Thermal stability and water uptake of high performance epoxy layered silicate nanocomposites

Intercalated and ordered exfoliated layered silicate nanocomposites based on three different epoxy resins of different structures and functionalities were synthesized using an octadecyl ammonium modified smectite clay. Water uptake properties of series of each nanocomposite system with different organoclay concentrations were determined by gravimetric measurements over a period of time. The diffusion coefficients were determined and the effect of the absorbed water on the thermal relaxations investigated. The equilibrium water uptake of all nanocomposites was reduced compared to the neat epoxy system but the rate of water diffusion remained unaffected. Further, the thermal stability of the different nanocomposites was determined using thermogravimetric analysis. The nanocomposites showed slightly reduced thermal stability, as indicated by a slight decrease in onset of degradation, whilst the final char concentration increased for greater organoclay concentrations.     

Examination of the swelling of heat protective hydrocolloids by DSC

While the basic fermented (sour) milk products, such as yogurt and kefir can be produced only in live flora version, the post heat-treatment is preferred in their flavored variations to increase the storage time. Casein being in sour coagulum precipitates during heat-treatment; therefore protective colloids surrounding the protein should be used to prevent it. Protective colloids are plant extracts, the most known of them are pectin and amylopectin. Basic requirement of protective colloid effect is the lower swelling temperature of hydrocolloid than the temperature of precipitation of sour coagulum. In this work we have examined the precipitation of sour coagulum as a function of the type of lactic acid bacteria cultures applied during fermentation as well as the swelling of heat protective plant hydrocolloids as a function of the composition (mainly of sugar content) of medium. To investigate the precipitation of fermented coagulum skimmed milk was fermented with mesophilic butter culture, thermophilic yogurt culture as well as with exopolysaccharide (EPS)-producing Prebiolact-2 culture. Precipitation was indicated in the increase of great extent of viscosity. Amylopectin was dispersed into aqueous solution of pH 4.5, the saccharose concentration of which was changed during the investigation of the swelling of heat protective hydrocolloids. A definite exothermic peak was assigned to the swelling of hydrocolloids during the DSC experiments. We could conclude that the precipitation temperature was increasing in the mesophilic-thermophilic-EPS producing microbes line, i.e. the heat stability and swelling temperature of hydrocolloids depend on the saccharose content of aqueous medium and they increase with rising the concentration of saccharose.     

Thermal analysis of the influence of water content on glass transitions

Starch is an important natural substance in which the water content has a significant influence on its structure and properties. In the present study, the effect of the water content on glass transition temperatures T _g and heat capacities C _p of wheat, maize and potato starches were investigated by high-sensitivity differential scanning calorimetry (temperature modulated TMDSC and conventional DSC). Thermal analysis measurements were performed on starch samples with different water contents. The exact water mass percentage of each sample was determined using the Karl-Fischer method. The obtained results show that the water content does influence the starch thermal properties in a systematic and measurable trend, the higher the water% the lower the glass transition temperature, and the higher the heat capacity jump during gelatinisation. At this stage possible interpretations of the results are just put forward and should be confirmed through complementary measurements.     

On the uptake of ammonia by the water/vapor interface

The passage of a single ammonia molecule from an infinitely dilute gas through the water/vapor interface is studied by constrained molecular dynamics simulations. The free energy of the system as a function of the distance between the ammonia and the interface has a minimum in the interfacial region. It is found that the preference of the ammonia for the interface is mainly due the disruption of the solvent structure caused by the ammonia in the bulk region, which results in an increase of the solvent internal energy.     

Thermal analysis study on water freezing and supercooling

Water freezing and supercooling were experimentally studied by methods of thermal analysis in a water droplet of 5 mm in diameter depending on various temperatures and times of overheating and cooling rates. Degree of water supercooling was influenced by previous thermal treatment but only to a certain extent. It increased slightly with overheating temperature and time and decreased with cooling rate. Maximum found values of supercooling ranged between 12 and 13 K. Small degrees of supercooling and their changes indicate that water freezing was more controlled by heterogeneous nucleation (properties of container contact surface) than by previous thermal treatment and experimental conditions.     

Multiscale analysis of water uptake and erosion in biodegradable polyarylates

The role of hydration in degradation and erosion of materials, especially biomaterials used in scaffolds and implants, was investigated by studying the distribution of water at length scales from 0.1 nm to 0.1 mm using Raman spectroscopy, small-angle neutron scattering (SANS), Raman confocal imaging, and scanning electron microscopy (SEM). The measurements were demonstrated using l-tyrosine derived polyarylates. Bound- and free- water were characterized using their respective signatures in the Raman spectra. In the presence of deuterium oxide (D₂O), H-D exchange occurred at the amide carbonyl but was not detected at the ester carbonyl. Water appeared to be present in the polymer even in regions where there was little evidence for NH to ND exchange. SANS showed that water is not uniformly dispersed in the polymer matrix. The distribution of water can be described as mass fractals in polymers with low water content (∼5 wt%), and surface fractals in polymers with larger water content (15-60 wt%). These fluctuations in the density of water distribution are presumed to be the precursors of the ∼20 μm water pockets seen by Raman confocal imaging, and also give rise to the 10-50 μm porous network seen in SEM. The surfaces of these polymers appeared to resist erosion while the core of the films continued to erode to form a porous structure. This could be due to differences in either the density of the polymer or the solvent environment in the bulk vs. the surface, or a combination of these two factors. There was no correlation between the rate of degradation and the amount of water uptake in these polymers, and this suggests that it is the bound water and not the total amount of water that contributes to hydrolytic degradation.     

