Cross-linked Polyvinyl Research Articles

Removable/fluorescent adhesive made by melamine-formaldehyde cross-linked polyvinyl alcohol and its repair application in artifacts

Nowadays, most of adhesives used for artifacts are colorless and non-removable resins, which makes it difficult to detect repaired location and cause some damage to the artifacts. Herein, we devolved the removable and fluorescent adhesive with melamine-formaldehyde (MF) resin cross-linked polyvinyl alcohol (PVA). The polar sensitive fluorescent dye of 8-anilino-1-naphthalenesulfonic acid (ANS) was encapsulated in the branched MF pre-polymer, and the obtained ANS@MF was employed as cross-linker to prepare cross-linked PVA (ANS@MF-PVA) to yield a series of water-soluble fluorescent adhesives. The obtained ANS@MF-PVA adhesives are colorless and transparent and show strong blue-green fluorescence under UV excitation, enabling it easy to detect their precise location on artifacts. Compared with PVA adhesive, the fluorescent ANS@MF-PVA adhesives present a better thermal stability and enhanced mechanic performance. ANS@MF-PVA samples all show higher adhesive strength (298.25 N, 0.95 MPa to 466.63 N, 1.49 MPa) than pure PVA (201.25 N, 0.64 MPa), which is positively correlated with their MF content. The ANS@MF-PVA is applied to adhere the glass substrates, ceramics and pottery figurine, and demonstrated excellent fluorescence, easy removability, and high durability. We believe that the ANS@MF-PVA fluorescent adhesives will provide art conservators with a new tool to aid in the reconstruction or repair of artifacts.

Self-healable and pH-sensitive high-strength water-soluble chitosan/chemically cross-linked polyvinyl alcohol semi-IPN hydrogel

A kind of novel unique semi-IPN was formed through facile radical cross-linking reaction between PVA-based macromonomer (PVAM) and acrylic acid (AA) in the presence of water-soluble chitosan (WSC). WSC, PVAM and AA were dissolved in distilled water, mixed homogeneously and initiated with potassium persulphate to perform the reaction. WSC was well distributed within the chemical network, which enabled the hydrogen bonding to be formed between part of amino groups on WSC chain and some carboxylic groups on PVA-based gel. As a result, the tensile strength of WSC/PVAM-AA semi-IPN is as high as 6.25 MPa when 30 wt% WSC was fed. Both the WSC content and water content affected the mechanical properties of the semi-IPN. Hydrogen bonding imparted another characteristic, i.e. self-healing ability, to the semi-IPN. The functional groups including amino and carboxyl groups not only acted as the contributors of hydrogen bonding, but also provided the semi-IPN the third trait, pH-sensitive swelling behavior. As a result, the facilely prepared semi-IPN exhibited triple functions.

A thermodynamically-consistent phenomenological viscoplastic model for hydrogels

Today, hydrogels have a plethora of biomedical and biotechnological applications such as controlled drug delivery, tissue engineering and wound dressing. These materials possess high stretchability and are able to undergo large deformation. Hydrogels deform nonlinearly under the influence of external loads because of their nonlinear elasticity, plasticity and viscosity, which are manifestations of the interactions between the solvent and the cross-linked polymeric chains at different length and time scales. This paper attempts to model the mechanical behavior of hydrogels through a thermodynamically-consistent phenomenologically-motivated viscoplastic approach. Uniaxial compressive tests are conducted on cross-linked polyvinyl alcohol hydrogels with varying amounts of a chemical cross-linker (Gluteraldehyde) to check the validity of the model developed. Creep tests are carried out to understand the time-dependent mechanical response of the hydrogels. The results obtained from the theoretical model are found to be in close agreement with experimental observations.

