Aqueous Solution Of Polyvinyl Alcohol Research Articles

Thermal conductivity of hybrid multilayer graphene-fiber carbon membranes

Hybrid graphemne-fiber systems could present an alternative for various industrial applications in need of large area graphene sheets. One way to produce these carbon-based structures is by subjecting an aqueous polyvinyl alcohol solution containing sodium chloride to centrifugal spinning under high humidity conditions. The developed polymer fibers are then subjected to a dehydration and carbonization process to promote the formation of the hybrid carbon structure. Potential applications of this material are highly dependent upon their conducting properties. In this work we analyzed the effect of the NaCl content and humidity conditions during the spinning process and ultimate thermal conductivity of the resultant hybrid graphene-fiber carbon systems. Results show an optimum NaCl added to the carbon precursor solution and spun at a high relative humidity (around 70%) promote the development of veils of graphene oxide multilayer that interconnect with produced fibers. We applied for the first time a thermographic method to determine the thermal conductivity of carbon mats. The thermal conductivity of the hybrid fibers increases as graphene multilayers veils expand between carbon fibers, to reach values up to 28 W m K−1.

Disentangling proton-transfer and segmental motion relaxations in poly-vinyl-alcohol aqueous solutions by means of ultrasonic relaxation spectroscopy

A detailed temperature- and concentration-dependent ultrasonic relaxation study has been conducted in aqueous polyvinyl alcohol (PVA) solutions as a function of frequency under isobaric conditions. Concentration and temperature have similar effect on acoustic spectra. Two well-resolved relaxation processes were observed in the experimental acoustic spectra that seem to follow a Cole-Cole distribution function. The systematic analysis of the variation of the acoustic parameters with frequency, temperature and concentration revealed that both processes have collective and not local nature. The low-frequency relaxation mechanism is assigned to segmental motions of the polymer chains and the high-frequency relaxation to proton-transfer reaction, respectively. The characteristic relaxation frequencies were found independent of molecular weight, as expected for relative flexible vinyl-polymer chains with molecular weight above ~104. Based on Eyring's theory, the activation enthalpy of the low- and high-frequency relaxation were estimated equal to ΔΗ1* = 4.5 ± 0.2 kcal/mol and ΔΗ2* = 19.7 ± 0.8 kcal/mol, respectively. The contribution of the low-frequency lying normal mode relaxation has been quantitatively estimated in the context of relevant theories of the field and found almost four order of magnitude lower in amplitude compared to segmental motion process indicating that the experimentally detected relaxation is dominated by the latter. The experimental results were complemented with molecular mechanics calculations performed in parallel. The comparison between the experimental data and the outcome of the theoretical calculations evidenced that the length of the relaxing element in a PVA polymer chain is between 5 and 8 monomers in agreement with what is expected for vinyl-polymers and established the local segmental motions of the PVA polymer chains in the solution.

A combined interfacial polymerization and in-situ sol-gel strategy to construct composite nanofiltration membrane with improved pore size distribution and anti-protein-fouling property

Pore size distribution is crucial for the application of nanofiltration membrane in size-selective separation of industrial fluids. In this work, a novel combined interfacial polymerization (IP) and in-situ sol-gel strategy was proposed to fabricate composite nanofiltration membrane with narrow pore size distribution. Aqueous solution of piperazine and polyvinyl alcohol (PVA) was employed to perform interfacial polymerization with organic solution of trimesoyl chloride and tetraethyl orthosilicate (TEOS) on porous support. The non-reactive additive TEOS within the interfacially synthesized selective separation layer was then employed to perform sol-gel. The space-limited hydrolysis and condensation of TEOS molecules and their chemical bonding with PVA molecules were confirmed by analyzing membrane physico-chemical property and were found to be effective in tuning mean pore diameter, narrowing the pore size distribution and thus enhancing membrane perm-selectivity. Compared to those of membrane PA1 with similar mean pore size fabricated by only IP technique, the water permeability and rejection ratio of PEG1000 to raffinose (RPEG1000/Rraffinose) of membrane PA-TEOS0.5 fabricated by combined IP and sol-gel technique were higher by 25.0 and 20.1%, respectively. Moreover, static adsorption and dynamic deposition tests using aqueous bovine serum albumin solution proved that in-situ sol-gel process could endow the membrane with better protein fouling resistance.

