Chemistry: A Molecular Approach
Laundry detergent, or washing powder, is a substance which is a type of detergent (cleaning agent) that is added for cleaning laundry. Most commonly, "detergent" refers to mixtures of chemical compounds including alkylbenzenesulfonates, which are similar to soap but are less affected by "hard water." In most household contexts, the term detergent refers to laundry detergent vs hand soap or other types of cleaning agents. Most detergent is delivered in powdered form.
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]History
From ancient times, chemical additives were recognized for their ability to facilitate the mechanical washing with water. Egyptians added ashes and silicates to soften water. Soaps were the first detergents.[2] 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 1930's, commercially viable routes to fatty alcohols had been 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 Proctor 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 householddetergents, 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.[
Presently soap has largely been displaced as the main cleaning agent in developed countries. Soap is, by weight, relatively ineffective, and it is highly sensitive to deactivation by hard water. By the 1950's 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 forsynthetic detergent was promoted to indicate the distinction from so-called natural soaps.
]Chemistry of detergents
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.
]Components
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
Builders are water softeners. These chemical compounds are agents that remove calcium ions by complexation or precipitation. Typical builders aresodium carbonate, complexation agents, soap, andzeolites. They function by sequestering or precipitating the problematic ions. One of the most common builders is sodium triphosphate, which is used on very large scale for this application.
]Bleach
The main targets of bleaches are of vegetable origin include chlorophyll, anthocyanin dyes, tannins, humic acids, and carotenoid pigments. Most bleaches in laundry detergents are oxidizers, e.g. sodium perborate or sodium hypochlorite, Additionally, other agents are added as "bleach activators", to enhance the effectiveness of the bleaching agent, a popular one is tetraacetylethylenediamine.
]Enzymes
Many laundry detergents contain enzymes. 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.
]Other ingredients
Many other ingredients are added depending on the specific application. Such additives modify the foaming properties of the product by eitherstabilizing 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 includeoptical 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.
]Environmental concerns
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 arises from the heavy use of sodium triphosphate, which can comprise up to 50% by weight of detergents. The discharge of soluble phosphates into natural waters has led to problem with eutrophication of lakes and streams. The replacement of sodium triphosphate by zeolites offers some releif to this problem. With respect to the phosphate additives, between 1940 and 1970 "the amount ofphosphates in city wastewater increased from 20,000 to 150,000 tons per year." With the increase in phosphates, algal blooms grew splendidly on the excess phosphorus and consumed most of the oxygen in the waters, killing fish and plants.
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