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.     

Polymer-analogous transformations of polyvinyl alcohol

Modification of polyvinyl alcohol with monomethylolurea and 4,5-dihydroxyimidazolidin-2-one was performed in a wide temperature interval (40–80°С). Irrespective of the initial conditions, modification with the monofunctional agent yielded a non-cross-linked polyfunctional product, which was subsequently used for developing compounds for various purposes. The kinetics of the modifier grafting to the polymer was studied, which is important for controlling the process and choosing its optimum conditions.     

Biodegradable single-polymer composites from polyvinyl alcohol

The microstructure and thermomechanical behaviour of a novel fully biodegradable polyvinyl alcohol (PVOH)-based single-polymer composite (SPC) is presented. Three kinds of PVOH stapled fibres, having different melting temperatures and tensile mechanical properties, were considered as a reinforcement, whilst plasticized PVOH granules were selected as a continuous matrix. Calorimetric tests on the constituents showed significantly different melting temperatures between the matrix and the fibres, thus evidencing adequate processing windows for the preparation of SPCs. On the other hand, scanning electron microscopy on the cryofractured surfaces of melt-mixed and compression-moulded SPCs experimentally proved that the morphological integrity of the reinforcement was maintained only when high melting temperature fibres were utilized. Quasi-static mechanical tensile tests highlighted the capability of the selected PVOH fibres to remarkably increase the elastic modulus, the stress at yield and the Vicat softening temperature of the PVOH matrix. Moreover, dynamic storage modulus and glass transition temperature of SPC increased with respect to the neat PVOH over the whole range of considered temperatures, whilst short-term creep stability was strongly improved, proportionally to the fibre content. The application of a time–temperature superposition principle to creep data confirmed the effectiveness of these fibres in increasing the long-term creep stability of the resulting materials.     

Boron adsorption mechanism on polyvinyl alcohol

Recently, an increase in the use of boron compounds has led to an increase in boron emissions, and concern has grown regarding its detrimental effects on the human body. An adsorbent that adsorbs boron selectively has been developed as a countermeasure. Although certain commercially available boron selective adsorbents can be used to remove boron from aqueous solutions by utilizing the strong affinity between boron and hydroxyl groups, the adsorption capacity appears to be insufficient. So, we adopted polyvinyl alcohol (PVA), which contains many hydroxyl groups, as a model adsorbent. We investigated the boron adsorption characteristics of PVA, and then studied the relationship between the number of adsorption sites and actual adsorption amounts. We assessed the adsorption result by using adsorption site availability (ASA) as an indicator of the ratio of effectively functioning hydroxyl groups from the many hydroxyl groups in PVA. ASA was expressed as a percentage of the experimental equilibrium adsorbed amount in relation to the theoretical equilibrium adsorbed amount. We also compared the adsorption isotherms and ASA obtained with PVA, commercially available N-methylglucamine-type resin (CRB03 and CRB05) and the adsorbent we synthesized from polyallylamine (PAA) and glucose (PAA-Glu). Although PVA has many hydroxyl groups in a molecule, ASA analysis revealed that only 6% of the hydroxyl groups in PVA was used for boron adsorption. On the other hand, CRBs and PAA-Glu exhibited higher ASA values (about 15% and 35% respectively) and adsorption amounts, suggesting that the sterically congested adsorbent structure had a great influence on boron adsorption and ASA.     

Transport of water in polyvinyl alcohol films: Effect of thermal treatment and chemical crosslinking

Data on sorption and transport of water in polyvinyl alcohol films, modified by thermal treatment above T_g, or by chemical crosslinking with glutaraldehyde at different crosslinking degrees, are presented. Equilibrium swelling is constrained by both treatments, except for low degrees of crosslinking where the said reduction is counterbalanced by the partial loss of crystallinity. Analysis of the resulting water uptake kinetics indicates that viscous relaxation effects are, at least partly, responsible for the observed non-Fickian kinetic behavior. Thermodynamic diffusion coefficients of water, D_W, and relaxation frequencies of the swelling polymer, β_W, are determined by application of a theoretical model accounting for relaxation-dependent sorption kinetics in glassy polymers. The results indicate that the effect of both heat-treatment and chemical crosslinking is more intense on the macromolecular relaxation process than on the diffusion coefficient of water. Comparison of the release kinetics of a model drug from as-prepared, non-crosslinked and from crosslinked matrices indicate that the retardation of macromolecular relaxations process induced by crosslinking results in a more uniform release rate.     

Carbonized fibers based on polyvinyl alcohol

On the basis on polyvinyl alcohol (PVA), carbonized fibers were produced in the form of a complex technical thread with tensile strength above 200 MPa and specific electrical conductivity of at least 0.5 S/cm. Using thermogravimetric and differential thermal analysis, Raman scattering, and wide-angle X-ray diffraction, structures of these fibers were characterized. The structural parameters of carbonized PVA fibers are close to the parameters of carbonized coal tar pitch obtained by heat treatment at 1000°C. The structure and properties of carbonized fibers modified with potassium bisulfate were also studied.     