Cinnamon nanophytosomes embedded electrospun nanofiber: Its effects on microbial quality and shelf-life of shrimp as a novel packaging

Abstract The aim of this study was to develop a novel nanofiber-based structure to sustain the antibacterial effect of plant essential oils during a storage period in order to be used in active packaging applications. To this end, cinnamon essential oil nanophytosome (N/CEO) was prepared and embedded into cross-linked polyvinyl alcohol nanofiber (PVAc-N/CEO) using the electrospinning technique. The physicochemical characteristics and morphology of the nanofibers were evaluated by tensile, water vapor permeability, ATR-FTIR, TGA, and SEM analyses. Also, the cell toxicity and antibacterial effect of nanofibers were investigated. Finally, the antibacterial effect was validated on raw shrimp as a food model for 7 days storage. The results indicated that the N/CEO was successfully embedded into nanofiber matrix. In addition, PVAc-N/CEO, showed low cell toxicity, strong antibacterial effects and extension of shelf-life of shrimp compared to cross-linked PVA nanofiber containing CEO (PVAc/CEO). The results showed that the PVAc-N/CEO nanofiber has great potential in active packaging applications for shelf-life extension of perishable food products.

Lamellar phase behavior and molecular interaction of a thermoresponsive poloxamer and crosslinked poly (vinyl alcohol) hydrogel

A mixed hydrogel containing poloxamer 407 (P407) and cross-linked polyvinyl alcohol (cPVA) was prepared by varying the ratio of two polymer concentrations to make hydrogel formulations. The hydrogel formulations were determined for molecular interaction, viscoelastic, thermal properties and phase behavior. The results indicated that all hydrogels were clear and semi-solid. The cPVA was obtained from the crosslink between the PVA with borate and the PVA with borate and ascorbate. These molecules interacted to each other by forming the hydrogen bonding between borate ions, ascorbate and polymer chains or formed intermolecular and intramolecular hydrogen bonding. There is no chemical interaction between the molecules of cPVA and P407. The viscoelasticity of hydrogels exhibited sol-gel transition as frequency and temperature sweep. Incorporating cPVA into hydrogel elevated gelling temperature of P407 from 14.05 to 29.7 °C. The thermal properties of hydrogel revealed two melting point, 54–57 °C and 78–81 °C. The crystallization of hydrogel occurred at temperature lower than 40 °C and void spaces were presented at the cooling phase of the thermal study. The P407 has a lamellar structure and is stable even when the cPVA was added. The cPVA can be inserted into the interlamellar spacing of P407. It was concluded that a mixture of P407 and cPVA was suitable for the development of hydrogel.

GFRP-to-timber bonded joints: Adhesive selection

Recent research at the University of Queensland (UQ) has led to the development of a new type of structures called “Hybrid Fiber Reinforced Polymer (FRP)-Timber structures” (“HFT”). In HFT structures, FRP is combined with timber veneers to create high-performance, lightweight, easy-to-construct structural members. These HFT members take advantage (i) of the orthotropic properties of both, timber and FRP to orientate the fiber direction to produce optimal composite properties, and (ii) of the geometry of the cross sections to maximize the load bearing capacity for a given amount of material. While preliminary experimental work has revealed as such the effectiveness of HFT structural members, no work has been carried out so far to investigate the behavior of these HFT structures. Performance of these new HFT members relies significantly on the bond between FRP and timber. This paper presents the results of an experimental study aimed at selecting a suitable commercially available adhesive for glass fiber reinforced polymer (GFRP)-to-timber bonded joints. The experimental program included 393 single lap joint tests covering four different commercially available adhesives, two different curing temperatures, and two test methods (dry and moisture cycle tests). The test results revealed that both, polyurethane (PUR) and cross-linking polyvinyl acetate emulsion (PVAx) performed as the best under dry conditions, while PUR was shown to be superior to all other adhesives when subjected to moisture cycles. Epoxy and phenol resorcinol formaldehyde adhesive (PRF) commonly used in FRP structures and laminated timber structures, resp., were found to be less performing structural adhesives for HFT structures.

