Moisture Sorption Isotherms Research Articles

Equilibrium Moisture Sorption Isotherms of Aspirin

Equilibrium Moisture sorption isotherms are very important in drying and storage analysis. Experimental moisture equilibrium data (adsorption and desorption) of Aspirin were determined using the static method of saturated salt solutions and that by exposing the material to different conditions of temperatures and water activities. Three different temperatures (25, 30, 40Cº) and water activities in the range of (6.3- 83.6%) were used. The results showed that the equilibrium moisture content increased with the increase in water activity at any temperature and decreased with temperature increase at constant water activity. The water activity increases with increasing in temperature when moisture content was kept constant. The sorption isotherm curves are of type II according to Brunauer`s classification. The hysteresis effect was not distinctly expressed only for equilibrium sorption values of Aspirin at 25ºC. The experimental results were fitted to two sorption models (GAB and Henderson).The average relative deviation between the experimental and calculated data were obtained to select the best model. The GAB and Henderson models, obtaining values of 3.54 and 1.42 % average relative deviation and coefficient of regression of 0.98 and 0.977 respectively. The Henderson model was found to be the best fit out of the two models to predict the sorption behavior of Aspirin.

Moisture sorption isotherms and storage study of spray-dried probiotic finger millet milk powder

Moisture sorption isotherms provide information on the interaction between food and the storage environment. The sorption isotherms of spray-dried probiotic finger millet milk powder were studied with different salt solutions at different temperatures (25–45 °C). The storage behavior and quality parameters of the powder were characterized at different storage conditions and packaging materials. The isotherm data were tested with empirical models. The Peleg model was best fitted for the sorption isotherm study at 25 °C with the highest adj. R2 (0.999) confirming type III isotherm. The powder flow properties were in an acceptable range. The powder stored at 4 °C and 25 °C exhibited 56 and 35 days of shelf life, respectively, with acceptable probiotic viability of 6 log CFU/g. A laminated aluminum pouch was best suited as a packaging material to store the probiotic powder. The results could be adopted for the packaging and bulk storage of probiotic finger millet milk powder.

Reference isotherms for water vapor sorption on nanoporous carbon: results of an interlaboratory study

This paper reports the results of an international interlaboratory study sponsored by the Versailles Project on Advanced Materials and Standards (VAMAS) and led by the National Institute of Standards and Technology (NIST) on the measurement of water vapor sorption isotherms at 25 °C on a pelletized nanoporous carbon (BAM-P109, a certified reference material). Thirteen laboratories participated in the study and contributed nine pure water vapor isotherms and four relative humidity isotherms, using nitrogen as the carrier gas. From these data, reference isotherms, along with the 95% uncertainty interval (Uk=2), were determined and are reported in a tabular format.

Glacial rock flour reduces the hydrophobicity of Greenlandic cultivated soils

AbstractSoil water repellency (WR) is ubiquitous across Greenlandic cultivated fields, which may constrain agricultural production. Fine‐grained glacial rock flour (GRF) is available in the surrounding landscape, which could serve as a soil amendment. We tested whether the application of GRF (rates of 0, 50, 100, 300, and 500 ton ha−1) reduced the WR across two field trials in South Greenland. The field trials, Upernaviarsuk (UP) and South Igaliku (SI), differed in clay (UP: 0.05–0.11 kg kg−1; SI: 0.03–0.05 kg kg−1) and organic carbon (OC) contents (UP: 0.04–0.13 kg kg−1; SI: 0.01–0.03 kg kg−1). We measured WR across gravimetric water contents (W) from oven‐dry to the W where WR ceased (WNON) to obtain whole WR‐W curves. Most soils became hydrophilic around air‐dry conditions at application rates of ≥300 ton ha−1, likely due to increased clay:OC ratios. Application rates of ≥300 ton ha−1 generally reduced the trapezoidal integrated area of the WR‐W curve (WRAREA), WNON, and WR after heat treatments at 105°C (WR105) and 60°C (WR60). The WR105 was significantly reduced in both fields at 500 ton ha−1, while WR60 was significantly reduced in UP at application rates of ≥300 ton ha−1. The GRF effects were masked by texture and OC variations. Normalizing WRAREA to the water vapor sorption isotherms (utilizing the Campbell‐Shiozawa model) revealed that GRF consistently reduced the normalized WRAREA. The SI field showed the largest reduction in the normalized WRAREA, likely due to its lower OC and clay contents. Thus, GRF could reduce WR across two Greenlandic field trials.