Fabrication, characterisation and properties of polyvinyl alcohol/graphene nanocomposite for fused filament fabrication processing

ABSTRACT In this study, graphene nanoplatelet (GNP) fillers were first mixed with a polyvinyl alcohol (PVA) aqueous solution under ultrasonication, and then glycerol was added as a plasticiser to enhance the thermal processability of the PVA/GNP mixture. The interactions among glycerol, GNP and PVA, rheological behaviour, crystallisation behaviour, electrical properties, and mechanical properties of the 3D printed parts were carefully investigated. The results show that the incorporation of glycerol can effectively decrease the melting temperature of PVA, thus improving the thermal FFF processability of the PVA/GNP nanocomposite. Besides, compared with the glycerol modified PVA (mPVA), the electrical conductivity of the mPVA/GNP nanocomposite 3D printed part with only 1.0 wt-% GNP loading could increase by ∼300 times (from 7.8 × 10−7 S m−1 to 2.4 × 10−4 S m−1). The obtained functional mPVA/GNP nanocomposite filaments were successfully used in fabrication of various 3D printed functional parts with complex geometry/structure and good dimensional accuracy.

Effects of Polyvinyl Alcohol on Drug Release from Nanocomposite Particles Using Poly (L-lactide-co-glycolide).

The effects of polyvinyl alcohol (PVA) on the release behavior of polymer nanoparticles from nanocomposite particles using amino acids were investigated. Rifaximin (RFX) was used as a hydrophobic drug model. RFX-loaded poly(L-lactide-co-glycolide) (PLLGA) nanoparticles were prepared using an antisolvent diffusion method. They were then spray-dried with equal amounts of amino acids to prepare the nanocomposite particles. The mean diameters of nanocomposite particles were 2.86-5.42 μm. The particle size increased as the concentration of PVA aqueous solution increased. The mean diameters of RFX-loaded PLLGA nanoparticles were 150-160 nm; however, the particle size distributions of those prepared using 0.25% (w/v) PVA aqueous solution differed significantly immediately after preparation and after redispersion from nanocomposite particles. The release test results of nanocomposite particles revealed that those prepared using 0.25% and 0.50% (w/v) aqueous PVA solutions rapidly released RFX. In contrast, particles prepared using 2.00 and 4.00% (w/v) PVA aqueous solution showed sustained drug release. The results of drug release tests of nanoparticles redispersed from nanocomposite particles showed that the nanoparticles prepared using 0.50% and 2.00% (w/v) PVA aqueous solution suppressed the initial burst. Therefore, we considered that the results of the drug release behavior of the nanoparticles in these particles reflectsreflect the release behavior of the nanoparticles from the nanocomposite particles. These results indicate that the rate of redispersion from nanocomposite particles to nanoparticles can be controlled by changing the concentration of PVA aqueous solution.

Acoustical Parameters of Polyvinyl Alcohol

Ultrasonic investigation provides a wealth of information in understanding the intermolecular interaction of solute and solvent. An attempt has been made to measure density, viscosity and ultrasonic velocity of aqueous solution of polyvinyl alcohol of molecular weight approximately 140,000 at different temperatures 35οC, 40oC, 45οC, 50oC, 55οC, 60oC, 65οC at 0.8% concentration. Ultrasonic velocity is measured using ultrasonic interferometer at 1 MHz frequency. The acoustical parameters like, adiabatic compressibility, acoustic impedance, intermolecular free length and relaxation time have been calculated at different temperatures. These parameters were used to understand the behaviour of solute and solvent.

Surfactant-Laden Janus Droplets with Tunable Morphologies and Enhanced Stability for Fabricating Lens-Shaped Polymeric Microparticles.

Janus droplets can function as excellent templates for fabricating physically and chemically anisotropic particles. Here, we report new surfactant-laden Janus droplets with curvature controllability and enhanced stability against coalescence, suitable for fabricating shape-anisotropic polymer microparticles. Using a microfluidic flow-focusing device on a glass chip, nanoliter-sized biphasic droplets, comprising an acrylate monomer segment and a silicone-oil (SO) segment containing a surfactant, were produced in a co-flowing aqueous polyvinyl alcohol (PVA) solution. At equilibrium, the droplets formed a Janus geometry based on the minimization of interfacial energy, and each of the two Janus segments were uniform in size with coefficient-of-variation values below 3%. By varying the concentration of the surfactant in the SO phase, the curvature of the interface between the two lobes could be shifted among concave, planar, and convex shapes. In addition, the Janus droplets exhibited significantly improved stability against coalescence compared with previously reported Janus droplets carrying no surfactant that coalesced rapidly. Finally, via off-chip photopolymerization, concave-convex, planar-convex, and biconvex lens-shaped particles were fabricated.

