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Kinetics of the Thermal and Thermo‐Oxidative Degradation of Polystyrene, Polyethylene and Poly(propylene)

Full Paper: The thermal degradations of polystyrene (PS), polyethylene (PE), and poly(propylene) (PP) have been studied in both inert nitrogen and air atmospheres by using thermogravimetry and differential scanning calorimetry. The model-free isoconversional method has been employed to calculate activation energies as a function of the extent of degradation. The obtained dependencies are interpreted in terms of degradation mechanisms. Under nitrogen, the thermal degradation of polymers follows a random scission pathway that has an activation energy L200 kJ N mol ‐1 for PS and 240 and 250 kJ N mol ‐1 for PE and PP, respectively. Lower values (L150 kJ N mol ‐1 ) are observed for the initial stages of the thermal degradation of PE and PS; this suggests that degradation is initiated at weak links. In air, the thermoxidative degradation occurs via a pathway that involves decomposition of polymer peroxide and exhibits an activation energy of 125 kJ N mol ‐1 for PS and 80 and 90 kJ N mol ‐1 , for PE and PP respectively.