Ultrasound assisted extraction of red cabbage and encapsulation by freeze-drying: moisture sorption isotherms and thermodynamic characteristics of encapsulate.

Ultrasound assisted extraction of red cabbage and encapsulation by freeze-drying: moisture sorption isotherms and thermodynamic characteristics of encapsulate.

Thermal Expansion of Cement Paste at Various Relative Humidities after Long-term Drying: Experiments and Modeling

The coefficient of thermal expansion (CTE) of cement paste is an essential parameter for estimating cracks of cement-based structures, including under normal operating conditions. The CTE of low-heat Portland cement pastes dried for a long term at various relative humidities were measured by applying trapezoidal temperature history. The measured CTE was a convex function when displayed versus relative humidity and was highest at the relative humidity of 58%. At the relative humidity of 11%, the CTE was similar to the one of the fully dried sample. Based on a drying shrinkage model in the literature that classifies pore water as free liquid water and adsorbed water, we computed pore pressure change and corresponding strain, from which the CTEs were estimated. The microstructural rearrangements of cement paste due to long-term drying were taken into account by obtaining pore size distributions from water vapor sorption isotherm. The CTEs predicted with the model agree well with the measured ones.

Mathematical Models of Moisture Sorption Isotherms of Grains Sorghum (Sorghum bicolor (L.) Moench)

1U. of K. J. Agric. Sci. 22(1), 1-12, 2014Mathematical Models of Moisture Sorption Isotherms of GrainsSorghum (Sorghum bicolor (L.) Moench)Eman Abdu Abdalla1 , Mohamed Ayoub Ismail and AbdelmoniemElamin Mohamed2Department of Agricultural Engineering, Faculty of Agriculture,University of Khartoum, SudanAbstract: The objective of the study was to fit or test the experimentaldata of adsorption and desorption isotherms of grains sorghum The studywas carried out at the Department of Agricultural Engineering, Faculty ofAgriculture, University of Khartoum and the Food Processing ResearchCenter, Shambat, Sudan, during January 2007 - March 2008. Fourmathematical models namely modified Henderson, modified Chung-Pfost, modified Oswin and modified Halsey were used to predict sorptionisotherms. The adsorption and desorption isotherms were determinedusing standard static gravimetric method, six levels of water activitiesrang 0.112- 0.865 were maintained by using saturated salt solutions insideair-tight glass desiccators, while incubators were used to maintain three aconstant temperature namely 25oC,35 oC and 45oC. A non-linearregression analysis was used to evaluate the parameters of the fourselected models. The models were compared by using statisticalparameters: mean relative percentage deviation (P%), standard error ofestimates (Es), coefficient of determination (R2 ) and randomness ofresidual plots of difference between measured and predicted values. Forthe mathematical models, the results indicated that the modified Chung-Pfost model satisfactorily predicts the adsorption and desorptionisotherms of grains sorghum

Moisture Sorption Isotherms and Thermodynamic Properties of Biodegradable Polymers for Application in Food Packaging Industry.

This work aims to evaluate the influence of two starch-based materials (B16 and B20) on the moisture sorption isotherms, determined at 30, 40, and 50 °C, where B16 contains 5% (w/w) more starch than B20. Thermodynamic functions (differential enthalpy (∆Hdif), differential entropy (∆Sdif), integral enthalpy (Δhint), integral entropy (ΔSint), free Gibbs energy (∆G), and spreading pressure (φ)) were used to understand the water-binding behaviors and the energy requirements to remove the moisture content from the surface of these materials. The moisture sorption isotherms exhibited type III behavior, and the Guggenheim-Anderson-de Boer (GAB) model was the most suitable to fit the experimental moisture adsorption data. The adsorption isotherms of microparticles were enthalpy-controlled, with isokinetic temperature values of 221.45 and 279.77 K for B16 and B20, respectively, being higher than the harmonic mean temperature (312.94 K). The values of ∆G were positive (45.274 and 44.307 kJmol-1 for B16 and B20, respectively), indicating a non-spontaneous process. The spreading pressure values increased with increasing water activity (aw) for all isotherms. Higher values of ∆Hdif and ∆Sdif obtained from B16 confirmed its higher number of sorption sites available for binding with water molecules when compared to B20, making it less suitable for application in the food packaging industry.

