Kinetic modeling of an oxidation mechanism

This dossier describes the kinetic modeling of polymer oxidation in different scenarios: initiation by unimolecular or bimolecular decomposition of hydroperoxides, or extrinsic initiation at constant speed, covering a very wide range of practical cases.

We show that by considering restricted domains of variation in oxygen concentration, analytical solutions to the kinetic scheme can be found. Characteristic of these solutions is that the concentrations of the reactive species are always expressed as a power law of the O ₂ concentration. The velocities of the elementary processes are therefore also expressed as a power law of C. In the case of extrinsic initiation, the velocities can also be expressed as a power law of the initiation velocity r _i .

We have determined the values of the exponents of these power laws:

where C is the oxygen concentration and r the rate of an elementary reaction.

By comparing experimental values of m and/or n with theoretical values, practitioners should be able to identify interesting ageing mechanisms.