Kinetic study on the thermal degradation of polypropylene and polyethylene

Abstract

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.