Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
aqueous polymer dispersions. Natural-rubber latices are the most widespread of the group.
Natural latex is the milky fluid obtained by cutting, or tapping, the outer bark of rubber-bearing plants (mainly the Para rubber tree, Hevea brasiliensis). Natural latex contains 34–37 percent natural rubber, 52–60 percent water, and small quantities of proteins, resins, sugar, and mineral substances. Synthetic latices are aqueous dispersions of synthetic rubber, produced by emulsion polymerization. Synthetic latices also include plastic dispersions, such as of polyvinyl chloride and polyvinyl acetate. Synthetic latices (synthetic dispersions) are products made by the dispersion of “finished” polymers in water. As a rule, such latices are prepared from rubber synthesized by the polymerization in solution of, for example, butyl rubber and isoprene rubber. The rubber solution formed in hydrocarbon solvent is emulsified in water; the hydrocarbon is then removed by distillation.
Latices are colloidal systems whose dispersed phase consists of spherical particles, or globules. The colloid-chemical characteristics of latices, such as the dimensions of the globules, the viscosity, the concentration, or the amount of dry residue (see Table 1), and the aggregative stability, have a substantial influence on the engineering properties of the latices during processing. The viscosity of highly concentrated latices is inversely proportional to the size of the globules. For this reason, agglomeration of the globules is carried out when it becomes necessary to lower the viscosity (for example, by freezing). Low-solid latices can be concentrated by centrifuging, by separation on standing, or by evaporation. The stability of latices is due to a protective layer adsorbed at the surface of the globules that prevents spontaneous coagulation. This layer consists of anionic, cationic, or nonionic surface-active materials, or emulsifiers. The properties of products and materials made from latices depend to a large extent on the chemical composition and structure of the polymer in question.
The production volume of latices constitutes about 10 percent of all elastomer production. Latices are economical and offer extremely varied possibilities for use in a number of branches of industry. Latices also make it possible to produce items that cannot be made from solid elastomers at all (for example, thin-walled seamless articles). The use of rubbers in latex form precludes the danger of premature vulcanization; this increases the possible scope of use of some valuable rubbers, such as vinyl pyridines and carboxylates. Latices can be used in the production of adhesives and dyes that are free of toxic and flammable solvents. The use of latices in the production of paper increases the paper’s strength, flexibility, moisture and oil resistance, and appearance. Latices are used in sizing textiles; in impregnating tire cord; in the production of tufted carpets, pile fabrics, and man-made furs (strengthening the pile and helping to preserve the shape of the articles); and as binders in the production of nonwoven fabrics. They are also used in treating natural leathers and to produce simulated ones. They are widely used in the production of polymer cements, flooring materials, road surfacing materials, and sealants. Latices are components of materials used to protect soils from wind erosion, and they form the basic ingredient of anticorrosion coatings. Because of their wide range of properties, synthetic latices have the greatest importance in modern technology.
REFERENCESNoble, R. J. Lateks ν tekhnike. Leningrad, 1962. (Translated from English.)
Blackley, D. C. High Polymer Latices, vols. 1–2. London-New York, 1966.
Plenkoobrazovanie iz lateksov. Moscow, 1970.
V. V. CHERNAIA and M. I. SHEPELEV