Graphene quantum dots doped poly(vinyl alcohol)hybrid membranes for desalination via pervaporation

Pervaporation desalination by highly hydrophilic materials such as poly(vinyl alcohol)(PVA)based separation membrane is a burgeoning technology of late years.However,the improvement of membrane flux in pervaporation desalination has been a difficult task.Here,a novel hybrid membrane with doped graphene oxide quantum dots(GOQDs)which is rich in hydrophilic groups and small size into the matrix of PVA was prepared to improve the membrane flux.The membranes structures were described by field emission scanning electron microscopy(FESEM),atomic force microscopy(AFM),Fourier transform infrared(FT-IR),differential scanning calorimetry(DSC),thermogravimetric analysis(TGA)and X-ray diffraction(XRD).And more,Water contact angle,swelling degree,and pervaporation properties were carried out to explore the effect of GOQDs in PVA matrix.In addition,GOQDs content in the hybrid membrane,NaCl concentration,and feed temperature were investigated accordingly.Moreover,the hydrogen bonds between PVA chains were weakened by the interaction between GOQDs and PVA chains.Significantly,the hybrid membrane with optimized doped GOQDs content,200 mg·L^(-1),displays a high membrane flux of 17.09 kg·m^(-2)·h^(-1)and the salt rejection is consistently greater than 99.6%.

Improving physical properties of poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels via the Hofmeister effect

Hydrogel is a kind of three-dimensional crosslinked polymer material with high moisture content.However,due to the network defects of polymer gels,traditional hydrogels are usually brittle and fragile,which limits their practical applications.Herein,we present a Hofmeister effect-aided facile strategy to prepare high-performance poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels.Layered montmorillonite nanosheets can not only serve as crosslinking agents to enhance the mechanical properties of the hydrogel but also promote the ion conduction.More importantly,based on the Hofmeister effect,the presence of(NH_(4))_(2)SO_(4)can endow nanocomposite hydrogels with excellent mechanical properties by affecting PVA chains'aggregation state and crystallinity.As a result,the as-prepared nanocomposite hydrogels possess unique physical properties,including robust mechanical and electrical properties.The as-prepared hydrogels can be further assembled into a high-performance flexible sensor,which can sensitively detect large-scale and small-scale human activities.The simple design concept of this work is believed to provide a new prospect for developing robust nanocomposite hydrogels and flexible devices in the future.

Optimization of the Electrospinning Conditions by Box-Behnken Design to Prepare Poly(Vinyl Alcohol)/Chitosan Crosslinked Nanofibers

Electrospun poly(vinyl alcohol)/chitosan nanofibers had their solution and process parameters optimized using a Box-Behnken design and desirability function. Four factors (applied voltage, flow rate, distance tip-to-plate and amount of chitosan) were varied to produce electrospun mats with a low fiber diameter. An empirical model was developed for each response using response surface methodology (RSM), which revealed that flow rate had no significant influence on the assessed responses. With desirability function, the optimal conditions to produce the nanofibers were applied voltage of 13.1 kV, 30% chitosan concentration and distance tip-to-plate of 10 cm. The fiber diameter and standard deviation were 196.5 ± 28.3 nm, compared to the predicted values of 185.9 ± 26.8 nm. The desirability function allied with Box-Benhken design proved themselves important tools to predict process parameters for the development of nanofibers. The mats were crosslinked with glutaraldehyde for 24 h and 48 h and presented good water stability and enhanced mechanical properties.

Electro-spinning Antimicrobial N-halamine Modified Poly(vinyl alcohol)Nanofibers

Antimicrobial poly( vinyl alcohol)( PVA) nanofibrous composites were prepared by adding 3-( 2,3-dihydroxypropyl)-5,5-dimethylimidazolidine-2,4-dione( N-halamine diol) to the PVA solution using electro-spinning technique upon curing and exposure to diluted sodium hypochlorite. Scanning electron microscopy( SEM) demonstrates that PVA nanofibers formed with diameters of( 255 ±94) nm. Cross-linked PVA nanofibers with N-halamine diol precursor and 1,2,3,4-butanetetracarboxylic( BTCA) showed good water resistance. The chlorinated PVA nanofibrous mats completely inactivated Staphylococcus aureus( Gram-positive) and Escherichia coli O157: H7( Gram-negative) with 7 log reductions( the reduction of the bacterial concentration in logarithm) within 5min and 1 min of contact time,respectively.

