Equilibrium Moisture Sorption 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.

Preparation and characterization of crosslinked starch-albumin films for coating of prednisolone tablets for use in Covid-19 related respiratory disease

Steroidal products have been found useful in inflammations associated with Covid 19. Prednisolone is one readily available steroid, which is often found as uncoated normal release tablets. Modified release prednisolone may be desirable in Covid 19 for sustained actions. This is expected to reduce dosing frequency and enhance compliance. This study is concerned with development of controlled release prednisolone using coating technology with bio-compatible, cross-linked starch-albumin films. Starches and proteins are excellent film formers with good flexibility, transparency, and bio-compatibility. The cross-linked starch-albumin films were prepared using glycerol as the plasticizer: starch (A), starch-albumin (B), starch-albumin cross-linked with formaldehyde at 1 % (C), 5 % (D) and 10 % (E). Equilibrium moisture sorption (EMS) at 100 % relative humidity, equilibrium swelling (ESC) in buffer solutions of pHs 2, 7 and 9, and DSC thermal properties were evaluated. In-vitro drug release from the film coated prednisolone tablets were evaluated in 0.1N HCl, water and phosphate buffer 8.0 as dissolution media. Films showed ESC in the order A>D>E>B>C; D>C>A>E>B and A>D>C>B>E in acidic, neutral and alkali media respectively. EMS was in the order B>E>A>D>C; with slight shift in the melting temperatures. In-vitro release at 240 min varied from 78 to 117 % (E>D>C>A>B); 19 to 60 % (D>B>C>E>A) and 49 to 60 % (B>A>C>D>E) in 0.1N HCl, water and PBS respectively. Cross-linking improved the stability and swelling of films. The in-vitro release in alkaline medium suggests their usefulness for controlled drug delivery. New pH-responsive polymers, with improved physicochemical properties for coating prednisolone tablets were developed.

Study on the hygroscopic performances of poplar wood fiber biomass brick

Poplar fiber biomass brick is an energy-saving and environmentally friendly biomass building material developed in recent years. It has good hygroscopic performance, can adjust indoor air humidity, helps reduce building energy consumption for dehumidification and humidification, and improves indoor air comfort. This paper studies the hygroscopic performance of poplar fiber brick from the microscopic pore structure experiment, nitrogen physical adsorption experiment, equilibrium moisture content experiment, moisture sorption and desorption cycle experiment, and water vapor transmission experiment. The model of the sorption-desorption curve of poplar fiber biomass brick at 23 °C is established. Moreover, the ideal moisture buffering value (MBV) of poplar fiber brick and the ideal and practical MBV values under the experimental procedures of this article are calculated. The results show that the Peleg model is most suitable for poplar fiber brick's moisture absorption and desorption curve at 23 °C. The MBV value is the “Excellent” level and has good moisture sorption and desorption performance. The obtained data and models provide potent data support for promoting and applying biomass bricks and theoretical model research.

Modeling and Thermodynamic Analysis of the Water Sorption Isotherms of Cottonseed Products

Due to their hygroscopic characteristics, equilibrium moisture contents of agricultural products and byproducts are important factors of their quality. Defatted cottonseed meal (CSM), washed cottonseed meal (WCSM) and cottonseed protein isolate (CSPI) can be used as energy and protein sources of animal feedstuff or industrial raw materials. Information on their moisture adsorption behaviors is needed for their storage conditions and quality control. Thus, this work measured the equilibrium moisture sorption isotherms of CSM, WCSM and CSPI, at 15, 25, 35 and 45 °C. When the moisture contents of the samples were compared at a constant temperature, the general trend of decreasing moisture content was in the order of CSPI < WCSM < CSM for water activity <0.6, but the trend reversed to the order of CSM < WCSM < CSPI for water activity >0.6. Relevant sorption isotherm equations were tested for accurate fit to the moisture adsorption data. Modelling results indicated that the G.A.B. (Guggenheim-Anderson-de Boer) model was a consistently good fit for the data among all sample types and all temperatures. This work provides some insight on designing or selecting appropriate procedures for the handling, aeration, storage and processing of these cottonseed meal products. In particular, it suggests that moisture content should be kept at around 8% for safe storage of these products at room temperature (around 25 °C) but below 5% when they are exposed to higher temperature conditions (e.g., >45 °C).

