Skip to main content
Chemistry LibreTexts

21.2: Synthetic Detergents

  • Page ID
    152269
  • Learning Objectives

    • Describe different types of detergents.
    • List the key components of detergents and their functions.

    A detergent is a surfactant or a mixture of surfactants with cleansing properties in dilute solutions ((Figure \(\PageIndex{1}\))) . These substances are usually alkylbenzene sulfonates, a family of compounds that are similar to soap but are more soluble in hard water, because the polar sulfonate (of detergents) is less likely than the polar carboxylate (of soap) to bind to calcium and other ions found in hard water.

    In domestic contexts, the term detergent by itself refers specifically to laundry detergent or dish detergent, as opposed to hand soap or other types of cleaning agents. Detergents are commonly available as powders or concentrated solutions. Detergents, like soaps, work because they are amphiphilic: partly hydrophilic (polar) and partly hydrophobic (non-polar). Their dual nature facilitates the mixture of hydrophobic compounds (like oil and grease) with water. Because air is not hydrophilic, detergents are also foaming agents to varying degrees.

     

    Detergents.png

    Figure \(\PageIndex{1}\) Detergents. Source: Wikipedia

    Detergents are classified into three broad groupings, depending on the electrical charge of the surfactants.

    Anionic detergents

    Typical anionic detergents are alkylbenzenesulfonates (ABS). The alkylbenzene portion of these anions is lipophilic and the sulfonate is hydrophilic. An estimated 6 billion kilograms of anionic detergents are produced annually for domestic markets. Two different varieties have been popularized, those with branched alkyl groups and those with linear alkyl groups (see Figure \(\PageIndex{2}\)).

    Branched Alkylbenzenesulfonates: Nonbiodegradable

    Branched alkylbenzene sulfonates (BAS) were first introduced in the early 1930s and saw significant growth from the late 1940s onwards,[3] in early literature these synthetic detergents are often abbreviated as syndets.

    Compared to traditional soaps BAS offered superior tolerance to hard water and better foaming.[5] However, the highly branched tail made it difficult to biodegrade.[6] BAS was widely blamed for the formation of large expanses of stable foam in areas of wastewater discharge such as lakes, rivers and coastal areas (sea foams), as well as foaming problems encountered in sewage treatment[7] and contamination of drinking water.[8] As such BAS was phased out of most detergent products during the 1960s, being replaced with linear alkylbenzene sulfonates (LAS). It is still important in certain agrochemical and industrial applications, where rapid biodegradability is of reduced importance.

    Linear Alkylbenzensulfonates: Biodegradable

    Linear alkylbenzene sulfonates (LAS) are prepared industrially by the sulfonation of linear alkylbenzenes (LABs), which can themselves be prepared in several ways.[2] The term "linear" refers to the starting alkenes rather than the final product. The compound biodegrades far more quickly than BAS, making it the safer choice over time. It is biodegraded rapidly under aerobic conditions with a half-life of approximately 1–3 weeks. Under anaerobic conditions it degrades very slowly or not at all, causing it to exist in high concentrations in sewage sludge, but this is not thought to be a cause for concern as it will rapidly degrade once returned to an oxygenated environment.

    clipboard_e2336b4e590e5612485438cf82383091e.png

    Figure \(\PageIndex{2}\) Three kinds of anionic detergetns: a branched sodium dodecylbenzenesulfonate, linear sodium dodecylbenzenesulfonate, and a soap. Source: Wikipedia

    Cationic detergents

    Cationic detergents are similar to the anionic ones, with a hydrophilic component, but, instead of the anionic sulfonate group, the cationic surfactants have quaternary ammonium as the polar end. The ammonium sulfate center is positively charged.[3]

    Non-ionic and zwitter ionic detergents

    Non-ionic detergents are characterized by their uncharged, hydrophilic headgroups. Typical non-ionic detergents are based on polyoxyethylene or a glycoside. Common examples of the former include Tween, 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 include octyl thioglucoside and maltosides. HEGA and MEGA series detergents are similar, possessing a sugar alcohol as headgroup.

