Saturated Saline Solutions Research Articles

Water desorption isotherms and thermodynamic properties of Ora-pro-nóbis (Pereskia aculeata Miller)

Desorption isotherms of ora-pro-nóbis leaves were determined at storage (5 °C, 10 °C, 20 °C, 30 °C, and 40 °C) and drying (40 °C, 50 °C, 60 °C, 70 °C, and 80 °C) temperatures by the gravimetric static method using saturated saline solutions to obtain relative humidities ranging from 5.20% to 98.48%. The net isosteric heat of desorption and thermodynamic properties such as differential enthalpy, differential entropy, and Gibbs free energy were also estimated. The GAB model presented the best parameters of fitting and the lowest Akaike and Bayesian information criteria values. The desorption isotherm patterns presented a sigmoid shape and were categorized as BET Type II sigmoid shape. The monolayer moisture content was estimated in 0.06 kg of water/kg of dry matter using the GAB model, and it remained constant at all temperatures. The leaves presented an optimal water activity equal to 0.35 at storage temperatures. The net isosteric heat of desorption decreased with increasing Xeq, and differential entropy increased with rising equilibrium moisture content (Xeq > 0.07). The enthalpy-entropy compensation was evaluated, and the desorption process is revealed to be entropy-driven and non-spontaneous.

Influence of temperature and Thermodynamic Analysis on Adsorption/Desorption Isothermss for green menth.

The objective of this study is to experimentally determine the sorption isotherms and thermodynamic properties of green mint after undergoing thermal and biochemical treatment. The method employed is the gravimetric method using saturated saline solutions at various temperatures. In order to model and predict the hygroscopic behavior during drying and storage, we have utilized developed mathematical models (such as the Langmuir, GAB, modified BET, Peleg models, etc.). The adjustment and optimization of these models will be conducted using statistical techniques to analyze the obtained data. The isosteric desorption heats of green mint will be calculated using the Clausius-Clapeyron equation. This study will provide an expression to predict the thermodynamic properties of green mint.

Estimation of Thermodynamic Parameters for Better Conservation of Fresh Tomato (<i>Lycopersicum esculentum</i>)

Knowledge of the state of water balance of agro-food products is an essential step in drying or storage operations for preservation. Our study made it possible to determine the thermodynamic parameters which influence the storage conditions of fresh tomatoes grown in the south of Benin; and to predict its hygroscopic behavior during post-harvest storage. The desorption isotherms obtained at 40℃, 50℃ and 60℃, by the static gravimetric method using saturated saline solutions, are compared with those of the theoretical models of Brunauer, Emmet and Teller (BET), SMITH, PELEG and Guggenheim-Anderson-Boer (GAB). An adjustment of the experimental points, on the theoretical models, was made thanks to the numerical method which exploits the fminsearch algorithm under the MATLAB software, version R2018a. The GAB model at 50℃ faithfully reproduces the experimental desorption curves for water activities from 5.5% to 82.3%. The net isosteric heat of sorption was determined using the Clausius-Clapeyron equation, it increases when the degree of dehydration of the product increases. The applied isokinetic theory and enthalpy-entropy compensation are consistent.

Solubilidade de diferentes sais usados no controle da atividade de água de alimentos

ABSTRACT Saturated salt solutions produce environments with specific relative humidities used in several applications, such as determining water sorption isotherms of foods. However, the preparation of saturated solutions requires knowledge of solubility data. Thus, the objective of this work was to determine the solubility of 14 salts: lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI), magnesium chloride (MgCl2), sodium iodide (NaI), potassium carbonate (K2CO3), magnesium nitrate (Mg(NO3)2), sodium bromide (NaBr), potassium iodide (KI), sodium chloride (NaCl), ammonium sulfate ((NH4)2SO4), potassium chloride (KCl), potassium nitrate (KNO3), and potassium sulfate (K2SO4) in the temperature range of 275.15 to 363.15 K at 101.3 kPa. The apparatus for the solubility determination consists of a jacketed glass cell and a magnetic stirrer. Furthermore, polynomial and exponential empirical models were fitted to the observed data to determine salt solubilities. Salt solubilities ranged from 7.39 to 80.41 g of salt·(100 g of solution)-1. Sodium iodide (NaI) presented the highest (p<0.05) solubility, up to 343.15 K, and lithium iodide (LiI) up to 363.15 K. The specific equilibrium moistures afforded by saturated saline solutions were associated with water activity data. A general mathematical model to determine the solubility of different salts was not obtained because the dissolution behaviors of each salt are distinct. However, the availability of solubility data of saline solutions covering a wide range of temperatures is helpful since the salts have different behavior.

