Water Sorption Kinetics Research Articles

Study of the influences of film processing conditions and glycerol amount on the water sorption and gas barrier properties of novel sodium caseinate films

This study deals with water sorption characteristics and gas barrier properties of sodium caseinate based edible films as a function of processing type and processing additives. Two processing routes are adopted: solution casting and blown-film-extrusion. Two processing additives are used: glycerol as plasticizer and ethanol as protein denaturing agent. It is shown at first that the water and gas transport properties are neither affected by the processing technology nor by the use of ethanol during the fabrication step.Water sorption and thermal properties of blown films prepared for glycerol contents varying from 15 to 25wt% are then studied for a wide range of relative humidity. The determination of the water sorption isotherms and their modeling by Park׳s equation as well as the study of the water sorption kinetics parameters allow discussing the sorption mechanisms as a function of the respective plasticizing effect of glycerol and water, on one hand and of the ability of water molecules to form clusters within the material, on the other hand. The decrease of the glass transition temperature values of the films as a function of increasing water content is analyzed thanks to Gordon–Taylor equation and it is related to the respective plasticizing role of glycerol and water, as evidenced from water sorption analysis.

ADSORPTION EQUILIBRIUM AND EFFECTIVE DIFFUSIVITY IN CYLINDRICAL ALUMINA PARTICLES IMPREGNATED WITH CALCIUM CHLORIDE

Adsorption equilibrium and effective diffusion coefficients of water vapor, in cylindrical particles of activated alumina (A) and activated alumina impregnated with calcium chloride (MCA), are experimentally determined. The experiments were conducted at 303 K and 323 K using cylindrical particles with 2.5 mm in both length and diameter. Diffusion coefficients were determined from the kinetics of water sorption. The measurements were conducted in a constant pressure unit based on a magnetic suspension balance (Rubotherm) under isothermal conditions. The sorption capacity depends on temperature and it was found to be higher by 25 % for the MCA material compared with the A material. The water diffusion coefficient depends itself on the adsorption equilibrium taking into account the local slope of the water sorption isotherm. The effective diffusivity of water is almost 2 times lower in impregnated than in non-impregnated alumina. The obtained diffusion data could be used to model the dynamic adsorption.

The Influence of Woven Fabric Structure on Kinetics of Water Sorption

In this paper, the results of an experimental study designed to determine the kinetics of water sorption on cotton fabrics are presented. The dynamic water sorption of cotton fabrics was gravimetrically investigated at 20°C by using an experimental device, which assured the vertical suspension of the cloth surface and permitted the measurement of the mass of liquid rising in the fabric. A good fit of the experimental data with the parallel exponential kinetics model was found. The results show that the weave structure and the number of yarns per centimeter had a significant influence on the model parameters and the kinetic rate of sorption.

Water Sorption Kinetics of Wheat Noodle with Different Diameters

The water sorption properties of udon-like wheat noodle were measured at different temperatures to estimate changes in the moisture content and loss of mass; transient changes in these properties could be expressed by hyperbolic and exponential empirical equations, respectively. The maximum moisture content changed stepwise with temperature near the gelatinization temperature of wheat flour; however, the initial sorption rate with temperature obeyed the Arrhenius equation. These processes were also measured for wheat noodle with different initial diameters at 100°C. Changes in the moisture content could be expressed by a hyperbolic equation as a function of time divided by the square of the initial diameter. The loss of wheat noodle mass was proportional to the specific surface area, and the loss per specific surface area could be expressed solely as a function of time.

