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Rubber, also called India rubber, latex, Amazonian rubber, caucho, or caoutchouc,[1] as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, Indonesia, and Cambodia are four of the leading rubber producers.[2][3][4]

Currently, rubber is harvested mainly in the form of the latex from the Par rubber tree (Hevea brasiliensis) or others. The latex is a sticky, milky and white colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called "tapping". The latex then is refined into the rubber that is ready for commercial processing. In major areas, latex is allowed to coagulate in the collection cup. The coagulated lumps are collected and processed into dry forms for sale.

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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 and high resilience and also is water-proof.[citation needed]

Industrial demand for rubber-like materials began to outstrip natural rubber supplies by the end of the 19th century, leading to the synthesis of synthetic rubber in 1909 by chemical means.[citation needed]

The major commercial source of natural rubber latex is the Amazonian rubber tree (Hevea brasiliensis),[1] a member of the spurge family, Euphorbiaceae. Once native to Brazil, the species is now pan-tropical. This species is preferred because it grows well under cultivation. A properly managed tree responds to wounding by producing more latex for several years.[citation needed]

Congo rubber, formerly a major source of rubber, which motivated the atrocities in the Congo Free State, came from vines in the genus Landolphia (L. kirkii, L. heudelotis, and L. owariensis).[5]

Dandelion milk contains latex. The latex exhibits the same quality as the natural rubber from rubber trees. In the wild types of dandelion, latex content is low and varies greatly. In Nazi Germany, research projects tried to use dandelions as a base for rubber production, but failed.[6] In 2013, by inhibiting one key enzyme and using modern cultivation methods and optimization techniques, scientists in the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) in Germany developed a cultivar of the Kazakh dandelion (Taraxacum kok-saghyz) that is suitable for commercial production of natural rubber.[7] In collaboration with Continental Tires, IME began a pilot facility.

Many other plants produce forms of latex rich in isoprene polymers, though not all produce usable forms of polymer as easily as the Par.[8] 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)[9] and chicle from Manilkara species. Others that have been commercially exploited, or at least showed promise as rubber sources, 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 Kazakh dandelion, and, perhaps most importantly for its hypoallergenic properties, 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.[10]

Charles Marie de La Condamine is credited with introducing samples of rubber to the Acadmie Royale des Sciences of France in 1736.[13] In 1751, he presented a paper by Franois Fresneau to the Acadmie (published in 1755) that described many of rubber's properties. This has been referred to as the first scientific paper on rubber.[13] 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". It slowly made its way around England. In 1764, Franois Fresnau discovered that turpentine was a rubber solvent. Giovanni Fabbroni is credited with the discovery of naphtha as a rubber solvent in 1779.[citation needed] Charles Goodyear redeveloped vulcanization in 1839, although Mesoamericans had used stabilized rubber for balls and other objects as early as 1600 BC.[14][15]

South America remained the main source of latex rubber used during much of the 19th century. The rubber trade was heavily controlled by business interests but no laws expressly prohibited the export of seeds or plants. In 1876, Henry Wickham smuggled 70,000 Amazonian rubber tree seeds from Brazil and delivered them to Kew Gardens, England. Only 2,400 of these germinated. Seedlings were then sent to India, British Ceylon (Sri Lanka), Dutch East Indies (Indonesia), Singapore, and British Malaya. Malaya (now Peninsular Malaysia) was later to become the biggest producer of rubber.[16]

In the early 1900s, the Congo Free State in Africa was also a significant source of natural rubber latex, mostly gathered by forced labor.[citation needed] King Leopold II's colonial state brutally enforced production quotas. Tactics to enforce the rubber quotas included removing the hands of victims to prove they had been killed. Soldiers often came back from raids with baskets full of chopped-off hands. Villages that resisted were razed to encourage better compliance locally.[citation needed] .mw-parser-output div.crossreference{padding-left:0}(See Atrocities in the Congo Free State for more information on the rubber trade in the Congo Free State in the late 1800s and early 1900s.)

The rubber boom in the Amazon also similarly affected indigenous populations to varying degrees. Correrias, or slave raids were frequent in Colombia, Peru and Bolivia where many were either captured or killed. The most well known case of atrocities generated from rubber extraction in South America came from the Putumayo genocide. Between the 1880s-1913 Julio Csar Arana and his company that would become the Peruvian Amazon Company controlled the Putumayo river. W.E. Hardenburg, Benjamin Saldaa Rocca and Roger Casement were influential figures in exposing these atrocities. Roger Casement was also prominent in revealing the Congo atrocities to the world. Days before entering Iquitos by boat Casement wrote "'Caoutchouc was first called 'india rubber,' because it came from the Indies, and the earliest European use of it was to rub out or erase. It is now called India rubber because it rubs out or erases the Indians."[17][18]

In India, commercial cultivation was introduced by British planters, although the experimental efforts to grow rubber on a commercial scale were initiated as early as 1873 at the Calcutta Botanical Garden. The first commercial Hevea plantations were established at Thattekadu in Kerala in 1902. In later years the plantation expanded to Karnataka, Tamil Nadu and the Andaman and Nicobar Islands of India. Today, India is the world's 3rd largest producer and 4th largest consumer of rubber.[19]

In Singapore and Malaya, commercial production was heavily promoted by Sir Henry Nicholas Ridley, who served as the first Scientific Director of the Singapore Botanic Gardens from 1888 to 1911. He distributed rubber seeds to many planters and developed the first technique for tapping trees for latex without causing serious harm to the tree.[20] Because of his fervent promotion of this crop, he is popularly remembered by the nickname "Mad Ridley".[21]

Before World War II significant uses included door and window profiles, hoses, belts, gaskets, matting, flooring, and dampeners (antivibration mounts) for the automotive industry. The use of rubber in car tires (initially solid rather than pneumatic) in particular consumed a significant amount of rubber. Gloves (medical, household, and industrial) and toy balloons were large consumers of rubber, although the type of rubber used is concentrated latex. Significant tonnage of rubber was used as adhesives in many manufacturing industries and products, although the two most noticeable were the paper and the carpet industries. Rubber was commonly used to make rubber bands and pencil erasers.

Rubber produced as a fiber, sometimes called 'elastic', had significant value to the textile industry because of its excellent elongation and recovery properties. For these purposes, manufactured rubber fiber was made as either an extruded round fiber or rectangular fibers cut into strips from extruded film. Because of its low dye acceptance, feel and appearance, the rubber fiber was either covered by yarn of another fiber or directly woven with other yarns into the fabric. Rubber yarns were used in foundation garments. While rubber is still used in textile manufacturing, its low tenacity limits its use in lightweight garments because latex lacks resistance to oxidizing agents and is damaged by aging, sunlight, oil and perspiration. The textile industry turned to neoprene (polymer of chloroprene), a type of synthetic rubber, as well as another more commonly used elastomer fiber, spandex (also known as elastane), because of their superiority to rubber in both strength and durability.

On a microscopic scale, relaxed rubber is a disorganized cluster of erratically changing wrinkled chains. In stretched rubber, the chains are almost linear. The restoring force is due to the preponderance of wrinkled conformations over more linear ones. For the quantitative treatment see ideal chain, for more examples see entropic force.

Cooling below the glass transition temperature permits local conformational changes but a reordering is practically impossible because of the larger energy barrier for the concerted movement of longer chains. "Frozen" rubber's elasticity is low and strain results from small changes of bond lengths and angles: this caused the Challenger disaster, when the American Space Shuttle's flattened o-rings failed to relax to fill a widening gap.[22] The glass transition is fast and reversible: the force resumes on heating. 2351a5e196