Effect Of Moisture Sorption Research Articles

Sensitivity analysis of a physicochemical model of chloride ingress into real concrete structures subjected to long-term exposure to tidal cycles

In marine environments, reinforced concrete structures are exposed to tidal conditions and therefore susceptible to chloride ingress. Reliable models of transport are crucial in order to evaluate the service life of these structures. Unlike engineering models based on Fick's 2nd law and empirical coefficients, this study proposes a model based on a physicochemical description of the transport phenomena and on some assumptions restricting the number of inputs to 9 parameters and the computational costs. This model is validated for a long exposure to tidal cycles (28 years). Then, the sensitivity analysis, based on the Morris method, is performed through 100 simulations of tidal exposure considering different sets of the 9 input parameters. According to the critical times of initiation of corrosion predicted, the most sensitive parameters are the critical chloride concentration and the chloride diffusivity factors. The effects of moisture sorption and chloride binding parameters are moderate after long exposure. Then, the results of the simulations are compared to data of the literature in terms of convection depths and total chloride concentrations at the limit of the convection / diffusion zones. Finally, by quantitative considerations, the analysis goes further, providing analytical relations expressing the convection depth and the associated total chloride concentration as functions of input parameters. These provide physically informed guidelines in using an engineering model based on Fick's 2nd law in order to estimate the critical time of initiation of corrosion.

Moisture sorption by polymeric excipients commonly used in amorphous solid dispersions and its effect on glass transition temperature: III. Methacrylic acid-methyl methacrylate and related copolymers (Eudragit®)

Moisture sorption by polymeric carriers used in amorphous solid dispersion (ASD) plays a critical role in the physical stability of the dispersed drug as it can increase molecular mobility of drug in ASD by decreasing the glass transition temperatures (Tg) of the drug-polymer system, leading to drug crystallization. The present report describes Part III of a systematic investigation of moisture sorption by different polymers used in ASDs, where the results for four chemically different methacrylic acid-methyl methacrylate and related copolymers, namely, Eudragit® EPO, Eudragit® L100-55, Eudragit® L100, and Eudragit® S100, as the function of relative humidity (RH) are presented. Effects of moisture sorption on Tg of the polymers were also determined. Among the polymers, Eudragit® EPO is the least hygroscopic, having absorbed, for example, 1.3% w/w moisture at 25 °C/60% RH, while the three other polymers absorbed 4.7–7.5% w/w moisture at the same condition. The moisture sorption was relatively lower at 40 °C than that at 25 °C. The apparent Tg of polymers decreased with the increase in moisture content; however, Tg values remained higher than the usual storage temperature of ASD (25 °C) even at high RH, indicating that the effect of moisture sorption on the physical stability of ASD could be minimal when these polymers are used in ASDs.

Moisture sorption and swelling of flax fibre and flax fibre composites

This study evaluates the influence of moisture sorption on the properties of flax fibres and their composites. The radial swelling of both the elementary and technical flax fibres at a wide range of relative humidity (RH) values is determined. Moreover, the effects of moisture sorption on both the thickness swelling and flexural properties of flax/polyester and flax/epoxy composites are evaluated. Park's model is used to define the fibre moisture sorption curve. The model suggests that the moisture is first sorbed on hydrophilic fibre surfaces or microcavities until specific sites within the fibre reach saturation and later, the moisture forms aggregates at high RH. Flax elementary fibres have a lower radial swelling coefficient when compared to technical fibres , with radial swelling coefficients of β r = 1.2 and 1.9, respectively. At the composite level, flax/polyester and flax/epoxy systems have approximately the same thickness swelling coefficients, β t = 0.5 and 0.6, respectively, over the RH range , 11–97%. This behaviour could be explained by the constraining effect of the resins on flax fibres due to higher stiffness of matrix and probably due to resin penetrating the fibre lumen. Flexural properties of longitudinal and transverse fibre-oriented flax/polyester and flax/epoxy composites conditioned at different RH, and tested in fully dry condition, decreased as RH increased beyond 54%, likely due to moisture swelling which induced damage. This study provides new insights into the moisture sorption and dimensional changes of both the elementary and technical flax fibres and their composites and also the effects of moisture on the flexural properties of the composites.

