Polyvinyl Alcohol Samples Research Articles

Synthesis and characterization of poly (vinyl alcohol) hydrogels and hybrids for rMPB70 protein adsorption

Polyvinyl alcohol (PVA), PVA crosslinked with glutaraldehyde hydrogels (PVA/GA), PVA with tetraethylorthosilicate (PVA/TEOS) and PVA/GA/TEOS hybrids with recombinant MPB70 protein (rMPB70) incorporated were chemically characterized by Fourier transform infrared spectroscopy (FTIR). FTIR spectra of PVA hydrogel samples showed the absorption regions of the specific chemical groups associated with poly(vinyl alcohol) (-OH, -CO, -CH2) and PVA/GA confirming the formation of crosslinked hydrogel (duplet -CH). It was observed C-H broad alkyl stretching band (n = 2850-3000 cm-1) and typical strong hydroxyl bands for free alcohol (nonbonded -OH stretching band at n = 3600-3650 cm-1), and hydrogen bonded band (n = 3200-3570 cm-1). The most important vibration bands related to silane alcoxides have been verified on FTIR spectra of PVA/TEOS and PVA/GA/TEOS hybrids (Si-O-Si, n = 1080 and n = 450 cm-1; Si-OH, n = 950 cm-1). FTIR spectra of f PVA hydrogel with rMPB70 incorporated have indicated the specific groups usually found in protein structures, such as amides I, II and III, at 1680-1620 cm-1, 1580-1480 cm-1 and 1246 cm-1, respectively. These results have given strong evidence that recombinant protein rMPB70 was successfully adsorbed in the hydrogels and hybrids networks. These PVA based hydrogels and hybrids were further used in immunological assays (Enzyme-Linked Immunosorbent Assay - ELISA). Tests were performed to detect antibodies against rMPB70 protein in serum samples from bovines that were positive in the tuberculin test. Corresponding tests were carried out without PVA samples in microtiter plates as control. Similar results were found for commercially available microplates and PVA based hydrogels and hybrids developed in the present work regarding to immunoassay sensitivity and specificity response.

Anisotropic polyvinyl alcohol hydrogel for cardiovascular applications

Polyvinyl alcohol (PVA) is a hydrophilic polymer with various characteristics desired for biomedical applications and can be transformed into a solid hydrogel by physical crosslinking, using a low-temperature thermal cycling process. As with most polymeric materials, the mechanical properties of the resultant PVA are isotropic, as oppose to most soft tissues, which are anisotropic. The objective of this research is to develop a PVA-based hydrogel that not only mimics the nonlinear mechanical properties displayed by cardiovascular tissues, but also their anisotropic behavior. By applying a controlled strain to the PVA samples, while undergoing low-temperature thermal cycling, we were able to create oriented mechanical properties in PVA hydrogels. The oriented stress-strain properties of porcine aorta were matched simultaneously by a PVA hydrogel prepared (10% PVA, cycle 3, 75% initial strain). This novel technique allows the controlled introduction of anisotropy to PVA hydrogel, and gives a broad range of control of its mechanical properties, for specific medical device applications.

Effect of Microwave Irradiation on the Cross-Linking of Polyvinyl Alcohol

The possibility of dehydration (cross-linking) of polyvinyl alcohol upon microwave irradiation of thin polymer films was examined. The properties of polyvinyl alcohol samples treated by convection heating and irradiation were compared. Immobilization of polyvinyl alcohol on polymer matrices by microwave irradiation was studied.

An Analysis of Human Pathogens Found in Horse/Mule Manure Along the John Muir Trail in Kings Canyon and Sequoia and Yosemite National Parks