Theoretical model of water vapor absorption–desorption equilibrium of concrete considering the effect of temperature

The water vapor sorption equilibrium relationship of concrete determines the water transport rate in it, which affects the concrete structure’s durability. This study applied modeling to predict the water vapor sorption isotherms affected by temperature. Combined with the experimental data, the theoretical model predicted the effect of temperature on water vapor absorption–desorption isotherms and the hysteresis of desorption isotherms. The results showed that the hysteresis of capillary pores is larger than that of gel pores. An increase in temperature decreases the percentage of water hysteresis in gel pores, and increases the water hysteresis in small capillary pores.

Anisotropic wood–water interactions determined by gravimetric vapor sorption experiments

Gravimetric vapor sorption experiments were performed on beech wood samples to determine the directional permeability, diffusion and sorption coefficients in the three orthotropic wood directions. Dynamic Vapor Sorption (DVS) experiments allowed for the direct evaluation of the diffusion coefficient from the analysis of the kinetic sorption profile using a double stretched exponential model with values ranging from 0.10 × 10−10 to 1.52 × 10−10 m2/s and depending on the wood direction of the sample and the RH-values. Moisture sorption isotherms (MSIs) were constructed and fitted to a modified Guggenheim-Anderson-de Boer and a Sorption Site Occupancy model, which allowed for the calculation of the sorption coefficient which was found to be between 2.4 and 3.0 mol/(m3 Pa). Dynamic Vapor Transport (DVT) experiments were performed to calculate the permeability coefficient from the vapor flow rate and it ranges between 0.56 × 10−10 and 4.38 × 10−10 mol/(m s Pa) as a function of the flow direction and RH conditions. These results indicate that such an experimental approach is suitable for determining wood–moisture interactions.

Moisture sorption isotherms of whole and fractionated date-pits: Measurement and theoretical modelling

Moisture sorption properties of whole date-pits (WDP) and three fractionated date-pits; defatted date-pits (DDP), residue (REP) and supernatant (SUP) fractions were studied. Sorption isotherms were measured using Differential Thermal and Humidity chamber at different temperatures (10, 30, 50, 70 and 90 °C) and relative humidity ranged from 0.05 to 0.9. Crossovers of isotherm curves were observed for all fractions between different temperatures. At 30 °C, BET-monolayers of WDP, DDP, REP and SUP were 4.9, 4.2, 3.8 and 3.2 g/100 g ds, respectively. The complete isotherms (i.e. 0.05–0.90 water activity) were modelled by GAB with high coefficient of determination (i.e. 0.944 to 0.999). In the cases of WDP and DDP, the isosteric heat plots showed increasing trends with the decreased moisture and peaks at moisture 0.025 and 0.040 g/100 g ds. Unlike all fractions, DDP isokinetic temperatures Tis (i.e. 97.4 °C) was lower than isobound temperatures Tib (i.e. 145.0 °C) indicating complete removal of bound water occurred at higher temperature as compared to the temperature when all reactions reached at the same. The moisture sorption isotherm characteristics could be used in determining the end point of drying and storage stability as well as packaging design of the date-pits and their fractions.

A new analytical method to predict permeability properties of cementitious mortars: The impacts of pore structure evolutions and relative humidity variations

This research develops analytical models in respectively describing the water vapour sorption isotherm and permeability properties based on a probabilistic method for pore size distribution and two transformation models for pore radius of cementitious mortars. By adopting the water vapour sorption model, the water saturation degree in cement-based materials is acquired and the influence of ions on water vapour sorption isotherm is modelled by introducing the water activity in thermodynamic equilibrium relation between liquid and vapour phases. The results reveal that the presence of ions increases the susceptibility of mortars to be water-saturated. Additionally, intrinsic permeability and relative permeability of mortars are predicted and the reliability of the permeability model is investigated. Finally, the permeability model is further extended considering the evolutions of pore structure and variations of relative humidity when cementitious mortars are subjected to precipitation and dissolution, which attempts to give an understanding of interactions between permeability and evolved pore structure that are not yet very commonly mentioned in literature. Modelling results show that both pore size distribution and relative humidity significantly affect permeability properties of mortars, especially when the water saturation degree is large. This research provides a novel insight into quantifying the permeability of mortars undergoing pore structure degradations.

