A white, tacky, aqueous suspension of a hydrocarbon polymer occurring naturally in some species of trees, shrubs, or plants, or made synthetically. The most important natural latex is that of the tropical tree Hevea braziliensis, which was the only source of rubber up to 1945. It is composed of globules of rubber hydrocarbon coated with protein; the particles are of irregular shape, varying from 0.5 to 3 microns in diameter; the suspension is stabilized by electric charges. The composition is about 60% water, 35% hydrocarbon, 2% protein, and low percentages of sugars and inorganic salts. For commercial purposes, rubber latex can be concentrated by evaporation or centrifugation. Ammonia is added as a preservative. Coagulation is induced by addition of acetic or formic acid. A vulcanized form is available. Natural latex is used in the manufacture of thin articles (surgeons' gloves and other medical equipment), as an adhesive, in foamed products, and for coating various products such as tire cord. Conversion of latex to gasoline via zeolite catalysts has been reported. Other sources of rubber-containing latex are guayule, a shrub grown in Mexico and the southwestern U.S., and several types of dandelions and related species. The botanical function of latex in the plant is unknown. Synthetic latexes are made by emulsion polymerization techniques from styrene-butadiene copolymer, acrylate resins, polyvinyl acetate, and similar materials. Their particle size is much smaller than in natural latex, ranging from 0.05 to 0.15 micron; thus, they are truly colloidal suspensions. Their chief use is as a binder in exterior and interior paints, replacing drying oils; they are also used for foams and coatings.See Guayule; Gutta Percha; Electrophoresis; Paint; Emulsion; “Vultex.”.