The water vapour sorption behaviour of acetylated birch wood: how acetylation affects the sorption isotherm and accessible hydroxyl content

The water vapour sorption isotherms and sorption kinetics of birch (Betula pendula L) acetylated to different levels have been determined using a dynamic vapour sorption (DVS) apparatus. A DVS instrument was also used to determine the accessible hydroxyl content in the wood samples using deuterium exchange. The results are reported in terms of the reduced equilibrium moisture content (EMCR), in which the moisture content per unit mass of wood substance is used for the calculation. As the level of acetylation of the wood samples increased there was a corresponding reduction in EMCR of the wood samples, which was accompanied by a decrease in hysteresis in the same order. The sorption kinetics were also determined using the DVS and analysed using the parallel exponential kinetics model, in which the sorption kinetics curve is composed of two processes (labelled fast and slow). Using this analysis, it is possible to calculate two pseudo-isotherms associated with the two processes. The sorption isotherm is a composite of the sorption isotherms associated with the fast process water and the slow process water and there are significant differences in behaviour between the two. It is suggested in this paper that the fast process is related to diffusion limited kinetics, whereas the slow process is a relaxation-limited phenomenon. The reduction in accessible OH content due to acetylation was well correlated with the weight gain due to acetylation, although the relationship did not exactly correspond with that theoretically determined.

Structural features and functional properties of water in model DMPC membranes: thermally stimulated depolarization currents (TSDCs) and Fourier transform infrared (FTIR) studies

Thermally stimulated depolarization currents (TSDCs) and Fourier transform infrared (FTIR) spectroscopies were employed to investigate the state of water incorporated in a model DMPC (dimyristoyl-phosphatidylcholine) membrane. The lipid multilayers, highly inhomogeneous from the dielectric point of view, originate complex TSDC spectra critically dependent on the sample water content and thermal history. Different temperature ranges were chosen to polarize the sample, i.e. 100–300 K (type I) and 100–285 K (type II). The purpose of the latter choice was to avoid any sample heating above the DMPC phase transition temperature (295 K) along the sample polarization. According to the results, water in a fully hydrated system (aw = 0.92) (1) is ordered around the hydrophilic head molecular groups, (2) is layered in the interbilayer space and (3) penetrates among the hydrocarbon chains. It can assume different local structural configurations depending on the lipid packing. Irreversible conformational transitions in the lipid array system were monitored as a consequence of different dehydration treatments.FTIR absorption measurements were performed to study the water sorption kinetics into a DMPC thin film. The water related OH band was decomposed into three components, describing three water states, with different propensity to the H-bond formation. The changes of the lipid characteristic groups (CH2/CH3, and C=O) absorption bands as a function of increasing hydration level were monitored and discussed.

Multistep Thickening of Nafion Thin Films in Water.

Water sorption kinetics in thin Nafion films prepared on silver and silicon oxide substrates was examined by surface plasmon resonance and neutron reflectivity measurements. It was found that the films thickened in three regimes. The asymptotic swelling ratios in regimes I, II, and III were 1.05, 1.26, and 1.41, respectively. These values were independent of the substrate species and were coincident with the transition points of different hydration states in the bulk Nafion; water binding to sulfonic acid groups, the formation of sphere-like ionic clusters, and bridge formation between clusters. The swelling was much slower in thin films than in the bulk due to the mobility restriction of Nafion near the substrate.

Characterizing water sorption in 100% solids epoxy coatings

In the present work, water sorption kinetics and equilibrium in 100% solids epoxy coatings are investigated by immersion into distilled water baths from 20 to 85°C (absorption tests) and drying in a furnace between 60 and 85°C (desorption tests). The gravimetric liquid sorption measurements reveal a non-Fickian two-stage diffusion behaviour during both absorption and desorption. The effect of hydrothermal history was also investigated. Cycling the immersion bath temperature increases the saturation values. Alternating sorption–desorption cycles increases the speed of water movement. The hydrothermal-induced coating degradation and the sorption modes are discussed.

