Latex being collected from a tapped rubber
tree
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.
Synthetic rubber comprises the polymerisation of a variety of monomers to produce polymers. These form part of a broad study covered by Polymer science and Rubber technology.
The major commercial source of natural 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. Henry Wickham gathered thousands of seeds from Brazil in 1876 and they were germinated in Kew Gardens, England. The seedlings were sent to Colombo, Indonesia and Singapore.
Other plants containing latex include figs (Ficus elastica), euphorbias, and the common dandelion. Although these have not been major sources of rubber, Germany attempted to use such sources during World War II when it was cut off from rubber supplies. These attempts were later supplanted by the development of synthetic rubber. Its density is 920 kg/m3.
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 is 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. Synthetic 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 and a thermoset.
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, and to prevent it from perishing. 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.
This article source is from : http://en.wikipedia.org/wiki/Rubber