Silica Polyvinyl Alcohol Research Articles

Hybrid Polyvinyl Alcohol-Silica Antibacterial Nanofiber Fabricated by Combined Sol-Gel and Electrospinning Techniques

Hybrid Polyvinyl Alcohol-Silica Antibacterial Nanofiber Fabricated by Combined Sol-Gel and Electrospinning Techniques

Fabrication of PVA-Silica Sol Wood Composites via Delignification and Freezing Pretreatment.

The efficient exploitation of planted fast-growing wood is crucial for enhancing wood resource utilization. In this study, the fast-growing poplar wood was modified by in situ impregnation through vacuum impregnation with polyvinyl alcohol and nano-silica sol as impregnation modifiers, combined with delignification-freezing pretreatment. The samples were characterized by FTIR, XRD, SEM, and the universal mechanical testing machine. The results showed that the wrinkle deformation and cracking of the wood blocks were greatly alleviated after the delignification-freezing pretreatment and the polyvinyl alcohol and nano-silica sol were successfully integrated into the wood. The resulting polyvinyl alcohol-silica sol poplar composites exhibited about 216%, 80% and 43% higher compressive strength with respect to delignified wood, natural wood and impregnated natural wood, respectively, thereby demonstrating superior mechanical properties and potential opportunities for value-added and efficient utilization of low-quality wood.

Proton Conducting Organic-Inorganic Composite Membranes for All-Vanadium Redox Flow Battery.

The quest for a cost-effective, chemically-inert, robust and proton conducting membrane for flow batteries is at its paramount. Perfluorinated membranes suffer severe electrolyte diffusion, whereas conductivity and dimensional stability in engineered thermoplastics depend on the degree of functionalization. Herein, we report surface-modified thermally crosslinked polyvinyl alcohol-silica (PVA-SiO2) membranes for the vanadium redox flow battery (VRFB). Hygroscopic, proton-storing metal oxides such as SiO2, ZrO2 and SnO2 were coated on the membranes via the acid-catalyzed sol-gel strategy. The membranes of PVA-SiO2-Si, PVA-SiO2-Zr and PVA-SiO2-Sn demonstrated excellent oxidative stability in 2 M H2SO4 containing 1.5 M VO2+ ions. The metal oxide layer had good influence on conductivity and zeta potential values. The observed trend for conductivity and zeta potential values was PVA-SiO2-Sn > PVA-SiO2-Si > PVA-SiO2-Zr. In VRFB, the membranes showcased higher Coulombic efficiency than Nafion-117 and stable energy efficiencies over 200 cycles at the 100 mA cm-2 current density. The order of average capacity decay per cycle was PVA-SiO2-Zr < PVA-SiO2-Sn < PVA-SiO2-Si < Nafion-117. PVA-SiO2-Sn had the highest power density of 260 mW cm-2, while the self-discharge for PVA-SiO2-Zr was ~3 times higher than Nafion-117. VRFB performance reflects the potential of the facile surface modification technique to design advanced membranes for energy device applications.

Effect of the catalyst on the physical and aroma attributes of interesterified milk fat-vegetable oil blends

Abstract The present study aimed to verify the influence of the catalyst (sodium methoxide and the lipase from Rhizopus oryzae immobilized on a hybrid support - silica-polyvinyl alcohol) on the physical and aroma attributes of the products obtained from the interesterification of milk fat with vegetable oils (soybean and canola). The evaluation was carried out using an electronic nose (e-nose) and a texture analyzer. Interesterification reactions were carried out with binary blends (65% of milk fat and 35% of vegetable oil) using 0.75% sodium methoxide (60 °C for 60 min) and immobilized Rhizopus oryzae lipase at a fixed proportion of 500 units of activity per gram of blend (45 °C for 6 h). The results showed that the e-nose sensors discriminated satisfactorily the aromas of both raw materials and products and were able to distinguish them according to the catalyst used. In relation to the texture, both catalysts generated products with appropriate consistencies with satisfactory plasticity and spreadability at refrigerator temperatures.