Thermal analysis of water at x- and a-type zeolites

The nature of the sorbed water has been examined by differential scanning calormetry and effluent gas analysis at the zeolites of the types X and A, with univalent and bivalent cations. p]The desorption heats depending on the coverage and the cation form of zeolite have been determined. All these experiments point to the existence of only one general desorption mechanism independent of the ion-exchanging cation. The nature of the sorbed water is discussed.     

Thermal quality analysis of water on sythetic zeolite type a

The nature of the sorbed water on zeolites type A, with mono and bivalent cations, has been studied by DSC and effluent analysis. There have been found three types of sorbed water, independent of the nature of the exchanged cation. Further, a model for hydrogen binding in χ and β cavities is recommended.     

Thermal hazard analysis of inorganic peroxide initiators with varying water concentrations

Journal of Thermal Analysis and Calorimetry - Inorganic peroxide (IP) initiators are widely used as initiators in polymerization reactions. However, if IP initiators are in contact with water due...     

Study of interlayer water on the active sites of mineral sorbent: Thermal analysis

The programmed heating of montmorillonite samples is accompanied by their dehydration and dehydroxilation, this being registered by means of Derivatograph. The form of the endothermal effects within the 80–250°C interval can be of simple or double character depending on the nature of exchange cations. Though this phenomenon has been known for a long time, no satisfactory explanation has been provided so far. The herewith paper contains the results of bound water researches at various forms (Na, Ca, Al, Fe) of montmorillonite by means of thermal analysis as well as other physico-chemical methods. It has been found that the form of dehydration endoeffects depends on the state of the active centers of the mineral. In certain conditions, by means of thermal analysis one can determine corresponding quantities of bound water that are in agreement with various kinds of active centers of the mineral sorbent.This revised version was published online in November 2005 with corrections to the Cover Date.     

Reversible water uptake by a stable imine-based porous organic cage

A crystalline porous organic cage molecule, CC3, is shown to adsorb up to 20.1 wt% water reversibly. This was confirmed by both gravimetric sorption and by crystallographic analysis. Crystals of CC3 are stable in boiling water for at least 4 h. The surprising chemical and supramolecular stability of these imine-based molecular crystals suggests scope for practical applications in humid environments.     

Application of hydrocolloids as baking improvers

Hydrocolloids (or gums) belong to a group of biopolymers widely used in food technology. In the bakery industry, these compounds help to improve food texture and moisture retention, to retard starch retrogradation, and, finally, to enlarge the overall quality of the products during storage. Since recently, some hydrocolloids are being used due to their polymeric structure as fat replacers to obtain low calorie products and to substitute gluten in the formulation of gluten-free breads. This study describes the applications of some hydrocolloids in the bakery industry. Technological effects of these substances for different types of bakery products are also discussed.     

Thermal analysis of the system KCL-LiCI by differential scanning calorimetry

Thermal analysis of the binary system KCl-LiCl in the composition range 0.368–0.812 mol fraction of LiCl was studied by differential scanning calorimetry (DSC). On the basis of the DSC curves, the experimental data for the phase-diagram, the latent heat of fusion, and the average specific heat in the liquid and solid states are presented as a function of the composition of the mixture. The experimental results compared with literature data. The following empirical correlation between the heat of fusion (H) and of compositions of the mixture in mol fraction of LiCl (x) was obtained: ·GH=26.95–50.20x+43.06x² with a minimum value of 11.8 kJ(g mol)^–1 at the eutectic point of 0.587 mol fraction of LiCl at 354.4°C. These results are required as basic data to develop thermal energy storage materials, based on the phase change of a molten mixture of KCl-LiCI.     

Thermal stability and water content determination of glycerol by thermogravimetry

During the last years, the demand for biofuels has increased significantly. In Brazil, a production of 1 billion liters of biodiesel was produced by the end of 2007, due to its obligatory use in the composition of the diesel for vehicle use. In this production, a hundred thousand tons of glycerol are produced as by-product, for which alternative uses are needed. As glycerol has already been studied by other conventional characterization methods in the past, thermal analysis has been used mostly for characterization of sub ambient temperature properties of glycerol. In this paper, thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA) were used for its thermal characterization above room temperature. Thermal stability was determined from experimental data, which show that even in air, only a very small part of the volatilized glycerol is burned out. A thermogravimetric quantitative method was developed to determinate the water content of glycerol–water mixtures, which also was used to quantify the water impurity in pro-analysis samples of glycerol, showing compatible results with those obtained by Karl Fischer method.     

