Adetergent is aformulated and commercially sold product for cleaning that containssurfactants plus other components.[1] Detergents comprisesurfactants as main functional components to removehydrophobic grease ordirt bydispersing them in water. They often further comprise water (to facilitate application),builders (to soften water),enzymes (for breaking down proteins, fats, or starches), anddyes orfragrances (to improve the user's sensory experience).
Common surfactants used in detergents arealkylbenzene sulfonates, which aresoap-like compounds that are more soluble than soap inhard water, because the polarsulfonate is less likely than the polarcarboxylate of soap to bind to calcium and other ions found in hard water.
The worddetergent is derived from theLatin adjectivedetergens, from the verbdetergere, meaning to wipe or polish off. Detergent can be defined as asurfactant or amixture of surfactants with cleansing properties when indilutesolutions.[1] However, conventionally, detergent is used to mean synthetic cleaning compounds as opposed tosoap (a salt of the naturalfatty acid), even though soap is also a detergent in the true sense.[2] In domestic contexts, the termdetergent refers to household cleaning products such aslaundry detergent ordish detergent, which are in fact complex mixtures of different compounds, not all of which are by themselves detergents.
Detergency is the ability to remove unwanted substances termed 'soils' from a substrate (e.g., clothing).[3]
Detergents are formulated products used for cleaning, i. e. mixtures of various chemical components that are selected and mixed to achieve a good cleaning performance and applicants satisfaction. Detergents comprise surfactants or a surfactant as main functional component, aside usually water and auxiliary materials (builders, enzymes, etc.).
Surfactants are a group of compounds with anamphiphilic structure, where each molecule has ahydrophilic (polar) head and a longhydrophobic (non-polar) tail. The hydrophobic portion of these molecules may be straight- or branched-chainhydrocarbons, or it may have asteroid structure. The hydrophilic portion is more varied, they may beionic or non-ionic, and can range from a simple to a relatively elaborate structure.[4] Surfactants are called so since they can decrease thesurface tension of water. Their dual nature facilitates the mixture of hydrophobic compounds (like oil and grease) with water. Because air is not hydrophilic, surfactants are alsofoaming agents to varying degrees.
Surfactant molecules aggregate to formmicelles, which makes them soluble in water. The hydrophobic group of the surfactant is the main driving force of micelle formation, its aggregation forms the hydrophobic core of the micelles. The micelle can remove grease, protein or soiling particles. The concentration at which micelles start to form is thecritical micelle concentration (CMC), and the temperature at which the micelles further aggregate to separate the solution into two phases is the cloud point when the solution becomes cloudy and detergency is optimal.[4]
Many detergents work better in analkalinepH. The properties of detergents are dependent on the molecular structure of themonomer. The ability to foam may be determined by the head group, for exampleanionic surfactants are high-foaming, while nonionic surfactants may be non-foaming or low-foaming.[5]
Typical anionic surfactants arealkylbenzene sulfonates. Thealkylbenzene portion of theseanions islipophilic and the sulfonate ishydrophilic. Two varieties have been popularized, those with branchedalkyl groups and those with linear alkyl groups. The former were largely phased out in economically advanced societies because they are poorly biodegradable.[7]
Anionic surfactants are the most common form of surfactants, and an estimated 6 billion kilograms of anionic surfactants are produced annually for the domestic markets.
Bile acids, such asdeoxycholic acid (DOC), are anionic surfactants produced by the liver to aid in digestion and absorption of fats and oils.
Three kinds of anionic surfactants: a branched sodium dodecylbenzenesulfonate, linearsodium dodecylbenzenesulfonate, and a soap.
Cationic surfactants are similar to anionic ones, butquaternary ammonium replaces the hydrophilic anionic sulfonate group. Theammonium sulfate center is positively charged.[7] Cationic surfactants generally have poor detergency.
Non-ionic surfactants are characterized by their uncharged, hydrophilic headgroups. Typical non-ionic surfactants are based onpolyoxyethylene or aglycoside. Common examples of the former includeTween,Triton, and the Brij series. These materials are also known as ethoxylates or PEGylates and their metabolites,nonylphenol. Glycosides have a sugar as their uncharged hydrophilic headgroup. Examples includeoctyl thioglucoside andmaltosides. HEGA and MEGA series surfactants are similar, possessing asugar alcohol as headgroup.
Amphoteric or zwitterionic surfactants havezwitterions within a particular pH range, and possess a net zero charge arising from the presence of equal numbers of +1 and −1 charged chemical groups. Examples includeCHAPS.
