Moisture Sorption Rate Research Articles

Contrasting the Surface and Bulk Properties of Anhydrate and Dehydrated Hydrate Materials

Surface and bulk characterization of niclosamide and naproxen sodium between anhydrate and dehydrated hydrate were investigated. A comprehensive solid-state characterization was conducted using X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) for the identification and determination of physical properties of the materials. Surface properties were addressed by evaluating the various forms: by inverse gas chromatography (IGC) and water sorption tendency (dynamic vapor sorption, VTI). The XRPD, DSC, and TGA data show slight or no differences between anhydrate and dehydrated hydrate. However, the SEM, IGC, and water vapor sorption isotherms results provided evidence of the heterogeneity of surface for both compounds. The SEM microphotographs clearly showed the rugosity of the powders. Niclosamide dehydrated hydrate showed a higher dispersive surface energy and higher rate of moisture sorption than the correspon...

Moisture sorption and swelling of Norway spruce [Picea abies (L.) Karst.] impregnated with linseed oil

The moisture sorption and swelling of spruce specimens impregnated with linseed oil and unimpregnated controls were studied in two sorption experiments: from 0 to 55% relative humidity (RH) and from 55% RH to water saturation. Sorption isotherms were also determined using a sorption balance. The impregnated specimens had lower rates of both moisture sorption and swelling than the unimpregnated controls; however, there was no significant difference in final moisture contents. In addition, the linseed oil impregnation did not improve the dimensional stability of the wood; in most cases the specimens impregnated with linseed oil swelled more than the unimpregnated controls. For the impregnated specimens, reductions in swelling rates were in most cases seen without corresponding reductions in final swelling. The moisture sorption rate was reduced for the impregnated specimens but there were generally no reductions in equilibrium moisture content.

Effect of high-temperature drying on properties of Norway spruce and larch

In timber drying, mechanical properties may be changed due to treatment temperature and treatment duration. In general, when increasing the kiln temperature, drying time is decreased and some timber properties are negatively affected. In this study, the effect of different drying temperatures (80, 120 and 170 °C) on equilibrium moisture content and sorption rate, on bending strength and stiffness was investigated for Norway spruce and larch from four proveniences and the results were compared to those obtained for heat-treated wood (Thermowood

Moisture sorption and permeation in polyamide 6/clay nanocomposite films

AbstractThe moisture transport properties of a polyamide 6/clay nanocomposite have been studied through moisture sorption and permeation rate measurements. The temperature and concentration dependence of the steady state moisture uptake and permeation rate from the two types of experiment are distinctly different. The activation energy of moisture permeation obtained from the sorption experiment is lower than that derived from the permeation measurement. The interaction and contribution of the diffusion parameter and solubility parameter shows a complex moisture transport behavior in these nanocomposite films. Copyright © 2004 Society of Chemical Industry

Weathering Performance of Plant-Fiber/Thermoplastic Composites

Natural fiber/thermoplastic composites were made using aspen fiber and polypropylene. Several different levels of aspen fiber (30 to 60% by weight) were used with and without the addition of a compatibilizer (maleic anhydride grafted polypropylene, MAPP). These composites were tested for strength properties, exposed to boiling and cyclic liquid water and oven drying tests, and evaluated in an accelerated weathering test for 2000 hours. As the level of fiber increases without MAPP, flexural strength, flexural modulus, tensile strength and tensile modulus increases but notched and unnotched impact strength decrease as compared to pure polypropylene. The presence of MAPP has a very large positive effect on flexural strength, flexural modulus, tensile strength and tensile modulus as compared to composites made without MAPP. As the level of fiber increased in the composites, the rate and extent of thickness swelling and moisture sorption increased as compared to pure polypropylene. The presence of MAPP decreased the extent of swelling and moisture pickup. Weathering of composites under accelerated weathering conditions (water sprayed for 18 minutes followed by 102 minutes without water spray of UV radiation produced by a 6500-watt xenon arc light source) was restricted to the outer 0.5 mm of the surface. Weathering gave rise to the development of a white chalky surface layer which started at about 150–200 hours of weathering. After 2000 hours of accelerated weathering, weight loss increased with increasing fiber content and there was more weight loss in specimens containing MAPP as compared to specimens without the addition of MAPP. After scraping off the chalky white layer after 2000 hours of weathering, weight loss was greatest in specimens containing no fiber.