Characterization of Archaeological European White Elm (Ulmus laevis P.) and Black Poplar (Populus nigra L.)

The present study aims at characterization of freshly-cut and archaeological European white elm and poplar. The archaeological elm sample was buried at a depth of 8–10 m inside of soil with age approximation of ~1800–2000 years old, and the archaeological poplar sample was a part of a boat in a freshwater lake or river with age estimation of ~1000–1200 years. Alteration in the chemical structure of the elm and poplar samples due to the ageing process were confirmed by X-ray photoelectron spectroscopy (XPS). Both archaeological wood (AW) samples illustrated considerably lower cellulose crystallinity than the fresh samples as determined by X-ray diffraction. The sorption behavior of AW and fresh wood (FW) samples were evaluated by means of dynamic vapor sorption (DVS) analysis. Results exhibited a higher equilibrium moisture content (EMC) and sorption hysteresis values in archaeological elm and poplar as compared with the fresh samples. Higher hydrophilicity of the AW samples than the FW ones is attributed to their higher amorphous structure. The extensive degradation of AW samples were also confirmed by scanning electron microscopy (SEM) micrographs.

Tillandsia-Inspired Hygroscopic Photothermal Organogels for Efficient Atmospheric Water Harvesting.

Tillandsia species with degenerated roots have evolved into hygroscopic leaves that absorb moisture from air. This interesting biological adaptability has inspired us to develop an integrated hygroscopic photothermal organogel (POG) to achieve a solar-powered atmospheric water harvesting (AWH). The well-designed hydrophilic co-polymeric skeleton is fabricated to accommodate hygroscopic glycerin medium, which enables the POG self-contained property, mechanically flexibility and synergistic enhancement of moisture sorption. The integration of interpenetrated photothermal component of poly-pyrrole-dopamine (P-Py-DA) can endow the POG an efficient solar-to-thermal property for controllable solar-driven interfacial water releasing. The integrated POG has an equilibrium moisture sorption of 16.01 kg m-2 at the RH of 90 %, and daily water production as high as 2.43 kg m-2 day-1 is achieved in actual outdoor experiments.

Acacia Gum as a Natural Anti-Plasticizer for the Production of Date Syrup Powder: Sorption Isotherms, Physicochemical Properties, and Data Modeling.

The thermoplastic and hygroscopic behaviors of date syrup (DS) challenge the DS drying process. In this context, DS was mixed with 30%, 40%, 50%, and 60% acacia gum (AG) and subjected to a drum dryer. The chemical composition, bulk density (pb), caking degree (CD), glass transition temperature (Tg), and color values of DS powders were studied. The sorption isotherms were also obtained and compared to that of those predicted by mathematical models. According to the results, increasing the AG concentration enhanced the moisture content, pb, brightness, and Tg while it reduced the CD and equilibrium moisture sorption. All DS powders had type III isotherm behavior, i.e., similar to high-sugar foods. Guggenheim-Anderson-de Boer (GAB) and Peleg models were found to be suitable for fitting the experimental data and these models explained the monolayer moisture content decrease with increasing AG concentration. These results of the present study, for the first time, verified that the AG can be used as a natural anti-plasticizer agent for DS powder production.

