Moisture Sorption Kinetics Research Articles

The kinetics of moisture sorption by hair.

The rate process of moisture sorption by human hair has been analysed in order to hints for helping deepen knowledge on the hair structure and to explain the behaviour of hair in response to moisture. The isotherms of moisture sorption by hair were recorded, via dynamic vapour sorption (DVS), for untreated (virgin) and treated (heat-shaped and bleached) hair, as well as for separated cuticle and cortex. By considering that, during moisture uptake, the hair fibres also swell, it is possible to introduce a time-dependent rate constant for describing the kinetics of the moisture sorption. This model allows for clearly separating the moisture sorption processes occurring in Cuticle and in Cortex and for proposing a role of chain entanglement in the two main compartments of the fibre. It may also provide some hints on the structural changes occurring in the fibre after different cosmetic treatments. The influence of the weight of the sample on the kinetics of the sorption process has also been noted and quantified. The analysis pointed to a transition occurring at around 30% relative humidity, assigned to the opening of the hair inner structure, and accommodation of more water molecules. This allowed for an estimate of the value of the activation energy of the water molecules reacting with the active sites, which was found to be in good agreement with results published in the literature. The analysis of the kinetics of moisture sorption by hair was shown not only to provide information on the chain entanglement inside the fibre and the effect of cosmetic treatments but also to demonstrate and quantify the influence of fibre density on the sorption process. It is thus suggested that, along with examination of the hysteresis, the analysis of sorption kinetics helps reveal a more complete picture of hair moisture management.

Research of fiberglass and basalt textile laminates on the kinetics of sorption and desorption of moisture after exposure to cold climate conditions

A two-stage kinetics of moisture sorption is obtained at a temperature of 23 °C and a humidity of 68 % in fiberglass laminates and basalt textile laminates exposed in a cold climate (Yakutsk) for 2 and 4 years. The adequacy of the relaxation model of anomalous moisture diffusion at the first stage of sorption is shown and an assessment of the increase in moisture content at the second stage is given. Keywords:textile laminate, moisture sorption kinetics, anomalous diffusion, approximation, structure and properties of the composite, climatic aging kychkinplasma@mail.ru

Capsular Exopolysaccharides from Two Streptococcus thermophilus Strains Differ in Their Moisture Sorption Behavior.

Streptococcus thermophilus is a species frequently used in the manufacture of fermented milk. Apart from acid production, some strains additionally synthesize exopolysaccharides (EPS) which contribute to texture improvement and syneresis reduction, both being attributable to the EPS's high water binding capacity. There are two different types of EPS that may be produced, namely free exopolysaccharides (fEPS) which are secreted into the medium, and capsular EPS (cEPS) which remain attached to the bacterial cell wall. This study aims to analyze their individual contribution to techno-functional properties of fermented milk by determining the moisture sorption behavior of isolated fEPS and cell-attached cEPS from two S. thermophilus strains separately: ST-1G, a producer of non-ropy fEPS and cEPS, and ST-2E, a producer of ropy fEPS and cEPS. Differences in moisture load and sorption kinetics, determined for the first time for microbial EPS, were related to structural and macromolecular properties. The observed data are discussed by using previously published data on the physical properties of stirred fermented milk produced with these two strains. ST-1G EPS showed a higher cEPS fraction, a higher moisture load and slower moisture desorption than EPS produced by ST-2E, thus contributing to lower syneresis in fermented milk. For ST-2E, higher gel viscosity was related to a higher intrinsic viscosity and molecular mass of the ropy fEPS. Both strains produced complex EPS or EPS mixtures with clearly different molecular structures.

Water-sorption ability of fruit and vegetable stabilizers

The article presents the relevance of the development of new technologies and formulations of food products with a foamy structure. The kinetics of moisture sorption of fruits and vegetables subjected to hydrothermal and mechanical processing at various partial vapor pressures in the environment has been studied. Calculations of hygroscopic characteristics of fruit and vegetable stabilizers have been made. Such parameters of the monolayer as the concentration of substances in a continuous monomolecular layer, specific surface and relative air humidity at which the moisture monolayer is adsorbed, and the pore volume of the stabilizers were determined.

