Water Vapor Sorption Capacity Research Articles

Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 2: Physical Modeling of Adsorption Phenomena

We employ a rigorous thermodynamic modeling approach to investigate the water adsorption phenomena on two calcium sulfate compounds, AIII-CaSO4 and CaSO4·0.5H2O. In part 1 of this work ( Ind. Eng. Chem. Res., 2019, DOI: 10.1021/acs.iecr.9b00856), we prepared these two products by the dehydration of synthetic CaSO4·2H2O and obtained quantitative adsorption data as a function of the temperature and water vapor partial pressure. In this part, we develop macroscopic solution models (ideal and nonideal) to model monolayer adsorption on AIII-CaSO4. This allowed the calculation of the energies of adsorption for this phenomenon, evidencing a physisorption mechanism. For the CaSO4·0.5H2O, we interpreted the water adsorption using a multilayer adsorption model (BET model). For both materials, we showed that nitrogen adsorption data was not sufficient to represent their entire surface areas and porosity profiles compared to their water vapor sorption capacity.

Design of Pt-C/Fe-N-S-C cathode dual catalyst layers for proton exchange membrane fuel cells under low humidity

A novel Pt-C/Fe-N-S-C cathode dual catalyst layer (CDCL) is prepared using the method of catalyst sprayed membrane. The membrane electrode assembly (MEA) fabricated from CDCL exhibits excellent water absorption and retention ability, which improves the performance of the corresponding proton exchange membrane fuel cell (PEMFC) at low humidity conditions. Fe-N-S-C catalysts with high Brunauer-Emmett-Teller surface area exhibit a remarkable water vapor sorption capacity. The effects of Fe-N-S-C content, relative humidity, and operating temperature on the performance of MEAs are investigated systematically. It is found that the optimum Fe-N-S-C content is 1.5–2.0 mg cm−2 and the preferable operating temperature is 70 °C. The MEAs with CDCLs show superior performance at 20% relative humidity due to the enhanced water retention ability resulting from the Fe-N-S-C catalysts. At a constant voltage of 0.5 V at 70 °C and 20% relative humidity, the novel self-humidifying MEA shows better durability than the conventional MEA (60% loss after 4 h).

Functional properties of foamed and/or stretched polypropylene-films containing sodium chloride particles for humidity regulation

The relative humidity level in the immediate vicinity of objects such as foods and technical items has an influence on transpiration and undesired relative humidity dependent reactions on their surfaces such as water vapour condensation, chemical reactions and microbial growth. Desirable are therefore materials that regulate the relative humidity to predefined levels in closed spaces such as in packagings and also in housing spaces. Such materials should be able to adjust the surface humidity of objects via water vapour diffusion in the gas phase without being in direct contact. A strategy to create such humidity regulating materials is the use of substances that absorb and desorb high amounts of water vapour, such as sodium chloride. Sodium chloride (NaCl) particles absorb water vapour at a relative humidity above 75% at 23 °C and then they form NaCl solution. NaCl solution desorbs water vapour when the relative humidity in the immediate vicinity decreases below the equilibrium relative humidity of that salt solution. Therefore, this system is able to regulate the relative humidity in its immediate vicinity. A strategy to provide free space in polymeric structures for the NaCl solution is the creation of cavities by foaming and stretching. However, only little knowledge exists about the influence of the combination of both processes on the functional properties of humidity regulating films with salt as active substance. Hence, the aim of this study was to investigate how and to which extend foaming and/or stretching affects the functional properties, i.e. water vapour sorption and mechanical properties, of polypropylene (PP) films containing NaCl particles. For this study, foamed and non-foamed PP with 3 and 6 weight-% NaCl were extruded into films. In the next step, some of these samples were biaxially stretched and their structures, water vapour absorption, porosities and mechanical strengths were analysed. The only-foamed films had a porosity of 0.3, the porosity of only-biaxially stretched films was between 0.1 and 0.2. The porosity increased to 0.7 when the films were first foamed and stretched afterward. Foamed and then stretched films with 6 wt.-% NaCl absorbed a high amount of water vapour from air with a value of 0.8 g H2O/g film at 97% relative humidity. Stretching of filled and non-filled foamed films also resulted in higher mechanical strength of the pure matrix polymer in comparison to the pure matrix polymer of non-stretched films. By the results of this study is shown that humidity regulating films with high water vapour sorption capacity can be produced via extrusion, foaming and stretching processes which are established processes in the polymer industry.

