Kinetic study of the thermal oxidation of polypropylene

Abstract

The thermal oxidation of non-stabilized isotactic polypropylene was studied in air at 80, 90, 100 and 150 °C using gravimetric and IR spectrophotometric determinations (hydroxyls and carbonyls). A kinetic model in which radical production results only from unimolecular hydroperoxide decomposition was developed. This model predicts that: • • the induction time depends only on the rate constant of hydroperoxide decomposition. It must be almost independent of the polypropylene source (for low content of catalytic impurities and low initial hydroperoxide concentration) and its apparent activation energy must be about 100 kJ mol −1; • • the induction times relative to, respectively, weight, carbonyl and hydroxyl gain must be in the ratio 2:3:3; • • ‘the steady state’ oxidation rate must be independent of initiation rate constant. The experimental data on oxidation kinetics in the temperature range under study confirm all these predictions.