Hygroscopic Behavior Research Articles

The effect of graded fibrous structure of bamboo (Phyllostachys edulis) on its water vapor sorption isotherms

Hygroscopic behavior is an inherent characteristic of bamboo that strongly affects its mechanical properties, durability, and dimensional stability. In order to understand the effects of the unique graded fibrous structure of bamboo on its water vapor sorption behavior, this study used bamboo specimens (Phyllostachys edulis) collected from the inner to the outer part of culm wall to test the equilibrium moisture content (EMC) and hysteresis. A dynamic vapor sorption apparatus was used to measure the EMC of bamboo slices at relative humidity (RH) ranging from 0 to 95 % at a constant temperature of 25 °C. The results were analyzed by calculating the EMC of fiber and parenchyma cells and using the Guggenheim-Anderson-de Boer (GAB), Hailwood -Horrobin (H-H), and Henderson models. It was shown that the EMC of bamboo at varied radial positions of culm wall were different, especially at high RH. The EMCs of the inner and outer part were 26.7 % and 18.0 % at 95 % RH, respectively. It was also noted that fiber cell absorbed water mainly by forming hydrogen bonds between water and hydroxyl groups in the cell wall during the whole RH range, while parenchyma cell absorbed water via bonding to hydroxyl groups at low RH (below 60 %) and through forming water clusters at high RH (over 60 %). The hysteresis value increased from the inner to the outer part. Three models fitted the experimental data satisfactorily and can be used to calculate the monolayer moisture content. These models also confirm that the outer part of bamboo culm wall provided more sorption sites for water than the inner part, while more water clusters were formed in the inner part.

Hygroscopic properties of sodium and potassium salts as related to saline mineral dusts and sea salt aerosols

Mineral dust, soil, and sea salt aerosols are among the most abundant primary inorganic aerosols in the atmosphere, and their hygroscopicity affects the hydrological cycle and global climate. We investigated the hygroscopic behaviors of six Na- and K-containing salts commonly found in those primary organic aerosols. Their hygroscopic growths as a function of relative humidity (RH) agree well with thermodynamic model prediction. Temperature dependence of deliquescence RH (DRH) values for five of those salts was also investigated, which are comparable to those in literature within 1%–2% RH, most showing negative dependence on temperature. Hygroscopic growth curves of real-world soil and sea salt samples were also measured. The hygroscopic growths of two more-hydroscopic saline soil samples and of sea salt can be predicted by the thermodynamic model based on the measured water-soluble ionic composition. The substantial amounts of water-soluble ions, including Na+ and K+, in saline soil samples imply that even nascent saline soil samples are quite hygroscopic at high-RH (>80%) conditions. For three less-hygroscopic dust samples, however, measurements showed higher water uptake ability than that predicted by the thermodynamic model. The small amount of water taken up by less-hygroscopic dust samples suggests that dust particles might contain thin layers of water even to very low RH. The results of this study provide a comprehensive characterization of the hygroscopicity of Na- and K-containing salts as related to their roles in the hygroscopic behaviors of saline mineral dusts and sea salt aerosols.

Hygroscopic behavior of inorganic–organic aerosol systems including ammonium sulfate, dicarboxylic acids, and oligomer

Abstract The hygroscopic behavior of complex mixed organic–organic and organic–inorganic particles consisting of various dry mass ratios of ammonium sulfate (AS), oxalic acid (OA), malonic acid (MA) and polyethylene glycol-300 (PEG) has been studied using a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) setup. The measured growth factors (GFs) are compared to values predicted by the AIOMFAC-based thermodynamic equilibrium model and the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. The measured GFs for PEG–OA and PEG–MA systems are found to be significantly lower than those predicted by the two models, which assume the complete dissolution of the organic compounds. The observed behavior suggests that the presence of PEG substantially affects the solubility of organic acids and associated water uptake. For quinary systems containing PEG, organic acids, and AS, a complete deliquescence of the mixed particles is observed during hydration conditions at RH ~78–80% close to the deliquescence point of pure AS particles. A clear disagreement was observed between measurements and predictions from AIOMFAC and ZSR for hydration conditions prior to the full particle deliquescence. We provide indirect evidence for the presence of an organic solid alongside solid AS. Hypothetically, the observed disagreement could also be due to a preferential interaction between –COOH and –CH2OCH2- groups, which may prevent a fraction of the organic acid amount to interact with water. For fully deliquesced particles, good agreement between model predictions and measurements are found for the mixed PEG–organic acids–AS systems. Upon dehydration, when the mass fraction of PEG

Hygroscopicity of Waterlogged Archaeological Wood from Xiaobaijiao No.1 Shipwreck Related to Its Deterioration State.

