Alkyl ether sulfates

Alkyl ether sulphates (AES) are one of the three most important groups of anionic surfactants. The hydrophilic moiety of these surfactants is a sulphate group and a polyethylene chain. The hydrophobic part is usually a carbon chain derived from a fatty alcohol. The most common commercial form of alkyl ether sulphates are their sodium salts, such as Sodium Laureth Sulfate (SLES).

The starting raw materials for the synthesis of alkyl ether sulphates are alcohols of oleochemical origin (produced from vegetable oils or animal fats) and petrochemicals (from petrochemical raw materials). The most common for this purpose are alcohols with a chain length from 12 to 14 or from 12 to 15 carbon atoms. In the first stage of production, the alcohols are converted to alkyl ethers, which are then subjected to a sulfation reaction using sulphur trioxide, chlorosulfonic acid or oleum, i.e. a mixture of sulphur oxide (VI) with sulfuric acid. Typically, there are from 2 to 3 oxide moieties in the polyoxyethylene chain, however, this number can be up to 10 EO molecules depending on the application.

AES properties

One of the most important properties of this group of surfactants is the ability to create foams that are high and stable. In addition, the substances of the AES group are characterized by excellent water-solubility, which increases proportionally to the length of the polyoxyethylene chain in the molecule. At the same time, the value of critical micelle concentration (CMC), i.e. concentration of a surfactant in a bulk phase, above which aggregates of tenside molecules – so-called micelles – start to form, also increases. While the hydrophobicity of the alkyl ether sulphate particles increases with the increase of the carbon chain length of the alcohol. At the same time, their surface activity increases.

Alkyl ester sulphates are characterized by the ability to thicken under the influence of inorganic salts. This effect depends on the salt concentration and the structure of the alkyl ether sulphate. The smaller the amount of salt and the more branched alkyl chain in the molecule, the lower the viscosity increase. Another advantage of these anionic surfactants is their compatibility with all types of surfactants as well as with enzymes.

Applications of alkyl ether sulphates

Good wettability, emulsifiability and hard water resistance combined with high foam formation and dissolution capacity in water contribute to a wide range of applications for this group of anionic surfactants. Alkyl ether sulphates usually do not appear alone in the formulations, but instead are used with other anionic or non-ionic surfactants.

AES are used, among others, for the production of body wash gels and shampoos due to their milder effect on the skin compared to SLS. The more oxide groups are found in the AES molecule, the more delicate the effect. Alkyl ester sulphates are also characterized by excellent washing and detergent properties. For this reason, they are widely used in washing liquids and powders. They are also part of the washing and degreasing formulation used in car washes and the leather industry.

The compounds of this group are also used as emulsifiers in such applications as processing liquids and emulsion polymerization. They can also act as air-entraining agents in construction chemicals (e.g. in the production of drywall) and adjuvants that support the action of plant protection products.