Fabrication and Surface-Enhanced Raman Scattering Activities of Cross-Linked Polyvinyl Alcohol/Ag Nanofibers

This work describes the fabrication steps and surface-enhanced Raman scattering (SERS) activities of the cross-linked polyvinyl alcohol (PVA)/Ag nanofibers. The water-insoluble electrospun PVA/Ag nanofibers were achieved by post-electrospinning treatment processes. Physical crosslinking was induced by heat treatments, while chemical crosslinking took place through the reactions with glutaraldehyde (GA). Scanning electron microscopy (SEM) images have shown that cross-linked PVA/Ag nanofibers remained mostly intact after immerging in water for 30 min. The testing of SERS activities was performed on these substrates using the methylene blue (MB) molecules as tested substances. The results have shown that the PVA/Ag nanofibers can be used as SERS substrates for rapid screening of biochemical substances. The Raman enhancement factor (EF) of approximately 104 corresponding to the detection limit of 10-4 M of MB molecules was achieved.

Morphology of Novel Chitosan Oligosaccharides Mod-ified Cross-linked Polyvinyl Alcohol Complex Foam (COS/cPVACF) Dressings with Fully Open-cell and Open-channel Microstructures via Active Molecules Cleaning Process for Wound Managements

The design of medical devices could be applied and developed for new treatment proce-dures instead of the traditional therapy procedures.

Novel thin-film nanofibrous composite membranes containing directional toxin transport nanochannels for efficient and safe hemodialysis application

Polymeric hemodialysis (HD) membranes with limited porosities, tortuous pores, and broad pore size distributions suffer from a trade-off between permeability-i.e., how fast toxins pass through the membranes-and selectivity-i.e., to what extent necessary proteins are retained. Here, a novel thin-film nanofibrous composite (TFNC) membrane, composed of an electrospun polyacrylonitrile (PAN) nanofibrous support layer and a chemically cross-linked polyvinyl alcohol (PVA) separation layer filled with heparin functionalized multi-walled carbon nanotubes (Hep-g-pMWCNTs), was demonstrated for efficient and safe HD application. Combining dialysis simulation experiments and pore-flow model, we demonstrated that the formation of free nanogaps at the interface between Hep-g-pMWCNTs and PVA matrix provided additional directional nanochannels for toxins to transport. The membranes showed efficient toxins removal without sacrificing selectivity (with the urea clearance of 88.2%, lysozyme clearance of 58.6%, and bovine serum albumin retention of 98.4% in a 4 h simulating dialysis). Especially, the efficiency in removing middle molecule toxins increased obviously compared with the values reported to date. Besides, the membranes exhibited excellent hemocompatibility: high resistance to protein adsorption, suppressed platelet adhesion, favorable anticoagulant activity, limited hemolysis ratio, and low complement activation. These facts suggested that the Hep-g-pMWCNTs/PVA/PAN TFNC membranes with superior comprehensive performances presented great potential for HD application.

Sugar-responsive smart materials based on phenylboronic acid and cyclodextrin

This review focuses on sugar-responsive materials based on phenylboronic acid (PBA) as a sugar-sensing motif and cyclodextrins (CyDs) as a basic skeleton of smart materials. PBA modified α-CyD (PBA-α-CyD) forms a supramolecular polymer through intermolecular interactions between PBA part and CyD cavity. Similarly, PBA-β-CyD forms a head-to-head dimer. Meanwhile, combining PBA-γ-CyD and polyethylene glycol (PEG) produces a molecular necklace. Additionally, combining PBA-modified PEG and native α-CyD or γ-CyD results in another type of molecular necklace. These supramolecular structures are obtained as powders, and their solubility increases in the presence of sugar. Besides the powder type, a unique gel is formed through crosslinking polyvinyl alcohol with PBA-triazole-γ-CyD (PBA-Tri-γ-CyD). This gel can contain model drug, and it shows sugar-responsive drug release. The sugar response of all of these smart materials can be explained by the concept of equilibrium. The smart materials are constructed with CyD-guest interactions. The CyD-guest equilibrium moves by a reaction between sugar and PBA moiety attached to the smart material. In these smart materials, sugar induces a dissociation in the CyD-guest interaction, and this dissociation results in sugar-induced disintegration of CyD-guest supramolecular structures.

