in enhancing the graft copolymerization. The critical amount of water to afford the maximum grafting yield was evaluated. The effect of the comonomer composition on the grafting yield was also investigated and it was observed that using a mixture of AAc/Sty monomers influences the extent of grafting of each monomer onto the PVA substrate and the phenomenon of synergism occurs during such a reaction. Also, the degree of grafting increases as the content of the solvent decreases in the reaction medium. However, the grafting yield increased as the total dose increased. The graft copolymer was characterized by IR and UV spectroscopic methods. The permeation of heavy metals such as Ni and Co through the grafted membranes was investigated and the efficiency of the separation process was also determined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 806–815, 1999     

Poly(vinyl alcohol) and poly(vinyl amine) blend membranes for isopropanol dehydration

Blended membranes of hydrophilic polymers poly(vinyl alcohol) (PVA) and poly(vinyl amine) (PVAm) were prepared and crosslinked with glutaraldehyde. The prepared membranes were characterized using infrared (attenuated total reflection mode) spectroscopy, differential scanning calorimetry, X‐ray diffractometry, and scanning electron microscopy measurements. Pervaporation performances of the membranes were evaluated for the separation of water‐isopropanol (IPA) mixtures. As the PVAm content increased from PVAm0 to PVAm1.5, the flux through a 70 μm film increased from 0.023 to 0.10 kg/m² h at an IPA/water feed ratio of 85/15 at 30 °C. The driving force for permeation of water increased due to the temperature but it has no effect on IPA permeation. Activation energies for the permeation of IPA and water were calculated to be 17.11 and 12.46 kJ/mol, respectively. Controlling the thickness of the blend membrane could improve the permeation flux with only a marginal reduction in the separation factor. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45572.     

Separation characteristics of pervaporation membrane separation processes using modified poly(vinyl alcohol) membranes

Modified poly(vinyl alcohol) (PVA) membranes prepared by the ‘solution technique’ were tested for ethanol-water mixtures by varying the reaction density (X_cr = 0.05, 0.1) at various temperatures. The results are compared with those of PVA membranes (X_cr = 0.05) prepared by the technique of the GFT Company, Germany.     

Characterization of degraded hydrogels based on poly(vinyl alcohol) grafted with poly(lactide‐co‐glycolide)

Poly(vinyl alcohol) (PVA) grafted with poly(lactide‐co‐glycolide) and cross‐linked as a material of increased hydrophobicity relative to PVA was produced. The properties were examined with respect to the mass loss, water uptake, hydrophilicity, and mechanical characteristics upon hydrolytical degradation. The hydrogels investigated display water uptake increasing with degradation time because of increasing hydrophilicity. The mass loss amounts up to 15% after eight weeks of degradation. The mechanical properties of the hydrogels are within the range of those of natural tissue, the E modulus is 18 MPa, or even 100–200 MPa, depending on the structure of material. The mechanical characteristic and their dependence degradation show the most recognizable correlation with the chemical structure. Studies of the topography of degraded samples (scanning electron microscopy) and IR measurements demonstrate the degradation to occur at slow rate due to the high degree of grafting. The mass loss is rather low and a bulk degradation mechanism takes place. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of poly(vinyl acetate)‐graft‐polystyrene and application to preparation of porous membranes

Poly(vinyl acetate)–TEMPO (PVAc–TEMPO) macroinitiators were synthesized by bulk polymerization of vinyl acetate in the presence of benzoyl peroxide (BPO) followed by termination with 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO). Radicals were mainly transferred to the acetoxy methyl groups in PVAc during the polymerization. The PVAc–TEMPO macroinitiators had several TEMPO‐dormant sites and styrene bulk polymerization with the macroinitiators produced poly(vinyl acetate)‐graft‐polystyrene (PVAc‐g‐PS). All the TEMPO‐dormant sites of PVAc–TEMPO macroinitiators participated in the styrene polymerization with almost equal reactivity. Methanolysis of PVAc‐g‐PS broke the PS branches apart from the PVAc backbone chains. Hydrophobic or hydrophilic porous membranes with controlled pore size could be prepared by removing the PVAc domains or the PS domains from the graft copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1658–1667, 2001     

Improving the antifouling property of poly(vinyl chloride) membranes by poly(vinyl chloride)‐g‐poly(methacrylic acid) as the additive

To improve the antifouling property of poly(vinyl chloride) (PVC) membranes, a series of poly(methacrylic acid) grafted PVC copolymers (PVC‐g‐PMAA) with different grafting degree were synthesized via one‐step atom transfer radical polymerization process utilizing the labile chlorines on PVC backbones followed by one‐step hydrolysis reaction. PVC/PVC‐g‐PMAA blend membranes with different grafting degree and copolymer content were prepared by nonsolvent induced phase separation method. The surface chemical composition, surface charge, membrane structures, wettability, permeability, separation performances and the fouling resistance of blend membranes were carefully investigated. The results indicated that the PMAA chains were segregated towards the surface and the membranes were endowed with negative charge. The hydrophilicity and permeability of the blend membranes were obviously improved. Furthermore, the antifouling ability especially at neutral or alkaline environments was also significantly increased. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42745.     

