Cure Terms Glossary

Activator

Strictly speaking an activator is something which renders something active - without it, the system would be inactive. In a cure, the term might be applied to the curative itself, but this is not normally the case. However it is applied to a substance which can make a substrate active towards a cure in a contacting medium. Thus, in adhesive terminology, an activator is a formulation for treating the surface(s) to be bonded and so render the surface active in respect of the adhesive cure. For example, treating the surface with a redox metal will render it active towards a cure which uses peroxide or hydroperoxide initiation. The action is analogous to that of an accelerator in unsaturated polyester resin technology.

In the case of rubber vulcanisation, the role of an activator is quite different. Here the term is applied to additives which are used to develop the full potential of the accelerators in sulphur vulcanisation. The specific agent is zinc (as Zn2+) which has a special affinity for sulphur. Zinc ions can promote sulphur exchange and are catalysts for desulphurisation. Crosslink shortening (reduction in sulphur rank) can result from this action, and more stable networks may result. To avoid scorch, zinc is not necessarily added in soluble form - a common activator combination is zinc oxide with stearic acid.