Any solid (see States Of Matter) substance, usually elastic, that can be vulcanized to improve its elasticity
and add strength; the term includes natural rubber, or caoutchouc, and a wide
variety of synthetic rubbers, which have similar properties. Rubbers are
composed chiefly of Carbon and Hydrogen, but some synthetics also have other elements, e.g., Chlorine, fluorine, Nitrogen, or Silicon. All are compounds of high Molecular Weight; each consists of a series of one kind of Molecule (e.g., isoprene in natural rubber) hooked together in a long chain to form a
very flexible, larger molecule, the Polymer. Natural rubber is obtained as latex, a milky suspension of rubber globules
found in a large variety of plants, chiefly tropical and subtropical. An
important source is the PARÁ rubber tree. Latex can be shipped for processing either
as a liquid or coagulated by acid (see Acids And Bases) and rolled into sheets. For most purposes rubber is ground, dissolved in a
solvent, and compounded with other ingredients, e.g., fillers, pigments, and Plasticizers. Known in pre-Columbian Times by the indigenous peoples of South and Central America, rubber first
attracted interest in Europe in the 18th century. Vulcanization, a process invented
(1839) by Charles Goodyear, revolutionized the rubber industry. It usually
involves heating raw or compounded rubber with sulfur, causing sulfur bridges to form
between molecules. The product is nonsticky, elastic, and resistant to heat
and cold. Natural rubber is used chiefly to make tires and inner tubes because it
is cheaper than synthetic rubber and has greater resistance to tearing when
hot. Natural rubber can be treated to make foam rubber and sponge rubber. The
first synthetic rubber was made in Germany in World War I. Today synthetics, e.g.,
Buna S, neoprene, butyl, and nitrile, account for most of the world's rubber
production. Made from Coal, Petroleum, Natural Gas, and Acetylene, synthetic rubbers are resilient over a wider Temperature range than natural rubber and are more resistant to aging, weathering, and
attack by certain substances, notably, Oil, solvents, Oxygen, and Ozone. Silicone rubbers are used in insulation. Polyurethanes are used in tires, in shoes,
and as foams. Neoprene is used for making hose and tank linings. Butyl rubber is
used in inner tubes and as insulation.