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Abstract  

In the present work, the Coats-Redfern method was used to determine the kinetic parameters and the possible reaction mechanism of the thermal degradation of ultra-high molecular mass polyethene and its composites with fiber monocrystals in static air at three different heating rates − 6, 10 and 16 K min−1. The analysis of the results obtained showed that the thermal degradation process of pure ultra-high molecular mass polyethene corresponded to a diffusion controlled reaction (three-dimentional diffusion, mechanism D3), while its composites with fiber monocrystals degraded by two concurrent mechanisms (diffusion one D3 and A1,F1 mechanism). The fiber monocrystals used increased the thermal stability of the composite materials obtained. The values of the activation energy, frequency factor, the changes of entropy, enthalpy and Gibbs energy for the active complex of the composites were calculated.

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A simple procedure to obtain the derivative of the temperature integral with respect to the activation energy is presented.

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Abstract  

The free-radical bulk polymerization of 2,2-dinitro-1-butyl-acrylate (DNBA) in the presence of 2,2′-azobisisobutyronitrile (AIBN) as the initiator was investigated by DSC in the non-isothermal mode. Kissinger and Ozawa methods were applied to determine the activation energy (E a) and the reaction order of free-radical polymerization. The results showed that the temperature of exothermic polymerization peaks increased with increasing the heating rate. The reaction order of non-isothermal polymerization of DNBA in the presence of AIBN is approximately 1. The average activation energy (92.91±1.88 kJ mol −1) obtained was smaller slightly than the value of E a=96.82 kJ mol−1 found with the Barrett method.

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A near-linear representation of the linear heating rate is presented which converts the exponential integral into an integrable form and allows a simple determination of the activation energy to high accuracy.

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A simple and satisfactorily accurate solution of the exponential integral in the nonisothermal kinetic equation for linear heating is proposed:
\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} $$\mathop \smallint \limits_0^T e^{ - E/RT} dT = \frac{{RT^2 }}{{E + 2RT}}e^{ - E/RT}$$ \end{document}
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