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Natural rubber

Natural rubber, as initially produced, consists of polymers of isoprene with minor impurities of other organic compounds. Its main constituent is cis-1,4-polyisoprene, with a molecular weight of 100,000 to 1,000,000 daltons. It is harvested mainly as latex from the Pará 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 Pará rubber tree belongs to the spurge family, Euphorbiaceae, and is native to the Amazon basin, though it is now found throughout the tropics. Thailand, Malaysia, Indonesia, and Cambodia are four of the leading rubber producers.

The impurities in latex break down during storage or thermal degradation and produce volatile organic compounds. Gas chromatography and mass spectrometry indicate that these compounds contain sulfur, ammonia, alkenes, ketones, esters, hydrogen sulfide, nitrogen and low-molecular-weight fatty acids (C2-C5). When latex concentrate is produced, sulfuric acid is used for coagulation, which produces malodourous hydrogen sulfide.

Vulcanisation

Vulcanization forms cross-links between sections of the polymer chain, which results in increased rigidity and durability. The most common vulcanising methods depend on sulfur. Polyisoprene (natural rubber) and styrene-butadiene rubber are the main polymers subjected to sulfur vulcanization, and they are used for most street-vehicle tires. Accelerators for the sulfur vulcanization of rubber are based on 2-mercaptobenzothiazoles. Benzothiazoles are used in the vulcanization of rubber, which has drawn attention to their possible role in the environment, and evidence suggests that they biodegrade readily. Vulcanization is, like the curing of other thermosetting polymers, generally irreversible. Most rubber products are vulcanised because this greatly improves their lifespan, function, and strength.

Benzothiazole

Benzothiazole is an aromatic heterocyclic compound with the chemical formula C₇H₅NS. It is a colorless, slightly viscous liquid. Benzothiazoles consist of a 5-membered 1,3-thiazole ring fused to a benzene ring. The three structural isomers are 1,3-benzothiazole, 1,2-benzothiazole and 2,1-benzothiazole. Benzothiazole occurs naturally in some foods but is also used as a food additive.

History

In 1770, Joseph Priestley observed that a piece of the material was extremely good for rubbing off pencil marks on paper, hence the name rubber. In 1839, while trying to mix rubber with sulfur, Charles Goodyear accidentally dropped the mixture in a hot frying pan, and the rubber remained firm instead of melting. On 21 November 1843, Thomas Hancock took out a British patent for the vulcanization of rubber using sulfur, eight weeks before Goodyear did the same in the US. In 1875 about 70,000 seeds of the rubber tree were smuggled to Kew by Henry Wickham, and in 1876 about 2,000 seedlings were sent to Ceylon and 22 to the botanic gardens in Singapore. Industrial demand for rubber-like materials began to outstrip natural rubber supplies by the end of the 19th century, which led to the synthesis of synthetic rubber in 1909.

This note in PREMIEREPEAU. Nuit Élastique. Sample all seven extraits in the Discovery Set.

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