Effect of Moisture Sorption on Free Volume and Relaxation of Spray Dried Dispersions: Relation to Drug Recrystallization

The effect of vapor sorption on the free volume of drug-polymer spray-dried dispersions (SDDs) was investigated, along with the crystallization propensity of drug molecules in SDDs after exposure to humidity. Subsequently, the correlation of free volume change and relaxation time with drug recrystallization was examined. Four polymers, including polyvinylpyrrolidone, polyvinylpyrrolidone vinyl acetate copolymer, hydroxypropyl cellulose, and hydroxypropyl methylcellulose acetate succinate, and 2 drugs (indomethacin and ketoconazole) were selected for preparing SDDs. Free volume data of the exposed SDDs were obtained with positron annihilation lifetime spectroscopy, while the relaxation time was measured using a TA rheometer. Additionally, the crystallization propensity of active pharmaceutical ingredients (APIs) in the exposed SDDs was assessed using both polarized light microscopy and powder X-ray diffraction, followed by relating API crystallization inclination with expansion of holes and relaxation time. Finally, Cohen and Turnbull molecular transport model, along with its extensions by Vrentas and Duda, was qualitatively utilized for interpreting the recrystallization propensity of API molecules. In conclusion, API recrystallization is closely related to free volume change upon moisture sorption and relaxation time, but system dependent; overall, drug-hydroxypropyl methylcellulose acetate succinate SDDs appear physically stable against recrystallization due to less increase in free volume.

Sorption and dielectric properties of jute woven fabrics: Effect of chemical composition

The jute woven fabric was treated with sodium hydroxide and sodium chlorite under different conditions in order to study the influence of the chemical composition on their sorption and dielectric properties. After the alkali treatments, the hemicelluloses content decreased in the range of 14.4–46.7%, which leads to elementary fiber liberalization and increased moisture sorption of the jute fabrics up to 15.5% and 11.9% at 30% and 80% relative humidity, respectively. The X-ray diffraction analysis shows that the removal of hemicelluloses for 14.4% and 36.6% was followed by a decrease in the crystallinity index for 3.0% and 18.8%, respectively. The additional decrease in hemicelluloses content of 46.7% was accompanied by a slight increase in the crystallinity index for about 14%. These results are in a good agreement with the results obtained for the AC specific electrical conductivity (at 30% and 80% relative humidity). After the oxidative treatments, the lignin content decreased in the range of 37.8%–79.0%, which causes two parallel effects: a slightly increased moisture sorption (up to 7.4% and 4.6% at 30% and 80% relative humidity, respectively) and crystallinity index (from 4.8%–16.6%). The jute fabrics with 37.8% and 63.2% lower lignin content and similar moisture sorption values have the same AC specific electrical conductivities at both relative humidities (30% and 80%) revealing a dominant effect of moisture sorption. The AC specific electrical conductivity of the investigated jute fabrics increases with increasing the frequency as well as relative air humidity, where the highest difference between the values of AC specific electrical conductivity is obtained at the highest frequency (140 kHz).

Predicting the solubility enhancement of amorphous drugs and related phenomena using basic thermodynamic principles and semi-empirical kinetic models.

The accurate prediction of the solubility enhancement offered by neat amorphous drugs and amorphous solid dispersions, over their crystalline (API) counterparts, has been discussed in several landmark works dating back at least two decades. Against this backdrop, an assessment of the current state-of-the-art for rigorously, yet simply (circumventing computational methods), determining the amorphous:crystalline solubility ratio based on thermo-analytical quantities is presented herein. Included in this work is a brief survey of the literature together with a discussion of the advantages and shortcomings of some of the most popular approaches, to-date. While the focus is on neat amorphous drugs, both before and after moisture sorption, the methodology presented is readily extended to more complex (e.g. ternary) systems that form a single, homogeneous phase. Six key questions are addressed in the context of how to most accurately determine the amorphous:crystalline solubility ratio: (1) How is the lattice energy of the crystalline phase assessed? (2) What is the role of heat capacity? (3) How does the pKa impact the solubility ratio prediction (for ionizable drugs)? (4) How does one incorporate the effects of moisture sorption on the amorphous phase? (5) How might one characterize (predict) the rate of drug recrystallization under various conditions (since the duration of the solubility enhancement is a kinetic phenomenon)? (6) What is the best approach for linking the (loss in) solubility enhancement to the Tg-lowering of the amorphous drug (by water) and vice-versa? In addressing these questions, this work aims to put forth a standardized methodology for determining the amorphous solubility enhancement with improved accuracy.

