5 - Kinetics of thermal degradation

Abstract

Studies on the mechanism of the thermal degradation of polymers and polymeric materials shall include an inherent part dedicated to the kinetic analysis. Results of numerous studies in the area of kinetic investigations lead to the conclusion that the actual mechanism of a thermal process, including the true values of the kinetic triplet [the activation energy Ea, the preexponential factor A, and the model function f(α)] cannot be determined properly from the kinetic analysis of a single thermogravimetric trace. Recommended procedures include the complimentary use of an isoconversional method to determine the activation energy value at no less than three different temperature programs, and the linear or nonlinear model-fitting to fit the kinetic model to the experimental data by solving a set of (differential) equations describing the kinetic models and their combinations. The calculated kinetic parameters of the thermal degradation process provide useful information for the optimization of the successive treatment of the polymer materials to avoid or at least limit thermal degradation, and they help to develop efficient recycling routes for growing amounts of postconsumer plastic wastes. Importantly, kinetic parameters may be utilized to predict the course of thermally activated polymer decomposition processes in extrapolated time, temperature, and conversion range, and to provide reliable service life predictions.