Moisture Sorption Rate Research Articles

Experimental study on sorption–desorption characteristics of natural composite desiccant with metal embedment

The present study investigates the effect on total moisture sorption, moisture sorption rate, moisture desorption rate, and reduction in the temperature of dehumidified air of metal-embedded natural composite desiccants (MENCDs), which can be used in dehumidification systems. A natural composite desiccant, in which the unutilized portion of the spherical desiccant material is replaced with a metallic ball, is proposed. Stainless steel balls with a diameter of 4.75 and 6.35 mm are used to make different thickness ratios (TR = 1, 0.525, and 0.365) of MENCDs. The natural composite desiccant is prepared from dried cow dung and polyvinyl pyrrolidone with a ratio of 3:1. Experiments are conducted to find the optimum thickness ratio of MENCDs. The total moisture sorption, moisture sorption rate, total heat load reduction, and exergy efficiency of these dehumidification systems are investigated under different relative humidities (RH = 65% to 85%), and at a constant temperature and velocity. Desorption characteristics are tested under 328 K and 5% RH. The total moisture sorption of MENCDs with a TR of 0.365 is found to be 11.84 g/100 g, which is 17% higher compared to natural composite desiccants (i.e., TR = 1) at 85% RH, whereas, the total moisture sorption rate is 0.4 g/100 g⋅min, which is 20.57% higher for TR of 0.365 compared to TR = 1. Moisture desorption rate for TR = 0.365 is 16.66% higher compared to TR = 1. The average exergy efficiency of these systems is 60%. The average exergy efficiency of these composite desiccants with a TR = 0.365 is 9.6% higher compared to TR = 1. The average total heat load reduction for composite desiccants with a TR = 0.365 is 24% higher compared to TR = 1. The experimental study shows that the MENCDs will help to increase total heat load reduction, sorption and desorption rate, and total moisture sorption of dehumidified air with optimum thickness ratio for enhanced utilization of a composite desiccant for dehumidification systems.

Rheological performance of film-forming solutions and barrier properties of films fabricated from cold plasma-treated high methoxyl apple pectin and crosslinked by Ca2+: Impact of plasma treatment voltage

Sustainable and “green” technologies, such as cold plasma are gaining attention in recent times for improving the functional properties of hydrocolloids. Chemical modifications of hydrocolloids require several chemicals and solvents, which are not environment-friendly. The major objective of the study was to understand the impact of plasma treatment (170–230 V|15 min) on the rheology of film-forming solutions (FFS) and the barrier properties of pectin films. The film-forming properties of plasma-treated pectin were investigated in the presence of two plasticizers, namely, glycerol and polyethylene glycol (PEG) 400. The effects of cross-linking by CaCl2 on the rheology of FFS and barrier properties of the films were discussed. A voltage-dependent decrease in the apparent viscosity of FFS was observed. The viscoelastic properties of the FFS were enhanced due to cross-linking. Glycerol exhibited a better plasticizing effect than PEG. Cross-linking and increasing voltage synergistically contributed towards lower oxygen and carbon dioxide transmission rates. The moisture sorption rate and capacity of the films increased with the voltage of the treatment. The resistance to extension of the films made from glycerol and PEG decreased with voltage, with no significant change in extensibility. On the other hand, the cross-linking by Ca2+ and plasma treatment enhanced the resistance to extension for the films made from both the plasticizers. While the increasing hydrophilicity and opacity of the films were a major drawback of plasma modification, the increase in UV barrier property of the films was an advantage of the modification.

Discharging performance prediction of experimentally tested sorption heat storage materials with machine learning method

In this study, the usability of the machine learning method in predicting the discharge performance of experimentally tested sorption heat storage materials was investigated. Experimental data was obtained from a lab scale fixed-bed thermochemical heat storage unit. 9 candidate composites were tested under different inlet conditions. Based on the experimental data, moisture sorption rates, heat output, exergy output and energy storage densities were determined. For the 6 cycles testing, highest average heat and exergy output were obtained with vermiculite/LiCl composite with the values of 0.83 kW and 0.013 kW, respectively. On the other hand, P-CaCl2 was found as the most durable material in terms of energy storage density (296 → 209 kWh/m3). A multilayer perceptron artificial neural network was established to evaluate measured data and its prediction performance was extensively studied. In the model 54 experimental data sets were utilized, consisting of 6 cycles testing of 9 different composite sorbents. Levenberg-Marquardt algorithm was benefited as the training one in the artificial neural network model established and the Tan-Sig and Purelin functions were selected as the transfer one in the multilayer neural network with 7 neurons in the hidden layer. According to the mathematical definition of the discussed statistical metrics, experimental data were used to compare them to the predicted output in order to verify the reliability of the proposed ANN model; and the analysis of the model was performed by examining the coefficient of determination, mean squared error, and deviation values, which were assumed as performance parameters, in detail. The deviation rate between the prediction values acquired from the artificial neural network and the practical data was determined as less than ±5 %. The acquired findings showed that artificial neural networks, which is one of the common machine learning algorithms, is a preferable method that can be employed to estimate the discharge performance of sorption heat storage materials.

