Laundry detergent, or washing powder, is a type of detergent (cleaning agent) that is added for cleaning laundry, commonly mixtures of chemical compounds including alkylbenzenesulfonates, which are similar to soap but are less affected by hard water. While detergent is still sold in powdered form, liquid detergents have been taking major market shares in many countries since their introduction in the 1950s.
Laundry detergent pods have also been sold within the United States since 2012 when they were introduced by Procter & Gamble as Tide Pods. Earlier instances of laundry detergent pods include Salvo tablets sold in the 1960s and 1970s.
From ancient times, chemical additives were used to facilitate the mechanical washing of clothing with water. The Italians used a mix of sulfur and water with charcoal to clean cloth. Egyptians added ashes and silicates to soften water. Soaps were the first detergents. The detergent effects of certain synthetic surfactants were noted in Germany in 1917, in response to shortages of soap during World War I. In the 1930s, commercially viable routes to fatty alcohols were developed, and these new materials were converted to their sulfate esters, key ingredients in the commercially important German brand FEWA, produced by BASF, and Dreft, the US brand produced by Procter and Gamble. Such detergents were mainly used in industry until after World War II. By then, new developments and the later conversion of aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of domestic use in the late 1940s.
The use of enzymes for laundry was introduced in the early part of the 1900s by Otto Rohm. Only in the latter part of the century with the availability of thermally robust bacterial enzymes did this technology become mainstream.
Soap is, by weight, relatively ineffective and it is highly sensitive to deactivation by hard water. By the 1950s, soap had almost been completely replaced by branched alkylbenzenesulfonates, but these detergents were found to be poorly biodegradable. Linear alkylbenzenesulfonates (LABs), however, proved to be both highly effective in cleaning and more biodegradable than the branched relatives. LABs remain the main detergents used domestically. Other detergents that have been developed include the linear alkylsulfonates and olefinsulfonates, which also resist deactivation by hard water. Both remain specialty products, for example only an estimated 60 million kilograms of the sodium alkylsulfonates are produced annually. 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 from so-called natural soaps.
Early in the introduction of sulfonate-based detergents, concerns were voiced over the low rates of biodegradation of the branched alkylbenzenesulfonates.  This problem was addressed by the introduction of linear alkylbenzenesulfonates.
A more profound problem arose from the heavy use of sodium triphosphate, which could comprise up to 50% by weight of detergents. The discharge of soluble phosphates into natural waters has led to problems with eutrophication, or the growth of living things, of lakes and streams, often where it is not desirable. The replacement of sodium triphosphate by zeolites offers some relief to this problem. With respect to the phosphate additives, between 1940 and 1970 "the amount of phosphates in city wastewater increased from 20,000 to 150,000 tons per year." With an increase in phosphates, especially in the absence of species feeding upon algae, algal blooms grow splendidly on the excess phosphorus and can produce toxins, killing fish, dolphins and plants. They can also indirectly cause oxygen depletion at greater depths, through microbial breakdown of dead algal cells. Most modern laundry detergents do not contain phosphates, but bring about water softening using zeolites.
Chemistry of detergents
In general, laundry detergents contain water softeners, surfactants, bleach, enzymes, brighteners, fragrances, and many other agents. The formulation is strongly affected by the temperature of the cleaning water and varies from country to country.
The major components of laundry detergents is anionic surfactants, alkaline builders, water softening agents and anti re deposition agents. Higher end detergents contain enzymes and optical brighteners. Some liquid detergents contain non ionic surfactants.
Many kinds of molecules and ions can serve as high-efficiency surfactants. They are often classified according to the charge of the molecule or ion, the three main classes being anionic, neutral, and cationic detergents. Anionic detergents are most commonly encountered for domestic laundry detergents. Detergents are ions or molecules that contain both polar and nonpolar components. The polar component allows the detergent to dissolve in the water, whereas the nonpolar portion solubilizes greasy ("hydrophobic") materials that are the usual target of the cleaning process. An estimated 6 billion kilograms of detergents are produced annually for domestic markets.
Modern detergent formulations – the entire product vs just the surfactant – contain several components. Three main ingredients are builders (50% by weight, approximately), the alkylbenzenesulfonate surfactant (15%), and bleaches (7%).
Builders (also called complexation or sequestering agents) are water softeners. The calcium and magnesium ions present in hard water can cause many detergents to form soap scum, which is ineffective for cleaning. These ions are removed by builders either through chelation or ion exchange. One of the earliest builders was sodium carbonate (washing soda), however this was not particularly effective. Phosphorus-based agents were introduced during the 1940s, beginning with sodium triphosphate and continuing with the introduction of HEDP, ATMP, EDTMP HDTMP and DTPMP. While effective, these agents are now known to have serious environmental consequences leading to a drive towards more environmentally benign phosphorous-free agents, modern examples include chelators such as citric acid, gluconic acid and EDTA; or ion exchange agents like zeolites.
The main targets of bleaches are oxidisible organic stains; which are usually of vegetable origin (e.g. chlorophyll, anthocyanin dyes, tannins, humic acids, and carotenoid pigments). Despite the name, modern beaching agents do not include household bleach (sodium hypochlorite). Laundry bleaches are typically stable adducts of hydrogen peroxide, such as sodium perborate and sodium percarbonate, these are inactive as solids but will react with water to release hydrogen peroxide which performs the bleaching action. "Bleach activators" such as tetraacetylethylenediamine (TAED) may also be used, these react with hydrogen peroxide to produce peracetic acid, which is an even more effective bleach.
The amounts of enzyme can be up to about 2% by weight of the product. These agents are required to degrade recalcitrant stains composed of proteins, fats, or carbohydrates. Each type of stain requires a different type of enzyme, i.e., protease for proteins, lipases for greases, and amylases for carbohydrates.
Many other ingredients are added depending on the specific application. Such additives modify the foaming properties of the product by either stabilizing or counteracting foam. Other ingredients increase or decrease the viscosity of the solution, or solubilize other ingredients. Corrosion inhibitors counteract damage to washing equipment. "Dye transfer inhibitors" prevent dyes from one article from colouring other items. "Antiredeposition agents" are used to prevent fine soil particles from reattaching to the product being cleaned. Carboxymethyl cellulose is used for this purpose.
A number of ingredients affect aesthetic properties of the item to be cleaned or the detergent itself before or during use. These agents include optical brighteners, fabric softeners, and colourants. A variety of perfumes are also components of modern detergents, provided that they are compatible with the other components and do not affect the colour of the cleaned item. The perfumes are typically a mixture of many compounds, a popular component being cyclohexyl salicylate, which is related to oil of wintergreen.
Phosphates in detergent became an environmental concern in the 1950s and the subject of bans in later years. Phosphates make laundry cleaner but can also cause harmful algal bloom as the wastewater goes back to the natural environment.
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- Derbyshire, David (24 February 2008). "Don't bother with pre-wash (you're just wasting 6billion litres of water a year)". Mail Online. Retrieved 30 September 2010.
- About.com, Housewares/Appliances, What is HE Laundry Detergent & When are High-Efficiency Detergents Used by Mariette Mifflin
- Campbell tips for detergents chemistry, surfactants, and history related to laundry washing, destaining methods and soil.