Internal topology and water transport in tetrafunctional epoxy resins

AbstractWater sorption into epoxy resins limits the performance lifetime of many composites, adhesives, and coatings. One hypothesis for the well‐known hygroscopicity of epoxies is that the well‐known internal nodular topology of epoxy networks enhances permeability. This theory has however remained untested to date, since previous attempts to manipulate the internal topology have been accompanied by changes in the hydrogen bonding capability of resins, which dominates water uptake. Here, the nanostructure of highly cross‐linked network polymers based on tetra glycidyl diaminodiphenyl methane is varied in the absence of significant polarity effects by careful optimization of the cure schedule. The internal morphology of resins cured at 100, 150, and 200°C are characterized using Peakforce tapping mode atomic force microscopy, whilst the cure progression at each temperature is analyzed using in‐situ transmission mode infrared spectroscopy. Distinct nodular morphologies are found to form at high cure temperatures (150 and 200°C), where spectroscopic analysis demonstrates that excess epoxy consumption occurs prior to the gel point, as a result of intra‐cluster cross‐linking and reduced reaction selectivity. Surprisingly, the establishment of an internal nanostructure is, however, found to have negligible effect on the extent and kinetics of moisture sorption.

Model-based prediction of the moisture sorption kinetics and humidity-induced collapse for freeze–dried cakes

Freeze–drying produces highly hygroscopic porous materials derived from ice microstructures. Because of this feature, moisture sorption over time during storage in contact with moist air, in the worst case, induces collapse. In this study, a mathematical model of the moisture sorption kinetics applicable to glassy freeze–dried matrices is developed. The model is based on the glass transition properties and sorption equilibrium data with a sorption rate constant, which includes the specific surface area of the freeze–dried cake. The glass transition lines and moisture sorption isotherms of dextrins are experimentally obtained and applied to predict the durations before the humidity-induced collapse in the range of 0–24 h. The impacts of the combinations of the temperature and relative humidity (20–40 °C, 40–100%) are successfully visualized in stability maps. The proposed mathematical model can be a robust tool for guiding favorable formulations to produce stable freeze–dried products against storage.

Modeling of moisture sorption of a reinforced polymer composite using the example of basalt-plastic reinforcement

A model of moisture absorption by basalt-plastic reinforcement was developed and experimentally confirmed, taking into account Fickian diffusion, structural relaxation and design features of reinforcement at the initial stage of climatic aging. The analytical solution can be used to approximate the kinetics of moisture sorption of other reinforced polymer composites. Keywords: reinforced polymer composite, basalt-plastic reinforcement, climatic aging, moisture sorption, abnormal diffusion, relaxation model, time dependence of the diffusion coefficient. kychkinplasma@mail.ru

Theoretical and Experimental Investigation on the Moisture Sorption Kinetics of a PVA/LiCl Composite Membrane in a Dynamic Humidity Environment

The PVA/LiCl composite membrane is an important material with a selective permeation to moisture. In this study, the sorption kinetics characteristics of the PVA/LiCl composite membrane are investigated in a dynamic humidity environment. The sorption kinetics curves of the PVA/LiCl composite membranes with different LiCl contents were measured in the range from 10 to 90% relative humidity, and the kinetics characteristics of the sorption components of the total moisture uptake were analyzed with a triple-mode sorption model. The results show that the process of pooling adsorption occurs only when the amount of Henry absorption exceeds a threshold. With the increase in LiCl content, the threshold gradually decreases, indicating that introducing LiCl in the membrane mainly affects the process of pooling adsorption. In the desorption part of the kinetics curve, the amounts of Henry absorption and pooling adsorption gradually decrease, while the moisture adsorbed by the hydrophilic hydroxyls, i.e., the amount of Langmuir adsorption, is still largely retained in the membrane, resulting in the water-retaining performance in a low-humidity environment. It is noteworthy that in a high-humidity environment, the amounts of Henry absorption and Langmuir adsorption are almost evenly distributed in the film, while the amount of pooling adsorption near the surface is significantly higher than that at the center. The reason is that with the increase in humidity, the rate of pooling adsorption near the surface increases significantly, resulting in the majority of the moisture diffusing into the dense membrane clusters near the surface. The established theoretical method and model parameters can be adopted to predict the moisture sorption and desorption processes of the PVA/LiCl composite membrane in a dynamic humidity environment.

