Rubber

Rubber, elastic substance; that is, one which quickly restores itself to its original size after it has been stretched or compressed. Natural rubber is obtained from many plants, and commercially from Hevea brasiliensis, a tree native to South America and cultivated also in southeast Asia and West Africa. A slanting cut is made in the bark, and the milky fluid latex, occurring in the inner bark, is tapped off. The latex—an aqueous colloid of rubber and other particles—is coagulated with dilute acid, and the rubber creped or sheeted and smoked. Natural rubber is a chain polymer of isoprene, known as caoutchouc when pure; its elasticity is due to the chains being randomly coiled but tending to straighten when the rubber is stretched. Known to have been used by the Aztecs since the 6th century A.D., and first known in Europe in the 16th century, it was a mere curiosity until Goodyear invented the process of vulcanization. Synthetic rubbers have been produced since World War II. Some latex (natural or synthetic) is used as an adhesive and for making rubber coatings, rubber thread, and foam rubber. Most, however, is coagulated, and the rubber is treated by vulcanization and the addition of reinforcing and inert fillers and anti-oxidants, before being used in tires, shoes, rainwear, belts, hoses, insulation, and many other applications.