Hygro-Thermal, Hydric, and Mechanical Properties of Fibre and Aggregate-Reinforced Earth Plasters

Earth plasters have been used as a protective coating for buildings but, due to their low strength and low resistance to weather conditions, they have been abandoned for more resistant materials which in return lack vapour permeability. Earth plasters have usually a high moisture sorption rate, and their water vapour permeability is high, allowing the transfer of humidity through the material. These properties make them an interesting material for controlling vapour movement in humid rooms. Improving their strength can be done by adding aggregates and/or fibres, but the real impact of using one type or another of fibres or aggregate is unknown. This research aims to understand the consequence of the choice of fibre or sand in the improvement of strength of plasters and the conservation of the plaster hygro-thermal properties. Properties of plasters using alternative fibres or aggregates such as wool, cow hair, pine needles, sand aimed for concrete mixes, or not properly graded sand have been compared to plasters made more traditionally with chaff fibres and mason sand.

Relative humidity-temperature transition boundaries for anhydrous β-caffeine and caffeine hydrate crystalline forms.

Caffeine is a hydrate-forming polymorphic crystalline compound that can exist in α, β, and hydrate forms. Phase transitions between hydrate and anhydrous forms of a crystalline ingredient, and related water migration, can create product quality challenges. The objective of this study was to determine the relative humidity (RH)-temperature phase boundary between anhydrous β-caffeine and caffeine hydrate. The β-caffeine→caffeine hydrate and caffeine hydrate→β-caffeine RH-temperature transition boundaries were determined from 20 to 45 °C using a combination of water activity (aw ) controlled solution and vapor-mediated equilibration, moisture sorption, powder X-ray diffraction, and Fourier-transform infrared spectroscopy techniques. Two transition boundaries were measured: the β-caffeine→caffeine hydrate transition boundary (0.835±0.027 aw at 25 °C) was higher than the caffeine hydrate→β-caffeine transition boundary (0.625±0.003 aw at 25 °C). Moisture sorption rates for β-caffeine, even at high RHs (>84% RH), were slow. However, caffeine hydrate rapidly dehydrated at low RHs (<30% RH) into a metastable transitional anhydrous state with a similar X-ray diffraction pattern to metastable α-caffeine. Exposing this dehydrated hydrate to higher RHs (>65% RH) at lower temperatures (20 to 30 °C) resulted in full restoration to a 4/5 caffeine hydrate. This transitional anhydrous state was unstable and converted to a less hygroscopic state after annealing at 50 °C and 0% RH for 1 day. It was postulated that the caffeine hydrate→β-caffeine was the true β-caffeine↔caffeine hydrate phase boundary and that β-caffeine could be metastable above the caffeine hydrate→β-caffeine transition boundary. These caffeine RH-temperature transition boundaries could be used for selecting formulation and storage conditions to maintain the desired caffeine crystalline form. PRACTICAL APPLICATION: Caffeine can exist as either an anhydrous (without water) or hydrate (internalized water) crystalline state. The stability of each caffeine crystalline form is dictated by humidity (or water activity) and temperature, and these environmental stability boundaries for the caffeine crystalline forms are reported in this manuscript. Conversions between the two crystalline states can lead to deleterious effects; for example, the presence of caffeine hydrate crystals in a low water activity food (e.g., powder) could lead to the relocation of the water in caffeine to other ingredients in the food system, leading to unwanted water-solid interactions that could cause clumping and/or degradation.

