Showing papers on "Vinyl alcohol published in 2011"

Composite poly(vinyl alcohol)/poly(vinyl acetate) electrospun nanofibrous mats as a novel wound dressing matrix for controlled release of drugs

Abstract: The aim of this study was to develop novel biomedicated nanofiber electrospun mats for controlled drug release, especially drug release directly to an injury site to accelerate wound healing. Nanofibers of poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), and a 50:50 composite blend, loaded with ciprofloxacin HCl (CipHCl), were successfully prepared by an electrospinning technique for the first time. The morphology and average diameter of the electrospun nanofibers were investigated by scanning electron microscopy. X-ray diffraction studies indicated an amorphous distribution of the drug inside the nanofiber blend. Introducing the drug into polymeric solutions significantly decreased solution viscosities as well as nanofiber diameter. In vitro drug release evaluations showed that both the kind of polymer and the amount of drug loaded greatly affected the degree of swelling, weight loss, and initial burst and rate of drug release. Blending PVA and PVAc exhibited a useful and convenient method for electrospinning in order to control the rate and period of drug release in wound healing applications. Also, the thickness of the blend nanofiber mats strongly influenced the initial release and rate of drug release.

Study on polymer binders for high-capacity SiO negative electrode of Li-Ion batteries

Abstract: High-capacity SiO powder composite electrodes for rechargeable lithium-ion batteries are prepared with different polymer binders of poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), sodium carboxymethyl cellulose (CMCNa), and conventional poly(vinylidene fluoride) (PVdF). Electrode performance of the SiO composites highly depends on selection of binders, and their electrochemical reversibility is drastically improved by using PAA as the binder in comparison to the PVdF, CMCNa, and PVA binders. Coulombic efficiency at the initial cycle is improved for the SiO–PAA composite electrode, and the reversible capacity reaches 700–750 mAh g–1 for continuous fifty cycling test at a rate of 100 mA g–1. The improvement mechanism of SiO–PAA composite electrode is characterized by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, self-discharge test, and adhesive strength test. Amorphous PAA polymer not only tightly binds but also covers the individual SiO particles. Mo...

Preparation of graphene/poly(vinyl alcohol) nanocomposites with enhanced mechanical properties and water resistance

Abstract: The control and dispersal of graphene nanosheets in polymer hosts are challenges in the development of high-performance graphene-based nanocomposites due to the strong interlayer cohesive energy and surface inertia. Here we report a simple and practical approach to synthesize graphene-reinforced poly(vinyl alcohol) (PVA) composite films by incorporating graphene oxide and graphene into PVA aqueous solution. The resulting nanocomposites revealed increases of up to 212% in tensile strength and 34% in elongation at break with only 0.5 wt% graphene content. Water absorption measurements showed that the water absorption ratio of the graphene/PVA composites decreased from 105.2 to 48.8%, and the barrier properties were obviously improved. Contact angle measurements showed that the composites were hydrophobic (θ > 90°) in contrast to the highly hydrophilic (θ < 90°) pure PVA. Copyright © 2011 Society of Chemical Industry

Fabrication of Curcumin Encapsulated Chitosan-PVA Silver Nanocomposite Films for Improved Antimicrobial Activity

Abstract: The present study explores the in situ fabrication of chitosan-poly(vinyl alcohol)-silver nanocomposite films in view of their increasing applications as antimicrobial packaging, wound dressing and antibacterial materials. The reduction of silver ions into silver nanoparticles (AgNPs) is achieved in acidic solution of chitosan (C) and poly (vinyl alcohol) (PVA) using their functional groups (-OH, -COOH, -NH2 groups). The presence of silver nanoparticles in the chito-san-PVA film is confirmed by UV-Vis spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy and X-ray Dif-fraction (XRD) analysis. The Scanning Electron Microscopic (SEM) images illustrate the presence of embedded silver nanoparticles throughout the films. In addition, the formed silver nanoparticles have an average particle size of ~ 16.5 nm as observed by Transmission Electron Microscopy (TEM). The anti-microbial and anti-fungal activity of the chitosan-PVA silver nanoparticle films have demonstrated significant effects against Escherichia coli (E. coli), Pseudomonas, Staphylococcus, Micrococcus, Candida albicans, and Pseudomonas aeruginosa (P. aeruginosa). To improve further their therapeutic efficacy as anti-microbial agents, curcumin encapsulated chitosan-PVA silver nanocomposite films are developed which showed enormous growth inhibition of E. coli compared to curcumin and chitosan-PVA silver nanoparticles film alone. Therefore, the present study clearly provides novel antimicrobial films which are potentially useful in preventing/treating infections.

