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The possibility of describing the kinetics of thermal degradation of PVC samples under both isothermal and nonisothermal conditions with a unique model and using the same set of parameters was investigated. Analysis of the experimental data revealed good agreement at higher temperatures (above 175 °C) when the catalytic action of generated HCl and its distribution in the sample were considered. At lower reaction temperatures, further experimental conditions and/or sample characteristics must be considered, and a modification of the model is necessary.

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Formalkinetische Behandlung des Masseverlustes bei thermischen Abbauprozessen von Polymeren unter nichtisothermen Bedingungen

III. Auswertung experimenteller TG-Kurven am Beispiel des Abbaus von Polyphenylen

Journal of Thermal Analysis and Calorimetry
Authors:
J. Behnisch
,
E. Schaaf
, and
H. Zimmermann

Kinetic values from non-isothermal thermogravimetric curves of polyphenylene have been calculated using the method of Flynn and Wall and that of Zsakó. These methods at first give unreal kinetic parameters, for it has been established that the degradation of polyphenylene is a system of two mutually independent reactions occurring simultaneously. With the use of a special relation between the degree of conversion of the unit reaction and that of the components, the kinetic parameters of the two reactions could be investigated by the method of Zsakó.

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On the basis of the formal basic relation
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\frac{{d\alpha }}{{dt}} = A \cdot e^ - \frac{E}{{RT}}(1 - \alpha )^n$$ \end{document}
methods of calculating kinetic values from non-isothermal thermogravimetric curves have been critically evaluated. It has been established that in general integral methods are preferable to differential methods. Methods basing on a series expansion of the exponential integral
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\int\limits_0^T {e^ - \frac{{ET}}{{RT}}} dT$$ \end{document}
are applicable without limitations to any cases. It has been concluded that the integral method suggested by Zsakó is the most reliable.
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Methods of calculating kinetic values from non-isothermal thermogravimetric curves obtained at different heating rates have been critically evaluated. It has been established that these methods give unreal kinetic parameters, when applied to a system of two mutually independent reactions occurring simultaneously. Cases in which components of the unit reaction could be investigated by the method of Zsakó are discussed.

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