Moisture sorption of biochar from banana pseudostem fibers according to the pyrolysis temperature

Biomass has been widely used mainly for power generation or fertilizer and can be used in natura, torrefied or pyrolyzed form. For application in the generation of energy or fertilizer, it is necessary the knowledge of some properties such as the sorption of moisture. The main aim was to evaluate the sorption of moisture by the fibers from banana pseudostem in natura (wet basis), dry (100 °C), torrefied (200–300 °C) and pyrolyzed (400–600 °C). For the evaluation of the sorption of moisture was used climatized chamber at temperatures of 40 °C and 75% relative humidity (climatic zone IV). The results indicate that under the conditions used, when higher pyrolysis temperature is applied to the biomass, higher sorption of moisture occurs, with values close to 50% (w/w) for banana pseudostem fibers pyrolyzed at 600 °C. The significant increase in moisture was attributed initially by the presence of a high concentration of potassium oxalate that was later converted to carbonate in biochar obtained above 400 °C. In order to characterize the biomasses, thermogravimetry, differential scanning calorimetry, Fourier transform infrared spectroscopy and energy-dispersive spectroscopy were used. The exponential model was used to evaluate the kinetics of moisture sorption.

The parallel exponential kinetics model is unfit to characterize moisture sorption kinetics in cellulosic materials

Sorption of water vapor in cellulosic materials has been studied for more than 100 years. However, the last 2 decades have seen a surge in studies of sorption kinetics due to the adoption of automated sorption balances in laboratories worldwide. Sorption kinetic data is commonly fitted with the parallel exponential kinetics (PEK) model, which is the sum of two exponential functions. The PEK model parameters are often interpreted as representing physical quantities or material properties, but their exact definition remains undetermined. Nonetheless, PEK fitting of sorption data has been widely used to identify various physical properties. Recent work has called into question the protocols used to collect sorption data with automated sorption balances and the methods used to analyze the data. Typically, data acquisition is interrupted before equilibrium when the rate of mass change fulfills a user-specified criterion, and this has been shown to severely mischaracterize both the equilibrium moisture content and the full kinetic behavior. The objective of this work is to examine whether interrupting data acquisition before equilibrium affects the PEK model parameters and further explore whether PEK model interpretations have physical significance as claimed in the literature. The analysis shows that the PEK model cannot capture the actual form of the sorption curves for loblolly pine and microcrystalline cellulose across a range of relative humidity (RH) steps in both absorption and desorption. PEK model parameters depend not only on the mass stability criterion that controls the measurement hold time, but also on the RH step making even qualitative comparisons of a single sample across different RH steps meaningless. The PEK model cannot be used to derive physically meaningful properties from water vapor sorption measurements and its use as a tool for exploring the properties of cellulosic materials interacting with water is not recommended.

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.

Use of seaweed and filamentous fungus derived polysaccharides in the development of alginate-chitosan edible films containing fucoidan: Study of moisture sorption, polyphenol release and antioxidant properties

Alginate and fucoidan extracted from the brown macroalga Sargassum latifolium and chitosan derived from the filamentous fungus Aspergillus niger were used for the development of edible films with natural antioxidant properties. The incorporation of fucoidan and/or Ca2+ into the alginate-chitosan films decreased water solubility, but increased film thickness, water vapor permeability and oxygen permeability. The developed films showed good barrier properties against ultraviolet light. The interactions between film components were investigated using FTIR analysis which confirmed the presence of hydrogen bonded interaction. Kinetics of moisture sorption and polyphenol release exhibited a good fit to Peleg's model. Film moisture content at equilibrium was increased by fucoidan blending. Additionally, the water vapor diffusion and polyphenol release were expressed in terms of effective diffusion coefficient based on simplified Fick's second law. The developed films exhibited good antioxidant properties as measured by total antioxidant assay, ferric reducing antioxidant power and hydroxyl radical scavenging activity. Both film type and the type of the food simulant markedly affected the polyphenol release and the subsequent antioxidant activity of the films.