    Zwitterionic detergents possess a net zero charge arising from the presence of equal numbers of +1 and −1 charged chemical groups. Examples include CHAPS. CHAPS is an abbreviation for 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate.

    Laundry Detergent

    Laundry detergent, or washing powder, is a type of detergent (cleaning agent) used for cleaning laundry. Laundry detergent is manufactured in powder and liquid form.

    While powdered and liquid detergents hold roughly equal share of the worldwide laundry detergent market in terms of value, powdered detergents are sold twice as much compared to liquids in terms of volume.[1]

    21A.jpg

    Figure \(\PageIndex{3}\) The two forms of laundry detergent: powder and liquid. Source Wikipedia

    Components

    Laundry detergents may contain builders (50% by weight, approximately), surfactants (15%), bleach (7%), enzymes (2%), soil antideposition agents, foam regulators, corrosion inhibitors, optical brighteners, dye transfer inhibitors, fragrances, dyes, fillers and formulation aids.[4]

    Builders

    Builders (also called chelating or sequestering agents) are water softeners. Hard water contains calcium, magnesium, and metallic cations (primarily, iron, copper, and manganese). These cations react with surfactant anions to form insoluble compounds (metallic or lime soaps) which precipitate onto fabrics and washing machines and which are difficult to remove. Builders remove the hard water ions through precipitation, chelation, or ion exchange. In addition, they help remove soil by dispersion. In most European regions, the water is hard. In North America, Brazil, and Japan, the water is comparatively soft.

    The earliest builders were sodium carbonate (washing soda) and sodium silicate (waterglass). Since the 1930s, phosphates (sodium phosphates) and polyphosphates (sodium hexametaphosphate) were introduced, continuing with the introduction of phosphonates (HEDP, ATMP, EDTMP). These agents are now known to have serious environmental consequences leading to a drive towards more environmentally benign phosphorus-free agents, such as polycarboxylates (EDTA, NTA), citrates (trisodium citrate), silicates (sodium silicate), gluconic acid and polyacrylic acid; or ion exchange agents like zeolites.

    Surfactants

    Surfactants are responsible for most of the cleaning performance in laundry detergent. They provide this by absorption and emulsification of soil into the water and also by reducing the water's surface tension to improve wetting.

    Laundry detergents contain mostly anionic and non-ionic surfactants. Cationic surfactants are normally incompatible with anionic detergents and have poor cleaning efficiency; they are employed only for certain special effects, as fabric softeners, antistatic agents, and biocides. Zwitterionic surfactants are rarely employed in laundry detergents mainly for cost reasons. Most detergents use a combination of various surfactants to balance their performance.

    Bleaches

    Despite the name, modern laundry bleaches 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 release hydrogen peroxide upon exposure to water. The main targets of bleaches are oxidisible organic stains, which are usually of vegetable origin (e.g. chlorophyllanthocyanin dyes, tanninshumic acids, and carotenoid pigments). Hydrogen peroxide is insufficiently active as a bleach at temperature below 60°C, which traditionally made hot washes the norm. The development of bleach activators in the 1970s and 80s allowed for cooler washing temperatures to be effective. These compounds, such as tetraacetylethylenediamine (TAED), react with hydrogen peroxide to produce peracetic acid, which is an even more effective bleach, particularly at lower temperatures.[4]

    Enzymes

    The use of enzymes for laundry was introduced in 1913 by Otto Rohm. The first preparation was a pancreatic extract obtained from slaughtered animals, which was unstable against alkali and bleach. Only in the latter part of the century with the availability of thermally robust bacterial enzymes did this technology become mainstream.

