Hevea brasiliensis latex, natural rubber from

Allergy to natural rubber latex, first reported in 1989 in the United States, is a common cause of occupational allergy for health care workers. Natural rubber is a processed plant product from the commercial rubber tree, Hevea brasiliensis. Latex allergens are proteins found in both raw latex and the extracts used in finished rubber products. Latex gloves are the largest single source of exposure to the protein allergens. ... 

In the case of natural rubber from Hevea brasiliensis, which is almost entirely made of cis-isoprene units, it could be assumed that ci5-prenyltransferase is exclusively involved in phase 2. Unfortunately it is more complex. Authors agree on phase 1, which is traws -condensation catalyzed by a cytosolic soluble trans-prenyl transferase" Famesyl diphosphate synthase has been cloned from rubber latex.The most probable prenyldiphosphate used as a primer for phase 2 is famesyl-PP (15) or geranylgeranyl-PP (16)." " Phase 2 is catalyzed by a still not clearly identified rubber transferase system. Different proteins have been... 

Non-isoprene components of Hevea brasiliensis latex account for around 10% of its dry matter while they account for about 5% of the raw dry rubber derived from latex (Table 9.5.2). They comprise proteins, carbohydrates, hpids and inorganic constituents and represent the main composition dilference between natural rubber (NR) and its synthetic counterpart, namely poly(cis-1,4-isoprene) synthetic rubber (IR). They could therefore be involved in the irreplaceable specific qualities of NR. The nature and quantity of these non-isoprene components can vary greatly depending on the clones, the exploitation system and environmental conditions. Some of these components are either dissolved or suspended in the aqueous medium of the latex while the others are adsorbed on the surface of rubber particles. 

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. 

The Production of Natural Rubber from Hevea brasiliensis Latex Colloidal Properties, Preservation, Purification and Processing... 

In 1994, the worldwide consumption of rubber was approximately 14.5 million tons a year, of which about 40% consisted of natural rubber. Natural rubber is produced as latex by tropical rubber trees (Hevea brasiliensis). It is processed locally and therefore the quality of natural rubber fluctuates remarkably [ 140]. Due to increasing demand for rubbers, combined with a decreasing production capacity in Asia and a vast increase in labor costs, the price of natural rubber is still rising sharply. In 1990-1994, the average price of natural rubber was about 0.38 /lb, while in 1996 it was already over 0.80 /lb. The remaining 60% of the articles were manufactured from synthetic petroleum-based rubbers such as isoprene rubber, styrene-butadiene rubber, chloroprene rubber and polyurethanes. The quality of synthetic rubbers is constant, and their price varies between 2 and 5 US per kilogram [137-140]. 

Renewable raw materials are made or derived from short-term renewable sources (one to a few years or a few tens of years) such as plants, trees, wood wastes and other agricultural products. Not all these materials are necessarily biodegradable. Natural rubber, for example, comes from the latex of a tree (Hevea brasiliensis) and is not biodegradable. Renewable materials are often considered as opposites to fossil sources such as petroleum that are not renewable on a human timescale. On the other hand, some synthesized plastics such as certain polyesters are biodegradable. 

Synonyms Natural latex—milky fluid that consists of extremely small particles of rubber obtained from plants, principally from the Hevea brasiliensis (rubber) tree, dispersed in an aqueous medium. It contains a variety of naturally occurring substances in a colloidal suspension, including about 1% proteins (e.g., a-globulins, hevein), which are the allergenic fraction. ... 

Natural rubber can be found as a colloidal emulsion in a white, milky fluid called latex and is widely distributed in the plant kingdom. The Indians called it wood tears. It was not until 1770 that Joseph Priestly suggested the word rubber for the substance, since by rubbing on paper it could be used to erase pencil marks, instead of the previously used bread crumbs. At one time 98% of the world s natural rubber came from a tree, Hevea brasiliensis, native to the Amazon Basin of Brazil which grows to the height of 120 ft. Today most natural rubber is produced on plantations in Malaysia, Indonesia, Singapore, Thailand, and Sri Lanka. Other rubber-bearing plants... 

Natural rubber is isolated from a white fluid, called latex, that exudes from cuts in the bark of Hevea brasiliensis, the South American rubber tree. Many other plants secrete this polymer, as well. The name rubber was first used by Joseph Priestly, who used the crude material to rub out errors in his pencil writing. Natural rubber is soft and sticky. An enterprising Scotsman named Charles Macintosh found that rubber makes a good waterproof coating for raincoats. Natural rubber is not strong or elastic, however, so its uses were limited to waterproofing cloth and other strong materials. 

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... 

Natural rubber, a terpene composed of repeating isoprene units, is isolated from latex, a sticky white fluid that oozes from Hevea brasiliensis, the South American rubber tree, when its bark is cut. The word rubber was first suggested by English chemist Joseph Priestly in 1770, when he used latex to rub out pencil markings. Rubber is a polymer containing 1,5-diene units in which all the double bonds have the Z configuration. In Chapter 30, we learn about the synthesis and properties of polymers like rubber. 

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. 

Rubber is a natural product that exists as a colloidal dispersion named latex in the sap of certain plants from various families such as Moraceae, Compositae or Euphorbiaceae. From this last family, Hevea brasiliensis is the most common plant that produces natural rubber for practical use. The latex has rather large colloidal particles (in aqueous medium) with diameters up to 5 m (although the average is 0.5 jim). 

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. 

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