Formation of CoFe2O4/PVA-SiO2 nanocomposites: Effect of diol chain length on the structure and magnetic properties

The paper presents the influence of diol (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol) on the formation of magnetic crystalline cobalt ferrite embedded in polyvinyl alcohol-silica hybrid matrix at 200 °C. Formation of crystalline oxides (CoFe2O4, Co3O4 and Co2SiO4) was studied by X-ray diffraction and Fourier transformed infrared spectroscopy. The effect of annealing temperature and diol chain length on the cobalt ferrite nanocrystallites size was investigated. Using transmission electron microscopy, the size and shape of particles obtained at 200 °C were recorded and compared to those obtained by annealing at 500, 800 and 1100 °C. The saturation magnetization (Ms) and coercive field were calculated from the magnetic hysteresis loops of nanocomposites. The Ms was influenced by the particle size and crystallinity only for nanocomposites annealed at 800 and 1100 °C, when the magnetic domains started to form and to be larger than the critical particle size. The diols used in the synthesis influence both the oxidic phase formation and its properties.

Different organic components on silica hybrid matrices modulate the lipase inhibition by the glycerol formed in continuous transesterification reactions

Silica hybrid materials, functionalized via incorporation of three organic components: β-cyclodextrin (βCD), carboxymethyl-cellulose (CMC) and hydroxyethyl-cellulose (HEC) were synthesized by the sol–gel technique and results were compared to a well-defined matrix (silica–polyvinyl alcohol–SiO2–PVA) with respect to immobilizing Burkholderia cepacia lipase. The main objective was set to select organic components that can replace the PVA to obtain a hybrid composite with greater hydrophobic character, without compromising the remarkable features of SiO2–PVA. All the three selected compounds allowed obtaining matrices that presented similar textural and morphological properties and gave high activity (1451–1661Ug−1) and thermal stability (t1/2>70h) upon immobilization. Regarding glycerol affinity, all matrices had lower ability than SiO2–PVA to adsorb glycerol, with the SiO2–βCD matrix showing the lowest affinity due to the cyclic structure of the βCD. Transesterification reactions of palm kernel oil with ethanol mediated by B. cepacia immobilized on SiO2–βCD performed in a packed bed reactor under continuous flow confirmed the efficiency of the SiO2–βCD matrix in increasing the operational stability of system, revealing a half-life (t1/2=1040h), 2.5 times greater than that achieved in the same system using lipase immobilized on SiO2–PVA (t1/2=430h).

Zwitterionic chitosan–silica–PVA hybrid ultrafiltration membranes for protein separation

Zwitterionic (ZI) membranes are well-known for their high resistance to protein fouling during ultrafiltration (UF). In this work, zwitterionic chitosan (ZICS) was firstly obtained by a Schiff-base formation and a sulfonation reaction. Then a series of zwitterionic organic–inorganic hybrid ultrafiltration membranes were prepared through linking ZICS with poly vinyl alcohol (PVA) using tetraethyl orthosilicate as a bridge, where the density of zwitterionic groups in the membranes was adjusted by varying the dosage of zwitterionic chitosan. The prepared membranes were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and the measurements of water contact angle and zeta-potential of membrane surface. The ultrafiltration performance was examined using the separation of bovine serum albumin (BSA) and lysozyme (LYZ) as a model system. The results show that, zwitterionic chitosan–silica–PVA hybrid membranes can possess desirable porosity, hydrophilicity, permeability, antifouling capacity and selectivity which can be adjusted by the fraction of ZICS in membranes.

Assessing the potential of non-edible oils and residual fat to be used as a feedstock source in the enzymatic ethanolysis reaction

The focus of this work was to evaluate the potential of non-edible feedstocks to yield biodiesel by an enzymatic route. The ethanolysis of native oils from tropical crops, such as andiroba (Carapa guianensis), babassu (Orbignya sp.), jatropha (Jatropha curcas), macaw palm (Acrocomia aculeata), palm tree (Elaeis guineensis) and industrial waste (beef tallow) in solvent-free system was studied. All reactions were carried out with the microbial lipase from Burkholderia cepacia immobilized on a silica-polyvinyl alcohol matrix in a solvent-free system at 50°C for a maximum period of 24h. Under the conditions tested the biocatalyst was efficient in converting all fatty acids in the lipid feedstocks into the corresponding ethyl esters. Viscosity values for biodiesel samples obtained in each reaction (4.3 and 6.0mm2/s) showed consistent reduction in relation to their original feedstock material, which also confirms the high conversion of triglycerides to ethyl esters (>94.5%). This comparative study shows that the formation of ethyl esters from different non-edible feedstocks was feasible and can provide a considerable increase in the prospect of attaining an environmental sustainability of the process as a whole.