Moisture sorption and desorption properties of gelatin, HPMC and pullulan hard capsules

The moisture sorption and desorption properties of hard capsules have a great influence on the quality of capsule products. However, studies on them have rarely been reported. Herein, we studied the moisture sorption and desorption properties of three kinds of hard capsules (gelatin, hydroxypropyl methyl cellulose (HPMC) and pullulan capsules) in terms of hygroscopicity, crystallinity, thermal behaviors and so on. It is found that HPMC capsules have weaker moisture sorption ability and moisture keeping ability than pullulan or gelatin capsules with lower moisture sorption rates, equilibrium moisture contents, moisture keeping rates and higher critical relative humidity. In comparison with gelatin capsules, pullulan capsules have weaker moisture sorption ability and comparable moisture keeping ability. HPMC or pullulan capsules can more effectively protect high, moderate and low hygroscopic capsule contents (chitosan, potato starch or ethyl cellulose) from outside moisture absorption. The diffraction peaks of the moisture equilibrated gelatin, HPMC and pullulan capsules are much smaller than those of their dried ones. The dried and the moisture equilibrated gelatin, HPMC or pullulan capsules all have smooth surface morphology. HPMC or pullulan capsules can be an attractive alternative to animal gelatin capsules due to their appropriate moisture sorption and desorption properties.

Synthesis and experimental investigation of V-CaCl2 composite desiccant for performance enhancement in evaporative cooling applications

This study investigates novel vermiculite–calcium chloride composite solid desiccant material for desiccant-assisted evaporative cooling applications. In addition, comparative performance analyses between direct and desiccant-assisted evaporative cooling were performed. According to the study results, temperature drop around 10 ℃ with an average cooling rate of 700 W and coefficient of performance in the range of 5–6 were obtained for both processes. The specific cooling capacity was found 3.5 kJ/g for desiccant assisted and 2.6 kJ/g for direct evaporative cooling process. It was concluded that at low air mass flow rates, performances of both processes are similar whilst at higher air flow rates, desiccant-assisted evaporative cooling becomes more efficient in terms of specific cooling capacity and coefficient of performance. The experiments also showed that vermiculite–calcium chloride provides effective moisture sorption rates above 40% air relative humidity levels. Therefore, this desiccant material could be suitable for desiccant-assisted evaporative cooling applications.

Distorted oil paintings and wax-resin impregnation – A kinetic study of moisture sorption and tension in canvas

Abstract Wax-resin impregnation and lining are former widely used conservation methods. It is well-known that these methods slow down moisture diffusion into the canvas and changes the corresponding development of tension. However, the rate at which these processes happen are not well characterized and it is therefore unclear how long treated paintings are protected from high moisture environments. In the present work, moisture sorption characteristics of wax-resin impregnated linen samples were measured using dynamic vapor sorption (DVS) and tensile tests. Samples of untreated linen, wax-resin impregnated linen and Berger's Ethyl Vinyl Alcohol (BEVA) treated linen as well as an aged wax-resin treated lining canvas from 1958 were measured. The samples were in equilibrium at 42% relative humidity at 23 °C in DVS and tensiometer when the relative humidity was stepped to 69% RH while monitoring the development of mass and tension respectively in the canvases. This showed that there is no or little delay from the time moisture is taken up by linen fibers until swelling and the possible tension build up sets in. Both wax-resin impregnated and non-impregnated samples took up moisture when the relative humidity was stepped up, but the wax-resin impregnated samples did so at a much slower pace than the non-impregnated ones. Tension built up in some canvas samples already at 69% relative humidity whereas others stayed unaffected until a relative humidity of 82% was reached. The findings confirmed that a fine weave canvas, tightly spun thread and the presence of wax-resin matrix in the voids between fibers all are factors that characterize a painting at risk of climate related shrinkage damage. It was also demonstrated that BEVA gel treatment had very little effect on the rate of moisture sorption as there was no penetration of the canvas. In the aged lining canvas, moisture was taken up at a rate that was intermediate between untreated and wax-resin impregnated linen, which was ascribed to cracks in the wax-resin coating.

Microwave‐convective hot airdried jamun (Syzygium cumini L.) pulp powder: Optimization of drying aids

