Surfactant

Surfactants (from Latin tensus "clamped " ) are substances that lower the surface tension of a liquid or the interfacial tension between two phases and allow the formation of dispersions or service or act as solubilizers.

Cause surfactants that two immiscible liquids actually, such as oil and water, can be finely blended. Surfactants are also understood detergent surfactants (detergents) that are included in detergents, dishwashing detergents and shampoos. In detergent formulations, the surfactant is 1-40 %. Modern surfactants were developed in the first half of the 20th century and have the traditional surfactant soap (fatty acid salts) largely displaced. When used in the food industry, surfactants are referred to as emulsifiers.

Properties

The function of the surfactants can be explained by their molecular structure. Surfactants generally consist of a hydrophobic ( " water-repellent " ) hydrocarbon moiety and a hydrophilic ( " water-loving " ) part of the molecule; they say, they are amphiphilic ( " both loving" ). In the following illustrations, the " water-loving " parts of the molecule are indicated by a minus sign or a red dot.

When surfactants are added to water self-assemble from a critical concentration, the individual surfactant molecules and form within the water usually small, spherical aggregates called micelles. Here, the surfactant molecules align so that the hydrophobic ends accumulate in the interior of the micelles and the hydrophilic ends oriented toward the water. At high concentration of surfactants can also be rod-shaped micelles ( wormlike, Eng. Worm -like) or surfactant bilayers form that encapsulate water.

At the water surface, the surfactants form a thin layer and thus reduce the surface tension of the water. Again, the surfactant molecules arrange. The hydrophilic ends facing towards the water, the hydrophobic tails extend into the direction of the air.

• The influence of surfactants on the surface tension can be easily demonstrated: Man brings on a water surface ( surfactant- water) a light object (such as a pin ) on. This is not the normal case, but taken as a result of the high surface tension of water. Are you then a small amount of a surfactant ( eg detergent) are added, the surface tension decreases sharply. It can not counteract more which acts due to the higher density of the coated article on the surface of water of the weight of: the sink object.

Surfactants as emulsifiers cause that two immiscible liquids (eg oil in water) can mix to form an emulsion. Due to the amphiphilic nature of the surfactant molecule penetrates with its fat-soluble part in the oil. Through the hydrophilic portion of the oil droplet is dispersed by stirring in water.

Of wetting agents is when the objective of the use of surfactants, the mixing of two phases is not, but the reduction of the interfacial tension between a solid surface and a liquid. Water flows from place to form drops, light from a surface. In the photo lab as surfactants are used as a wetting agent to prevent dry spots on photographic materials after the final rinse.

Surfactants assist in separating small solid particles from solid surfaces, ie about the removal of dirt particles on garments. The solid particles are " held in abeyance " in the water. Their use aids in the formation and maintenance of a so-called suspension. The surfactants are deposited emulsion similar to the solid particles and inhibit the clumping together, drop ( = sedimentation ) and re- attachment to other solid surfaces, which are themselves subject to a " surfactant ". The coated with the surfactant solid particles form a so-called colloid with the water. As dispersing surfactants are referred to that hold the solid pigments in a (still) liquid paint in the balance.

The formation of foam due to the characteristics of surfactants. The surfactant molecules form a two -layer film in which the hydrophobic tails of the surfactant, the two surfaces. The hydrophilic ends, into the film. A strong foaming can be a nuisance when using or in the presence of surfactants, defoamers and therefore find use.

Anionic surfactants form insoluble precipitates with alkaline earth metal cations, which are commonly referred to as lime soaps. Calcium soaps no longer have the properties shown above the " soluble " surfactants. The formation of lime soap due to the water hardness. Where surfactants are used as detergents, detergent in a water softener is buried.

Structure and preparation

All surfactants are composed of a non-polar and a polar part (functional groups ) (see polarity). As a non-polar part is usually provided by an alkyl group or an alkyl benzene. The polar part may be constructed differently, and is summarized in the table:

Attempts are often made to distinguish between natural and synthetic surfactants. This distinction is not easy and not always useful. Naturally occurring surfactants are, for example, saponins or phospholipids such as lecithin.