    Enzymes are required to degrade stubborn stains composed of proteins (milk, cocoa, blood, egg yolk, grass), fats (chocolate, fats, oils), starch (flour and potato stains), and cellulose (damaged cotton fibrils, vegetable and fruit stains). Each type of stain requires a different type of enzyme: proteases (savinase) for proteins, lipases for greases, α-amylases for carbohydrates, and cellulases for cellulose.

    Other ingredients

    Many other ingredients are added depending on the expected circumstances of use. 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" such as carboxymethyl cellulose are used to prevent fine soil particles from reattaching to the product being cleaned.[4]

    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 brightenersfabric 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, common classes include terpene alcohols (citronellolgeraniollinaloolnerol) and their esters (linalyl acetate), aromatic aldehydes (helionalhexyl cinnamaldehydelilial) and synthetic musks (galaxolide).

    Dishwashing Detergents

    Dishwashing liquid (or washing-up liquid in British English), also known as dishwashing soapdish detergent, and dish soap is a detergent used to assist in dishwashing. It is usually a highly-foaming mixture of surfactants with low skin irritation, and is primarily used for hand washing of glasses, platescutlery, and cooking utensils in a sink or bowl. In addition to its primary use, dishwashing liquid also has various informal applications, such as for creating bubbles, clothes washing and cleaning oil-affected birds.

    Hand dishwashing is generally performed in the absence of a dishwashing machine, when large "hard-to-clean" items are present, or through preference.[4] Some dishwashing liquids can harm household silver, fine glassware, anything with gold leaf, disposable plastics, and any objects made of brass, bronze, cast ironpewter, tin, or wood, especially when combined with hot water and the action of a dishwasher.[6] When dishwashing liquid is used on such objects it is intended that they be washed by hand.[6]

    Hand dishwashing detergents utilize surfactants to play the primary role in cleaning.[4] The reduced surface tension of dishwashing water, and increasing solubility of modern surfactant mixtures, allows the water to run off the dishes in a dish rack very quickly. However, most people also rinse the dishes with pure water to make sure to get rid of any soap residue that could affect the taste of the food.[16]

    Dishwashing liquid can be a skin irritant and cause hand eczema. Those with "sensitive skin" are advised amongst other things to persuade someone else to do the washing up.[17]

    Dishwasher detergent is a detergent made for washing dishes in a dishwasher. Dishwasher detergent is different from dishwashing liquid made to wash dishes by hand.

    When using a dishwasher, the user must select a special detergent for its use.[1] All detergents are designed for use after the user scrapes leftover food from the dishes before washing.[2] To function, the user places dishes in the dishwasher in such fashion that the surface of all dishes is open to the flow of water.[2]

    Most dishwasher detergents are incompatible for use with silverbrasscast ironbronzealuminumpewter, and goldleaf.[2] They can also harm disposable plastic, anything wood, knives with hollow handles, and fine glassware.[2]

    Dishwashing detergents for dishwashers are manufactured and marketed variously as cartridges, gel, liquids, pacs, powder, and tablets.[6] Any dishwashing liquid may contain bleachenzymes, or rinsing aids.[6] Some dishwashing detergents may be homemade, using ingredients such as boraxessential oileucalyptus oil and grated bar soap, among others.[7]

    Dishwashing detergents can be formulated to work under different circumstances. In some cases suitably formulated they can be used with cold water or sea water, although they will not generally work as well as those intended for, and used with, hot water.

    Different kinds of dishwashing detergent contain different combinations of ingredients. Common ingredients include:

    Dishwashing detergent may also contain:[citation needed]

    • Anti-foaming agents:[citation needed] Foam interferes with the washing action. Foam may affect operation of the machine's water-level sensors and will leak past the door seals.
    • Additives to slow down the removal of glaze & patterns from glazed ceramics
    • Perfumes
    • Anti-caking agents (in granular detergent)
    • Starches (in tablet based detergents)
    • Gelling agents (in liquid/gel based detergents)
    • Sand (inexpensive powdered detergents)[7]

    Dishwasher detergents are generally strongly alkaline (basic).[8]

    Inexpensive powders may contain sand. Such detergents may harm the dishes and the dishwasher. Powdered detergents are more likely to cause fading on china patterns.[7]

    Besides older style detergents for dishwashers, biodegradable detergents also exist for dishwashers. These detergents may be more environmentally friendly than conventional detergents.

