KINETICS OF WATER VAPOR SORPTION BY FREEZE DRIED PAPAYA

The hygroscopic potential of freeze dried papaya in the form of powder and granules was studied for several temperatures (23,33 and 43PC) and relative humidities (49 to 90%). For such conditions the kinetics of water sorption was established. The results show the influence of the amount of water absorbed, the environmental relative humidity and temperature on water sorption rates for this type of product. An intriguing behavior was found far the rates of water sorption as influenced by the absolute temperature, and at the critical level of 60% relative humidity, this influence is very much reduced.     

Sorption characterization of poly(vinyl alcohol)/chitosan interpenetrating polymer network hydrogels

Poly(vinyl alcohol) (PVA)/chitosan interpenetrating polymer networks (IPN) were prepared by UV irradiation. The water sorption behavior of the IPNs was measured at various temperatures and humidity levels. The water uptake of IPN13 is greater than that of other IPNs. Vapor sorption behavior is more affected by the density of water vapor than by hydrophilic properties with increasing temperature. Equilibrium water uptake increases as humidity increases, and the increase is more noticeable at high humidity. The sorption system of all IPNs is a relaxation‐controlled mechanism at a relative humidity (RH) of 90%, but it is a Fickian diffusion‐controlled mechanism when the RH is below 50%. With an increase in humidity, the diffusion coefficients were found to increase due to greater penetration of water into the IPNs. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 86–90, 2003     

Effect of Relative Humidity on the Antioxidant Activity of Spray-Dried Banana Passion Fruit (Passiflora Mollisima Baley)-Coated Pulp: Measurement of the Thermodynamic Properties of Sorption

The antioxidant activity of the spray-dried banana passion fruit-coated pulp with maltodextrin10 DE was evaluated throughout 30 days of storage at a temperature of 25°C for different relative humidity values It was influenced by the relative humidity throughout the 30 days of storage. In addition, the sorption equilibria of water for spray-dried banana passion fruit-coated pulp with maltodextrin 10 DE at 25, 35, 45, and 55°C, over a range of relative humidity levels from 0.113 to 0.843, was determined using a gravimetric static method. The isosteric heat and Gibbs free energy were calculated from the sorption equilibrium. The Guggenheim-Anderson-Boer (GAB) and Brunauer-Emmett-Teller (BET) models were tested to fit the experimental data. The GAB model was found to be the most suitable for describing the sorption curves, exhibiting an error smaller than 10% and an r greater than 0.99. The monolayer moisture content values for the sorption at different temperatures that were calculated using the GAB model ranged between 0.05315 to 0.05716 g water/g dry matter. The sorption curves exhibited a Type III behavior. The isosteric heat decreased with increasing moisture content while the Gibbs free energy increased.     

Bestimmung der sorptionsisothermen lösungsmittelfeuchter sorbentien nach der durchströmungsmethodeDetermination of sorption isotherms of solvent wetted sorbents by the through flowing method

The sorption isotherm is defined as the equilibrium moisture content of a sorbent as a function of the relative humidity at constant temperature. It is a measure for the hygroscopic behavior of the sorbent. In this work a simple and reliable method for the determination of sorption isotherms of solvent wetted sorbents is described. The sorption isotherm is determined by passing a nitrogen stream with a given relative humidity through a U-tube filled with the sorbent (through flowing method). The sorption isotherms of gas concrete, brick and clay for the sorbates isopropyl alcohol and water at 20 °C were measured. The reliability of the method was tested by comparing it with two other methods.     

Experimental Determination and Modeling of Sorption Isotherms of Erythrina Fusca Lour Bark

The water sorption isotherms of the Erythrina fusca Lour bark at 30 and 40°C were determined over relative humidity ranging from 55 to 85%. The equilibrium moisture content was determined gravimetrically. The moisture sorption isotherms showed that the equilibrium moisture decreases with increase of temperature. Six models were used for to fit the experimental curves of equilibrium humidity. Parameters of each equation were determined by nonlinear regression analysis. The isosteric heat of moisture sorption was calculated using the Claussius-Clapeyron equation.     

