Natural rubber coagulated

In rubber latex, the process whereby the dispersed rubber globules separate out from the watery serum the globules clot together to form a jelly-like mass, the coagulum. In the preparation of natural rubber, coagulation of the latex is... 

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). 

Cure Characteristics. Methods of natural rubber production and raw material properties vary from factory to factory and area to area. Consequentiy, the cure characteristics of natural mbber can vary, even within a particular grade. Factors such as maturation, method and pH of coagulation, preservatives, dry mbber content and viscosity-stabilizing agents, eg, hydroxylamine-neutral sulfate, influence the cure characteristics of natural mbber. Therefore the consistency of cure for different grades of mbber is determined from compounds mixed to the ACSl formulation (27). The ACSl formulation is as follows natural mbber, 100 stearic acid, 0.5 zinc oxide, 6.0 sulfur, 3.5 and 2-mercaptobenzothiazole (MBT), 0.5. 

Natural rubber is harvested as latex by tapping trees in a manner similar to maple syrup. Tree latex contains about 35 wt% rubber solids, as well as small quantities of carbohydrates, resins, mineral salts and fatty acids. Ammonia should be immediately added to the latex to avoid coagulation by these other ingredients and to prevent bacterial degradation. After collection, the latex can be concentrated to 60-70% solids if the latex product is required for end-use. Otherwise, the latex is coagulated, washed, dried, and pressed into bales for use as dry rubber. 

Any substance which will bring about coagulation. In the preparation of natural rubber the usual coagulants are acetic or formic acids. In the manufacture of dipped goods from latex, the coagulant used depends on the method of dipping employed. 

In the preparation of natural rubber, the coagulum is the soft clot or mass of rubber particles which separates out from the serum after addition of the coagulant. 

HCOOE1, an organic acid which may be used in diluted form as the latex coagulant in the production of natural rubber. 

Coagulation of natural rubber latex by stages with the object of removing the yellow colouring matter in the first fraction. The latex in the second fraction produces a white crepe rubber. See Bleaching Agent. 

Processing aid-80, a masterbatch in the form of pressed crumb consisting of an 80 20 blend of crosslinked to ordinary natural rubber. The correct proportions of vulcanised latex and field latex are blended, coagulated and the resulting crumb pressed into 100 lb bales. The use of PA 80 confers Superior Processing properties on any natural or styrene-butadiene rubber with which it may be mixed. See Superior Processing Rubber. 

When natural rubber latex is concentrated by centrifuging there are produced approximately equal volumes of concentrate containing most of the rubber, and skim latex with a low proportion of rubber. The rubber obtained by coagulation of skim latex is termed skim rubber. Due to the high content of non-rubber substances such rubber may give difficulty in processing. 

Elastomeric fibers can be made out of natural rubber. Rubber latex, which is a suspension of rubber spheres in water, is mixed with a vulcanizing agent, and the mixture is wet spun. The fibers from the spinneret are extruded into a coagulating bath and then vulcanized to produce the cross-linking of chains. Such fibers are used in woven and knitted fabrics, and more often than not they are mixed with other textile fibers to form fabrics for garments. Most natural rubber fibers, however, have been supplanted by synthetic elastomeric fibers, especially in the area of athletic wear. This is attributable to the poor dyeability, abrasion resis-... 

Prior to the eastern adventures of Linschoeten and Tradescant, the sailors of Columbus had discovered the natives of Central America playing with lumps of natural rubber. These were obtained, like gutta percha, by coagulation from a latex the first recorded reference to natural mbber was in Valdes La historia natural y general de las Indias, published in Seville (1535-1557). In 1731 la Condamine, leading an expedition on behalf of the French government to study the shape of the earth, sent back from the Amazon basin rabber-coated cloth prepared by native tribes and used in the manufacture of waterproof shoes and flexible bottles. 

Natural rubber is obtained by cutting (tapping) the bark of Hevea braziliensis, a wild tree originally found in South America. The rubber is in a milky form containing about 35% latex. The latex is separated by coagulation with a weak acid and it is soluble in a range of solvents, including hydrocarbons, chlorinated hydrocarbons, certain ketones, esters and carbon disulphide. 

Natural rubber latex will coagulate (form lumps) as it comes from the plant. Strain off the thick part for use in flame fuel. If the rubber latex does not form lumps, add a small amount of acid to coagulate the latex and use the rubbery lump for gelling. It is best to air-dry the wet lumps before adding them to gasoline. 

S. Natural rubber latex coagulates readily. If acids are not available, use one volume of... 

Various vinyl latexes, previously polymerized, were mixed with natural rubber latex, both still in aqueous dispersion, and then coagulated. Thus, core-shell latex and latex blend materials were known very early. 

Natural rubber adhesives can be classified into two principal types latex adhesives and solution adhesives. Natural rubber latex is obtained by tapping the tree Havea brasiliensis. The latex consists of about 35% solids. Ammonia is added to the latex immediately after the tapping to prevent bacterial attack and coagulation. Before marketing, the latex is concentrated to a total solids content of about 60 to 70%. 

Solution adhesive is obtained from solid rubber obtained by coagulation of latex as acquired from the tree. The coagulation is effected by dilute aqueous solution of organic acids. The solid rubber can be graded in terms of dirt content, ash content, nitrogen content, and volatile matter. It can also be categorized by plasticity retention index and Mooney viscosity. To maintain uniformity it is necessary to choose solid natural rubber of known characteristics. 

Gutta-percha. The name, derived from Malayan ge-tah pertcha=latex of the percha tree, for a natural rubber (structure, see there) from the gutta-percha trees Palaquium gutta and P. oblongifolia, Sapotaceae) with properties similar to those of balata. In Sumatra, Java, and south east India, the rapidly coagulating latex of incised trees is collected, rapidly kneaded, and marketed as raw G. Pure G. is the all-trans-isorntr of polyisoprene, related to balata molecular mass ca. 100000. In contrast to the cis-isomeric natural rubber, G. is hard and less elastic but not brittle, it softens at 25-30°C, becomes plastic at 60 °C, and melts at >100°C with decomposition and formation of a sticky mass. For uses, see literature. 

As a corollary, if a natural product is processed by any means other than those listed in 40 C.F.R. 710.4(b), then the result is a chemical substance, and not a mixture. For example, natural latex from trees is a naturally occurring substance. Natural rubber is made from latex by adding chemical coagulants, and because adding coagulants is not one of the types of processing permitted by 40 C.F.R. 710.4(b), natural rubber is not a natural substance and must be on the Inventory." ... 

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