Source Year: 2000

A fundamental kinetic model is developed for the sulphur vulcanisation of NR with a 2-4-morpholinothio-benzothiazole sulphenamide (MBS) accelerator. The model is developed using population balance methods that explicitly acknowledge the polysulphidic nature of the crosslinks and various reactive intermediates. This approach allows for a more faithful incorporation of the underlying molecular mechanisms that control the vulcanisation process. For the MBS vulcanisation system a total of nine rate constants is required: two to describe the formation of the sulphur-accelerator intermediate, four to describe the primary cure reaction including scorch delay, two to describe the regeneration and degradation of the accelerator, and one final constant to describe the long-term reversion of the crosslinks. The rate constants can be efficiently and robustly determined from isothermal oscillating disk rheometer cure data at three different sulphur/accelerator concentrations. The kinetic model can quantitatively predict the complete cure response including induction, curigng and the reversion for a complete range of compositions; moreover, the population balance model can be readily extended to also include the retarder chemistry. The model not only predicts the evolution of the crosslink density, but also the concentration of all the intermediates of different polysulphidic lengths- important information that is difficult to measure experimentally. The level and detail of information obtained from the model can be used effectively to understand the cure and post-cure behaviour of an accelerated vulcanisation system and to determine the optimal amounts of accelerator. Sulphur activator and other ingredients needed to design the formulation for a particular engineering application.