The linear expansion of gelatin films by moisture sorption

Summary The gelatin films which are cast from water solutions have an anisotropy which disappears by annealing. The linear expansibility depends on theph of solutions, and on the temperature, films are dried, or on the hardening and on the contents of ash. Both specimens (hardening and non-hardening) in which theph is close to the iso-electric point have the minimum linear expansion. The high temperature film has more expansibility than the low temperature film.

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Zusammenfassung Gelatinfilme, aus w?\riger L?sung gegossen, sind anisotrop, Die Anisotropie l?\t sich durch Temperatur-Feuchtigkeit-Behandlung beseitigen. Das lineare Ausdehnungsverm?gen ist vomph der L?sungen, der Trockentemperatur, sowie von H?rtung und Aschegehalt abh?ngig. Beide Sorten der Filme (geh?rtete sowie nicht geh?rtete) dehnen sich um so weniger, je n?her derph-Wert dem des isoelektrischen Punktes liegt. Die bei h?herer Temperatur gefertigten Filme dehnen sich st?rker als die bei niedrigerer Temperatur bereiteten.

     

Complexities associated with moisture in foamed polysiloxane composites

An understanding of mechanisms of moisture outgassing from silicones and the impact on material mechanical properties is important for compatibility and life prediction in sealed systems containing these materials. A series of thermomechanical (TMA) stress relaxation experiments have been performed to provide information on the important load bearing properties of these materials as a function of time and temperature. Two different silica reinforced foamed polysiloxane materials were tested, a peroxide cured rubber (M97) and a condensation-cured elastomer (S5370). The M97 foam showed unexpectedly complex stress relaxation profiles at temperatures around 100 °C, whereas the S5370 samples showed the expected smooth stress decay behaviour. Dried M97 foam samples show different stress relaxation behaviour to the non-dried materials. Furthermore, stress relaxation studies performed in controlled humidity environments showed that moisture has a significant accelerating influence on the underlying relaxation process. In dry regimes, a reduced stress relaxation rate was observed, with an increase in the force required to maintain a given amount of compression on the sample. To further develop our understanding of the effects of moisture, we have exposed samples to water enriched to 40% in ¹⁷O and used ¹⁷O nuclear magnetic resonance (NMR) spectroscopy to assess labelled hydrolysis reaction products. Our studies show that Si-¹⁷O-Si hydrolysis products are readily incorporated in the polymer and the degradation is enhanced by the influence of gamma radiation and/or heat. In addition, the polysiloxane foams showed different age related trends in sealed (where moisture is retained) and ventilated (open-to-air) regimes. Our observations have been explained by moisture influencing both physical and chemical degradation processes. Our findings on moisture induced changes in silicone stress relaxation rates are novel and demonstrate the importance of controlling humidity in service applications involving these materials.     

Gravimetric measurement of water vapour sorption, moisture and dry mass

The gravimetric measurement of the moisture content of solids is discussed in comparison to other usual methods. Results of measurements of silica gel are reported. Furthermore, we inform on standardisation work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamic moisture sorption behavior of cotton fibers with natural brown pigments

The moisture sorption behavior of white and naturally colored cotton fibers is studied by dynamic vapor sorption. Dark brown and brown fibers show a higher sorption capacity compared to beige and white fibers. The differences in sorption capacity are found to be related to the maturity and crystallinity index of the fibers. All fibers exhibited sorption hysteresis to varying degrees throughout the full relative humidity range. The variations in hysteresis behavior are mainly attributed to the differences in crystallinity index of the fibers. In addition the monolayer and polylayer moisture content is analyzed using the Hailwood Horrobin model. Monolayer sorption is most closely related to the crystallinity index and, to a lower extent, maturity of the fibers. For beige and white fibers monolayer sorption remains almost constant, whereas for darker fibers it shows a substantial increase with increasing color difference. In contrast, polylayer sorption shows a general increasing trend over the whole studied color spectrum. Also a noticeable relationship was found between the total hysteresis and the monolayer sorption. Yet such relation was less evident for polylayer sorption. This study contributes to the better understanding of the dynamic moisture sorption behavior of white and naturally colored cotton fibers. This improved understanding is important for optimal application of naturally colored cotton fibers in novel materials.     