Creep and dynamic mechanical behavior of cross-linked polyvinyl alcohol reinforced with cotton fiber laminate composites

Abstract The objective of this investigation was to fabricate cross-linked polyvinyl alcohol (PVA) based laminate composites reinforced with biaxial cotton sheets. Cross-linking was done with sulfuric acid, to overcome the water solubility of PVA. A water uptake test was performed to evaluate the effect of cross-linking on the water absorption properties of the composites. Morphology, distribution and bonding between the matrix and reinforcement of the fabricated composites were studied using scanning electron microscopy. Mechanical properties such as the tensile strength (TS), modulus of elasticity and elongation of the fabricated composites material were evaluated. There was about a 56.25% increase in the TS of the cross-linked composite as compared to the neat PVA, and at 64 wt.% of cotton fiber, there was about a 56% increase in the TS as compared to the cross-linked PVA. The thermal degradation analysis of fabricated composites material was carried out by thermogravimetric analysis. The thermal stability increased with increase in cotton fiber wt.%. The viscoelastic properties of the fabricated composites material were determined by dynamic mechanical analysis. The effects of stress (4 MPa, 6 MPa and 8 MPa) and temperature (20°C and 40°C) on creep and recovery behavior of the laminated composites were studied.

Thermally cross-linked polyvinyl alcohol as gate dielectrics for solution processing organic field-effect transistors

Poly(vinyl alcohol) (PVA) thin-films were cross-linked by N,N’-methylene bisacrylamide (MBA) in a thermal induced radical process at 100℃. The cross-link improved the dielectric properties of PVA thin-films. The effect of surface passivation by cross-linked polymethyl methacrylate (PMMA) thin-films on the electrical properties and the surface characteristics of the PVA gate dielectrics were also investigated. The surface passivation layer significantly reduced surface hydrophilicity and improved the morphology of semiconductor layers. The bilayer dielectrics were applied in solution processed OFET devices with a bottom-gate bottom-contact structure.

Synthesis, Characterization and Application of Disodium Tetraborate Cross-Linked Polyvinyl Alcohol Membranes for Pervaporation Dehydration of Ethylene Glycol

Dehydration of ethylene glycol-water mixture was carried out in a laboratory pervaporation unit using a flat sheet membrane test cell. Polyvinyl alcohol-polyether sulfone (PVA-PES) composite membranes were synthesized and cross linked with two different concentrations, viz 0.2 and 0.5% of disodium tetraborate (borax). The derived membranes were extensively characterized for their morphology, intermolecular interactions, thermo-mechanical stability, and physicochemical properties using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and water uptake studies. The membrane performance was evaluated in terms of pervaporation flux, separation factor, selectivity, permeability and solute diffusion coefficients of EG-water mixture at varying feed flow rate. Both in terms of flux and separation factor PVA-PES-0.2% borax composite membrane was found superior to PVA-PES-0.5% borax crosslinked and its uncrosslinked counterpart. Cross-linking the composite with borax produced a membrane with lower crystallinity and a smaller swelling degree, but having improved thermostability and mechanical properties.