Modeling moisture adsorption isotherms for extruded dry pet foods

Two mathematical models were used to determine the moisture adsorption isotherm curves of dry pet foods. Ten extruded commercial diets for dogs (n = 6) and cats (n = 4) were tested within 7 days of manufacture. The equilibrium moisture content of each food at 30 and 40 °C was determined by gravimetry. Six saturated saline solutions (lithium chloride, potassium acetate, sodium nitrite, magnesium chloride, sodium chloride, and potassium chloride) were prepared and used to obtain pet food samples at different water activities. Solutions were placed in airtight flasks containing food samples (without direct contact) and oven-dried to constant weight. The relationship between water activity and equilibrium moisture content was modeled by the exponential Peleg and Guggenheim–Anderson–de Boer (GAB) models. All pet foods exhibited a type II isotherm. Akaike information criterion, R2, and standard deviation values were − 29.79, 0.914, and 3.89, respectively, at 30 °C by the Peleg model; − 28.86, 0.876, and 6.36 at 40 °C by the Peleg model; − 31.17, 0.937, and 4.34 at 30 °C by the GAB model; and − 29.63, 0.888, and 7.71 at 40 °C by the GAB model. At 0.60 water activity, equilibrium moisture contents by the Peleg and GAB models were 12.04 ± 0.84 and 11.67 ± 0.78 g H2O/g dry matter, respectively, at 30 °C and 7.83 ± 1.31 and 8.09 ± 0.81 g H2O/g dry matter at 40 °C. The GAB model also allowed estimating monolayer moisture content (5.81 ± 0.81%). Both models provided similar results and may be useful for determining quality parameters for pet foods. Adsorption isotherm studies can provide practical information about the moisture ranges of pet foods, contributing to the optimization of food safety, palatability, and processing conditions.

Decay resistance of thermally modified Eucalyptus grandis wood against wild strains of Trametes versicolor and Pycnoporus sanguineus

ABSTRACT Eucalyptus grandis presents low durability, and due to its anatomical characteristics, impregnation with chemicals is not an effective alternative to increase it. This work analyses the effect that thermal modification carried out in an oxygen depleted atmosphere has on mass, density, hygroscopicity, chemical composition of the cell wall and decay resistance against locally collected wild strains of wood destroying Basidiomycetes, Trametes versicolor and Pycnoporus sanguineus. E. grandis boards were modified in a vacuum environment (P = –100 kPa) at 160°C, 180°C and 200°C for 1, 2 and 3 h. Hygroscopicity was determined by a sorption isotherm over saturated saline solutions at 25°C. The cell wall composition was characterized by the content of structural carbohydrates, lignin and total extractives. A mini-block fungal test was performed by exposing treated wood samples to mycelia, using Populus sp. as reference. The results showed that the thermal treatment caused mass and density reduction. Modified samples showed a reduction in xylose content while lignin content increased, and cellulose content remained constant. Treated samples presented lower hygroscopicity, especially the ones modified at higher temperatures. The analysis by the Hailwood-Horrobin model showed that the main effect occurred at the monomolecular level, causing a reduction of the sorption capacity of the treated wood. The fungi test evidenced that the modification increased the decay resistance of E. grandis against T. versicolor and P. sanguineus. Both fungi were capable of degrading modified wood, but had limited activity, explained by a reduction of moisture content and a change in the chemical composition of the wood.

