Preparation and Properties of Polyvinyl Alcohol/Collagen Hydrogel

Hydrogel scaffolds based on poly(vinyl alcohol) (PVA) collagen films were prepared by a chemical cross-linking method. The effects of the contents of PVA and cross-linker on compressive strength and swelling ratio were studied, and the effect of the pH value of the immersion medium on the swelling ratio was also investigated. The results showed that the introduction of PVA improved the compressive strength of PVA/collagen hydrogel, and the swelling ratio of the hydrogel scaffold increased with increasing PVA content in the blends. With increasing cross-linker content, the swelling ratio decreased; however, the compressive strength increased. The swelling ratio of PVA/collagen scaffold increased when pH was decreased. In conclusion, swelling ratio and compressive strength in PVA/collagen blends can be controlled by variation of their contents, cross-linking agent content, and pH value.     

PVA–APTEOS/TEOS Hybrid Sol–Gel Pervaporation Membrane for Dehydration of Ethanol

Novel organic–inorganic hybrid membranes were prepared by co-hydrolysis and co-condensation reactions of aminopropyltriethoxysilane (APTEOS) and tetraethylorthosilicate (TEOS) in poly(vinyl alcohol) (PVA) aqueous solution. These sol–gel reactions make a silica nanoparticles network which cross-links the structure of membranes. As a result, swelling properties of the membranes change due to these cross-linking reactions. The relative molar content of APTEOS to (APTEOS + TEOS) was changed from 0.0 to 0.75. The effect of APTEOS to (APTEOS + TEOS) on morphology as well as pervaporation performance of the membranes for dehydration of ethanol was investigated. It was found out that the hybrid membranes with a certain mass ratio of 1:1 (APTEOS + TEOS to PVA) exhibit higher permselectivity and more permeation flux for dehydration of ethanol aqueous mixtures compared with the PVA–TEOS membranes. Because hydrolysis and condensation reactions of mixed silanes make smaller silica nanoparticles, the permeability properties of the membranes improve in comparison with those of the membranes prepared using a single silane.     

Preparation and characterization of anhydrous polymer electrolyte membranes based on poly(vinyl alcohol-<Emphasis Type="Italic">co</Emphasis>-ethylene) copolymer

Anhydrous polymer electrolyte membranes with cross-linked structure have been prepared based on poly(vinyl alcohol-co-ethylene) (PVA-co-PE) copolymer. The PVA units of copolymer served to induce thermal cross-linking with 4,5-imidazole dicarboxylic acid (IDA) via esterification while PE units controlled the membrane swelling and the mechanical properties of films. Upon doping with phosphoric acid (PA, H₃PO₄) to form imidazole-PA complexes, the proton conductivity of membranes continuously increased with increasing PA content. As a result, proton conductivity reached 0.01 S/cm at 100 °C under anhydrous conditions. X-ray diffraction analysis revealed that both the d-spacing and crystalline peak of membranes were reduced upon introduction of IDA/PA due to the cross-linking effect. The PVA-co-PE/IDA/PA membranes exhibited good mechanical properties, e.g., 150 MPa of Young’s modulus, as determined by a universal testing machine. Thermal gravimetric analysis also represented that the thermal stability of membranes was increased up to 200 °C upon introduction of IDA/PA.     

Fabrication of highly selective PVA-g-GO/SPVA membranes via cross-linking method for direct methanol fuel cells

Organic/inorganic composite membranes were prepared using sulfonated poly(vinyl alcohol) (SPVA), mixed and cross-linked with different amounts of poly(vinyl alcohol)-grafted graphene oxide (PVA-g-GO). The introduction of PVA-g-GO to the membranes not only reduced the methanol permeability but also positively affected the mechanical properties: Increasing the PVA-g-GO content increased the blocking effect of GO. The PVA-g-GO/SPVA membranes were cross-linked with glutaraldehyde, resulting in the formation of cross-linking chains within the matrix, as well as between the matrix and the filler. Therefore, the microstructure of the PVA-g-GO/SPVA cross-linking membrane was different from that of the existing membranes. This structure also reduced the methanol permeability. The composite membranes exhibited proton conductivities ranging from 0.0141 to 0.0319 S/cm at 60 °C, and low methanol permeability ranging from 3.13?×?10^?7 to 1.53?×?10^?7 cm² s^?1 at 25 °C.     

