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Background The thermal decomposition of cephalexine, cefadroxil and cefoperazone under non-isothermal conditions using the TG, respectively DSC methods, was studied. In case of TG, a hyphenated technique, including EGA, was used. Results The kinetic analysis was performed using the TG and DSC data in air for the first step of cephalosporin’s decomposition at four heating rates. The both TG and DSC data were processed according to an appropriate strategy to the following kinetic methods: Kissinger-Akahira-Sunose, Friedman, and NPK, in order to obtain realistic kinetic parameters, even if the decomposition process is a complex one. The EGA data offer some valuable indications about a possible decomposition mechanism. The obtained data indicate a rather good agreement between the activation energy’s values obtained by different methods, whereas the EGA data and the chemical structures give a possible explanation of the observed differences on the thermal stability. A complete kinetic analysis needs a data processing strategy using two or more methods, but the kinetic methods must also be applied to the different types of experimental data (TG and DSC). Conclusion The simultaneous use of DSC and TG data for the kinetic analysis coupled with evolved gas analysis (EGA) provided us a more complete picture of the degradation of the three cephalosporins. It was possible to estimate kinetic parameters by using three different kinetic methods and this allowed us to compare the E a values obtained from different experimental data, TG and DSC. The thermodegradation being a complex process, the both differential and integral methods based on the single step hypothesis are inadequate for obtaining believable kinetic parameters. Only the modified NPK method allowed an objective separation of the temperature, respective conversion influence on the reaction rate and in the same time to ascertain the existence of two simultaneous steps.

Solid polymer electrolytes (SPEs) are promising candidates for replacing liquid electrolytes in lithium ion batteries because of their excellent properties such as enhanced safety, flexibility and manufacturability, but ionic conductivity of SPEs has to be improved. Practically, poly(ethylene oxide) (PEO) is the only favourable candidate as SPE because of its ability to dissolve large amounts of inorganic (lithium) salt and its structure which supports lithium ion transport. However, high crystallinity of PEO limits ionic conductivity of these electrolytes. Nanocomposite technology offers possible solution to this problem since the incorporation of inorganic nanophases such as nanoclays in the PEO matrix is one of the promising ways to reduce the crystallinity of PEO. This investigation is focused on the preparation and characterization of PEO nanocomposites with montmorillonites as nanophase. PEO nanocomposites are prepared by a melt intercalation method and characterized by Small/Wide angle X-ray scattering (SAXS/WAXS), Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), Thermogravimetry (TGA) and Electrochemical impedance spectroscopy (EIS). Kinetic analysis of the non-isothermal thermogravimetric decomposition is performed. Influence of montmorillonites as nanophase on the structure, crystallinity, conformation, thermal properties and kinetics of the thermal decomposition of PEO is explained.

Poly(ethylene oxide) (PEO) is a semi- crystalline, biocompatible, water-soluble polyether, commercially available in wide range of molecular weights (20 000 – 8 000 000). Depending on molecular weight, PEO finds considerable application in many different branches of industry. PEO based electrolytes are among the most extensively studied polymer ionic conductors, but high crystallinity of PEO limits ionic conductivity of these electrolytes at room temperatures. One of the possible ways to reduce the crystallinity of PEO is the incorporation of nanoparticles such as polyhedral oligomeric silsesquioxanes (POSSs) in the PEO matrix. POSSs are nanoparticles composed of inorganic Si8O12 skeleton surrounded by eight organic groups. In this case the general formula is R7R'(SiO1.5)8 where R is isobutyl group and R' is phenyl group or monosupstituted phenyl group. The various POSS nanoparticles were prepared by corner capping reaction of isobutyltrisilanol with the suitable aryltrimethoxysilane. Substituents on phenyl group are methyl, metoxy, fluorine and chlorine. In this work, the series of PEO nanocomposites with different hepta isobutyl polyhedral oligomeric silsesquioxanes were prepared and the influence of POSSs on PEO melting was investigated by means of differential scanning calorimetry (DSC). It was observed that the glass transition temperature, melting temperature and crystallinity of PEO decrease when POSSs with methyl, fluorine or chlorine substituent on phenyl groups are present. Since polymer nanocomposites can be subjected to thermal degradation during processing and application as well, a good knowledge of thermal stability is important. To investigate the thermal behaviour of PEO/POSSs nanocomposites accelerated thermal degradation was performed by means of dynamic thermogravimetric analysis in an inert atmosphere. From the thermogravimetric curves (TG) it is evident that the thermal degradation of PEO matrix occurs through one basic degradation step. To estimate the influence of POSSs nanoparticles on the thermal stability of the PEO matrix, the following characteristics of TG curves were determined: the temperature at 5% mass loss (T5%), the temperature at the maximal degradation rate(Tmax), the maximal degradation rate (Rmax), the conversion at the maximal degradation rate (αmax) and the final mass loss (mf).