Kinetic modelling of the thermal oxidation of polyisoprene elastomers. Part 3: Oxidation induced changes of elastic properties

This paper is the third of a series elaborating a non-empirical kinetic model for the thermal oxidation of a sulfur vulcanized polyisoprene. Here, we try to identify kinetic parameters for post-crosslinking and reversion (“decrosslinking”) from torsion measurements, under nitrogen at temperatures ranging from 100 to 160 °C. The kinetic parameters relative to oxidative reversion (selective scissions on sulfur crosslinks) are also determined. Then a system of 13 differential equations is derived from the mechanistic scheme composed of 15 elementary reactions. Diffusion and reactions are coupled in the balance equation of oxygen in order to establish the degradation thickness profiles from which it is possible to determine the modulus profiles. The latter are used, through a composite mechanics model, to predict the global torsion stiffness of a rubber barrel. The results obtained at 100, 110, 130, 140, 150 and 160 °C are in good agreement with experimental data.