    Informal Uses

    Reader's Digest notes its use as an ant killer, weed killer, to help spread water-borne fertilizer, and to wash human hair.[18] Good Housekeeping says it can be used mixed with vinegar to attract and drown fruit flies.[19] Dishwashing detergent has been used to clean mirrors as well as windows.[20]

    • Pling, an open source general purpose cleaner for glazed, plastic, chrome and inox bathroom and kitchen surfaces, published by Twibright Labs, uses dishwashing liquid as one of active ingredients.[21]
    • Dishwashing liquid can be mixed with water and additional ingredients such as glycerin and sugar to produce a bubble-blowing solution.[22]
    • Dishwashing liquid may be used for cleaning delicate clothing fabrics such as hosiery and lingerie.[23]
    • Dishwashing liquid is frequently recommended in a dilute solution to make decals and vinyl graphics easier to position when applying.[24][25]
    • In industry, dishwashing liquid is also used to inspect pressurized equipment for leaks, such as propane fittings.[26][27] It is used to inspect pneumatic tires for flats, as well as for quality assurance during the installation process, and as a mounting bead lubricant.[28][29][30]
    • Dishwashing liquid has uses as an ingredient in making homemade garden pest deterrents. Oregon State University's Cooperative Extension Service notes the use of dishwashing liquid to get rid of spidermites.[31] Dish soap has also been used to deter aphids.[31][32] In some instances, the dish soap may be toxic to plant leaves and cause them to "burn".[31] Use of soap or dish detergent to help spread pesticide on plants is noted by University of Georgia extension service, but not recommended.[33]
    • A solution of dishwashing liquid and water may be used to remove coffee, tea, olive oil, soda and fruit juice stains from fabrics.[34][35] One dishwashing liquid brand has been used to remove stains from white or lightly-colored cloth napkins.[36]
    • Dishwashing liquid has been used to treat birds affected by oil spills.[37][38] After the Exxon Valdez oil spill in 1989, the International Bird Rescue Research Center received hundreds of cases of dishwashing liquid that were used for this purpose.[39][40][41] More dishwashing liquid was donated during the Deepwater Horizon oil spill to the International Bird Rescue Research Center and the Marine Mammal Center.[42]

     

    Figure \(\PageIndex{4}\) An oiled Gannet being washed. Source Wikipedia

    Environmental concerns

    Phosphates in detergent became an environmental concern in the 1950s and the subject of bans in later years.[8] Phosphates make laundry cleaner but also cause eutrophication, particularly with poor wastewater treatment.[9]

    A recent academic study of fragranced laundry products found "more than 25 VOCs emitted from dryer vents, with the highest concentrations of acetaldehyde, acetone, and ethanol. Seven of these VOCs are classified as hazardous air pollutants (HAPs) and two as carcinogenic HAPs (acetaldehyde and benzene)".[10]

    The EEC Directive 73/404/EEC stipulates an average biodegradability of at least 90% for all types of surfactants used in detergents. The phosphate content of detergents is regulated in many countries, e.g., Austria, Germany, Italy, The Netherlands, Norway, Sweden, Switzerland, United States, Canada, and Japan.

    Summary

    • Detergents are classified into anionic, cationic, and non-ionic detergents and zwitterionic detergents based on the electrical charge of the surfactants.
    • Variations in detergent formulations are based on its end-use (i.e. laundry or for kitchenware).
    • Phosphates make laundry cleaner but also cause eutrophication, particularly with poor wastewater treatment.[9]

    ntributors and Attributions

    • Was this article helpful?