Early electrical experimenters risked spine-tingling success or life-threatening failure while perfecting direct current generators and alternating current transmission lines. The concept of insulators eventually made public consumption of electricity safe and reliable. Non-metal materials such as rubber were among the first insulators, used for plugs, wire covers, transmission tower arms and switch parts.
Rubber comes from the dense sap of the Hevea brasiliensis tree. The tree, originally native to the Amazon rainforest, was imported to the rainforests of Southeast Asia, where it became a major crop. Although natural rubber insulates well, heat softens it and cold makes it stiff or brittle. An American, Charles Goodyear, discovered a process called Vulcanization, which combined raw rubber, sulfur and heat that stabilized rubber over a wide range of temperatures.
During the latter part of the 19th century and first quarter of the 20th century, rubber provided great fortunes for planters who supplied tire makers and the growing number of uses for electricity. Rubber provided insulation for early electric railways, some of which are still operating in American cities such as Chicago and New York at the time of publication. Rubber was widely used to insulate wires and appliances produced at the turn of the century by inventor Thomas Edison and alternating current developer Nicholas Tesla. The rubber glove, patented in 1933, protected experimenters and workers.
The supply of the material contracted severely with the Japanese expansion into Southeast Asia and the Pacific during World War II. Because rubber was so important to communications and transportation, however, research into synthetic rubber produced a variety of materials for use in appliances, communication and transportation. A variety of petroleum-based synthetics, including neoprene, silicone and others, also insulate against heat and cold. The dominance of synthetic elastomer rubber was finally broken by the oil crisis in the early 1970s, and by the 1990s, natural rubber had recaptured nearly 40 percent of the market.
By the end of the 20th century, nearly 85 percent of the world’s natural rubber was again being produced in Southeast Asia. Rubber and its elastomers are used as insulators in appliances, wiring and protective clothing, including gloves and boots for those who work with electricity. Black rubber also is wound around connections and wires as adhesive-backed tape. Rubber feet insulate ladder bases and rubber blankets cover wires for crews who are repairing storm-ravaged power lines. Although elastomers provide a non-allergenic alternative to those sensitive to latex, rubber remains the superior insulator for many applications.
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