Authors:N. Sbirrazzuoli, L. Vincent, J. Bouillard, and L. Elégant
In the case of a complex mechanism of two parallel independent reactions, peak maximum evolution methods and model-fitting
methods give only a mean value of the kinetic parameters, while isoconversional methods are useful to describe the complexity
of the mechanism. Isothermal and non-isothermal isoconversional methods can be used to elucidate the kinetics of the process.
Nevertheless, isothermal isoconversional methods can be limited by restrictions on the temperature regions experimentally
available because of duration times or detection limits.
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
Authors:S. Du, G. Zhang, H. Li, P. Wang, and X. Wang
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 (Ea) 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 Ea=96.82 kJ mol−1 found with the Barrett method.
Authors:J.-J. Zhang, R.-F. Wang, J.-B. Li, H.-M. Liu, and H.-F. Yang
The thermal decomposition of Eu2(BA)6(bipy)2 (BA=C2H5N–2, benzoate; bipy=C10H8N2, 2,2'-bipyridine)and its kinetics were studied under the non-isothermal condition by TG-DTG, IR and SEM methods. The kinetic
parameters were obtained from analysis of the TG-DTG curves by the Achar method, the Madhusudanan-Krishnan-Ninan (MKN) method,
the Ozawa method and the Kissinger method. The most probable mechanism function was suggested by comparing the kinetic parameters.
The kinetic equation for the first stage can be expressed as: dα/dt=Aexp(–E/RT)3(1–α)2/3.
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.