Physico-chemical, spectroscopical and thermal characterization of biodiesel obtained by enzymatic route as a tool to select the most efficient immobilized lipase

Two microbial lipases from Burkholderia cepacia and Pseudomonas fluorescens were evaluated as catalysts for the enzymatic transesterification of beef tallow with ethanol and the most efficient lipase source was selected by taking into account the properties of the product to be used as fuel. Both lipases were immobilized on an epoxy silica-polyvinyl alcohol composite by covalent immobilization and used to perform the reactions under the following operational conditions: beef tallow-to-ethanol molar ratio of 1:9, 45oC and 400 units of enzymatic activity per gram of fat. Products, characterized using Fourier Transform Infrared spectroscopy (FTIR), viscosimetry, thermogravimetry and 1H NMR spectroscopy, suggested that the biodiesel sample obtained in the reaction catalyzed by Burkholderia cepacia lipase has the best set of properties for fuel usage.

Polyvinyl alcohol Silica compositeの人工血管への応用

Polyvinyl alcohol Silica compositeの人工血管への応用

The temperature effect on electrokinetic properties of the silica–polyvinyl alcohol (PVA) system

The influence of polyvinyl alcohol (PVA) adsorption on the structure of the diffuse layer of silica (SiO2) in the temperature range 15–35 °C was examined. The microelectrophoresis method was used in the experiments to determine the zeta potential of the solid particles in the absence and presence of the polymer. The adsorption of PVA macromolecules causes the zeta potential decrease in all investigated SiO2 systems. Moreover this, decrease is the most pronounced at the highest examined temperature. Obtained results indicate that the conformational changes of adsorbed polymer chains are responsible for changes in electrokinetic properties of silica particles. Moreover, the structure of diffuse layer on the solid surface with adsorbed polymer results from the following effects: the presence of acetate groups in PVA chains, the blockade of silica surface groups by adsorbed polymer and the shift of slipping plane due to macromolecules adsorption.

Thermoplastic starch–silica–polyvinyl alcohol composites by reactive extrusion

Thermoplastic starch–silica (SiO2) PVOH composite films were created via a reactive extrusion process using tetraethyl orthosilicate (TEOS) as a precursor. Reaction efficiency was determined by X-ray fluorescence measurement of film Si content and was observed to improve with increasing TEOS concentration. Films with high SiO2 content were noted to have varying morphology and some SiO2 clusters. Mechanical properties of the starch composite films were enhanced by even a small amount of SiO2. Tensile strength and Young's modulus increased, while elongation at break decreased with increasing SiO2 content. Dynamic mechanical analysis results showed that the starch–silica composite storage modulus increased and the loss modulus decreased with increasing SiO2 content.

Organomineral composite materials for drying of gaseous streams

Specific features of the synthesis of the organomineral binding agent, polyvinyl alcohol—silica sol, with high sorption activity were studied. The adsorption properties of the new material towards water were examined under equilibrium and dynamic conditions. The kinetics of water adsorption and granules based on the new material were investigated. The possibility of using the organomineral binder in technology of the preparation of granulated and block adsorbents designed for drying of gaseous streams was evaluated.

Development of Silica Polyvinyl Alcohol Wheels for Wet Mirror Grinding of Silicon Wafer

It is strongly desired to develop a cup grinding wheel which enables mirror finishing of a device wafer on the same machine after back grinding. Silica wheels have the capability of mirror finish in a dry condition but there remain serious problems in flatness and thermal damage to a dicing tape. A new silica wheel which can be used in a wet condition has been developed. The PVA (polyvinyl alcohol) was adopted as the bonding agent, by which the absorbent swell resulted in disturbance of water infiltration to the inside in cup grinding. A series of experiments show that mirror finishing will be achieved within 2 min. This could not be accomplished utilizing phenol wheels.

Microanalytical systems for separations of stratum corneum ceramides

The small amount of lipids from human skin obtained with noninvasive sampling method led us to investigate microanalytical separation techniques. The lipid class analysis was performed with a micro polyvinyl alcohol-silica (PVA-Sil) column. The gradient elution was from heptane to acetone/butanol 90:10 v/v in 4%/min at 78 microL/min. In addition an evaporative light scattering detector (ELSD) was modified for micro-LC. All solvents contained 0.1% of triethylamine and formic acid in stoichiometric amount, which increased the ELSD response. In these conditions, the cholesterol eluted before free fatty acid, and squalene and triglycerides close to the dead volume. The various ceramide classes eluted following the order of the increased number of hydroxyl groups. The LOD for ceramides was 2.2 ng. The advantages of this method are the use of a normal stationary phase more reliable due to its chemical stability, its surface homogeneity and its development in microchromatography without chlorinated solvents which offers small LOD and the whole profile of lipids present in stratum corneum (SC). A method using a narrow-bore PVA-Sil column was used to collect ceramide fraction. Then the molecular species were analysed with a porous graphitic carbon column in capillary LC using a gradient from CH3OH/CHCl3 70:30 v/v to CHCl3 at 2%/min with a flow rate at 5 microL/min. The LOD obtained for ceramide was 1 ng. Both methods were assessed with SC samples obtained by rinsing a 5.7 cm2 area of the forearm with 25 mL of ethanol.

