What is the chemistry of rubber cure or rubber vulcanization?

The chemistry of rubber cure or rubber vulcanization is complex. There are several rubber vulcanization systems possible based on reactions with different chemicals. The selection of an accelerator will depend on the specific vulcanizing system.

What vulcanizing agent is used in rubber?

Elemental sulfur is the predominant vulcanizing agent for general-purpose rubbers. It is used in combination with one or more accelerators and an activator system comprising zinc oxide and a fatty acid (normally stearic acid). The most popular accelerators are delayed-action sulfenamides, thiazoles, thiuram sulfides, dithocarbamates and guanidines.

How does rubber vulcanization occur?

Natural rubber and many synthetic rubbers, contain unsaturated molecules (i.e., molecules that contain double bonds providing sites for the vulcanization or crosslinking reaction). It is through these double bonds that vulcanization occurs. The most common curing systems for rubber vulcanization are based on sulfur.

Why are accelerators used in vulcanizing elastomers?

Accelerators are added in small amounts to speed up the curing of adhesives by reducing the cure time and temperature of elastomers, particularly latex systems. The selection of an accelerator will depend on the specific vulcanizing system and curing properties.

Which elastomers can be vulcanized?

Certain elastomers such as chloroprene can be vulcanized by the action of metal oxides such as zinc oxide as well as sulfur. As a result, several of the same accelerators that are used with sulfur vulcanization systems can be used with zinc oxide/neoprene systems. Because there are so many, accelerators are generally classified by chemical family.