Effect of Polyvinyl Alcohol in Inner Aqueous Phase on Stability of Millimeter-scale Capsules

The millimeter-scale capsules with controllable morphology,ultra-low permeability and excellent mechanical stability were fabricated by millifluidics.Viscosity of inner phase was adjusted to control the morphology and properties of the capsules.In detail,as the concentration of polyvinyl alcohol(PVA)increased from 0 to 8% in the inner phase of the capsules,the diameter of capsules decreased from 3.33 ± 0.01mm to 2.97 ± 0.01 mm,the shell thickness of capsules decreased from 0.183 ± 0.004 mm to 0.155 ± 0.003 mm.While the capsules had round shape and high sphericity.Notably,the capsules with 2% PVA in the inner phase had remarkably decreased water permeability and good morphological stability.Specifically,the end-time of water losing of the capsules was up to 49 days,while the dehydrated capsules maintained spherical appearance,and crushing force of the capsules was up to 13.73 ± 0.79 N,which ensured stability during processing and transportation.This research provides a new strategy for stable encapsulation of small molecules.

A Polyvinyl Alcohol/Acrylamide Hydrogel with Enhanced Mechanical Properties Promotes Full-Thickness Skin Defect Healing by Regulating Immunomodulation and Angiogenesis Through Paracrine Secretion

Hydrogel-based tissue-engineered skin has attracted increased attention due to its potential to restore the structural integrity and functionality of skin.However,the mechanical properties of hydrogel scaffolds and natural skin are substantially different.Here,we developed a polyvinyl alcohol(PVA)/acrylamide based interpenetrating network(IPN)hydrogel that was surface modified with polydopamine(PDA)and termed Dopa-gel.The Dopa-gel exhibited mechanical properties similar to native skin tissue and a superior ability to modulate paracrine functions.Furthermore,a tough scaffold with tensile resistance was fabricated using this hydrogel by three-dimensional printing.The results showed that the interpenetration of PVA,alginate,and polyacrylamide networks notably enhanced the mechanical properties of the hydrogel.Surface modification with PDA endowed the hydrogels with increased secretion of immunomodulatory and proangiogenic factors.In an in vivo model,Dopa-gel treatment accelerated wound closure,increased vascularization,and promoted a shift in macrophages from a proinflammatory M1 phenotype to a prohealing and anti-inflammatory M2 phenotype within the wound area.Mechanistically,the focal adhesion kinase(FAK)/extracellular signal-related kinase(ERK)signaling pathway may mediate the promotion of skin defect healing by increasing paracrine secretion via the Dopa-gel.Additionally,proangiogenic factors can be induced through Rho-associated kinase-2(ROCK-2)/vascular endothelial growth factor(VEGF)-mediated paracrine secretion under tensile stress conditions.Taken together,these findings suggest that the multifunctional Dopa-gel,which has good mechanical properties similar to those of native skin tissue and enhanced immunomodulatory and angiogenic properties,is a promising scaffold for skin tissue regeneration.

Fabrication of High-Efficiency Polyvinyl Alcohol Nanofiber Membranes for Air Filtration Based on Principle of Stable Electrospinning

A mass flow matching model(MFMM)was established for studying the stable status of solution electrospinning.The study of the solution droplet status at the needle tip focused on various combinations of applied voltages and injection rates to figure out their influence on steadily fabricating polyvinyl alcohol(PVA)nanofibers prepared from PVA spinning solutions with two different mass fractions(10%and 16%).The results revealed that during the stable electrospinning,the influence resulted from the change of the injection rate approximately canceled out the impact brought by adjusting the applied voltage,leading to almost the same morphology as that of the PVA nanofibers.And the mass fraction of PVA in the spinning solution dominated the structure and the diameter distribution of the electrospun nanofibers.Under stable electrospinning conditions,the composite membrane was produced by depositing PVA nanofibers on the polyethylene terephthalate(PET)nonwoven substrate for an air filtration test.Furthermore,the prepared composite membrane exhibited a high air filtration efficiency(99.97%)and a low pressure drop(120 Pa)for 300-500 nm neutralized polystyrene latex(PSL)aerosol particles,demonstrating its potential as an alternative for a variety of commercial applications in air filtration.

