Hevea tree

The environmental implications of rubber usage are very easily understood by considering NR, a versatile industrial material obtained from the Hevea trees as outlined in the tabular format below [4] ... 

The rubber industry has a long and colorful history. Natural rubber is produced from latex, a milky fluid found in cells that lie between the bark and the wood of many plants. You may have seen latex flow from the broken stalks of milkweed plants, but the source of commercial rubber is the Hevea tree, a native of Brazil. When the bark of this tree is slashed, its milky white sap oozes out and can be collected in cups mounted on the tree s trunk. The people of the Amazon jungle made bouncing balls, shoes, and water Jars out of rubber, and Portuguese explorers sent waterproof boots and a rubber-coated coat back to their king. The first commercial exports included some rubber shoes shipped to Boston in 1823. 

The best grade of wild rubber formerly obtained from Hevea trees indigenous to the Amazon Valley, and originally exported from the town of Para. 

The most important species of the Hevea genus of the order Euphorbiaceae. All but a tiny proportion of the world supply of natural mbber is obtained from the Hevea tree originally native to the Amazon valley but now cultivated on a plantation scale in Indonesia, Thailand, Malaysia and a number of other equatorial countries. 

A term applied to clones of Hevea trees which give a much higher yield of latex than ordinary rubber trees. The average yield in the 1950s was under 500 kg of rubber per hectare per annum. It is now more common to achieve a two- to threefold increase on these figures from modem planting material. 

The absence of dimethylallyl-group in NR indicates that the initiating species for rubber formation in Hevea tree is not FDP, but FDP modified at the dimethylallyl-group, which is abbreviated here as (o [103,109,110]. This was confirmed by 13C-NMR analysis of in vitro polymerised rubber by incubation of the bottom fraction of fresh latex and isopentenyl diphosphate (IDP) [111]. The newly synthesised in vitro rubber formed in the presence of FDP and IDP showed the dimethylallyl group derived from FDP. On the other hand, no dimethylallyl group was detected in the in vivo rubber prepared without the addition of FDP [112]. 

Derivation From latex obtained from Hevea trees, coagulated with acetic or formic acid. Also made synthetically. 

Natural rubber of the best quality is prepared by coagulating the latex of the Hevea brastliensis tree that is primarily cultivated in the Far East. However, there are other sources such as the wild rubbers of the same tree growing in Central America, guyayule rubber coming from shrubs grown mostly in Mexico, and balata. Balata is a resinous material and carmot be tapped like the Hevea tree sap. The balata tree must be cut down and boiled to extract balata that cures to a hard, tough product used as golf ball covers. 

NR is today obtained mainly from Hevea trees on plantations in tropical Asia, from where it is exported throu out the world as an industrial raw matmaL As noted by Thomas Edison, howevo , many plants in tempmrate climates, like the goldenrod and the dandelion, also contain rubber in small amounts [2,3]. Consequently, rubberdegrading microorganisms can be expected to be present widely in the natural environment. 

Gum rubber (pure gum) n. Raw, unvulcanized rubber recovered from the latex of the hevea tree or from polymerization of synthetic rubber. Gum runner has almost no useful properties prior to being... 

Resin, synthetic (synthetic polymer). A Resin that has been produced from simple materials, or intermediates made from such chemicals, by either addition or condensation polymerization. Of the commercial plastics, all but the cellulosics are based on synthetic resins. Among commercial elastomers, only natural rubber, or refined from the sap of the Hevea tree, is natural. 

Rubber is obtained from latex, which exudes from the bark of the Hevea tree when it is cut. The latex is an aqueous dispersion, containing 25-40 percent rubber hydrocarbon, stabilized by a small amount of protein material and fatty acids. As the latex is gathered, a small amount of anunonia is added as a preservative. The latex is later coagulated by the addition of a 5 percent solution of acetic acid. The coagu-lum is washed and dried. 

Today s environmental concerns demand clean reaction processes that do not use harmful organic solvents.Water is without doubt the most environmentally friendly solvent. NR latex is exuded from the Hevea tree as an aqueous emulsion therefore, it would be desirable to modify the NR latex. Many chemical reactions, such as hydrogenation, epoxidation, chlorination,graft copolymerization and oxidative degradation have been performed on the reactive double bonds of the isoprene structure along the molecular chain. 

The latex as obtained from Hevea trees by tapping (called field latex) is a dilute aqueous dispersion of latex particles. It contains a host of organic molecules... 

On the plantations, the Hevea trees are tapped , i.e., the bark is cut and the latex which flows is collected in small cups. The latex is a stable dispersion of rubber in water, proteinous material being the dispersing agent a typical analysis might be as follows ... 

Hevea trees are ready for tapping about 5 to 6 years after planting. This has been a focus of research at the RRIM, and certain clones can now be tapped in... 

Gum Rubber n (pure gum) Raw, unvulcanized rubber recovered from the latex of the hevea tree or from polymerization of synthetic rubber. Gum runner has almost no useful properties prior to being vulcanized. (Langenheim JH (2003) Plant resins Chemistry, evolution ecology and ethnobotany. Timber, Portland, OR Industrial gums Polysaccharides and their derivatives. Whistler JN, BeMiller JN (eds). Elsevier Science and Technology Books, New York, 1992). 

Cis-1,4-polyisoprene (TiCVAlR3) (roughly equivalent to natural rubber from Hevea tree) 100 240 500 700... 

The first polymers used were all obtained from natural products. Natural rubber from Hevea trees was being used by the American Indians when Columbus arrived in 1492. Cellulose in different forms, starch and collagen in leather are other examples of natural polymers used. Modification of native polymers started in the mid-nineteenth century and the first wholly synthetic polymer was made at the beginning of the twentieth century. The science of polymers began in the 1920s. 

In the future, there may be two possible alternatives to obtaining natural rubber latex from the Hevea tree (a perennial crop). One of these alternatives is extracting natural rubber from Guayule (a desert shrub which grows in the American Southwest). It is now technically feasible to harvest this shrub with patented processes that have been developed. The natural rubber obtained from Guayule also reportedly contains much less of the harmful proteins that can cause allergic reactions. 

Natural Rubber Latex (from Hevea tree)... 

Caoutchouc soon became an item of commerce. The firm of Thomas Hancock (1786-1865) developed a line of products based on both the elasticity and the water repellency of caoutchouc [7]. In order to learn more about the substance that was the basis of his wealth, in 1824 Hancock gave some caoutchouc to his friend Michael Faraday (1791-1867) at the Royal Institution. Faraday was the foremost analytical chemist of this era. As was his custom, Faraday repeated the known experiments on Hevea tree sap, verified the ones that were true and became proficient in the purification and processing of caoutchouc [8]. A copy of the title page of Faraday s classic Experimental Researches in Chemistry and Physics is shown as Fig. 2.1. 

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