Use of the brown seaweed Sargassum latifolium in the design of alginate-fucoidan based films with natural antioxidant properties and kinetic modeling of moisture sorption and polyphenolic release

Alginate and fucoidan are unique polysaccharides present in brown algae and widely used in food and medical technologies. Alginate and fucoidan were sequentially extracted from Sargassum latifolium and used for the preparation of alginate and alginate-fucoidan blend films with or without Ca-crosslinking. The incorporation of fucoidan and Ca2+ decreased water solubility, but increased film thickness, water vapor permeability and oxygen permeability. The films showed good properties against ultraviolet light, however, incorporation of fucoidan and/or Ca2+ decreased the color parameter L* value and increased the a* and b* values of the films. The interaction of Ca2+ and fucoidan with alginate was investigated using FTIR analysis which confirmed the presence of hydrogen bonded interaction. Kinetics of moisture sorption and polyphenol release exhibited a good fit to Peleg's model. Ca2+ crosslinking decreased initial moisture sorption and increased the maximum sorption capacity of the films. Additionally, the water vapor diffusion and polyphenol release were expressed in terms of effective diffusion coefficient based on simplified Fick's law. The developed films showed good antioxidant properties as measured by total antioxidant assay, ferric reducing antioxidant power and hydroxyl radical scavenging activity. Both film type and the type of the food simulant markedly affected the polyphenol release and the antioxidant activity of the films.

Kinetics of moisture sorption and improved tribological performance of keratinous fiber-reinforced ortho-phthalic polyester biocomposites

ABSTRACTThis paper presents the influence of randomly oriented bovine hair fibres on the kinetics of moisture sorption and abrasive wear resistance of unsaturated polyester. The investigated properties were studied dependent on predetermined volume fractions of hair fibres in polyester matrix. Test samples were developed according to appropriate test standards and subjected to preferred characterizations. It was found that a linear relationship exists between water absorption and fibre volume fraction of biocomposites. The biocomposites exhibited Non-Fickian, Case II, and Super Case II Kinetics in correlation with diffusion mechanisms. Also, improved resistance to abrasion of the biocomposites was independent of fibre volume fraction. Overall, the biocomposites evinced better anti-abrasion properties than the monolithic polymer and carbon was revealed as the principal element in the hair fibre.

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.

Analysis of moisture sorption in lyocell-polypropylene composites

The preparation of composites by thermoforming of intermingled fibre slivers is an efficient method to receive high performance and lightweight materials. Cellulosic fibres have benefits like low density and sustainability but the sorption of water due to the high hydrophilicity of the cellulose requires attention. The swelling of the wet fibres changes the fibre-matrix adhesion and as a consequence, the mechanical strength of the composite is influenced negatively. In this study, the thermoplastic polypropylene was combined with lyocell fibres as reinforcement. Moisture sorption isotherms of cellulose/polypropylene composites were recorded as function of relative humidity. Additionally, the specific surface area was analysed by the Brunauer–Emmett–Teller model. It has been found, that the moisture sorption is influenced by the polypropylene (PP) ratio in the composites. At 60% relative humidity the moisture uptake of the lyocell fibres was reduced from 10.8 to 5.8% for lyocell embedded in a composite with 50% polypropylene. Besides the hysteresis between moisture sorption/desorption cycles was found to be proportional to the increased content of PP. The “Parallel Exponential Kinetics” (PEK) model was used to analyse the kinetics of moisture sorption of these composites in more detail. With the help of the PEK model the sorption/desorption kinetics were described by a fast and slow moisture sorption/desorption process. The capacity for rapid moisture sorption is reduced by the formation of PP layers on the lyocell surface. The share of slow moisture sorption increased with increasing PP content in the composite. The results support understanding of the interaction of water with cellulose containing composites.