Preparation of Film Based on Polyvinyl Alcohol Modified by Alkaline Starch and Lignin Fiber

This study presents an easily prepared film based on alkaline starch-polyvinyl alcohol hybrid and lignin fiber as an additive(SPL film).The SPL film was prepared under acidic conditions through a polycondensation reaction of PVA and a mixture incorporating alkaline starch and lignin fiber from agriculture or forest source.The examination using scanning electron microscopy(SEM)showed that the surface of SPL film was smooth and the lignin fiber had good compatibility within the film hybrid.Electrospray ionization mass spectroscopy(ESI-MS)and fourier transform infrared(FTIR)investigations indicated that alkaline starch and lignin fiber reacted with PVA under acidic conditions and that–CH_(2)–O–groups were involved in the cross-linking of the SPL system.In addition,the SPL film exhibited only 4%light transmittance,which effectively reduces the ultraviolet and visible light(UV-Vis)penetration,along with good performance when exposed to thermal degradation,in which the mass loss reached around 60%at 400℃.More-over,the SPL film acquired excellent tensile strength,which is much higher than that of PVA-lignin(PL)composite film.

Experimental study on mechanical and frost heave behaviors of silty clay improved by polyvinyl alcohol and polypropylene fiber

Silty clay is widely used as subgrade filler in cold regions,which suffer from frost heave in winter and mud pumping in spring.In this study,polyvinyl alcohol(PVA)and polypropylene(PP)fiber were used to improve the mechanical and frost heave behavior of silty clay in cold regions,and the direct shear test and one-dimensional frost heave test were employed in studying improvement effects.Moreover,improvement mechanisms of PVA and PP fiber were analyzed based on test results.The main findings are as follows.(1)Both PP and PVA can heighten the strength of silty clay and suppress frost heave,but the PVA solution has a more decisive influence on improving mechanical properties than PP fiber.(2)The improvement mechanism of the PVA solution is cementing.The improvement effect of 2%PVA solution is the best,which can increase the shear strength by approximately 40%–60%at different stress levels and decrease the frost heave ratio from 0.89%to 0.16%at optimal water content.(3)For 2%PVA improved samples,0.25%PP fiber can further increase soil cohesion by approximately 20–30 kPa at different stress levels and further decrease the frost heave ratio from 0.16%to 0.07%at optimal water content.The improvement effect is neglectable when the PP fiber content exceeds 0.25%.Overall,2%PVA with 0.25%PP fiber is the optimum combination to improve silty clay in cold regions.

2,4-Dinitrophenyl Ether of Polyvinyl Alcohol and Polymer Bound Anionic SIGMA Complexes

A new electrophilic polymer, 2,4-dinitrophenyl ether of polyvinyl alcohol (PVA-DNP), having a degree of substitution of 0.5 was prepared from polyvinyl alcohol (PVA) and 1-fluro-2,4-dinitrobenzene (DNFB). The PVA-DNP polymer was characterized by NMR, IR, and UV-visible spectroscopy. The reaction of PVA-DNP with sodium methoxide was followed by NMR and UV-visible spectroscopy. Evidence of polymer bound spirocyclic SIGMA complex, C-1 and C-3 polymer bound DNP-methoxy SIGMA complexes and the formation and C-1 methoxy complex of 2,4-dinitroanisole was observed.

Enhanced photo-catalytic activity of the composite of TiO_2 and conjugated derivative of polyvinyl alcohol immobilized on cordierite under visible light irradiation

A novel visible light active photo-catalyst named CHC/C-PVA/TiO2, the composite of titanium dioxide（TiO2）with conjugated derivative of polyvinyl alcohol（C-PVA） loaded on a cordierite honeycomb ceramic（CHC）substrate, was fabricated by combining the synthesis of TiO2 sol, preparation of C-PVA via thermally treating polyvinyl alcohol, and immobilization of TiO2 sol and C-PVA on CHC. By detecting the change of UV–vis absorption spectra of the model organic pollutant（methyl orange（MO）） in the presence of the composite under visible light irradiation, the photo-catalytic activity was evaluated and the results show that the CHC/C-PVA/TiO2 composite has an enhanced photo-catalytic activity when compared to the CHC/TiO2 composite. Besides, the CHC/C-PVA/TiO2 shows a good photo-catalytic stability after the fourth cycles. The structure analyses by scanning electron microscope（SEM） and energy dispersive X-ray spectroscopy（EDS） show the coexistence of C-PVA and TiO2 on the CHC and the cracks on the surface of CHC/C-PVA/TiO2. Result of ultraviolet-visible diffuse reflection spectroscopy（UV–vis DRS） reveals that the CHC/C-PVA/TiO2 can absorb both ultraviolet and visible light while result of X-ray photoelectron spectroscopy（XPS） indicates the existence of C, O and Ti elements in the CHC/C-PVA/TiO2. The typical structures as well as the optical characteristics of the CHC/C-PVA/TiO2 are responsible for the enhancement in the photo-catalytic activity.

