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Barely explored in the prior literature, ruby chocolate was investigated in this study to explore its thermal properties. The fatty acid composition of ruby chocolate (RC) fat was determined using gas chromatography. Differential ...
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Barely explored in the prior literature, ruby chocolate was investigated in this study to explore its thermal properties. The fatty acid composition of ruby chocolate (RC) fat was determined using gas chromatography. Differential scanning calorimetry (DSC) was successfully used to determine the melting behavior and polymorphic forms of the cocoa fat and milk fat present in the RC. The oxidative stability of the fat extracted from the RC was studied with the use of pressurized differential scanning calorimetry (PDSC). The thermal behavior of the chocolate and the fat were investigated using thermogravimetry (TGA). The thermal profile and characteristics of the RC showed how the parameters compared with those of dark and milk chocolate. The melting temperature of the RC obtained by DSC was more similar to that of milk chocolate than to that of dark chocolate. Regression analysis of the PDSC data for the fat extracted from the RC was characterized by very high correlation coefficients (>0.99). It was noticed there was no statistically significant difference between the values of the activation energy (Ea) of the oxidation process for the fat extracted from the RC, obtained by the means of maximum temperature (dynamic mode) and maximum induction time (isothermal mode).
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The glass transition of thermoplastics of different polydispersity and thermosets of different network structure has been studied by conventional differential scanning calorimetry(DSC)and temperature modulated DSC(TMDSC).The cooli...
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The glass transition of thermoplastics of different polydispersity and thermosets of different network structure has been studied by conventional differential scanning calorimetry(DSC)and temperature modulated DSC(TMDSC).The cooling rate dependence of the thermal glass transition temperature T_g measured by DSC,and the frequency dependence of the dynamic glass transition temperature T_alpha measured by TMDSC have been investigated.The relation between the cooling rate and the frequency necessary to achieve the same glass transition temperature has been quantified in terms of a logarithmic difference DELTA =log_(10)[|q|]- Iog_(10)(omega),where \q\ is the absolute value of the cooling rate in K s~(-1)and omega is the angular frequency in rad s~(-1)necessary to obtain T_g(q)= T_alpha(omega).The values of A obtained for various polymers at a modulation period of 120 s(frequency of 8.3 mHz)are between 0.14 and 0.81.These values agree reasonably well with the theoretical prediction [Hutchinson JM,Montserrat S.Thermochim Acta 2001;377:63 [6]] based on the model of Tool-Narayanaswamy-Moynihan with a distribution of relaxation times.The results are discussed and compared with those obtained by other authors in polymeric and other glass-forming systems.
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In Modulated-Temperature Differential Scanning Calorimetry (MTDSC) a conventional heating programme is modulated cyclically. The heat-flow signal is split into an underlying and an approximately periodic part. We summarise the pre...
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In Modulated-Temperature Differential Scanning Calorimetry (MTDSC) a conventional heating programme is modulated cyclically. The heat-flow signal is split into an underlying and an approximately periodic part. We summarise the present state of the method with regard to chemical reactions and melting. We also give a more extensive treatment of the glass transition. (C) 1997 Elsevier Science B.V. [References: 18]
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The reaction of hardening of melamine-urea-formaldehyde (MUF) adhesive resins in the presence of wood and cellulose was confirmed to have a lower energy of activation than the MUF adhesive alone, both in the presence or absence of...
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The reaction of hardening of melamine-urea-formaldehyde (MUF) adhesive resins in the presence of wood and cellulose was confirmed to have a lower energy of activation than the MUF adhesive alone, both in the presence or absence of ammonium chloride hardener, thus both in mildly acid and mildly alkaline environments. DSC exotherms showed that during hardening of melamine to melamine, melamine to urea, and urea to urea crosslinks through methylene bridges occur. Only the earliest reaction, mainly melamine to melamine crosslinking, presents a decrease in energy of activation which can be assigned to catalytic activation by the cellulosic substrate. The other types of crosslinking reactions (i) appear not to occur due to the more favorable and rapid melamine to melamine reaction which precedes them at lower temperature or (ii) do not present catalytic activation by the substrate but rather hindrance by it or (iii) variation of their energy of activation appears to be due to increased diffusion hindrance by the substrate caused by the increasing molecular weight of the resin while hardening. This because the Kissinger equation plots of the resin alone are in the main linear, for all the exotherms, indicating that in hardening of the resin alone diffusion problems appear to be limited. (C) 1995 John Wiley & Sons, Inc. [References: 34]
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Conventional methods of thermal analysis provide only a sample-averaged response. The instrument described here combines two measurement technologies, conventional thermal analysis and scanning probe microscopy, to provide materia...