To determine the prevalence of microorganisms that are potentially pathogenic for humans in horse/mule manure along the John Muir Trail (JMT). Random samples of horse/mule manure were collected along sections of the JMT in Yosemite, Kings Canyon, and Sequoia national parks (NP), as well as in portions of the Pacific Crest Trail (PCT) and selected JMT/PCT access trails. Convenience samples of wild animal scat found within I mile of trails were also collected. The fresh specimens were individually preserved both in 0.9% saline and polyvinyl alcohol (PVA)-containing tubes and stored at 4 degrees C until time of analysis. Bacteriological analysis was performed using standard microbiology laboratory procedures. PVA samples were stained with trichrome and were then examined by a parasitologist. Collection: A total of 186 trail miles were sampled, including 113 on the JMT (Yosemite 37, Kings 53, and Sequoia 23). The PCT samplings included 24 miles, and NP and wilderness area access trails added an additional 49 miles. A total of 102 samples were collected, which included 81 samples from pack animals and 21 identified as having come from wild animals. Pack Animal Bacteria: All plated specimens grew large numbers of commensal gut flora. Potential pathogenic bacteria were found in only 12 samples and included Hafnia alvei (4), Serratia odorifera (1), Citrobacter freundii (1), Escherichia vulneris (1), Clostridium clostridioforme (1), Yersinia enterocolitica (1), Sherwinella putraformus (1), and Enterobacter spp (4). No Escherichia coli O157, Salmonella, or Aeromonas were found. Microscopic examination for protozoal organisms revealed occasional commensal ciliates and I Giardia. Wild Animal Pathogens: One specimen grew Y enterocolitica, and another grew Enterobacter amnigenus. We found a low prevalence of human pathogens in pack animal manure on the JMT.

Cut‐out filter for ultraviolet radiation from poly(vinyl alcohol)

AbstractThe effects of ultraviolet (UV) radiation and thermal annealing on the optical and mechanical properties of polyvinyl alcohol (PVA) were studied. Pure PVA samples were prepared by casting technique. Xenon arc lamp was used to irradiate the sample. The irradiated PVA sample was heated at 150°C for 2 h. The optical and mechanical properties of original, irradiated, and irradiated and then heated samples were measured. The irradiated and then heated sample showed lower transmission in the wavelength range from 190 to 320 nm and the transmission was higher in the visible region than the original and irradiated samples. The stress–strain measurements were performed. Modulus of elasticity of the double‐treated sample was approximately four times higher than that of original sample. The obtained results show the possibility of using this sample as cut‐out filter for UV radiation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1295–1299, 2002; DOI 10.1002/app.10486

Degradation of polyvinyl alcohol (PVA) by homogeneous and heterogeneous photocatalysis applied to the photochemically enhanced Fenton reaction

The reaction mechanism of the oxidative degradation of polyvinyl alcohol (PVA) by the photochemically enhanced Fenton reaction was studied using a homogeneous (Fe2+(aq) + H2O2) and a heterogeneous reaction system (iron(III)-exchanged zeolite Y+ H2O2). In the homogeneous Fenton system, efficient degradation was observed in a batch reactor, equipped with a medium pressure mercury arc in a Pyrex envelope and employing 80% of the stoichiometric amount of H2O2 required for the total oxidation of PVA and a concentration ratio as low as I mole of iron(II) sulfate per 20 moles of PVA sub-units (C2H40). Model PVA polymers of three different molecular weights (15,000, 49,000 and 100,000 g mol(-1)) were found to follow identical degradation patterns. Strong experimental evidence supports the formation of supermacromolecules (MW: 1-5 x 10(6) g/mol) consisting of oxidized PVA and trapped iron(III) at an early reaction stage. Low molecular weight intermediates, such as oxalic acid, formic acid or formaldehyde were not found during PVA degradation in the homogeneous Fenton system, and we may deduce that the manifold of degradation reactions is mainly taking place within the super-macromolecules from which CO2 is directly released. However, in the heterogeneous Fenton system, the reaction behavior was found to be distinctly different: a decrease of the molecular weights of all three tested monodisperse PVA samples was observed by the broadening of the GPC-traces during irradiation, and oxalic acid was formed. The results lead to the mechanistic hypothesis that during the heterogeneous Fenton process, the cleavage of the PVA-chains may occur at random positions, the reactive centres being located inside the iron(III)-doped zeolite Y photocatalysts.