THE MECHANISM OF SURFACE METALLIZATION OF POLYVINYL ALCOHOL COMPLEX METAL CHELATE FILMS

A novel method for preparing metalllzed film has been studied.The reduction process and properties of the poly(vinyl alcohol)(PVA)were probed by several analytic means.According to the etudies,a mechanism for the polymer surface reduction metallization was proposed and proved.

PREPARATION OF NANOCRYSTALLINE MATERIALS OF PEROVSKITE-TYPE La_(1-x)Sr_xFeO_3 bY USINO GEL OF POLYVINYL ALCOHOL

Precursors of La_(1-x)Sr_xFeO_3(x=0.0,0.1,0.4 and 0.6)nanocrystalline materials were prepared by the mixed salts dissolved in an aqueous solution of polyvinyl alcohol(PVA).XRD,DTA and TEM were used to characterize the samples. Well-nanocrystalline perovskite-type La_(1_x)Sr_xFeO_3 could be synthesized at the temperatures as low as 400～550℃ for 2h by the calcination of these amorphous precursors,and the calcination of wet LaFeO_3 gel was investigated at 300℃ for lh and 700℃ for 0.5h.

Immobilization of activated sludge using improved polyvinyl alcohol (PVA) gel

The microbial immobilization method using polyvinyl alcohol （PVA） gel as an immobilizing material was improved and used for entrapment of activated sludge. The oxygen uptake rate （OUR） was used to characterize the biological activity of immobilized activated sludge. Three kinds of PVA-immobilized particles of activated sludge, that is, PVA-boric acid beads, PVA-sodium nitrate beads and PVA-orthophosphate beads were prepared, and their biological activity was compared by measuring the OUR value. The bioactivity of both autotrophic and heterotrophic microorganisms of activated sludge was determined using different synthetic wastewater media （containing 250 mg/L COD and 25 mg/L NH4^＋ -N）. The experimental results showed that the bioactivity and stability of the three kinds of immobilized activated sludge was greatly improved after activation. With respect of the bioactivity and the mechanical stability, the PVA-orthophosphate method may be a promising and economical technique for microbial immobilization.

Hydrogen generation from polyvinyl alcohol-contaminated wastewater by a process of supercritical water gasification

Gasification of polyvinyl alcohol （PVA）-contaminated wastewater in supercritical water （SCW） was investigated in a continuous flow reactor at 723-873 K, 20-36 MPa and residence time of 20-450 s. The gas and liquid products were analyzed by GC/TCD, and TOC analyzer. The main gas products were H2, CH4, CO and CO2. Pressure change had no significant influence on gasification efficiency. Higher temperature and longer residence time enhanced gasification efficiency, and lower temperature favored the production of H2. The effects of KOH catalyst on gas product composition were studied, and gasification efficiency were analyzed. The TOC removal efficiency （RTOC）, carbon gasification ratio （RCG） and hydrogen gasification ratio （RHG） were up to 96.00%, 95.92% and 126.40% at 873 K and 60 s, respectively, which suggests PVA can be completely gasified in SCW. The results indicate supercritical water gasification for hydrogen generation is a promising process for the treatment ofPVA wastewater.

