Modification Of PVA Research Articles

Development and modification of PVA–alginate as a suitable immobilization matrix

This study reports the immobilization of invertase in the PVA–alginate matrix via a modified method. The PVA–alginate modified method involved the treatment of immobilized beads in sodium sulfate solution. In this study, the steps involved in the preparation of matrix were analyzed. The influence of the sodium sulfate concentration on the bead formation was investigated and its mechanism of immobilization was further elucidated by means of FTIR and EDX. In addition, the stability of invertase in sodium sulfate and boric acid solution was also studied. EDX results revealed that borates were completely replaced by sulfates as the cross-linking agent. Through the mechanism of nucleophilic substitution, it was revealed that sulfate attacked the carbon atom bearing borate on the opposite side to the side bonded to borate due to steric hindrance. Carbon therefore underwent backside attack by sulfate and inverted its original configuration through a phenomenon known as Walden Inversion. The presence of sulfate was also supported by FTIR spectra. The best sodium sulfate concentration was found to be 0.5M.

Synthesis and characterizations of nano sized MgO and its nano composite with poly(vinyl alcohol)

Magnesium oxide (MgO) nano particle was synthesized by ultrasound assisted one pot method and thus synthesized nano MgO was mixed with poly(vinyl alcohol) (PVA) to prepare the polymer nano composite. The influence of the nano sized MgO on the structural modification of PVA was evaluated. The particle size and morphology of MgO was confirmed by High Resolution Transmission Electron Microscopy (HRTEM). The properties of PVA/MgO nano composite materials were characterized by Fourier Transform Infrared analysis (FTIR), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) like analytical tools.

Synthesis, characterizations, and mechanical properties of structurally modified poly(vinyl alcohol)

AbstractPoly(vinyl alcohol) (PVA) was structurally modified with two different types of chemicals under nitrogen atmosphere in the presence of Sb2O3 as a catalyst at 80°C in an aqueous medium. An FTIR and NMR spectrum confirmed the structural modification of PVA. DSC and TGA counseled the thermal properties of structurally modified PVA. Urea modified PVA exhibited higher mechanical strength than the pristine PVA. The FTIR‐relative intensities of olefin formation and ketone formation were increased with the increase of weight of water. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Two step modification of poly(vinyl alcohol) by UV radiation with 2-hydroxy ethyl methacrylate and sol–gel process for the application of polymer electrolyte membrane

Two step modification of poly(vinyl alcohol) (PVA) by UV radiation and sol–gel process was used to prepare the modified PVA membranes. From the first step modification of PVA by UV radiation with 2-hydroxy ethyl methacrylate (HEMA) monomer, the poly(2-hydroxy ethyl methacrylate) (PHEMA) modified poly(vinyl alcohol), PVAHEMA, was obtained and characterized by Fourier transfer infrared spectra (FTIR) and optical polarizing microscopy for the chemical compositions and morphology. With the second step modification of sol–gel process, the organic–inorganic hybrid sol–gel material, PVAHEMA–SiO 2, was prepared. Both of the modified PVA, (PVAHEMA and PVAHEMA–SiO 2), were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetry analysis (TGA). To prepare the alkaline solid polymer electrolyte, the various PVAHEMA and PVAHEMA–SiO 2 membranes were immersed in 40 wt% KOH solution to form the KOH containing polymer electrolyte membranes. And then their performances were conducted with ac impedance spectroscopy to evaluate the ionic conductivity through the membranes. At room temperature, the ionic conductivity increased from 0.044 to 0.073 S/cm for the PVAHEMA membrane; whereas the ionic conductivity was about 0.11 S/cm for the PVAHEMA–SiO 2 membranes. Compared to other reports in references, our hybrid sol–gel membrane is a highly ionic conducting alkaline solid polymer electrolytes membrane.

Preparation and applications of a variety of fluoroalkyl end-capped oligomer/hydroxyapatite composites

A variety of fluoroalkyl end-capped oligomers were applied to the preparation of fluorinated oligomer/hydroxyapatite (HAp) composites (particle size: 38–356 nm), which exhibit a good dispersibility in water and traditional organic solvents. These fluoroalkyl end-capped oligomer/HAp composites were easily prepared by the reactions of disodium hydrogen phosphate and calcium chloride in the presence of self-assembled molecular aggregates formed by fluoroalkyl end-capped oligomers in aqueous solutions. In these fluorinated HAp composites thus obtained, fluoroalkyl end-capped acrylic acid oligomers and 2-methacryloyloxyethanesulfonic acid oligomer/HAp nanocomposites afforded transparent colorless solutions toward water; however, fluoroalkyl end-capped N , N -dimethylacrylamide oligomer and acryloylmorpholine oligomer were found to afford transparent colorless solutions with trace amounts of white-colored HAp precipitants under similar conditions. HAp could be encapsulated more effectively into fluorinated 2-methacryloyloxyethanesulfonic acid oligomeric aggregate cores to afford colloidal stable fluorinated oligomer/HAp composites, compared to that of fluorinated acrylic acid oligomers. These fluorinated oligomer/HAp composites were applied to the surface modification of glass and PVA to exhibit a good oleophobicity imparted by fluorine. HAp formation was newly observed on the modified polyethylene terephthalate film surface treated with fluorinated 2-methacryloyloxyethanesulfonic acid oligomers and acrylic acid oligomer/HAp composites by soaking these films into the simulated body fluid.