Structural analysis of PVA-based proton conducting membranes

We have synthesized and characterized a new family of proton conducting membranes based on cross-linked poly(vinyl alcohol), PVA, and functionalized silica filler. Glutaraldehyde, GLA, was used as the cross-linking agent in order to improve chemical and thermal stabilities. The functionalization of the silica particles is such that terminal –SO₃H groups are formed during membrane preparation, thus possibly providing additional mobile protons. We find that the crystallinity of the PVA-based membranes is enhanced by the presence of the functionalized silica particles, whereas it is reduced by means of cross-linking. The thermal stability of the ternary system PVA:GLA:silica is improved due to the additive contribution of GLA and silica. The conductivity of membranes swelled in a sulfuric acid solution was found to be of the order of 10^− 1 S cm^− 1.     

Preparation of poly(vinyl alcohol)–silicone based hybrid membranes for the pervaporation separation of water–acetic acid mixtures

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle x-ray diffraction and differential scanning calorimetry. A remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen bonding and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as cross-linking agent. The membrane containing 1 : 2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10^?2kg/m²h at 30°C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values obtained, showing that water permeation is lower than that of acetic acid, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal because of the higher selective nature of membranes. The negative heat of sorption values (ΔH _s) for water in all the membranes suggests a Langmuir mode of sorption.     

Stabilization of solvent-impregnated resins (SIRs) by coating with water-soluble polymer and chemical cross-linking and its application in mercury removal

Stabilization of solvent impregnated resins was achieved by the formation of a surface coating with the absorptive layer of poly(vinyl alcohol) and cross-linking with the protective layer of vinyl sulphone (VS). Amberlite XAD-4 and vinyl sulphone proved to be effective matrix and cross-linking agents, respectively, in the preparation of a protective layer of SIRs containing Cyanex 923 as extractant. The stabilized SIRs were characterized by the amount of vinyl sulphone contributing to the N and S content in the stabilized resin as well as to its operational stability. Optical and single electron microscope pictures were used to examine the appearance and the morphology, respectively, of the external protective barrier of SIR. Batch and column mode of sorption/elution studies for the removal of mercury from aqueous solution at pH 4 were carried out with Cyanex 923 containing SIR coated with PVA cross-linked with VS. Stabilized SIR was found to be effective for the mercury removal and showed great stability during the batch recycle runs. Elution of mercury from SIR was quantitatively achieved with 3M HNO₃. Kinetic and column performances were influenced by the degree of cross-linking of resin coating. Chemical stability and sorption capacity of stabilized SIR remained almost constant after several recycle runs whilst uncoated SIRs lose extractant with time as confirmed by efficiency studies.     

Fabrication and electro chemical properties of poly vinyl alcohol/para toluene sulfonic acid membranes for the applications of DMFC

The novel acid–base membranes composed of para toluene sulfonic acid (pTSA) as an acidic compound, and poly vinyl alcohol (PVA) as a basic compound were fabricated. The morphological and structural properties of the prepared membranes were analyzed by scanning electron microscopy and Infra red spectroscopy. Inclusion of Glutaraldehyde (GLA) and para toluene sulfonic acid (pTSA) promotes the amorphous character of a polymer which causes the free volume for the movement of ions. Thermal and mechanical stability of the acid–base membranes were influenced by the crosslinking agent glutaraldehyde. By the suitable charge carriers of pTSA, hydrophilic channels were promoted for the composite membranes which ensure the ionic conductivity. A high ionic conductivity-methanol permeability selectivity ratio obtained for the prepared PVA/pTSA membrane influences its viable application in direct methanol fuel cells.     

Synthesis and characterization of radiation crosslinked nano silver- polyvinyl alcohol/polyethylene oxide composites

Poly (vinyl alcohol)/poly (ethylene oxide) (PEO/PVA) blends were modified by gamma irradiation in the presence of acrylic acid (AAc) monomer. The modified PVA/PEO blends were then complexed with silver nitrate salt and lithium trifluoromethanesulfonate. Transmission electron microscopy was used to determine the distribution as well as the particle size of the silver nanoparticles (NP) formed in the matrix. The UV–vis absorbance spectra of the prepared grafted nanocomposite membranes confirmed the formation of Ag NP based on their surface plasmon band at 438?nm. The electrical properties of the blended electrolyte polymer films were characterized and discussed.     

Incorporation of Benzocyclobutene Cross-Linkable Moieties in Poly(Methyl Acrylate): A Novel Approach to Shape-Memory Polymers Accompanied with Microphase Separation

Benzocyclobutene (BCB) moieties were incorporated into a typical polyolefin, poly(methyl acrylate), by free radical copolymerization of benzocyclobutene-4-yl acrylate and methyl acrylate. The subsequent cross-linking of the generated copolymers by ring-opening reaction of BCB gave rise to shape-memory polymers. This new cross-linking process did not require cross-linker and yielded small molecules. Most importantly, submicron-sized particles within the cross-linked polymers, which were observed using atomic force microscope, were induced by this cross-linking strategy. The results of the shape-memory tests suggested that the cross-linked polymers displayed good shape-memory performance.     

