Concentration Of Polyvinyl Alcohol Solution Research Articles

Preparation of hydrogel containing chitosan and virgin coconut oil using the freeze-thawing method

This study aimed to formulate a hydrogel membrane containing chitosan (CS) and virgin coconut oil (VCO) using repeated cycles of freezing and thawing (F-T) for wound dressing applications. This study evaluated the effects of degree of hydrolysis of polyvinyl alcohol (PVA), solution concentration and thickness, number of F-T cycles, CS proportion on the sensory properties, swelling ratio, and gel fraction of hydrogels. The antibacterial ability of PVA/CS/VCO membrane against methicillin-sensitive Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans was evaluated by disk diffusion method. The results showed that PVA with a high degree of hydrolysis (over 99%) easily generated hydrogel after several F-T cycles. The thicker the hydrogel membrane or the higher the concentration of PVA solution was, the lower the flexibility, elasticity, swelling ratio was, and the higher the gel fraction was. The formula including 10% PVA solution, the ratio of CS to PVA is 40%, 5% w/w VCO, through 3 F-T cycles created hydrogel with suitable properties and good antibacterial activity.

Preparation of HNS microspheres by rapid membrane emulsification

In order to improve the dispersibility and loading efficiency of 2,2′,4,4′,6,6′-hexanitrostilbene (HNS), HNS microspheres were prepared by rapid membrane emulsification method with nitrocellulose (NC) as binder. The effects of NC solution concentration, stirring speed and polyvinyl alcohol (PVA) solution concentration on microspheres were investigated. It was characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), differential thermal analysis (DTA) and angle of repose analyzer. The results show that the HNS microspheres prepared with 5 wt% NC solution concentration, stirring speed of 100 rpm and 2 wt% PVA solution concentration have better regular morphology, higher sphericity, unchanged crystalline shape, increased activation energy and significantly improved dispersibility compared with the refined HNS. Rapid membrane emulsification has a series of advantages such as green, low cost and easy scale up, which provides a better way to prepare microspheres of energy materials.

Synthesis of Nanofiber Polyvinyl Alcohol (PVA) with Electrospinning Method

PVA nanofibers are PVA solution-based nanofibers. PVA solution is a synthetic polymer that is non-toxic, soluble in air, and has excellent thermal, gas permeability, and chemical resistance qualities. Nanofibers were synthesized using PVA (Polyvinyl alcohol) solutions at concentrations of 8%, 10%, and 12%. The electrospinning method is used in this investigation, with input voltages of 17 kV and 20 kV, needle distances of 7 cm, 10 cm, and 15 cm from the collector, and a flow rate of 5 ml/hour for each concentration. An optical microscope was used to examine the nanofiber synthesis results in order to assess the morphology and diameter of the fiber. PVA nanofiber with the best fiber from electrospinning has a diameter of 1.06 μm and homogeneous fiber without beads is a synthesized nanofiber with a variation of 10% PVA solution concentration, 15 cm distance from the syringe needle to drum collector, and 20 kV voltage.

Study on anti-corrosion of PVA-treated wheat straw and its application in reinforcement of a silty soil

Silty soils are usually with poor mechanical performance and thus need reinforcement to meet the requirements in geotechnical practices. Wheat straw is low-cost, environment-friendly and wide spread, which has a great potential for use as reinforcement of the silty soils. In this study, the anti-corrosion effect of polyvinyl alcohol (PVA) treated wheat straw was investigated through the pore area ratio tests and the tensile tests. Test results indicated that the wheat straw was greatly improved in anti-corrosion, and tensile strength was considerably enhanced after the treatment. The optimum concentration of PVA solution and immersion duration were suggested. The PVA-treated wheat straw was then buried in the silty soil, and its corrosion resistance to the environment in the soil was validated under different moisture conditions. The treated wheat straw was then used as the reinforcing material for improvement of a silty soil. Triaxial compression were carried out on the samples reinforced with the material of various inclusion contents and lengths. Stress–strain curves and strength of the reinforced soil samples were analyzed, and the optimum inclusion content and length were discussed. The California bearing ratio (CBR) tests were then performed for the reinforced soil with the optimum inclusion content and length, and the test results showed that the reinforced silty soils met the requirements on CBR of the subgrade.