Grafting of Epoxy Resin on Surface-modified Poly(tetrafluoroethylene) Films

An epoxy/PTFE composite was prepared by curing the epoxy resin on the surface-modified PTFE film. Surface modification of PTFE films was carried out via argon plasma pretreatment, followed by UV-induced graft copolymerization with glycidyl methacrylate (GMA). The film composite achieved a 90°-peel adhesion strength above 15 N/cm. The strong adhesion of the epoxy resin to PTFE arose from the fact that the epoxide groups of the grafted GMA chains were cured into the epoxy resin matrix to give rise to a highly crosslinked interphase, as well as the fact that the GMA chains were covalently tethered on the PTFE film surface. Delamination of the composite resulted in cohesive failure inside the PTFE film and gave rise to an epoxy resin surface with a covalently-adhered fluoropolymer layer. The surface composition and microstructures of the GMA graft-copolymerized PTFE (GMA-g-PTFE) films and those of the delaminated epoxy resin and PTFE film surfaces were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and scanning electron microscope (SEM) measurements. The delaminated epoxy resin surfaces were highly hydrophobic, having water contact angles of about 140°C. The value is higher than that of the pristine PTFE film surface of about 110°. The epoxy resin samples obtained from delamination of the epoxy/GMA-g-PTFE composites showed a lower rate of moisture sorption. All the fluorinated epoxy resin surfaces exhibited rather good stability when subjected to the Level 1 hydrothermal reliability tests.

Sorption Behaviour and Dimensional Changes of Wood-Coating Composites

Summary The moisture related properties of wood-coating composites have been studied to evaluate the influence of coating penetration on the protection of wood against moisture. Pine sapwood samples were vacuum-impregnated with 7 pigmented and unpigmented coatings, both water and solvent borne. The retention and void filling of the coating have been determined. After drying, the samples were exposed to relative humidities between 33 and 98 % and to liquid water and equilibrium moisture content and dimensional changes were measured. The rate of swelling and moisture sorption has been measured, the latter was also used to calculate diffusion coefficients. The sorption isotherms were analysed by the Hailwood-Horrobin equation. In order to obtain additional information on the hygroscopicity of coatings, similar measurement were made on free coating films. The void filling of wood with coating material has the strongest impact on the uptake of liquid water. A limited reduction was observed for the equilibrium moisture content, the diffusion coefficient during adsorption and the rate of dimensional change. No influence on the equilibrium swelling have been found but the shrinkage during desorption was however often slightly increased for the wood-coating composites. The limited impact of the penetrated coating on moisture related properties can to a large extent be explained by the low void filling after drying (20–60%) and the relatively high moisture sorption and swelling of the coating film itself. In general, it can be concluded that the moisture protection of penetrated coating material is low in comparison to coating applied as a film on the surface of wood.

Effect of relative humidity and temperature on moisture sorption and stability of sodium bicarbonate powder

The effects of relative humidity and temperature on moisture sorption rate and stability profile of sodium bicarbonate powder exposed to various storage conditions were investigated using gravimetrical and acid-titration methods. In the study, samples were placed in desiccators, which contained various saturated salt solutions to generate desired levels of relative humidity, denoted as RH, ranging from 30–93% RH. The weight of each sample was determined periodically. The results show that both the temperature and relative humidity are key factors in moisture sorption isotherm and decomposition kinetics. The threshold relative humidity RH th is defined as the relative humidity above which sodium bicarbonate powder starts to rapidly gain weight. The critical relative humidity RH c is defined as the relative humidity above which sodium bicarbonate powder either starts to rapidly gain weight or starts to rapidly hydrolyze (resulting in losing weight). The moisture sorption isotherm shows an unusual phenomenon at high RH, where the weight of the sodium bicarbonate powder either increases or decreases with time, depending on the storage temperature. When the powder is exposed to a lower temperature and high humidity level (e.g. at 25°C and 93% RH), the weight increases rapidly, due to the fact that the relative humidity exceeds the RH th at this temperature. On the other hand, when the powder is exposed to higher temperature and high humidity levels (e.g. at 40°C, 89% RH and at 55 oC, 82% RH), the weight of the powder decreases with time since the relative humidity is below the RH th at these temperature levels and the decomposition rate is higher than the moisture sorption rate. The decomposition of sodium bicarbonate results in the release of carbon dioxide. The values of RH c at 25 and 40°C were determined to be between 76 and 88% RH and between 48 and 75% RH, respectively. The accurate moisture content and the stability profiles of sodium bicarbonate were determined using a titration-drying-titration procedure. The results of determination show that sodium bicarbonate powder is stable below 76% RH at 25°C and below 48% RH at 40°C, respectively.