Adsorption/Desorption of Polyvinyl Alcohol on Solid Substrates and Relevant Biodegradation

The rates and extents of absorption and desorption of polyvinyl alcohol (PVA) samples on different solid substrates comprising montmorillonite, quartz sand, and farm soil, as well as humic acid mixture are reported. The uptake of PVA by the substrates was analyzed as a function of PVA hydrolysis (72–98%), molecular weight, and molecular weight distribution. Higher adsorption was detected on montmorillonite followed by farm soil, whereas the quartz sand did not display any specific adsorption affinity for the PVA. An increase in the hydrolysis degree of PVA increased the adsorption rate and extent whereas this feature was reversed by an increase in PVA molecular weight. The desorption of PVA samples from the different substrates was performed both under various pH conditions and in the presence of concentrated HF that was used to dissolve the silicon derivatives present in the substrates. Biodegradation experiments carried out in liquid cultures of PVA adsorbed on montmorillonite showed that the mineralization of the adsorbed PVA was much lower than that detected for the nonadsorbed PVA. This investigation suggests that irreversible adsorption of PVA on the clay component occurs in soil, thus substantially inhibiting PVA biodegradation.

The wall effect on viscosity measurement of dilute aqueous solutions of polyethylene glycol and polyvinyl alcohol using a paraffin-coated capillary viscometer

The relative viscosities of aqueous solutions of a polyethylene glycol sample and a polyvinyl alcohol sample were measured in a viscometer, the capillary wall surface of which was coated with paraffin. The results were compared with the data obtained from the original non-coated viscometer. Slippage occurs in the former case due to the hydrophobic nature of paraffin, while in the latter case, conventional viscous flow operates since both the solvent water and solution either wet and/or are adsorbed on to the glass capillary surface of the viscometer. The experimental data were analyzed with the aid of the recently proposed theory of the effect of solute adsorption on relative viscosity measurements. The formula, accounting for the effect of solute adsorption of polymer solutions down to the extremely dilute concentration region, are also applicable to non-wetting polymer solutions in which solute adsorption is eliminated. The results obtained were compared and analyzed using the idea of extrapolation length of slip flow proposed by de Gennes PG. CR Acad Sci Paris 1979;288B:219. The extrapolation length could be evaluated unambiguously from the relative or reduced viscosity data for polymer solutions down to the extremely dilute concentration region.

Study of optical properties of pure and MoO3-doped polyvinyl alcohol films irradiated with γ-rays

Cast thin films of pure and MoO3-doped polyvinyl alcohol (PVA) have been prepared. The optical transmission spectra in ultraviolet to near-infrared regions are investigated before and after irradiation by different doses of γ-rays in the range 102 to 107 Gy. The analysis of transmission spectra showed that the intensity of the bands is remarkably affected by both dopant concentration and γ-irradiation doses. The disappearance of the transmission band at 265 nm in 1.0 wt% and 2.0 wt% MoO3 is attributed to the structural change due to dopant. It was found that doping with molybdenum oxide results in an additional band at 600 nm. The optical energy gap and band tail of pure and MoO3-doped PVA samples at different γ-doses are estimated.

Electrical and optical studies on γ-irradiated pure and chromium-chloride-doped polyvinyl alcohol

Measurements of optical absorption, electrical conductivity and of the dielectric constant were used to study the changes that occur due to γ-radiolysis of pure and CrCl3-doped polyvinyl alcohol (PVA) thin films. Identification of the structure and assignments of energy bands were derived in terms of ligand field theory. Induced changes in the absorbance at 282 and 222 nm bands in pure and doped PVA samples, respectively, appeared to be dose dependent. The direct-current (d.c.) electrical conductivity of the samples was measured in the temperature range 296–433 K, and the results obtained revealed that γ-irradiation enhances the conductivity. The calculated activation energy in the lower temperature region also proved to be dose dependent. Plots of the dielectric constant, ɛ′, against temperature show an interesting behaviour which depends on the dopant concentrations and exposure to γ-irradiation. The results obtained suggest that these materials may have an application in dosimetry.