Soap is known to have been used as a surfactant for washing clothes since theSumerian time in 2,500 B.C.[8] Inancient Egypt,soda was used as a wash additive. In the 19th century, synthetic surfactants began to be created, for example from olive oil.[9]Sodium silicate (water glass) was used in soap-making in the United States in the 1860s,[10] and in 1876,Henkel sold a sodium silicate-based product that can be used with soap and marketed as a "universal detergent" (Universalwaschmittel) in Germany. Soda was then mixed with sodium silicate to produce Germany's first brand name detergent Bleichsoda.[11] In 1907, Henkel also added a bleaching agentsodium perborate to launch the first 'self-acting' laundry detergentPersil to eliminate the laborious rubbing of laundry by hand.[12]
During theFirst World War, there was a shortage of oils and fats needed to make soap. In order to find alternatives for soap, synthetic detergents were made in Germany by chemists using raw material derived fromcoal tar.[13][14][9] These early products, however, did not provide sufficient detergency. In 1928, effective detergent was made through thesulfation offatty alcohol, but large-scale production was not feasible until low-cost fatty alcohols become available in the early 1930s.[15] The synthetic detergent created was more effective and less likely to form scum than soap in hard water, and can also eliminate acid and alkaline reactions and decompose dirt. Commercial detergent products with fatty alcohol sulphates began to be sold, initially in 1932 in Germany byHenkel.[15] In the United States, detergents were sold in 1933 byProcter & Gamble (Dreft) primarily in areas with hard water.[14] However, sales in the US grew slowly until the introduction of 'built' detergents with the addition of effectivephosphate builder developed in the early 1940s.[14] The builder improves the performance of the surfactants by softening the water through thechelation of calcium and magnesium ions, helping to maintain an alkaline pH, as well as dispersing and keeping the soiling particles in solution.[16] The development of the petrochemical industry after the Second World War also yielded material for the production of a range of synthetic surfactants, andalkylbenzene sulfonates became the most important detergent surfactants used.[17] By the 1950s,laundry detergents had become widespread, and largely replaced soap for cleaning clothes in developed countries.[15]
Over the years, many types of detergents have been developed for a variety of purposes, for example, low-sudsing detergents for use in front-loading washing machines, heavy-duty detergents effective in removing grease and dirt, all-purpose detergents and specialty detergents.[14][18] They become incorporated in various products outside of laundry use, for example indishwasher detergents, shampoo, toothpaste, industrial cleaners, and in lubricants and fuels to reduce or prevent the formation of sludge or deposits.[19] The formulation of detergent products may includebleach, fragrances, dyes and other additives. The use ofphosphates in detergent, however, led to concerns overnutrient pollution and demand for changes to the formulation of the detergents.[20] Concerns were also raised over the use of surfactants such as branched alkylbenzene sulfonate (tetrapropylenebenzene sulfonate) that lingers in the environment, which led to their replacement by surfactants that are more biodegradable, such as linear alkylbenzene sulfonate.[15][17] Developments over the years have included the use ofenzymes, substitutes for phosphates such aszeolite A andNTA,TAED asbleach activator, sugar-based surfactants which are biodegradable and milder to skin, and othergreen friendly products, as well as changes to the form of delivery such as tablets, gels andpods.[21][22]
One of the largest applications of detergents is for household and shop cleaning includingdish washing and washinglaundry. These detergents are commonly available as powders or concentrated solutions, and the formulations of these detergents are often complex mixtures of a variety of chemicals aside from surfactants, reflecting the diverse demands of the application and the highly competitive consumer market. These detergents may contain the following components:[21]
^abEduard Smulders, Wolfgang Rybinski, Eric Sung, Wilfried Rähse, Josef Steber, Frederike Wiebel, Anette Nordskog, "Laundry Detergents" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim.doi:10.1002/14356007.a08_315.pub2
^Werner Dabelstein, Arno Reglitzky, Andrea Schütze, Klaus Reders "Automotive Fuels" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheimdoi:10.1002/14356007.a16_719.pub2
^Doyle, DA; Morais Cabral, J; Pfuetzner, RA; Kuo, A; Gulbis, JM; Cohen, SL; Chait, BT; MacKinnon, R (1998). "The structure of the potassium channel: molecular basis of K+conduction and selectivity".Science.280 (5360):69–77.Bibcode:1998Sci...280...69D.doi:10.1126/science.280.5360.69.PMID9525859.