FITTINGS OF ADSORPTION ISOTHERM MODELS AND THERMODYNAMIC PROPERTIES OF URUNDAY SEEDS

ABSTRACT This study aimed to obtain and evaluate thermodynamic properties and hygroscopic equilibrium isotherms of urunday seeds as a function of air relative humidity and temperature, as well as identify the best-fitted mathematical models for adsorption phenomenon. A static-gravimetric method was used to obtain hygroscopic equilibrium moisture content. Seeds were placed in airtight containers with different saturated saline solutions for relative humidity control. These were then kept in BOD incubator chambers at 10, 20, 30, and 40 °C. Hygroscopic equilibrium moisture content decreased as temperature increased, for the same water activity. The Sigma-Copace model best-fitted seed adsorption data for equilibrium water activity intervals between 0.1129 and 0.8232 (dry basis). Both vaporization latent-heat and differential sorption entropy increased with decreasing hygroscopic equilibrium moisture content. Adsorption process in urunday seeds was controlled by enthalpy.

Isotermas de sorção e propriedades termodinâmicas de sementes de maracujá doce

Objetivou-se com o presente trabalho determinar as isotermas de adsorção de sementes de maracujá doce, selecionar o modelo matemático que melhor descreve o comportamento higroscópico dessas sementes e estimar o calor isostérico integral, a entropia diferencial e a energia livre de Gibbs, para as condições estudadas. O teor de água de equilíbrio das sementes foi obtido pelo método estático-gravimétrico. Para condicionar o ambiente de equilíbrio, as sementes foram inseridas em recipientes herméticos contendo diferentes soluções salinas saturadas e esses recipientes foram colocados em BODs reguladas para as temperaturas de 10, 20, 30 e 40 °C. Analisando-se os resultados obtidos pode-se concluir que: O teor de água de equilíbrio higroscópico das sementes de maracujá é diretamente proporcional à atividade de água e decresce com o aumento de temperatura; Dentre os modelos testados, o modelo de Chung Pfost é aquele que melhor representa a higroscopicidade das sementes de maracujá doce; Com a redução do teor de água das sementes ocorre um aumento do calor isostérico integral de adsorção, da entropia diferencial e da energia livre de Gibbs; O processo de adsorção das sementes de maracujá doce é controlado pela entalpia.

Barrier Properties of Poly(Propylene Cyclohexanedicarboxylate) Random Eco-Friendly Copolyesters.

Random copolymers of poly(propylene 1,4-cyclohexanedicarboxylate) containing different amounts of neopentyl glycol sub-unit were investigated from the gas barrier point of view at the standard temperature of analysis (23 °C) with respect to the three main gases used in food packaging field: N2, O2, and CO2. The effect of temperature was also evaluated, considering two temperatures close to the Tg sample (8 and 15 °C) and two above Tg (30 and 38 °C). Barrier performances were checked after food contact simulants and in different relative humidity (RH) environments obtained with two saturated saline solutions (Standard Atmosphere, 23 °C, 85% of RH, with saturated KCl solution; Tropical Climate, 38 °C, 90% RH, with saturated KNO3 solution). The results obtained were compared to those of untreated film, which was used as a reference. The relationships between the gas transmission rate, the diffusion coefficients, the solubility, and the copolymer composition were established. The results highlighted a correlation between barrier performance and copolymer composition and the applied treatment. In particular, copolymerization did not cause a worsening of the barrier properties, whereas the different treatments differently influenced the gas barrier behavior, depending on the chemical polymer structure. After treatment, Fourier transform infrared analysis confirmed the chemical stability of these copolymers. Films were transparent, with a light yellowish color, slightly more intense after all treatments.

Hygroscopic equilibrium of microencapsulated extract of passion fruit seed and its effect on the antioxidant capacity

AbstractThe hygroscopic behavior of microcapsules of antioxidant extract of defatted passion fruit seed, produced using spray drying technique, was analyzed at 20 and 40 °C by the static method with saturated saline solutions. The isosteric heat of sorption of the microcapsules, concentration of phenolic compounds and piceatannol, and the antioxidant capacity using ABTS and DPPH methods were measured during storage at different relative humidities. The isotherms were classified as GAB isotherms, exhibiting a Type II behavior. Isosteric heat of sorption decreased when the relative humidity increased and critical equilibrium moisture reached 61%. The microencapsulated extracts retained their antioxidant capacities within the evaluated conditions, what suggests that it may be applied in food at any of these water activity values.Practical applicationsPiceatannol is a stilbene with expressive antioxidant capacity which can be found in passion fruit seeds. In this work, the seeds were used to obtain the crude hydroethanolic extract which was microencapsulated by spray drying. The hygroscopic behavior of the microencapsulated extract of piceatannol was evaluated by fitting the data on different isotherm theoretical models. It was possible to verify the interference of the water activity in the antioxidant capacity and establish a relationship with possible critical storage conditions of the microencapsulated extract.

