Rubber before the fix
Natural rubber is the latex of certain tropical trees, above all Hevea brasiliensis, which grows in the Amazon basin. Mesoamerican peoples used it centuries before Europeans arrived, for balls and for waterproofing, and they are known to have processed it with plant juices to change its properties. European interest grew in the 1700s and 1800s, when it was found to rub out pencil marks (hence the name rubber) and to waterproof cloth.
The material had a severe flaw. Raw rubber turned sticky and soft in summer heat and stiff and brittle in cold. In the 1820s and 1830s, several companies in the United States and Europe made rubber shoes, coats and other goods, and many were returned as they melted or cracked. Some firms went bankrupt in the downturn of the late 1830s. Charles Macintosh’s waterproof fabric of the 1820s, made with rubber between layers of cloth, was a partial answer, but it still had the same weaknesses.
What vulcanization does
Vulcanization is the process of heating rubber with sulfur. The effect is chemical: sulfur forms bridges, called cross-links, between the long polymer chains that make up rubber. In raw rubber, the chains can slide past one another, so the material flows when warm. After cross-linking, the chains are tied together enough that the material springs back after stretching, stays firm in heat and does not become as brittle in cold.
Nobody understood this at the time. The idea that rubber consists of very long molecules was only worked out in the twentieth century, and it was only then that cross-linking was explained. The inventors worked by trial, observing what happened under heat.
Charles Goodyear’s trials
Charles Goodyear was an American hardware merchant who became fascinated with rubber after seeing the failures of the 1830s. He spent years experimenting, often in poverty and in debt. He found that treating rubber with sulfur gave better results, and by his own account he found the key step, heating the sulfur-rubber mixture, around 1839. A well-known story says a piece of rubber and sulfur fell onto a hot stove by accident and charred without melting. Goodyear told versions of this later, and historians doubt it was so sudden. It is better to think of a long series of experiments, some of them accidents.
He received a US patent in 1844, and his invention was soon applied to shoes, belts, hoses and gaskets.
Thomas Hancock and the English side
In England, Thomas Hancock, a coachmaker and manufacturer who had worked with rubber for years, patented a vulcanization process in 1843. Hancock said he developed it after examining samples of Goodyear’s treated rubber that were brought to England, and Goodyear’s supporters argued that Hancock copied him. Hancock claimed he reached the result independently by working out how the samples had been made. Priority was disputed at the time and remains unsettled, because the order of events is hard to reconstruct from the evidence we have.
The word vulcanization is associated with Hancock’s circle. William Brockedon, a friend of Hancock, is credited with suggesting the name, after Vulcan, the Roman god of fire. Another entrepreneur, Nathaniel Hayward, had earlier found a sulfur treatment for rubber and sold his rights to Goodyear, complicating who owned what.
Patents and lawsuits
Goodyear’s patent was widely infringed. Rubber manufacturers made vulcanized goods without paying fees, and Goodyear spent heavily on lawsuits. The best-known case, Goodyear v. Day (1852), was argued for Goodyear by the statesman Daniel Webster, and the court upheld the patent. Even so, Goodyear remained deeply in debt for much of his life, because licensing income did not keep pace with legal costs. He died in 1860. The Goodyear tire company founded decades later took his name but had no direct connection to him.
The story is often used as an example of how inventors may be right about a technical step and still not profit from it, though the legal and business details are complicated.
From a patent to a necessity
Vulcanized rubber became an industrial material quickly. It was used for hoses, belts, packing and seals in machinery, which mattered for steam engines and for factories generally. Rubber was used for insulating telegraph and electrical wires and in waterproof clothing and footwear. Later in the century, the pneumatic tires revived by John Boyd Dunlop in 1888 gave bicycles a smoother ride, and the rubber demand grew dramatically with the arrival of motor cars. Surgical gloves and tubing for medical use also relied on vulcanized rubber.
Supply and later chemistry
Demand turned rubber into a major commodity. In 1876, Henry Wickham collected Hevea seeds in Brazil and sent them to Kew Gardens in England, from which seedlings were shipped to British territories in Asia. Plantations in Southeast Asia eventually supplied most of the world’s rubber, replacing wild collection in the Amazon. This was a major shift in labor and trade, and the wild rubber era had a record of severe abuses in places such as the Congo and parts of the Amazon.
In the early twentieth century, chemists found additives called accelerators that made vulcanization faster and used less sulfur, and carbon black was found to strengthen tire rubber. Synthetic rubbers were developed in the 1900s, particularly under wartime shortages, and many are still cured with sulfur or other cross-linking agents.