High sphericity and diameter controllable B4C ceramic pellets prepared via simple low-cost PVA assisted planet-type rotation method

B4C ceramic pellets with diameter smaller than 0.7 mm have been simply fabricated via polyvinyl alcohol (PVA) assisted planet-type rotation method. Only commercial B4C powders and tiny amounts of PVA are needed in the experiment. The PVA solution is used to modify the commercial B4C powders. And the powders with adhesive properties are spheroidized to form green pellets during the rotation process. Results show that the green B4C pellets exhibit uniform size distribution and high sphericity. The appropriate diameter of 0.61 mm and high sphericity of 97.15% can be obtained by controlling the rotation time and the concentration of PVA solution. This fabrication method provides a low-cost and simple way to prepare B4C ceramic pellets with various diameters and high sphericity, and also sheds light on the mass production of other ceramic microspheres.

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.

Thin film composite membranes: Preparation, characterization, and application towards copper ion removal

A novel thin film composite (TFC) membrane was fabricated from a thin layer of hybrid membrane formulated from a blend of polyvinyl alcohol (PVA)/chitosan and cross linked with tetraethylorthosilicate (TEOS), which was layered on the polysulfone (PSF) membrane. Besides producing membrane from polymer blend of PVA/chitosan only, concentrations of TEOS as cross linker was varied at 1 wt%, 3 wt% and 5 wt% with fixed concentration of PVA solution (10 wt.%) and chitosan (2 wt.%) respectively during the formulation of hybrid membranes. The thermal properties, mechanical strength, water contact angle, swelling measurement and anti-fouling behaviour of these membranes were investigated. The performance of the thin film composite was evaluated through filtration of the pure copper ion solution and the industrial wastewater containing copper respectively. The fabricated TFC with 3 wt.% TEOS was found to possess better tensile strength and strain, and thermal stability as compared with other concentration of TEOS. The membrane also exhibit good rejection of copper ion (> 90%) from pure copper solution especially at pH 7 of feed solution. A further treatment conducted on the wastewater reveals that TFC with 3 wt.% TEOS could remove the copper ion, where the filtered water could be directly discharged to the river. Furthermore, the TFC portrayed good anti fouling behaviour, where it have 3% of relative flux decay and 76% of relative flux recovery even with the presence of humic acid as NOM (natural organic matter).

Preparation and adsorption mechanism of polyvinyl alcohol/graphene oxide‐sodium alginate nanocomposite hydrogel with high Pb(II) adsorption capacity

ABSTRACTA series of polyvinyl alcohol (PVA)/graphene oxide (GO)‐sodium alginate (SA) nanocomposite hydrogel beads were prepared through in situ crosslinking for Pb2+ removal. It was found that PVA and SA molecules were intercalated into GO layers through hydrogen bonding interactions, leading to the destruction of orderly structure of GO, while GO uniformly distributed in PVA matrix. With increasing PVA solution concentration, the hydrogel beads became more regular, a large number of polygonal pores with thin walls and open pores formed, the average pore size decreased, and the dense network structure formed. Meanwhile, the permeability of the composite hydrogel decreased, leading to the decline of Pb2+ adsorption capacity of the composite hydrogel. With increasing GO content, the ballability of the hydrogel beads was weakened, the pore size increased, and relatively loose network structure formed, resulting in an increase in permeability and Pb2+ adsorption capacity of the hydrogel, reaching up to 279.43 mg g−1. Moreover, the composite hydrogel presented relatively good reusability for Pb2+ removal. The adsorption mechanism was explored and showed that the adsorption system of the composite hydrogel belonged to the second‐order kinetic model and fitted Langmuir adsorption isotherm model for Pb2+ removal, which might be mono‐layer chemical adsorption. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47318.

Comparison of the Release of <i>Aloe vera</i> Extracts from Poly(Vinyl Alcohol) Electrospun Fibers and Hydrogel Films for Wound Healing Applications