DEVELOPMENT OF EXPERIMENTAL EQUIPMENT FOR DIE ELECTROFORMING

This article presents the results of the creation of laboratory equipment for the production of nano- and microfibres by the method of multi-layer electrospinning, a detailed description of the parts of the resulting device is given, such as a device for feeding a polymer solution into the electrospinning zone and a collector assembly. The main parameters of the device, the principle of operation and modes of electrospinning are
 described. Comparison with similar devices, advantages and disadvantages of different options for supplying solutions to the electroforming zone are presented. The results of experimental studies on this installation are presented on the example of aqueous solutions of sodium alginate and polyvinyl alcohol, and their mixtures.
 The regimes of stable electrospinning are experimentally determined. Samples of nanomaterials were
 obtained from mixtures of these polymer solutions. A morphological analysis of the obtained materials and a
 histogram of the fibre diameter distribution were carried out.

The Carbon-Coated ZnCo2O4 Nanowire Arrays Pyrolyzed from PVA for Enhancing Lithium Storage Capacity

In this paper, ZnCo2O4 nanowire arrays with a uniform carbon coating were introduced when polyvinyl alcohol (PVA) served as the carbon source. The coating process was completed by a facile bath method in PVA aqueous solution and subsequent pyrolyzation. The PVA-derived carbon-coated ZnCo2O4 nanowire array composites can be used directly as the binder-free and self-supported anode materials for lithium-ion batteries. In the carbon-coated ZnCo2O4 composites, the carbon layer carbonized from PVA can accelerate the electron transfer and accommodate the volume swing during the cycling process. The lithium storage properties of the carbon-coated ZnCo2O4 composites are investigated. It is believed that the novel carbon-coating method is universal and can be applied to other nanoarray materials.

Generation of Q-switched and mode-locked pulses using neodymium oxide as saturable absorber

Generations of Q-switched and mode-locked pulses were successfully demonstrated in an erbium-doped fiber laser (EDFL) cavity using Neodymium oxide (Nd2O3) as saturable absorber (SA). Nd2O3 nano-powder was mixed with aqueous solution of polyvinyl alcohol (PVA) to form a thin film after a drying process. The thin film was used to form a SA device. A stable Q-switched EDFL pulses operating at a wavelength of 1558.5 nm were successfully obtained by incorporating the device into the laser cavity. The pulse’s repetition rate rose from 89.45 to 104 kHz while the pulse width shrunk from 2.56 to 2.19 µs as the pump power was varied from the threshold of 91.17 to 142.08 mW. The output power steadily increased from 9.57 to 13.94 mW with a slope efficiency of 8.42% as the pump power was raised in the same range. Meanwhile, a stable mode-locked laser operating in soliton regime was also realized as the additional 100 m SMF was incorporated into the laser cavity. The laser operated at a central wavelength of 1559 nm with visible Kelly sidebands. The soliton pulses operated at a fixed repetition rate of 1.809 MHz with a pulse width of 4.62 ps as the pump power was varied within 25.03 to 75.92 mW. The peak power of the mode-locked laser increased from 0.37 kW to 1.26 kW as the pump power was varied within the pump power range. The finding reveals the outstanding optical nonlinearity of Nd2O3, which can open new potential in pulsed laser development for various applications including, optical communication, material processing, biomedical diagnostic etc.

Preparation of Polymer Composite Membrane Reinforced by Natural Fibers (Fiber and Stem of Date Palm) for Treatment of Industrial Waste Water Residue

The developed industries are utilized natural waste fibers as a clean criteria device. This work utilized natural composite membranes in the treatment of wastewater to remove different pollutants such as heavy metals (Cd, Cr, Cu), chemical groups as (phenolic compound, acid and basic surfactants) in addition to modify pH values. This membrane was manufactured by solution polymerization between polyvinyl alcohol aqueous solution (1/3 PVOH/H2O) and date palm wastes (leaf and stems) at different mixing ratios 30/70, 50/50, and 70/30 wt % from PVOH and different date palm wastes (leaf and stem). These reactants are introduced at 80°C in a batch reactor for one hour with continuous mixing until reach homogenous aqueous solutions. Then left it for half an hour to give stable form then put it in a suitable moulds coated by paraffin film, dried under insulated oven for 3 h. Afterward different utilization conditions were studied such as type of natural waste (leaf and stem), particle size of these wastes 150 and 250 µm, and additive ratios of them 30/70, 50/50, and 70/30, respectively. All prepared composite membrane give good removal for different pollutants as heavy metals and chemical groups with preferences for samples used stem natural wastes and small particle size 250 micron rather than leaf type with 100% removal efficiency for industrial waste water from petroleum refinery . Optimum conditions that give high efficiency for removal are 250 micron particle size, stem type, and 70/30 mixing ratio from this waste, respectively. XRD, SEM, and EDS analysis proved the same above results of excellent selective adsorptive separation of both heavy metals and chemical pollutants groups (phenol and surfactant) for optimum samples nos. 4 and 8.

