Hevea natural rubber

The infrared spectra of hevea (natural rubber), balata (or guttapercha), the latter both in the crystalline (a) and the amorphous forms, and of synthetic polyisoprene are compared in Fig. 32. The hevea and balata (amorphous) spectra offer calibrations for cfs-1,4 and irans-1,4 structures, respectively, in the synthetic polymer. Owing to the presence of the methyl substituent, however, the spectral difference between the as and trans forms is slight both absorb at about 840... 

The use of alkali metals for anionic polymerization of diene monomers is primarily of historical interest. A patent disclosure issued in 1911 (16) detailed the use of metallic sodium to polymerize isoprene and other dienes. Independendy and simultaneously, the use of sodium metal to polymerize butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene was described (17). Interest in alkali metal-initiated polymerization of 1,3-dienes culminated in the discovery (18) at Firestone Tire and Rubber Co. that polymerization of neat isoprene with lithium dispersion produced high t /s- 1,4-polyisoprene, similar in structure and properties to Hevea natural rubber (see Elastomers, synthetic-polyisoprene Rubber, natural). 

Natural Rubber. To obtain natural mbber (NR), the Hevea hrasiliensis tree is tapped for its sap. The off-white sap is collected and coagulated. This process produces a high molecular weight substance which is natural mbber. The principal producing countries are Malaysia, Indonesia, Thailand, India, China, and Sri Lanka (see Rubber, natural). 

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 obtained from the bark of the rubber tree, Hevea brasiliensis, grown on enormous plantations in Southeast Asia. 

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. 

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]. 

Rubber obtained from botanical sources. The bulk of natural rubber is obtained from the Hevea Brasiliensis free with small amounts from other vines, shrubs and plants mainly the Guayule shrub and the Kok-Saghyz plant. See Isoprene. 

Hevea rubber is undoubtedly one of the unique crops of history and of all agriculture, and one of the most interesting. It is not easy to produce rubber. Research is the tool by which it is possible to grow vast acreages of the tree as a profitable crop. This could never have been done without the past /and present intensive investigations of careful scientists over more than 30 years. Repeated reference in the literature indicates that diseases are the limiting factors in natural rubber production, and that planters owe a debt to disease-control workers. 

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. 

The chlorination of low molecular weight natural rubber from Guayule (Parthenium Argentatum Grey) has been accomplished. The structure of the chlorinated product is consistent with that of chlorinated Hevea rubber. The use of Azo-bis-isobutyronitrile was as a catalyst resulted in increased chlorine content with a concomitant reduction in molecular weight, thereby allowing the preparation of lower viscosity grades of chlorinated rubber. 

The small peak at 1.25 ppm is representative of an impurity(ies) that was not removed during the extraction process. Further purification from an ethanolic solution reduces the impurity(ies) to an insignificant level. These peak positions are in excellent agreement with literature values for natural rubber (Hevea). 

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... 

Until the 1930s natural rubber from Hevea brasiliensis was the only available elastomer. The United States had to, and still does, import every pound. Although research on synthetic substitutes began before 1940 in this country. World War II influenced speedy development of substitutes when our supply of natural rubber from the Far East was cut off. Gasoline had to be rationed not because of its shortage, but because of the automobile tire shortage. 

Little rhyme or reason is associated with many of the common names of polymers. Some names are derived from the place of origin of the material, such as Hevea brasilliensis literally rubber from Brazil —for natural rubber. Other polymers are named after their discoverer, as is Bakelite, the three-dimensional polymer produced by condensation of phenol and formaldehyde, which was commercialized by Leo Baekeland in 1905. 

Before 1800 Cotton, flax, wool, and silk fibers bitumens caulking materials glass and hydraulic cements leather and cellulose sheet (paper) natural rubber Hevea brasiliensis), gutta percha, balata, and shellac 1839 Vulcanization of rubber (Charles Goodyear)... 

Natural rubber (Hevea brasiliensis) is as-poly-2-methyl-1,4-butadiene, and gutta-percha (Palaquium oblongi/olium) and balata (Minusops globosa) are polymers of isoprene (2-methyl-1,4-butadiene) with trans configurations. Neoprene is a polymer of 2-chloro-1,3-butadiene (chloroprene). 

Any elastomer capable of rapid elastic recovery after being stretched to at least twice its length at room temperature from 0°F to 150°F at any humidity. Hevea or natural rubber can be considered as an elastomer. 

Natural rubber - Rubber formed in a living plant or tree, usually referring to Hevea Brasiliensis. ASTM designation NR. 

Several biomass species have been found to contain oils and/or hydrocarbons (Table 13). It is apparent that oil or hydrocarbon formation is not limited to any one family or type of biomass. Interestingly, some species in the Euphorbiaceae family, which includes Hevea bra iliensis, form hydrocarbons having molecular weights considerably less than that of natural rubber at yields as high as 10 wt% of the plant. This corresponds to hydrocarbon yields of about 3.97 m3/hm2-yr(25bbl/hm2-yr). 

---