蛭石/氯化钙复合吸附剂的吸附特性和储热性能

为了储存120℃以下的热能,提出了以水为介质的热化学吸附储热方法。配制了一种以膨胀蛭石为多孔基质、氯化钙为反应盐的新型复合吸附剂,并对其进行了微观形貌表征、吸附性能测试、同步热分析测试和储热密度的理论计算。扫描电子显微镜（SEM）观测显示膨胀蛭石特有的片层状的大孔结构产生了相对巨大的孔体积;利用恒温恒湿箱实验排除有溶液泄漏问题的含盐量;通过恒温恒湿箱对30℃、3种相对湿度下的动态吸附过程进行测试,分析了含盐量和相对湿度对吸附特性的影响,证实了该复合吸附剂具有3个不同的吸水阶段,包括物理吸附、化学吸附和溶液的气-液吸收过程;利用同步热分析测试（STA）和数值计算进一步对上述3个吸附过程的吸水量、吸附热和反应温度进行分析。最终优选出含盐量47.9%（质量分数）的复合吸附剂,其吸水量高达1.24 g·g^-1,质量和体积储热密度分别高达1.25 kW·h·kg^-1和213.56 kW·h·m^-3。     

Bestimmung der sorptionsisothermen lösungsmittelfeuchter sorbentien nach der durchströmungsmethode

The sorption isotherm is defined as the equilibrium moisture content of a sorbent as a function of the relative humidity at constant temperature. It is a measure for the hygroscopic behavior of the sorbent. In this work a simple and reliable method for the determination of sorption isotherms of solvent wetted sorbents is described. The sorption isotherm is determined by passing a nitrogen stream with a given relative humidity through a U-tube filled with the sorbent (through flowing method). The sorption isotherms of gas concrete, brick and clay for the sorbates isopropyl alcohol and water at 20 °C were measured. The reliability of the method was tested by comparing it with two other methods.     

Sorption properties of wood impregnated with aqueous solution of boric acid and montan wax emulsion

Nonbiocidal techniques for wood protection have become more and more important in the last few years. One of the possible treatments to enhance wood durability is use of water repellents. In this research, the influence of one of the possible water repellents, the montan wax emulsion, on the moisturizing and the sorption characteristics of impregnated wood was investigated. To achieve a better protection against wood decay fungi, wood was impregnated with montan wax emulsion enriched with boric acid. The equilibrium moisture content (MC) was monitored during the adsorption and the desorption processes at five levels of relative air humidity (RH₁ = 20%, RH₂ = 33%, RH₃ = 65%, RH₄ = 88%, and RH₅ = 98%). Water repellence efficiency was monitored in the chamber with high RH (87%) and during dipping in the water. Impregnated samples were also exposed outdoors in a covered position for 5 months to determine MC changes according to changes in outdoor humidity and temperature. The results showed that the sorption properties of the impregnated wood are strongly related to retention of preservative solutions after impregnation and its composition. Montan wax reduced equilibrium MC of the impregnated wood up to 25% (relatively), whereas specimens impregnated with combination of montan wax and boric acid resulted in decreased MC in some cases and in increased MC in some cases. The Guggenheim–Andersen–deBoer model of sorption isotherms was fitted to experimental data to explain the sorption mechanisms. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Deconstructing water sorption isotherms in cement pastes by lattice density functional theory simulations

The moisture content in cement pastes influences their mechanical properties and durability. However, the complex, multiscale nature of cement pastes makes it challenging to isolate the contributions of each scale to their macroscopic water sorption isotherms. In particular, the contribution of the calcium–silicate–hydrate gel (the binding phase of cement pastes) remains only partially understood. Here, we introduce a density functional theory lattice model describing water sorption in calcium–silicate–hydrate, which properly reproduces experimental water sorption isotherms in cement pastes. Based on this model, we deconstruct the contribution of each pore scale (interlayer spacing, gel pores, and capillary pores) to the total sorption isotherm. We show that, when the relative humidity is below 80%, the calcium–silicate–hydrate gel accounts for more than 90% of the moisture content adsorbed in cement pastes. In turn, we find that the contribution of the interlayer space within the calcium–silicate–hydrate grains is governed by the competition between the rate of interlayer space opening and the increasing propensity for water to fill larger pores upon increasing relative humidity. Overall, our results highlight the key role played by the calcium–silicate–hydrate in governing the sorption isotherms of cement pastes.     