Models of Sigmoid Equilibrium Moisture Sorption Isotherms With and Without the Monolayer Hypothesis

Among the numerous moisture sorption models, the GAB, an expanded version of the BET equation originally derived for inert gases adsorption on solid surfaces, is the most prominent. Both models are based on distinction between the adsorbate molecules settling on the bare surface in a monolayer (Langmuir adsorption) and those settling on already absorbed molecules forming multilayers. The BET theory has been successfully used to determine porous catalysts’ and fine powders’ specific surface area to this day. In contrast, applying the BET and GAB equations to water vapor sorption by solid foods (and non-foods) has at least three major problems: The calculated food powders’ specific surface area is independent of their particle size; the expected shoulder in foods’ enthalpy vs. moisture plot is absent; and there is a huge discrepancy between the specific surface areas calculated from moisture sorption isotherms and those of nitrogen. An alternative modeling approach posits the non-existence of a water monolayer, and suggests that moisture sorption is governed by at least two simultaneous mechanisms having different scaling exponents. Mathematical analysis and comparison of the resulting sorption models with the GAB equation show that they produce practically indistinguishable moisture sorption isotherms even with the same number of adjustable parameters. They also demonstrate that the sigmoid shape of a moisture sorption isotherm does not contain enough information to identify and quantify the underlying sorption mechanisms, and that a model’s good fit by statistical criteria in itself does not validate mechanistic assumptions.

The effect of thermo-mechanical treatment of moso bamboo (Phyllostachys Pubescens) on its sorption and physicomechanical properties

The aim of this study was to examine some properties of heat-treated (200 °C) and densified (treated) bamboo. Density (ρ), equilibrium moisture content (EMC), sorption hysteresis (H), swelling (S), and Brinell hardness (HB) were examined and compared with untreated bamboo (Phyllostachys sp.) and common oak (Quercus robur L.). The density of heat-treated bamboo (ρ = 1170 kg/m3) was higher than that of untreated bamboo (ρ = 850 kg/m3) and oak wood (ρ = 670 kg/m3). The sorption isotherms were parameterized with the Guggenheim-Anderson-deBoer (GAB) model. Treated bamboo showed lower EMC than untreated bamboo and oak wood in the entire hygroscopic range. The swelling anisotropy index of treated bamboo was the lowest (1.09). The mean HB of treated bamboo (HB=132 MPa) was significantly higher than that of oak and untreated bamboo.

Effects of internal structure and chemical compositions on the hygroscopic property of bamboo fiber reinforced composites

Abstract As a kind of bioresource material, the hygroscopic property of the Bamboo Fiber Reinforced Composite (BFRC) plays the key role in their physical, mechanical and adhesive interface properties which further seriously influence both the indoor and outdoor applications. Herein, the effects of internal structure and chemical compositions on the hygroscopic property of the BFRC was systematically investigated. The results showed that the Equilibrium Moisture Content (EMC) values and sorption rate of the BFRC with the density of 1.02 g/cm3 were much lower than those of the raw bamboo at the same Relative Humidity (RH) level. The decrease in the hygroscopic property for the BFRC was related to the changes in physical structure and chemical properties. Physically, the internal cellular structures with the large diameter and the thinner wall were broken and compressed together to enhance the bulk density and to decrease the porosity. This reduction in the internal voids inhibited the entrance of water molecules and decreased the hygroscopic capacity of the BFRC. Simultaneously, the Phenol Formaldehyde (PF) resin, which was impregnated into ground tissue lumens, intercellular gaps and pits, covered the cell wall surface and protected the raw bamboo substrate from water molecules. Meanwhile, both the thermal treatment and PF resin impregnation changed the chemical compositions, which caused the reduction of the hygroscopic groups in the BFRC contributing to the decrease of the moisture sorption.

Dimensional stability and hygroscopic properties of waterlogged archaeological wood treated with alkoxysilanes

Archaeological waterlogged elm wood was treated with methyltrimethoxysilane (MTMS) and (3-mercaptopropyl)trimethoxysilane (MPTES), respectively, and anti-shrink efficiency and sorption properties of the impregnated wood samples were determined. The applied impregnants stabilized wood dimensions efficiently enough, i.e. the obtained anti-shrink efficiency was 81 and 98% for MTMS- and MPTES-treated wood, respectively. Both alkoxysilanes can be considered as potential new consolidants. Hygroscopic properties of untreated and impregnated wood were investigated with the DVS experiments. The application of MTMS and MPTES reduced wood equilibrium moisture content (EMC) and sorption hysteresis e.g. hysteresis relative change was −83.7 and −73.7% for MTMS- and MPTES-treated wood, respectively. The EMC reduction was observed in the whole hygroscopic range and it was primary due to the monolayer capacity decrease to 50 and 30% of the value for untreated wood and observed for adsorption and desorption modes, respectively. The DVS experiments revealed chemical instability of the MTMS-wood system which was neutralized after the cyclic sorption. The possible scenarios of the interaction of both alkoxysilanes with wood structure were discussed.

