VULCANIZATION OF RUBBER

• The process was carried out first by Goodyear in 1839 using sulphur for effecting cross-linking of poly-isoprene molecules of natural rubber.
• Vulcanization process is important to improve the properties of crude or raw rubber; it is compounded with some chemicals like sulphur, hydrogen sulphide, benzoyl chloride, etc. It is a process of cross-linking the rubber molecules using a vulcanizing agent.
• The process consists of heating the crude rubber with sulphur to a high temperature. The sulphur combines chemically at the double bonds in the rubber molecule of different rubber springs.
• Vulcanization brings about a stiffening of the rubber by a sort of cross-linked & consequently preventing intermolecular movement or sliding of rubber springs. The extent of stiffness or loss of elasticity of vulcanized rubber depends on the amount of sulphur added.
• Addition of 0.5 to 5% sulphur gives soft & elastic rubber where as vulcanite or ebonite (hard rubber) contains 52% sulphur.
• Thus vulcanite is tough, has abrasion resistance, can be sawn, drilled & polished. It has extremely good electrical insulation properties.