Sulphur vulcanization is a chemical process for converting natural rubber or related polymers into materials of a variety of hardness, elasticity, and mechanical durability by heating them with sulphur or other equivalent curatives or accelerators. Sulphur forms cross-linking bridges between sections of polymer chains which affects the mechanical and electronic properties. Many products are made with vulcanized rubber, including tires, shoe soles, hoses, and conveyor belts. The term vulcanization is derived from Vulcan, the Roman god of fire.
The main polymers subjected to sulphur vulcanization are polyisoprene (natural rubber, NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR), all of which are rich in unsaturated bonds. Several other speciality rubbers may also be vulcanized, such as nitrile rubber (NBR), butyl rubber (IIR) and EPDM rubber. Vulcanization, in common with the curing of other thermosetting polymers, is generally irreversible. However, significant efforts have focused on developing 'de-vulcanization' processes for recycling of rubber waste.