Post-curing effect on the chemical structure and its relationship with heat resistance and thermal-mechanical properties of crosslinked PVC foams

Crosslinked polyvinyl chloride (PVC) foams were post-cured in 65 °C water for 5, 10, and 15 days. The effects of post-curing time were investigated regarding the chemical structure of semi-interpenetrating polymer networks (SIPNs) and its relationship with heat resistance and thermal-mechanical performances, and selected properties, such as cellular morphology, apparent density, compressive and flexural behaviors of the resulting PVC foams. The post-cured PVC foam with 5 days was specifically beneficial to the compressive and flexural properties as well as storage modulus, because this process promoted the crosslinking reaction and led to increasing polyimide proportion in the matrix. A longer post-curing time (10 days) would improve the chain interactions and limit the initial dehydrochlorination of PVC macromolecules, due to the increased H-bonded polyurea and polyamide groups in the SIPNs. The post-cured foam with 10 days increased the degradation temperature from 198.3 °C to 236.5 °C, with a 5% weight loss, and the glass transition temperature (Tg) from 73.4 °C to 91.6 °C. With the formation of a large amount of free urea groups, severe irreversible damage to the cellular microstructure was observed after 15 days of post curing, resulting in deteriorations in heat resistance, mechanical and thermal-mechanical properties of foams.

Positively charged nanofiltration membrane based on cross-linked polyvinyl chloride copolymer

A polyvinyl chloride (PVC)-based positively-charged nanofiltration membrane was fabricated from polyvinyl chloride-graft-poly(N,N-dimethylaminoethyl methacrylate) by heating and crosslinking treatment. We characterized the surface chemical compositions, membranes structures, surface hydrophilicity and surface charges of the prepared membrane. The estimated membrane pore diameter is 1.98 nm and the pore diameters are in the range of 0.5–2.0 nm. The membrane exhibits excellent water permeability (9.3 L m−2 h−1 bar−1) and salt rejection (93.1% with MgCl2 solution). Both the heating treatment and crosslinking reaction can diminish the pore size of the precursor membrane. The membrane hydrophilicity is improved after quaternization, leading to higher water permeability compared with the membrane treated by heating only. Moreover, surface quaternization and crosslinking offer the membrane excellent pressure resistance and long-term stability. The prepared nanofiltration membrane has great promise in many applications including water softening and multivalent ion removal.

Mechanism of formation of soft and elastic nanoflowers; a key major guideline

Water-born flower-like nanostructures have been produced via electrospinning of an innovative bicomponent polymeric solution of cross-linkable amino-functional polysiloxane (X-AFPs) resin and polyvinyl alcohol (PVA) in a special condition, after an after-washing process. It is the first report on production of a resin-based flower-like nanostructure as well as a siliconic flower-like nanostructure. It is also a well-engineered water-based green technique. An interesting mechanism has been proposed according to the SEM outcomes as well as the principles of electrospinning. The paper gives an explanation of how some physicochemical phenomena such as specific interactions among the polymeric components as well as high-level differences in terms of electrical charge density, viscosity and elasticity can direct the formation of these amazing structures. Accordingly, this research can be considered as a key major guideline to develop other polymeric flower-like nanostructures and their associated cutting-edge applications. Developing an anti-adhesive membrane was also followed in this research. A super-hydrophobic feature was achieved on the post-treated flower-like structures with a hydrophobic X-AFPs layer, after elimination of the PVA residue. Cytocompatibility as well as anti-adhesive properties of the treated flower-like structures have been assayed and perfectly confirmed through an in vitro study on a highly adherent cell type in a high cell seeding concentration. Accordingly, these three dimensional multiple-scale flower-like nanostructures can be offered for a wide-range of biomedical applications especially for anti-adhesive requirements such as cardiovascular applications and/or controlled cell response approaches.

Carbon Nanotube/PVA Aerogels Impregnated with PEI: Solid Adsorbents for CO2 Capture

A series of ultra-light aerogels made of oxidized carbon nanotubes and cross-linked polyvinyl alcohol has been prepared by freeze drying of hydrogels, characterised, and tested as amine impregnated solid supports for CO2 capture. The prepared spongy aerogels have demonstrated mechanical, chemical and thermal stabilities, and are electrically conducting. Polyethyleneimine impregnated aerogels with an amine content of 75–83% demonstrated CO2 capacity values ≥3.3 mmol g−1 in a dilute gas stream, which makes the prepared aerogels highly promising supports for amine impregnation in carbon capture applications.

