Caoutchouc coagulation

Rubber is obtained from the juice of various tropical trees, mainly the tree Hevea brasiliensis. The juice is a latex consisting of a dispersion of polymer phase at a concentration of about 35% by mass, together with traces of proteins, sterols, fats, and salts. The rubber is obtained either by coagulation of the latex with acid, either ethanoic or methanoic, or by evaporation in air or over a flame. The material that results from this process is a crumbly, cheeselike substance, sometimes called raw rubber or caoutchouc. In order to... 

Rubber or caoutchouc is obtained by coagulation of the latex of numerous plants belonging to different families, principally to the Euphorbiaceae, Artocarpeae and Apocyneae. Whatever its origin and method of preparation, its value depends essentially on the content in hydrocarbons pure rubber) and on the substances accompanying it (resinous matters, various impurities). 

Source.—The common substance which is known as rubber is the product obtained by the coagulation of the juice or latex which is present, usually in the bark, but sometimes in the woody tissue, of certain tropical or sub-tropical trees, shrubs and vines. Gutta-percha is a variety of rubber differing in physical properties. The chemical individual present in rubber is a terpene hydrocarbon known as caoutchouc. 

Coagulation of the Latex.—Pure rubber or caoutchouc is an emulsion colloid and in most cases is held in emulsion by the protective action of other colloids, principally proteins. The breaking up of the emulsion with the coagulation of the caoutchouc depends thus upon the removal or destruction of the protective colloids. This is accomplished by different means. The latex of the para rubber from the Amazon is coagulated by heat and smoke, while the latex from the same species of tree on the plantations of the Malay States is usually coagulated by treatment with acid. Boiling of the latex, the addition of formaldehyde, and simple dilution with water are other methods in use. Enzymes are also present associated with the protective colloid proteins but their function seems not to be connected with the coagulation of the caoutchouc. 

Isoprenoids with more than eight isoprene units are classified as polyterpenes Natural rubber (caoutchouc), formerly an important raw material for the rubber industry, is primarily obtained by coagulating the milk juice (latex) of Hevea bra-siliensis (Euphorbiaceae) growing in the Amazonian area of Brazil and southeastern Asia. It consists essentially of c -polyisoprene. The milky juice is an emulsion of this polyterpene in water stabilized by proteins as protecting colloids. 

The study of the physical and chemical properties of rubber has received a decided impetus as a result of recent developments in colloidal chemistry, for it cannot be denied that in caoutchouc, the fundamental substance from which commercial rubber is ma de, we have a typical colloidal body. Many of the processes in the manufacture of both the crude rubber, caoutchouc, and the finished product, rubber, such as the coagulation of the latex, find no explanation from the purely crystalloidal chemical standpoint. Unfortunately in the discussions on the subject it has not always been recognized that in most instances both the colloidal and crystalloidal processes take place simultaneously. Consequently important facts are often ignored by the extreme advocates of the colloidal and the purely chemical schools. Only by a proper perspective involving both views, can we arrive at the true explanation of many of the phenomena connected with the chemistry of rubber. 

The objections to be raised against the first and third methods, viz, heating and smoking, and evaporation, are that many of the undesirable constituents such as dirt, bark, resin, protective colloids, etc., are left in the coagulant, caoutchouc. Some of these substances can be removed, of course, by subsequent treatment such as grinding and washing, drying in air or vacuo, but mineral matter, resins, and proteins still remain and cannot be eliminated except by expensive processes. It must be confessed, however, that Para rubber obtained by the natives of Brazil is superior to that made by the most scientific methods yet devised on plantations. It is a matter not yet decided whether the superiority of Para rubber is due to the method, or to the inherent qualities of the latex. 

There is a want of conformity of opinion among different investigators with regard to what actually happens during the last step. If the particles are composed of liquid caoutchouc surrounded by a film of protective colloid, then we must conclude that a solidification occurs as well as coagulation. Some writers are inclined to the belief that a polymerization takes place whereby larger molecules are formed. According to E. Fickendey this ip a pure but not imposdble assumption for which we have no direct experimental proof. 

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