Studies on aluminum-isopropoxide doped poly(ethylene oxide), poly(vinyl alcohol), and poly(ethylene oxide)-poly(vinyl alcohol) blends

Poly(ethylene oxide), poly(vinyl alcohol), and their blend in a 40 : 60 mole ratio were doped with aluminum isopropoxide. Their structural, thermal, and electrical properties were studied. Aluminum isopropoxide acts as a Lewis acid and thus significantly influences the electrical properties of the polymers and the blend. It also acts as a scavanger for the trace quantities of water present in them, thereby reducing the magnitude of proton transport. It also affects the structure of polymers that manifests in the thermal transformation and decomposition characteristics. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2147–2157, 1998     

Plasma‐modified poly(vinyl alcohol) membranes for the dehydrationof ethanol

Non‐porous poly(vinyl alcohol) (PVA) membranes prepared by a cast‐evaporating technique were covered with an allyl alcohol or acrylic acid plasma‐polymerized layer. The wettability and the surface energy, as well as the chemical nature of the deposit, were assigned by X‐ray photoelectron spectroscopy (XPS) and Fourier‐transform infrared spectroscopy (FTIR). The ability of the modified membranes for dehydrating the water/ethanol azeotropic mixture by pervaporation was studied at 25, 40 and 60 °C. The best selectivity (α = 250 at 25 °C) was obtained in the case of the allyl alcohol plasma treatment. The results obtained are discussed on the basis of the hydrophilicity as well as in terms of the weakly crosslinked superficial layer that favoured the membrane swelling. Copyright © 2003 Society of Chemical Industry     

Preparation and characterization of poly(vinyl alcohol)‐poly(vinyl pyrrolidone) blend: A biomaterial with latent medical applications

Aqueous solutions of poly(vinyl alcohol) and poly(vinyl pyrrolidone) are blended and films are produced by casting method with the further intention of being used as bio‐materials with latent medical application. Glutaraldehyde, 4,4′‐diazido‐2,2′‐stilbenedisulfonic acid disodium salt tetra‐hydrate are used as crosslinker agents, whereas lactic acid is the plasticizer in the blend. The obtained films are characterized by differential scanning calorimetry (DSC), mechanical properties, swelling and solubility behavior. DSC measurements show that the blends exhibit a single glass transition temperature indicating that they are miscible, even in the presence of the plasticizer and crosslinker agents. By the combination of all mentioned additives, a relevant enhancement of the swelling is observed, accompanied by a stabilization of the solubility during the tested time. Finally, mechanical properties show an appropriate performance in the studied parameters. As a consequence, the obtained films could be suitable for use as medium or long‐term implants. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) and poly(vinyl alcohol)‐graft‐poly(lactide) in melt with magnesium hydride as catalyst

Grafting of poly(ε‐caprolactone) (PCL) and poly(lactide) (PLA) chains on poly(vinyl alcohol) backbone (PVA degree of hydrolysis 99%) was investigated using MgH₂ environmental catalyst and melt‐grown ring‐opening polymerization (ROP) of ε‐caprolactone (CL) and L ‐lactide (LA), that avoiding undesirable toxic catalyst and solvent. The ability of MgH₂ as catalyst as well as yield of reaction were discussed according to various PVA/CL/MgH₂ and PVA/LA/MgH₂ ratio. PVA‐g‐PCL and PVA‐g‐PLA were characterized by ¹H‐ and ¹³C‐NMR, DSC, SEC, IR. For graft copolymers easily soluble in tetrahydrofuran (THF) or chloroform, wettability and surface energy of cast film varied in relation with the length and number of hydrophobic chains. Aqueous solution of micelle‐like particles was realized by dissolution in THF then addition of water. Critical micelle concentration (CMC) decreased with hydrophobic chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and spectroscopic studies of poly(N‐vinyl pyrrolidone)/poly(vinyl alcohol) blend films