Infrared study of the thermal behavior of ?-irradiated poly-(vinyl alcohol)

Infrared spectroscopy was applied for the investigation of the combined effects of γ-irradiation and heat on polyvinyl alcohol (PVA). The samples were exposed in an atmosphere of air at room temperature to doses ranging form 0.5 to 15 M rads. The obtained results revealed that exposure to γ-irradiation produces no considerable changes in the IR spectra of PVA apart from very slight changes in the intensities of the absorption bands. The crystallinity of the irradiated samples was determined by following the induced changes in the absorbances of the crystalline bands. The IR spectra of PVA samples heated at 180°C exhibited two absorption bands at 1580 and 1710 cm−1 due to carbonyl groups. Alken double bonds and possibly also carboxyl groups. IR spectroscopy was also used for the examination of the effect of time of heating in air or in vacuum and also the effect of quenching of the degree of crystallinity of γ-irradiated PVA. Careful examination of the IR spectra led to the conclusion that the temperature induced changes depend on time of heating, rate of cooling and γ-dosage used. The highest crystallinity was obtained by heating in vacuum at 140°C and quenching at −40°C.

A differential scanning calorimetry study of polyvinyl alcohol

Polyvinyl alcohol samples prepared by radical polymerization of vinyl acetate in methanol solution and having different MM and different acetate group contents are studied by a DSC method. With increase in the number of acetate groups the proportion of crystalline phase and the melting point, and also the quantity of water bound in the polyvinyl alcohol, which attains 2 wt% under 80% humidity conditions, are significantly decreased. Moreover, half the water is in the strongly bonded state, and enters preferentially into the polymer crystal lattice.

Contact electrification of chemically modified surfaces

We have studied charge transfer from a variety of metals to solution-cast samples of polyvinyl-alcohol chemically treated to introduce superficial halogens (F, Cl, Br and I). Even though surface analysis shows that only a fraction of the hydroxyl groups are converted to halogen we find that the chemical treatments change the sign of the charge transfer from positive to negative; moreover, the charge transfer becomes much less dependent on metal work function as a result of the chemical treatment. Just such changes are expected if it is supposed that the Cl treatment (for example) converts the surface of the polymer from polyvinylalcohol to polyvinylchloride, and our experiments thus provide striking support for the opinion, expressed by many workers, that the contact electrification of polymers is intimately connected with their chemical composition. Chemical modification of a thin surface layer may provide a controlled means of adjusting the contact charging properties of a polymer with minimum disturbance of desirable bulk properties.

Steric stabilization of polyvinyl alcohol adsorbed on silica/water and water/oil interfaces

The steric hindrance of various polyvinyl alcohol samples was investigated by measuring the force-distance curves between crossed quartz filaments with adsorbed layers of PVA. Results were obtained by changing the concentration of macromolecules, the average macromolecular weight, the electrolyte concentration, the kind of electrolytes, the temperature and by adding organic solvents. The results were compared with calculations using the Hesselink-Vrij-Overbeek Theory. It could be shown that only a small amount of “longer” tails is responsible for the stabilization but the segment distribution functions are different for different samples.

Aqueous GPC of Water Soluble Polymers by High Pressure Liquid Chromatography Using Glyceryl CPG Columns

Glyceryl Controlled-Pore Glass column packings have been evaluated for use in high pressure gel permeation chromatography of water soluble polymers. Results show that these materials are uniquely suitable for molecular weight distribution studies of proteins and industrial glues. In the molecular weight distribution measurement of polyvinyl alcohol samples, the use of uncoated Controlled Pore Glass (CPG) columns was found to be preferable.

Adsorption of polyvinyl alcohol on the paraffin—water interface. II. Spread and adsorbed monolayers

Properties of polyvinyl alcohol (PVA) at the paraffin-water interface were studied with the aid of three different monolayer techniques: (a) spreading on a constant small area (b) spreading on a large area, followed by compression and expansion cycles and (c) compressing and expanding adsorbed monolayers. Attention was paid to the influence of the percentage of acetate residues in the molecule and to the influence of the molecular weight. Spread PVA monolayers are relatively expanded. The singularity with PVAsamples containing 2% acetate groups as previously detected in measurements of the interfacial tension as a function of time and of polymer concentration, was encountered again in the π- A curves. For low molecular-weight polymers the spread monolayers exhibit hysteresis, but for high molecular-weight polymers they are completely reversible. Marked differences were observed between adsorbed monolayers of polymers of different acetate content. In PVA samples with 2% acetate groups there were clear indications of structure formation; the resulting films showed considerable hysteresis upon aging. The time effects observed with samples of PVA containing 12% acetate groups could largely be ascribed to reconformation effects, encountered before in the interfacial tension studies.

