The thermal degradation kinetics of polypropylene .3. Thermogravimetric analyses

Thermogravimetric data were obtained for the pyrolysis of polypropylene, and several previously published interpretation methods were applied to the data. However, the wide temperature range used in this work (45-580 degrees C) encompassed a change in the decomposition mechanism and this greatly limited the utility of the methods. To accommodate this mechanism change, the data were treated as a pseudo first-order reaction. It was observed that the data conformed to a first-order fit at temperatures of less than 404 to 421 degrees C (depending upon heating rate) with an activation energy of 98.3+/-3.1 kJ/mol. At higher temperatures the data could again be fit as a pseudo first-order reaction, but with an activation energy of 327.9+/-8.6 kJ/mol. The two regions were separated by a relatively narrow transition region. The lower activation energy occurring at lower degradation temperatures is attributed to scission of 'weak links' in the polymer. The higher activation energy was similar to the carbon-carbon bond dissociation energy and is associated with random scission throughout the polymer. (C) 1997 Published by Elsevier Science Limited.