Dilute solutions of poly(vinyl alcohol) derived from vinyl trifluoroacetate

The dilute-solution behavior of poly(vinyl alcohol) (PVA_VTFA), derived from vinyl trifluoroacetate, in water-dimethylsulfoxide (DMSO) mixtures was investigated. With solvent mixtures ranging from 10 to 20 vol % DMSO, the relation between the reduced viscosity η_sp/C and the polymer concentration C was linear for polymer concentrations above 0.2 g/dL, whereas in solutions in mixed solvents of other compositions the dependence was linear for polymer concentrations above 0.1 g/dL. The relation between the intrinsic viscosity [η] obtained for aqueous solutions of PVA_VTFA and the molecular weight M estimated from viscosity measurements in solutions of poly(vinyl acetate) (PVA_VTFA), obtained by acetylation of PVA_VTFA, was given by [η] = 7.34 × 10^?4 M^0.63. The value of [η] was greatest for the solvent mixture with 10 vol % DMSO and smallest for about 50 vol % DMSO, and Huggins constants k were smallest and greatest for these two cases, respectively. The turbidity of the solutions of low-molecular-weight PVA_VTFA, was higher than that of high-molecular-weight PVA_VTFA up to 30 vol % DMSO, and the reverse relation held for 40-70 vol % DMSO.     

Rheological investigation of aqueous solutions of poly(vinyl alcohol) during ageing

The changes in viscosity and normal stress difference during the ageing of concentrated aqueous solutions of poly(vinyl alcohol) prepared at 80 °C and the effect of the procedure used in the preparation of solutions on the course of these changes are described. The results are interpreted by means of shear complianceJ _e and relaxation time ₀.     

Stabilization of electrospun poly(vinyl alcohol) nanofibrous mats in aqueous solutions

<正>The stability ofpoly(vinyl alcohol)(PVA) nanofibrous mats in water media was improved by post-electrospinning treatments.Bifunctional glutaraldehyde(GA) in methanol was used as a crosslinking agent to stabilize PVA nanofiber,but fiber twinning was observed frequently,and the highly porous structure of PVA nanofibrous mats was destroyed when the crosslinked fiber was soaked in water.To overcome this shortcoming,chitosan(CS) was introduced into the PVA spinning solution to prepare PVA/CS composite nanofibers.Their treatment in GA/methanol solution could retain the fiber morphology of PVA/CS nanofibers and porous structure of PVA/CS nanofibrous mats even if they were soaked in aqueous solutions for 1 month.Scanning electron microscopy(SEM),X-ray diffraction(XRD),thermal gravimetric analysis(TGA) and differential scanning calorimetry(DSC) were applied to characterize the physicochemical structure and thermal properties of PVA nanofibers.It was found that the water resistance of PVA nanofibrous mats was enhanced because of the improvement of the degree of crosslinking and crystallinity in the electrospun PVA fibers after soaking in GA/methanol solution.     

Electrical conduction of poly(vinyl alcohol) films

PVA films (30–45 μm thickness) were prepared by casting. dc electrical measurements were done over the temperature range 293–353 K. Two different conduction mechanisms are suggested. The first one is ohmic and extends to 303 K. Above this temperature a space-charge-limited conduction mechanism, with protons as charge carriers, predominates. Dependences of the voltage-reversion current temperature and field were investigated and were attributed to a clean-up effect of charge carriers. The variance in the activation energy, calculated from the conductivity curves and from the mobility curves, led to a discussion of the origin of the charge carriers. No change in conductivity was observed for the PVA films irradiated with UV (of wavelength 365 nm) at 303 K, i.e., PVA is a photostable material under these conditions.     

Effect of poly(ethylene oxide) on the structure and properties of poly(vinyl alcohol)

To improve the drawability of poly(vinyl alcohol) (PVA) thermal products, poly(ethylene oxide) (PEO), a special resin with good flexibility, excellent lubricity, and compatibility with many resins, was applied, and the Fourier transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WXRD) were adopted to study the hydrogen bonds, water states, thermal properties, crystal structure, and nonisothermal crystallization of modified PVA. It was found that PEO formed strong hydrogen bonds with water and PVA, thus weakened the intra‐ and inter‐hydrogen bonds of PVA, changed the aggregation states of PVA chains, and decreased its melting point and crystallinity. Moreover, the interactions among PVA, water, and PEO retarded the water evaporation and made more water remain in the system to plasticize PVA. The existence of PEO also slowed down the melt crystallization process of PVA, however, increased the nucleation points of system, thus made more and smaller spherulites formed. The weakened crystallization capability of PVA and the lubrication of PEO made PVA chains to have more mobility under the outside force and obtain high mechanical properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1946–1954, 2010     

