gutta-percha
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gutta-percha
Gutta-Percha
a metabolic product of gutta-percha-yielding plants. The main constituent of gutta-percha (up to 90 percent)—high-molecular-weight trans-polyisoprene (gut-ta) with the empirical formula (C5H8)n—is an isomer of cis-polyisoprene, a hydrocarbon of natural rubber. The average molecular weight of gutta is about 50,000. Besides gutta, industrial gutta-percha contains resins, proteins, moisture, and other substances.
At room temperature, industrial gutta-percha is a solid skinlike substance that is white to yellowish-brown in color, with a density of 0.945–0.955 g/cm3, and an index of refraction nD20 = 1.523. Gutta-percha is resistant to the action of acids, including hydrochloric and hydrofluoric acids. When heated (50°-100° C), gutta-percha softens and becomes plastic and soluble in aromatic and chlorinated hydrocarbons. Its most valuable properties are waterproofness (moisture absorption in two years does not exceed 0.2 percent) and high electric insulation properties (dielectric permeability, 2.6; specific volume electric resistance 1012 ohm․m [1014 ohm •cm]). Like natural rubber, gutta-percha can be vulcanized with sulfur. The tensile strength of vulcanized gutta-percha is 17–30 meganewtons/m2 (170–300 kilograms-force/cm2) and the relative elongation, 500–550 percent.
Gutta-percha is used mainly as insulation for underwater cables and in the manufacture of acid-resistant and adhesive substances. The use of gutta-percha is declining because it is being replaced by synthetic trans-polyisoprene, trans-polychloroprene (so-called synthetic gutta-percha), and some other synthetic polymers.
REFERENCES
Voinovskii, A. B. Guttapercha. Moscow-Leningrad, 1951.Spravochnik rezinshchika. Materialy rezinovogo proizvodstva. Moscow, 1971. Page 251.