Rubber (natural, vulcanized)
A natural hydrocarbon polymer formed from the latex of Euphorbiaceae trees, such as Hevea brasiliensis or Parthenium argentatum. To prepare natural rubber, the latex is collected from a cut in the bark, precipitated with acid, then washed and dried. Rubber is very elastic and was used for bowls, shoe soles, adhesives and bouncy balls. However, when cooled, rubber becomes brittle and when warmed it becomes sweaty and tacky. Prior to the development of synthetic resins, unvulcanized rubber was used for adhesive tapes and crepe shoe soles.
In 1839, Charles Goodyear discovered that rubber can be hardened with the vulcanization process in which sulfur is used to initiate crosslinking of the hydrocarbon strands. Higher sulfur content produces a harder, denser material. Vulcanized rubber is used to make rubber bands, foams, fabric coatings, small objects, combs, pens and musical instruments. Vulcanized rubber, however, will emit sulfur when exposed to light or heat causing the rubber to degrade and become brittle. Since the 19th century, small amounts of wax have been added to the rubber during vulcanization. The wax slowly migrates to the surface and provides a thin layer of protection from oxidation.
Synonyms and Related Terms
caucho (Esp.); caoutchouc naturel (Fr.); gomma naturale (It.); borracha natural (Port.); Vulcanite; Ebonite; natural rubber; Hevea brasiliensis; Parthenium argentatum
Burns with dark yellow, sooty flame; smells of burnt rubber. Nonvulcanized rubber becomes brittle at cold temperatures (-34 C) and weakens when heated (66 C). Vulcanized rubber degrades at temperatures above 93 C.
Spot test for vulcanized rubber: Iodine/sodium azide reagent for presence of reducible sulfur compounds - positive reaction generates bubbles (Daniels and Ward, 1982)
Hazards and Safety
Vulcanized rubber may emit sulfur fumes that will tarnish metals and stain organic materials.
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