Modification of pore structure in activated carbons by heat treatment with thermoplastic resins

Three activated carbons having different surface areas, coconut-shell based (AC-C), pelletized (AC-P) and bamboo-derived (AC-B) were modified by mixing them with four thermoplastic precursors, poly(vinyl alcohol) (PVA), hydroxy propyl cellulose (HPC), citric acid (CiA) and fluorine-containing polyimide (FPI), followed by heat treatment at 900°C for 1 h. The porous structures of the modified activated carbons were characterized by nitrogen adsorption and SEM. It was found that the thermoplastic precursors modified the porous structure of AC-B more significantly compared with the other two: AC-P and AC-C. PVA, HPC, and CiA modification resulted in the reduction of surface area of AC-B, which is attributed to a different modification of the micropore structure; PVA eliminated all micropores, HPC eliminated ultra-micropores preferentially, and CiA decreased the volume of ultra-micropores, whereas it increased that of super-micropores. On one hand, the addition of 30 mass% CiA to AC-B resulted in an increase in external surface area by 170 %. On the other hand, the modifier FPI increased the surface area by increasing ultra-micropores to approximately twice that of the original activated carbons. By the selection of modifier, the distribution of micropore size in the substrate-activated carbons can be modified, either by decreasing or by increasing ultra-micropores.

Poly(vinyl alcohol)-Based Hydrogels Formed by “Click Chemistry”

Novel poly(vinyl alcohols) (PVA) functionalized with pendant acetylene and azide groups were prepared by carbonyldiimidazole (CDI)-mediated couplings of the amines terminated with functional groups, 1-azido-2-aminoethane, propargylamine, or N-methylpropargylamine, to PVA. Low degrees (1−5%) of PVA modification were required in order to retain solubility in water. Azide-modified PVA and alkyne-modified PVA components were cross-linked by mixing of their solutions together with Cu(I) catalyst, a type of Huisgen's 1,3-dipolar azide−alkyne cycloaddition, recently defined as a powerful “click” chemistry. Reaction of the two different polymers results in a chemoselective coupling between alkynyl and azido functional groups with the multiple formation of triazole cross-links to give hydrogel formation. In another version the PVA-based hydrogels were obtained by cross-linking of alkyne-modified PVA with the telechelic bifunctional poly(ethylene glycol)−diazide cross-linker. The hydrogels prepared by these two met...

Abrasion-resistant solgel antireflective films with a high laser-induced damage threshold for inertial confinement fusion

To prepare abrasion-resistant antireflective (AR) films for inertial confinement fusion, four solgel routes have been investigated on polysiloxane-modified and polyvinylalcohol- (PVA-) modified SiO2 sols. As confirmed with a transmissive electron microscope, different fractal structure characteristics of the modified SiO2 particles are disclosed by small-angle x-ray scattering technology. And it is these special fractal characteristics that determine the performance of AR films on the level of internal microstructure. A Si29 magic angle spinning and nuclear magnetic resonance study has been successfully applied in explaining the fractal microstructure and its relation to the laser-induced damage threshold (LIDT) of AR films. The films modified by PVA120000 or acetic acid-catalyzed polysiloxane have higher LIDTs than those films modified by PVA16000 or hydrochloride acid-catalyzed polysiloxane. The films from PVA-modified SiO2 sols have a stronger abrasion resistance but lower antireflection than those films from polysiloxane-modified SiO2 sols. In addition, the films from polysiloxane-modified SiO2 sols can possess high transmittance and high LIDT if the polysiloxane synthesis condition is appropriately chosen, but the abrasion resistance is not as good as that from PVA modification. If strong abrasion resistance is necessary, a possible resolution may be to choose a more appropriate hydrophilic polymer than PVA. If not, polysiloxane-modified silica sol can also work when polysiloxane is synthesized under acetic acid catalysis.

Novel approach to the chemical modification of poly(vinyl alcohol): Phosphorylation

AbstractThe chemical modification of poly(vinyl alcohol) (PVA) was performed through oxidation followed by nucleophilic addition. PVA was oxidized by KMnO4 to form vinyl ketone units along the polymer backbone. The chemical modification of PVA was then conducted through the reaction of the carbonyl group of the vinyl ketone unit with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) as a nucleophile. Through this approach, the phosphorous DOPO group was attached onto the carbon atom of the polymer main chain rather than onto the pendent hydroxyl groups of PVA. The formed DOPO‐containing PVA showed improved thermal stability, organosolubility, and flame retardance. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1107–1113, 2003

Preparation and viscosity behavior of hydrophobically modified poly(vinyl alcohol) (PVA)

AbstractIn this study, a novel series of water‐soluble hydrophobically modified poly(vinyl alcohol) (PVA) is prepared by chemical modification of PVA, with the objective of investigating the polymer's rheological behavior for enhanced oil recovery applications. The solution viscosity of the polymer obtained is studied with respect to the polymer concentration, temperature, salinity, polymer modification, aging, shear rate, and polymer molecular weight. The solution viscosity of the PVA is greatly enhanced by the modification. The modified PVA exhibits a relatively high salt tolerance, typical of nonionic polymers, in the range of 0–7.0 wt % NaCl concentrations, and the viscosity of the polymer solution is relatively invariant with NaCl above 3.0 wt % NaCl concentration. Below 3 wt %, the viscosity shows a maximum then a minimum, an unusual behavior. Generally, the polymer exhibits an almost constant viscosity at high shear rates and a typical shear thinning behavior at low shear rates. In addition, increasing polymer concentration and molecular weight leads to an increase in the polymer solution viscosity. Moreover, the polymer exhibits smaller solution viscosity at a high temperatre, and a slight decrease in viscosity is also exhibited by the modified polymer with aging. Comparison of the viscosities of 18 polymer modifications indicates that the larger the numbers of hydrophobic groups (side chains) in the polymer structure, the smaller the viscosity. Moreover, the longer the hydrophobic groups (side chains) in the polymer structure, the greater the viscosity, if their number is small. © 1995 John Wiley & Sons, Inc.