Dynamic Models for Predicting the Moisture

The main problem in storage of dry food chips is water absorption. Dried foods tend to absorb moisture from free air. Flexible packaging can reduce the water absorption on foods and as the result it may prolong the shelf lives of the products. However, most flexible package materials are not fully impermeable. The moisture of the products in the package slowly increases until it reaches the moisture equilibrium. Accordingly, the objectives of this study were to develop mathematical models for predicting and to simulate the estimation of the moisture content of food chips during stored on permeable packages. The mathematical models developed were based on water vapor migration trough a permeable film, rate of moisture sorption by foods, equilibrium moisture content and water mass balance. Samples for the experiment were food chips made from gnetum seeds of local production. The gnetum (emping) chips were placed on stainless steel cups. The mouth of the cups were covered using polypropylene plastics as the package models. The cups were stored in glass bottles. The relative humidities of the storage atmosphere in the bottles were adjusted using saturated solution of salts such that the humidity ranges were between 10% to 95%. The changes of moisture content of the fried chips were observed for about twenty five (25) days until they reach their equilibrium moisture contents. The results indicate that the dynamic models can predict the moisture contents of fried chips in package quite well. The estimation of the water vapor migration trough the plastic film seems slower than the observed moisture absorption especially at low moisture contents.

OPTIMIZATION OF DEHYDRATED EGG QUALITY BY MICROWAVE ASSISTED FREEZE-DRYING AND HYDROCOLLOID INCORPORATION

Enhancement of the physical and sensory properties of rehydrated egg products as a consequence of microwave assisted freeze-drying and addition of hydrocolloids to the formulation was assessed. When compared to conventional freeze-drying (CFD), microwave assisted freeze-drying (MFD) led to products with greater water-holding capacity and reduced elastic modulus. Comparisons were also made of moisture sorption rates. The addition of xanthan gum and, to a lesser extent, microcrystalline cellulose increased both water-holding capacity and elastic modulus. Magnitude estimation by a trained texture panel of critical sensory properties (chewiness, rubberiness, moistness, moisture release, and roughness) revealed that MFD samples were superior to CFD samples and that MFD samples containing xanthan were closest to the optimal for the egg products. It was concluded that the more uniform and less heat stressing process of microwave assisted freeze-drying coupled with the presence of xanthan gum leads to a rehydrated product that best retains its structural integrity and ability to bind (reabsorbed) water and that, in turn, has highly acceptable textural properties most similar to fresh eggs.

MOISTURE SORPTION and VOLUMETRIC CHANGES of CANOLA DURING HYDROTHERMAL PROCESSING

The moisture content and volume change of canola seeds immersed in water or exposed to steam were measured. Three water temperatures of 22, 50 and 75C and one wet steam treatment (atmospheric pressure ∼ 100C) were used in the experiments. the maximum moisture attained by the canola seed was 0.67 decimal (db) in soaking and 0.54 decimal (db) in steaming. the moisture sorption rates were higher at higher temperatures of soaking. the coefficient of expansion did not vary significantly among treatments and an average coefficient of 1.032 per unit change in moisture content was obtained.

Moisture sorption mechanism of aromatic polyamide fibres: diffusion of moisture into regular Kevlar as observed by time-resolved small-angle X-ray scattering technique

