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Abstract  

The thermal behaviour of ultra-high molecular weight polyethylene (UHMWPE) of different molecular weights was examined by thermal analysis methods. The melting temperatureT m and the heat of melting δH were measured by the DSC method. The thermooxidative degradation process was investigated by using a MOM Q-1500 D derivatograph at various heating rates in air atmosphere. The initial decomposition temperatureT i was determined from the TG curves, and other characteristic temperatures of decomposition were calculated. It was found thatT m and δH are higher for UHMWPE than those for HDPE, i.e. 146‡C and 195 J g−1 for UHMWPE as compared with 133‡C and 166 J g−1 for HDPE. The thermal behaviour of the investigated UHMWPE samples is not significantly influenced by molecular weight.

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stabilizers . J Therm Anal Calorim . 2006 ; 84 : 679 – 692 . 10.1007/s10973-005-7549-z . 13. Šimon , P , Polavka , J . Thermooxidative degradation of dried milk studied by non

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Abstract  

The thermooxidative degradation of three models of oily soils was studied under non-isothermal conditions, at heating rates of 5, 10, 15 and 20�C min−1. Di-octyl-sebacate, as model for synthetic oil, was adsorbed on silica, alumina and silico-alumina, considered models for the inorganic micelle of a soil. For a kinetic analysis, the TG data were processed by three methods: Flynn-Wall-Ozawa, Friedman and NPK (Nomen-Sempere). The results indicate the NPK as the less speculative method that allows a separation of the elementary steps and at the same time a separation of the temperature, respective conversion dependent part of the reaction rate.

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Abstract  

Many of the isomers of polybutadiene and polyisoprene elastomers can be characterized by thermal analysis.T g is sensitive to side chain units (1,2 or 3,4 structure) for both polymers. Crystallinity measurements can characterizecis andtrans isomers. DMA and DEA master curves provide an idea of the heterogeneity of the chain units from the width of the loss factor curves in theT g region. Thermal and thermooxidative degradation, as followed by DSC and DTG, can differentiate specific natural and synthetic isomers of polyisoprenes in raw and vulcanized states.

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Abstract  

Metal or metal oxide nanoparticles possess unique features compared to equivalent larger-scale materials. In this paper we present the synthesis of grafted titania with phosphonic acids, their characterization and an extended non-isothermal kinetic study. The obtained results show that there in no significant difference between acids and esters in grafting reaction. The phosphorus content wary between 0.9 and 1.80% and is comparable with literature data. IR and AFM studies confirmed the formation of grafted titania. Extended non-isothermal kinetic study using different methods confirmed the complexity of thermooxidative degradation processes in non-isothermal conditions.

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Abstract  

Humic acids represent a complicated mixture of miscellaneous molecules formed as a product of mostly microbial degradation of dead plant tissues and animal bodies. In this work, lignite humic acids were enriched by model compounds and the model-free method suggested by Šimon was used to evaluate their stability over the whole range of conversions during the first thermooxidative degradation step. The kinetic parameters obtained were used to predict the stability at 20 and 180�C, respectively, which served for the recognition of processes induced by heat and those naturally occurring at lower temperatures. Comparison of the conversion times brought a partial insight into the kinetics and consequently into the role of individual compounds in the thermooxidative degradation/stability of the secondary structure of humic acids. It has been demonstrated that aromatic compounds added to humic acids, except pyridine, increased stability of humic acids and intermediate chars. The same conclusion can be drawn for acetic and palmitic acids. Addition of glucose or ethanol decreased the overall humic stability; however, the char of the former showed the highest stability after 40% of degradation.

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Abstract  

Simultaneous DTA/TG technique has been used to study the influence of various model compounds (aromatics, organic acids, alkanes, ketone, heterocyclic and sterole) on the thermo-oxidative behavior of lignite humic acids. As a measure of stability the shift of the onset temperature of the exothermic degradation peak has been used. Further, the ratio of mass loss recorded in the high and low temperature ranges (thermogravimetric index) was used to evaluate the role of added compounds on the recombination reactions occurring during the thermooxidative degradation of humic acids. It has been demonstrated that most of added compounds play a role during those processes at relatively low concentrations (1% mass/mass) and affect the humic acid stability as well as the value of thermogravimetric index (i.e. the degree of the apparent aromaticity). It has been clearly shown, that the latter parameter reflects more the ‘qualitative’ than the ‘quantitative’ relationship between biodegradable humified parts in the extracted pool of organic matter.

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Abstract  

Samples of an organic–inorganic hybrid were prepared by solvolysis and polycondensation in formic acid of tetraethoxysilane and diethylbenzyl phosphonate, simultaneous with the oxidative polymerization of aniline. The thermal behavior of the samples in dynamic air atmosphere and non-isothermal conditions was determined by a coupled thermogravimetric/evolved gas analysis. Two significant thermal events were established: the elimination from the polymeric matrix of low mass molecules, respectively the thermooxidative degradation of the organic part of the matrix. The kinetic analysis was performed with the Flynn-Wall-Ozawa, Friedman and modified Non-Parametric-Kinetic methods. Only the last one allowed an objective analysis of the first process as a process of two simultaneous thermally induced phenomena with the kinetic functions of the type αm(1 − α)n.

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Abstract  

Methods for kinetic description of induction periods, based on the single-step kinetics approximation and various expressions of the temperature functions, are presented. The formulas for evaluation of both isothermal and non-isothermal lengths of induction periods are derived. Use of the formulas is demonstrated on the thermooxidative degradation of polyolefines. The kinetic parameters obtained from isothermal and non-isothermal experiments are compared and possible reasons of inconsistencies are analyzed. Applications of the determination of induction periods for thermooxidation of various systems are reviewed. The theory outlined in this paper can be applied not only for thermooxidation in condensed phase, but also for other processes exhibiting the induction period, such as the curing of rubber compounds, recrystallization of nickel sulfide and crystallization of silicate and metal glasses.

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Abstract  

The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate, starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min−1. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min−1. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears. These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates: 5, 7, 10 and 12 °C min−1. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C).

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