Fabrication and Characterization of One Interpenetrating Network Hydrogel Based on Sodium Alginate and Polyvinyl Alcohol

One interpenetrating network hydrogel based on sodium alginate (SA) and polyvinyl alcohol (PVA) was synthesized by combining the raw materials of PVA and SA with the double physical crosslinking methods of freezing thawing and Ca2+ crosslinking. The PVA-SA composite hydrogel have been characterized by scanning electron microscopy for surface morphology, infrared spectroscopy for investigating the chemical interactions between PVA and SA, X-ray diffraction for studying the PVA-SA composite structure property and thermal gravimetric for understanding the PVA-SA composite thermal stability. The swelling behavior and the degradation rate of the PVA-SA composite hydrogel were studied in simulated gastrointestinal fluid. Using bovine serum albumin (BSA) and salicylic acid as the model drugs, the release behavior of the PVASA composite hydrogel on macromolecular protein drugs and small molecule drug were evaluated. The results showed that the water absorption and degradation ability of the PVA-SA composite hydrogel was much better compared to the pure SA hydrogel or pure PVA hydrogel. The hydrogel exhibited remarkable pH sensitivity and the network was stable in the simulated intestinal fluid for more than 24 h. With the advantages such as mild preparation conditions, simple method, less reagent and none severe reaction, the PVA-SA composite hydrogel is expected to be a new prosperous facile sustained drug delivery carrier.

Electrically induced gel-sol transition of polyvinyl alcohol/polyacrylamide semi-interpenetrated hydrogels

Polyvinyl alcohol/polyacrylamide semi-interpenetrated hydrogels were prepared via freeze-thaw process. When a 20 V of DC was applied across the gels, the gels with lower polyacrylamide content underwent a contraction or partly turned into solution, while for the gels. with higher polyacrylamide concentration, a complete gel-sol transition was observed in a short time.

Starch-g-poly (vinyl alcohol) as Compatibilizer for Reducing the Phase Separation Rates of Polyvinyl Alcohol/Cornstarch Pastes

Starch- g-poly(vinyl alcohol) as a compatibilizing agent for reducing the phase separation rates of polyvinyl alcohol/starch pastes has been investigated by blending and dissolving the two polymers in distilled water. The separation rates were quantitatively evaluated by the term of initiul demixing time. The grafted starches, with a series of grafting ratios, were prepared by grafting a number of vinyl acetate onto granular cornstarch in aqueous dispersion and then alcoholating in methanol. It was found that the addition of small amounts of starch- g poly (vinyl alcohol ) in the size compositions can effectively decrease the separation rates of the blended pastes in comparison to pure starch/PVA ones.Moreover, the influence of the grafting ratio, starch content, and PVA variety on the separation rates was also studied.

Fracture and Tensile Properties of Polyvinyl Alcohol Fiber Reinforced Cementitous Composites

Experiments were carried out to design polyvinyl alcohol （PVA） fiber reinforced cementitous composites （PVA-FRCCs） holding high ductility and energy consumption ability. Besides, the properties of each ingredients in composites, mixing method and technology for fresh mixture were described in detail. Then, the pseudo-strain-hardening （PSH） behavior was investigated in uniaxial tension test. As a result, the maximum ultimate tensile strain can reach 0.7 percent. On the other hand, the single edge notch （SEN） thin sheet specimens were employed to gain the normal tensile load via crack mouth opening displacement （CMOD） curves, which can show obvious PSH behavior. In addition, the curves can be divided into four zones whose fracture toughness calculation methods were discussed. The wedge splitting （WS） test method can be applied to discuss the fracture toughness. Moreover, fracture energy of SEN and WS specimens were both approximately evaluated.

Preparation and Properties of Bio-Based Flame Retardant Polyvinyl Alcohol

Polyvinyl alcohol (PVA) has been widely used in the fields of medical, food and packaging due to its excellentbiocompatibility, good fiber-forming and film-forming properties. However, the high flammability of PVA hasgreatly limited its wider applications. The flame-retardant PVA was prepared by melt blending of a bio-basedflame retardant (prepared from lignin, phosphoric acid and carbamide) with thermoplastic PVA (TPVA). Thechemical structure, morphology, thermal properties, mechanical properties, fire property and fluidity of thisflame retardant PVA were investigated by Fourier transform infrared spectrometer(FTIR), field emission scanning electron microscope(SEM), thermogravimetric analyzer(TGA), impact tester, universal testing machine,horizontal-vertical burning tester, limiting oxygen indexer(LOI) and melt flow rate meter(MFR). The resultsshowed that the prepared flame retardant had good compatibility with the PVA substrate;The impact strength,melt flow rate, fire property and char residue of this PVA material increased with the content of bio-based flameretardant. When the content of flame retardant was of 20%, the five indices including impact strength, meltflow rate, UL-94 level, LOI and char residual were 11.3 KJ/m^(2), 21.2 g/10 min, V-0 UL-94 level, 33.1%, and19.2%, respectively. This research can promote the high-value utilization of lignin and the application ofPVA in the fields of fire protection.