The general trend of equatorial and meridional small-angle X-ray scattering (SAXS) was investigated for four kinds of Kevlar fibres: regular Kevlar, Kevlar 49, Kevlar 149 and a heat-treated PPTA fibre, over a scattering angle 2θ from 0.3 to 6.0°. Reflecting the fibre structure of highly oriented and extended chain conformation, the equatorial scattering is much more intensive and decreases in intensity more gradually with increasing scattering angle than the meridional scattering: i.e. the electron density fluctuations in the radial direction of the fibre due to interfibrillar and interstitial microvoids were expected to have Bragg spacings in the range from several to a few decades of angstroms, while no particular periodic fluctuation could be found in the fibre axis direction. The effects of total reflection upon the equatorial scattering intensity distribution were also discussed. The moisture sorption rate in a bone-dry regular Kevlar was observed at 25°C at saturated vapour pressure by the time-resolved SAXS technique. The experimental results were analysed assuming the moisture to be sorbed only in the microvoids to form various sizes of water cluster. Normalized moisture sorption rate, {1 − [ J(t) J(0) ] 1 2 } {1 − [ J(∞) J(0) ] 1 2 } , determined from the change in integrated scattering intensity over the angular range 0.3–6.0° with time, J( t), was compared with that observed by a gravimetric method, M(t) M(∞) , at a relative vapour pressure of 0.896 at 25°C. Although both rate curves attained equilibrium at almost the same time of about 670 min, the rate curve from the SAXS method showed a sigmoidal shape and the moisture diffusivity was much smaller than that determined from the gravimetric method. The large discrepancy between the two diffusivities was explained using the assumption that the gravimetric method detects the sorbed water in the form of both ‘micro-water clusters’ and ‘macro-water clusters’, but the SAXS method detects only the ‘macro-water clusters’.

The Effect of Moisture Sorption and Desorption on Furosemide Tablet Properties

AbstractThe effect of moisture sorption and desorption on the physical characteristics of furosemide tablet was studied at moderately elevated temperatures and different relative humidity conditions over 20 days. The rate of moisture sorption and desorption was founud to follow first order kifietics within first hours. Except ambient conditions (RT/Amb.RH), moisture sorption caused a decrease in hardness values of furosemide tablets. Also the disintegration times of hydrated tablets showed a remarkeable decrease. Changes in hardness and disintegration time were dependent on the amount of water sorbed into the tablets. These significant changes occured during the first days of the test and then became invariant. The variations in hardness and disintegration times of tablets were irreversible as demonstrated by desorption experiments.Furthermore, except storage at high temperature and high relative humidity dissolution parameters of tablets were less affected by moisture sorption and desorption.

Desiccant Moisture Sorption as Altered by Dust

ABSTRACT THE moisture sorption characteristics of silica gel, activated alumina and a molecular sieve each having 0 percent and 5 percent dust were compared. Inorganic dust particles of 10 to 20 micrometers did not affect the equilibrium moisture content of either silica gel, ac-tivated alumina or molecular sieve. Dynamic moisture sorption rates of all three desiccants were reduced by dust contamination. The molecular sieve adsorbs moisture rapidly until saturation, unlike that described by the common falling rate sorption model. While silica gel and activated alumina may be useful in drying air for agricultural applications, the molecular sieve is least likely to be useful due to its low hygroscopic capacity.

Moisture sorption and volume expansion of lactose anhydrate tablets (author's transl)

The moisture sorption and volume expansion of anhydrous α- and β-lactose tablets were examined under various conditions of relative humidity. In the case of anhydrous α-lactose tablets, the moisture sorption and expansion of tablets occurred even at a relatively low humidity, leading to the formation of the α-monohydrate. The rate of moisture sorption and expansion increased with an increase in water vapor pressure and with a lowering in temperature. The effect of tablet thickness and of compaction pressure in tablet making were also examined using anhydrous α-lactose tablets. β-Lactose was less hygroscopic at below 90% relative humidity (R.H.). Moisture uptake was small and the expansion of tablets was not observed. When the water vapor pressure rose to almost saturation, β-lactose absorbed a large amount of moisture to form the α-monohydrate gradually.

The Expansion of Compressed Tablets due to Moisture Sorption

The expansion of the compressed tablets in diameter and thickness due to their sorption of moisture has been studied, using starch and microcrystalline cellulose tablets.Of the starch tablets, the values of equilibrium volume expansion were very low as compared with the equilibrium moisture contents at low relative humidities below 20%. Above this relative humidity, the values of volume expansion were approximately at 1cm3 per gram of the sorbed water.In the kinetic measurement under different conditions of relative humidity, the rate constant of moisture sorption increased with increasing relative humidity. The values of rate constants of volume expansion were approximately equal to those of moisture sorption.For the microcrystalline cellulose tablets both the rate of moisture sorption and the rate of volume expansion decreased with increasing compaction pressure in tablet preparation.