Properties and Water Sorption Characteristics of Spaghetti Prepared Using Various Dies

Spaghetti was prepared using dies made of different materials. The surface was observed using digital and optical microscopes, and was rougher for the spaghettis prepared using the Teflon, polypropylene, polycarbonate, aluminum, and bronze dies in this order. The extrusion velocity when passing through the die was faster, the bulk density was higher, and the rupture strength was greater for the spaghetti having the smoother surface. The die material did not affect the gelatinization temperature. The water sorption curves in boiling water containing 0.5% (w/v) sodium chloride were also observed. The curves were expressed by an equation of the hyperbolic type except for the early stage of sorption in order to estimate the equilibrium amount of water sorbed based on the bone-dry sample. The momentarily-sorbed amount of water, which is a hypothetical quantity to characterize the initial water intake, was estimated by fitting the experimental points within 60 s. The amount was higher for the spaghetti having the rougher surface.

Water Sorption Kinetics of Spaghetti Prepared under Different Drying Conditions

Water Sorption Kinetics of Spaghetti Prepared under Different Drying Conditions

Effect of Salts on the Water Sorption Kinetics of Dried Pasta

The water sorption kinetics of dried pasta were measured in the 20-90 °C range in 1.83 mol/L of NaCl and at 80 °C in 1.83 mol/L of LiCl, KCl, NaBr and NaI solutions in order to elucidate the role of salt in the kinetics. At the temperatures higher than 70.8 °C, the change in the enthalpy of sorption, ΔH, in the 1.83 mol/L NaCl solution was 33.1 kJ/mol, which was greater than the ΔH value in water, and the activation energy for the sorption, E, in the salt solution was 25.6 kJ/mol, which was slightly lower than the E value in water. The Hofmeister series of ions was an index for their effect on the equilibrium amount of the sorbed solution of pasta. The apparent diffusion coefficient of water into pasta was not correlated with the crystal radius of the salts, but was with the Stokes radius of the hydrated ions. Equations were formulated to predict the amount of sorbed solution under any condition of temperature and NaCl concentration.

Influence of Chemical Structure on Hydration and Gas Transport Mechanisms of Sulfonated Poly(aryl ether ketone) Membranes

This work reports the influence of the chemical structure of two sulfonated poly(aryl ether ketone)s (SPAEK) on the hydration and gas transport mechanism of thin membranes made thereupon. For this purpose, two sulfonated poly(aryl ether ketone)s having the same ionic exchange capacity (IEC) but bearing a different repartition of the sulfonic acid groups along the polymer backbone were prepared. These polymers were synthesized by direct copolymerization of two specific sulfonated precursors, bisphenol AF and 4,4'-difluorobenzophenone. The morphology of the membranes was studied by transmission electron microscopy, and the thermal properties of the ionomers were determined from differential scanning calorimetry and thermogravimetric analyses. A detailed analysis of the water sorption isotherms and kinetics was performed. The gas transport properties were also determined for He, H(2), and CO(2) in the full range of water activity. From the detailed analysis of the water sorption isotherm and of the relative contributions of the Fickian diffusion and relaxation phenomena, a water sorption mechanism was proposed in relation with the SPAEK architectures and polymers' chain mobility. This mechanism allowed explaining the different evolution of the gas transport properties observed as a function of the gas nature and hydration rate.

Dilatometry of powder compacts — Characterizing amorphous-crystalline transformations

A new dilatometry method has been developed for studying small cylindrical powder compacts based on non-contact white light interferometry which offers a z resolution of < 10 nm. In-situ compact dimensions were measured as a function of time with controlled relative humidity and temperature, allowing the study of recrystallization and other volumetric changes for amorphous lactose compacts. Complementary X-ray powder diffraction and dynamic vapor sorption data confirmed both water sorption and recrystallization kinetics. At 35% RH the compacts exhibited 0.6% height expansion consistent with vapor sorption in a glassy material. For 55% RH and 75% RH, small initial shrinkages (~ 2.5%) associated with the moisture induced plasticization of the lactose particles and their relaxation or collapse were observed, followed by a significant height expansion (~ 15%) of the compacts due to swelling of the rubbery lactose phase prior to crystallization. The kinetics at 55% and 75% RH indicated a smooth dimensional transition from water swollen to crystalline lactose compacts. A detailed surface area study by N2 BET adsorption of a range of compacts showed no statistically significant surface area changes above or below the Tg.