Modelling Moisture Sorption Isotherms of Superabsorbent Polymer Fabric for Desiccant Drying of Crops

Desiccants are important in the drying of temperature-sensitive grains such as seeds for planting. Superabsorbent polymers (SAPs) have previously been identified for possible application in the drying of crops. Applying the gravimetric technique to measure the sorption isotherms and the effectiveness of the desiccant in crop drying was determined at temperatures 20, 25, 30, 35, 40, 45, 50, and 55°C. Using R statistical software, eleven sorption isotherm models were fitted to the experimental data using the nonlinear regression functions. The coefficients of each model were obtained. The modified Freundlich, modified Henderson, and modified Oswin models best predicted the experimental data for the study temperature range. Using symbolic regression and nonlinear regression in R software, four mathematical models were obtained. R software codes were assembled for the analysis of sorption isotherm models. Compared to the existing models, the developed models were found to give a more statistically accurate association between the temperature, moisture content of SAP fabric, and relative humidity.

Convective Drying of Purple Basil (Ocimum basilicum L.) Leaves and Stability of Chlorophyll and Phenolic Compounds during the Process.

This study evaluated the effect of convective drying on the degradation of color and phenolic compounds of purple basil (Ocimum basilicum L.) leaves, and the hygroscopic behavior of dried leaves. The fresh leaves underwent drying at 40 °C, 50 °C, 60 °C, and 70 °C. Degradation of chlorophyll, flavonoids, and phenolic compounds were evaluated during drying and the hygroscopicity was evaluated through the moisture sorption isotherms. The drying mathematical modeling and the moisture sorption data were performed. The effective diffusivity for the drying increased from 4.93 × 10−10 m2/s at 40 °C to 18.96 × 10−10 m2/s at 70 °C, and the activation energy value (39.30 kJ/mol) showed that the leaves present temperature sensibility. The leaves dried at 40 °C had less degradation of phenolic compounds and color variation, but the drying process was too slow for practical purposes. Modified Page, Diffusion Approximation, and Verna models had excellent accuracy in drying kinetics. The isotherms showed that, in environments with relative humidity above 50%, the purple basil leaves are more susceptible to water gain, and at 8.83 g H2O/100 g db moisture, it guarantees the microbiological stability of the dried leaves. The Oswin model was the most suitable for estimating the moisture sorption isotherms of the dried leaves.

Probabilistic multi-objective optimization of wood torrefaction conditions using a validated mechanistic model

This paper uses a comprehensive computational model to propose optimal wood torrefaction conditions by probabilistic optimization. Its main outcome is to propose tailor-made heat treatment conditions (temperature levels-duration of mild pyrolysis at temperature levels ranging from 200 to 300 °C) to meet users’ expectations in terms of overall mass loss, duration and homogeneity of treatment. To this purpose, beech wood boards were torrefied with a usual 3-steps treatment schedule (drying, heating and cooling) under contrasting configurations in a well-instrumented device. The heterogeneity of the treatment within the wood sample was assessed through X-ray attenuation profile and water vapour sorption isotherm. These results allowed the model to be validated. In particular, it predicts the evolution of the mass loss and internal temperatures with good accuracy, including the temperature overshot. The results highlight the need to adjust the heat treatment schedule to each input parameter such as the wood piece dimensions and its initial moisture content or density, in order to limit the effect of exothermic reactions. The torrefaction model was then embedded in a probabilistic optimization process. A case study demonstrates the ability of the model to propose an alternative 3-steps treatment schedule able to reach the target mass loss while controlling the temperature overshot within the wood piece.

Active packaging of chitosan film modified with basil oil encapsulated in silica nanoparticles as an alternate for plastic packaging materials

Active packaging based on biomaterials and essential oils is an alternate for plastic ones. But, essential oils are chemically and physiologically labile, and they have strong scents, limiting their use as antimicrobial additives in food. Thus, in this investigation, basil oil was encapsulated in silica nanoparticles (basil oil@SiNPs) and combined with chitosan films (basil oil@SiNPs@chitosan). Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), surface area and Brunauer-Emmett-Teller (BET) analysis, encapsulation and loading % were used to evaluate basil oil@SiNPs. The surface area of SiNPs decreased from 59.006 to 43.86 cm2/g due to basil oil encapsulation. The encapsulation and loading % were 81.96, 65.87, 48.48 and 43.13, 37.64, 33.44% for 2, 1.5, and 1 mL of basil oil, respectively. Fourier-transform infrared (FT-IR), XRD, thermogravimetric analysis (TG), mechanical, wettability, water vapor permeability (WVP), oxygen permeability (OP) features; water vapor sorption isotherms and antimicrobial inhibition tests were used to describe the produced basil oil@SiNPs@chitosan films. Water contact angles and activation energy increased from 89.0° to 110.9° and −11.97 to −20.40 kJ/mol, respectively after addition of basil oil@SiNPs. However, WVP decreased from 5.9580 × 10−1±0.33 to 4.2413 × 10−1±0.55 g.mm.m−2.h−1.kPa−1 and OP increased from 4.094 × 10−4±0.52 to 6.715 × 10−5±0.32 (g.m−2.day−1.atm−1). The four models Guggenheim–Anderson–de Boer (GAB), Smith, Henderson and SIPSI were suitable for describing the moisture sorption of basil oil@SiNPs@chitosan films. Basil oil@SiNPs has antimicrobial inhibition against Gram positive and negative bacteria, pathogenic yeast.

