Search Results
Abstract
The DSC method was used to obtain more information on changes of thermal properties connected with different comonomers bound in the (co)polymer chains. The copolyamides propered were block ones which were less crystalline and compatible with poly-&-caprolactam. The results have confirmed the crystalline nature of polyamides and copolyamides.
Abstract
The critical furnace chamber temperature (T′ign) of the thermal explosion synthesis reaction Ti+3Al→TiAl3 is studied by isothermal and non-isothermal DSC. The reaction product is characterized by using the X-ray powder diffraction. The value of T′ign is between 740 and 745C obtained from the isothermal DSC observations, and 729C obtained from non-isothermal DSC curves. It shows that these two values have a good consistency. With the help of the apparent activation energy of the reaction obtained by Friedman method and the value of T′ign0 by the multiple linear regression of the T′igns at different heating rates (β), the critical temperature (T b) of thermal explosion for Ti–75at%Al mixture is estimated to be 785C.
Abstract
New approaches to the analysis of differential scanning calorimetry (DSC) data relating to proteins undergoing irreversible thermal denaturation have been demonstrated. The experimental approaches include obtaining a set of DSC curves at various scanning rates and protein concentrations, and also reheating experiments. The mathematical methods of analysis include construction of a linear anamorphosis and simultaneous fitting of a theoretical expression for the dependence of the excess heat capacity on temperature to a set of experimental DSC curves. Different kinetic models are discussed: the one-step irreversible model, the model including two consecutive irreversible steps, the Lumry and Eyring model with a fast equilibrating first step, and the whole kinetic Lumry and Eyring model.
Abstract
The applicability of the kinetic analysis of data obtained by non-isothermal differential scanning calorimetry (DSC) is discussed. The Johnson-Mehl-Avrami (JMA) model was used for the computer simulation of DSC traces subsequently analysed by common methods of kinetic analysis of non-isothermal data. For the temperature-independent kinetic exponent n of the JMA equation, the kinetic analysis was shown to provide correct results, e.g. a correct kinetic model and apparent activation energy. On the other hand, for the temperature-dependent kinetic exponent, there is a great possibility of erroneous determination of the correct kinetic model and apparent activation energy, especially at higher heating rates. Since the temperature dependence of n cannot be determined on the basis of non-isothermal DSC experiments, conclusions must be drawn with appropriate caution.
Abstract
Differential scanning calorimetry (DSC) was applied to investigate the thermal behaviour of a series of segmented polyurethanes based on diphenylmethane-4,4'-diisocyanate (MDI), polyoxypropylenediol (POPD) and 3-chloro-1,2-propanediol (CPD)/1,2-propanediol (PD).It has been found that the heat of thermal transition in the range of 250–300°C increases with the amount of CPD, which also causes a decrease of polyurethanes' flammability, characterised by its Limited Oxygen Index (LOI) value. On the basis of obtained results it can be concluded that DSC may be applied for flammability evaluation of segmented polyurethanes.
Summary A kinetic study of cure kinetics of epoxy resin based on a diglycidyl ether of bisphenol A (DGEBA), with poly(oxypropylene) diamine (Jeffamine D230) as a curing agent, was performed by means of differential scanning calorimetry (DSC). Isothermal and dynamic DSC characterizations of stoichiometric and sub-stoichiometric mixtures were performed. The kinetics of cure was described successfully by empirical models in wide temperature range. System with sub-stoichiometric content of amine showed evidence of two separate reactions, second of which was presumed to be etherification reaction. Catalytic influence of hydroxyl groups formed by epoxy-amine addition was determined.
Abstract
The fact that small bowel is extremely sensitive to ischemia/reperfusion (I/R) injury had encouraged us to compare the conventional histology and differential scanning calorimetry (DSC) methods in intestinal structural changes following experimental warm I/R models. Our histological findings showed that longer warm I/R period caused more severe damage in structure of mucosa and crypts, but there were no changes in the muscular layer. According to our DSC data (transition temperature, calorimetric enthalpy) suggest that the thermal destruction of mucosa, muscular layer and total intestinal wall following I/R injury revealed significant differences compared to normal bowel structure.
Abstract
Avascular necrosis of human femoral head (ANFH) causes incongruity in the joint that leads to disability in patients requires total hip arthroplasty (THA). Several etiological factors of ANFH have been proposed in the literature but there are cases of idiopathic origin. We observed macroscopic variation in quality of the subcutaneous fat tissue in patients with ANFH compared to patients with osteoarthritis or hip fracture during THA procedures. The samples were analysed by histology, gas chromatography (GC) and differential scanning calorimetry (DSC). Conclusion: the alteration in the fatty acid profile did not cause histological changes, however we could detect biochemical changes using DSC and GC.
Abstract
The effect of ionising radiation on the physico-chemical properties of salts of three alkaloids has been studied: codeine phosphate (COD), papaverine hydrochloride (PAP) and pilocarpine hydrochloride (PIL). These compounds in the solid state were irradiated with an e-beam of the energy of 9.96 MeV to achieve doses ranging from 25 to 400 kGy, and then they were subjected to organoleptic analysis, thermal analysis (differential scanning calorimetry, DSC), electron resonance (EPR) spectroscopy, scanning electron microscopy observations and X-ray diffraction study. The most informative were the results provided by the EPR and DSC methods. The EPR spectra revealed the presence of long-lived radicals whose concentration was directly proportional to the dose of irradiation for all the compounds studied. (PIL 2.14 × 1016 spin/g, COD 6.85 × 1015 spin/g, PAP 2.50 × 1014 spin/g—for the dose of 100 kGy). The DSC results revealed a decrease in the melting point by 5.9 °C for COD and by 0.8 °C for PIL after irradiation with 200 kGy, which is indicative of products of radiolysis, of which at least one is non-white, and changes the colour of the compounds. PAP, for which no decrease in the melting point and no colour change was observed and for which the concentration of free radicals was the lowest, was found to be most stable from among the compounds studied. It will probably be suitable for radiation sterilisation. The other two compounds COD and PIL show much lower radiochemical stability and should be subjected to more detailed examination to establish the mechanism of radiolysis and the possibility of radiation sterilisation. Our results have confirmed the earlier reports on high radiochemical stability of PAP, but do not confirm the resistance to ionising radiation of COD and PIL.
Quantitative determination of acetylsalicylic acid in commercial drugs using DSC
Comparison with titration and UV spectrophotometric methods
Abstract
In this article, the quantitative determination of acetylsalicylic acid (ASA) contained in two of the most commercially available pharmaceutical formulations was performed using differential scanning calorimetry (DSC) after a thermoanalytical characterization and a preliminary test on compatibility of ASA with three of the most commonly considered excipients [cellulose (CE), starch (ST) and sodium saccharin (SS)]. Finally, the analytical results obtained were compared with those derived by titrimetry and two UV spectrophotometric methods: i.e. a ‘direct method’ and a method based on first-order derivative UV spectra.