ISOTERMAS DE DESSORÇÃO DE SEMENTES DE BETERRABA

Alterações físicas e químicas de produtos agrícolas podem ocorrer durante o armazenamento, levando à perdas quantitativas e qualitativas. Portanto, o conhecimento acerca da relação entre o produto, a temperatura (T) e a umidade relativa (UR) do ambiente é necessário para diminuir possíveis alterações. Dito isto, este trabalho objetivou determinar o modelo matemático mais adequado para predizer o teor de água de equilíbrio (Xeq) de sementes de beterraba, cv. “Chata do Egito”, em diferentes T e UR. Xeq foi alcançado por meio do método estático, utilizando soluções salinas saturadas, com valores de UR entre 11 e 96 %. Sementes foram colocadas no interior de dessecadores contendo as soluções salinas, posteriormente armazenadas em câmaras BOD em diferentes T (10; 20; 30; 40 e 50 ºC). Xeq foi obtido quando a variação entre três pesagens consecutivas fosse igual ou menor a 0,01 g. O teor de água foi determinado pelo método gravimétrico usando estufa a 105 ± 1°C até a massa constante. Cinco modelos matemáticos (Chung Pfost, Copace, Halsey Modificado, Henderson e Henderson Modificado) foram ajustados aos dados experimentais de Xeq. O modelo mais adequado foi escolhido considerando a magnitude do erro médio relativo (MRE), desvio padrão da estimativa (SE) e análise de resíduos. O modelo de Chung-Pfost foi o que mais se ajustou aos dados experimentais, apresentando valores de 8,04 % e 0,62 % b.s. de MRE e SE, respectivamente.

On the mechanisms and kinetics of evaporation of a compacted silt

In order to define a convective evaporation model able to reproduce the evaporation rates according to the atmospheric conditions, drying tests have been performed on cylindrical samples of a compacted silt in a closed chamber where the relative humidity of the air is controlled by means of saturated saline solutions. Calibrating such models using experimental results from small sample sizes can indeed be an interesting alternative to simplify the experimental procedures and to reduce the test duration in comparison with the standard in-situ tests (e.g. lysimeter). However the influence of the size of the samples on the kinetics of evaporation has to be investigated. Samples with different diameters and heights are therefore tested. The results show that the observed mechanisms of drying are similar to those at the scale of the geostructure if the dimensions of the sample are higher than a critical height and a critical diameter. We show then that the experimental critical height is consistent with the concept of critical length proposed by Lehman et al. (2008), who expresses analytically when the hydraulic connection between the sample surface and the drying front is upset. Finally the kinetics of evaporation recorded under different relative humidities highlight that the mass transfer coefficient defined in the convective evaporation model does not depend on the relative humidity.

Metallic, oxygen-containing reaction products after polarisation of iron in H2S saturated saline solutions

Corrosion of Fe in H2S containing solutions is a general problem in oil production. Here, layers rich in the the tetragonal FeS modification mackinawite were grown by polarisation of iron 200 mV above the corrosion potential in H2S saturated acetic saline solution. These layers have no band gap above room temperature thermal energy, hence behave metallic. The sulfide layers are duplex layers, with an inner, oxide-rich and an outer, oxide-poor region. Strain induced by differences in oxygen content may be responsible for the poor adhesion between the two layers, which leads to eventual loss of the outer layer.