The effects of incorporating fluorinated polyhedral oligomeric silsesquioxane, [F3C(CH2)2SiO1.5]n on the properties of the silicones

A hydrophobic filler with the siloxane skeleton, fluorinated polyhedral oligomeric silsesquioxane (F-POSS), was incorporated in varying percentages (2.5, 5, and 10 wt%) in a polydimethylsiloxane-α,ω-diol (PDMS) of molecular weight 230,000g/mol, in solution. Some structural characteristics and properties derived from F-POSS (low polarizability, weak intermolecular force, low surface energy), similar to those of polydimethylsiloxane, create prerequisites for good compatibility of these two components and enrichment of some of their features: better mechanical parameters, increased hydrophobicity and lower dielectric constant useful for practical applications such as insulators. The composites processed as films and stabilized by condensative crosslinking of OH ends of PDMS with a tetrafunctional silane were studied in terms of morphology, mechanical properties, hydrophobicity of the surface, and water vapor sorption capacity, optical properties, dielectric behavior, conductivity, and dielectric strength. Results showed that, although the mixing of the two components was made in solution, it did not occur at the molecular level. However, the expected results are achieved except the hydrophobicity which is not affected noticeable.

Alginate/bacterial cellulose nanocomposite beads prepared using Gluconacetobacter xylinus and their application in lipase immobilization

Alginate/bacterial cellulose nanocomposite beads, with well-controlled size and regular spherical shapes, were prepared in a simple manner by entrapping Gluconacetobacter xylinus in barium alginate hydrogel beads, followed by cultivation of the entrapped cells in culture media with a low sodium ion concentration. The entire surface of the alginate hydrogel beads containing the cells was covered with cellulose fibers (∼30nm) after 36h of cultivation. The cellulose crystallinity index of the alginate/bacterial cellulose beads was 0.7, which was slightly lower than that of bacterial cellulose prepared by cultivating dispersed cells. The water vapor sorption capacity of the alginate/bacterial cellulose beads increased significantly from 0.07 to 38.00 (g/g dry bead) as cultivation time increased. These results clearly indicate that alginate/bacterial cellulose beads have a much higher surface area, crystallinity, and water-holding capacity than alginate beads. The immobilization of lipase on the surface of the nanocomposite beads was also investigated as a potential application of this system. The activity and specific activity of lipase immobilized on alginate/bacterial cellulose beads were 2.6- and 3.8-fold higher, respectively, than that of lipase immobilized on cellulose beads. The alginate/bacterial cellulose nanocomposite beads prepared in this study have several potential applications in the biocatalytic, biomedical, and pharmaceutical fields because of their biocompatibility, biodegradability, high crystallinity, and large surface area.

Cationic hybrids from poly(N,N‐dimethylaminoethyl methacrylate) covalently crosslinked with chloroalkyl silicone derivatives effective in binding anionic dyes

ABSTRACTThe synthesis and characterization of some novel ionic organic/inorganic hybrids containing quaternary ammonium salt groups in the side chain, built on the basis of poly(N,N‐dimethylaminoethyl methacrylate), as an organic component and cation provider, and chloroalkyl‐functionalized silicone derivatives as crosslinkers and anion generators, are reported in this work. The resulted structures were investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and energy dispersive X‐ray spectroscopy. The swelling behavior of the ionic hybrids in water as a function of pH as well as the water vapor sorption capacity in dynamic regime was also studied. The cationic hybrids have a higher swelling capacity at pH 2 compared with deionized water (pH 6) due to the presence of tertiary amine groups belonging to the organic compound. The ionic organic/inorganic hybrids were tested as potential sorbents for anionic species such as dyes [e.g., methyl orange (MO)]. The equilibrium sorption capacity increased with the increase of the organic component up to around 32 mg MO/g hybrid. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43942.

Silica-containing polyetherimide hybrid films based on methyltriethoxysilane as precursor of inorganic network

Polyetherimide hybrid films containing 5–40% silica were prepared through a sol-gel process and thermal imidization by using methyltriethoxysilane as precursor of the inorganic network and a poly(amic acid) resulting from polycondensation reaction of 2,2-bis[4-(4-aminophenoxy)phenyl]propane with 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride. The properties of these films, morphology, water vapor sorption capacity, free surface energy, mechanical, thermal and electrical characteristics, were studied. The films exhibited good thermal stability, having an initial decomposition temperature above 470 °C and glass transition temperature in the range of 187–200 °C. They showed low dielectric constant and low dielectric loss in a large frequency field. Gas permeation tests using small molecules (He, N2, O2 and CO2) at 6 bar and 30 °C indicated that the hybrid films containing higher silica content showed higher permeability for all the tested gases.