Electrospun Bioactive Wound Dressing Containing Colloidal Dispersions of Birch Bark Dry Extract

Novel birch bark dry extract (TE)-loaded polyvinyl alcohol (PVA) fiber mats intended for wound therapy were developed through an electrospinning process. Colloidal dispersions containing TE as the active substance were prepared by the high-pressure homogenization (HPH) technique using hydrogenated phospholipids as stabilizer. Subsequently, the colloidal dispersions were blended with aqueous PVA solutions in the ratio of 60:40 (wt.%) and electrospun to form the nanofiber mats. Fiber morphology examined using scanning electron microscopy (SEM) indicated that fibers were uniform and achieved diameters in the size range of 300–1586 nm. Confocal Raman spectral imaging gave good evidence that triterpenes were encapsulated within the electrospun mats. In vitro drug release and ex vivo permeation studies indicated that the electrospun nanofibers showed a sustained release of betulin, the main component of birch bark dry extract, making the examined dressings highly applicable for several wound care applications. Ex vivo wound healing studies proved that electrospun fiber mats containing TE accelerated wound healing significantly more than TE oleogel, which was comparable to an authorized product that consists of TE and sunflower oil and has proved to enhance wound healing. Therefore, our results conclude that the developed TE-PVA-based dressings show promising potential for wound therapy, an area where effective remedy is needed.

Proton-Conducting Polyoxometalates as Redox Electrolytes Synergistically Boosting the Performance of Self-Healing Solid-State Supercapacitors with Polyaniline

Energy storage devices with high volumetric and gravimetric capacitance are in urgent demand due to the booming market of portable and wearable electronics. Using redox-active molecules as electrol...

Influence of polyvinyl alcohol on the rheology and morphology of an l-cysteine-AgNO3 supramolecular system

A good compatibility of an aqueous solution of polyvinyl alcohol (PVA) of various concentrations with a cysteine—silver solution (CSS) was revealed. It was found by viscosimetry that an increase in the polymer concentration leads to an increase in the viscosity. This effect for hydrogels is more substantial than that for solutions. The self-assembly processes in the systems were studied by UV spectroscopy and dynamic light scattering. The morphology of hydrogels and solutions of the CSS—PVA system was studied by scanning electron microscopy. The formation of a single regular spatial network was found for the hydrogels, whereas two fluctuation networks were observed for the solutions. The network is formed from aggregates, which are particles of interacting CSS and polymer molecules. A possible mechanism was proposed for self-assembly in the systems. The possibilities of practical application of the new systems are discussed.

Catalytic ozonation for the degradation of polyvinyl alcohol in aqueous solution using catalyst based on copper and manganese

Polyvinyl alcohol (PVA) is widely used in industries and exists in corresponding effluents. As a refractory water-soluble polymer, PVA is hard to be biologically degraded and may cause membrane blockage problem in reclaiming the wastewater. Therefore, it is necessary for PVA-containing wastewater to be pretreated. In this study, the heterogeneous catalytic ozonation to degrade PVA was investigated. The composition of catalysts was screened, the catalyst preparation and the reaction conditions were optimized, and the degradation mechanism was discussed. According to the results, γ-alumina was selected as support, copper and manganese were selected as active components, and subsequently the complex catalyst, copper-oxygen-manganese/γ-alumina (CMA), was formed. The optimal preparation conditions of CMA were as follows: molar ratio of copper to manganese was 1:2 while loading rate was 4 wt%; copper and manganese loaded on γ-alumina successively by ultrasonic impregnation at 25 °C for 2.5 h, then dried at 100 °C for 4 h, and calcined at 500 °C for 4 h. When the initial concentration of PVA solution was 20 mg/L, the optimal dosage of the catalyst for catalytic ozonation was 100 mg/L. The removal rate of PVA reached 97.8% in 15 min at pH = 7, and 99.3% in 10 min at pH = 10. The leaching of the metals in CMA could be neglected, and the catalyst still had a satisfactory result after five cycles of reuse. The catalytic ozonation followed the mechanism of hydroxyl radical reaction. Although only a small fraction of PVA was mineralized after reaction, the long chains of PVA molecules were broken into smaller pieces. Therefore, it is an effective pretreatment method for reclaiming PVA-containing wastewater.