Radiolysis of aqueous solutions of poly(vinyl alcohol) at 77 K

Paramagnetic products of low-temperature X-ray radiolysis of aqueous poly(vinyl alcohol) solutions (2.5 and 5% by weight) were studied by ESR spectroscopy. Experimental spectra were ascribed to a superposition of signals from hydroxyl radicals and –CH₂?^?C(OH)–CH₂? macroradicals (C_α-macroradicals), respectively. No ESR signals corresponding to trapped electrons were observed that was attributed to the peculiarities of microheterogenous structure of the frozen aqueous polymer solutions. Annealing at 115 K resulted in partial conversion of OH radicals to C_α-macroradicals. It was suggested that main part of hydroxyl radicals was stabilized in phase of polycrystalline ice while macroradicals were formed in “mixed” water–polymer phase. The radiation–chemical yields of paramagnetic species stabilized in the systems under study were determined.     

An investigation of aging aqueous poly(vinyl alcohol) solutions by the light scattering method

Aqueous poly(vinyl alcohol) solutions of various concentrations were investigated. The aged solutions were diluted and then analyzed by the light scattering method, size exclusion chromatography, and viscometry. It was found that a relatively small quantity of supermolecular formations arise during aging; they are dispersed in the molecular solution of the predominant part of the polymeric material present. The amount of these aggregated structures and their formation rate increase with concentration of the aging solution.     

Fractionation of poly(vinyl alcohol) derived from poly(vinyl acetate) from its aqueous solution induced by shearing force-IV

Summary In order to clarify the mechanism of crystallization under molecular orientation, the fractionation for poly(vinyl alcohol) (VAc-PVA) derived from vinyl acetate from its aqueous solution was carried out under shearing force. The fibrillar crystals grown by shearing force from solutions were produced on the stirrer and in solution simultaneously. The fibrillar crystals had a diameter of approximately 1 mm and a length of 1 cm in the case of the initial polymer concentration of 2.0%, and approximately 1 mm and 5 cm in the case of 0.5%. The initial rate of precipitation (Rs) for the precipitates produced in solution was higher than that (Rr) on the stirrer. The difference betweenRs andRr increased with an increase in initial polymer concentration. The difference in the percentages of syndiotactic diads of precipitates grown on the stirrer and those in solution was not found, and the percentages of syndiotactic diads of each fraction decreased in the order of fractionation. Furthermore, the difference in the molecular weight of precipitates grown on the stirrer and those in solution was not found in the case of the higher polymer concentration, whereas it was found clearly in the case of lower one.

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Zusammenfassung Um den Mechanismus der Kristallisation unter molekularer Orientierung zu klären, wurde die Fraktionierung von Polyvinylalkohol (VAc-PVA), der aus Vinylacetat hergestellt war, in wäßriger Lösung unter Scherkräften durchgeführt. Die von Lösung unter Scherung gewachsenen flbrillären Kristalle erscheinen gleichzeitig in Lösung und auf dem Rührer. Die aus Lösung gewonnenen Faserkristalle hatten einen Durchmesser von etwa 1 mm und eine Länge von etwa 1 cm bei einer anfänglichen Konzentration des Polymeren von 2.0%, etwa 1 mm und 5 cm resp. für 0.5%. Die anfängliche Fällungsgeschwindigkeit (Rs) der in Lösung wachsenden Niederschläge war höher als diejenige (Rr) auf dem Rührer. Ein Unterschied im Gehalt an syndiotaktischen Diaden zwischen den vom Rührer und aus der Lösung entnommenen Faserkristallen ließ sich nicht feststellen, und die syndiotaktischen Diaden nahmen in beiden Proben mit der Ordnung der Fraktionierung ab. Darüber hinaus ließ sich ein Unterschied im Molekulargewicht zwischen den auf dem Rührer und in der Lösung gewachsenen faserigen Kristallen bei der höheren Anfangskonzentration des Polymeren nicht feststellen, aber bei der niedrigeren Anfangskonzentration des Polymeren war die Auswirkung des Molekulargewichtes deutlich.

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Mechanical Denaturation of High Polymers in Solutions, XXV.     