Waterlogged archaeological wood (WAW) artifacts, made of natural biodegradable polymers, are important parts of many precious cultural heritages. It is of great importance to understand the hygroscopic behavior of WAW in different deterioration states for the development of optimal drying processes and choices of safe storage in varying conditions. This was investigated in a case-study using two Hopea (Giam) and two Tectona (Teak) WAW samples collected from the Xiaobaijiao No.1 shipwreck. The deterioration state of WAW was evaluated by the maximum water content (MWC) method and by the cell morphological structure. Both Hopea and Tectona WAW could be classified into moderately and less decayed WAW. The hygroscopic behavior of moderately and less decayed WAW was then comparatively investigated using Dynamic Vapor Sorption (DVS) measurements alongside two sorption fitting models. Compositional analysis and hydroxyl accessibility measurements of WAW cell walls were shown to correlate with the hygroscopicity of WAW in different deterioration states. It was concluded that moderately decayed WAW possessed higher hygroscopicity and hysteresis than less decayed WAW because of the lower relative content of polysaccharides and the higher relative content of lignin, including the slow hydrolysis of O-acetyl groups of xylan and the partial breakage of β-O-4 interlinks, accompanied by an increased hydroxyl accessibility. This work helps in deciding on which consolidation measures are advised for shipwreck restauration, i.e., pretreatments with specific consolidates during wood drying, particularly for wooden artifacts displayed in museums.

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.

Size-resolved hygroscopic behaviour and mixing state of submicron aerosols in a megacity of the Sichuan Basin during pollution and fireworks episodes

In-situ measurements were carried out to study the size-resolved hygroscopic behaviour of submicron aerosols during pollution and fireworks episodes in winter from late January to February 2019 in Chengdu, a megacity in Sichuan Basin, using a hygroscopicity tandem differential mobility analyser (H-TDMA). The H-TDMA data were acquired at 90% relative humidity for dry aerosol diameters between 40 and 200 nm. Aerosol particles were usually externally mixed and consisted of nearly hydrophobic mode (NH), less hygroscopic mode (LH) and more hygroscopic mode (MH) in the urban area. The average ensemble mean hygroscopicity parameter values (κMean) over the entire sampling period were 0.16, 0.19, 0.21, 0.23 and 0.26 for aerosols with diameters of 40, 80, 110, 150 and 200 nm, respectively. These averages were lower than those in Shanghai and Nanjing. κMean for aerosols larger than 110 nm, however, were higher than those in Beijing and Guangzhou during winter. Distinct diurnal patterns for all measured sizes were observed for aerosol hygroscopicity and mixing state because of the photochemical reactions and the activities of the planetary boundary layer (PBL). The number fractions of the NH (NFNH) was low, but κMean was high, and more aerosols were internally mixed during daytime. The number fraction of LH (NFLH) for the 40-nm diameter aerosols in clean periods (CPs) was larger than that in the pollution episodes (PEs) because of the increasing amount of SOA formation. More aerosols of diameters larger than 80 nm were internally mixed during CPs and pollution accumulation period, resulting in higher κMean values. More strong hygroscopic components of fireworks were found in the larger aerosols during the fireworks episode (FE). The average κMean values of 0.19, 0.19, 0.21,0.23 and 0.27 for the 40, 80, 110, 150 and 200-nm diameter aerosols, respectively, during the FE were higher than those during the pre- and post-FE periods. The findings of this study contribute to the preliminary understanding of the hygroscopic behaviour of urban aerosol particles in the Sichuan Basin, which are essential for understanding the formation and evolution of severe haze events in the Sichuan Basin.

Hygroscopic Behavior and Thermodynamic Properties of Ziziphus joazeiro Mart. Kernel Flour

The hygroscopic and thermal behavior of kernel flour from Ziziphus joazeiro fruits were investigated. Adsorption isotherms were obtained at temperatures of 293, 303 and 313 K and adjusted to GAB, Oswin and Peleg models. The best fit of the experimental data was obtained with the GAB model with R² values> 0.994 and mean percentage deviation P <10%. The isotherms obtained were sigmoidal type II. Isosteric heat and other thermodynamic properties were calculated as a function of moisture content. Adsorption isosteric heat decreased exponentially with increasing moisture content and differential entropy increased with moisture content, while differential enthalpy decreased. The theory of compensation confirmed that these properties are dependent on moisture content. The isotherms presented a spontaneous and enthalpy process.