Adsorption of polyvinyl alcohol on the paraffin—water interface. III. Emulsification of paraffin in aqueous solutions of polyvinyl alcohol and the properties of paraffin-in-water emulsions stabilized by polyvinyl alcohol

A study has been made of the emulsification of paraffin in water with polyvinyl alcohol (PVA) as the emulsifier. Attention was paid to the influence of the composition of the mixture and the molecular weight and acetate group content of the polymer on the properties of the emulsions formed. For each emulsion, the specific area and the amount of PVA adsorbed were determined. The most remarkable result is that for relatively hydrophobic PVA samples (acetate content > 10%) the specific area of the emulsion does not increase indefinitely with increasing polymer concentration c p but passes through a maximum. The polymer concentration where this maximum is reached increases with decreasing molecular weight. No such irregularity was observed with relatively hydrophilic PVA samples (acetate content <10%). An explanation is presented in terms of the various phenomena occurring during the emulsification process. Important quantities are interfacial tension gradients, the rate of adsorption of polymers by diffusion and reconformation, and the rate of coalescence, all during emulsification. The obtained emulsions are generally very stable. At high c p the adsorbed molecules are subjected to considerable lateral constriction, the more so the more hydrophobic the molecule.

Adsorption of polyvinyl alcohol on the paraffin—water interface. I. Interfacial tension as a function of time and concentration

A systematic experimental study has been made of the interfacial tension γ of paraffin-water interfaces on which polyvinyl alcohol (PVA) was adsorbed. Special attention has been paid to time effects and to the influence of the acetate content and molecular weight of the polymer. The measurements have been performed by the static Wilhelmy plate technique. Prolonged time dependencies up to several tens of hours, are generally observed. At very low polymer concentration ( c p ) the process is diffusion controlled, at high c p it is reconformation controlled. Plots of steady-state values of γ against c p over the 0.4–4000 ppm range are convex with respect to the concentration axis for PVA samples in which the content of acetate groups exceeds 10%. In this respect the trend is opposite to that of low molecular weight surfactants below the CMC. For samples of PVA with 2% acetate groups, however, the γ-log c p plots consist of two linear stretches separated by a discontinuity. At polymer concentrations below that corresponding to the discontinuity, γ is almost independent of c p . In this region the equilibration time is also very short. The effect of molecular weight is not univocal and depends on the source of the PVA. Explanations of these findings are sought in terms of the conformation of the adsorbed polymer.

Complexation of polyvinyl alcohol with iodine: Analytical precision and mechanism

Polyvinyl alcohol (PVA), boric acid and tri-iodide form a characteristic blue complex. For a number of PVA samples, prescribed conditions were used to examine the precision of the formation and spectrophotometry of the complex. The precision of calibration curves was 1–2 % over the range 0–4 mg of PVA per 50 ml of final solution, over which Beer's law holds. Greater deviations can be caused by faulty preparation and aging of individual PVA solutions. The absorbance is independent of the content of residual acetate groups in the PVA for the range 0–15 %. The limit of detection is about 0.01 mg of PVA in 25 ml of sample. A pink colour in the system is due to association of iodine with acetate groups in the PVA. A blue or green colour is due to helical envelopment of iodine molecules by PVA chains stiffened by scattered cyclic groups. The mechanisms of these effects are discussed.

The effect of temperature on the water solubility of polyvinyl alcohol

QUITE a number of the reports published on polyvinyl alcohol (PVA) deal with its aqueous solutions, bu t there is still no clear knowledge of the effect cf tempera ture on the miscibili ty of the two substances. One of the invest igators indicated t h a t the solubili ty of P V A in water increases as a funct ion of t empera tu re [1]; while others reckon t h a t PVA dissolves bet ter in water during cooling [2, 3]. This contradic t ion was due firstly to the PVA samples used in these studies having had different numbers of acetyl groups, which must have affected their solubility in water, and secondly to the fact tha t different invest igators worked with solutions in different ranges of t empera ture and composition. The work described in this paper aims at s tudying the miscibili ty of P V A with water in a wide range of t empera tu re and composition. Apar t f rom the composi t ion d iagram of this system, we also examined the t empera tu re coefficients of light scat ter ing and of t h e r m o d ~ l a m i c affinity of the components .