Natural rubber plant sources

Prior to the identification of Hevea brasiliensis as the most important commercial source of natural rubber, plants belonging to a wide spectmm of families had been explored for extraction of rubber. Among these, extractable quantities of mbber could be obtained from a few sources as given in Table 14.1. 

In 1942 the Japanese overran Malaya and the then Dutch East Indies to cut off the main sources of natural rubber for the United States and the British Commonwealth. Because of this the US Government initiated a crash programme for the installation of plants for the manufacture of a rubber from butadiene and styrene. This product, then known as GR-S (Government Rubber-Styrene), provided at that time an inferior substitute for natural rubber but, with a renewed availability of natural rubber at the end of the war, the demand for GR-S slumped considerably. (Today the demand for SBR (as GR-S is now known) has increased with the great improvements in quality that have been made and SBR is today the principal synthetic rubber). 

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. 

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. 

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. 

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. 

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. ... 

Another unusual plant of the American Southwest and Mexico is the bushlike guayule, which produces a form of natural rubber or latex, as do many other plants, even the dandelion, but not in sufficient quantity. The guayule, however, was employed during WWII when the Malaysian sources of natural rubber were cut off. 

The vitamin K structure shown earlier is that of K, primarily found in green plants. Vitamin K2 contains from three to six isoprene units (depending on the source), each of which has a double bond. Isoprene, 2-methyl-1,4-butadiene, is found in polymerlike repetitive isoprenoid units in natural rubber, carotenoids, steroids, and smaller compounds... 

During World War I German chemists, whose coxmoy was cut off from its sources of natural rubber by the British blockade, polymerized 3-methyl-isoprene (2,3-dimethyl-1,3-butadiene) units, (CH2=C(CH3)C(CH3)=CH2), obtained from acetone, to form an inferior substitute called methyl rubber. By the end of the war Germany was producing 15 tons (13.6 metric tons) of this rubber per month. The USSR (Union of Soviet Socialist Republics), which built a pilot plant at Leningrad (now St. Petersburg) in 1930 and three factories in 1932 and 1933, was the first country to institute a full-scale synthetic rubber industry. 

The branched isoprene unit, which is also synthesized from the C, pool, is the basic structure of terpenoids. Less condensed structures are used as volatile pheromones, e.g., jasmonic acid, menthol, or camphor, or as natural rubber material. More condensed structures such as steroids and hopanoids are part of membranes, influencing their fluidity. They are also highly specific to their source organisms. Best known are cholesterol (in animals and plants), ergosterol (in fungi), and brassicasterol (in diatoms). Besides cellulose, hopanoids are the most abundant biomolecules. 

NATURAL SOURCES Natural rubber occurs in over 200 species of plants. However, only one tree source, Hevea Brasiliensis, is of commercial importance, and it accounts for over 99 percent of the world s natural rubber production. 

Natural macromolecular products such as natural rubber, natural wool, cotton, starch, and collagen, and their derivatives, such as leather, cellulose acetate, and cellulose ethers, are often used in large quantities. But the quantity of natural products used to provide monomers is small. Animal raw materials sources can be excluded since animals feed on vegetables and other animals, and, so, many of the raw materials can be more simply obtained from plants. In general, supply of raw materials from vegetable sources is relatively insecure since quality and quantity can vary according to weather conditions, or may be completely cut off for political reasons. 

This chapter gives a general introduction to the book and describes briefly the context for which the editors established its contents and explains why certain topics were excluded from it. It covers the main raw materials based on vegetable resources, namely (i) wood and its main components cellulose, lignin, hemicelluloses, tannins, rosins and terpenes, as well as species-speciflc constituents, like natural rubber and suberin and (ii) annual plants as sources of starch, vegetable oils, hemicelluloses, mono and disaccharides and algae. Then, the main animal biomass constituents are briefly described, with particular emphasis on chitin, chitosan, proteins and cellulose whiskers from molluscs. Finally, bacterial polymers such as poly(hydroxyalkanoates) and bacterial cellulose are evoked. For each relevant renewable source, this survey alerts the reader to the corresponding chapter in the book. 

These adhesives are soluble or dispersible in water and are produced or extracted from natural sources. Other adhesives, such as rubber cements, lutrocellulose, and ethyl cellulose lacquer cements, are also produced from plant sources, but are not water-soluble or water-dispersible and are therefore not classified as vegetable glues. 

NR is a naturally existing elastomer composed mainly of cis-l, 4-poly-isoprene. It is collected from more than 400 different species of plants but the main source is Hevea brasiliettsis. The collection is in the form of latex, a colloidal solution of NR, which contains about 70% of water and other materials in smaller quantities such as proteins, fatty acids, resins, etc. After removing the excess water by centrifugation two products based on NR can be obtained concentrated latex and dry natural rubber. Concentrated latex has about 60%... 

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