Surfactants of natural origin, for example, soaps of natural raw materials ( renewable raw materials, for example from vegetable or animal fats ) can be prepared by hydrolysis. On the basis of fats and fatty alcohols derived therefrom to also let surfactants such as fatty alcohol polyglycol ether ( FAE), fatty alcohol sulfates (FAS ), fatty alcohol produced ( FAES, sulfated fatty alcohol polyglycol ether ) and methyl ester sulfonates (MES, sulfonated fatty acid methyl ester). Also from renewable raw materials leads to sugar surfactants, such as Alkyl glycosides from hexoses or pentoses and fatty alcohols. However, the production requires a profound chemical reaction.

Synthetic surfactants are made from petroleum raw materials ( petrochemicals ) or synthesized from them derived products, such as alkanes, benzene, alkylbenzenes, olefins, ethylene oxide and fatty alcohols, for example, alkyl benzene sulfonates (ABS), secondary alkane sulfonates (SAS ) and corresponding surfactants, such as based on out fatty alcohols derived fats converted.

An important property of a surfactant is its biodegradability. By washing and cleaning Substances Act ( WRMG ) is required of each surfactant producers that the surfactant of at least 90 % (often 95 %) can be biodegraded. Often this test to determine the biological ( BOD ) and chemical oxygen demand (COD ) can be performed. Some surfactants ( eg, alkyl benzene sulfonate ) the nature of biodegradation is known very accurately. As a suspected fish toxicity alkylphenol polyglycol ethers became known, the producers took the product off the market immediately.

History

About soap-like compounds have been reported around 2500 BC in the Sumerian cuneiform. By boiling olive oil with wood ashes (potash ) soap-like compounds could be obtained. Even with Egyptians, Romans, Teutons, Gauls surfactant- products of fats were known.

Even in the Middle Ages and the Renaissance soap-like products made of wood ash and fat were obtained. Only through the synthetic soda ash from common salt, sulfuric acid and lime according to the Leblanc process soap could be produced inexpensively.

In the 20th century detergent were also increasingly used for the cleaning of textiles in washing machines.

Normann K. Adam developed an easily accessible surfactant tetrapropylenebenzenesulfonate (TPS). This surfactant covered at the beginning of the 1960s, 65 % of Tensidbedarfes the Western world. Due to the poor biodegradability but foam mountains arose in rivers. As of 1964, more biodegradable, linear alkyl benzene sulfonates ( LAS) have been developed.

Since the early 1980s, the research also focused on the search of renewable Tensidrohstoffen. Since 1990, manufactured by Henkel Alkylpolyglycosides. These contain a sugar residue as hydrophilic moiety and are therefore assigned to the sugar surfactants. Since the sugar moiety has no charge, they are among the nonionic surfactants.

Surfactants used today meet the legally required primary degradation degree, although there are significant differences in the ultimately reached degradation. The primary degradation rate refers to the loss of surface activity. The final degradation is complete until the full implementation of the organic compound. This final degradation of laws is not included.

Use

Food industry

Certain surfactants are used as emulsifiers or foaming agent in foodstuffs. The authorized food additives are listed in the article List of approved in the European Union food additives.

The alkalization or saponification of cocoa fat in drinking cocoa powder serves to reduce the surface tension of the milk and to achieve a faster wetting or suspension of the semi-fat cocoa powder.

Detergents and cosmetics

In detergents, detergents, shampoos, shower gels, etc. Surfactants are used in order to increase the " solubility" of grease and dirt particles that stick in the wash or body in water. They form the most important component in cosmetics to produce fatty skin cream. Surfactants are used, among other things linear alkyl benzene sulfonates ( LAS), Alkylpolyglycosides ( APG), Esterquats (EQ), fatty alcohol ethoxylates ( FAEO ), fatty alcohol sulfates (FAS ) and fatty alcohol ether (FES ). However, will not be used alkylphenol ethoxylates (APEO ) and tetrapropylenebenzenesulfonate (TPS).

