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Abstract  

Dielectric experiments are often performed in non-isothermal conditions. Thus, there is a difference between the temperature of the sample and the sensor temperature. In this work we propose and compare three temperature calibration methods based on the detection of transitions or relaxations: i) the melting of high-purity metallic standards (indium and tin), ii) the 2nd order phase transition of a ferroelectric crystal (TGS); iii) the -relaxation of an amorphous polymer (poly(carbonate)). The results obtained from the three different methods were used to construct a calibration curve for a given heating rate.

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Introduction Triglycine sulfate [(NH 2 CH 2 COOH) 3 · H 2 SO 4 ] (TGS) is an interesting material for its wide range of applications and has an excellent pyroelectric and ferroelectric properties [ 1 ]. This crystal is

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Abstract  

To study the corrosion resistance of metals and alloys, an analysis system needs to be able to simulate the harsh environments to which these materials are subjected. The system must also collect data from metal and alloy samples at elevated temperatures over long periods of time (typically days). Thermogravimetric analyzers (TGs) are well accepted systems for both corrosion studies and long-term elevated temperature studies. However, until now, TGs could conduct either corrosion studies or long-term studies, but not both. This paper presents a TG system specifically designed to satisfy the requirements of long-term corrosion resistance studies of metals and alloys.

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Abstract  

An inherent challenge with polymer blends is the difficulty in resolving the glass transition, T g, for the smaller mass fraction component. The objective of this work was to determine the practical scanning conditions for identifying the dual T g’s for a 75:25 polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend using a thermomechanical analyzer (TMA). Scanning rates up to 20°C min−1 using dilatometer and expansion modes were studied. Heating and cooling rates were found to affect both T g values but the effects were not simple relationships. T g values could either increase or decrease depending on the scanning rate applied. Higher rates resulted in large thermal lags which opened the accuracy of measurements to question. Generally, higher rates tended to display only one T g but the duality of T g’s can be detected with scanning rates between 0.5 and 5°C min−1 for both modes.

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Abstract  

The ultra-slow modes with a relaxation time much longer than 1 ns are discovered by a time-resolved spectroscopy in uniaxial ferroelectric (NH2CH2COOH)3H2SO4 (TGS) and in glass-former HOCH2(CHOH)4CH2OH (D-sorbitol). A mode discovered in TGS is a thermal relaxational mode and is proved to be the physical origin of the central peak found by Brillouin scattering. Two modes are discovered in D-sorbitol. One is a thermal relaxational mode. The other is a mode characterized by the Kohlraush-Williams-Watts function with a relaxation time R. A remarkable result is that R indicates a critical behavior not at the liquid-glass transition temperature T g =–7°C but at the ergodic to nonergodic transition temperature T c=33°C.

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Abstract  

The effect of excipients on the secondary structure of lyophilized proteins was studied through second-derivative Fourier transform infrared (FTIR) spectroscopic analysis. The glass transition temperature (T g), denaturation temperature (T d) and moisture content were determined by differential scanning calorimetry (DSC) and thermogravimetry (TG). T g, T d and the preservation of protein secondary structure were found to be dependent upon the type and amount of the excipient included in the formulation. Meanwhile, the lyophilized proteins easily adsorbed amounts of moisture during storage to reduce their T gs and stability.

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Journal of Thermal Analysis and Calorimetry
Authors: Marta Sánchez-Cabezudo, Margarita Prolongo, Catalina Salom and Rosa Masegosa

Abstract  

The cure kinetics and morphology of diglycidyl ether of bisphenol A (DGEBA) modified with polyvinyl acetate (PVAc) using diaminodiphenylmethane (DDM) as hardener were investigated through differential scanning calorimetry (DSC) and environmental scanning electron microscopy (ESEM). Isothermal curing measurements were carried out at 150, 120 and 80C. The kinetic parameters were obtained using the general autocatalytic chemically controlled model. The comparison of the kinetic data indicates that the presence of PVAc does not change the autocatalytic nature of the cure reaction. Two T g’s were observed in the fully cured samples of the modified systems. ESEM micrographies confirm the biphasic morphology.

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Abstract  

Thermal analysis of phenylethynyl end-capped imide oligomer AFR-PEPA-4 was performed to characterize cure reaction, thermal stabilities and semicrystalline behavior of AFR-PEPA-4 oligomer and its cured polyimide. Cured AFR-PEPA-4 polyimide showed high T gs up to 418C. Both AFR-PEPA-4 oligomer and polyimide exhibit excellent thermal stabilities comparable to PETI-5 polyimides. AFR-PEPA-4 imide oligomer has a T m of 330C and exhibits spherulite crystalline morphology in the film. The crystallinity in AFR-PEPA-4 films could not be regenerated under any annealing conditions after the initial melt.

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Abstract  

Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (T gs) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsistent smoothing of data acquired under different conditions can lead to the misinterpretation of results. A quantitative method for the selection of smoothing factors for the analysis and comparison of (M)DSC results is presented. The method is most useful for the analysis of the derivative of the heat capacity, dC p/dt or dC p/dT, plots which best highlight overlapping T gs. Four equations are shown to relate the heating rate and the smoothing factor. The equations allow a comparison of data acquired i) at different heating rates and plotted vs. temperature, ii) at a single heating rate and plotted vs. both time and temperature, i.e., dC p/dt vs. dC p/dT, iii) at different heating rates and plotted vs. both time and temperature, and iv) at different heating rates, and shown exclusively in the time domain. Examples of the use of the equations are provided for the analysis of bitumen, a complex mixture of natural origin.

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Abstract  

Diglycidyl ether of bisfenol-A (DGEBA)/poly(vinyl acetate) (PVAc)/poly(4-vinyl phenol) brominated (PVPhBr) ternary blends cured with 4,4’-diaminodiphenylmethane (DDM) were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). Homogeneous (DGEBA+DDM)/PVPhBr networks with a unique T g are generated. Ternary blends (DGEBA+DDM)/PVAc/PVPhBr are initially miscible and phase separate upon curing arising two T gs that correspond to a PVAc-rich phase and to epoxy network phase. Increasing the PVPhBr content the T gof the PVAc phase move to higher temperatures as a consequence of the PVAc-PVPhBr interactions. Different morphologies are generated as a function of the blend composition.

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