Water vapor sorption properties of TEMPO oxidized and sulfuric acid treated cellulose nanocrystal films

For cellulose nanocrystal film, water adsorption is extremely important for its product performance. For gaining a deeper understanding of hygroscopic behavior, two cellulose nanocrystal films, such as TEMPO oxidized cellulose nanocrystal film (TOCNF) and sulfuric acid treated cellulose nanocrystal film (SACNF) were investigated using dynamic water vapor sorption apparatus. During the water vapor sorption process, the running time, real-time sample mass, target relative humidity (RH), actual RH and real-time temperature were all collected. Through the comparison of these collected data, significant differences in the equilibrium moisture content, sorption hysteresis and sorption kinetics were confirmed. It was important to note that TOCNF and SACNF had equilibrium moisture contents of 28.2% and 22.8, respectively, at a RH of 95%. Then, using parallel exponential kinetics (PEK) model, sorption kinetics data were accurately fitted. Furthermore, two Kelvin-Voigt elements were introduced to interpret the fitting results and calculate the modulus of TOCNF and SACNF.

Application of response surface methodology for optimization study of equilibrium moisture sorption content for efficient drying and storage of pearl millet flour

Pearl millet due to its high nutritional quality and adaptability to adverse cultivation is highly consumed in Asia and Africa. Prevalent flour form of pearl millet is susceptible to oxidation and microbial growth, demanding proper drying and storage conditions. Moisture sorption isotherm plays an essential role for proper storage and drying operation optimization. This study used response surface methodology to optimize equilibrium moisture content (EMC) of adsorption and desorption (closely related to moisture sorption isotherm) as response and the independent variables affecting the response were sorption temperature, water activity of sorption of flour and time of pre-treatment of grains before grinding them to flour. Linear relationship was found for water activity and time of pre-treatment with the response but an inverse relation was noted between the sorption temperature and the response. The optimized conditions obtained for minimized response of adsorption EMC were 19.85 °C temperature, 1.34 h of pre-treatment time and 0.41 sorption water activity which gave optimized EMC of 9.0554 g/100 g dry basis. Optimization condition for minimized desorption EMC were 24.47 °C temperature of sorption for 0.13 h pre-treated pearl millet grain flour and 0.360 sorption water activity providing an optimized EMC of 11.07 g/100 g dry basis. Isosteric sorption heat was also calculated and was found to be in range 22.03–0.736 kJ/mol for adsorption and 33.03–1.067 kJ/mol for desorption. Present work was an effort to evaluate optimized conditions to develop effective storage and drying processes to preserve pearl millet flour thereby increasing its shelf life.

Water vapor sorption properties of cellulose nanocrystals and nanofibers using dynamic vapor sorption apparatus

Hygroscopic behavior is an inherent characteristic of nanocellulose which strongly affects its applications. In this study, the water vapor sorption behavior of four nanocellulose samples, such as cellulose nanocrystals and nanofibers with cellulose I and II structures (cellulose nanocrystals (CNC) I, CNC II, cellulose nanofibers (CNF) I, and CNF II) were studied by dynamic vapor sorption. The highly reproducible data including the running time, real-time sample mass, target relative humidity (RH), actual RH, and isotherm temperature were recorded during the sorption process. In analyzing these data, significant differences in the total running time, equilibrium moisture content, sorption hysteresis and sorption kinetics between these four nanocellulose samples were confirmed. It was important to note that CNC I, CNC II, CNF I, and CNF II had equilibrium moisture contents of 21.4, 28.6, 33.2, and 38.9%, respectively, at a RH of 95%. Then, the sorption kinetics behavior was accurately described by using the parallel exponential kinetics (PEK) model. Furthermore, the Kelvin-Voigt model was introduced to interpret the PEK behavior and calculate the modulus of these four nanocellulose samples.