Impact sensitivity and moisture adsorption on the surface of CL-20/TNT cocrystal by molecular dynamics simulation

Water molecules in the air can be absorbed on the surface of the explosives in storage and transport process, which may lead to the transformation of sensitivity and storage safety. The interactions between cocrystal and water molecules are identified as a process of physical adsorption. To explore the effects of moisture sorption on the storage safety, this paper took the cocrystal composed of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 2,4,6-trinitrotoluene (TNT) in a 1:1 M ratio as the research object, and molecular dynamics simulation was conducted on the cocrystal for (0 0 1), (0 1 0), (1 0 0) crystal plane in COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) force field. It turns out that there are hydrogen bonding interactions between the water molecules and the molecules in the cocrystal by analyzing the Radial distribution function diagrams. The length of trigger bond and the cohesive energy density of the cocrystal are adopted as theoretical criterion of sensitivity. The results indicate that it takes less energy for the NN bonds to rupture and the explosives would have higher sensitivity when water molecules are absorbed on the surface.

Film forming properties of Cissus pulpunea (Guill and Perr) and Irvingia gabonensis (O'Rorke) gums.

Natural polymers such as gums have gained attention in drug delivery systems due to their availability, compatibility and degradation under natural and physiological conditions. The aim of the present study was to investigate the film forming properties of gums obtained from the stem of Cissus polpunea (Guill and Perr) and the seed of Irvingia gabonensis (O'Rorke). Gums were extracted from the relevant plant parts and characterized using functional, proximate and elemental properties. Films were prepared by the casting method using gum concentrations of 1-4% w/v and varied with propylene glycol (PG). The films were assessed through physical observation, thickness, swelling power and moisture sorption effects using the relative humidity of 0, 27, 43, 57, 75 and 90%. The gum yielding optimal film properties was used as coating material in ibuprofen tablet formulations. The mechanical and release properties of the tablets were determined. The functional and proximate properties of gums showed a similarity in the majority of the parameters, but significant (p < 0.05) variation existed in their solubility, while elemental assessment revealed the absence of toxic metals. Generally, the films were homogenous, opaque and demonstrated high swelling power in phosphate buffer, which was pH-dependent. Moisture sorption properties of the gums increased with the increase in relative humidity in the order HPMC < Cissus < Irvingia. Film-coated ibuprofen tablets showed higher mechanical properties and disintegration and dissolution times compared with uncoated tablets. Cissus and irvingia gums have demonstrated acceptable functional, proximate and elemental properties. Film-coated ibuprofen tablets showed higher mechanical and release properties than was the case in uncoated tablets.

Effect of moisture sorption on the performance of crospovidone

Crospovidone is a commonly used tablet disintegrant. However, the synthetic disintegrant has been known to be hygroscopic and high moisture content in crospovidone used could exert deleterious effects on tablets formulated with it. The objective of this study was to elicit a better understanding between crospovidone-water interaction and its effect on disintegrant performance. Moisture sorption and desorption isotherms were obtained together with the enthalpy of immersion. Crospovidone samples stored at four relative humidities were used to formulate tablets and the resultant tablets were evaluated for their mechanical, dimensional and disintegratability attributes. Analyses of the moisture sorption isotherms indicated that externally adsorbed moisture accounted for the bulk of the total moisture content in crospovidone, with minimal amount of moisture absorbed intramolecularly. Enthalpy of immersion became less exothermic with crospovidone samples stored at increasing storage humidity. Correspondingly, improvement in disintegration time became less pronounced. This was postulated to be a consequence of premature wetting of the particle surfaces by externally adsorbed moisture. High humidity was also detrimental to tablet hardness and thickness. In conclusion, the impact of moisture sorption during storage by excipients such as crospovidone could be better understood by the appreciation of crospovidone-water interaction and its consequence on tablet quality.