Aloe vera extracts, consisting of active compounds that decrease pain and inflammation and stimulate skin growth and repair, are selected as a drug model in this work. Polyvinyl alcohol (PVA) was used as base material. Release profiles of Aloe vera extracts from PVA electrospun fibers were compared to those from PVA hydrogel films prepared by freezing/thawing method. This method provided a physical crosslinked polymer. The concentration of PVA solution used for electrospinning and hydrogel preparation was 10% wt with different contents of Aloe vera extracts (0, 30, 50, 70 and 90% w/w). The properties of electrospun fibers and hydrogel films were evaluated in terms of morphology, chemical structure, swelling behavior and release profiles. The morphological properties of electrospun fibers and hydrogel film were observed by SEM. Electrospun fibers were smoothly round, high surface area, and non-woven, while hydrogel film possessed rough surface and was covered with porous. Fourier transform infrared spectroscopic measurement exhibited the existence of relevant functional groups of both PVA and Aloe vera extracts. The results showed relevant functional groups of Aloe vera extracts in both electrospun fibers and hydrogel film. The release of Aloe vera extracts from both electrospun fibers and hydrogel film was evaluated in phosphate buffer of pH 5.5 at 25 °C and was monitored by UV–vis spectroscopy. It was revealed that as the content of Aloe vera increased, the amount of Aloe vera extracts released from electrospun fibers decreased. This result contrasts with the release of aloe vera from hydrogel film which increased when the content of aloe vera increased. It was also noticed that the amount of Aloe vera extracts released from electrospun fibers was more than that from hydrogel films at 600 minutes. The results also showed that the releasing rate of Aloe vera from electrospun fibers was faster than that from hydrogel films. This is probably because electrospun fibers had much higher surface area than that of hydrogel film thus, the release was faster.

Manufacturing Technique and Property Evaluations of Biodegradable Nanofiber Membrane for Medication

This study formulates polyvinyl alcohol (PVA) solution and Bletilla striata (BS) extractive with various mixing ratios into various mixtures, which are then electrospun into composite membrane with settings of a specified voltage of 12 kV, collection distances of 12 cm, PVA concentrations of 12 wt%, and BS additions of 0.1, 0.3, and 0.5 %. The various PVA/BS mixtures are tested for conductivity and viscosity, and the resulting electrospinning composite membranes are evaluated with surface morphology analysis, Fourier transform infrared spectra (FT-IR), and diameter analysis. The test results show that the content of BS is proportional to the conductivity of the mixtures. The addition of *BS decreases the diameter of the electrospinning fibers, while also creating beads on the fibers. The diameter of the electrospinning fibers increases as a result of the increasing concentration of PVA solution or the increasing collection distance. The FT-IR results indicate the absent chemical reaction between PVA and BS.

Preparation and applications of poly vinyl alcohol (PVA) modified cellulose acetate (CA) membranes for forward osmosis (FO) processes

Polyvinyl alcohol (PVA)-coated cellulose acetate (CA)-based flat-sheet membranes have been fabricated and tested in the forward osmosis (FO) process. PVA was used as a surface modifying agent. CA membranes prepared by conventional immersion precipitation were treated in an aqueous solution of PVA and tested water flux and salt rejection. The effects of PVA concentration, treatment time on the hydrophilicity of membrane surface, water permeability, and salt retention property of the membrane were estimated. The modified membrane was characterized by X-ray photoelectron spectroscopy and contact angle measurement. A hydrophilicity of membrane surface was observed in longer modification times and the higher PVA solution concentration accounted for a attaching of the PVA chains by glutaraldehyde as cross-linking agent. The best condition of salt rejection and permeability performance was obtained by using 1 wt% PVA solution and treatment time of 2 min. In the FO process, modified CA membrane exhibited water flux 20% higher than unmodified CA membrane without salt leakage. This result indicated that PVA coating improved water flux performance for FO processes.

High-flux microfiltration filters based on electrospun polyvinylalcohol nanofibrous membranes

A novel class of high-flux microfiltration filters consisting of an electrospun nanofibrous membrane and a conventional non-woven microfibrous support is being presented. The nanofibrous non-woven layer was fabricated by electrospinning of polyvinylalcohol (PVA) directly onto the microfibrous support and then followed by chemical cross-linking with glutaraldehyde (GA) in acetone. By altering the processing parameters, such as the applied voltage and the distance between the spinneret and the collector, as well as the concentration of PVA solution, electrospun PVA membranes with an average fiber diameter of 100 ± 19 nm were obtained. Characterizations revealed that the mean pore size of the electrospun PVA membranes ranged from 0.30 μm to 0.21 μm with the electrospun PVA membrane thickness varying from 10 m to 100 μm. Due to the high porosity, microfiltration filters based on these electrospun membranes showed 3–7 times higher pure water flux than the Millipore GSWP 0.22 μm membrane. The nanofibrous PVA membranes with an average thickness of 20 μm could successfully reject more than 98% of the polycarboxylate microsphere particles with a diameter of 0.209 ± 0.011 μm, and still maintain 1.5–6 times higher permeate flux than that of the Millipore GSWP 0.22 μm membrane.