Poly(N‐vinyl pyrrolidone) (PVP) and poly (vinyl alcohol) (PVA) homopolymers and their blended samples with different compositions were prepared using cast technique and subjected to X‐ray diffraction (XRD) measurements, infrared (IR) spectroscopy, ultraviolet/visible spectroscopy, and thermogravimetric analysis (TGA). XRD patterns of homopolymers and their blended samples indicated that blending amorphous materials, such as PVP, with semicrystalline polymer, such as PVA, gives rise to an amorphous structure with two halo peaks at positions identical to those found in pure PVP. Identification of structure and assignments of the most evident IR ‐ absorption bands of PVP and PVA as well as their blends in the range 400–2000 cm^?1 were studied. UV–vis spectra were used to study absorption spectra and estimate the values of absorption edge, E_g, and band tail, E_e, for all samples. Making use of Coats‐Redfern relation, thermogravimetric (TG) data allowed the calculation of the values of some thermodynamic parameters, such as activation energy E, entropy ΔS^#, enthalpy ΔH, and free energy of activation ΔG^# for different decomposition steps in the samples under investigation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pervaporation separation of water/dimethylformamide mixtures using poly(vinyl alcohol)‐g‐polyacrylamide copolymeric membranes

Grafted copolymeric membranes of poly(vinyl alcohol) with acrylamide (PVA‐g‐AAm) were developed and used in the pervaporation separation of water–dimethylformamide mixtures by varying the amount of water in the feed from 0 to 100%. From these data, the permeation flux, pervaporation separation index, diffusion coefficient, swelling index, and separation selectivity were calculated at 25, 35, and 45°C. The Arrhenius activation parameters for permeation flux ranged between 22 and 63 kJ/mol, while the activation energy for diffusion ranged between 23 and 67 kJ/mol. Separation selectivity was between 15 and 22. The highest permeation flux of 0.459 kg m^?2 h^?1 was obtained for the 93% grafted membrane at 90% of water in the feed mixture. The results are discussed using the principles of the solution–diffusion model. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 273–282, 2002     

Formation of porous poly(ethylene‐co‐vinyl alcohol) membrane via thermally induced phase separation

Crystalline poly(ethylene‐co‐vinyl alcohol) (EVOH) membranes were prepared by a thermally induced phase separation (TIPS) process. The diluents used were 1,3‐propanediol and 1,3‐butanediol. The dynamic crystallization temperature was determined by DSC measurement. No structure was detected by an optical microscope in the temperature region higher than the crystallization temperature. This means that porous membrane structures were formed by solid–liquid phase separation (polymer crystallization) rather than by liquid–liquid phase separation. The EVOH/butanediol system showed a higher dynamic crystallization temperature and equilibrium melting temperature than those of the EVOH/propanediol system. SEM observation showed that the sizes of the crystalline particles in the membranes depended on the polymer concentration, cooling rate, and kinds of diluents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2449–2455, 2001     

Novel Poly(vinyl alcohol)‐tetraethoxysilane hybrid matrix membranes as oxygen barriers

Novel type of membranes based on poly(vinyl alcohol) crosslinked with tetraethoxysilane have been prepared by solution casting and solvent‐evaporation method. The membranes thus formed were characterized by Fourier transform infrared spectroscopy (FTIR) to study the chemical interactions, X‐ray diffraction (XRD), and thermogravimetry (TGA) to investigate morphological and thermal properties. Membranes were prepared in two different thicknesses (30 and 55 μm) and used for measuring the oxygen permeability under varying feed pressures (maintaining the desired pressure differential across the membrane) in the range from 1 to 50 kg/cm² pressure. Oxygen permeability of the membranes ranged from 0.0091 to 1.6165 Barrer for 30 μm and 0.0305 to 0.1409 Barrer for 55‐μm thick membranes by increasing the feed pressures on the feed side. Except at 50 kg/cm² pressure, the observed oxygen permeability values are almost close to total permeability. Membranes of this study could be useful as oxygen barriers for applications in food packaging industries. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 273–278, 2007     

Thermal characteristics of poly(vinyl alcohol) and poly(vinylpyrrolidone) IPNs

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and 1‐vinyl‐2‐pyrrolidone (VP) were prepared by radical polymerization using 2,2‐dimethyl‐2‐phenylacetophenone (DMPAP) and methylene bisacrylicamide (MBAAm) as initiator and crosslinker, respectively. The thermal characterization of the IPNs was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dielectric analysis (DEA). Depressions of the melting temperatures of PVA segments in IPNs were observed with increasing VP content via the DSC. The DEA was employed to ascertain the glass transition temperature (T_g) of IPNs. From the result of DEA, IPNs exhibited two T_gs indicating the presence of phase separation in the IPN. The thermal decomposition of IPNs was investigated using TGA and appeared at near 270°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1844–1847, 2002     