Utilization of xylan-rich steam explosion liquid from processing of poplar for hydrogel synthesis

A high-performance hydrogel was successfully fabricated using xylan-rich concentrated steam explosion liquid (CSEL). The method used was a free-radical graft copolymerization of acrylic acid (AA) and acrylamide (AM) onto a primarily xylan backbone in CSEL, with a redox system of ammonium persulfate/anhydrous sodium sulfite as the indicator and N,N`-methylenebisacrylamide (MBA) as the cross-linker. The effects of independent parameters (the dosages of the indicator, AM, AA, and the cross-linker) on the swelling ratio of the as-prepared hydrogel were studied via an optimal design of the response surface methodology (RSM). Under the optimal conditions (80.9 mg of initiator, 349.6 mg of AM, 988.7 mg of AA, and 9.39 mg of cross-linker), the swelling ratio of the prepared hydrogel (Xyl-AM-co-AA) was 276.6 g/g, which was close to the predicted value (255.7 g). The swelling behaviors of Xyl-AM-co-AA at different temperatures and pH values were also analyzed. The results showed that the swelling ratios varied at different temperatures and pH values, implying their potential use as smart materials. Analysis by Fourier transform infrared spectroscopy and scanning electron microscopy confirmed the cross-linked and hygroscopic behavior of Xyl-AM-co-AA.

Moisture sorption measurements and Thermophysical characterization of the Taraxacum officinale leaves and root

This paper aims at investigating the hygroscopic behavior and the thermodynamic characterization of the dandelion (Taraxacum officinale) leaves and root during moisture sorption phenomena. This study has been conducted by using the saturated salt solutions at different temperatures 30 °C, 40 °C and 50 °C. The obtained isotherms curves of all samples were of sigmoidal Type II. The optimal water activity was determined. Moreover, thirteen models are fitted and compared in order to choose the most suitable model that perfectly represents the relationship between moisture sorption content and water activity. The comparison of these models has been based on the coefficient of correlation as well as the standard error of estimate. Furthermore, several equations are used to determine the net isosteric heat of sorption, the sorption differential entropy, the spreading pressure, the specific surface area of sorption, and the enthalpy-entropy compensation theory. All these thermodynamic properties allow us to analyze the thermodynamic behavior of the leaves and the dandelion root during the sorption processes.

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.

Study on the Moisture Absorption and Thermal Properties of Hygroscopic Exothermic Fibers and Related Interactions with Water Molecules.

The aim of this paper is to study the hygroscopic behavior of hygroscopic exothermic fiber-based materials and to obtain a better understanding of the thermal performance of these fibers during the moisture absorption process. The temperature distribution of different kinds of hygroscopic exothermic fibers in the process of moisture absorption, observed by infrared camera, demonstrated two types of heating performance of these fibers, which might be related to its hygroscopic behavior. Based on the sorption isotherms, a Guggenheim-Anderson-de Boer (GAB) multi-layer adsorption model was selected as the optimal moisture absorption fitting model to describe the moisture absorption process of these fibers, which illustrated that water sorption capacity and the water–fiber/water–water interaction had a significant influence on its heating performance. The net isosteric heats of sorption decreased with an increase of moisture content, which further explained the main factor affecting the heat dissipation of fibers under different moisture contents. The state of adsorbed water and water vapor interaction on the fiber surface were studied by simultaneous thermal analysis (TGA-DSC) measurement. The percentage of bound and unbound water formation at low and high humidity had a profound effect on the thermal performance of fibers. It can therefore be concluded that the content of tightly bound water a strong water–fiber interaction was the main factor affecting the heating performance of fibers at low moisture content, and the content of loosely bound water reflected that water sorption capacity was the main factor affecting the heating performance of fibers at high moisture content. This was further proven by the heat of desorption.