Fabrication and characterization of biodegradable composites based on microfibrillated cellulose and polyvinyl alcohol

Microfibrillated cellulose (MFC) based thin membrane-like fully biodegradable composites were produced by blending MFC suspension with polyvinyl alcohol (PVA). Desired MFC content in the composites could be easily obtained by varying the PVA solution concentration. Chemical crosslinking of PVA was carried out using glyoxal to increase the mechanical and thermal properties of the composites as well as to make the PVA partially water-insoluble. Examination of composite surfaces and fracture topographies indicated that the MFC fibrils were well bonded to PVA and uniformly distributed. Infrared spectroscopy showed that acetal linkages could be formed in the MFC–PVA composites by a glyoxal crosslinking reaction. Sol–gel and swelling results indicated that crosslinking reaction made PVA partially insoluble and reduced its swelling ability. The MFC–PVA composites had excellent tensile properties which were further enhanced by crosslinking. Thermogravimetric analysis (TGA) showed higher thermal stability for MFC–PVA composites compared to PVA. The crosslinked MFC–PVA composites showed even higher thermal stability. Differential scanning calorimetry (DSC) indicated that crosslinking increased the glass transition temperature and reduced melting temperature and crystallinity of PVA in MFC–PVA composites. Results also indicated that nano- and micro-fibrils in MFC inhibit the crystallization of PVA. These composites could be good candidates for replacing today’s traditional non-biodegradable plastics.

Bacterial cellulose-based membrane-like biodegradable composites using cross-linked and noncross-linked polyvinyl alcohol

Bacterial cellulose (BC)-based membrane-like biodegradable composites were produced by immersing wet BC pellicles in polyvinyl alcohol (PVA) solution. The BC content in the BC–PVA composites can be adjusted by varying the concentration of PVA solution. Chemical cross-linking of PVA was carried out using glutaraldehyde to increase the mechanical properties of the composites as well as to make the PVA partially to highly water insoluble. Examination by scanning electron microscopy indicated that the PVA not only penetrated the BC network, but also filled the pores within the BC pellicle. Attenuated total reflectance-Fourier transform infrared spectroscopy showed that acetal linkages could be formed in the BC–PVA composites by a cross-linking reaction. Sol–gel results indicated that cross-linking reaction increasingly made PVA insoluble in water resulting in higher gel (cross-linked fraction) content in the PVA. Wide-angle X-ray diffraction results showed decreased crystallinity in cross-linked BC and PVA, as expected. It was also found that crystal size was smaller in PVA after cross-linking. The BC–PVA composites had excellent tensile properties and cross-linking increased these properties further. Thermogravimetric analysis showed higher thermal stability for BC–PVA composites compared to PVA. The cross-linked specimens, especially the highly cross-linked ones, showed even higher thermal stability. The methods developed in this study make it possible to control the PVA content in the composites as well as the cross-linking level of PVA. These composites could be good candidates for replacing traditional non-biodegradable plastics.

Effect of deacetylation on wicking behavior of co-electrospun cellulose acetate/polyvinyl alcohol nanofibers blend

Abstract Cellulose acetate (CA) nanofibers webs deserve a special attention because of their very good water retention properties. CA nanofibers based biosensor in certain application come into contact with various liquids and requires high degree of wicking rate to transport liquid to its destination. Cellulose acetate (CA)/polyvinyl alcohol (PVA) blended nanofibers were prepared via co-electrospinning using double nozzle for jetting cellulose acetate and polyvinyl alcohol independently. The CA/PVA blend nanofibers webs were deacetylated in aqueous alkaline solution to convert CA in to regenerated cellulose and to remove PVA nanofibers from the raw web. The resultant nanofibers webs were characterized by wicking rate, water contact angle, SEM and FTIR analysis. The results revealed that by varying concentration of PVA solution enhances the wicking rate. Such a nanofibers web may be used in biosensor strip and other medical applications where the high wicking rates are desired.

