KINETICS OF THE LOW-TEMPERATURE PYROLYSIS OF POLYETHENE, POLYPROPENE,AND POLYSTYRENE MODELING, EXPERIMENTAL-DETERMINATION, AND COMPARISON WITH LITERATURE MODELS AND DATA

The pyrolysis kinetics of low-density polyethylene, high-density polye thylene, polypropylene, and polystyrene has been studied at temperatur es below 450 degrees C. In addition, a literature review on the low-te mperature pyrolysis of these polymers has been conducted and has revea led that the scatter in the reported kinetic data is significant, whic h is most probably due to the use of simple first-order kinetic models to interpret the experimental data. This model type is only applicabl e in a small conversion range, but was used by many authors over a muc h wider conversion range. In this investigation the pyrolysis kinetics of the forementioned polymers and a mixture of polymers has been stud ied at temperatures below 450 degrees C by performing isothermal therm ogravimetric analysis (TGA) experiments. The TGA experimental data was used to determine the kinetic parameters on the basis of a simple fir st-order model for high conversions (70-90%) and a model developed in the present study, termed the random chain dissociation (RCD) model, f or the entire conversion range. The influence of important parameters, such as molecular weight, extent of branching and beta-scission on th e pyrolysis kinetics was studied with the RCD model. This model was al so used to calculate the primary product spectrum of the pyrolysis pro cess. The effect of the extent of branching and the initial molecular weight on the pyrolysis process was also studied experimentally. The e ffect of the extent of branching was found to be quite significant, bu t the effect of the initial molecular weight was minor. These results were found to agree quite well with the predictions obtained from the RCD model. Finally, the behavior of mixtures of the aforementioned pol ymers was studied and it was found that the pyrolysis kinetics of the polymers in the mixture remains unaltered in comparison with the pyrol ysis kinetics of the pure polymers.