Effect of particle size and temperature on the hygroscopic behaviour of cassava flour from dry group and storage time estimation

ABSTRACT The cassava flour from dry group is marketed and consumed under three different particle sizes (coarse, medium and fine), mostly in the North and Northeast regions of Brazil. Thus, as a contribution to the packaging, storage and handling of this type of flour, moisture sorption isotherms were made at 25°C, 35°C and 45°C, for three different particle sizes. Five mathematical models were fitted to the moisture sorption data and the isosteric heat of sorption (Qst) was calculated. The sorption isotherms indicated that the particle size did not interfere on the product’s hygroscopicity and moistures below 9.55 g H2O/100 g ensures the product’s microbiological stability when stored between 25°C and 45°C. The Oswin model displayed the best fit and the Qst values indicated that great amount of energy is involved in the product’s drying process. The storage time of the product was estimated in 136 days.

Characterization of Water Binding Properties of Apple Pectin Modified by Instant Controlled Pressure Drop Drying (DIC) by LF-NMR and DSC Methods

Effects of instant controlled pressure drop drying (DIC) on the hygroscopic behavior of water-soluble pectin (WSP), chelator-soluble pectin (CSP), and sodium-carbonate-soluble pectin (NSP) were explored to reveal the modification effect of DIC treatment on apple pectin and the correlations between water binding capacity and the inherent characteristic of pectin. The results showed that DIC treatment significantly increased the water binding properties of CSP even though it was decreased slightly in WSP and NSP. Meanwhile, the methylesterification degree (DE) of CSP decreased significantly by 43.04% whereas it was increased slightly in WSP and NSP. Although the effect of DIC on GalA contents and the changes in the functional group structures were negligible, the changes in the crystalline state of three pectin fractions were significant. The results suggest that there are strong correlations between the water binding properties and the DE and the crystalline state of the three pectin fractions after DIC drying.

Measurement of the relative air permeability of compacted earth in the hygroscopic regime of saturation

The hygroscopic behavior of earthen materials has been extensively studied in the past decades. However, while the air flow within their porous network may significantly affect the kinetics of vapor transfer and thus their hygroscopic performances, few studies have focused on its assessment. For that purpose, a key parameter would be the gas permeability of the material, and its evolution with the relative humidity of the air. Indeed, due to the sorption properties of earthen material, an evolution of the water content, and thus of relative permeability, are foreseeable if the humidity of in-pore air changes. To fill this gap, this paper presents the measurement of relative permeabilities of a compacted earth sample with a new experimental set-up. The air flow through the sample is induced with an air generator at controlled flow rate, temperature, and humidity. The sample geometry was chosen in order to reduce, as much as possible, its heterogeneity in water content, and the tests were realized for several flow rates. The results, which show the evolution of gas permeability with the relative humidity of the injected air and with the water content of the material, either in adsorption or in desorption, were eventually successfully compared to predictions of the well-known Corey's law.

Building incorporated bio-based materials: Experimental and numerical study

In building environments, several research on dynamic moisture storage in hygroscopic building materials has improved interest in moisture buffering capacity of bio-based materials and demonstrated the potential of these materials to improve thermal comfort and buildings energy consumption. This paper presents an investigation, which aims to compare the hygroscopic behavior of different bio-based materials to identify their hygric proprieties. For this, an experimental facility is used to measure the moisture buffer value (MBV) for different categories of building materials. Thereafter, a dynamic simulation has been carried out by using TRNSYS software in order to evaluate heating and cooling loads. The results showed that the wood-cement composite still has excellent moisture regulator when compared to wood panels or fibrous materials. It has a buffer capacity superior to 3 [g/m2.% RH] very close to that of wood fiber panels. The simulation results of the different cases showed that the insulation reduces significantly total energy demand, but it does not lead heat evacuation in the summer season. Thus, from this study, it can be concluded that a natural ventilation mechanism is recommended to improve energy efficiency in the building.

Aerosol Optical Tweezers Constrain the Morphology Evolution of Liquid-Liquid Phase-Separated Atmospheric Particles

Summary Chemical models of atmospheric particles are vital in understanding the role of aerosol particles in atmospheric chemistry, air pollution, human health, and climate change. Advancing these models requires new frameworks that can realistically predict how critical particle properties evolve. We present such a framework for predicting particle phase separation and which morphology will prevail; this controls how each particle interacts with and affects the atmosphere. We studied the mixing behavior of α-pinene secondary organic aerosol (SOA) with different organic phases, as relative humidity was varied to determine the interplay between polarity, miscibility, interfacial tension, and the resulting morphology. Using measurements from aerosol optical tweezers experiments and literature data, a general trend in morphology with increasing atmospheric oxidation was observed, from biphasic partially engulfed (where both phases are immediately accessible to the gas phase) to biphasic core shell (where the organic shell conceals the core) and finally to a single-phase, homogeneous morphology.