Thermal analysis by EMF-measurements on solid electrolytes

Galvanic cells of the type (C+Cl₂)(NaCl_(s))(MCl_2(s))(C+Cl₂) give e. m. f. 's above 280°, which are due to the formation of ternary chlorides Na_nMCl_n+2. By the change in slope of continuously measured e.m.f.vs. T curves, the temperatures of solid-state reactions in systems NaCl-MCl₂ can be found. This method was applied for the systems of NaCl with NiCl₂, CoCl₂ and CdCl₂, and for KCl-NiCl₂. With the exception of the system NaCl-NiCl₂, all phase diagrams must be corrected.

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Zusammenfassung Mit galvanischen Zellen des Typs (C+Cl₂)/NaCl_(s)/MCl_2(s)/(C+Cl₂) lassen sich oberhalb 280° EMK's messen, die auf der Bildung ternärer Chloride Na_nMCl_n+2 beruhen. Durch die Änderung der Steigung kontinuierlich gemessener EMK- gegen T-Kurven lassen sich in Systemen NaCl/MCl₂ die Temperaturen von Festkörperreaktionen nachweisen. Diese Methode wurde auf die Systeme des NaCl mit NiCl₂, CoCl₂ und CdCl₂ sowie auf das System KCl-NiCl₂ angewendet. Alle Phasendiagramme, mit Ausnahme des Systems NaCl-NiCl₂, mußten auf Grund dieser Messungen revidiert werden.

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(C+Cl₂)/NaCl./MCl₂./(C +Cl₂) 280 °C . . , Na_nMCl_n+2. . . , NaCl-MCl₂. NaCl NiCl₂, CoCl₂, CdCl₂ KCl-NiCl₂. NaCl-NiCl₂,ce .

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This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.     

Effect of hydrocolloids on starch thermal transitions,as measured by DSC

Differential scanning calorimetry (DSC) was used to analyze the influence of different hydrocolloids (xanthan, guar, and locust bean gums, carboxymethylcellulose and sodium alginate) on the gelatinization of corn starch in systems with starch concentration ranging between 0.1 and 0.7 g starch/g mixture. The reduction of available water produced a shift in gelatinization temperature, especially of the conclusion temperature. The effect was more marked for ionic hydrocolloids. The influence of hydrocolloids on glass transition temperature (T _g) of gelatinized starch suspensions and on the glass transition temperature of the maximally freeze-concentrated solute/unfrozen water matrix (T _g) was also studied.T _g onset values ranged between –4.5 and –5.5C for corn starch pastes with and without hydrocolloids. Those hydrocolloids that increased the viscosity of the unfrozen matrix inhibited additional ice formation during thawing (devitrification).Starch concentration and final heating temperature were found to be relevant factors affecting the kinetics of amylopectin retrogradation during frozen storage at –4C. Xanthan gum failed to prevent amylopectin retrogradation; this observation could be attributed to the fact that gums act outside the starch granule, while amylopectin retrogradation takes place within the granule.     

Thermal analysis at the evaluation of concrete damage by high temperatures

Summary Concrete damage by high temperatures includes mass loss, strength and modulus reductions and the formation of cracks and large pores. Thermal treatment reduces the amount of chemically bound water in the hydrate phase. With a rise in temperature, the spatial distribution of Ca(OH)₂ crystals becomes more compact; smaller crystals occur in a unit volume of the cement paste. A rise in temperature affects the pore structure by reducing the specific surface of hydration products. Cement paste becomes more heterogeneous in microstructure and coarser in pore structure. Compressive strength is not only significant parameter showing structural integrity of concrete; permeability influences concrete durability as well. To demonstrate this, permeability coefficients at various high temperatures are presented. The key quantitative insight into the hydrate phase behavior is based on thermal analysis results. Thermogravimetric (TG) mass losses are related to the phase changes represented either by DTA or DTG. Based on these, the tests employing TG mass losses and related DTA and DTG curves answer the question if the hydrate phase is present at individual high-temperature levels and what its quantitative state is. Method of thermal analysis is suitable for the interpretation of concrete behavior when subjected to high-temperature attack. Conclusions are drawn about thermal stability and residual properties of concrete specimens made at the construction site of Mochovce nuclear power plant (Slovakia); and subjected to temperatures up to 800°C. Relations among mechanical properties, permeability, pore median radius and bound water content in concrete are discussed and evaluated.     

Thermal analysis of the system triamterene-d-mannitol

Thermal analysis (DSC and HSM), and equilibrium solubility determinations were carried out to elucidate the mechanism of interaction at the solid state in the binary system triamterene-D-mannitol. Physical mixtures (5–90% w/w triamterene) and solid dispersions (5 up to 40% w/w triamterene) were prepared and studied. From DSC and HSM results, the thermal changes were associated with the variations in composition of the binary mixture, being more pronounced in the range 20–50% w/w. The binary phase diagram was proposed, although the exact position of the eutectic was uncertain. This is in accordance with a partial dissolution process detected by HSM. A linear increase in the solubility of triamterene with increasing aqueous mannitol concentration was obtained. The thermodynamic parameters of the solution properties were calculated, with an activation energy value of 96.081 kJ/mole. The solubilization increase was associated with complexation processes and hydrogen bonding formation. Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65^th birthday