Cross-linked polyvinyl amidoxime fiber: a highly selective and recyclable adsorbent of gallium from Bayer liquor

Gallium, a scarce metal produced mainly from Bayer liquor, is widely used in semiconductors. Ion-exchange method is currently considered as the most effective method to recover gallium from Bayer liquor. In this article, fibrous amidoxime adsorbents are introduced to recover gallium from Bayer liquor. In addition, hydrazine cross-linked polyvinyl amidoxime (HPAO) fibers have been prepared. The structure of the as-prepared fibers was ascertained by FTIR, elemental analysis and weight gain rate. The adsorption kinetics, adsorption isotherm and recycling performance were investigated by batch method. Cross-linking duration was studied and it turned out to be an important factor to optimize the adsorption capacity and recycling performance. After 1.5 h cross-linking time, the fiber showed the highest gallium adsorption capacity of 14.83 mg/g in Bayer liquor. After 3 h cross-linking time, the fiber showed the best recycling performance, which retained 82.9% of the initial adsorption ability after four cycles. Adsorption capacity of vanadium was lower than 1 mg/g for all samples. HPAO displayed very fast adsorption kinetics with an equilibrium at 60 min. The EDS results confirmed the low extraction of aluminum and vanadium provided by HPAO fibers. The gallium-loaded fiber could be effectively eluted by acidified thiourea. With proper control of the cross-linking duration by hydrazine, HPAO fiber with high selectivity towards gallium, high adsorption capacity and good recycle performance could be obtained, which is promising for recovering gallium needed for industrial applications.

Flexible/Rechargeable Zn-Air Batteries Based on Multifunctional Heteronanomat Architecture.

The increasing demand for advanced rechargeable batteries spurs development of new power sources beyond currently most widespread lithium-ion batteries. Here, we demonstrate a new class of flexible/rechargeable zinc (Zn)-air batteries based on multifunctional heteronanomat architecture as a scalable/versatile strategy to address this issue. In contrast to conventional electrodes that are mostly prepared by slurry-casting techniques, heteronanomat (denoted as "HM") framework-supported electrodes are fabricated through one-pot concurrent electrospraying (for electrode powders/single-walled carbon nanotubes (SWCNTs)) and electrospinning (for polyetherimide (PEI) nanofibers) process. Zn powders (in anodes) and rambutan-shaped cobalt oxide (Co3O4)/multiwalled carbon nanotube (MWCNT) composite powders (in cathodes) are used as electrode active materials for proof of concept. The Zn (or Co3O4/MWCNT) powders are densely packed and spatially bound by the all-fibrous HM frameworks that consist of PEI nanofibers (for structural stability)/SWCNTs (for electrical conduction) networks, leading to the formation of three-dimensional bicontinuous ion/electron transport channels in the electrodes. The HM electrodes are assembled with cross-linked polyvinyl alcohol/polyvinyl acrylic acid gel polymer electrolytes (acting as zincate ion crossover-suppressing, permselective separator membranes). Benefiting from its unique structure and chemical functionalities, the HM-structured Zn-air cell significantly improves mechanical flexibility and electrochemical rechargeability, which are difficult to achieve with conventional Zn-air battery technologies.

Physical, tensile, and biodegradability properties of cross-linked polyvinyl alcohol/palm kernel shell powder biocomposites

Polyvinyl alcohol/palm kernel shell powder biocomposites were prepared by using a solution casting method. To enhance the properties, the crosslinking agent glutaraldehyde (GA) was added to the composition. The effect of the crosslinking agent on the biocomposite was studied based on the change in the tensile properties, physical properties, and biodegradability. The optimum GA content was found to be 2 phr because the tensile properties tended to decrease with higher GA contents. The water absorption percentages and water vapour transmissibility decreased until the GA content reached 2 phr and then increased. It was found that the biodegradability of the film decreased when GA was added.