Totally-organic near-infrared shielding materials by conductive cellulose nanofibers

We synthesized poly(3,4-ethylenedioxythiophene) (PEDOT) thin films by using a microcrystalline sulfated cellulose nanofiber (s-CNF) dopant. Specifically, we examined the ratio of EDOT monomer and CNF dopant, the quantity of initiator for the monomer, and the pH during polymerization. By doing so, we produced a PEDOT/s-CNF thin film with a conductivity that is 700 times higher than commercial simple PEDOT/polystyrene sulfonate (PSS) without adding agent. The optical adsorption of PEDOT/s-CNF thin film in the near-infrared (NIR) range (700–2000 nm) increased in accordance with the electrical conductivity increased. We estimated the visible light (380–700 nm) and NIR (700–2000 nm) transmittance τ by multiplying the spectral transmittance τ(λ) and weighting coefficients (Eλ•Δλ), and taking the weighted average. Although the τvis of the optimized PEDOT/s-CNF thin film with the highest conductivity remained at 85.0%, the τNIR decreased to 69.8%. We dispersed the optimized PEDOT/s-CNF in the polyvinyl alcohol aqueous solution and coated the polymer onto a glass plate to provide NIR shielding. By testing the PEDOT-coated glass by irradiation with simulated sunlight, we confirmed that the film suppressed the temperature rise.

Preparation and characterization of polyvinyl alcohol/sodium alginate/Pyrovatex CP composite fibers

Pyrovatex CP which was used as a flame retardant was added into polyvinyl alcohol (PVA) and sodium alginate (SA) aqueous solution. PVA/SA composite fibers modified with Pyrovatex CP (PSC) were prepared by wet spinning. It was characterized by FT-IR, SEM and TG. The results showed that Pyrovatex CP reacted with hydroxyl groups of PVA and SA. The breaking strength of PSC was slightly improved and the elongation at break of PSC increased rapidly. The flame retardancy and thermal stability of PSC were characterized by limiting oxygen index (LOI) and thermogravimetric analysis, respectively. The results showed that when Pyrovatex CP was 33 wt%, the elongation at break and LOI of PSC were 66.29% and 30.4%, respectively. The residue of the PSC at 600 °C is 27%.

Synergistic effects of a novel method of preparing graphene/polyvinyl alcohol to modify cementitious material

This paper presents a new method of improving mechanical and physical properties of a composite cementitious material, by a one-step combined modification using graphene and polyvinyl alcohol (PVA) to overcome limitations of other modification methods by polymer and nanomaterials. The complementary and combined effect of graphene and PVA can solve key problems such as high cost, low production of graphene and poor dispersion of graphene in the cementitious matrix. The proposed method of graphene/PVA aqueous dispersions by shear exfoliation has high stability and can directly replace water in cement casting. The exfoliation and dispersion mechanisms of graphene by PVA aqueous solution are revealed by molecular dynamics simulation. Compared to plain cement, the graphene/PVA modified cementitious material has up to 71.1% higher compressive strength, 106.5% higher flexural strength and 75.8% increase in thermal conductivity, whilst PVA-modified cement has only 0.8% increase in compressive strength and 36.2% increment in flexural strength.

The experimental study of polyvinyl alcohol (PVA) textile material degradation by ozone oxidation process

Polyvinyl alcohol (PVA), a water-soluble polymer, is widely used in the disposable textile industry and, in particular, in the manufacture of one-off work clothes that cannot be effectively treated by biological processes. The present study investigated the effect of the initial PVA concentration, reaction temperature, ozone penetration rate and initial pH value on the degradation rate of PVA. Additionally, the PVA degradation reaction mechanism was preliminarily explored. Initially, we identified the optional operative conditions: an initial PVA concentration of 20 g/L, an aqueous solution temperatureof 20 °C, an ozone penetration rate of 18 g/h and an initial pH value of 9. Subsequently we demonstrated that the PVA concentration of sample could decrease from 20 g/L to 0.286 mg/L with a degradation rate of PVA of almost 100%. Furthermore, in absence of ozone, almost no PVA polymer degradation was achieved. This study also proved that the feeding strategy of ozone could have a significant impact on the degradation of PVA molecules in the ozone oxidation process. We, therefore, provided new insights into the degradation process of PVA in aqueous solution.

INCREASING OF THERMAL FIRE RESISTANCE OF COTTON THREADS

The results of studies of fire - resistant impregnating compositions based on an aqueous solution of polyvinyl alcohol and an antipyretic additive-methylphosphite borate are presented. The effectiveness of single-stage processing of cotton threads with these impregnating compositions has been proved. It is established that the developed impregnating compositions for cotton threads have shown high efficiency of thermal and fire-retardant action. The influence of the developed impregnation formulations on water absorption and strength of cotton threads was evaluated.