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The glass transition temperatures ( T g ) of the cured epoxy resins were determined by DSC upon the second heating with a rate of 10 °C min −1 . The data are recorded in Table 3 . The T g of the cured E-51/LCECA2 and LCE/LCECA2 is 124 and 136 °C
melting temperature ( T m ) and enthalpies of fusion (Δ H m ) are also listed in Table 3 . DSC is one of the tools to investigate miscibility in polymer blends. A single compositional-dependant glass transition temperature ( T g ) is an indication of
-physical properties of polymer blends are, however, characteristic of individual glass transition temperature ( T g ) of the component phases. The changes in T g of blend versus neat components, however, are dependent on the processing conditions and resulted
samples (~40 mg) were heated in platinum crucibles at a rate of 10 °C min −1 in dry nitrogen atmosphere up to 1,100 °C. The glass transition temperature ( T g ) was determined from the inflection point on the enthalpy curve and all thermal parameters were
rates and last peak visibility increases with increasing heating rate. Second peak is not much prominent in the 5, 10, and 15 deg/min heating rates. In this paper, the first peak is taken into consideration for the kinetic analysis. Glass transition
min −1 and then cooled to 25 °C to minimize the enthalpy relaxation. The calorimeter was calibrated using indium standard before the measurements. A re-scan treatment at low heating rate of 2 °C min −1 was used to estimate the glass transition
In the range from −50° to +130°C, the temperature dependence of the heat capacity for different kinds of gelatins with water contents of from 2 to 95% was studied by the DSC method. It was shown that, in all studied cases, metastable collagen-like structures are formed in gels or crystalline gelatins, with thermodynamic parameters depending on the formation conditions. The characteristic properties of the glass transitions in amorphous gelatins and crystalline gelatins with different melting heats and different contents of the ordered phase were established. Special attention is paid to the structural properties of free and bound water. The dependence of the glass transition temperatureT g on the bound water content was shown to be of general applicability for many denatured biopolymers. Free water in gelatins, in distinction to the bound water, does not act as a plasticizer, but forms a rigid matrix inhibiting the glass transition.
Abstract
The object of the paper is an investigation of the glasses of the (As2S3)x(AsSe0.5Te0.5I)100-x. type for 65≤;x≤;95, using methods of thermomechanical analysis. Values of the thermal coefficients of linear expansion in solid and visco-plastic phase were determined. it was shown that introducing arsenic-sulfide in glass-matrix AsChI, i.e. (AsSe0.5Te0.5I), leads to an increasing stability of these glasses. The characteristic temperatures of softening Tg and the temperature of the beginning of deformation t w increase by increasing content of As2S3. The analytical forms of dependence of four significant physical values αg, αl, Tg, Tw, as a function of As2S3 content in the structure of glasses were fitted.
Abstract
In the present study, we report on the thermal properties of a series of benzodiazepines. The heat of fusion varied between approximately 25 and 40 kJ mol–1, except for oxazepam and lorazepam where dimerization in the solid state increased the heat of fusion to 78.54(±0.37) and 77.03 (±0.84)kJ mol–1, respectively. Heating alprazolam at a low rate (0.5 K min–1) showed that polymorphs I and II are an enantiotropic pair with a solid-solid transition at 481.4 K It was shown that all benzodiazepines could be transformed to the glassy state by cooling fused samples, irrespective of the cooling rate. The size of the relaxation endotherm accompanying the glass transition increased by heating the glassy drugs at a higher rate through T g or by cooling the fused samples at a slower rate. The time dependence of the glass to liquid transition can be described to a good approximation as a first order transformation. The Gordon-Taylor equation was used to predict T g of a binary mixture of temazepam, diazepam or prazepam with polyHEMA. It was shown that the predictability was acceptable as long as the drug concentration was below 10%w/w; at higher concentration, specific drug-polymer interactions causing changes in free volume of the system could not be ignored.
