Numerical model for the interpretation of sulfur vulcanization through the oscillating disk cure meter test.

Sulfur was the first agent used to vulcanize the first commercial elastomer, i.e. natural rubber (NR). At present, accelerated sulfur vulcanization is suitable not only for natural rubber (NR) and its synthetic counterpart (IR), but also for other synthetic rubbers such as polybutadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), butyl rubber (IIR) and ethylene-propylene-diene rubber (EPDM). Even though the sulfur vulcanization of natural rubber was discovered more than 150 years ago, its mechanism is still not completely understood. In fact, one of the fundamental issues to establish is whether the predominant reaction pathway is via ionic or free-radical intermediates or both and which is the influence of the number and variety of the ingredients used in the vulcanization recipe in terms of network properties. In this contribution, a numerical model useful to correlate reaction kinetic parameters and experimental oscillating disk cure meter (ASTM test D 2084) curves, fitted by means of a simple mathematical model, is presented. The numerical approach is applied to systems with marching behavior, plateau level and reversion. Combining the present mathematical model with all analytical data for single recipes, it is possible to estimate in advance the optimal vulcanization temperature of real items, also in relation with their dimensions.