1839

Rubber

Thomas Hancock (1786–1865), Charles Goodyear (1800–1860)

Rubber, a well-known example of a natural polymer, is built from molecules of isoprene, a five-carbon compound found in a variety of plants that is believed to protect them from heat stress. When isoprene is polymerized, the first product created is the sticky latex sap given off by plants such as the South American rubber tree.

This sap can be processed further to natural rubber—as it has been for hundreds of years in Central and South America—but natural rubber has a lot of limitations, among them its relentless stickiness in hot weather and its propensity to crack in the cold. Many inventors tinkered with it, trying to turn it into something more useful, and after many impoverished years of experimentation, American chemist Charles Goodyear famously succeeded. With the addition of sulfur and heat, he discovered, whether by accident or by design (one version has him sticking a lump of rubber to a hot stove), the rubber was cured into an elastic, durable, nonsticky substance that looked as if it would have huge potential, if it could be made industrially. More years of experimentation followed, with Goodyear stretching the patience of his family and his creditors. By 1844 he had filed for a patent for what would come to be known as the vulcanization (after the Roman god of fire) of rubber and had built a factory to produce goods made from it. There were still many wild swings in his fortunes as he fought patent disputes in Europe, most notably with English manufacturing engineer Thomas Hancock, who was simultaneously experimenting with rubber and had received a British patent for the same process.

Chemically, the sulfur in vulcanized rubber crosslinks the polymer chains, altering the properties of the material by changing the ways that the molecules can move relative to each other. Serendipitous or not, the vulcanization of rubber was a significant industrial and commercial advance, and today is responsible for consumer goods as varied as tires, hoses, shoe soles, and hockey pucks, as well as many parts of the industrial machinery involved in making them.

Rubber-tree sap, harvested the old-fashioned way.