Tannin-based extracts of Mimosa tenuiflora bark: features and prospecting as wood adhesives

Stability of PVDF hollow fibre membranes in sodium hydroxide aqueous solution

The molecular size of an alkaline cation has been reported to affect the dissolution of resist film in an alkaline aqueous solution. However, the details are still unclear. In this study, the dissolution dynamics of poly(4-hydroxystyrene) (PHS) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions were investigated to clarify the effects of small alkaline cations on the dissolution dynamics of typical backbone polymer for chemically amplified resists by a quartz crystal microbalance (QCM) method. The temporal changes in the frequency and impedance of QCM substrates during development were measured. The maximum impedance reachable during development significantly exceeded that of the developer saturated with PHS, unlike the case of tetramethylammonium and tetraethylammonium cations. This means that the PHS matrix near the surface was swollen by decreasing the size of the alkaline cation. By either increasing or decreasing the size of the alkaline cation from tetramethylammonium and tetraethylammonium cations, the transient swelling layer became thick.

Formation and characterization of silver nanoparticles in aqueous solution via ultrasonic irradiation

The properties of wool after treatment with sodium hydroxide in a series of 2 M aqueous salt solutions show that anions protect from alkaline degradation in the order S2O3z, SO8z, citrate > CO3z> 504z > C2H 3O2- > Cl- > Br- > NO2- > I- > CNS-, while cations protect in the order Li+, Na+ > K+. The swelling of wool is decreased by some 2 M salt solutions (S2O2 z) but is unaffected by others (CNS-). However, the rate of sorption of OH- by wool is the same from all the alkaline 2 M salt solutions and from pure NaOH. The anion concentration in solution either increases (S2O2z) when wool is added, or is unaffected (2 M CNS-); that is, water is sorbed preferentially from some salt solutions, but no specific anion sorption occurs. Salt effects on wool are therefore unlikely to be due to dehydration of the wool or to ion binding. The present results, and many other protein properties, can be simply explained on the basis of the "effective pressure" exerted by salts in solution, a concept introduced by Gibson [8]. Results of practical interest are that wool can be shrinkproofed without damage by treatment with certain aqueous sodium hydroxide solutions and that yellowing of wool in alkali can be prevented by the addition of reducing agents, such as sodium bisulfite, to the solution.

The process of carbon dioxide chemisorption by aqueous ammonia solutions underlies many technological processes, for example, in technology of soda ash production by ammonia method and in technology of purification of waste gases of chemical enterprises from carbon dioxide. Analysis of literature data showed that the known patterns of the kinetics of carbon dioxide chemisorption process by aqueous ammonia solutions are contradictory. The process of carbon dioxide chemisorption by aqueous ammonia solutions is considered in literature as a mass transfer complicated by chemical reactions only in the liquid phase. The reaction in the gas between ammonia and carbon dioxide is not considered. The aim of the study: to show that the laws of carbon dioxide chemisorption kinetics by aqueous ammonia solutions differ significantly from the laws of carbon dioxide chemisorption kinetics by aqueous sodium hydroxide solutions. Experimental study of the kinetics of processes was carried out in a specially designed device for determining the volume of gas involved in the mass exchange process in the gas-liquid system. In all experiments the amount of alkaline component remained constant. The concentration of NaOH and NH3 in the solutions was varied in the range from 1.2 to 5 mol/L. The volume fraction of carbon dioxide in the gas phase was 100%. The study was conducted at solution temperature of 20 ℃ and and pressure 0,1 MPa. The concentration of ammonia and sodium hydroxide in the solutions was determined by standard methods of chemical analysis. Comparison of the obtained patterns of the kinetics of the two processes showed that the process of chemisorption of carbon dioxide by aqueous solutions of ammonia begins with the reaction in the gas between ammonia and carbon dioxide. The rate of carbon dioxide chemisorption by aqueous ammonia solutions is proportional to the concentration of ammonia in the gas in the first degree. When the contact surface area is equal and the concentration of alkali compounds in solution is equal to 5 mol/l, the chemisorption process speed of CO2 with aqueous ammonia solutions is two times higher than the chemisorption process speed of CO2 with aqueous sodium hydroxide solutions. However, when the concentration of alkaline compounds in the solution is less than 1 mol/l, the chemisorption rate of CO2 with aqueous solutions of ammonia is 2-2.5 times lower than that of CO2 chemisorption with aqueous solutions of sodium hydroxide.