Studies on mechanical and swelling behavior of polymer networks on the basis of the scaling concept. 6. Gels immersed in polymer solutions

In order to describe the mechanical and swelling behavior of gels immersed in polymer solutions, theoretical considerations based on both classical and scaling theories are discussed and compared with experimental findings. Three situations are studied: (1) the gel is separated from the surrounding solution by a semipermeable membrane; (2) the gel is immersed in the semidilute solution of a chemically identical polymer; (3) the gel is directly immersed in the semidilute solution of a chemically different polymer. An attempt is made to take into account the effect of the penetrating polymer on the elastic modulus and the swelling pressure of the gel. Experimental data referring to chemically cross-linked poly(vinyl alcohol) and poly(vinyl acetate) networks are presented. It was found that the concentration of the free chains inside moderately cross-linked networks may be considerable even for polymers having relatively long chains (27,000 < < M _n < 130,000). Experimental results indicate that the presence of free chains only slightly alters the elastic modulus; however, the swelling pressure is considerably affected by the penetrating polymer. The analysis of mechanical and equilibrium deswelling measurements carried out on several series of gel homologues shows that scaling theory satisfactorily describes the experimental data.     

A ZnO/PVA/PAADDA composite electrode for rechargeable zinc-air battery

Ionics - A ZnO/PVA/PAADDA composite electrode for rechargeable zinc-air battery was prepared by chemical cross-linked PVA (polyvinyl alcohol) with poly(acrylamide-co-diallyldimethylammonium...     

Fabrication and Characterization of Ultrathin Graphene Oxide/Poly(Vinyl Alcohol) Composite Films via Layer-by-Layer Assembly

Novel multilayer ultrathin films comprised of graphene oxide (GO) and poly(vinyl alcohol) (PVA) were fabricated through a layer-by-layer (LBL) assembly technique. GO could self-assemble onto quartz substrates alternately with PVA via hydrogen-bonding interactions. X-ray diffraction, atomic force microscopy, and transmission electron microscopy analysis revealed that GO was exfoliated to monolayers. The ultrathin films, with PVA/GO multilayer structures fabricated by LBL assembly, were characterized by ultraviolet-visible spectroscopy and X-ray diffraction analysis, confirming that the assembly of the multilayer films was quantitative and reproducible.     

Liposomal Templating,Association with Mammalian Cells,and Cytotoxicity of Poly(vinyl alcohol) Physical Hydrogel Nanoparticles

The assembly, cellular internalization, and cytotoxicity of nanoparticles based on physical hydrogels of poly(vinyl alcohol) (PVA) are reported. PVA nanoparticles are assembled using a liposomal templating technique followed by removal of the lipids using isopropanol, a process that requires the presence of a custom‐made block copolymer, poly(vinyl alcohol‐b‐vinyl pyrrolidone), to avoid aggregation of the nanoparticles. Polymer hydrogelation is induced via incubation in aqueous isopropyl alcohol solution, which results in PVA hydrogel nanoparticles (PVA HNP) with excellent colloidal stability and stability towards disintegration over at least 24 h. Pristine PVA HNP are found to be remarkably stealth‐like and exhibit negligible cellular internalization. This feature is likely inherent with the low fouling nature of PVA and makes PVA HNP attractive for targeted drug delivery with a low level of association with non‐targeted cells and tissues. Blending PVA with varied amounts of collagen results in colloidal hydrogel particles with a well pronounced tendency towards association with mammalian cells, specifically hepatocytes and endothelial cells. The association of PVA HNP elicits minimal changes in cellular proliferation, making these novel hydrogel particles convenient tools for drug delivery applications and creation of implantable artificial organelles and sensors.     

Effect of carbon nanotubes dispersion on morphology, internal structure and thermal stability of electrospun poly(vinyl alcohol)/carbon nanotubes nanofibers

The current work reports the effect of multi walled carbon nanotubes and single walled carbon nanotubes dispersion on morphological, structural and thermal degradation of electrospun poly(vinyl alcohol) (PVA)/carbon nanotubes (CNTs) dispersed in sodium dodecyl sulfate (SDS) (PVA/CNTs–SDS) composites nanofibers. (PVA/CNTs–SDS) nanocomposites fibers were elaborated using the traditional electrospinning process to disperse and align CNTs into the fibers, especially for low CNTs loading fraction: 0.3 and 0.7 wt%. The morphology of the electrospun fibers was studied using the scanning electronic microscopy. The average diameter of the fibers changes significantly after the incorporation of the CNTs in the PVA. Furthermore, Fourier transform infrared spectroscopy elucidated the effect of CNTs on the crystallization of the PVA which was confirmed by X-ray diffraction analysis. Thermogravimetric analysis showed that the thermal stability of the composite fibers depends on the loading fraction and on the type of carbon nanotubes.     