Novel zeolite composites and consequences for rapid sorption processes

Novel sorbents for rapid dynamic sorption processes based on the concept of sorption-active shell/sorption-inert core composite granules are presented. Tailoring such composites to a technical sorption process is exemplified by NaX and LiLSX zeolites as sorption-active components. Composite granules are characterized by various techniques specifically by oxygen-VPSA pilot-scale tests and liquid-phase sorption experiments. The composite sorbents exhibit excellent potential for efficiency enhancement of existing processes by lowering investment and operating costs. This paper is dedicated to the memory of John D. Sherman     

Irreversible effects of moisture on the epoxy matrix in glass-reinforced composites

The irreversible effects of moisture exposure on anhydride-crosslinked epoxy resin films are investigated by means of Fourier-transform infrared spectra. Hydrolytic attack of water at the ester linkages is accelerated in alkaline media and is a mechanically activated process. Matrix hydrolysis is also enhanced in the presence of inorganic fillers.     

Toluene and naphthalene sorption by iron oxide/clay composites

Commercial bentonite (BFN) and organoclay (WS35), as well as iron oxide/clay composite (Mag_BFN) and iron/oxide organoclay composite (Mag_S35) were prepared for toluene and naphthalene sorption. Mag_BFN and Mag_S35 were obtained, respectively, by the precipitation of iron oxide hydrates onto sodium BFN and S35 clay particles. The materials were characterized by powder X-ray diffraction (XRD), X-ray Fluorescence (XRF), and TG and DTA. From XRF results and TG data on calcined mass basis, a quantitative method was developed to estimate the iron compound contents of the composites, as well as the organic matter content present in WS35 and Mag_S35.     

Water sorption heats on silica-alumina-based composites for interseasonal heat storage

CaCl₂-containing composites have been prepared by depositing the hydrated salt (by incipient wetness impregnation) on three different silica-aluminas with various Si/Al ratios. The surface area and porosity of all the samples were determined by N₂-adsorption at ?196 °C, and their water sorption properties were investigated by thermogravimetry linked to differential scanning calorimetry (TG–DSC) in order to determine the quantity of adsorbed/desorbed water and the related heats. The heat released and the quantity of adsorbed water were found to depend on parameters such as the silica-alumina pore diameters, the Si/Al ratio, and the presence of accessible CaCl₂ active phase. The short-term stability of both supports and composites has been also checked by performing successive hydration–dehydration cycles. The sample with the lower Si/Al ratio provided the highest heat per surface area of material, and the heat released per mol of water increased with the amount of Al₂O₃ present in the samples. The deposition of CaCl₂ positively acted on the quantity of heat released during the water sorption, and the composite with the higher alumina content (75 mass% Al) showed the largest heat released per m² of material (2.4 J m^?2) compared to those containing 25 and 13 mass% Al (1.4 and 1.2 J m^?2, respectively).     

A thermal study on moisture absorption by epoxy composites

The water sorption kinetics of an epoxy matrix-carbon fiber composite with different degrees of polymerization was studied. It was observed that the diffusion coefficients, determined perpendicularly to the fiber direction, are increased by increasing the cure degree. Only a small portion of the bonded water is released when the specimen are heated to 200 °C.The effects of moisture on some properties of the composite were also investigated. TheT _g values determined on fully polymerized samples, show lowerings of 70 degrees; moreover, the plasticization power of the bonded water increases on decrease of the temperature of conditioning of the specimens.Finally, the water present in the matrix considerably reduces the thermal stability of the composite.

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Zusammenfassung Es wurde die Wassersorptionskinetik eines Graphitfaserverbundstoffes auf Epoxymatrixbasis mit verschiedenen Polymerisationsgraden untersucht. Es zeigte sich, daß die senkrecht zur Faserrichtung bestimmten Diffusionskonstanten mit anwachsendem Vernetzungsgrad zunehmen. Beim Erhitzen des Materials auf 200 °C wird nur ein geringer Teil des gebundenen Wassers abgegeben. Der Einfluß des Feuchtgehaltes auf einige Eigenschaften des Verbundstoffes wurde ebenfalls untersucht. Die an vollkommen polymerisierten Proben bestimmtenT _g Werte zeigen eine Abnahme von 70 Grad; die Plastifizierungswirkung des gebundenen Wassers ist um so höher, je niedriger die Konditionierungstemperatur der Probe war. Das in der Matrix gegenwärtige Wasser senkt beträchtlich die Wärmebeständigkeit des Verbundstoffes.