Due to excellent mass transfer characteristics with energy efficiency jet ejectors can be used in place of conventional countercurrent systems, namely, packed bed contactors as well as venturi scrubbers, cyclones and airlift pumps. The removal of chlorine from certain gases by absorption in aqueous solutions of sodium hydroxide is industrially important in several chemical processes particularly in pollution control. Although, a number of papers have been published in the past, none of them provided a theoretical basis for the prediction of rate of absorption of chlorine from certain gases by absorption in aqueous solutions of sodium hydroxide in jet ejector. In this work, the rates of absorption of chlorine from different concentration of gas into aqueous sodium hydroxide solutions of various concentrations were measured at 30°C using a liquid jet ejector. The experimental results were analyzed on the basis of the penetration theory for gas absorption. The theoretical model to calculate rate of absorption is developed. The rate of absorption predicted from developed model is compared with experimental results. They were in good agreement. In this work, an attempt also has been made to develop mathematical model to estimate enhancement factor for jet ejector applying Higbie penetration theory. Key words : Higbie penetration theory, jet ejector, chlorine, aqueous solutions, gases.

The following basic conclusions were drawn from the published data examined; cellulose treated in steamblast conditions can form solutions and gelling pastes in an aqueous solution of sodium hydroxide; the solubility of cellulose in aqueous sodium hydroxide solution is primarily a function of the intramolecular bonds in the cellobiose unit with constant DP; intramolecular bonds are most efficiently broken in steamblast treatment in the cellobiose unit of cellulose I and cellulose III; monofilaments and yarns were obtained from solutions and gelling pastes of cellulose in aqueous sodium hydroxide solution; the physicomechanical properties of the monofilaments and yarns obtained from solutions and gelling pastes of cellulose in aqueous sodium hydroxide solution are still significantly lower than these indexes for viscose textile yarn.

The core focus of this research study was preparation of high-purity silica by the wet-chemical process for solar grade silicon (SOG-Si) using diatomaceous earth expecting a huge amount of resources in the earth crust. Our purification method involved dissolution and precipitation of silica in sodium hydroxide (NaOH) and tetramethylammonium hydroxide (TMAH) aqueous solution followed by acid leaching with HCl solution. By decreasing the pH, more than 90% of the impurities like Al and Fe were precipitated. A large amount of Na impurities were noticed in the final silica product as NaOH was used for the preparation of aqueous alkaline solution. To overcome this serious issue deteriorating the semiconductor characteristics, the mixture of NaOH and TMAH was introduced in order to lower the Na levels during the preparation of alkaline solution. Experimental results suggested that the Na+ ions were needed to have a better dissolution rate of silica in aqueous alkaline solution. This also resulted in the optimum concentration of 0.05 M NaOH and 1.40 M TMAH for the dissolution and precipitation process in order to help the purification of silica. The 3 stages of leaching process with the above mentioned concentration helped us in achieving the 5 N (99.999 wt%) level of silica purity.

Introduction: High surface/volume ratio and 3-dimensionality of nanofibers increases cell-scaffold interactions and promote migration and proliferation of cells. Wet electrospinning is a variant of electrospinning technology that is utilized to produce nanofibrous scaffolds. Altering the parameters governing the wet electrospinning process such as applied voltage, polymer concentration, composition and depth of the coagulation bath, and tip to bath distance can affect the morphology of the produced scaffolds. In this study, the influence of various coagulation baths on the physicochemical properties of the wet-electrospun nanofibers was investigated. Materials and Methods: Poly (ε-caprolactone)/Poly (L-lactic) acid 15% (w/v) blends under an applied voltage of 15 kV, and a tip-to-bath distance of 10 cm. were used to prepare fibrous scaffolds via wet-electrospinning technique into aqueous solution of sodium hydroxide (NaOH) (pH~13), distilled water, ethanol, water/ethanol (3:7) (v/v) and water/ethanol/methanol (6:2:2) (v/v). The final products were characterized by scanning electron microscopy (SEM), liquid displacement technique, contact angle measurement, compressive and tensile tests. As well as, cell adhesion and cell viability through human adipose-derived stem cells (hADSCs) cell culture. Results: Wet-electrospun fibers, except in the almost fully beaded structure of water/ethanol (3:7) (v/v) specimen exhibited random, dispersive and non-woven morphology under SEM observation. The coagulation bath composition significantly influenced on porosity, wettability, mechanical properties and biocompatibility of the scaffolds. The porosity measurement via liquid displacement method showed that except for the specimen in which the blend was spun into NaOH, other scaffolds could not meet the accepted ideal porosity percentage of above 80%. According to the contact angle measurement data, it was expected that all scaffolds experience low cellular attachment and proliferation. Conversely, in vitro hADSCs culture demonstrated that the scaffolds presented a non-toxic environment and enhanced cell proliferation and attachment. Conclusion: The data indicated that the scaffold spun into NaOH was the best candidate among other specimens to culture hADSCs.