AbstractDrying of fruit pulp into powder needs drying aids for achieving desirable powder properties. This article aims to optimize drying aids, such as maltodextrin (MD), tricalcium phosphate (TCP), and glycerol monostearate (GMS) in jamun (Syzygium cumini L.) pulp blend formulation to produce microwave‐convective hot air‐dried jamun pulp powder. Response surface methodology using rotatable central composite design was followed with independent variables MD (1–15), TCP (0–2), and GMS (1–3), % dry basis of pulp, on hygroscopicity (HG), rate of moisture sorption estimated at 60 min (RMS60), flow time (FT), and overall color difference (ΔE*) as responses of the product. The statistically significant factors were: MD for HG; MD, TCP, and GMS for RMS60 and FT; and TCP and GMS for ΔE*. The optimized formulation reduced HG, RMS60, and FT by 29.67, 45.24, and 60%, respectively with respect to the control, with ΔE* being 6.98.Practical ApplicationsThe antidiabetic and antioxidant properties of jamun (Syzygium cumini L.) fruit are well established. The therapeutic values of jamun pulp and skin are mainly due to the presence of various phytochemicals. However, it is considered as underutilized fruit due to its highly perishable nature. Properly matured fruit can be stored for maximum 2 days at room temperature and 3 weeks at low temperature. Hence, immediate processing and conversion into value‐added products of jamun fruits are needed for better distribution and utilization during off‐season. Processing of fruit pulp into dry powder is a popular practice to obtain shelf‐stable product having wide scope of utilization. However, preparation of fruit powder has many challenges, the main problem being their stickiness due to the presence of low molecular weight sugars and organic acids. Therefore, production of stable free‐flowing jamun pulp powder with selection of suitable drying aids in proper concentration has enough industrial relevance.

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.

Dipalmitoylphosphatidylcholine (DPPC): Annealing Strategy to Mitigate Variability in Thermotropic and Moisture Sorption Behavior

Dipalmitoylphosphatidylcholine (DPPC) demonstrated complex differential scanning calorimetry (DSC) thermal behavior. Transitions below 100°C showed variability in their thermotropic reversibility. An experimental design employing a DSC heat-cool-heat-cool-heat cycle and modulated DSC were used to gain insight into the DPPC's complex thermal nature. An annealing strategy was developed to reduce DPPC's thermotropic variability, moisture uptake rate, and rate variability. Samples annealed at 110°C for 5 min provided a reproducible, thermally reversible material. The annealed material also exhibited an 8-fold decrease in moisture sorption rate and a statistically significant (p = 0.0233) 100-fold decrease in water sorption rate variability compared to DPPC “as is.” An optimized validated stability-indicating high performance liquid chromatography with evaporative light scattering detection method was developed and showed no change in DPPC chemical stability under the annealing treatment conditions.

Moisture sorption and diffusion determination of Chinese herbal granules: Moisture-resistant effects of fluidized bed granulation with dextrin

ObjectiveTo investigate the effects of fluidized bed granulation with dextrin on moisture sorption and diffusion of Zexie Decoction granules. MethodsThe particle characterization was studied by the particle size, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR). The moisture sorption isotherm, equilibrium moisture content (EMC), and moisture diffusion coefficients were determined by using the saturated salt solution method. ResultsThe particle size increased from 6.04 µm (powder) to 1201.47 µm (granule). The glass transition temperature of dextrin, Zexie Decoction powder, and granule was 107.13 °C, 94.82 °C, and 126.25 °C. As the increase of temperature, the initial rate of moisture sorption become higher. Furthermore, the initial rate of moisture sorption of Zexie Decoction granules was lower than those of powders and dextrin. The EMC and moisture diffusion coefficients were reduced significantly after granulation (P < 0.01). Critical relative humidity and diffusion activation energy of granules were higher than powders. ConclusionResults suggested that fluidized bed granulation with dextrin could reduce the hygroscopicity of the Zexie Decoction extract powders and inhibited moisture diffusion, which is mainly related to the microstructure reorganization by fluidized bed granulation and anti-plasticizing effects of dextrin.

Moisture Adsorption Rate and Effective Diffusivity in Chinese Milled Rice

Four varieties of Chinese milled rice samples with 11.90–15.56% initial moisture content (IMC, wet basis) were used to determine the rate of moisture adsorption using the gravimetric method at 10, 20, 25, 30, and 35°C under 65%, 86%, and 100% relative humidity (RH), respectively. A moisture diffusion equation was modified to fit the relationship between the moisture ratio (MR) of samples and exposure time. In the range of 65% to 100% RH, the lower IMC of milled rice samples corresponded to higher moisture adsorption rate at temperatures of 10 to 35°C. The moisture adsorption rate of samples increased with an increasing temperature. The moisture sorption rate of samples with the same IMC increased with increasing RH at certain temperatures. A single milled rice kernel was geometrically considered a finite homogeneous cylinder shape, and the analytical solution of the partial differential equation of moisture diffusion was given. The effective moisture diffusivity was calculated using a slope method by plotting the experimental data in terms of ln (MR) versus rewetting time. In the range of 10–35°C, the effective moisture adsorption diffusivity of milled rice kernels with normal moisture was 4.321×10-9–1.117×10-7 m2h-1. For the same IMC, the effective moisture diffusivity of milled kernels tended to increase with increases in surrounding temperature at certain relative humidity levels, but decreased with an increase in RH at certain temperatures. It was concluded that the milled rice samples from different types had similar effective moisture diffusivity when similar IMC was given.