Application of Empirical Peleg Model to Study the Water Adsorption of Full Cream Milk in Drying Process

The ability of spray dryer in producing full cream milk at different inlet temperatures and the effectiveness of empirical model used in order to interpret the drying process data is evaluated in this study. In this study, a lab-scale spray dryer was used to dry full cream milk into powder with inlet temperature from 100 to 160°C with a constant pump speed 4rpm. Peleg empirical model was chosen in order to manipulate the drying data into the mathematical equation. This research was carry out specifically to determine the equilibrium moisture content of full cream milk powder at various inlet temperature and to evaluate the effectiveness of Peleg empirical model equation in order to describe the moisture sorption curves for full cream milk. There were two conditions set for this experiments; in the first condition (C1), further drying process of milk powder in the oven at 98°C to 100°C while the second condition (C2) is mixing the milk powder with different salt solutions like Magnesium Chloride (MgCl), Potassium Nitrite (KNO2), Sodium Nitrite (NaNO2) and Ammonium Sulfate ((NH4)2SO4). For C1, the optimum temperature were 160°C with equilibrium moisture content at 3.16 weight dry basis and slowest sorption rates (dM/dt) at 0.0743 weight dry basis/hr. For C2, the best temperature for the mixture of dry samples with MgCl is at 115°C with equilibrium moisture content and sorption rates is -78.079 weight dry basis and 0.01 weight dry basis/hr. The best temperature for the mixture of milk powder with KNO2 is also at 115°C with equilibrium moisture content and sorption rates at -83.9645 weight dry basis and 0.0008 weight dry basis/hr respectively. For mixture of dry samples with NaNO2, the best temperature is 160°C with equilibrium moisture content and sorption rates at 84.1306 weight dry basis and 0.0013 weight dry basis/hr respectively. Lastly, the mixture of dry samples with ((NH4)2SO4 where the best temperature is at 115°C with equilibrium moisture content -83.8778 weight dry basis and sorption rates at 0.0021 weight dry basis/hr. The best temperature selected best on the lowest moisture content formed and also the slowest sorption rates.

Sorption and diffusion of moisture in silica-polyacrylamide nanocomposite films

Nanoparticles (NPs) have been demonstrated in recent years to simultaneously enhance polymeric nanocomposite membrane selectivity and permeability according to the polymer/NP/penetrant. With a repulsive polymer-NP interaction, permselectivity is enhanced by NP loading, which is thought to adjust the permeability by locally disturbing polymer conformation. In this paper, we examine another mechanism for controlling nanocomposite permeability. We focus on the interfacial sorption capacity and mobility of water-vapour through nanocomposites comprising spherical silica NPs embedded in cross-linked polyacrylamide. Equilibrium and dynamic moisture sorption data are interpreted with a quantitative theoretical model that addresses equilibrium and dynamic partitioning of the tracer between interfacial and continuous phases. The results demonstrate significant and systematic changes in non-classical diffusion behaviour. Our interpretation indicates that polyacryamide adsorption on silica NPs varies the number of available surface adsorption sites, thus controlling adsorption capacity and interfacial mobility. Such effects can therefore be tuned by varying the specific NP surface area, which increases with NP loading and decreases with NP size. These insights will hopefully improve rational design strategies for nanocomposite membranes.