Effects of Relative Humidity on the Ultraviolet Induced Inactivation of Airborne Bacteria

Ultraviolet germicidal irradiation (UVGI) as an engineering control against infectious bioaerosols necessitates a clear understanding of environmental effects on inactivation rates. The response of aerosolized Serratia marcescens, Bacillus subtilis, and Mycobacterium parafortuitum to ultraviolet irradiation was assessed at different relative humidity (RH)levels in a 0.8 m³ completely-mixed chamber. Bioaerosol response was characterized by physical factors including median cell aerodynamic diameter and cell water sorption capacity and by natural decay and UV-induced inactivation rate as determined by direct microscopic counts and standard plate counts. All organisms tested sorbed water from the atmosphere at RH levels between 20% and 95% (up to 70% of dry cell mass at 95% RH); however, no concomitant change in median aerodynamic diameter in this same RH range was observed. Variations in ultraviolet spherical irradiance were minor and not statistically significant in the 20-95% RH range. Cell water sorption and inactivation response was similar for each of the pure cultures tested: when RH exceeded approximately 50%, sorption increased markedly and a sharp concurrent drop in UV-induced inactivation rate was observed.     

Letter to the Editor

Abstract

The water sorption isotherms of the Erythrina fusca Lour bark at 30 and 40°C were determined over relative humidity ranging from 55 to 85%. The equilibrium moisture content was determined gravimetrically. The moisture sorption isotherms showed that the equilibrium moisture decreases with increase of temperature. Six models were used for to fit the experimental curves of equilibrium humidity. Parameters of each equation were determined by nonlinear regression analysis. The isosteric heat of moisture sorption was calculated using the Claussius-Clapeyron equation.     

Sorption Properties of Wood Impregnated with Boron Compounds,Sodium Chloride and Glucose

Chemical protection is one of the possible treatment processes that influence the sorption characteristics of wood. In the present research we have investigated the influence of biocides (boric acid, borax) and their concentrations on the sorption characteristic of impregnated wood. For comparison, two other chemicals were included in the research as well (NaCl and glucose). The equilibrium moisture content during the adsorption and desorption process at five levels of relative humidity (?₁ = 20%, ?₂ = 33%, ?₃ = 65%, ?₄ = 88%, and ?₅ = 98%) was monitored. The results showed that impregnation does not influence the wood moisture content of specimens conditioned at low relative air humidity. In the upper hygroscopic region, moisture content is significantly influenced by the concentration and properties of impregnation chemicals. The Guggenheim-Andersen-deBoer (GAB) and Dent models of sorption isotherms was fitted to experimental data to explain the sorption mechanisms in detail.     

Competitive sorption of water vapor and CO2 in photocrosslinked PVCA film for a capacitive‐type humidity sensor

The sorption behavior of water vapor and CO₂ gas in photocrosslinked poly(vinyl cinnamate) (PVCA) film was examined at 30°C under atmospheric pressure. Both the water sorption isotherm and the CO₂ sorption isotherm obtained with quartz crystal microbalance (QCM) method obeyed the simple Langmuir's equation. Water vapor/CO₂ mixed‐gas sorption isotherms were also obtained. Total amount of sorbed mixed gases was clearly influenced by the partial pressure of water vapor (p_w) and CO₂ gas (p_c) in the atmosphere. A modified Langmuir's equation based on a dual‐site model was employed for predicting the competitive adsorption isotherm, and the isotherm was clearly described by the equation. The theoretically estimated amount of adsorbed water at the constant p_w decreased slightly with increasing p_c. The effect of this phenomenon on the sensitivity of the capacitive‐type relative humidity sensor was examined. As expected, the electrical capacitance of the sensor at the constant relative humidity decreased because of the coexistence of CO₂ gas. However, the influence was quite small in the CO₂ concentration range in the ordinary environment. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 401–407, 2002     

Humidity regulation by stretched PP and PLA films with dispersed CaCl2

Polymer materials that regulate the relative humidity in their environment are relevant for applications in the packaging and building sectors. By integration of salts in polymer structures, such materials are able to absorb and desorb high amounts of water vapor. In this study, films of polylactic acid and polypropylene with dispersed calcium chloride (2 and 4 wt %) were produced and biaxially stretched to induce the formation of cavities. The resulting cavities in these films account up to 10 vol % and are able to contain emerging calcium chloride solution formed by water vapor absorption. These films absorb reversibly up to 15 wt % water vapor at 75% relative humidity at 23 °C. This absorption behavior is described by effective diffusion and effective sorption coefficients. Using a simple model, the effective water vapor diffusion coefficient of these films can be estimated from the permeation coefficient of the polymer and the sorption coefficient of the absorber. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45713.     

