importance of television in our life

Topics: Rubber, Natural rubber, Latex Pages: 10 (3478 words) Published: October 16, 2013
"Rubber" and "India rubber" redirect here. For other uses, see Rubber (disambiguation). This article is about the polymeric material "natural rubber". For man-made rubber materials, see Synthetic rubber.

Latex being collected from atapped rubber tree

Rubber tree plantation of Thailand (7 August 2011)
Natural rubber, also called India rubber or caoutchouc, as initially produced, consists of suitable polymers of the organic compound isoprene, with minor impurities of other organic compounds plus water. Forms of polyisoprene that are useful as natural rubbers are classified aselastomers. Currently, rubber is harvested mainly in the form of the latex from certain trees. The latex is a sticky, milky colloid drawn off by making incisions into the bark and collecting the fluid in vessels in a process called "tapping". The latex then is refined into rubber ready for commercial processing. Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In most of its useful forms, it has a large stretch ratio, high resilience, and is extremely waterproof.[1]

Varieties[edit]
The major commercial source of natural rubber latex is the Pará rubber tree (Hevea brasiliensis), a member of the spurge family, Euphorbiaceae. This species is widely used because it grows well under cultivation and a properly managed tree responds to wounding by producing more latex for several years. Many other plants produce forms of latex rich in isoprene polymers, though not all produce usable forms of polymer as easily as the Pará rubber tree does; some of them require more elaborate processing to produce anything like usable rubber, and most are more difficult to tap. Some produce other desirable materials, for example gutta-percha (Palaquium gutta)[2] and chicle from Manilkara species. Others that have been commercially exploited, or at least have shown promise as sources of rubber, include the rubber fig (Ficus elastica), Panama rubber tree (Castilla elastica), various spurges (Euphorbia spp.), lettuce (Lactuca species), the related Scorzonera tau-saghyz, various Taraxacum species, including common dandelion (Taraxacum officinale) and Russian dandelion (Taraxacum kok-saghyz), and guayule (Parthenium argentatum). The term gum rubber is sometimes applied to the tree-obtained version of natural rubber in order to distinguish it from the synthetic version.[1] Discovery of commercial potential[edit]

The Para rubber tree is indigenous to South America. Charles Marie de La Condamine is credited with introducing samples of rubber to the Académie Royale des Sciences of France in 1736.[3] In 1751, he presented a paper by François Fresneau to the Académie (eventually published in 1755) which described many of the properties of rubber. This has been referred to as the first scientific paper on rubber.[3] In England, Joseph Priestley, in 1770, observed that a piece of the material was extremely good for rubbing off pencil marks on paper, hence the name "rubber". Later, it slowly made its way around England. South America remained the main source of the limited amounts of latex rubber used during much of the 19th century. In 1876, Henry Wickham gathered thousands of Para rubber tree seeds from Brazil, and these were germinated in Kew Gardens, England. The seedlings were then sent to India, Ceylon (Sri Lanka), Indonesia, Singapore, and British Malaya. Malaya (now Malaysia) was later to become the biggest producer of rubber. In the early 1900s, the Congo Free State in Africa was also a significant source of natural rubber latex, mostly gathered by forced labor. Liberia and Nigeria also started production of rubber. In India, commercial cultivation of natural rubber was introduced by the British planters, although the experimental efforts to grow rubber on a commercial scale in India were initiated as early as 1873 at the Botanical Gardens, Calcutta. The first commercial Hevea plantations in...
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