Thermal Decomposition Behavior of Poly (Vinyl Alcohol) with Different Hydroxyl Content

The thermal decomposition behavior of poly(vinyl alcohol) (PVA) with two different hydroxyl contents, 88 and 99%, was investigated. UV-Vis spectroscopy, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and TGA-FTIR were used to detect the volatile and nonvolatile products of the thermal decomposition of PVA. The results suggest that the PVA, after thermal treatment, can form chromophoric polyene structure, as well as carbonyl groups. The PVA with 88% hydroxyl content underwent slower decomposition below 280°C and generated water and carboxyl acid as the dominant volatile products, however, as for the PVA with 99% hydroxyl content, the dominant volatile products were water, unsaturated aldehydes, and other unsaturated compounds.     

pH-Sensitive Poly(Vinyl Alcohol)/Sodium Carboxymethylcellulose Hydrogel Beads for Drug Delivery

A series of pH-sensitive hydrogel beads were prepared composed of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) by using Fe³⁺ crosslinking and freeze-thawing (FT) cycle techniques. The mixed solution of CMC and PVA was firstly crosslinked with Fe³⁺ to form beads and then subjected to freezing-thawing cycles for further crosslinking. The formation of hydrogel was confirmed by Fourier transform infrared spectroscopy (FTIR). The gelling rate in ferric solution and the swelling and pH-senstive properties of the hydrogel beads were investigated. The encapsulation efficiency and in-vitro release properties of beads were also evaluated using Bovine serum albumin as model drug. The pH sensitivity and the release rate increased with increasing CMC content. These results suggest that the PVA/CMC hgdrogel beads should be useful as pH-sensitive drug delivery systems for bioactive agents.     

Solution-grown crystals of poly(vinyl alcohol)

The growth mechanism and crystalline texture of solution-grown crystals of poly(vinyl alcohol) have been studied by electron microscopy. From morphological data it is shown that single crystals of poly(vinyl alcohol) (PVA) have two growth faces, i.e., the (100) and (101) fold planes. It is suggested that the parallelogrammic single crystals grow from the center by molecular folds. The rate of addition on the (100) plane is about three times larger than that on the (101) plane. Twinning of the PVA crystals takes place at the (100), (001), (101), and (101) planes at the time of the nucleation or during the growth. The single crystal and twins of PVA are corrugated lamellae. Granulated structure is observed on the surface in a figure similar to the external form of the crystals. Dark-field micrographs show that the PVA single crystals possess a mosaic structure with the arrangement of the blocks deviating slightly from parallel alignment in the lamella. The reactivities of single crystals to various aldehydes indicate that the single crystals contain crystal lattice defects.     

Properties of nano-ZnO/poly(vinyl alcohol)/poly(ethylene oxide) composite thin films

A series of poly(vinyl alcohol)/nano-ZnO composites were prepared by dispersing nano-ZnO in aqueous solutions containing mixtures of the biodegradable polymers poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO), and composite thin films were prepared by casting. The introduction of nano-ZnO into PVA/PEO mixed solutions significantly decreased the resistivity of the solutions. Ultraviolet absorption, thermal behaviour and visco-elastic properties of the thin films were determined as a function of nano-ZnO content up to 15 wt%. Optimum film properties were obtained with 1 wt% nano-ZnO, higher proportions of nano-ZnO resulting in agglomeration of ZnO particles and deterioration in film properties. The Forouhi and Bloomer model was used for the modelling of ZnO thin films.     

Collagen fibril formation in poly(vinyl alcohol) and poly(vinyl pyrrolidone) films

The formation of collagen fibrils in poly(vinyl alcohol) (PVA) and in poly(vinyl pyrrolidone) (PVP) was investigated using Atomic Force Microscopy (AFM). The water solutions of PVA and PVP containing 1%, 3% and 5% of collagen were cast onto glass plate. After slow solvent evaporation thin polymeric films were obtained. AFM images showed the fibril formation in both, PVA and PVP films containing collagen. The amount of collagen in PVA and PVP matrix has an important effect on the structure and size of collagen fibril formed. The diameter of collagen fibrils in PVA films is bigger than the diameter of collagen fibrils formed in PVP films.