Different Approaches to the Kinetic Analysis of the Thermal Degradation of Polymeric Materials

Thermal stability of polymeric materials is their very important property since it determines the range of their processing and application. Due to the enormous number of polymeric materials and their applications, the possibility of making reliable kinetic predictions of their behaviour under different thermal conditions from the relatively small number of experiments can be very useful. These kinetic predictions can be made using kinetic parameters (the preexponential factor (A), the activation energy (E) and kinetic model f()) obtained from the kinetic analysis of the thermal degradation of polymers. Therefore, the correct and meaningful kinetic analysis which gives true kinetic parameters is very important from the practical point of view. In reality, thermal degradation of polymeric materials is a multistep process and for the correct kinetic analysis the number of steps and relationship between them (i.e. the reaction mechanism) should be firstly determined and followed by calculation of kinetic parameters. There are numerous graphical and computational methods for these actions. They are usually time consuming and are limited for kinetic analysis of multistep processes. Recently, a specially developed softwares for kinetic analysis are getting more used more. They are advantageous and fast in obtaining reliable kinetic parameters of both simple and multistep processes, especially in cases when degradation mechanism is known. However, if the degradation mechanism is completely unknown, what is often the case, the application of these specialized softwares can also be very demanding, time consuming and confusing for non-experienced users. The statistical analysis of these softwares gives advantage to the quality of fit rather than to the physical meaning of calculated kinetic models and it may happen that the mechanism that gives the best fit does not represent the real process at all. Also, the number of steps needed to obtain 'the best fit' can sometimes be very high. So, the idea to combine and compare these two approaches in order to obtain reliable kinetic parameters and establish reliable procedure is tested on a few examples and the results are presented.