Preparation of polyvinyl alcohol–silica hybrid heterogeneous anion-exchange membranes by sol–gel method and their characterization

Polyvinyl alcohol–silica hybrid heterogeneous anion-exchange membranes were prepared by sol–gel method by dispersing the anion-exchange resin in the gel formed by acid/base hydrolysis of tetraethylorthosilicate in polyvinyl alcohol solution. The effect of acid and base-catalyzed hydrolysis on membrane preparation and extent of resin loading was studied. Various membranes were prepared with 60% (w/w) anion-exchange resin (Indoin FFIP) loaded with different extents of silica. Membrane potential and membrane resistance measurements have been carried out with different counter-ion to investigate the relationship between ionic migration and silica content in the membrane forming material. Counter-ion transport number and permselectivity of these membranes were found to very due to the silica content and nature of counter-ion. Data indicates that, with increase in compactness of the membranes, its ability to discriminate between counter-ions also increases. Decrease in relative transport of bulkier ions are useful, especially, desirable for selective removal of these type of ions or membrane based electrochemical sensors.

Density fluctuation in silica–PVA hybrid gels determined by small-angle X-ray scattering

A series of silica–polyvinyl alcohol (PVA) hybrids were prepared by acid-catalyzed hydrolysis of tetraethoxysilane (TEOS) in the mixture of ethanol and water containing dissolved polyvinyl alcohol via a sol–gel process. A small-angle X-ray scattering (SAXS) study on those hybrid gels has been performed utilizing synchrotron radiation. Intensive positive deviation from Porod’s law indicated that there existed density fluctuation within the matrix of silica–PVA hybrid gel. Using the differential d[ q 3 I( q)]/d( q 2) as a variant slo, plotting ln(slo) versus ln( q) can produce the dimension n and the amplitude F l of density fluctuation. Density fluctuation resulted from both the micropores in gel and Si–O–PVA–O–Si bridge between SiO 2 particle and PVA chain. When PVA increased in gel, the decreased micropores reduced the fluctuation but PVA enhanced the fluctuation. With the conjunction of correlation function C( r), it was clear that the bridge of Si–O–PVA–O–Si enlarged the compositional heterogeneity within gel matrix and made n increase with the increase of PVA. In addition, the fluctuation dimension n is a fraction rather than an integer that was formerly predicted by Ruland, which may relate to the fractal structure of hybrid gel.

Influence of the porous texture of silica gels on the enzymatic activity of lipases in esterification reactions

Pseudomonas Cepacia lipases were encapsulated in hybrid silica-polyvinyl alcohol gels, which were dried either supercritically in order to form aerogels or by evaporation so as to obtain xerogels. In each case, the catalytic activity of the encapsulated enzymes was studied and compared to free enzyme biocatalysis. This study demonstrates that the activity of the enzyme is increased when the procedure used allows it to resist capillary stresses occurring during the drying of the gel. That is, esterification rates are higher when the gels are synthesized with a base catalyst, such as NaF, in the presence of polyvinyl alcohol and then dried supercritically.

Encapsulation of deoxyribonucleic acid molecules in silica and hybrid organic-silica gels.

The encapsulation of small DNA molecules was attempted in pure silica and in hybrid polyvinyl alcohol-silica gels. The materials which were obtained were examined by nitrogen adsorption, and by 29Si and 31P NMR spectroscopy. The extraction of the DNA molecules from the gels was examined in a buffer aqueous solution as well as in an acidic medium. The results suggested that the DNA molecules remained trapped inside the gels due to a permanent bonding to the gel network.

HPLC Separation of Two Novel Oiketopiperazine Isomers on Polyvinyl Alcohol Functionalized Silica Gel

Abstract An HPLC method is described for the analytical separation of two novel diketopiperazine isomers isolated from a fungal culture, Tolypocladium sp. (SCF-0729). Separation was achieved on a high-performance polyvinyl alcohol silica gel column with a 1-chlorobutane: methanol gradient system. Selectivity, retention and resolution obtained with this support were all highly reproducible. Direct scale up of analytical methodology allowed for the preparative separation of this isomeric pair.