Systematic investigation of the pore structure and surface properties of SBA-15 by water vapor physisorption

In order to establish a structure-property correlation in water vapor sorption, various sets of the ordered mesoporous silica SBA-15 with systematically varying properties were synthesized and characterized. General trends concerning the surface polarity, aging temperature during synthesis and micropore volume were observed. Calcining the materials with increasing temperatures of 300–800 °C decreases the performance in water vapor sorption which correlates mainly with the amount and type of silanol groups on the silica surface. Furthermore, the aging temperature during synthesis influences the water vapor sorption capacity of SBA-15 at low relative pressure. The best results in terms of an increased uptake of water over a broad range of relative pressure can be obtained for materials with high micropore volume and high surface polarity. They can be tailor-made by using a routine to remove the template, i.e., a combination of extraction with ethanol and subsequent calcination at 300 °C.

Nanoporous composites prepared by a combination of SBA-15 with Mg-Al mixed oxides. Water vapor sorption properties.

This work presents two easy ways for preparing nanostructured mesoporous composites by interconnecting and combining SBA-15 with mixed oxides derived from a calcined Mg–Al hydrotalcite. Two different Mg–Al hydrotalcite addition procedures were implemented, either after or during the SBA-15 synthesis (in situ method). The first procedure, i.e., the post-synthesis method, produces a composite material with Mg–Al mixed oxides homogeneously dispersed on the SBA-15 nanoporous surface. The resulting composites present textural properties similar to the SBA-15. On the other hand, with the second procedure (in situ method), Mg and Al mixed oxides occur on the porous composite, which displays a cauliflower morphology. This is an important microporosity contribution and micro and mesoporous surfaces coexist in almost the same proportion. Furthermore, the nanostructured mesoporous composites present an extraordinary water vapor sorption capacity. Such composites might be utilized as as acid-base catalysts, adsorbents, sensors or storage nanomaterials.

Impregnation of cinnamaldehyde into cassava starch biocomposite films using supercritical fluid technology for the development of food active packaging

In this work, supercritical solvent impregnation (SSI) has been tested for the incorporation of natural compounds into biocomposite materials for food packaging. Cinnamaldehyde, with proved antimicrobial activity against fungi commonly found in bread products, was successfully impregnated on biocomposite cassava starch based materials using supercritical carbon dioxide as solvent. Different process experimental conditions were tested (pressure, impregnation time and depressurization rate) at a fixed temperature (35°C) in order to study their influence on the amount of impregnated cinnamaldehyde as well as on the morphology of the films. Results showed that all conditions permitted to impregnate antimicrobial active amounts superior to those previously obtained using conventional incorporation methods. Moreover, a significant decrease of the equilibrium water vapor sorption capacity and water vapor permeability of the films was observed after SSI processing which is a clear advantage of the process, considering the envisaged applications.

Modification of hemicelluloses with polycarboxylic acids

Abstract Polycarboxylic acids (PCAs) aroused interest as crosslinking agents for natural polymers, such as cellulose, starch, chitosan, and hemicelluloses (HC), for improving their water resistance and imparting them new properties. Here, PCAs were studied for the crosslinking of HC films. HCs were isolated from gray alder (Alnus incana L.) wood as a water-soluble fraction by sawdust extraction with 7% potassium hydroxide. Citric acid (CA), maleic acid (MA), and butane tetracarboxylic acid (BTCA) served as crosslinking agents in the presence of sodium hypophosphite as a catalyst. The crosslinking reaction was followed by the analysis of free and esterified COOH groups in HC films. At temperatures below 100–110°C, the HC esterification process with BTCA proceeded very slowly. At 140°C, most of the acids’ COOH groups reacted with HC during 1–1.5 h. BTCA had a higher esterification activity than CA and MA. The obtained films retained their form on immersing in water and subsequent drying in the open air. The water retention value of films followed the reaction kinetics, that is, decreased with increasing reaction time. Water-resistant films were obtained with no <10–11% of BTCA and 20% of CA based on the weight of HC. The water vapor sorption capacity of the films after modification with 10% BTCA decreased approximately twice in the whole range of the relative humidity of air compared with the case of unmodified HC films.