Study of humidity-responsive behavior in chiral nematic cellulose nanocrystal films for colorimetric response

This study focuses on the preparation and characterization of an iridescent chiral nematic cellulose nanocrystal (CNC) film in relation to their use as a humidity-responsive material. A free-standing film with Bragg reflection was successfully prepared. Thermogravimetric analysis demonstrated gradual thermal transitions with two major weight loss regions, while the crystallinity index obtained from X-ray diffraction method was about 78%, implying the presence of disordered regions. A scanning electron microscope confirmed the orientation of CNCs in a chiral nematic pattern with a pitch in the wavelengths of visible light. A dynamic vapor sorption study showed that water vapor can penetrate into the CNC film, leading to an increase of overall mass of up to 20% at 95% RH. The moisture sorption and desorption rates of the CNC film were faster at higher humidity (80% RH). The exposure of CNC film to elevated humidity was simulated to investigate the effect of humidity on their optical semaphore. As the humidity increased, the complementary color was red-shifted upward by about 60–100 nm, which was observable to the naked eye. This is potentially explained by the swelling of the nanocrystals and the expansion of the interspace between the quasi-nematic layers of the CNCs.

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.

Correlation of Structural and Macroscopic Properties of Starches with Their Tabletability Using the SM2 Approach

The effects of PURE-DENT® and SPRESS® starch properties on their compression behavior was characterized using "SM(2) " approach (structural properties, macroscopic properties, and multivariate analysis). Moisture sorption rate constants, moisture content, amylose and amylopectin degradation enthalpy, percent crystallinity, amylose-amylopectin ratio, and cross-linking degree were used to profile starch structural properties. Particle density, particle size distribution, and Heckel compression descriptors [yield pressure (YP) of plastic deformation, and elastic recovery] were used as macroscopic descriptors. The structural and macroscopic properties were correlated qualitatively [principal component analysis (PCA)] and quantitatively [standard least square regression (SLSR)] with the tablet mechanical strength (TMS). These analyses revealed that the differences correlated with amylose-amylopectin content, particle density, compression mechanisms, and TMS between the starch grades. Univariate analysis proved lacking; however, PCA identified the particle size, moisture content, percent crystallinity, amylose-amylopectin ratio, and YP of plastic deformation and elastic recovery as the main factors influencing the starch TMS. SLSR quantified the positive influence of Fourier transform infrared spectra absorbance ratio at 1022-1003 and YP of the immediate elastic recovery, and the negative contribution of amylopectin content on the TMS. Therefore, starch amylose and amylopectin content, crystallinity, and lower elastic recovery are mainly responsible for better TMS.

Influence of Bark on the Physical and Thermal Decomposition Properties of Short-Rotation Eucalyptus

Highly productive short-rotation woody crops is one group of biomass feedstocks that has been identified as having the potential of meeting the goal of reducing the world’s reliance on crude oil. The goal of this project is to quantify the influence of bark on the physical properties, moisture sorption properties, and thermal decomposition of short-rotation (3 years old) Eucalyptus—the most widely planted short-rotation hardwood grown in the world. Results obtained from the study show that the physical properties of ground samples were significantly different between “no-bark” and “with-bark” samples with the bulk density of the with-bark samples decreasing by up to 20 % with a corresponding increase in compressibility of up to 75 %. The moisture sorption rate and the equilibrium moisture relations of the two samples were also significantly different. The susceptibility of no-bark sample to microbial degradation was higher. Thermal decomposition rate and peak temperatures for cellulose and hemicellulose were not affected by the presence of bark. The information obtained from this study will be important in the design and selection of systems for handling, storage, transporting, and thermochemical conversion of short-rotation Eucalyptus.

