Kinetic study on the thermal degradation of polypropylene and polyethylene

In this work, a kinetic study on the thermal degradation of polyethylene and polypropylene is presented. The thermal degradation of these polymers is investigated under isothermal conditions using a gradient free reactor with on-line mass spectrometry. Apparent kinetic parameters for the overall degradation are determined. In the case of polyethylene degradation, a change of the apparent reaction order with temperature is observed, whereas in the case of polypropylene degradation, a constant apparent order of reaction within the investigated temperature range was found. Fractional pyrolysis under dynamic conditions of polypropylene performed at temperatures below the isothermal measurements reveal a decreasing amount of alkenes and alkanes and an increasing amount of dienes with temperature. On the basis of these data and corresponding literature, a detailed discussion of the reaction mechanisms is possible. Rate equations are formulated and kinetic models for polyethylene and polypropylene degradation are discussed, which are consistent with the measured rate coefficients. (C) 1999 Elsevier Science B.V. All rights reserved.