Hevea brasiliensis Tree

Natural rubber can be obtained from the sap of a number of plants and trees, the most common source is the Hevea brasiliensis tree. Although natural rubber was known in Central and South America before the arrival of Christopher Columbus in 1492, the first use as an adhesive was established in a patent dated in 1891. As rubber became an important part of the industrial revolution, the rubber adhesives market grew in importance. To comply with the increasing demand on natural rubber materials, plantations of Hevea brasiliensis trees were established in southeast Asia in the early 20th Century, mainly to supply the demand from the automobile industry. 

Natural rubber is extracted from the hevea brasiliensis tree which is grown in tropical regions. When its bark is slit with a cutter, a liquid, named latex, is obtained. Latex is an emulsion of rubber in water. When acid is added to this emulsion, natural rubber is precipitated. This precipitate is the polymer of a hydrocarbon with the molecular formula CgHg... 

It is obtained from latex extracted from the Hevea brasiliensis tree. There exists another structural isomer called gutta-percha formed from po y trans-1,4-isoprene), whose elastic properties differ from those of natural rubber. 

Natural rubber accounts for about 25% of total rubber consumption. It is produced from the Hevea brasiliensis tree, being formed by isoprene units with cis-1,4 links. Natural rubber is used in tyres and for retreading, latex, mechanical goods, etc. 

Silicone, natural, and synthetic rubbers have been used for the fabrication of implants. Natural rubber is made mostly from the latex of the Hevea brasiliensis tree and the chemical formula is the same as that of cw-1,4 polyisoprene. Natural rubber was found to be compatible with blood in its pure form. Also, cross-linking by x-ray and organic peroxides produces rubber with superior blood compatibility compared with rubbers made by the conventional sulfur vulcanization. 

It may be enquired why it is that natural rubber is highly stereoregular, and in this respect is ery different from butadiene polymers obtained by free-radical polymerization which contain a mixture of microstructures. The reason is that the polyisoprene produced by the Hevea brasiliensis tree is formed not by polymerization of isoprene, free-radical or otherwise, but by an enzyme-catalysed condensation of isopentenyl pyrophosphate (see Section 23.5.2). Natural rubber usually contains some crosslinked polyma- gel, at least after it has left the tree and become exposed to the atmospha-e. Crosslinking does not, however, occur by polymerization through the olefinic double bonds of the polyisoprene chain, but by reactions involving minor concentrations of other functional groups which are attached to the polyisoprene chain. 

Natural rubber, a product of the Hevea brasiliensis tree, is a hydrocarbon with the empirical formula GgHg. When rubber is decomposed in the absence of oxygen, the monomer isoprene is obtained... 

Natural rubber Poly-c/s-isoprene from the Hevea brasiliensis tree... 

An important example of cross-linking is the vulcanization of natural rubber, a process discovered by Charles Goodyear in 1839. Natural rubber is formed from a liquid resin derived from the inner bark of the Hevea brasiliensis tree. Chemically, it is a polymer of isoprene, CsHg (A Figure 12.41). Because rotation about the carbon-carbon double bond does not readily occur, the orientation of the groups boimd to the carbons is rigid. In natural rubber, the chain extensions are on the same side of the double bond, as shown in Figure 12.41(a). 

The first material known as rubber was a polyisoprene produced from latex extracted from Hevea brasiliensis trees. Currently latex world production is concentrated in three areas Asia (93,3%), Africa (4,5%) and Latin America (2,2%). In Latin America the production reaches 195,000 tons, subdivided between Brazil, Ecuador, Guatemala and Mexico, and 54% of this production refers to Brazilian supply, with approximately 105 thousand tons, representing 1.2% of world production." ... 

Natural rubber-based adhesives constitute many nsefnl types of adhesives. They have been made from the latex that is collected from the sap of rubber trees grown in Malaysia and other countries of Sonth East Asia. Rnbber of this type was first collected from the Hevea brasiliensis tree - seeds from the tree were first taken from the Amazon forests in Brazil, propagated in Kew in London, and then supplied, over a century ago, to Malaya and adjacent counuies, where there are now many millions of rubber trees, yielding cis-polyisoprene-based natnral rnbber. This has similar properties to the principal SBR synthetic rubber, derived from styrene and butadiene, both of which are obtained by the cracking process from crnde oil, with subsequent chemical reactions. Natural rubber is obtained from the uee by tapping the bark, when the latex flows out spontaneously as the tree is wounded. This latex is about 33% solids - most natural rubber latex is concentrated to 60% and preserved with ammonia for transport and storage. 

Parth, M. Aust, N. Lederer, K. Distribution of molar mass and branching index of natural rubber from Hevea brasiliensis trees of different ages by SEC coupled with online viscometry. Macromol. Symp. 

Rubber, natural (India rubber, Caoutchouc) n. An amorphous polymer consisting essentially of ds-1,4-polyisoprene, obtained from the sap (latex) of certain trees and plants, mainly the Hevea brasiliensis tree. The material is shipped from tropical plantations in one of two primary forms latex, usually stabilized and preserved with ammonia and centrifuged to remove part of the water or sheets made by milling the coagulum from the latex. Natural rubber has very high molecular weight and is usually masticated to reduce the molecular weight and improve processability. A major use is sidewalls of automotive tires. 

An examination is made of the mechanisms by which NR latex is formed in the Hevea brasiliensis tree. Factors influencing yield and regeneration and methods used in yield stimulation are discussed. 

Despite the increasingly more frequent reports of allergic contact dermatitis (ACD) to natural latex, the exact chemical nature of the allergen(s) remains unknown. In contrast, proteins present in latex obtained from the Hevea brasiliensis tree are the cause of the immunoglobulin (Ig)E-mediated hypersensiti-vity/allergic contact urticaria (ACU) to natural latex rubber. Since Hevea brasiliensis accounts for more than 99% of natural rubber used worldwide, ACU to latex is a significant problem. 

Natural Rubber. Natural rubber is obtained from the Hevea brasiliensis tree as a latex. It is primarily cis-l,4-polyisoprene with small amoimts of bound proteins and other contaminants (see Rubber, Natural). 

An important example of cross-linking is the vulcanization of natural rubber, a process discovered by CTiarles (Goodyear in 1839. Natural rubber is formed from a liquid resin derived from the inner bark of the Hevea brasiliensis tree. Chemically, it is a polymer of isoprene, CsHg. 

Natural rubber latexes occur in many plants. The white sap of the common milkweed and dandelion is a rubber latex. The most important source of natural rubber latex is the Hevea brasiliensis tree, now grown in plantations in many tropical parts of the world. 

The source of rubber latex at that time was the Hevea brasiliensis tree, which is native to the Amazon valley. Brazil became the primary source of mbber, but as mbber use grew questions arose as to this coimtry s ability to... 

The polymer in natural rubber (from the Hevea brasiliensis tree) is pure cis polyiso-prene gutta percha and balata are composed of the trans isomer. 

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