Any substance that reduces the surface tension of water, specifically a surface-active agent that concentrates at oil-water interfaces, exerts emulsifying action, and thus aids in removing soils. The older and still widely used types are the common sodium soaps of fatty acids, which are relatively weak. The much stronger synthetic detergents are classed as anionic, cationic, or nonionic, depending on their mode of chemical action. The latter functions by a hydrogen-bonding mechanism. The most widely used group comprises linear alkyl sulfonates (LAS), often aided by “builders.” LAS are preferable to alkyl benzene sulfonates (ABS) because they are readily decomposed by microorganisms (biodegradable). LAS are straight-chain compounds having 10 or more carbon atoms in the chain. The branched-chains characteristic of ABS resist decomposition; these have been largely replaced by LAS because of water pollution.See Surface Tension; Emulsion; Wetting Agent; Soap (1); Alkylate (3); Biodegradability; Eutrophication; Builder Detergent.