Effect of Processing Parameters on Morphology and Mechanical Properties of Hollow Gel-Spun Lignin/Graphene Oxide/Poly(Vinyl Alcohol)Fibers

To investigate the influence of various processing parameters on the mechanical properties of fibers,lignin/graphene oxide(GO)/poly(vinyl alcohol)(PVA)fibers with different mass ratios of lignin and GO to PVA were prepared by gel spinning technique.Air drawing process and spinneret diameters were tuned as the main factors.The tensile strength increased up to 472 MPa with air drawing process applied in 30L0.05GO0.72D-A PVA fibers(air-drawn PVA fibers reinforced by 30%lignin and 0.05%GO spun with a spinneret diameter of 0.72 mm),indicating 17.4%higher than that of the fiber without air drawing process(402 MPa).Similarly,at least a 14.6%increase in Young's modulus has been achieved for 30L0.05GO0.72D-A fiber.In addition,a smaller spinneret diameter(0.72 mm)also led to a 24.9%increase in tensile strength and a 7.7%increase in Young's modulus in comparison with those of 5L0.05GO0.84D-A fibers.

Structure Investigation of Poly(vinyl alcohol)-Collagen Composite

Naturally derived collagen protein was mixed thoroughly with medical grade poly (vinyl alcohol)(PVA) at the ratio of 90:10 (w/w) and was crosslinked by formaldehyde to form a homogeneous composite membrane. The buIk structure of the membrane was characterized ly means of Xray diffraction (XRD) and transmission electron microscoor (TEM). The membrane surface Structure was investigated using Fourier transform-infrared spectroscopy (attenuated totalrefraction) (FTIR-ATR), electron spectroscopy for chemical analysis (ESCA) and contact angle measurement. lt was found that collagen and PVA can remain Stable. This was supported by the fact that no sign of phase separation had been observed. The use of crosslinking agent can Substantially influence the Structure of the composite. It is suggested that this new compositedeserves further investigation and is potentially usable as a biomedical material.

Controlled delivery of ibuprofen from poly(vinyl alcohol)-poly(ethylene glycol) interpenetrating polymeric network hydrogels

Hydrogels composed of poly(vinyl alcohol)(PVA) and poly(ethylene glycol)(PEG) were synthesized using glutaraldehyde as crosslinker and investigated for controlled delivery of the common anti-inflammatory drug, ibuprofen(IBF). To regulate the drug delivery, solid inclusion complexes(ICs) of IBF in β–cyclodextrin(β–CD) were prepared and added to the hydrogels. The ICs were prepared by the microwave irradiation method, which is more environmentally benign. The formation of IC was confirmed by various analytical techniques and the synthesized hydrogels were also characterized. Controlled release of drug was achieved from the hydrogels containing the ICs in comparison to the rapid release from hydrogels containing free IBF.The preliminary kinetic analysis emphasized the crucial role of β–CD in the drug release process that influences the polymer relaxation, thereby leading to prolonged release. The cytotoxicity assay validated the hydrogels as non-toxic in nature and hence can be utilized for controlled delivery of IBF.

A Hybrid Membrane of Poly(vinyl alcohol) and Phosphotungstic Acid for Fuel Cells

Proton conducting membranes composed of phosphotungstic acid (PWA) and poly(vinyl alcohol) (PVA)were prepared. Conductivity and Fourier transform infrared spectrometer(FTIR) measurements show that most ofthe acid embedded are stable in the PVA matrix when the membrane is immerged in water or methanol solution atroom temperature. Conductivity of the composite membranes scatters around 10-3 S.cm-1 at room temperature.The methanol crossover through the membranes is about an order of magnitude lower than that through Nafion117 membrane.