Moisture adsorption of glucomannan and xylan hemicelluloses

Wood and wood materials are highly sensitive to moisture in the environment. To a large extent this relates to the hygroscopicity of wood hemicelluloses. In order to increase our understanding of the effects of moisture sorption of the major wood hemicelluloses, glucomannan and xylan, model experiments using films of amorphous konjak glucomannan and rye arabinoxylan were conducted. Moisture-induced expansion and stiffness softening were characterized using dynamic mechanical testing. Both hemicelluloses showed a threshold around 5 % of moisture content above which swelling increased whereas the modulus decreased by more than 70 %. FTIR spectra, using H2O and D2O, indicated that even at high RH about 15 % of the hydroxyl groups were not accessible to hydrogen exchange by D2O. For xylan both hydroxyl groups were found to exchange in the same manner while for the glucomannan the O(6)H group seemed to be the most accessible.

Experimental Determination of Innovative Plaster Moisture Expansion

The problem of the reconstruction of the historical building surface layers is in material compatibility. The basics of the convenient choice of materials for reconstruction is understanding some physical properties of used materials. The crucial properties are moisture and temperature induced deformation. The effect of moisture sorption on the elastic behavior of innovative plaster for renovation is investigated. The measurements are performed for moisture content from the dry state to the saturation water content and temperature range of 10 - 40°C.

Determination of Poroelastic Parameters of Porous Building Materials

Variations of sorption moisture in the capillary porous materials result in strong fluid-skeleton interactions due to molecular and surface forces, which produce moisture-induced deformation. The effect of moisture sorption on the non-linear elastic behavior of hygroscopic porous building materials has been experimentally investigated showing strong influence of moisture especially in the lower moisture content range. In the framework poroelasticity moisture influence on elastic behavior is described by two poroelastic coefficients, which present the fluid-skeleton coupling. This paper presents an application of the procedure for the determination of the coupling coefficients for medieval brick.

Conductive Anodic Filament Failures in Fine-Pitch Through-Via Interconnections in Organic Package Substrates

Failures due to conductive anodic filament (CAF) formation in copper-plated through-vias have been a concern in printed wiring boards since the 1970s. With the continuous reduction in through-via pitch to meet high circuit density demands in organic packages, the magnitude of CAF failures is expected to be significantly higher. In this study, an accelerated test condition [130°C, 85% relative humidity (RH), and 100 V direct current (DC)] was used to investigate CAF in two organic package substrates: (1) cyclo-olefin polymer–glass fiber composite (XR3) and (2) epoxy–glass fiber composite (FR4). Test coupons with through-via spacing of 100 μm and 200 μm were investigated in this study. CAF failures were not observed in either substrate type with spacing of 200 μm. With spacing of 100 μm, insulation failures were observed in FR4, while XR3 exhibited stable insulation resistance during the test. The substrates were characterized using gravimetric measurement, and XR3 was found to exhibit significantly lower moisture absorption compared with FR4. The CAF failures in FR4 were characterized using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The results suggest a strong effect of moisture sorption of organic resins on CAF failure at smaller through-via spacing in package substrates.

Effect of Tropical Climatic Conditions on the Stability of Cefaclor Dry Powder for Suspensions

Purpose: Two critical factors that govern the stability of pharmaceutical formulations in the tropics are humidity and temperature. This study was carried out to investigate the effect of moisture sorption at two different storage conditions on Cefaclor dry powder for oral suspension and predict the effect of moisture interaction on the reconstituted formulations Method: Cefaclor dry powder for suspension formulation was taken as a model formulation for this study. Different formulations were manufactured and placed in twelve amber coloured glass bottles for each test condition. One set of bottles was sealed by heat induction technique under vacuum to ensure the integrity of the seal while the other set was without a seal but had a child-resistant cap. Both types of bottles were stored in humidity chambers at 30°C/65%RH or 40°C/75%RH. Weight changes were monitored on a dynamic moisture balance over a period of 3 months. Results: The results were recorded in terms of moisture content, colour, and excipient interaction and their effect on product appearance. The data were analyzed using Students t-test and one way analysis of variance (ANOVA), and differences were considered statistically significant at P < 0.05. Conclusions: The study revealed that the product with enhanced packaging and also contained nonwater soluble colourants were more protected against the deleterious effects of moisture and temperature. The findings provide an insight into a possible approach for formulating moisture-sensitive pharmaceutical products, especially dry powder preparations for use in the tropics.Keywords: Dry powder for suspension; Moisture content; Colour; Stability; Moisture migration; Interaction

