A continuous kinetic model of rubber vulcanization predicting induction and reversion

The kinetics of sulfur vulcanization of rubber presents two specific aspects: The main crosslinking reaction is preceded by an induction period during which the crosslink density increases very slowly (these two steps are generally described separately by existing kinetic models); and can be followed by reversion due to the thermal degradation of unstable polysulfide crosslinks formed during vulcanization. This phenomenon, which results in lower final mechanical properties for high curing temperatures, is studied here by combining classical isothermal kinetic experiments with high temperature post-cure experiments on rubber samples previously vulcanized at low temperature where reversion is negligible. The isoconversional analysis of experimental data is shown to allow the development of an efficient kinetic parameter estimation technique for an existing semi-mechanistic kinetic model describing reversion, and leads to the development of a new continuous kinetic model allowing the simulation of the whole kinetic process including the induction, main vulcanization and reversion steps.