Research on the Long Time Swelling Properties of Poly (vinyl alcohol)/Hydroxylapatite Composite Hydrogel

Poly(vinyl alcohol)/hydroxylapatite(PVA/HA)composite hydrogel was prepared by repeated freezing and thawing.Thewater loss properties of the resultant hydrogel were investigated by using optical microscope.Long time immersion tests ofPVA/HA composite hydrogel were carried out in the diluted calf serum solution to study the change laws of swelling propertieswith the freezing-thawing cycles and HA content.The micro-morphologies of PVA/HA composite hydrogel after long timeimmersion were observed by means of the high-accuracy 3D profiler.The results show that the swelling process of PVA/HAcomposite hydrogel is the converse process of its water loss.Long time swelling ratio curves of PVA/HA composite hydrogel inthe calf serum solution are manifested as four stages of quick increase,decrease,slow decrease and stable balance,and itsequilibrium swelling ratio decreases with the increase of freezing-thawing cycles and HA content.It is revealed that the networkstructure of the composite hydrogel immersed for a long period is significantly improved with the increase of HA content.Perfect network structures of PVA/HA composite hydrogel as well as full and equilibrium tissues after swelling equilibrium areobtained when the HA content is 3% and the number of freezing-thawing cycles is 7.

Miscibility of Poly(hydroxybutyrate)/Poly(vinyl alcohol)Melt Blends Plasticized With Glycerol

Poly(hydroxybutyrate)/poly(vinyl alcohol)(PHB/PVA)blends plasticized with glycerol were prepared by melt blending of PHB and glycerol plasticized PVA.The PHB/PVA-glycerol compositions were 90:10,75:25 and 50:50 w/w,being the concentration of glycerol in the PVA mixture of 10 wt%.The blends were characterized by infrared spectroscopy,dynamic-mechanical thermal analysis,and scanning electron microscope of the fragile fractured surface.The results showed one single phase blend,indicating miscibility corroborated by the presence of a single glass transition temperature.The blending method proved to be an efficient way to tune PHB properties keeping its biodegradable nature since both PVA and glycerol are fully biodegradable materials.

Thermal and structural studies of poly (vinyl alcohol) and hydroxypropyl cellulose blends

Polymers and polymeric composites have steadily reflected their importance in our daily life. Blending poly(vinyl alcohol) (PVA) with a potentially useful natural biopolymers such as hydroxypropyl cellulose (HPC) seems to be an interesting way of preparing a polymeric blends. In the present work, blends of PVA/HPC of compositions (100/0, 90/10, 75/25, 50/50, 25/75, and 0/100 wt/wt%) were prepared to be used as bioequivalent materials. Thermal analyses [differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)], and X-ray diffraction (XRD) were employed to characterize and reveal the miscibility map and the structural properties of such blend system. The obtained results of the thermal analyses showed variations in the glass transition temperature (Tg) indicating the miscibility of the blend systems. Moreover, the changes in the melting temperature (Tm), shape and area were attributed to the different degrees of crystallinity and the existence of polymer-polymer interactions between PVA and HPC molecules. The X-ray diffraction (XRD) analysis showed broadening and sharpening of peaks at different HPC concentrations with PVA. This indicated changes in the crystallinity/amorphosity ratio, and also suggested that the miscibility between the amorphous components of homo-polymers PVA and HPC is possible. The results showed that HPC doped in PVA film can improve the thermal stability of the film under investigation, leading to interesting technological applications.

DEVELOPMENT OF A CATALYST FOR SOLUTION OF POLY(VINYL ALCOHOL) IN NON-AQUEOUS MEDIUM

Chloro ethane dimethyl sulfoxide,C_2H_5Cl·DMSO(ECI·DMSO)was prepared by interaction of acrylic acid with conc.Hydrochloric acid in dimethyl sulfoxide(DMSO)and subsequent decarboxylation with H_2O_2 solution.The formation of the compound was confirmed by spectral and analytical methods;the molecular weight was determined by cryoscopic method.The solubility of poly(vinyl alcohol)(PVA)in different solvents or mixed solvents at 40℃,50℃and 60℃temperature in the presence of 0.01% of EC1·-DMSO was determined.It...