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.

Humidity-Regulating Trays: Moisture Absorption Kinetics and Applications for Fresh Produce Packaging

For packaged fresh produce, inappropriate high relative humidity (RH) levels and condensation of water vapour cause premature spoilage. Humidity-regulating trays were developed to solve this issue. They were made from a thermoformed multilayer structure: polyethylene (outside)/foamed hygroscopic ionomer (active layer) with 0 or 12 wt% NaCl/hygroscopic ionomer (sealing layer, inside). Moisture absorption kinetics of the humidity-regulating trays with 0 and 12 wt% NaCl (T-0 and T-12, respectively) was investigated under different RH conditions (76, 86, 96 and 100 %) at 13 °C for 16 days. Additional trays containing 7 g of distilled water were closed with a high barrier lidding film, and the headspace RH was continuously monitored as a function of time. As control, a polypropylene (control-PP) tray was used. Strawberries and tomatoes were used to test capability of the trays to regulate in-package RH. The amount of water absorbed by the T-0 and T-12 trays was 7.6 and 13.2 g, respectively. Active hygroscopic ionomer layer was effective in water vapour absorption, and the integration of NaCl into this active layer increased the water vapour absorption capacity of the tray. The Weibull model adequately described the moisture sorption kinetics of the individual packaging trays as a function of time. The headspace RH of trays covered with a lidding film was found to be 89.8, 99.6 and 100 % in the T-12, T-0 and control-PP trays, respectively. The T-12 trays containing fresh produce best regulated the in-package RH below 97 % and maintained overall quality, but at the expense of slightly higher product weight loss (2–3 wt% for strawberry, 1 wt% for tomatoes) compared to the control-PP trays (0.3–0.6 wt%).

NARX Neural Network Modelling of Mushroom Dynamic Vapour Sorption Kinetics

Abstract: This paper is concerned with the study, optimization and control of the moisture sorption kinetics of agricultural products at temperatures typically found in processing and storage. A nonlinear autoregressive with exogenous inputs (NARX) neural network was developed to predict moisture sorption kinetics and consequently equilibrium moisture contents of shiitake mushrooms ( Lentinula edodes (Berk.) Pegler) over a wide range of relative humidity and different temperatures. Sorption kinetic data of mushroom caps was separately generated using a continuous, gravimetric dynamic vapour sorption analyser at temperatures of 25-40 °C over a stepwise variation of relative humidity ranging from 0 to 85%. The predictive power of the neural network was based on physical data, namely relative humidity and temperature. The model was fed with a total of 4500 data points by dividing them into three subsets, namely, 70% of the data was used for training, 15% of the data for testing and 15% of the data for validation, randomly selected from the whole dataset. The NARX neural network was capable of precisely simulating equilibrium moisture contents of mushrooms derived from the dynamic vapour sorption kinetic data throughout the entire range of relative humidity.

Physical, antimicrobial and antioxidant properties of starch‐based film containing ethanolic propolis extract

SummaryPropolis is a natural product that meets the requirements as functional additive for food packaging due to its antioxidant and antimicrobial activities. In this work, ethanolic propolis extract (EPE) was incorporated in cassava starch films, and characterisations with respect to their microstructure, mechanical properties, water vapour permeability (WVP), moisture sorption kinetics as well as antimicrobial and antioxidant capacities were performed. The results showed that tensile strength was not affected (P > 0.05) by the presence of EPE but Young's modulus decreased about 50% when compared to control films possibly because of EPE plasticiser effect. When 1% EPE was used, changes in moisture sorption properties were detected by a slightly hydrophobic character at films WVP. When extracted from the films, propolis retained its antioxidant activity. The films exhibited antimicrobial activity against Staphylococcus aureus and Escherichia coli even at low EPE concentrations (0.5%) mainly due to its phenolic compounds.