Poly(vinyl alcohol) Nanocomposites with Nanodiamond

Abstract: Carbon-based nanomaterials, such as carbon nanotubes, are well-known for their unique physical properties. They have attracted interest as reinforcing fillers because of their superb mechanical properties (Young’s modulus ≥1 TPa and tensile strength = 100–150 GPa). However, the success of the reinforcement has been limited because of their tendency to form agglomerates in polymer matrices. We report the excellent reinforcement properties of polymer nanocomposites by the incorporation of nanodiamond (ND). ND has been expected to offer polymer nanocomposites optimal properties because of its smooth surface and excellent optical, mechanical, and thermal properties, which can approach the values of single diamond crystal. We prepared poly(vinyl alcohol) (PVA)/ND nanocomposites by a simple casting method from aqueous medium and achieved the high dispersibility of ND in the PVA matrices. The resulting nanocomposites had excellent properties derived both from ND and PVA. The Young’s modulus of the nanocomposites...

Reinforcement with cellulose nanocrystals of poly(vinyl alcohol) hydrogels prepared by cyclic freezing and thawing

Abstract: Cellulose nanocrystals (CNCs) were incorporated into polyvinyl alcohol (PVA) hydrogels prepared by repeated freeze–thaw processing. The CNC-loaded hydrogels had improved structural stabilities and distinct microstructures, characterized by ordered domains of CNCs. The water sorption of the gels increased with CNC content due to the hydrophilic nature of the cellulose and the decrease in PVA crystallinity. A reinforcement effect was observed in the CNC-loaded samples upon the application of uniaxial, confined compression, with the elastic moduli of the PVA–CNC samples increased relative to pure PVA hydrogels. Hydraulic permeability values were derived from the stress transients: at strains of ∼15 to 20% and greater, the permeability of all samples approached a plateau value reflective of the hindered flow in soft gels which have been compressed, densified and dehydrated.

Conducting Polyaniline Nanoparticles and Their Dispersion for Waterborne Corrosion Protection Coatings

Abstract: A novel approach for preparing waterborne corrosion protection polyaniline (PANI)-containing coatings was developed. First, conducting polyaniline/partially phosphorylated poly(vinyl alcohol) (PANI/P-PVA) spherical nanoparticles with significant dispersibility in aqueous media were prepared by the chemical oxidative dispersion polymerization in presence of partially phosphorylated poly(vinyl alcohol) (P-PVA). The PANI/P-PVA-containing coatings with different PANI/P-PVA contents were then prepared, employing waterborne epoxy resin as the matrix. The corrosion protection property of PANI/P-PVA-containing coatings on mild steel was investigated by salt spray test and electrochemical impedance spectroscopy (EIS) technique in 3.0 wt % NaCl aqueous solution. The results indicated that the waterborne PANI/P-PVA-containing coatings (PANI/P-PVA content, 2.5 wt %) could offer high protection because the impedance values remained at higher than 1 × 10(7) Ω cm(2) after 30 days of salt spray tests. All the results were compared with these of the waterborne coatings containing PANI nanoparticles in the emeraldine salt form (PANI ES), and the protection mechanism was also proposed with the evidence of scanning electron microscope (SEM) and X-ray photoelectron spectrometry (XPS).

A review of membrane selection for the dehydration of aqueous ethanol by pervaporation

Abstract: Four broad types of membranes are categorised: organic polymers generally, crosslinked poly(vinyl alcohol), organic–inorganic hybrids and charged polymers. The best performers in terms of flux, which reaches a maximum of 5 kg/m2h, are anionic or cationic polymers, including polysalts. Polyanion and polysalt membranes are superior. Two examples are thin layers of the active polysalt membrane on a supporting membrane. The best combination for flux and selectivity is a polyethyleneimine/poly (acrylic acid) polysalt deposited on a reverse osmosis membrane, at 4 kg/m2h and 1075 respectively. It is noticeable that hybrid poly(vinyl alcohol)/inorganic membranes do not show enhanced fluxes. Very high separation factors were observed, covering a range of polymers, of neutral, anionic or cationic character. The top results (>10,000) were for charged membranes, either cationic or anionic, but not polysalts. The fluxes encountered here were miniscule, the best being caesium alginate at about 1 kg/m2h. The ideal structure for high fluxes would appear to be one containing discrete domains of oppositely charged species of optimal size. Fresh approaches are being actively studied, such as layer-by-layer deposition of oppositely charged polyelectrolytes, with due attention to appropriate separation of the sites of opposite character.