Dynamic determination of sorption isotherm of cement based materials

A dynamic method of determining sorption isotherm is proposed. Changes in humidity boundary conditions were applied to specimens of hardened cement paste having various water–cement ratios, as well as to autoclaved aerated concrete, and water adsorption rates were continuously recorded in a sufficiently short period. The diffusion equation was analytically solved and was fitted to the adsorption rates resulting in the rapid estimation of equilibrium moisture content. Results of equilibrium moisture content, the primary data of moisture capacity, showed good agreement with literature values. The adsorption rate measurement took 8 h for autoclaved aerated concrete and 12 h for hardened cement paste with a measurement interval of 60 s to predict an equilibrium moisture content at an ambient relative humidity.     

Properties of interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(N‐isopropylacrylamide)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) and poly(N‐isopropylacrylamide) were prepared by the sequential‐IPN method. The IPN hydrogels were analyzed for sorption behavior of water at 35°C and at a relative humidity of 95% using a dynamic vapor sorption system, and water diffusion coefficients were calculated. Differential scanning calorimetry was used for the quantitative determination of the amounts of freezing and nonfreezing water. Free water contents in the IPN hydrogel of IPN1, IPN2, and IPN3 were 45.8, 37.9 and 33.1% in pure water, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2041–2045, 2003     

Effect of water presence on the sorption of organic compounds in ethylene–vinyl alcohol copolymers

Sorption isotherms of methanol, ethanol, propanol, butanol, hexanol, ethyl caproate, and limonene in 4 ethylene–vinyl alcohol (EVOH) copolymers with different ethylene contents were determined by inverse gas chromatography (IGC) at 25°C and different relative humidity conditions. From sorption isotherms, solubility coefficients were determined and used as a tool for comparison. Besides affecting the morphology of the polymers by plastification, sorbed water seems to increase the polarity of the medium. Sorption of alcohols increases at high relative humidity; both plasticization and polarity cause this behavior. The effect is more important for the smaller alcohols and among polymers for those with low ethylene content. As the sorbant becomes nonpolar, plasticization and polarity effects become antagonistic. Indeed, the effect of water presence in sorption of hexanol is not significant, and sorption of limonene and ethyl caproate is even reduced at high water content. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 711–716, 1998     

The Effect of Humidity on the Adhesion Behavior of AC Anodised Aluminium

The effect of humidity on the surface forces of hot AC anodised AA6060 alloy was studied. The surface adhesion forces were measured in various humidity environments using an atomic force microscope (AFM). The environmental durability of the joints bonded at different humidity conditions was investigated using wedge test experiments. The results from AFM and durability tests indicate that there is a strong capillary effect at around 70–80% relative humidity. This effect was attributed to the change in the adsorption behavior of water on the anodised oxide surface forming bulk liquid and hence dissociating the bonds across the interface. At the lower humidity levels below 60% RH, no capillary effect was observed and the total adhesion forces followed the dry case values.     

Mg2+在胜利褐煤中的负载量对其平衡复吸水含量的影响及其机理分析（英文）

Mg ion-exchanged samples were prepared with acid-washed Shengli lignite. The chemical composition of the ash of the raw sample was determined by X-ray fluorescence. The equilibrium adsorption water contents of sam-ples were determined in a range of relative humidity. The ion-exchange process was characterized by FT-IR, ash content, and pH value. A possible mechanism is proposed for equilibrium adsorption water of ion-exchanged samples at different humidities. The extent of ion-exchange reaction between Mg2+and lignite is control ed by the concentration of Mg2+in MgSO4 solution. The effect of Mg2+on equilibrium adsorption water content varies with relative humidity and content of Mg2+. The factor that controls equilibrium adsorption water content at low relative humidity is water interactions with sorption sites, which are Mg2+–carboxyl group complex. At middle relative humidity capil ary force between Mg2+–water clusters Mg+(H2O)n and capil ary is more impor-tant. At high relative humidity, free water–free water interactions are more significant.