In Situ Observation of Efflorescence and Deliquescence Phase Transitions of Single NaCl and NaNO3 Mixture Particles in Air Using a Laser Trapping Technique

Abstract A novel experimental approach to study the hygroscopic properties of multi-component inorganic aerosols was demonstrated using a laser trapping technique. The efflorescence and deliquescence phase transitions of the equimolar mixture of NaCl and NaNO3 particles levitated in air were reversibly induced by controlling relative humidity. The two-stage phase transitions of the particles during the dehumidifying and humidifying processes were successfully observed in air. To our knowledge, this is the first experimental result to observe the reversible hygroscopic behavior of single optically-levitated multi-component inorganic aerosols in air. Furthermore, to elucidate the influence of solid substrates on the homogeneous and heterogeneous nucleation processes, the efflorescence relative humidity (ERH) and mutual efflorescence relative humidity (MERH) in air were compared with those observed on a hydrophobic glass substrate. The average ERH and MERH values of the NaCl–NaNO3 particles levitated in air were lower than those obtained for the particles deposited on the hydrophobic glass substrate.

Hygroscopic swelling of moso bamboo cells

Bamboo is a natural cellulosic material which is strongly reactive to water. Its hygroscopic behavior affects almost all other physical and mechanical properties of bamboo. This study investigated the hygroscopic swelling of moso bamboo (Phyllostachys edulis) cells in response to changes in environmental humidity using a confocal laser scanning microscope. The swelling strains of fiber, vessel and parenchyma cells were obtained and compared. The interactions between adjacent cells were also analyzed. The results demonstrated that the swelling strain of the cell walls increased with relative humidity, and was independent of its location and orientation, but dependent on the cell type. The absolute swelling of fiber cells was highest among all cells because of dominantly high fiber wall thickness. In contrast, the relative swelling of fiber cells was lowest due to constraint of adjacent fibers. Fiber cells governed the deformation and movement of other cell lumens. The difference between tangential and radial swelling of bamboo was insignificant compared to that of wood, possibly due to the similar microfibril angle in both directions, the circular cell shape and the random embedment of vascular bundles.

Determination of Effective Coefficient of Chinese Fir (Cunninghamia Lanceolata) During Adsorption and Desorption Process

Establishing an accurate moisture transport model in wood is essential to analyze the hygroscopic behavior and estimate the stability of wood structures in the ambient environment. In this article, the effective diffusion coefficients (EDCs) of Chinese fir in radial and tangential directions during absorption and desorption processes were measured based on the differential model, and numerical simulations were performed to verify the rationality of measured results. The results show that 1) for adsorption process, the surface emission coefficient (SEC) and EDC of Chinese fir are all greater in the radial direction; 2) for desorption process, the SEC is higher in the radial directions, whereas the EDC in the tangential direction is higher than that in the radial direction when the MC is greater than 10%; 3) the SEC and EDC in the adsorption process are larger than those in the desorption process. Because there is a reasonable agreement between experimental and mumerical simulation results, the measured results could be used to predict the MC distribution of Chinese fir in the ambient environment.

A comparative study on hygroscopic and physiochemical properties of chicken powders obtained by different drying methods

Different drying methods (spray drying (SD), vacuum drying (VD), microwave vacuum drying (MVD), and infrared vacuum drying (IFVD)) were applied in order to compare the hygroscopicity behavior of chicken powders. The hygroscopicity curves and glass transition temperature were used to evaluate the influence of ambient humidity and temperature on moisture absorption of powders. The results showed that the chicken powder dried by MVD had the lowest moisture absorption, followed by IFVD, VD, and SD. The hygroscopicity of SD chicken powders was different from other three kinds of chicken powders due to the physical properties of particles and the changes of protein secondary structure as detected by the Fourier transform-infrared spectrometer. For the three vacuum drying methods, the difference of protein secondary structure was the main reason of differences in hygroscopicity. Although MVD chicken powders were slightly inferior to SD chicken powders in taste, MVD chicken powders were the best in terms of smell and color as suggested by instrumental sensory parameter evaluations. It was found that MVD had a positive effect on reducing moisture absorption and maintaining sensory quality of chicken powders.