Vulcanization

Vulcanization is the process of cross-linking elastomer molecules to make the bulk material harder, less soluble and more durable. It is also called curing. It is the heart of the art and science of rubber compounding.

Vulcanization is a chemical process in which individual polymer molecules are linked to other polymer molecules by atomic bridges. The end result is that the springy rubber molecules become locked together to a greater or lesser extent. This makes the bulk material harder, much more durable and also more resistant to chemical attack. It also transforms the surface of the material from a sticky feel to a smooth, soft surface which does not adhere to metal or plastic substrates.

Vulcanization is an irreversible process, like baking a cake, and must be contrasted strongly with thermoplastic processes (the melt-freeze cycle) which characterize the behavior of the vast majority of modern polymers. This irreversible cure reaction defines cured rubber compounds as thermoset materials, which do not melt on heating, and places them outside the class of thermoplastic materials (like polyethylene and polypropylene).