Effect of moisture sorption of underwear material on clothing microclimate in a hot environment

AbstractIn this study, to investigate the thermal comfort of underwear, it was experimentally evaluated how the moisture sorption of underwear material affected the transient condition on the clothing microclimate under the summer heat environment by using a perspiration thermal manikin. Three kinds of underwear with different mixed spinning rates of moisture absorbing synthetic fiber (MAS) were compared. It was shown that the higher the mixed spinning rate of MAS, the larger the decline of the humidity in the clothing was in insensible perspiration. In comparison, for PET70 with 100% cotton (COT100), though each of the official moisture regions was almost the same, the microclimate humidity declined more rapidly in COT100 and returned to the original humidity in a shorter time. The integration value of the humidity decline which returned to the original value was the same between the two materials. To show the effect of the initial condition of the material, the underwear in a moderate humid condition, which was 30°C, 65% RH, was compared with one in a dry condition. The fall in the clothing microclimate of the humid condition was about one third that of the dry one. In sensible perspiration, though the humidity decline was seen, it returned to the original humidity faster than in the insensible condition. A temperature rise in the clothing and a temperature drop occurred as frequently as in the standard underwear during drying on the skin surface. This suggested that the endothermic reaction occurred as moisture desorbed. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20220

Thermoplastic modification of urea–formaldehyde wood adhesives to improve moisture resistance

AbstractUrea–formaldehyde (UF) resins are prone to hydrolytic degradation, which limits their use to indoor applications. This study examined the modification of UF resin with various thermoplastics as a means to increase the moisture resistance of the adhesive. UF adhesives were modified in situ with various hydrophobic and hydrophilic thermoplastic formulations, using either polar or nonpolar initiators. Unmodified and modified UF resins were characterized in terms of viscosity, pH, and gel time in their prepolymer suspension state. Cured solid UF resin plaques were prepared to isolate moisture sorption effects of the cured UF resin from that of the wood component in composites, which dominates their moisture uptake. Relative crosslink density and moisture sorption tests were run on cured UF resin plaques. Results indicated that viscosity increased after modification in most cases, with higher viscosities resulting from formulations using an acidic (polar) initiator. In all cases, activation energies of the curing reactions of thermoplastic‐modified UF suspensions were lower than the unmodified UF. High relative crosslink density compared to the unmodified UF was found for one sample, which correlated well with lower overall moisture sorption. Higher relative crosslink density of cured UF resin plaques appeared to be an indicator of lower moisture uptake. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4222–4229, 2006

The Stability of Poly(lactic acid) Packaging Films as Influenced by Humidity and Temperature

ABSTRACTThe effect of moisture sorption on stability of poly(lactic acid) (PLA) films at food‐packaging conditions, obtained by different humidities (11% to 98% RH) and temperatures (5 °C and 25 °C), was investigated by decrease in number average molecular weight (Mn) and loss of tensile strength. Hydrolysis of the PLA ester linkages resulted in a 75% decrease over 130 d at 25 °C and 98% RH. At cooling conditions the decrease amounted to 35%. An equilibrium moisture sorption isotherm could not be determined as the irreversible hydrolysis of PLA induced an ongoing moisture uptake. The rate increased when the humidity and temperature increased from 5 °C to 25 °C. After 189 d at 98% RH, moisture sorption was 7 g/100 g and 86 g/100 g at 5 °C and 25 °C, respectively. Loss of tensile strength was minor and primarily due to reversible plastization by moisture. Only at 98% RH and 25 °C, loss of tensile strength became pronounced (45%). Consequently, the present PLA material is in general expected to be mechanically stable when packaging foods covering the region from dry to moist food and storage conditions from chill to ambient temperatures.

