Vulcanisation

Vulcanisation is a chemical process that converts natural or synthetic rubber into a more durable, elastic material by creating cross-links between polymer chains, typically through sulfur or other vulcanizing agents, under heat and pressure. The process increases the rubber’s resilience, heat resistance, and strength, while reducing tack and deformation under repeated use. Traditional vulcanisation usually occurs at temperatures around 140–180°C.

In the conventional method, small amounts of sulfur are mixed with rubber along with accelerators and fillers, and the mixture is heated. The sulfur forms cross-links, primarily sulfur bridges, between long polymer chains (such as polyisoprene in natural rubber). The extent of cross-linking, or cross-link density, governs the final properties: more cross-links yield a stiffer, hotter-resistant material with higher tensile strength but reduced elongation.

The history of vulcanisation dates to the 19th century. Charles Goodyear, who in 1839 discovered that heating rubber with sulfur produced a more durable material, is credited with its practical development; Thomas Hancock independently refined the process in Britain. The term vulcanisation derives from Vulcan, the Roman god of fire, reflecting the heat-driven chemical change.

Variants and related techniques include accelerated sulfur vulcanisation, which uses accelerators to lower processing temperature and time, and peroxide vulcanisation, which forms carbon–carbon cross-links instead of sulfur bridges. Vulcanisation is largely irreversible, meaning vulcanised rubber cannot be remelted and reprocessed by simple heating.

Applications are broad but dominated by tires and inner tubes; vulcanised rubber is also used in belts, hoses, seals, gaskets, footwear, and various molded or extruded components. Advances continue in lightweight, heat-resistant, and chemically resistant formulations for specialized needs.