Search Results
This is a study for criteria to judge the melting point of semi-crystalline polymers from the DSC endotherm for polymer melting. Beyond standard indium DSC melting results an evaluation has been made on a series of polyethylenes for which crystal sizes were measured and predicted from Raman LAM analysis. The results confirm the conclusion of Prof. Wunderlich that the DSC content of melting is the proper basis of reporting melting points.
Abstract
The re-oxidation of low-pressure methanol synthesis catalyst was followed by means of DSC, with the aim of contributing to a better understanding of the processes taking place during catalyst blanketing, stabilization and re-oxidation. The investigations were carried out with previously hydrogen-reduced samples, and their successive re-oxidation was performed with different oxygen contents in the oxygen/nitrogen gas mixtures. A procedure for catalyst stabilization and/or catalyst discharge is proposed.
Abstract
The kinetics of thermooxidation of edible oils: soybean oil, rapeseed oil, corn and peanut oil was investigated in two ways. The DSC and its pressure version (PDSC) were used for measurements under the isothermal and non-isothermal conditions in atmosphere of oxygen. Comparing these two methods for each oil the differences between the values of activation energies were observed. However, mechanism of oxidation in both method was different.
Abstract
An experimental mixture design was applied to a differential scanning calorimetry (DSC) study performed to evaluate naproxen compatibility in tablet formulations consisting of four classic excipients (sorbitol, sodium carboxymethylcellulose, poly(ethylene glycol) 20000 and Veegum) each in adequate concentration ranges accounting for the relevant values actually used in pharmaceutical formulations. Twenty-seven different tablets were obtained from as many mixtures prepared according to the experimental design plan and analyzed in a random order by DSC. Statistical evaluation of experimental data enabled correlation of both enthalpy and onset temperature variations of drug melting endotherm (selected as responses indicative of the presence of drug-excipient interactions) with the mixture composition. Variance analysis (Anova) confirmed the reliability of the postulated polynomial model in providing adequate prediction of true system behaviour.
Abstract
In this study, isothermal crystallisation kinetic data of poly(propylene terephthalate) (PPT) are obtained using differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Data from each method are analyzed according to the secondary nucleation theory of Lauritzen–Hoffmann and the procedures and results are critically presented. The assumption that the growth rates obtained from PLM can be equally well described from crystallisation rate data using the half-crystallisation time, is tested.
Abstract
Temperature calibration of DSCs is usually carried out on heating. In order to accurately control the temperature during cooling experiments, the calibration has to be carried out on cooling. Therefore, three high-purity, thermally stable liquid crystals were used to perform a temperature calibration of an electrcial compensation DSC on cooling. All three liquid crystals have several liquid crystalline phases, and they all were purified to a 99.9% lovel. Temoperatures of the isotropic to nematic or cholesteric and the mesophase to mesophase transitions were used. It was verified that these liquid crystals have sufficient thermal stability for carrying out the calibration on cooling. The dependence of the real temperature on the indicated temperature has been established for all the combinations of the heating and cooling rates of practical interest. It is also shown that the vant's Hoff equation can only be applied to the crystal to a liquid crystal transition, but not to the liquid crystal to liquid crystal or liquid crystal to isotropic transitions.
Abstract
Chiral drugs are generally resolved through formation of diastereoisomeric salts of different solubility. When the diastereoisomer salts from a eutectic in the solid phase, a good estimate can be made for the efficiency of the resolution (S), through a calculation based on the eutectic composition (x eu). The eutectic composition can be computed from thermal data of a differential scanning calorimetric (DSC) measurement of the diastereoisomeric salts [1]. In this work we investigated the influence of uncertainties of thermal data on the estimation of the efficiency of resolution (S), spreading throughout the calculations involved. Performance of our error-estimating method is demonstrated on 6 diastereoisomer salt pairs. The obtained deviations are close to the deviations of resolution experiments. Thus, it can be concluded that the DSC measurements are useful means in predicting the efficiency of resolutions.
Heat capacity of aqueous 2-(2-hexyloxyethoxy)ethanol solutions by DSC
Application of two-point scaling to pseudophases coexistence
Summary
The specific heat capacities of aqueous solutions of 2-(hexyloxyethoxy)ethanol (C6E2) have been measured from 2 to 55C within the whole available composition range by DSC. Changes of specific, partial and apparent molar heat capacities of investigated system were analysed and considered as an effect of structural transformations. The two-point scaling theory was applied to the description of the binary mixtures properties in the pseudophases coexistence region.
Abstract
The physical aging of a system containing tetraglycidyl-4-4′-diaminodiphenylmethane (TGDDM), with a multifunctional novolac glycidyl ether resin hardened by 4,4′-diaminodiphenylsulphone (DDS) has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Samples fully cured were aged at temperatures between 200 and 250C, during periods of time from 1 to a maximum of 336 h. Furthermore, the dynamic mechanical relaxation behaviour annealed at temperature of 220C, was studied, aging during 24 and 168 h. The effect of the enthalpy relaxation during DSC heating scan is shown by the presence of an endothermic peak whose position and intensity depends on the aging conditions, both temperature and time. DSC studies suggest that enthalpy relaxation increases gradually with aging time to a limiting value for each temperature where structural equilibrium is reached. DMA results show that the effect of aging is to cause chain stiffening and a decrease in the height of the peak value of the loss factor.
Abstract
For kinetic evaluation by TG and DSC of simple and complex reactions we used a direct fit on the basis of TG differential equations and DSC non-linear equations. The advantages of an overall evaluation, i.e. the simultaneous inclusion of all data sets at different heating rates, are described. TG and DSC measurements of the dehydration of calcium oxalate monohydrate and the decomposition of calcium oxalate are used as examples.