Mechanical, thermal and surface properties of polyacrylamide/dextran semi-interpenetrating network hydrogels tuned by the synthesis temperature

Abstract The mechanical, rheological, thermal, and surface behaviors of three polyacrylamide/dextran (PAAm/Dx) semi-interpenetrating polymer network (semi-IPN) hydrogels, prepared at 22°C, 5°C and −18°C, were investigated. The results were compared with those obtained on cross-linked PAAm without Dx synthesized under the same conditions. Hydrogels prepared at the lowest temperature were the most mechanically stable. The thermal stability of the semi-IPN hydrogels is slightly lower than the corresponding PAAm gels, irrespective of preparation temperature. The water vapor sorption capacity depended on the presence of Dx as well as preparation temperature, which determines the network morphology.

1,3-Bis(3-ammonium-propyl)tetramethyldisiloxane-sulfate: Structural characterization and evaluation of some properties

1,3-Bis(3-ammonium-propyl)tetramethyldisiloxane sulfate resulted from the reaction between 1,3-bis(3-aminopropyl)tetramethyldisiloxane with a proper transition metal (iron(III) or vanadium(IV) oxide) salt as anion generator and a carbonylic compound (4-imidazole carboxaldehyde or 2-hydroxybenzaldehyde) as a metal collector, in methanol, was thoroughly characterized. The compound’s structure was proved by single-crystal X-ray diffraction and spectral (FT-IR, 1H NMR) analysis, while the thermal behavior was evaluated by thermogravimetry. Water vapor sorption capacity on the crystalline compound was measured in dynamic regime. The co-existence of hydrophobic bis(propyl)tetramethyldisiloxane moiety and telechelic hydrophilic groups constitutes a premise for surface activity, as confirmed by tensiometry. Formation of micelles and aggregates in solution was emphasized by dynamic light scattering and confirmed by AFM images taken on the spin coated films, both revealing closed values for size of the micelles (100–200nm).

Chemical modification of cellulose acetate by allylation and crosslinking with siloxane derivatives

AbstractA new pathway to cellulose–siloxane hybrid materials was investigated. Allylated cellulose was prepared by chemical modification of cellulose acetate using three different procedures and was crosslinked afterwards by hydrosilylation in the presence of Karstedt's catalyst. Poly[dimethyl(methyl‐H)siloxane] with 25 mol% SiH side groups and 1,1,3,3‐tetramethyldisiloxane were used as crosslinking agents in different ratios as regards the unsaturated component. The occurrence of the reaction was verified using Fourier transform infrared spectrometry following the reduction until disappearance of bands corresponding to SiH and CC bonds with the formation of new SiC bonds that led to the crosslinking of the cellulose derivative. The reaction products were processed as films that were insoluble in common solvents. Surface (static contact angle, water vapour sorption capacity and swelling in various solvents), mechanical and thermal properties of the networks processed as films were investigated and the results were correlated with the reactant ratios. The crosslinking density was determined based on differential scanning calorimetry data. Copyright © 2012 Society of Chemical Industry

Poly(siloxane‐urethane) crosslinked structures obtained by sol‐gel technique

AbstractPoly(siloxane‐urethane) crosslinked structures were prepared from isophorone diisocyanate, α,ω‐bis(hydroxybutyl)oligodimethylsiloxane and a new hybrid diol containing hydrolysable SiOC2H5 groups besides OH groups. The latest was synthesized by the acid‐catalyzed reaction between 1,3‐bis(3‐glycidoxypropyl)tetramethyldisiloxane and 3‐aminopropyltriethoxysilane. The formations of the urethane groups along the polymer backbone as well as the formation of the silica domains were first confirmed by the presence of the specific bands in Fourier transform infrared spectra. The resulted materials were characterized using differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. The results of the dynamic mechanical analysis (DMA) performed at various frequencies revealed shape memory capabilities for some of the obtained structures. The silica formed because of the hydrolysis‐condensation reactions proved to have reinforcing effect upon siloxane‐urethane structure also evidenced by DMA and increasing water vapor sorption capacity as was measured by dynamic vapor sorption. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Dynamics and isotherms of water vapor sorption on mesoporous silica gels modified by different salts

The mesoporous silica gels impregnated with different metal salts were prepared and studied. The pore structure and specific surface area of adsorbents were evaluated using nitrogen adsorption. Then, the sorption isotherms and dynamics of water vapor were carried out at 303 K and different relative humidity (RH). The temperature programmed desorption experiments were conducted to estimate the activation energy (Ed) of water desorption on the silica gels. The results showed that the sorption capacity for water decreased with the increase of the ionic radius (except the calcium ion) and that CaCl2 and LiCl were particularly suitable for use in modification of the mesoporous silica gel to improve their sorption rates and capacities for water vapor at the lower and medium RH (RH < 80%). The larger the average pore diameter and pore volume of the initial silica gels, higher the accrual rates of the water vapor sorption rate and capacity were after modification with hygroscopic salts. The activation energy of the water desorption on the mesoporous silica gel modified by CaCl2 were much higher than that on the silica gel modified by LiCl, because the polarizability of the Ca2+ was higher than that of Li+.

