A Review on Heat and Reversion Resistance Compounding

Abstract

When sulfur vulcanized natural rubber compounds are exposed to a thermal ageing environment significant change in physical properties and performance characteristics are observed. These changes are directly related to modifications of the original crosslink structure. Decomposition reactions tend to predominate and thus leading to reduction in crosslink density and physical properties as observed during extended cure and when using higher curing temperatures. The decrease in network density is common when vulcanizates are subject to an anaerobic ageing process. However, in the presence of oxygen, the network density is increased with the main chain modifications playing a vital role.

Over the years the rubber industry has developed several compounding approaches to address the changes in crosslink structure during thermal ageing. This paper gives a review of these compounding approaches. As with many formulation changes in rubber compounding, there is a compromise that must be made when attempting to improve one performance characteristic. For example, improving the thermal stability of vulcanized natural rubber compounds by reducing the sulfur content of the crosslink through the use of the more efficient vulcanization systems will reduce dynamic performance property such as fatigue resistance. The challenge is to define a way to improve thermal stability while maintaining dynamic performance characteristics.