:''This article is about the material rubber, for other uses see
Rubber (disambiguation)
Rubber is an elastic
hydrocarbon polymer which occurs as a milky
emulsion (known as
latex) in the sap of a number of plants but can also be produced synthetically. The major commercial source of the latex used to create rubber is the
Para rubber tree,
Hevea brasiliensis (
Euphorbiaceae). This is largely because it responds to wounding by producing more latex.
Other plants containing latex include
figs (
Ficus elastica), euphorbias, and the common
dandelion. These have not been a major source of rubber, though when
Germany was cut off from supplies of rubber during
World War II, attempts were made to use such sources, before being supplanted by the development of
synthetic rubber.
In places like
Kerala, where coconuts are in abundance, the shell of half a coconut is used as the collection container for the latex. The shells are attached to the tree via a short sharp stick and the latex drips down into it overnight. This usually produces latex up to a level of half to three quarters of the shell. The latex from multiple trees are then poured into flat pans and this is mixed with
formic acid, which serves as a coagulant. After a few hours, the very wet sheets of rubber are wrung out by putting them through a press before they are sent onto factories where
vulcanization and further processing is done.
Aside from a few natural product impurities, natural rubber is essentially a polymer of
isoprene units, a hydrocarbon
diene monomer. Syntheic rubber can be made as a polymer of isoprene or various other monomers. Rubber is believed to have been named by
Joseph Priestley, who discovered in 1770 that dried latex rubbed out pencil marks. The material properties of rubber make it an
elastomer.
History
In its native
Central America and
South America, rubber has been collected for a long time. The
Mesoamerican civilizations used rubber mostly from
Castilla elastica. The Ancient Mesoamericans had a ball game using rubber balls (''see:
Mesoamerican ballgame), and a few Pre-Columbian rubber balls have been found (always in sites that were flooded under fresh water), the earliest dating to about 1600 BC. According to Bernal Díaz del Castillo, the Spanish Conquistadores were so astounded by the vigorous bouncing of the rubber balls of the Aztecs that they wondered if the balls were enchanted by evil spirits. The Maya also made a type of temporary rubber shoe by dipping their feet into a latex mixture. Rubber was used in various other contexts, such as strips to hold stone and metal tools to wooden handles, and padding for the tool handles. While the ancient Mesoamericans did not have vulcanization, they developed organic methods of processing the rubber with similar results, mixing the raw latex with various saps and juices of other vines, particularly Ipomoea alba, a species of
Morning glory.
In
Brazil the natives understood the use of rubber to make water-resistant cloth. A story says that the first European to return to
Portugal from Brazil with samples of such water-repellent rubberized cloth so shocked people that he was brought to court on the charge of witchcraft.
When samples of rubber first arrived in
England, it was observed that a piece of the material was extremely good for rubbing out
pencil marks on paper. This was the origin of the material's English name of
rubber. Blocks of the material are still used for this purpose, and known as
rubbers in
British English, causing occasional amusement to speakers of
American English, to whom a
rubber is a
condom (usually made from
latex). (American English uses
eraser to refer to the rubber block.)
The para rubber tree initially grew in
South America, where it was the main source of what limited amount of latex rubber was consumed during much of the
19th century. About 100 years ago, the
Congo Free State in Africa was a significant source of natural rubber latex, but after repeated efforts (see
Henry Wickham) it was successfully cultivated in
Southeast Asia, where it is now widely grown.
Current sources of rubber
Today
Asia is the main source of natural rubber. Over half of the rubber used today is
synthetic, but several million tonnes of natural rubber are still produced annually, and is still essential for some industries, including automotive and military.
Hypoallergenic rubber can be made from
Guayule.
Early experiments in the development of
synthetic rubber led to the invention of
Silly Putty.
Natural rubber is often
vulcanized, a process by which the rubber is heated and
sulfur is added to improve resilience and elasticity. The process of vulcanization greatly improved the durability and utility of rubber from the
1830s on. The successful development of vulcanisation is most closely associated with
Charles Goodyear. Carbon black is often used as an additive to rubber to improve its strength, especially in vehicle tires.
Rubber as a clothing material is
fetishized by some people, perhaps on the basis that the garment forms a "second skin" that acts as a surrogate for the wearer's own skin. This is known as rubber fetishism.
See also
External link
International Rubber Research & Development Board
Category:Materials
Category:Organic polymers
Category:Terpenes and terpenoids
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