detergent

detergent

[dih-tur-juhnt]
detergent, substance that aids in the removal of dirt. Detergents act mainly on the oily films that trap dirt particles. The detergent molecules have a hydrocarbon portion, soluble in oil, and an ionic portion, soluble in water. The detergent acts as an emulsifier, i.e., by bridging the water and oil phases, it breaks the oil into tiny droplets suspended in water. The disruption of the oil film allows the dirt particles to become solubilized. Soap, the sodium salt of long-chain fatty acids, is a good detergent although it has some disadvantages, e.g., it forms insoluble compounds with certain salts found in hard water thus diminishing its effectiveness, and in acid solutions, frequently used in industry, it is decomposed (thus precipitating the free fatty acid of the soap). Synthetic detergents were produced experimentally in France before the middle of the 19th cent. and were further developed in Germany during World War I. However, not until the 1930s were chemical processes developed that made production in quantity feasible in any country. Synthetic detergents were first developed for commercial use in the 1950s. Detergents are classified as anionic, or negatively charged, e.g., soaps; cationic, or positively charged, e.g., tetraalkyl ammonium chloride, used as fabric softeners; nonionic, e.g., certain esters made from oil, used as degreasing agents in industry; and zwitterionic, containing both positive and negative ions on the same molecule. Detergents are incorporated in such products as dry-cleaning solutions, toothpastes, antiseptics, and solutions for removing poison sprays from vegetables and fruit. Laundry detergent preparations may contain substances called builders, which enhance cleansing; however, phosphate-containing builders have been found to contribute to eutrophication of waterways and their use has been banned in many areas. Detergents that can be decomposed by microorganisms are termed biodegradable. Detergents are important chemicals used for enhanced petroleum recovery.

Any of various surfactants (substances that reduce surface tension) used to dislodge dirt from soiled surfaces and retain it in suspension, allowing it to be rinsed away. The term usually refers to synthetic substances and excludes soaps. The characteristic features of a molecule of any detergent are a hydrophilic (water-attracting) end and a hydrophobic (oil-attracting) end. In ionic detergents, the hydrophilic property is conferred by the ionized part of the molecule. In nonionic detergents, hydrophilicity is based on the presence of multiple hydroxyl groups or other hydrophilic groups. Besides those used in water to clean dishes and laundry, detergents that function in other solvents are used in lubricating oils, gasolines, and dry-cleaning solvents to prevent or remove unwanted deposits. They are also used as emulsifying agents (see emulsion).

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A detergent (as a noun) is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning. As an adjective pertaining to a substance, it (or "detersive") means "cleaning" or "having cleaning properties"; "detergency" indicates presence or degree of cleaning property.

Composition

Detergents, especially those made for use with water, often include different components such as:

  • Surfactants to 'cut' (dissolve) grease and to wet surfaces
  • Abrasive to scour
  • Substances to modify pH or to affect performance or stability of other ingredients, acids for descaling or caustics to break down organic compounds
  • Water softeners to counteract the effect of "hardness" ions on other ingredients
  • oxidants (oxidizers) for bleaching, disinfection, and breaking down organic compounds
  • Non-surfactant materials that keep dirt in suspension
  • Enzymes to digest proteins, fats, or carbohydrates in stains or to modify fabric feel
  • Ingredients that modify the foaming properties of the cleaning surfactants, to either stabilize or counteract foam
  • Ingredients that affect aesthetic properties of the item to be cleaned, or of the detergent itself before or during use, such as optical brighteners, fabric softeners, colors, perfumes, etc.
  • Ingredients such as corrosion inhibitors to counteract damage to equipment with which the detergent is used
  • Preservatives to prevent spoilage of other ingredients
  • Washing agents may contain soap for the purpose of reducing foam rather than cleaning fabric.

Sometimes materials more complicated than mere mixtures of compounds are said to be detergent. For instance, certain foods such as celery are said to be detergent or detersive to teeth.

Types

There are several factors that dictate what compositions of detergent should be used, including the material to be cleaned, the apparatus to be used, and tolerance for and type of dirt. For instance, all of the following are used to clean glass. The sheer range of different detergents that can be used demonstrates the importance of context in the selection of an appropriate glass-cleaning agent:

  • a chromic acid solution—to get glass very clean for certain precision-demanding purposes, namely in analytical chemistry
  • a high-foaming mixture of surfactants with low skin irritation—for hand-washing of drink glasses in a sink or dishpan
  • other surfactant-based compositions—for washing windows with a squeegee, followed by rinsing
  • any of various non-foaming compositions—for glasses in a dishwashing machine
  • an ammonia-containing solution—for cleaning windows with no additional dilution and no rinsing
  • ethanol or methanol in Windshield washer fluid—used for a vehicle in motion, with no additional dilution
  • glass contact lens cleaning solutions, which must clean and disinfect without leaving any eye-harming material that would not be easily rinsed off.

Terminology

Sometimes the word detergent is used to distinguish a cleaning agent from soap. During the early development of non-soap surfactants as commercial cleaning products, the term syndet, short for synthetic detergent was promoted to indicate the distinction. The term never became popular and is incorrect, because most soap is itself synthesized (from glycerides). The term soapless soap also saw a brief vogue. There is no accurate term for detergents not made of soap other than soapless detergent or non-soap detergent.

Plain water, if used for cleaning, is a detergent. Probably the most widely-used detergents other than water are soaps or mixtures composed chiefly of soaps. However, not all soaps have significant detergency and, although the words "detergent" and "soap" are sometimes used interchangeably, not every detergent is a soap.

The term detergent is sometimes used to refer to any surfactant, even when it is not used for cleaning. This terminology should be avoided as long as the term surfactant itself is available.

History

The detergent effects of certain synthetic surfactants were noted in 1913 by A. Reychler, a Belgian chemist. The first commercially available detergent taking advantage of those observations was Nekal, sold in Germany in 1917, to alleviate World War I soap shortages. Detergents were mainly used in industry until World War II. By then new developments and the later conversion of USA aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of household use, in the late 1940s. In the late 1960s biological detergents, containing enzymes, better suited to dissolved protein stains, as egg stains, were introduced in the USA by Procter & Gamble.

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