Detergents

substances or mixtures of substances used in aqueous solutions for removing soil from the surface of solid objects. Detergents include synthetic detergents, which are multicomponent mixtures of soaplike substances and various auxiliary components (mineral salts and organic additives); all types of commercial fatty soaps; and a number of natural products (for example, saponins and bile).

Alkali salts (potash from plant ash and natural soda), hydrophilic clays (such as bentonite clays), and the juice or water extracts of a number of plants have been used as detergents since ancient times. With the appearance of the soap-making industry in the 19th century, such natural detergents rapidly lost their industrial significance. The industrial production of synthetic detergents was first undertaken in Germany as early as the 1930’s. Since the 1950’s, the production of synthetic detergents has grown sharply in all industrially advanced countries, and the fraction of fatty soaps in the total production of detergents has been reduced significantly. As early as 1965, synthetic detergents accounted for 50–90 percent of the total production of detergents in the major capitalist countries (see Table 1).

The decrease in the production of fatty soaps has resulted from a decrease in the production of industrial soap. However, the production of toilet soap in all countries is increasing every year. In the USSR, the production of toilet soap in 1970 was 1.4 times greater than in 1965. The total production of synthetic detergents and soap (based on a 40 percent fatty acid content) in the USSR in 1965 was 1, 926, 000 tons (of which 144, 000 tons was synthetic detergents), and in 1972, 1, 757, 000 tons (of which 534, 000 tons was synthetic detergents).

Cleansing agents are the basis of all detergents and determine their properties. They are micelle-forming surface-active agents that impart cleansing capability to solutions (more properly, hemicolloidal systems). There are two classes of cleansing agents: ionogenic substances, which dissociate into ions in water, and nonionogenic substances, which do not undergo electrolytic dissociation. Ionogenic cleansing agents are called anion-active if the surface-active ions have a negative charge, cation-active if the surface-active ions are positively charged, and amphoteric, or ampholytic, if the surface-active ions have a negative charge in basic media and positive charge in acidic media. Anion-active cleansing agents are most widely used; they are the basis for the production of all fatty soaps and most synthetic detergents. Sodium or potassium salts of the higher fatty acids prepared from vegetable oil and animal fat are mainly used in the production of commercial fatty soaps.

The most important synthetic anion-active cleansing agents are salts of sulfonic acids and sulfonic acid esters (alkyl sulfonates, alkyl aryl sulfonates, and alkyl sulfates), and also sulfonated fats, oils, and fatty acids. Other anion-active detergents are produced in relatively small quantities.

Nonionogenic cleansing agents that are components of some detergents are second in volume of production, after anion-active agents. Most nonionogenic agents are polyhydroxyethylene (polyglycol) esters with various organic acids and ethers with various alcohols, alkylphenols, and alkylnaphthols, as well as polyhydroxyethylene derivatives of aliphatic amines and amides and mercaptans.

Cation-active and amphoteric substances account for a small percentage of the total volume of production of cleansing agents and are of limited industrial significance. The most important cation-active agents are tertiary ammonium and pyridine salts, which have bactericidal action. Molecules of amphoteric agents have both basic radicals (usually amino groups) and acid radicals (carboxyl, sulfonic, or sulfonic acid ester groups).

Synthetic detergents require the addition of a number of auxiliary agents, which improve their cleansing power. Alkali salts of weak inorganic acids (sodium carbonate and bicarbonate, sodium silicates, and various types of phosphates), neutral salts (sodium sulfate and chloride), and salts of peroxide acids, which have bleaching and disinfecting properties (sodium perborate and percarbonate), are added to detergent formulas. The organic components of detergents play an important role. Carboxymethyl cellulose prevents the resorption of soil from the detergent solution on the cleansed surface. Optical bleaches (dyes) eliminate the yellow hue of undyed fabrics. Hydrotropic substances increase the solubility of cleansing agents in water and accelerate their rate of dissolution.

Some detergents contain enzymes, which make possible removal of insoluble protein soils; organic bactericides (hexachlorophene and trichlorcarbanilide); and foam stabilizers (for example, alkanolamides) or foam extinguishers. Odoriferous substances (fragrances) are added to many detergents. The formulas of detergents are determined by their intended use and by economic and sanitary requirements.

Most currently marketed synthetic detergents (80–90 percent) are powders. Tablets, “vermicelli,” flakes, pastes, and liquids are also produced. Synthetic detergents are formulated for laundering, for washing dishes and cleaning household utensils, and for toilet and industrial use.

Laundry detergents are divided into the following groups: detergents for washing wool and silk fabrics, detergents for washing cotton and linen fabrics, all-purpose detergents for various types of fabrics (including chemical fibers), and detergents for washing greatly soiled items made of coarse fabrics. Modern synthetic laundry detergents are equal in quality to the best brands of fatty soaps, and their detergency, unlike that of soaps, is not decreased when removing acidic soils or if hard water is used. Table 2 shows the composition of powders produced in the USSR for washing cotton and linen fabrics (Era), wool and silk fabrics and fabrics made from synthetic fibers (Novost’), and all-purpose powder for any fabric (Lotos).

In light of the increasing pollution of the environment by industrial and household wastes, special attention is devoted to the development of new formulations for synthetic detergents composed of biologically “soft” substances—that is, substances that are easily degraded by bacteria under natural conditions. Preparations made with such substances (for example, derivatives of linear aliphatic acids and alcohols) are gradually replacing detergents containing biologically “hard” (nondegradable) components (for example, derivatives of branched alkylaromatic compounds).

Powdered synthetic detergents are most often produced by spray drying of a liquid composition. The composition is usually a highly disperse suspension containing 55–65 percent solids. When spray drying is impossible, powders are prepared by mixing the components. This method produces liquid and paste detergents. Automated production lines are widely used for the continuous production of detergents.