Water sorption kinetics of superabsorbent hydrogels of saponified cassava starch‐graft‐poly(acrylamide)

AbstractSuperabsorbent polymers (SAPs) are hydrophilic polymeric networks that can absorb, swell and retain large quantity of water and other physiological fluids. In this paper, the water sorption pattern and kinetics of cassava starch based SAP hydrogels were studied under different conditions of swelling such as soaking duration, pH, presence of salts, and particle size of the hydrogel. The kinetics was studied using Voigt‐based viscoelastic model to determine the rate parameter and the swelling rate (SR). It was noted that under all conditions, the water sorption followed a second order kinetics. The absorbency was directly proportional to the rate of swelling. But when the sample was allowed to swell in aqueous solutions of CaCl2 and AlCl3, the absorbency as well as the SR was irregular. The particle size also had significant effect on water absorption by the SAP and the polymer with smaller particles showed more absorption than those with larger particle size. The solvent induced phase transition of the superabsorbent hydrogel was also studied.

Water sorption in ionic liquids: kinetics, mechanisms and hydrophilicity

Most of the ionic liquids (ILs) are hygroscopic in air. The effects of structural factors of ILs (cation, anion, alkyl chain length at cation, and C2 methylation at cation) and external factors (temperature, relative humidity, and impurity) on the kinetics of water sorption by 18 ILs were investigated. A modified two-step sorption mechanism was proposed to correlate the water sorption data in the ILs. Three type of parameters (sorption capacity, sorption rate and degree of difficulty to reach sorption equilibrium) based on the modified two-step mechanism were derived to comprehensively characterize the water sorption processes. These parameters have similar tendencies, providing an efficient way to evaluate them by one parameter that can be easily obtained. The hydrophilicity of the ILs was classified to four levels (super-high, high, medium, low) according to the water sorption capacity. The results show that cation of the ILs also plays an important role in water sorption, and the impurities affect the water sorption enormously. Acetate and halogen-based ILs have the highest hydrophilicity when combined with the imidazolium or pyridinium cation.

Water transport in aluminium oxide-poly(ethylene- co-butyl acrylate) nanocomposites

Polymer composites with metal oxide nanoparticles are emerging materials for use as insulation in electrical applications. However, the extensive interfacial surfaces and the presence of polar groups on the particle surfaces make these composites susceptible to water sorption. Water sorption kinetics were studied at 23 °C and different relative humidities (18–90%) for composites based on poly(ethylene- co-butyl acrylate) and aluminium oxide (⩽12 wt.%); the latter being in three different forms: uncoated and coated with either octyltriethoxysilane or aminopropyltriethoxysilane. The equilibrium water uptake increased linearly with increasing overall concentration of polar groups on the nanoparticle surfaces. Composites with well-dispersed nanoparticles showed Fickian diffusion (constant diffusivity and invariant boundary conditions) with a diffusivity that decreased with increasing filler content; the maximum factorial decrease in diffusivity was 300 with reference to that of the pristine polymer. This effect was most pronounced for composites with accessible polar groups on the particle surfaces, suggesting that water saturation of the composites is retarded by dual water sorption. Composites that contained a sizeable fraction of large nanoparticle agglomerates showed a two-stage sorption process: a rapid process associated with the saturation of the matrix phase and a slow diffusion process due to water sorption by the large nanoparticle agglomerates.

