ELASTOMER (NATURAL AND SYNTHETIC RUBBER)

any rubbery material composed of long, chainlike molecules that are capable of recovering their original shape after being stretched to great extents. Under normal conditions the long molecules making up an elastomeric material are irregularly coiled. With the application of force, however, the molecules straighten out in the direction in which they are being pulled. Upon release, the molecules spontaneously return to their normal compact, random arrangement. The elastomer (from elastic polymer) with the longest history of use is natural rubber, which is made from the milky latex of various trees, most usually the Hevea rubber tree. Natural rubber is still an important industrial polymer, but it now competes with a number of synthetic elastomers, such as styrene-butadiene rubber and polybutadiene, which are derived from by-products of petroleum and natural gas. More than half of all rubber produced goes into automobile tires; the rest goes into mechanical parts such as mountings, gaskets, belts, and hoses, as well as consumer products such as shoes, clothing, furniture, and toys. Outline of Coverage This article reviews the composition, structure, and properties of both natural and synthetic rubbers and then describes their production and processing into useful products. For a fuller understanding of the materials from which elastomers are made, the reader is advised to begin with the article industrial polymers, chemistry of. For an overview of the position of elastomers within the broader field of industrial polymers, see Industrial Polymers: Outline of Coverage.