Rubber

RUBBER (Cautschuk, Kautschuk, Gummi elasticum, India rubber), purified coagulated milky sap obtained from many species of tropical plants growing wild in South America, Asia, and Africa, and now obtained primarily from various varieties of Hevea cultivated on the Malay Peninsula and the Malay Archipelago, especially Hevea brasiliensis (Humboldt, Bonpl.), Mull. The other numerous plants that yield rubber (Manihot Glaziovii, Castilloa elastica, Ficus elastica, Hancornia speciosa, Landolphia, and others) belong to the families Moraceae, Euphorbiaceae, Apocynaceae, Campanulaceae, Asclepiadaceae, and others. For medical and pharmaceutical purposes, almost exclusively Para-Kautschuk from Hevea is used. Fresh sap from Hevea contains: rubber—31.7%; nitrogenous bitter substances—7%; substances soluble in water and alcohol—2.9%; protein bodies—1.9%; wax—0.13%; resin—traces; water—56.4%. Purified rubber consists mainly of the hydrocarbon polyterpene (C₁₀H₁₆)_n (rubber-gutta, according to Tschirch); upon dry distillation, rubber forms, along with other hydrocarbons (cinene, caoutchine, C₁₀H₁₆, heveene, C₁₅H₂₄), mainly isoprene C₅H₈ or CH₂:C(CH₃).CH:CH₂, which upon polymerization can again be converted back into rubber. Based on these data and a whole series of others obtained experimentally (ozonides, the action of halides, nitrous acid, etc.), the German scientist Harries, a great specialist in matters of rubber, initially advocated for an eight-membered formula for the basic hydrocarbon of rubber: CH₃-C-CH₂-CH₂-CH II

CH-CH₂-CH₂-C-CH₃, which, however, he subsequently replaced with a cyclic product of the condensation of five isoprene molecules in the form of a ring of 20 links, and finally settled on the schematic formula: CH₂.(CH₃)C:CH.CH₂.CH₂.CH:C(CH₃).CH₂]n, which does not predetermine how many isoprene molecules are condensed. At present, it is believed that rubber contains a mixture of hydrocarbons of varying degrees of polymerization, partly with an open chain, partly cyclic, with rings of different sizes. Rubber is a colloidal mass ranging in color from yellow to brown, non-sticky, non-brittle, non-plastic, but elastic; at 0° it loses its elasticity, at 50° it becomes soft, at 120° it begins to melt, and at 180° it becomes liquid; upon cooling, it does not solidify and remains thick and sticky. Specific gravity 0.92–0.96. It does not conduct electricity; when rubbed, it becomes electrified itself. Unlike gutta-percha, it does not dissolve in hot water and does not become plastic; it dissolves relatively easily in gasoline, benzene, chloroform, carbon disulfide, and especially easily in a mixture of 100 parts carbon disulfide and 6–8 parts absolute alcohol, as well as in so-called rubber oil (a product of the dry distillation of rubber). It was noted (Goodyear; 1839) that the resistance of rubber to fluctuations in temperature and many reagents and solvents is greatly increased if it is subjected to treatment and impregnation with sulfur; this process is called "vulcanization"; it is produced in various ways: by heating, in the cold, with the help of solvents, etc.; the maximum amount of sulfur with which rubber can combine reaches 38% and corresponds to the formula (C₁₀H₁₆S₂)n. Rubber is used in the form of a vulcanized elastic mass for the manufacture of so-called rubber goods (syringes, tubes, stoppers, ice bags, gloves, galoshes, tires, balls, rubber bands, toys, and many others) and in the form of a solid mass (ebonite) for the manufacture of cases, handles for instruments, insulators, and many medical devices (uterine rings, dilators, plates for artificial teeth, etc.). Unvulcanized rubber is used for the manufacture of very sticky rubber plasters and for obtaining rubber solutions (rubber cement). It is recommended to store rubber tubes and gloves at a temperature of +15° in carbolic water with an admixture of 5% glycerin, and it is best to store other rubber objects in a suspended state in well-closed jars or in tightly closing cabinets in a slightly humid atmosphere (a vessel with water is kept constantly open in the jar or cabinet). Fats and oils have a harmful effect on rubber: it swells, softens, and loses its elasticity. In the event that rubber objects harden, they are washed with warm (40°) water containing 5% ammonia and kneaded. After 15 minutes, the objects are kneaded again for a short time in warm (40°) water containing 5% glycerin, after which the restored rubber items are dried well and placed in a vessel or cabinet. Lit.: Wolf-Czapek K., Kautschuk, seine Gewinnung und Verarbeitung, L., 1926; Chaplet A., Manuel de l'industrie du caoutchouc, P., 1925; Harries C., Untersuchungen über die natürlichen u. künstlichen Kautschukarten, Berlin, 1919.