Compatibility and Properties of Biodegradable Blend Films with Gelatin and Poly(vinyl alcohol)

The blend films with gelatin and poly(vinyl alcohol)(PVA) were prepared by a solution casting method. The compatibility between gelatin and PVA in the blend films was investigated. The transmittance, Fourier-transform infrared spectroscopy(FTIR), x-ray diffraction(XRD), thermogravimetry analysis(TG), and differential scanning calorimetry(DSC) were employed to characterize the resultant blend films. According to optic result, the opacity of the blend film at the ratio of 20/80(w/w, Gel to PVA) was the lowest, indicating the best compatibility between Gel and PVA at the ratio. The results of IR, XRD, DSC, and TG revealed an intensive interaction and good compatibility between them in the blend film at the ratio. The mechanical properties and solubility showed that PVA content in the blend films obviously affected the elongation at break and solubility. The mechanical properties and water resistance of gelatin film may be improved by the introduction of PVA.

Adsorptive Stripping Voltammetric Study of the Enhancement of Copper(Ⅱ) by Poly(vinyl alcohol), Starch and Polyallylamine

Adsorptive enhancements of several water-soluble polymers on copper(Ⅱ) were studied by adsorptive stripping voltammetry with a hanging mercury drop electrode. Increases in peak current of cu(Ⅱ) were observed in alkaline carbonate media. The enhancing power of poly(vinyl alcohol), starch and polyallylamine is 15, 4. 1, and 2.5 times,

Functionalised Poly(Vinyl Alcohol)/Graphene Oxide as Polymer Composite Electrolyte Membranes

Crosslinked poly(vinyl alcohol)(PVA)based composite films were prepared as polyelectrolyte membranes for low temperature direct ethanol fuel cells(DEFC).The membranes were functionalised by means of the addition of graphene oxide(GO)and sulfonated graphene oxide(SGO)and crosslinked with sulfosuccinic acid(SSA).The chemical structure was corroborated and suitable thermal properties were found.Although the addition of GO and SGO slightly decreased the proton conductivity of the membranes,a significant reduction of the ethanol solution swelling and crossover was encountered,more relevant for those functionalised with SGO.In general,the composite membranes were stable under simulated service conditions.The addition of GO and SGO particles permitted to buffer the loss and almost retain similar proton conductivity than prior to immersion.These membranes are alternative polyelectrolytes,which overcome current concerns of actual commercial membranes such as the high cost or the crossover phenomenon.

Effects of coagulation bath temperature on structure and performance of poly(vinyl butyral) hollow fiber membranes via thermally induced phase separation

Poly(vinyl butyral)(PVB) hollow fiber membranes were fabricated via thermally induced phase separation(TIPS).The effects of coagulation bath temperature(CBT) on the structure and performance of membranes were investigated in detail.The morphologies of the membranes were studied by scanning electron microscopy(SEM),the performances of water permeability,rejection,breaking strength and elongation were measured,respectively.The results indicate that all the membranes have the asymmetric morphology and the thickness of the skin layer decreases and the pore size of the outer layer increases with the increase of CBT.The permeability of membranes prepared at air gap 1.0 cm and take-up speed 0.253 m/s increases from 1.047×10-7 to 5.909×10-7 m3/(m2·s·kPa) with the CBT increasing from 20 °C to 40 °C,and sharply increases to 35.226×10-7 m3/(m2·s·kPa) once the CBT arrives at 50 °C.While the carbonic ink rejections have no significant decrease,totally exceed 98%,but that of acid-maleic acid copolymer greatly decreases with the increase of CBT.Both the breaking strength and elongation decrease with the increase of CBT.

