The process of curing natural rubber with sulpur, heat and pressure in a one way reaction to form a thermosetting material.
Vulcanization or vulcanisation refers to a specific curing process of rubber involving high heat and the addition of sulfur or other equivalent curatives. It is a chemical process in which polymer molecules are linked to other polymer molecules by atomic bridges composed of sulfur atoms or carbon to carbon bonds. The end result is that the springy rubber molecules become cross-linked to a greater or lesser extent. This makes the bulk material harder, much more durable and also more resistant to chemical attack. It also makes the surface of the material smoother and prevents it from sticking to metal or plastic chemical catalysts.
This heavily cross-linked polymer has strong covalent bonds, with strong forces between the chains, and is therefore an insoluble and infusible, thermosetting polymer. The vulcanization process is a progressive reaction and is therefore allowed for a specified time.
The process is named after Vulcan, Roman god of fire.
A vast array of products are made with vulcanized rubber including ice hockey pucks, tires, shoe soles, hoses and many more.
Hard vulcanized rubber is known as ebonite or vulcanite and is used to make bowling balls and clarinet mouth pieces.
Reason for vulcanizing
Uncured natural rubber is sticky, can easily deform when warm, and is brittle when cold. In this state it cannot be used to make articles with a good level of elasticity. The reason for inelastic deformation of unvulcanized rubber can be found in its chemical nature: rubber is made of long polymer chains. These polymer chains can move independently relative to each other, which results in a change of shape. By the process of vulcanization, crosslinks are formed between the polymer chains so the chains can no longer move independently. As a result, when stress is applied the vulcanized rubber will deform, but upon release of the stress, the rubber article will go back to its original shape.