Effect of moisture sorption state on transverse dimensional changes in wood

The purpose of the study was to understand the transverse dimensional changes and corresponding anisotropicity in wood during different states of moisture sorption. Oven dried samples of Erythrina variegata, Lannea coromandelica, Gmelina arborea and Albizia chinensis were adsorbed and subsequently desorbed at constant temperature (35°C). Tangential and radial dimensional changes (swelling) were analysed with respect to relative humidity and moisture content during both the states of sorption. Dimensions in tangential direction were found to change at a relatively greater rate than in radial direction at high humidities. It was observed that transverse dimensions were more during desorption compared to adsorption at a given equilibrium moisture content. This confirms presence a second order effect of moisture sorption on dimensional movement. This effect was found to be more prominent in tangential direction compared to radial direction resulting in higher coefficient of anisotropy (α T /α R ratio) during desorption. The magnitude of this phenomenon was found to vary from species to species.

The effect of moisture sorption on electrostatic charging of selected pharmaceutical excipient powders

An experimental investigation has been undertaken to determine the effects of moisture sorption propensity on the triboelectrification of pharmaceutical excipients in contact with materials used for the fabrication of pharmaceutical processing equipment and drug delivery devices. Moisture sorption and desorption isotherms were determined for α-lactose monohydrate, dextrose monohydrate, spray-dried sorbitol and sodium starch glycolate. The isotherms show that α-lactose monohydrate and dextrose monohydrate are non-hygroscopic over a wide range of relative humidity (rh) from 0% to 80% and have negligible hysteresis on desorption. Sodium starch glycolate was the most hygroscopic, spray-dried sorbitol was of intermediate hygroscospicity and both isotherms showed hysteresis on desorption. The sorption data was analysed to estimate the distribution of monolayer adsorbed, multilayer adsorbed and absorbed moisture. The effect of storage relative humidity on the triboelectrification of the powders was investigated using steel, polypropylene and polyvinylchloride (PVC) as contact surfaces. The results showed that moisture sorption and distribution data could be useful in predicting the electrostatic charging of pharmaceutical powders. There was negligible effect of rh on the charging of the excipients with low hygroscopicity, whereas the charging of the sodium starch glycolate was inversely related to the storage rh. The relationship between moisture sorption/distribution and electrostatic charging for spray-dried sorbitol was more complex and attributed to the greater distribution of sorbed water in the pore structure of the sorbitol. The non-hygroscopic excipients charged negatively with steel and positively with PVC and polypropylene, whereas sodium starch glycolate charged negatively with all contact surfaces.

Moisture Sorption Effects on and Properties of a Carbon Fiber-reinforced Phenylethynyl-terminated Poly(etherimide)

This paper reports the results of anin vestigationof moisture sorption effects on the properties of a carbon fiber-reinforced high-performance phenylethynyl-terminated poly(etherimide). Due to the relative newness of this material, minimal information regarding its performance under the duress of environmental effects is known. Composite and neat resin specimens were cycled to effective moisture equilibrium during exposure to a 85% relative humidity/90 C environment followed by exposure to a 10% relative humidity/90 C environment. The composite through-the-thickness moisture diffusion coefficients (Dz) ranged from 2.3 × 10 -6 to 6 mm2/s. The value of Dz for moisture absorptionwas measured to be about 67% greater thanthe value of Dz for moisture desorption; residual stress-accelerated diffusion, void-assisted diffusion, and diffusion hindered by moisture–matrix interactions are discussed as possible explanations for this difference. At 85% relative humidity, the effective moisture equilibrium content of the composite and neat resin were 0.52 ± 0.02% and 1.60 ± 0.01%, respectively. The average transverse moisture expansion coefficient of the composite was 1.1 × 10 -3±0.7 × 10-3. The 1.2% retention (85% 7.0% retention (10% relative humidity) of the control 9.5 MPa. No conclusive results were obtained from open-hole compression strength and apparent interlaminar shear strength tests. The majority of the surfaces of the TFS specimens displayed moisture sorption induced damage. The dramatic impact that inadequate matrix cure can have on a composite’s ability to transverse flexural strength (TFS) specimens exhibited 60.7 ± relative humidity) and 83.6 ± value of 135.9 ± endure a single moisture sorption cycle is illustrated by comparison with a previous moisture exposure study of this material.