Preparation of Cu(II)‐chelated poly(vinyl alcohol) nanofibrous membranes for catalase immobilization

Poly(vinyl alcohol) (PVA) nanofibers were formed by electrospinning. Metal chelated nanofibrous membranes were prepared by reaction between Cu(II) solution and nanofibers, and which were used as the matrix for catalases immobilization. The constants of Cu(II) adsorption and properties of immobilized catalases were studied in this work. The Cu(II) concentration was determined by atomic absorption spectrophotometer (AAS), the immobilized enzymes were confirmed by the Fourier transform infrared spectroscopy (FTIR), and the amounts of immobilized enzymes were determined by the method of Bradford on an ultraviolet spectrophotometer (UV). Adsorption of Cu(II) onto PVA nanofibers was studied by the Langmuir isothermal adsorption model. The maximum amount of coordinated Cu(II) (q_m) was 2.1 mmol g⁻¹ (dry fiber), and the binding constant (K_l) was 0.1166 L mmol⁻¹. The immobilized catalases showed better resistance to pH and temperature inactivation than that of free form, and the thermal and storage stabilities of immobilized catalases were higher than that of free catalases. Kinetic parameters were analyzed for both immobilized and free catalases. The value of V_max (8425.8 μmol mg⁻¹) for the immobilized catalases was smaller than that of the free catalases (10153.6 μmol mg⁻¹), while the K_m for the immobilized catalases were larger. It was also found that the immobilized catalases had a high affinity with substrate, which demonstrated that the potential of PVA‐Cu(II) chelated nanofibrous membranes applied to enzyme immobilization and biosensors. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dialdehyde polyethylene glycol cross-linked poly(vinyl alcohol) membranes with enhanced CO2/N2 separation performance

The development of carbon dioxide (CO₂) separation technology is crucial for mitigating global climate change and promoting sustainable development. In this study, we successfully synthesized an array of cross-linked poly(vinyl alcohol) (PVA) membranes, xALD-PEG-ALD-c-PVA, with enhanced CO₂/N₂ separation performance by employing dialdehyde polyethylene glycol (ALD-PEG-ALD) as a cross-linker. The formation of the cross-linked network structure not only inhibits the crystallization of PVA but also disrupts hydrogen bonding and thus increases fractional free volume of PVA chains. Under the synergistic effect of these multiple factors, the cross-linked PVA membranes exhibit a significantly improved CO₂ permeability. Moreover, they maintain high CO₂/N₂ selectivity, attributing to the CO₂-philic characteristic of ethylene oxide groups in the cross-linked structure. At the ALD-PEG-ALD content of 1.6 mmol g⁻¹, the xALD-PEG-ALD-c-PVA membrane demonstrates a CO₂ permeability of 41.4 barrer and a CO₂/N₂ selectivity of 57.4 at 2 bar and 25°C. Furthermore, compared with the pristine PVA membrane, xALD-PEG-ALD-c-PVA membranes manifest superior mechanical properties and outstanding separation performance for a CO₂/N₂ (15/85, vol%) gas mixture. The excellent combination of permeability and selectivity makes xALD-PEG-ALD-c-PVA membranes highly promising for various CO₂ separation applications.     

Modification of poly(vinyl alcohol) membranes using sulfur-succinic acid and its application to pervaporation separation of water–alcohol mixtures

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     

Development of quaternarized poly(vinyl alcohol) anion‐exchange membranes for applications in electrodialysis

The main objective of this work is the development of anionic exchange membranes for the treatment of solutions containing metallic ions using the electrodialysis process. Anionic membranes were synthesized from poly(vinyl alcohol), with the insertion of quaternary ammonium groups in the polymeric matrix and subsequent crosslinking with glutaraldehyde and maleic anhydride. Different membranes were synthesized in order to evaluate the combination of physical–chemical properties and ionic transport. The morphology and structure of the membranes were investigated by scanning electron microscopy and infrared spectroscopy. The thermal transitions and stability of all the membranes were characterized using calorimetric techniques: thermogravimetric analysis, and differential scanning calorimetry, and compared with those of the individual polymers. The physical properties (ion‐exchange capacity, water absorption, and dimensional stability) showed that the different crosslink agents used significantly affect the membrane properties. The electrodialysis performance of the membranes in the transport of chloride and nitrate ions showed that the membranes produced can be successfully used in this separation process. Selemion® AMV commercial membrane was used to compare the percentage extractions of the indicated ions with the produced membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44946.