Monday, December 17, 2012
A brief history of rubber
Rubber comes in two types: natural, which comes directly from tropical plants and synthetic, which is man-made from petroleum and natural gas. Because of its strength, along with its elasticity and resilience, rubber is the basic component in tires. In fact, more than half of all rubber produced worldwide is used to make automobile tires. The rest is used for a wide variety of products including rubber flooring.
Natural rubber exists in the inner bark of many tropical and subtropical trees and shrubs. However, Hevea brasilienes, a tall tree indigenous to Brazil is, by far, the plant that is tapped the most frequently for its natural rubber. The basic component of rubber, is harvested in a similar fashion to the harvesting of tree sap. The tree bark is slashed and the plant secretes an elastic, liquid substance that is the basic component of rubber. Although scientists aren’t entirely sure why the substance is secreted, most conclude that it is a type of self-healing salve.
Discovered centuries ago, rubber was described scientifically for the first time in 1735 by Francois Fresneau of France who was following an expedition to South America. It was later called “rubber” by an English chemist who discovered that it could be used to rub out pencil marks. It came into its wide ranging commercial success years later, in 1839, when the vulcanization process was invented by Charles Goodyear. By 1900 more than 40,000 tons of rubber were used each year with about one-half coming from Brazil and the other half from Central Africa, where rubber was obtained principally from Landolphia vines. However, as an important industrial material, rubber was required in larger amounts than could easily be obtained from the wild and widely dispersed trees in the Brazilian jungle or from African vines. They produced only about one kilogram per hectare and had to be destroyed to obtain the rubber. In 1876, seeds of the Hevea brasiliensis tree from the upper Orinoco basin were taken from Brazil to England at the instigation of the British India Office. Seedlings were raised at Kew Gardens and shipped to Ceylon (Sri Lanka) and Singapore. These trees were the origin of the rubber plantation industry in Asia which now produces more than 90 percent of the world’s supply.
The demand for natural rubber continues to be high due to its resistance to heat buildup. This makes it valuable for racing car tires, trucks, buses, and airplanes. However, of all the rubber produced commercially, natural rubber constitutes less than half. The rest is synthetic.
The origins of the elastomers that make up the base of synthetic rubber can be traced to the first half of the 19th century when several scientists tried to replicate natural rubber. By 1940 the Soviet Union had the largest synthetic rubber industry in the world, producing more than 50,000 tons per year. Because synthetic rubber can be made from petroleum, grain alcohol, or coal, it was in great demand during World War II. Immense amounts were made—as much as 100,000 tons per year in Germany and the Soviet Union. About 800,000 tons were produced per year in the United States.
After World War II, increasing sophistication in synthetic chemistry led to many new polymers and elastomers. Several advances characterized the postwar years. Over the centuries a wide variety of substances has been mixed with rubber to strengthen it. Rubber can be plasticized to be more rigid or mixed with other agents to make it more pliable. Certain additives provide resistance to heat, sunlight, oxygen, and ozone. Paraffin wax forms a protective coating that helps to protect the rubber from staining.
World consumption of synthetic rubber reached nine million tons in 1993. Today, about 55 percent of all synthetic rubber produced is used in automobile tires.