Using water vapour and N2 isotherms to unveil effects of SCMs on nanopores and evaluate hydration degree

Nanopores are critical for the durability of cement-based materials, but the refinement of these pores by SCMs is yet to have a clear understanding. This paper studied effects of the water–binder ratio, SCMs and the drying on the distribution of nanopores using water vapour and N2 sorption isotherms. Results show that data of water vapour sorption can be used for a practical evaluation of the hydration degree of SCMs with thermodynamic simulation. Fly ash increases the volume of large gel and capillary pores. It lowers the difference between the sorption of water vapour and N2. Slag evidently refines the nanopores by increasing the volume of ink-bottle gel pores with an interlayer-size neck. A higher w/b produces more large pores to reduce the effect of drying. Removal of water induces contraction of interlayer and reduces gel pores volume, which causes large difference between sorption of water vapour and N2.

Noninvasive Moisture Detection in Lyophilized Drug Product Using NIR Spectrometer and Headspace Moisture Analyzer

Utilization of laser headspace and near-infrared (NIR) methods provides rapid and non-destructive approaches for moisture detection of lyophilized drug products to facilitate lyophilization formulation characterization and process development. In the present study, the NIR method was developed based on a partial least square regression (PLSR) model calibrated and validated with Karl Fisher (KF) data, whereas the laser headspace method was developed with aid of dynamic vapor sorption (DVS) method so that the water vapor pressure measured from the headspace of a lyophilized drug product vial can be converted directly to water content value through the water vapor sorption isotherm of the lyophilized drug product bypassing KF calibration. The water contents of lyophilized samples obtained from both methods agreed well with KF data, with a root mean squared error of prediction (RMSEP) of less than 0.15%. The pros and cons of NIR and laser headspace method were evaluated. The results suggest that traditional off-line KF method can be potentially replaced by at-line laser headspace method combined with water sorption isotherm data from DVS. Further studies may be needed to evaluate the quantitation limit and generality of this method to a variety of lyophilized formulations.

Moisture Sorption Isotherms of Sweet Cherry (Prunus Avium L.): Comparative Study of Kinetics and Thermodynamic Modeling of Five Varieties

Moisture sorption isotherms of five sweet cherry cultivars (Prunus avium L.) at three temperatures of 30°C, 40°C, and 50°C, and water activity range of 0.057-0.898 were determined using the static gravimetric method. The sorption isotherms of all cultivars decreased with increasing temperature, and they all exhibited type II behavior according to the classification of IUPAC (International Union of Pure and Applied Chemistry). The isosteric heat of sorption, differential entropy, spreading pressure, and water surface area were determined, and the energy associated with the sorption processes was defined. The curves were fitted to GAB, PELEG, and ENDERBY models, and the GAB model gave the best fit for the whole set of data. The enthalpy-entropy compensation proved that the process occurs spontaneously and is fully controlled the enthalpy. The spreading pressure value varied with temperature in all sweet cherry cultivars in both the desorption and adsorption processes. The average surface area varied from 78.05 to 214.02 m2/g for desorption and from 49.0 to 204.4 m2/g for adsorption from 30 to 50°C.

Comparison of shrinkage and mass change of hardened cement paste under gradual drying and rapid drying

To identify the impact of drying rate on mechanisms of drying shrinkage, two hardened cement paste (hcp) samples were prepared. Mature samples were dried directly at the target relative humidity (RH), “rapid drying”, or at RH decreasing from 95% step by step till 11%, “gradual drying”. When comparing the relation of mass change versus drying shrinkage, at high RH range over 80%, gradually dried samples showed less mass change for same amount of shrinkage comparing to rapid drying samples. For the range of RH of 80%-40%, the incremental values of both mass change and drying shrinkage were same for two drying methods. The specimens were characterized by XRD, TG-DTA and water vapor sorption isotherms. By combining the results with findings in the literature, we postulated that an additional part of drying shrinkage is activated when dried at high relative humidity for a longer time and we attributed this additional part to gel pores of calcium silicate hydrates.