Study On the Method for Evaluating the Compatibility of Polyvinyl Alcohol-starch Pastes

A revising method for evaluating the separation behavior of polyvinyl alcohol - starch pastes used as warp sizes had been studied and developed. Cosolvent method involves two important indexes for appraising the separation behavior: (l) initial demising time, and (2) subsidence ratio. However, they sometimes gave confused results because of the different measuring conditions. For obtaining the indexes accurately, the measuring parameters such as paste concentration, component content, and subsidence period of time were carefully studied and proposed. Besides accuracy, the proposed condition could give larger measuring scope and higher sensitiveness than the old one. Moreover, the influences of the paste concentration, component content, and molecular structure of polyvinyl alcohol upon the separation were also investigated. The experiments indicated that the paste concentration and starch content had much effect on the phase separation, whereas the influence of the molecular structure of polyvinyl

Development of Antioxidant Packaging Film Based on Chinese Bayberry Tannin Extract and Polyvinyl Alcohol

The current work explores the potential use of commercial Chinese bayberry tannin(BT)to develop antioxidant PVA-based films using solvent casting process for packaging applications.The effect of BT concentration on opa-city,water resistance and antioxidant capacity of resulting films was investigated.Properties like tensile strength,thermal behavior,and morphological aspects were also characterized.The experimental results showed that PVA/BT films formed with uniformly brown color and generally good transparency,offering good antioxidant ability.The PVA film containing BT presented slightly higher water resistance according to the results of moisture content and water vapor permeability,especially at low BT content(<10 wt%).The PVA can be compounded with up to 10 wt%BT without any obvious deterioration in the tensile strength.The PVA/BT films exhibited better thermal degradation behavior compared with PVA alone because of the chemical bonds of PVA-BT and the for-mation of char at high temperature.Based on the results,PVA incorporated with Chinese bayberry tannin may provide broader formulation options for packaging materials with antioxidant action.

Study on Various Compositions of Polyvinyl Alcohol and Starch Blends by Cross-Linking with Glyoxal

The aim of this study is to analyze the various compositions of polyvinyl alcohol (PVA) and starch blends. The blends have been cross-linked with glyoxal to enhance its properties. The hydroxyl groups of PVA and starch react with glyoxal via formation of acetal bonds;hence crosslinking could take place. The cross-linking of glyoxal is observed in various analytical methods such as DSC and FTIR. The cross-linked blends showed better thermal and mechanical properties. Viscosity, tensile shear strength, pencil hardness and ultimate stress were evaluated to estimate the changes due to cross-linking. It was observed that the cross-linking is directly proportional to starch, since the starch hydroxyl groups are easily accessible for reacting. The cross-linked blend showed better cohesion between its chains, thereby increasing glass transition temperature. It was reflected in the subsequent increase in tensile strength properties.

Study of Cross-Linking between Boric Acid and Different Types of Polyvinyl Alcohol Adhesive

Polyvinyl alcohol (PVA) is water-soluble polymer manufactured by the saponification of polyvinyl acetate. The physical properties and its specific application depend on the degree of hydrolysis. To enhance the properties of different hydrolyzed PVA grades, it is generally chemically modified with various cross-linkers. Here, different degree hydrolyzed PVA grades with enhanced properties were achieved by cross-linking with boric acid. These samples were then characterized by Differential Scanning Calorimetry (DSC) and Gel permeation chromatography (GPC). For further analysis a film of samples were prepared by casting on glass plate. The effects of amount of boric acid and degree of hydrolysis of PVA on performance properties like tensile strength, pencil hardness and thermal properties like glass transition temperature were studied. The results showed that by cross-linking there was an increase in mechanical strength and thermal property.