Biochemistry

In biochemistry, surfactants are used, among other things, for denaturation of proteins and for the solubilization of membrane proteins:

• Sodium lauryl sulfate ( SLS or SDS)
• Cetyltrimethylammonium bromide ( CTAB)
• Octoxinol 9
• Polysorbate 20
• Polyalkylenglycolethersche research
• Salts of bile acids such as cholate or deoxycholate
• Digitonin
• Dodecylmaltoside
• Octylglucoside
• Fissile surfactants

Earth sciences

In Geology and Paleontology surfactants are often used for gentle processing of sediment samples. Using this method, for example, can be prevented that occur in samples containing pyrite to form sulfurous acid, which would be the case if they were treated with hydrogen peroxide normally used for sample preparation.

Technology

Plastics Technology

A specific application of surfactants found in plastics technology. Here aqueous surfactant solutions are used to test the susceptibility of polymeric materials to stress cracking. Further surfactants are used in order to shorten the time to failure of long-term studies; especially in crack growth tests on polyethylene finds this application. The Full Notch Creep Test for examining polyethylene pipes wetting agents may be used.

Nonionic surfactants also function as an external anti-static agents, in order to prevent the electrostatic charge from plastic surfaces. For both anionic and cationic surfactants are used.

Metalworking

Surfactants herein ingredient in water-mixed cooling lubricants.

Photography

This can be prevented when developing the film drying spots and streaks.

Paper Recycling

Surfactants help in paper recycling to replace the ink particles from the paper fibers and the transport of the ink to the surface during the deinking ( de-inking ).

Cleaning of tools

They also play an important role in the cleaning tool.

Fire-fighting

A method for fire fighting is the deletion with " tension water ", also known as " network water ", ie water with a greatly reduced surface tension. This brings to one the advantage that the extinguishing water can penetrate better into burning materials such as wood or fabric and thus draws an even better cooling effect by itself. Secondly, offset with surfactants extinguishing water are sprayed due to their effect as a flow improver for the same pump power over a greater distance. The latter effect is not consciously used. Special foaming agent ( Aqueous film forming foam (AFFF ) ) for fighting liquid fires contain perfluorinated surfactants that form a gas-tight liquid film between the burning material and foam, which also gives the foam carpet better gliding and thus deletion of larger liquid fires in the first place.

Natural Occurrence

Certain larvae of insects spit predators with a surfactant -containing secretions. This acts as a deterrent to the attacking ants and allows the crawler to escape. It was observed this behavior in caterpillars of the moth Spodoptera originating from Southeast Asia exigua.

Economic importance

The world production of surfactants in 2000 stood at 10.5 million tonnes. Anionic surfactants ( 56 % of world production of surfactants ) and nonionic surfactants (35 % of world production of surfactants ) are the most economically important classes of surfactants. In 2010, approximately 6.5 million tons of anionic surfactants were in demand worldwide. Together with the non-ionic surfactants, these two groups of approximately 85 % of global surfactant - demand.

In Western Europe, about 3.0 million tonnes of surfactants were produced in 2008, in the U.S. 1.6 million tons, China 1.4 million tons, 0.98 million tons in Japan. In Western Europe in 2008 1.22 million tons of anionic surfactants, nonionic surfactants, 1.41 million, 0.28 million tons of cationic surfactants and amphoteric surfactants 80,000 tons were produced.

The world's most important surfactant is linear alkylbenzene sulfonate the (LAS ) with an annual production of 4 million tons. Another important surfactant with ever-increasing importance ( current production quantity: 90,000 tons ) is the methyl ester sulfonate (MES, sodium alpha- sulfoalkancarbonsäuremethylester ). By 2020, the annual production is estimated at 1 million tonnes. "Green surfactants " as N- acyl glutamates, N- acyl sarcosinate, sorbitan find due to the higher price, especially in the cosmetic industry important application fields.

A very large international manufacturer of surfactants (especially for LAS) is the company Sasol. Other major companies in the surfactant market are BASF, Clariant, Cognis, Huntsman, Shell, Russia Nizhnekamskneftekhim and Kirishinefteorgsintez, in China Jilin United Petrochemical Co., in India Indian Petrochemicals Corp.. Ltd. .. Particularly in the Asian region is expected to continue growing surfactant market.