Comparison of Body Distribution of Poly(vinyl alcohol) with Other Water‐soluble Polymers after Intravenous Administration

Abstract: The body distribution of poly(vinyl alcohol) (PVA) with molecular weights (MW) from 14,800 to 434,000 Da was investigated after intravenous administration and compared with that of other water-soluble polymers such as poly(ethylene glycol) (PEG), gelatin, dextran, and pullulan. The half-life of PVA in the circulation was prolonged from 90 min (MW 14,800 Da) to 23 h (MW 434,000 Da), similar to that of PEG which had a half-life of 30 min (MW 6000) and 20 h (MW 170,000). However, the half-life of PVA was much longer than that of other polymers when compared at a similar molecular weight. PVA was located in most organs but with very small accumulation. An insignificant interaction of PVA with cell components, such as macrophages and blood cells, was observed. Similar to PEG, the excretion rate of PVA at the glomeruli was rapidly reduced around 30,000 Da, as the molecular weight increased. These results indicate that the half-life of intravenously injected PVA in the blood was mainly determined by the permeation characteristics of the kidney.

Water dispersible graphene noncovalently functionalized with tryptophan and its poly(vinyl alcohol) nanocomposite

Abstract: Graphene sheets functionalized noncovalently with aromatic amino acid, tryptophan (Tryp), were prepared by reducing graphene oxide through hydrazine hydrate Tryp-functionalized graphene is water dispersible and can be stabilized for several months Atomic force microscopy (AFM), X-ray diffraction (XRD), UV–vis absorption and Raman spectroscopy were used to investigate the nanostructures and the properties of graphene Application of the graphene dispersion to poly(vinyl alcohol) (PVA) with the help of tryptophan to prepare nanocomposite was also carried out And the PVA/graphene nanocomposite was characterized by thermogravimetric analysis (TGA) and tensile testing A 23% improvement in tensile strength and moderate increases in Young’s modulus and thermal stability for PVA were achieved by adding only 02 wt% graphene sheets

Thermal and mechanical properties of poly(vinyl alcohol) plasticized with glycerol

Abstract: Thermomechanical behavior of membranes based on blends of poly(vinyl alcohol) (PVA) with different weight percentage (wt %) of glycerol has been studied. Solid-state PVA/Glycerol polymer membranes were prepared by a solution casting method. The films were studied for thermal characteristics by differential scanning calorimetry (DSC) and thermogravimetric analysis and for the mechanical properties including hardness and modulus by nanoindentation method. The dispersion of glycerol within the polymer matrix was examined using scanning electron microscopy. Fourier transform infrared spectroscopy was used to confirm the formation of hydrogen bonding between the plasticizer and PVA in their blends and also to provide information on compatibility and physical interactions between the glycerol and PVA. It was found that the thermal properties particularly the melting point (Tm) for PVA blends exhibit a reduced value proportional to the glycerol content. The hardness and elastic modulus were also found to decrease with an increase in plasticizer content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Evolution of PVA gels prepared without crosslinking agents as a cell adhesive surface

Abstract: Physical parameters (such as crosslinking density, crystallinity and mechanical properties) have been found to largely affect cellular behavior on polymer scaffolds. This study demonstrated that transparent pure Poly (vinyl alcohol) hydrogels prepared via a freeze–thaw method can be made to support cell adhesion by controlling physical parameters such as concentration and the number of freeze–thaw cycles. For a given number of freeze–thaw cycles, (specifically 45), polymer concentration dependent structural and mechanical properties (such as tensile strength and stiffness) were correlated with cell adhesion. The maximum cell attachment occurred on the hydrogels with the greatest mechanical properties, crystallinity and crosslinking density. The hydrogel surfaces were more favorable to human dermal fibroblasts than human lens epithelial cells and retained their transparency as well as dimensional stability with only a small degree of swelling. Fibroblast laden hydrogels showed extensive alkaline phosphatase activity which confirmed their healthy proliferation and function. In this manner, this study suggests that transparent Poly (vinyl alcohol) hydrogels prepared by the freeze thaw method described here should be further studied for numerous tissue engineering applications.

Physically crosslinked poly(vinyl alcohol) hydrogels with magnetic field controlled modulus

Abstract: Physically cross-linked isotropic and anisotropic poly(vinyl alcohol) (PVA) hydrogels containing micron-sized carbonyl iron particles were prepared through a cyclic freezing–thawing process. The PVA hydrogel can respond to a magnetic field and shows a magnetorheological (MR) effect, i.e., the modulus of the PVA hydrogel can be adjusted under a magnetic field. The chain-like structures of carbonyl iron are formed in the PVA hydrogel after orientation under a magnetic field of 1.5 T. Also some magnetic field induced oriented pores with a tunable diameter are observed in the dried PVA gel. The MR effect can be adjusted by changing the carbonyl iron content, the initial concentration of PVA solution and test frequency. The formation of aligned chain-like structures of carbonyl iron in the anisotropic PVA MR hydrogel improves the compression properties and the MR effect. At a carbonyl iron content of 70 wt%, the maximum absolute and relative MR effect of anisotropic PVA MR hydrogels are ∼1.24 MPa and ∼230%, respectively. The PVA hydrogels with good MR effects and moderate mechanical strength have potential applications in artificial muscle, soft actuators and drug release.