Facile synthesis of improved room temperature gas sensing properties of TiO2 nanostructures: Effect of acid treatment

Mass transfer between the liquid and solid phases of the reaction mix during the metakaolin crystallization into the powdered Zeolite LTA has been studied. The metakaolin crystallization has been shown to occur through the formation stage of the amorphous sodium aluminosilicate close by its composition to the Zeolite LTA (Linde type A). It has been established that during thermochemical processing of the metakaolin in aqueous sodium hydroxide solution the solid-liquid mass transfer occurred already at 30oC on account of the interaction of the metakaolin with polyhydroxy complexes of sodium. The stage rate grows as the temperature is elevated, and the sodium hydroxide concentration in the liquid phase of the reaction mix increased. All the above mentioned witnesses the crystallization centers to arise at the boundary of the solid and liquid phases of the reaction mix.

The thermodynamic Henry's law constant (K{sub H}/mol kg{sup {minus}1} atm{sup {minus}1}) of the weak electrolyte NH{sub 3} is described by the equation ln (K{sub H}) = {minus}8.09694 + 3917.507/T {minus}0.00314T, from 372 to 313 K. Measured NH{sub 3} solubilities in both pure aqueous and multicomponent solutions agree well with calculations using the Pitzer thermodynamic model to predict osmotic and activity coefficients. Partial pressure and heat of dilution data were used to determine the activity coefficient of NH{sub 3} ({gamma}{sub NH{sub 3}}). In pure aqueous solutions where dissociation is not significant this is given by {gamma}{sub NH{sub 3}} = exp(2m{sub NH{sub 3}}{lambda}{sub NH{sub 3}}{sub NH{sub 3}}), where {lambda}{sub NH{sub 3}}{sub NH{sub 3}} = 0.033161 - 21.12816/T + 4665.1461/T{sup 2} from 273 to 313 K. Ion-NH{sub 3} interaction parameters were obtained by using partial pressure, salt solubility, and partitioning data for the following ions at 298.15 K; Li{sup +}, Na{sup +}, K{sup +}, NH{sub 4}{sup +}, Mg{sup 2+}, Ca{sup 2+}, Sr{sup 2+}, Ba{sup 2+}, F{sup {minus}}, Cl{sup {minus}}, Br{sup {minus}}, I{sup {minus}}, OH{sup {minus}}, CNS{sup {minus}}, NO{sub 3}{sup {minus}}, NO{sub 2}{sup {minus}}, ClO{sub 3}{sup {minus}}, ClO{sub 4}{sup {minus}}, S{sup 2{minus}}, SO{sub 3}{sup 2{minus}}, CH{sub 3}COO{sup {minus}}, HCOO{sup {minus}} and (COO){sub 2}{sup 2{minus}}.more » Parameter values are found to be simply related to ion charge and size.« less

The mass transfer and reaction kinetics of sulfuryl fluoride (SO2F2) absorption with aqueous sodium hydroxide (NaOH) solutions were studied in an experimental double-stirred cell. Results showed that SO2F2 absorption with NaOH was followed by a reaction model employing a fast pseudo-first-order. The second-order rate constant for SO2F2 absorption with aqueous NaOH solutions was determined to be 1.44 m3/(mol·s) at 298 K. Three models were used in this chemical absorption process, and in each case, the same expression of enhancement factor was obtained. A comparison was made between the experimental enhancement factor and the value calculated from the model, and the maximum relative deviation was less than 4.2%. The proposed model expression gave a reasonable fit with the experimental values, indicating that mass transfer correlations are valid for scaling up design.

An attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali‐soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam‐explosion method, and alkali‐soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non‐Newtonian property at relatively smaller γ than the former solution did. Spin‐lattice relaxation time T1 (by 13C‐NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra‐ and intermolecular hydrogen bondings at the C6 position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra‐molecular structure of the solid is at least partly reserved in the above solutions.

Polarography of vitamin B 12 in aqueous solutions and in water-alcohol mixtures