Cellulose whiskers reinforced polyvinyl alcohol copolymers nanocomposites

Nanocomposite materials were prepared from copolymers of polyvinyl alcohol and polyvinyl acetate and a colloidal aqueous suspension of cellulose whiskers prepared from cotton linter. The degree of hydrolysis of the matrix was varied in order to vary the hydrophilic character of the polymer matrix and then the degree of interaction between the filler and the matrix. Nanocomposite films were conditioned at various moisture contents, and the dynamic mechanical and thermal properties were characterized using dynamic mechanical analysis and differential scanning calorimetry, respectively. Tensile tests were performed at room temperature to estimate mechanical properties of the films in the non linear range. All the results show that stronger filler/matrix interactions occur for fully hydrolyzed PVA compared to partially hydrolyzed samples. For moist samples, a water accumulation at the interface was evidenced. The reinforcing effect was found to be all the higher as the degree of hydrolysis of the matrix was high.     

Reaction of polyvinyl alcohol with aluminium isopropoxide

The uncatalyzed and oxalic acid catalyzed modification of polyvinyl alcohol (PVA) with aluminium isopropoxide have been studied for reaction in a suspension of powdered PVA in boiling benzene. Isopropyl alcohol (IPA) formed during the reaction was removed by continuous distillation of an IPA-benzene mixture. The reaction was initially quite fast but slowed up rapidly and practically stopped when only 4–12% of the OH-groups had reacted. Thermogravimetric analysis (TGA) showed that products with 6.8 mole A1/100 mole VA exhibit a significant rise in decomposition temperature from 250 to 285°. The characteristics are attributed to the occurrence of vicinal OH-groups in PVA.     

Recovery of polyvinyl alcohol and hot water from the textile wastewater using thermally stable membranes

The recovery of polyvinyl alcohol from the textile process waste streams is presented. Three filtration systems are described that are able to operate at 100°C or above. Two systems are tubular. One uses carbon tubes to support a zirconium oxide membrane and the other uses stainless steel tubes coated with a fused titanium dioxide layer to support a zirconium hydroxide membrane. The third system described is an asymmetric polyvinyl sulfone membrane in a spiral wound configuration. All three systems have been in operation for several years displaying the successful recovery of polyvinyl alcohol. The economics of the recovery process are described. Also presented is the application of automated control to the PVA recovery process and to the recycle of bleaching rinse water to the scouring process.     

Short cellulose nanofibrils as reinforcement in polyvinyl alcohol fiber

Short cellulose nanofibrils (SCNF) were investigated as reinforcement for polyvinyl alcohol (PVA) fibers. SCNF were mechanically isolated from hard wood pulp after enzymatic pretreatment. Various levels of SCNF were added to an aqueous PVA solution, which was gel-spun into continuous fibers. The molecular orientation of PVA was affected by a combination of wet drawing during gel spinning and post-hot-drawing at a high temperature after drying. A maximum total draw ratio of 27 was achieved with various SCNF contents investigated. The PVA crystal orientation increased when small amounts of SCNF were added, but decreased again as the SCNF content was increased above about 2 or 3 %, likely due to SCNF percolation resulting in network formation that inhibited alignment. SCNF fillers were effective in improving PVA fiber tensile properties (i.e., ultimate strength and elastic modulus). For example, the ultimate strength and modulus of PVA/SCNF composite fiber with a SCNF weight ratio of 6 were nearly 60 and 220 % higher than that of neat PVA. Shifts in the Raman peak at ~1,095 cm^?1, which were associated with the C–O–C glycosidic bond of SCNF, indicated good stress-transfer between the SCNF and the PVA matrix due to strong interfacial hydrogen bonding. Cryogenic fractured scanning electron microscopy images of filled and unfilled PVA fibers showed uniform SCNF dispersion.     

Optically-induced second-order nonlinear optical effect in polyvinyl alcohol photopolymers

IR induced picosecond nonlinear optical effects in polyvinyl alcohol photopolymer is investigated. The second harmonic generation (SHG) is studied versus the pump power and delaying time between the pump and probing beam (λ=1.55 and 1.32 μm, respectively). The phenomena are explained within a framework of fifth-order nonlinear optical susceptibilities. An explanation of the observed dependences is given within a framework of photostimulated vibrations, which enhance acentric electron-phonon anharmonicity. Temperature dependences of the observed phenomena fully confirm the electron-phonon anharmonic origin of the observed effect.     

Novel TEMPO-oxidized cellulose nanofiber/polyvinyl alcohol/polyethyleneimine nanoparticles for Cu2+ removal in water

Cellulose - In this study, environmentally friendly TEMPO-oxidized cellulose nanofiber (TO-CNF)/polyvinyl alcohol (PVA)/polyethyleneimine (PEI) nanoparticles were obtained by assembling PEI into...     

Photochemical synthesis of silver nanoparticles in polyvinyl alcohol matrices

Photochemical synthesis was used to obtain silver nanoparticles in a polymer matrix. The structural and optical properties of the composite material were studied by electron and IR spectroscopy, X-ray diffraction, and electron microscopy. The chemical reactions in polyvinyl alcohol in the preparation of the nanoparticles were studied.     

聚乙烯醇颗粒的急性毒性实验

将30只新西兰大白兔分成6组:低、较低剂量、中、较高剂量、高剂量PVA组、对照组组(1.0mg.kg-1,1.6mg·kg-1,2.0 mg·kg-1,2.5 mg·kg-1,5.0mg·kg-1,40％泛影葡胺2ml/只),经皮穿刺肝动脉给药,连续观察给药后的急性毒性表现,共14d,并检测血液生化指标,进行病理组织学...