Detergent Builders

Detergent builders are chemical compounds that are added to a detergent product to improve its cleaning properties. In this broad definition, cleaning is measured by the net amount of soil removed; that is, the total soil removed, less the amount that is redeposited. Thus only those materials are considered to be builders that perform both functions: (1) increasing the removal of soil and (2) preventing or minimizing its redeposition.

These overall functions of detergent builders in turn result from a combination of several individual effects:

• Removing or sequestrating Ca2+ and Mg2+ ions from both the wash water and the soiled wash load
• Providing an alkaline environment
• Enhancing surfactant performance
• Desorbing soil (from the wash load) and stabilizing its dispersion in the wash liquor.

In the absence of or with low concentrations of Ca ions, both the surfactant performance is improved and the destabilization (or flocculation) of soil dispersion is prevented. Ca2+ and Mg2+ ions are introduced into the wash system mainly in the wash water, in which they constitute the major sources of hardness, although some hardness ions can enter the wash liquid from soil in the wash load. The immediate deleterious effects of these ions consist of precipitating the surfactant (when anionic surfactants are used) and of promoting soil flocculation (by a colloidal destabilization mechanism). However, the beneficial effect of detergent builders exceed the mere elimination of these deleterious effects. Builders improve detergent performance even when nonionic surfactants are used and result in better soil stabilization (and hence removal), even when distilled water is used. Furthermore, the alkaline environment (pH >9.5) produced by detergent builders not only favors both these actions but also provides ions (usually Na) that react with the fatty acids originating from the sebaceous skin secretions (a common fabric soil) to form soaps. Those soaps, In turn, assist the surfactant in the removal and emulsification of nonpolar soil components.

When major growth of synthetic detergent formulations was first occurring shortly after World War II, sodium tripolyphosphate (STPP) emerged as the predominant and almost exclusive choice among builder materials. In the late 1960's, environmental attention focused on water eutrophication problems, which had become especially serious in the North American Great Lakes. The discharge of phosphates from various sources as largely responsible for this phenomenon and legislation to limit or ban the use of phosphates in detergents began to be enacted in many states by the late 1970s. Similar actions in some Western European countries and in Japan followed. Nonetheless, although STPP consumption has declined in developed countries, as a result of such bans, it is still the leading detergent builder.

The search for suitable substitutes for STPP intensified during the 1970s. Among the newer builder materials in commercial production, the sodium salt of nitriloacetic acid (NTA) and zeolite A (a crystalline sodium aluminosilicate) are the most significant. Of these two, NTA is not used for detergents in the United States, given a history of doubts about its safety that culminated in an August 1985 ban by the New York State government on the sale of household products containing NTA. NTA is used, however, in Canada and in many Western European countries. Zeolite A, which poses no environmental problems, has gained wide acceptance for nonphosphate (or low-phosphate) formulations in the United States, Western Europe, and Japan. However, neither of these two substitutes matches STPP's overall performance.

Other STPP substitutes currently in use include long-established commodity chemicals, the principal examples of which are sodium carbonate, citrates (in particular sodium citrate), and sodium silicate. None is used singly; rather, they serve as cobuilders with other phosphate substitutes.

This report examines the economics and manufacturing technology for STPP (from wet process phosphoric acid), NTA, and zeolite A. It also presents a brief overview of the detergent builder business and surveys the industry status with respect to the three builders examined.