Preparation and Swelling Behavior of Physically Crosslinked Hydrogels Composed of Poly(vinyl alcohol) and Chitosan

The physically crosslinked poly(vinyl alcohol)/chitosan (CS) composite hydrogels were prepared by cyclic freezing/thawing techniques,and the microstructure and swelling behavior of the hydrogels in the simulated gastric (pH 1.0) and intestinal (pH 7.4) media were investigated.The experimental results of infrared spectra (IR),scanning electron microscope (SEM) and differential scanning calorimetry (DSC) demonstrated that poly(vinyl alcohol) and chitosan had good miscibility in the composite hydrogels,and the addition of chitosan perturbed the formation of poly(vinyl alco-hol) crystallites.The swelling kinetics results indicated that the composite hydrogels had good pH sensitive properties to the acidic environments,and with the increase of chitosan content in the blend,the maximum swelling degreed and the swelling rate both increased,but it led to more dissolution at pH 1.0.And the composite hydrogels also exhibited good reversible swelling behavior with pH value of the swelling medium altering between 1.0 and 7.4.In addition,the higher freezing/thawing cycle times resulted in the lower swelling rate.Therefore,the swelling behavior of the composite hydrogels could be adjusted by changing the chitosan contents and the freezing/thawing cycle times.

Effect of Polyvinyl Alcohol with a Thiol End Group on the Properties of Polyacrylic Dispersions and Spray-dried Powder

The emulsion polymerization of highly shear-stable copolymer dispersions of methyl methac-rylate and butyl acrylate were carried out using poly(vinyl alcohol)with a thiol end group(PVA-SH)as protec-tive colloid.The dispersions can be transformed into corresponding redispersible powder via a spray drying-cooling process.On-line FT-IR monitoring shows that grafting polymer of PVA-g-PMMA was formed mainly at the stage-1 of the emulsion polymerization.TEM images show,the PVA-SH shell was fragmentary when adding SDS at initial stage and integrated when adding at particle growing or final stage.The particle size turns to be smaller when delayed adding SDS surfactant.Triethanolamine,a co-regulator of PVA-SH,controlled the M n to 50 000-70 000 and reduced the PDI to 1.5-1.7.The acrylic dispersions with 0.8wt%-1.5wt%PVA-SH 1 can be spray-dried into super dispersible polymer powder(SDPP),which can easily disperse in water and form recon-stituted dispersions with an average particle size smaller than 1 micron.

Chemical and physical properties of poly (vinyl alcohol) hydrogel films formed by irradiation

Chemical and physical properties of poly(vinyl alcohol) (PVA) hydrogel films were investigated as a function of production factors. The experimental results show that the gel fraction depends strongly on the radiation dose, the degree of swelling is inversely dependent on the concentration of PVA solution, the tensile strength depends mainly on the PVA blending ratio and the elongation at break is inversely dependent on the radiation dose.

The Impact of Clay Loading on the Relative Intercalation of Poly(Vinyl Alcohol)-Clay Composites

Polymer clay nanocomposites (PCN) materials are industrially applied because of their unique properties. However many of their physical and chemical properties have not been determined. The formed structures of polymer/clay nanocomposite depend on the nature of interactions between polymer chains and clay platelets. According to the possible modes of interactions between polymer matrix and clay sheets, these nanocomposites can be classified into: intercalated, flocculated and exfoliated nanocomposites. In this work, the morphology of the nanocomposite was studied using X-ray diffraction (XRD) and nanoscaning electron microscopy (NSEM). XRD and NSEM measurements confirmed the intercalation between poly(vinyl alcohol) chains and cloisite®20A sheets. Because of the intercalation between the clay platelets and the PVA chains, as the clay concentration increases as the band intensities in FT-IR spectra increase. On the other hand, the XRD did not provide clear shift of any of the clay peaks for PVA/cloisite® 10A nanocomposites and confirm the non-intercalation between PVA matrix and cloisite®10A platelets. The relative intercalation (RI) of PVA/Cloisite®20A nanocomposites declined with increase in the clay loadings. In contrast, for PVA/Cloisite®10A, RI values slightly increased with increasing the clay loading.