vulcanize

Vulcanization is a chemical process by which polymer chains in rubber are cross-linked, typically with sulfur, to improve elasticity, strength, and heat resistance. The reaction occurs when rubber is heated with sulfur (and often accelerators and fillers), forming sulfide bonds between adjacent polymer chains. The resulting material is less tacky, more resilient, and more resistant to solvents and temperature changes, making it suitable for everyday rubber goods.

Vulcanization was discovered by Charles Goodyear in 1839 after years of experimenting with sulfur and heat. He demonstrated that natural rubber could be transformed from a sticky, undeveloped substance into a durable material. Goodyear's work led to improvements by Thomas Hancock in Britain and to the development of industrial vulcanization methods that allowed mass production of tires and rubber goods.

Typical formulations include natural or synthetic rubber mixed with sulfur and accelerators such as zinc oxide and various organic compounds, plus processing aids. The mixture is heated under pressure to cure, with cure times and temperatures usually in the range of 140–180 °C, depending on the compound and desired properties. Increasing cross-link density strengthens the material but can reduce elasticity at low temperatures; excessive heat can cause reversion, a loss of properties over time.

Vulcanization remains essential in the rubber industry, enabling tires, belts, seals, hoses, and footwear. While sulfur vulcanization is most common, alternative curing systems (e.g., peroxide vulcanization) are used for specialized rubbers, including heat- or chemical-resistant grades.