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- . , , , . 200 °. . Tg, , 70 °. . , , .

     

Investigation of acid-base and sorption properties of surface of metal–ceramic composites

The acid-base properties of the surface of composites based on boron, silicon, and sialon nitrides were investigated by the indicator method of Hammett and Tanabe with spectrophotometric indication. Identification of the surface sites of the composites under study was carried out. On the surface of composites based on boron and sialon nitrides the Lewis base sites dominate, while on the surface of samples based on silicon nitride the Brønsted acid sites. Sorption of dyes and oxalic acid by cermet materials was studied. It is shown that the adsorption activity depends on the nature and amount of surface active sites of the composites.     

Dynamics of the sorption of phosphatidylcholine by mesoporous composites based on MCM-41

The possibility of predicting the breakthrough curves of a phospholipid (PL) during its sorption by mesoporous composites based on MCM-41 using models of the dynamics of sorption that consider the kinetics of adsorption (the Thomas model) and mixed diffusion (the asymptotic model) is demonstrated using phosphatidylcholine (PC) as an example. The effect the kinetic parameters have on the tailing of the sorption front with respect to the mixed diffusion limitation of the sorption of nonpolar biologically active substances (BASes) is shown. It is found that the ordered structure of composite materials based on MCM-41 ensures a high rate of mass transfer and thus little tailing of the sorption front, when compared to sorbents with a lower degree of order (silica gel and polymer materials) during the sorption of a phospholipid under dynamic conditions. Based on calculations of the parameter of pattern Λ under the conditions of the dynamic mode of sorption in mixed diffusion kinetics, it is shown that the sorption of phosphatidylcholine from hexane solutions by mesoporous composites based on MCM-41 allows the sorption chromatographic process to proceed in the most advantageous (quasi-equilibrium) mode.     

Structural characteristics and moisture sorption behavior of nylon‐6/clay hybrid films

The structure of nylon‐6 hybrids with synthetic or natural clays was investigated for melt‐pressed films with Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and differential scanning calorimetry in comparison with the nylon‐6 homopolymer. In contrast to the development of familiar α‐form crystals in plain nylon‐6 film, the hybrid films produced γ‐form crystals when nylon‐6 was conjugated with synthetic mica, whereas the hybridization with natural montmorillonite gave rise to both α‐ and γ‐crystalline modifications. The degree of crystallinity of the nylon‐6 hybrid with synthetic mica was the highest of the three series. Moisture sorption isotherms obtained for these nylon‐6‐based films were all typically sigmoid‐shaped, although the prevalence of a higher crystallinity in the hybrid samples lowered the degree of moisture regain. The sorption behavior was analyzed well in terms of the parameters of a Brunauer–Emmett–Teller multiplayer adsorption model and a Flory–Huggins treatment. It was also observed that the cluster formation of the water adsorbed into the nylon‐6 matrix tended to be restricted by the hybridization with clay. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 479–487, 2002; DOI 10.1002/polb.10106     

Evaluation of the moisture sorption behaviour of several excipients by BET, GAB and microcalorimetric approaches

Moisture content of solid-state pharmaceutical products is one of the main factors that affect drug stability, therefore suitable sorption studies need to be performed to assure drug quality throughout their shelf life. The Brunauer-Emmett-Teller (BET) and the Guggenheim-Anderson-de Boer (GAB) models are usually used for this purpose. Using gravimetrically obtained data, both methods were applied in the present work to evaluate the sorption characteristics of several excipients. Microcalorimetric analysis was also performed in order to evaluate the interaction between water and the substances. The results of these experiments show excellent agreement between data and the BET model up to 55% RH and the GAB model over the entire humidity range, confirmed by high values of the statistical determination coefficients. Furthermore, microcalorimetric measurements suggested that the hygroscopicity of solid materials could be estimated approximately using this approach.     