Silicone-based Composite for Relining of Removable Dental Prosthesis

A high molecular weight dimethylmethylvinylsiloxane copolymer (Mv = 450, 000) has been synthesized, analyzed, and used as matrix to prepare a composite by mixing with a proper amount of silica. A mixture of Fe2O 3/TiO2 was added to obtain a color close to the natural. 2,4-Dichlorobenzoyl peroxide was also incorporated as a crosslinking catalyst. This heat curable silicone-based formulation was used for relining removable dental prosthesis. The optimum conditions to appliance and hardening of the silicone composite on the prosthesis were established. The main surface (morphology, water contact angle, and water vapor sorption capacity) and mechanical characteristics were evaluated for the crosslinked silicone processed as thick film. The prosthesis relined with silicone was tested on a machine simulating mandible biomechanics both from kinematics and dynamic points of view. The results revealed a good behavior of our composite that remained unmodified after 700,000 mastication cycles.

Morphology and surface properties of some siloxane-organic copolymers

BACKGROUND: It is well known that, due to their extremely low polarity, polysiloxanes are incompatible with almost any organic system. This incompatibility leads to phase separation in mixed siloxane–organic systems. RESULTS: Three siloxane–organic copolymers, poly[(5,5′-methylene-bis-salicylaldehyde)-imine-(1,3-bis(propylene)tetramethyldisiloxane)] (Paz1), poly[(2,5-dihydroxy-1,4-benzoquinone)-imine-(1,3-bis(propylene)tetramethyldisiloxane)] (Paz2) and poly[1,3-bis(propylene)tetramethyldisiloxane diamide] (Pam), were prepared by the reaction of 1,3-bis(3-aminopropyl)tetramethyldisiloxane with appropriate organic partners (5,5′-methylene-bis-salicylaldehyde, 2,5-dihydroxy-1,4-benzoquinone and oxalyl chloride, respectively). The morphologies dictated by the incompatibility between siloxane and polar organic moieties were investigated using differential scanning calorimetry and scanning electron microscopy. The surface activity of the copolymers and water vapour sorption capacity were also measured. CONCLUSION: Even though the polar sequences are very short ones, the highly flexible siloxane-containing sequence permits the self-assembly of these into more or less polar domains. Such an organization influences the properties of the resulting materials, an important place being occupied by the surface properties. Copyright © 2009 Society of Chemical Industry

Measuring moisture sorption and diffusion kinetics on proton exchange membranes using a gravimetric vapor sorption apparatus

The understanding of water sorption and diffusion properties of proton exchange membranes is crucial to the fuel cell's ultimate performance. In this study, a dynamic gravimetric vapor sorption (DVS) instrument was used to measure the water vapor sorption properties of three Nafion ® based fuel cell membranes: N-117 (extruded film, 183 μm thick); N-112 (extruded film, 51 μm thick); and NR-112 (dispersion cast film, 51 μm thick). Water sorption characteristics were studied between 0 and 95% relative humidity (RH) at 30, 40, 50, 70, and 80 °C. The thicker dispersion cast, N-117, film had a lower water vapor sorption capacity (based on percentage weight gain) than the thinner, N-112 sample. The dispersion cast, NR-112, film had a lower percentage water uptake than the extruded, N-112, film. Below 80% RH, the water sorption capacity increases with temperature for all three samples. Above 80% RH, the moisture sorption capacity increases from 30 to 50 °C, but decreases at 70 and 80 °C compared to the lower temperature data. Moisture diffusion coefficients were also calculated over the humidity and temperature range studied. In general, maximum diffusion coefficients were measured at intermediate humidities. Water heat of sorption calculations at low coverages yielded higher values for the extruded (N-112) film compared to the dispersion cast (NR-112) film indicating a higher affinity for water.

Effect of Synthesis Conditions of Magnetite on Its Water-Vapor Sorption Capacity

The water-vapor sorption capacity of magnetite obtained by precipitation with solutions of NaOH, NH3 · H2O, and urea in a single stage was studied. It was found that the type of a precipitating agent, thermal treatment temperature, concentration of the starting FeSO4 solution, and order in which the reagents are poured together affect the water-vapor sorption capacity of the magnetite obtained.