The word elastomer is the combination of two nouns: “elastic” and “polymer” and describes a solid material whose main property is elasticity.
In other words we can assert that an “elastic” material, when undergoes to a considerable deformation under tensile stress, returns to its original shape once the added force is removed.
Whereas metals are made of single chemical units (molecule) formed by atoms that are strictly connected and bonded to each other by electromagnetic forces, a polymer is made of molecules set by a continuing basic structure (monomer) that generates long molecules chains where the attraction force among the chains themselves is quite low.
Although vulcanization chemical process differs according to the different elastomer types and classifications, the basic mechanism stays the same. Usually the rubber industry classification of the different type of elastomers refers to the Norm ISO 1629 derived from the Norm ASTM D 1418-79.
The group to which each polymer belongs to is identified by the last letter of the identification code; the rest of the same code uniquely identifies the elastomer type.
The elastomers belonging to the group
“M” contain polymer chains saturated with polyethylene.
“O” contain oxygen atoms.
“Q” contain oxygen and silicon atoms.
“R” contain unsaturated carbon.
“U” contain carbon, oxygen and nitrogen.
To be able to reach elasticity and thermal stability contiguous-polymer- molecular-chains require stable chemical bonds keeping the electromagnetic forces really low.
These three-dimensional bonds among polymer chains are obtained heating the material while using active chemical elements. This process is commonly defined as “vulcanization”, or technically, “reticulation”.
Here’s why, when a vulcanized elastomer gets deformed, the molecular chains, wound up as a spiral, get stretched, but the inter-molecular bridges allow the material to basically get back to its original shape once the force that caused the deformation gets interrupted.