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Conventional methods of thermal analysis provide only a sample-averaged response. The instrument described here combines two measurement technologies, conventional thermal analysis and scanning probe microscopy, to provide material scientists with analysis on the nanoscale. [References: 6]
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Adifferential scanning calorimeter (DSC) is a benchtop instrument used to determine thermodynamic transitions and heat capacities of a variety of substances. A small sample—typically 5-20 mg, around the size of the tip of a #2 pe...
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Adifferential scanning calorimeter (DSC) is a benchtop instrument used to determine thermodynamic transitions and heat capacities of a variety of substances. A small sample—typically 5-20 mg, around the size of the tip of a #2 pencil—is placed in the instrument's furnace, the temperature is ramped up (or down), and the amount of heat or power necessary for the sample and the reference to achieve (or hold) a temperature is measured and compared.
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Periodic heating has been applied more than a century ago to study thermophysical properties of materials. The measurement of heat capacity using a.c. calorimetry was first performed by Corbino in 1910. In connection with the tech...
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Periodic heating has been applied more than a century ago to study thermophysical properties of materials. The measurement of heat capacity using a.c. calorimetry was first performed by Corbino in 1910. In connection with the technological development and the progress in science and technology, new and sophisticated apparatus have been constructed in an a.c. calorimetric heat capacity measurements. In this measurement, the noise level of a.c. temperature can be reduced markedly as opposed to the other nonperiodic methods and, therefore, high precision determination can be attained. Furthermore, not only the amplitude but also the phase in a.c. temperature is a useful parameter in constructing much advanced apparatus. (C) 1997 Elsevier Science B.V. [References: 24]
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Recently a small amount of locally reversible melting was observed in semicrystalline poly(ethylene terephthalate) during temperature-modulated differential scanning calorimetry (TMDSC). To further study the reversibility of melti...
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Recently a small amount of locally reversible melting was observed in semicrystalline poly(ethylene terephthalate) during temperature-modulated differential scanning calorimetry (TMDSC). To further study the reversibility of melting, poly(oxyethylene) (POE) is analyzed. Low molar mass POE is known to be able to form extended-chain, equilibrium crystals, while at higher molar mass and less favorable crystallization conditions, nonequilibrium, folded-chain crystals grow. The TMDSC of POE reveals variable amounts of reversible melting depending on crystallization conditions and molar mass. The crystals closest to equilibrium show no reversible melting, proving the inherently irreversible nature of polymer melting. Crystals of high molar mass show a small amount of the prior discovered locally reversible melting. Poorly crystallized POE of low molar mass have, because of their lower zero-entropy-production melting temperature, a sufficiently smaller gap between crystallization and melting temperature to show some reversing melting. [References: 34]
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A recent development in thermal analysis is described that will provide spatial resolution in the measurement of complex samples. This novel technique will find application in the analysis of modern polymeric materials that are bl...
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A recent development in thermal analysis is described that will provide spatial resolution in the measurement of complex samples. This novel technique will find application in the analysis of modern polymeric materials that are blends or composites. [References: 13]
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Montmorillonite nanocomposite systems obtained from epoxy cured using anhydride and the addition of a reacting flame retardant are studied in this paper. In particular, a thermokinetic analysis of the behavior of five different co...
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Montmorillonite nanocomposite systems obtained from epoxy cured using anhydride and the addition of a reacting flame retardant are studied in this paper. In particular, a thermokinetic analysis of the behavior of five different compounds was performed, using a differential scanning calorimeter. The isothermal tests showed double reaction peaks, due to the cure reactions of DGEBA/acid anhydride systems. The comparisons between dynamic thermograms (and between isothermal ones, too) for the different mixtures also showed that the addition of other active substances (such as a nanofiller or a flame retardant additive) does not change the mechanism of crosslinking from a qualitative point of view, but both the nanoreinforcement and the flame retardant seemed to exert an evident catalytic action on the cure reactions. A model describing the cure behavior of the aforementioned materials is proposed in this work. This model takes into account the fact that the reaction mechanism of each analyzed system is composed of a couple of parallel phenomena: the fast opening of anhydride ring (corresponding to a first exothermic peak and characterized by "n-th order" kinetics) and resin networking (corresponding to a second exothermic peak and characterized by an "auto-catalytic with zero initial velocity" behavior). The verification of the proposed model was performed by means of a comparison between experimental data (normalized curves derived from DSC thermograms) and theoretical data (derived from a numerical integration-using the second order Runge-Kutta method-of the model-representative equation) and provided very good results. This allows one to apply such a model to any engineering process problem concerning the cure of DGEBA/acid anhydride/phyllosilicate nanocomposite systems. (C) 2004 Wiley Periodicals, Inc.
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