LATEX

colloidal suspension, either the milky white liquid emulsion found in the cells of flowering plants such as the Para rubber tree (Hevea brasiliensis) or any of various manufactured water emulsions consisting of synthetic rubber or plastic. The plant product is a complex mixture of substances, including various gum resins, fats, or waxes and, in some instances, poisonous compounds, suspended in a watery medium in which salts, sugars, tannins, alkaloids, enzymes, and other substances are dissolved. It is produced especially by the cells of plants of the family Asclepiadaceae but also by those in the families Apocynaceae, Sapotaceae, Euphorbiaceae, Papaveraceae, Moraceae, and Asteraceae (Compositae). The latex circulates in branched tubes that penetrate the tissues of the plant in a longitudinal direction, conducting substances and acting as an excretory reservoir. The chief commercial products of latex are rubber, gutta-percha, chicle, and balata (qq.v.). The latex of the opium poppy (Papaver somniferum) is the source of opium and the alkaloid morphine. In the paint and coatings industry, aqueous dispersion polymers, or polymer emulsions called latexes, have come into widespread use since the late 1940s. These synthetic latexes include a binder dispersed in the water and form films by fusion of the plastic particles as the water evaporates. The properties of the filmssuch as hardness, flexibility, toughness, adhesion, colour retention, and resistance to chemicalsdepend on the composition of the plastic. Polymers based on butadiene, styrene, vinyl acetate, and acrylic monomers have been used commercially.