Effect of stress on water retention of needlepunched geosynthetic clay liners

Geosynthetic clay liners (GCLs) are placed at the bottom of waste disposal facilities where they hydrate from the subsoil and eventually from a hydraulic head on geomembranes (GMs) defects. Predicting hydration behavior of GCLs requires knowledge of the water-retention properties of the GCL along wetting paths. Given that GCLs could be subjected to different ranges of vertical stresses that are induced by the weight of the supported waste, the confining stress could affect water-retention properties of GCLs and should be investigated. To do so, a laboratory methodology to establish the water-retention curves (WRCs) of needlepunched GCLs under stress was undertaken. Various constant vertical stresses corresponding to different weights of the supported waste were applied to GCL specimens placed in controlled-suction oedometers. Suction values were selected so as to mimic a wetting path from the initial dry state to zero suction. Suction was controlled by using controlled suction techniques with controlled humidity imposed by a saturated saline solutions and using the osmotic technique with polyethylene glycol (PEG) solutions. Measurements were undertaken on oedometer systems as to apply confining stresses and have been complemented by standard saturated oedometer swelling tests. The data obtained confirm that increasing the stress on to the GCL results in less, albeit faster, water uptake, which could emphasize on recommendations about rapidly covering GCLs after they are placed at the bottom of a waste disposal facilities. Finally, the potential validity of the state-surface concept, which was developed in unsaturated soil mechanics, is discussed using van Guenuchten's and Fredlund and Xing's equations for water retention curves.

Characterization of artificially dried biofilms for air biofiltration studies

One of the main problems associated with the operation of air biofilters is the loss of performance caused by drying of the bioactive support, as the removal capacity of contaminants by the microorganisms is dependent on their water content. In this work, biofilms from a microbial consortium adapted to toluene were grown on stainless steel slides. The biofilms were dried in stoppered flasks with saturated saline solutions to obtain final water activities of 97.4 %, 83.9 %, 74.8 % and 32 %. The biofilms were characterized by a sorption isotherm Type III with toluene; the water desorption isotherm was fitted to the BET model and the biofilm hydrophobicity was also determined. Specific oxygen consumption rates decreased at lower Aw from 60 μg O2/mg protein/h to zero activity. Biofilm activity, represented by a toluene consumption rate, and others physical properties presented a critical point between Aw 0.84 and 0.97. Biological activity of dried biofilms was restored either partially or completely, depending on the extent of drying and rewetting method.

Conformational Transitions of Flexible Hydrophobic Polyelectrolytes in Solutions of Monovalent and Multivalent Salts and Their Mixtures

Conformations of cationic polyelectrolytes (PEs), a weak poly(2-vinylpyridine) (P2VP) and a strong poly(N-methyl-2-vinylpyridinium iodide) (qP2VP), adsorbed on mica from saline solutions in the presence of counterions of different valences are studied using in situ atomic force microscopy (AFM). Quantitative characteristics of chain conformations are analyzed using AFM images of the adsorbed molecules. The results of the statistical analysis of the chain contour reveal collapse of the PE coils when ionic strength is in a range from tens to hundreds of millimoles per kilogram and re-expansion of the coils with a further increase of ionic strength up to a region of the saturated saline solutions. The competition between monovalent and multivalent counterions simultaneously present in solutions strongly affects conformations of PE chains even at a very small fraction of multivalent counterions. Shrinkage of PE coils is steeper for multivalent counterions than for monovalent counterions. However, the re-expansion is only incremental in the presence of multivalent counterions. Extended adsorbed coils at low salt concentrations and at very high concentrations of monovalent salt exhibit conformation corresponding to a 2D coil with 0.95 fraction of bound segments (segments in "trains") in the regime of diluted surface concentration of the PE. Shrunken coils in the intermediate range of ionic strength resemble 3D-globules with 0.8 fraction of trains. The incrementally re-expanded PE coils at a high ionic strength remain unchanged at higher multivalent salt concentrations up to the solubility limit of the salt. The formation of a strong PE complex with multivalent counterions at high ionic strength is not well understood yet. A speculative explanation of the observed experimental result is based on possible stabilization of the complex due to hydrophobic interactions of the backbone.