The effect of hydration on molecular chain mobility and the viscoelastic behavior of resilin-mimetic protein-based hydrogels

The outstanding rubber-like elasticity of resilin and resilin-mimetic proteins depends critically on the level of hydration. In this investigation, water vapor sorption and the role of hydration on the molecular chain dynamics and viscoelastic properties of resilin-mimetic protein, rec1-resilin is investigated in detail. The dynamic and equilibrium swelling behavior of the crosslinked protein hydrogels with different crosslink density are reported under various controlled environments. We propose three different stages of hydration; involving non-crystallizable water, followed by condensation or clustering of water around the already hydrated sites, and finally crystallizable water. The kinetics of water sorption for this engineering protein is observed to be comparable to hydrophilic polymers with a diffusion coefficient in the range of 10 −7 cm 2 s −1. From the comparison between the absorption and desorption isotherms at a constant water activity, it has been observed that rec1-resilin exhibits sorption hysteresis only for the tightly bound water. Investigation of molecular mobility using differential scanning calorimetry, indicates that dehydrated crosslinked rec1-resilin is brittle with a glass transition temperature ( T g ) of >180 °C, which dramatically decreases with increasing hydration; and above a critical level of hydration rec1-resilin exhibits rubber-like elasticity. Nanoindentation studies show that even with little hydration (<10%), the mechanical properties of rec1-resilin gels change dramatically. Rheological investigations confirm that the equilibrium-swollen crosslinked rec1-resilin hydrogel exhibits outstanding elasticity and resilience of ∼92%, which exceeds that of any other synthetic polymer and biopolymer hydrogels.

New methods to assess water diffusion in amorphous matrices during storage and drying

Water diffusion coefficient is an important parameter for food processing and stability, strongly influenced by the composition and the physical state of the matrix (amorphous glassy or rubbery/crystalline). In this study, two different methods to assess water diffusion in amorphous matrices were compared. First, an automatic sorption device was used to measure the water sorption kinetics of powders of maltodextrin DE21 and DE47 with defined shapes when equilibrating at different air relative humidity (0–60% at 25°C). Calculation of water diffusion coefficients was done according to Crank’s and Weibull’s models, and it was not possible when powders undergo glass transition. In the second part of the study a thin film dryer was used to assess the drying kinetics of aqueous solutions of maltodextrin (DE 6-12-29-40). The Yamamoto’s model allowed calculating water diffusion as a function of water content and temperature, above and below glass transition temperature.

Water sorption by the calcium chloride/silica gel composite: The accelerating effect of the salt solution present in the pores

The kinetics of isothermal water sorption by the CaCl2/silica gel composite initiated by a small stepwise pressure rise over the sample has been investigated at a constant underlying plate temperature of 35°C. The initial portion of the kinetic curves is consistent with Fick’s diffusion model: the amount of sorbed water increases in proportion to the square root of the sorption time. This makes it possible to determine the effective diffusivity of water (Deff). At small amounts of sorbed water (w 0.1 g/g. The contribution from this channel increases markedly when the amount of adsorbed water is above 0.25 g/g. This can be explained by the formation of the “connected” phase of the solution in the pores.

Water mobility within arabinoxylan and β-glucan films studied by NMR and dynamic vapour sorption

The main purpose of this research was to determine the impact of the structure and organisation of polysaccharides on the hydration properties of the cell walls of cereal grains. In order to remodel the lamellar assembly of arabinoxylan (AX) and (1 → 3)(1 → 4)-β-D-glucan (BG) within the endosperm cell walls, films were prepared and analysed using dynamic vapour sorption and time domain nuclear magnetic resonance spectroscopy. The water diffusivities within the AX and BG films were measured at 20 °C by observing the water sorption kinetics within a mathematical model based on Fick's second law. The evolution of spin-spin relaxation times of water protons measured by increasing the temperature is explained by the additional contributions of motion of the protons of polysaccharides and/or rapid chemical exchanges of protons between water and hydroxyl groups of polysaccharides. The difference between patterns of water behaviour within the AX and BG films can be related to the difference in their nanostructures. The smaller nanopores of the BG films cause their nanostructure to be more compact.