Assessment of suitability of some chosen functions for describing of sorption isotherms in building materials

This paper presents results of tests and studies conducted on six common building materials, used for constructing and finishing of external walls. These included: ceramic brick, silicate brick, autoclaved aerated concrete, cement mortar, cement–lime mortar and cement mortar modified with polypropylene fibers. Each of these materials is distinguished by the other structure of porousness, affecting both the course of sorption processes and the isotherms obtained. At first, measurements of moisture sorption kinetics at temperatures of 5, 20 and 35 °C were performed, each time at six levels of relative humidity. Then, when the sorption processes expired, equilibrium moisture sorption values were determined for the materials in 18 individual temperature and humidity conditions. The experimental data were used to determine the sorption isotherm courses for each material at the three temperatures. Then, theoretical analysis was performed in order to determine, which of the models available in the literature described the sorption isotherms of the concerned building materials the best. For each material and each of the three temperature values, twenty-four equations were tested. In each case, those of them were identified which ensured the best matching between the theoretical courses and the experimental data. The obtained results indicate that the Chen’s model proved to be the most versatile. It ensured a detailed description of the sorption isotherms for each material and temperature tested.

Hygroscopic properties of PEG treated archaeological wood from the rampart of the 10th century stronghold as exposed in the Archaeological Reserve Genius loci in Poznań (Poland)

Abstract The archaeological wood from the rampart of the Poznan stronghold built in the 10th century was subjected to the investigations. The material was obtained during the excavations and conservation works of the earthen and wooden relicts. The archaeological wood, both untreated and treated with polyethylene glycol (PEG), was characterized by determining adsorption and desorption isotherms, which were formed by GAB and GDW models. The anomalous increase of the equilibrium moisture content for air relative humidity values above 80% was found for the PEG treated wood. It was clearly presented that the safety of wood exposition strongly depends on the proper maintaining of air parameters. The mechanisms of the reduction of equilibrium moisture content and sorption hysteresis for the PEG treated wood were explained. It was not recommended to predict equilibrium moisture content values with the Hailwood-Horrobin model fitted to the sorption data collected by the US Forest Products Laboratory as it was not accounting for sorption hysteresis, decay of archaeological wood and the influence of the PEG treatment.

Assessment of drying temperature of sugarcane bagasse on sorption of reactive blue 5G dye

We studied the effect of drying temperature of sugarcane bagasse (SB) on sorption of reactive blue 5G (RB5G) dye to test whether SB is a suitable biosorbent for industrial dye removal. First we assessed a set of SB characteristics that could influence the sorption capacity of dried biomass. Kinetic drying of the SB biomass was measured at different drying temperatures, ranging from 30 °C to 80 °C. We used a static gravimetric method to perform equilibrium moisture sorption experiments at drying temperatures of 35–65 °C. In addition, we measured activation energy and net isosteric heat of sorption. SB biomass was characterized as a heterogeneous low-porous and hygroscopic material, with a series of functional groups on its surface. A Lewis thin-layer model best represented the kinetic drying data. In addition, moisture diffusion into the SB biomass was characterized by a rate-controlling step in the drying process. Equilibrium moisture sorption data showed the expected effects of temperature controlling the sorption capacity and a multilayer sorption process. A sigmoidal sorption isotherm data was best represented by a BET model. A high energy demand is required for moisture removal from biomass as suggested by the measured isosteric heat of moisture sorption. Drying temperature did not influence the RB5G adsorption capacity of bagasse, therefore any drying temperature in the range of 30 °C to 80 °C could be used to make this material feasible as an industrial adsorbent.

A study of wet and dry strength properties of unaged and hygrothermally aged paper sheets reinforced with biopolymer composites

ABSTRACTBiopolymers and their composites were added during the formation of unbleached Kraft bagasse pulp paper sheets to improve the mechanical strength properties of the produced hand sheets. The biopolymers (cellulose, chitosan, and chitosan‐cellulose composite) were either crosslinked or noncrosslinked and they were added in series of concentrations from 0.1% to 1.5%. The characterization of the samples using the Fourier transform infrared (IR) technique identified differences in the intensities of the characteristic IR absorption bands for chitosan, cellulose, and their composites, these differences are due to the various degrees of hydrogen bonding. The surface morphology of the biopolymers composites and the treated paper sheets were studied using SEM technique. Both the equilibrium moisture sorption and the diffusion coefficient of the paper sheets containing 1% additives were evaluated at regular time intervals. The long‐term stability of the treated paper with biopolymers was verified by exposing the treated and the untreated sheets to hygrothermal ageing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40761.