Potassium sorbate release from poly(vinyl alcohol)-bacterial cellulose films

Active packaging materials are the subject of research because their performance exceeds that of traditional packaging. From this class, antimicrobial materials extend the shelf-life of products and reduce the risk of contamination by pathogens. In this paper, new composite materials with antimicrobial properties are obtained by using polyvinyl alcohol and bacterial cellulose powder. Potassium (2E,4E)-hexa-2,4-dienoate was used as the antimicrobial agent. The films thus obtained were characterised using Fourier-transform infrared spectroscopy and scanning electron microscopy. Mass transfer phenomena concerning the release of potassium (2E,4E)-hexa-2,4-dienoate were investigated. The results indicated that the new biocomposite films could be used as antimicrobial packaging materials.     

Conformational changes in poly(vinyl alcohol)-graft-polyacrylamide in aqueous solutions vs graft content

Conformational changes have been studied in intramolecular polymer-polymer complexes (intraPC) of graft copolymers of poly(acrylamide) and poly(vinyl alcohol) (PVA-g-PAA) with various numbers of grafts (4-42) per molecule as a function of temperature and copolymer concentration. It is shown that the magnitude of conformational change depends on the grafts content while the temperature range over which the conformation changes occur is essentially determined by copolymer concentration. The conformational changes are reversible on heating and cooling.     

Effect of non-associated electrolyte solutions on the behaviour of poly(vinyl alcohol)-based hydrogels

The aim of this paper is to present the behaviour of the poly(vinyl alcohol) hydrogels [PVA-HG] in sodium and potassium chlorides aqueous solutions, due to their interactions. The tested [PVA-HG]-s have been obtained by repeated freezing and thawing cycles. White, heterogeneous hydrogels have been obtained. These hydrogels exhibit a mechanical active behaviour at their contact with electrolytes aqueous solutions, manifested by important changing in mass, volume and density of the hydrogel samples. These modifications could be explained by water elimination from the hydrogels that initially reached the equilibrium of swelling. The kinetic of the water desorption and the reversibility of this process, have been studied and some of the factors that influence this behaviour have been evidenced. The sensitivity of PVA hydrogels to electrolyte nature and concentration could be used in sensors design and also could explain some aspects of electrolytes diffusion through PVA membranes and targeted drugs delivery.     

The properties and behavior of supermolecular formations in aging aqueous poly (vinyl alcohol) solutions

The structure of supermolecular formations and the interparticle interaction in aqueous poly(vinyl alcohol) solutions aging at different concentrations were investigated. Integral light scattering was used to determine the single particle scattering functionP(K), the structure functionS(K), and hence the radial distribution functiong(r). Nonrandom arrangement of the supermolecular formations in solutions under study is much less intensive than that of particles in polymer latices.     

Mechanical and thermal properties of cryogels and foamed cryogels produced from aqueous solutions of poly(vinyl alcohol)

The effect of sodium chloride and technical-grade carbon (carbon black) on the mechanical and thermal properties of cryogels and foamed cryogels produced from homogeneous and heterogeneous (foamed) solutions of poly(vinyl alcohol) was studied.     

Effect of syndiotacticity on the aqueous poly(vinyl alcohol) gel 2. Syneresis of gel

Summary The mechanism of syneresis of an aqueous gel of syndiotacticity-rich poly(vinyl alcohol) (PVA) with the rise of temperature was studied using the PVA having the content of syndiotacticity in diad from 58.4 to 66.2%. The extent of syneresis was estimated by gravimetry. Syneresis of gel with the rise of temperature depends upon the syndiotacticity and gelling temperature. The gel chilled at lower temperature of PVA having the content of syndiotacticity in diad above 60.9% showed remarkable syneresis with the rise of temperature. The maximum of the extent of syneresis appeared between the content of syndiotacticity in diad of 60.9% and that of 64.2%. The phenomena of syneresis was not thermally reversible. Syneresis occurs accompanying the breakdown of the unstable junction and further growth of the crystallite.

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Zusammenfassung Der Mechanismus der Synärese an wäßrigen Gelen von Polyvinylalkohol, reich an syndiotaktischem Anteil, wurde mit steigender Temperatur untersucht, wobei der Polyvinylalkohol in Bezug auf seinen Gehalt an syndiotaktischen Diaden zwischen 58,4 und 66,2% variiert. Die Synärese wurde gewichtsmäßig verfolgt. Die Synärese hängt von der Syndiotaktizität und der Gelierungstemperatur ab. Gele, erstarrt bei tieferen Temperaturen mit einer Syndiotaktizität von 60,9%, zeigten beträchtliche Synärese mit steigender Temperatur. Das Maximum an Synärese wurde zwischen 60,9 und 64,2% Syndiotaktizität beobachtet. Das Phänomen der Synärese ist nicht thermisch reversibel. Die Synärese läuft ab unter Zusammenbruch von unstabilen Bindungen und weiterem Wachstum der Kristallite.

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Part 1. cf. reference 4.