Moisture Sorption Kinetics of Switchgrass, Big Bluestem, and Bromegrass Biomass

<abstract><title><italic>Abstract.</italic></title> Moisture content of biomass is the most influential factor in biomass storage. Moisture sorption kinetics control the dynamic moisture condition of the biomass, thus affecting biomass storage, processing operations, and final utilization applications. Moisture sorption characteristics of switchgrass, big bluestem, and bromegrass, potential biomass feedstocks for the Northern Great Plains of the U.S., were studied. Study objectives were to determine the moisture sorption kinetics, mathematically model the sorption process using standard models, and evaluate the effect of temperature on moisture sorption. Moisture sorption experiments were conducted at temperatures of 20°C, 40°C, and 60°C and a fixed high relative humidity of 95% using a controlled-environment chamber. Standard moisture sorption kinetics models (exponential, Page, and Peleg) were used to analyze the experimental sorption characteristics of the feedstocks. Bromegrass had the highest moisture sorption rates and final moisture contents, followed by big bluestem and switchgrass. On average, at 20°C, 50% of moisture sorption completion occurred at 1.5, 1.9, and 1.7 h and 90% completion occurred at about 8.5, 13.4, and 12.8 h for switchgrass, big bluestem, and bromegrass, respectively. For the temperatures studied, on average 41% ±3%, 40% ±5%, and 39% ±1% of moisture sorption completion occurred in 1 h and 82% ±2%, 76% ±4%, and 73% ±1% completion occurred in 5 h for switchgrass, big bluestem, and bromegrass, respectively. Moisture sorption rates decreased very sharply during the first hour (≥78%) from their initial values and quickly plateaued thereafter. Increase in temperature increased the moisture sorption rates for all the biomass types tested. Both the Page and Peleg models effectively described the observed sorption characteristics for the selected biomass types (R² ≥ 0.96). The Arrhenius equation adequately described the temperature dependence of the model parameters (0.77 ≤ R² ≤ 1.00). Based on this study, the Peleg model in combination with the Arrhenius equation is recommended for moisture sorption predictions. Fitted moisture sorption kinetics models, developed nomograms, and combined prediction equations (R² ≥ 0.83) form baseline data essential for storage of the selected biomass types and various handling, conditioning, and processing operations.

Moisture sorption in artificially aged wood-plastic composites

Moisture sorption in wood-plastic composites (WPCs) affects their durability and dimensional stability. In certain outdoor exposures, the moisture properties of WPCs are altered due to e.g. cracks induced by swelling and shrinkage of the components, as well as UV degradation or biological attack. The aim of this work was to study the effect of different artificial ageing routes on the moisture sorption properties of WPCs. Extruded WPCs were prepared with either unmodified or acetylated wood and recycled high-density polyethylene (HDPE). The WPC samples were artificially aged involving water soaking, artificial weathering, and white- or brown-rot decay in different combinations. After the ageing, the samples were conditioned in either 65% or 90% relative humidity (RH) until equilibrium moisture content was reached. A dynamic moisture sorption analyzer was used to monitor the sorption rate of samples subjected to a climate change from 65% to 90% RH. Scanning electron microscopy was used to study the surface morphology of the aged composites. Results showed that the artificial weathering caused cracking of the HDPE matrix at the composite surface, as well as a wood-matrix debonding, resulting in an increased moisture sorption rate. The WPC samples subjected to white-rot decay showed the highest moisture sorption rate.

Moisture Sorption Properties of Modified Porous Clays for Roof Evaporative Cooling Applications

This research concentrates on evaporative cooling, a sustainable and alternative way to cool a roof surface by taking advantage of the properties of porous materials. During periods of rain or high humidity nights, water sorbents store moisture in their small pores inside their particles. During a warm sunny day, the latent heat released due to evaporation of moisture, maintains the surface temperature at low level. Lower roof temperatures contribute to smaller heat flow inside the building while reducing the cooling load. In this work, materials consisting of ordinary soil, montmorillonite and modified clays were used. Prior to moisture sorption experiments, materials were characterized by techniques including X–ray diffraction, X–ray fluorescence, thermogravimetric analysis and porosimetry. In order to determine the sorption isotherms, dry specimens were placed initially in desiccators above four different saturated salts in water solutions (32.8% to 93.6%). The modified clay was found to have the highest equilibrium state (10% after almost 4 days of sorption at high relative humidity). Also the moisture sorption rate of the modified clay was faster than the rest of the materials and equilibrium was attained in less than 12 hours. Moreover, a specific environment chamber was developed and tested for the evaporative cooling properties of the materials. The lower observed surface temperatures under simulating radiation of the modified clays in comparison to ordinary soil, indicated their significant potential for evaporative cooling applications.