Photodegradation and weathering effects on timber surface moisture profiles as studied using dynamic vapour sorption

The moisture sorption kinetic profiles of Scots pine (Pinus sylvestris) earlywood and latewood were studied using a Dynamic Vapour Sorption apparatus and the equilibrium isotherms determined. The samples were chosen to give an insight to the effects that photodegradation and weathering have on the moisture behaviour of the surface layers of timber. Samples were subjected to indoor and outdoor exposure regimes. Significant differences were found between the sorption isotherms of exposed and unexposed wood, as well as with the sorption kinetics profiles. The reasons for these differences are discussed.     

A novel model for quantification of the moisture absorption of polymeric laminated composites

In the present study, a new model was developed that considers the amount of the environmental fluid absorption by different constituents of polymeric laminated composites including fibers, resin, fiber-matrix interphase region, ply interface region, and voids. By knowing the fluid absorption behavior of the composite constituents, the present model can predict the amount of fluid absorption of different constituents of polymeric laminated composites with an arbitrary resin volume fraction and stacking sequence. Test specimens were fabricated by glass fibers and vinyl ester resin. The environmental fluids, examined in this study, were distilled and saline water under different temperatures and salt concentrations. To investigate the absorption behavior of different constituents of polymeric composite, various tests were conducted on fibers, pure cured resin, unidirectional composite specimens, and laminated composites. Based on the results of the tests, a new theoretical model was developed to quantify and predict the amount of fluid absorption of different constituents of laminated polymeric composites. The thickness of the interphase region between the fiber and matrix was also measured using the scanning electron microscope (SEM) images and nano-indentation tests. The consistency of experimental results with the outcomes of the theoretical model indicates the accuracy of the model.     

Thermal Analysis of new soil sorption regulators

After mechanochemical treatment of multicomponent mixtures complex fertilizers containing nitrogen, phosphorous, potassium and sulphur (NPKS) with higher water capacity were obtained. As raw materials some solid wastes and ammonia and potassium sulfates were used. Due to the different ratio used, new solid phases in the mixtures are formed. New solid phases are confirmed by the stages and rate of mass changes and also by the thermal effects at different temperature ranges. New phases are also confirmed by using X-ray diffraction method. On the base of data obtained mechanism of chemical transformations is proposed. It was found that the kinetics of mechanical activated mixtures decomposition is significantly influenced by the time of treatment and proceeds in few stages. The results have shown that the soluble nutrients forms ratio and sorption capacity could be controlled by the initial components ratios and treatment conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

The use of moisture sorption isotherms and glass transition temperature to assess the stability of powdered baby formulas

The influence of adverse conditions of environment in the case of baby formulas, which are multiple mixtures, should be minimised. Water activity (a _w) and moisture content, correlated through sorption isotherms, and glass transition temperature have been considered relevant parameters to describe food stability. The aim of the study was to analyse water activity and glass transition temperature as the function of water content for samples of baby formulas. Three types of baby formulas (mixture, agglomerate, coated agglomerate) were determined by sorption isotherms, DSC and MDSC. DSC curves of mixture, agglomerate and coated agglomerate did not show differences in shape and course. The glass transition temperature of powders stored at different water activities was measured and it decreased with the increase in moisture content, confirming the strong plasticising effect of water on this property. Critical water activities varied from 0.14 to 0.68 and critical moisture contents varied from 0.032 to 0.062 g g^?1 powder.     

Analysis of hydrocarbon gas sorption and transport in ethyl cellulose using the dual sorption/partial immobilization models

Low pressure sorption and transport data reported by Barrer et al. [1] for various C₄ and C₅ hydrocarbons in ethyl cellulose are analyzed in terms of current models of sorption and transport in glassy polymers. The popular dual sorption model, which was first qualitatively justified by these investigators, is used to estimate the frozen free volume fraction in the polymer which can accommodate Langmuir sorption. New CO₂ sorption data in ethyl cellulose are also presented and shown to be consistent with the dual sorption model and the frozen free volume fraction estimated from the hydrocarbon sorption. p]Transport of the hydrocarbons in ethyl cellulose is adequately described in terms of the partial immobilization model which attributes mobilities to each of the two sorbed species. The ratio of the mobility of the Langmuir species to that of the Henry's law species was found to be considerably less than unity for all of the gases.