Effect of solution concentration on diameter and morphology of PVA nanofibres in bubble electrospinning process

Bubble elecrospinning is an excellent and novelty method to fabricate nanofibres with high throughout. This paper investigates experimentally the effects of solution concentration and its viscosity on diameter and morphology of bubble electrospun polyvinyl alcohol (PVA) nanofibres, where pure water is used as a solvent for environmental consideration. The experiment shows that the as spun fibres change their morphology from few beads, smooth surfaces and finally to larger diameter fibres when PVA solution concentration increases gradually. An allometric relation between the fibre diameter and the solution concentration is obtained. The minimal diameter is as small as 38·3 nm.

Using Orthogonal Design in Optimizing Parameters for Bubble Electrospinning of Polyvinyl Alcohol (PVA) Nanofibers

The present work was aimed at studying the effects of process parameters on morphologies of Polyvinyl alcohol (PVA) nanofibers in a novel electrospinning technique, bubble electrospinning. The process was optimized by constructing L 9(34) orthogonal experimental array design. Three factors were investigated and nine tests were run under lower, medium and higher levels of these factors. The results showed that PVA solution concentration plays an important role in affecting the morphologies of PVA nanofibers in bubble electrospinning process. With the increase of the concentration of PVA solution, the morphologies of fibers were changed from beaded fibers to uniform cylinder fibers and the average nanofiber diameter also increased. The optimization process was 12w% for PVA solution, 30kV for applied voltage and 10cm for spinning distance.

Properties of concrete prepared with PVA-impregnated recycled concrete aggregates

This paper reports an experimental study to improve the properties of recycled concrete aggregates (RCA) by their impregnation with polyvinyl alcohol (PVA). The effects of PVA on the development of strength and durability properties of the recycled aggregate concrete were evaluated. The experimental investigation was conducted in two parts. Firstly, the optimal concentration of PVA solution required to improve the recycled aggregates was determined. The RCA was soaked in 6%, 8%, 10%, 12% PVA solutions, and impregnation was conducted under a controlled laboratory environment. Density, crushing value (10% fines value), and water absorption of the PVA impregnated RCA (PI-RCA) were determined. Secondly, the slump, slump loss, compressive and tensile splitting strength, dimensional change (shrinkage) and chloride penetrability of the concretes prepared with the RCA that had been impregnated with the optimal (10%) PVA concentration were determined. It was found that the 10% fines value of the PI-RCA was higher, and the water absorption of the PI-RCA were lower when compared to the untreated RCA. The results show that there was not only an improvement in the mechanical properties of the concrete made with PI-RCA, but also the shrinkage of PI-RCA decreased while the resistance to chloride-ion penetration of the concrete produced increased.

Tailoring Mechanical Behavior of PVA-Bioactive Glass Hybrid Foams

Porous scaffolds have been developed in many forms and materials, but few have reached the combination of adequate physical, biological and mechanical properties. In previous works hybrid foams bioactive glass polyvinyl alcohol (PVA) were prepared by the sol-gel process for application as scaffold for bone tissue engineering. We observed that synthesis parameters such as PVA hydrolysis grade, PVA solution concentration, and PVA content in the hybrids affected both synthesis results and structural characteristics of the obtained foams. A marked change in foaming behavior occurs for PVA contents around 60%. In this work we analyze the effect of different compositions and synthesis parameters on the mechanical behavior of PVA-bioative glass foams. The compression tests showed that an increase of PVA fraction changes the mechanical behavior due to different mechanisms leading to cell collapse. For hybrids with lower PVA contents (20 to 30%) the cell collapse is due to brittle crushing. For intermediate polymer content (40-60%) the contribution of plastic yielding in the plateau region increases and it becomes the predominant mechanism of cell collapse for samples with higher polymer content (70-80%).

Features of rheological and electrophysical properties of compositions based on polyvinyl alcohol and carboxymethylcellulose

A study has been made of the rheological and electrophysical properties (conductivity and dielectric loss angle) of aqueous solutions of polyvinyl alcohol (PVA), water-soluble carboxymethylcelluloses (Na-CMC), and compositions based on PVA and Na-CMC or methylcellulose, with PVA solution concentration 1% to 10% by weight and cellulose ether content in the polymer mixture up to 50% by weight. It was found that anisotropic structures can be formed in solutions based on PVA compositions under the influence of an orienting mechanical field; this is related to the formation of structure-sensitive associates in solution in the form of complexes.