Determination of the water sorption isotherms for cassava flour

<p>Cassava is a nourishing food and widely consumed in Brazil in the form of flour. However, it is necessary a more detailed study of the physical-chemical properties of the cassava flour and thus optimize its processing steps such as drying. The objective of this work was to obtain the water sorption isotherms for the cassava flour at different temperatures. For this aim, experiments were carried out using the static method with saturated saline solutions at 30, 40, 60 and 70°C. The data obtained were adjusted on available literature equations using the software MATLAB R2007b. The results indicate that the temperature ranging from 40 to 70°C does not significantly influence the cassava flour equilibrium moisture. It was also found  that both Halsey and Smith's isotherm can be used to predict the cassava flour equilibrium moisture. Furthermore, it was observed a small variation in the equilibrium moisture for water activity ranging from 0 to 0.8.</p><p> </p><p>DOI: http://dx.doi.org/10.14685/rebrapa.v1i2.21</p>

Comparative evaluation of the effects of an alum-containing mouthrinse and a saturated saline rinse on the salivary levels of Streptococcus mutans

The literature is replete with studies establishing Streptococcus mutans as a major player in the formation of pit and fissure caries in all dentitions. Salivary bacterial levels in turn are related to the number of colonized surfaces. Therefore, decreasing the salivary levels of S. mutans would have a great benefit in decreasing the incidence of dental diseases. Keeping in mind the potential antimicrobial effects of saturated saline and alum solutions, the present study was attempted to compare and evaluate the effects of saturated saline rinse and 0.02 M alum mouthrinse on salivary S. mutans levels in children. The investigation was a double-blind, stratified comparison of three parallel groups of children who used either saturated saline rinse, 0.02 M alum mouthrinse or distilled water (placebo) rinse twice daily under professional supervision for a 21-day period. A total of three saliva samples were taken from each individual - at baseline, on the 10 th day and on the 21 st day, and colony counts of S. mutans were determined. All data were subjected to statistical analysis using Wilcoxon's Signed Ranks Sum and Mann-Whitney "U" test. Children using saturated saline rinse and alum rinse showed statistically significant reductions in salivary S. mutans counts after 10 days and also after 21 days. After 21 days, the saturated saline rinse and alum rinse groups showed statistically significant differences over the placebo rinse group. Again, the alum rinse group showed a statistically significant difference over the saturated saline rinse group.

A Capacitive Humidity Sensor Based on Multi-Wall Carbon Nanotubes (MWCNTs)

A new type of capacitive humidity sensor is introduced in this paper. The sensor consists of two plate electrodes coated with MWCNT films and four pieces of isolating medium at the four corners of the sensor. According to capillary condensation, the capacitance signal of the sensor is sensitive to relative humidity (RH), which could be transformed to voltage signal by a capacitance to voltage converter circuit. The sensor is tested using different saturated saline solutions at the ambient temperature of 25 °C, which yielded approximately 11% to 97% RH, respectively. The function of the MWCNT films, the effect of electrode distance, the temperature character and the repeatability of the sensor are discussed in this paper.

A Rockfill Triaxial Cell with Suction Control

Abstract This paper describes the development of a new triaxial cell specifically built to test coarse granular material under partially saturated conditions. The partial saturation is achieved by imposing a total suction that is correlated with the relative humidity. Relative humidity control was achieved by water vapor transfer using a forced convection system, which is driven by an air pump transporting the air humidity to the sample, and it is controlled by saturated saline solutions placed in a vessel. A double-wall cell was designed to monitor global volume changes of the material on compression and shearing. In addition, the cell uses a novel technique to measure local axial and radial deformations. The use of both global and local measurements allows detecting experimental problems such as membrane penetration on isotropic compression and shearing, as well as membrane sliding on shearing at low confining stresses. Selected test results are presented to show the capability of the cell during isotropic compression and shearing made with strain and stress control. The results of the test with strain control show a nonlinear increase in strength and dilatancy of the material in relation to the decrease of the relative humidity. Also they have a tendency to reach the critical state, and it can be seen that such a critical state line is a function of the relative humidity. Under a constant deviator stress, a collapse test of the rockfill was carried out and the results showed that the deformation depends strongly on the time. Furthermore, it is larger than that produced by making a test under saturated conditions, commonly taken as final reference.