Vulcanization

Vulcanization is a chemical process that transforms raw rubber or related polymers into a more durable material by creating cross‑links between individual polymer chains. The term originates from the mythological god of fire, Vulcan, reflecting the heat‑based nature of the reaction. In practice, natural rubber or synthetic elastomers are mixed with sulfur, accelerators, and sometimes additional agents such as zinc oxide, then heated to temperatures typically between 140 °C and 180 °C. Sulfur atoms form covalent bridges between carbon atoms on adjacent polymer chains, increasing tensile strength, elasticity, abrasion resistance, and resistance to solvents and temperature variations.

The process was pioneered in the 1830s by Charles Goodyear, who discovered that heating rubber with sulfur prevented it from becoming sticky in heat and brittle in cold. Early commercial vulcanization used long heating periods and high sulfur concentrations; modern methods employ precise formulations of accelerators that reduce cure time and allow fine control of mechanical properties. Different vulcanization systems—such as full cure, semi‑cure, and cold cure—are selected according to the intended application, ranging from tires and hoses to conveyor belts and medical devices.

Vulcanization can be performed using batch ovens, continuous rollers, or extruders, and may involve additional steps like molding or compression. Over‑cure can degrade material performance, while under‑cure leaves insufficient cross‑linking. Analytical techniques such as rheometry, differential scanning calorimetry, and spectroscopy are used to monitor cure progression. The technology remains central to the rubber industry, enabling the production of components that combine flexibility with robust mechanical stability.