Surfactants General Information Surfactants are also known as wetting agents. They may be liquids or powders. Surfactants are used in aqueous cleaners to provide detergency, emulsification, and wetting action. Surfactants used in aqueous cleaners are usually biodegradable. The various soils and parts used in your process and the concentrations of your cleaner will affect biodegradability. Lowering the surface tension of the cleaning solution helps the solution drain from the part being cleaned. Surfactants have several roles: they modify or "wet-out" the surface being cleaned or the soil being removed, and they help form an emulsion of solvent in water for cleaning or of soil in water for flushing away. The four major classifications of surfactants are: anionic, cationic, nonionic, and amphoteric. Anionic surfactants are water soluble and have a negative charge in aqueous solution. Cationic surfactants have a positive charge in aqueous solution and are considered to be poor cleaners. Nonionic surfactants are the most widely used for surface cleaning and have no charge in aqueous solutions. Amphoteric surfactants develop a negative or positive charge depending on whether the solution is alkaline or acidic. Anionic surfactants are good detergents; however, they are made insoluble by many hard water metal ions, such as calcium and magnesium. Nonionic surfactants are a class of synthetic surfactants. They are prepared by attaching ethylene oxide molecules to a water-insoluble molecule. The ethylene oxide molecules, derived from petroleum, are water-soluble polymers. Depending on the number of ethylene oxides and the number of carbon atoms, the synthetic surfactants can be classified as a wetting agent, a detergent, or an emulsifier. Foams can be used with neutral, alkaline, or acid detergents. Foams can be used to increase contact time with a vertical surface. Foams may vary in stability. The more stable foams remain in position for longer periods but it appears that the interaction of detergent or germicide and the surface is not as good as with wet foam, which slides off in short times of 15 to 60 seconds. One advantage of foam cleaning is that the operator can easily see where the solution has been applied. Another use for foams is to provide volume where cost prevents filling the entire vessel with liquid cleaner. The foam effectively spreads out the cleaner allowing small amounts of clean large volumes, especially in upper areas. Dow Chemical Co.'s Dowell Division reports filling a refinery tower with foam carrying muriatic acid for descaling the towers. Foam is usually a nuisance. It prevents the use of high agitation in many applications and can create wastewater disposal problems. Foam derived from the soil must be considered. If the soil was originally an emulsion, it still contains soaps or other emulsifiers that will be redissolved and become potent foamers. They may even assist cleaning. Soils rich in fatty acids, such as buffing or drawing compounds or fats and fatty oils in foodstuffs, react with alkali (saponification) in the cleaner to form soaps which that may be foamy when sprayed. Cleaners of low alkalinity reduce saponification of fats, but high alkalinity may be necessary to obtain good bath life. Soils derived from petroleum reduce foaming. Finely divided soil particles may stabilize foam. Methods for breaking the foam: Add volatile petroleum solvent Higher boiling solvents reduce foam more slowly and permanently but may deactivate the cleaner Silicone-type antifoaming agents are extremely effective but may be expensive and can interfere with downstream paint adhesion Heavy metal ions will decrease foam Temperature control range depends on foaming components Use cold water spray, especially applied to overflow Use hot metal rod, especially applied to overflow Decrease agitation. Soap derived from fatty acids produces foam that varies with the titer (level of unsaturation) of the fatty acid stock. Soft soaps foam a lot at moderate temperatures; high-titer soaps, e.g., tallow soap, may not foam much at low temperatures but may form copious stable foams at > 160 ° F. Rosin soap (sodium resinate) foams copiously at lower temperatures but relatively little at higher temperatures, above 170 F. Wetting agents, as contrasted with detergent or emulsifier surfactants, form copious but fragile foams. Branched chain surfactants that cannot form close-packed films form brittle foams that tend to be unstable. Most nonionic surfactants are modest foamers. Low-foaming nonionic surfactants exist but are poor detergents. Mixing with other surfactants gives acceptable detergency if some foam can be tolerated. Sodium lauryl sulfate and lithium lauryl sulfate give very dry foams that are sometimes stabilized by small quantities of lauryl alcohol. These materials are used to produce dry foams in carpet shampoos. The type of surfactant will affect waste treatment plans. Foaming of the effluent stream may be unacceptable under local law. State Information | Glossary | Conversion Checklist | Comments Home | Process Advisor | Alternatives | Links | Search All SAGE material, Copyright© 1992, Research Triangle Institute Last Update: 22 November 1997 sage@rti.org http://clean.rti.org/alt.cfm?id=sf&cat=gi