Alkyl ether sulphate

This class of surfactants has possibly the widest range of use of any anionic surfactant. It is found in almost every product where foaming is desirable, in industrial, household and personal care applications. Alkyl ether sulphates are described in terms of their parent alcohol and the degree of ethoxylation. Thus, sodium laureth-2 is the sodium salt of a sulphated (predominantly) C12 alcohol, with an average of 2 mol of ethylene oxide added. Often, the alcohol is assumed to be the typical C12-14 and the surfactant simply called a 2-or 3-mol ether sulphate. 

Chemistry and general properties. The chemistry of ether sulphates is very similar to that of alkyl sulphates. The backbone of the molecule is a fatty alcohol and often the same alcohols are used as feedstocks for alkyl sulphates, and alkyl ether sulphates and, with higher degrees of ethoxylation, as non-ionic surfactants. The ethoxylation process is more fully described in Chapter 5. 

European users whose demand exceeds 500 Te of surfactant per year will use high active material. 

The addition of an ethylene oxide chain to what is essentially an alkyl sulphate changes its properties in several important ways. Firstly the Kraft point is very significantly reduced. Low active solutions of ether sulphates are clear are fluid at temperatures close to 0°C, and the Kraft point reduces with increasing levels of ethoxylation. Secondly, the nature of foam changes, from the dense stable foam of an alkyl sulphate to a much more open foam structure. The tolerance of the surfactant to water hardness is also improved, with ether sulphates showing better foaming in the presence of moderate hardness. 

Raw materials. Feedstocks for ethoxylated alcohols are made from a large number of alcohols and practically every fatty alcohol used to make alkyl sulphates is also ethoxylated to make non-ionic surfactants, or feedstock for ether sulphates. 

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Polyglycol ethers Alkanolamides Alkyl ether sulphates Alkylbenzene sulphonates (amine salts) Alkylphenol ethoxylates Alkanolamides Alkylbenzene sulphonates (amine salts)... 

Ci2 i4 olefin sulphonates are also used in personal care formulations since they are less aggressive than LAS and will not over-strip (i.e. degrease to leave an excessively dry or squeaky feel) the skin or hair although some care maybe required in formulating to compensate for a dry feel to the foam. AOS-based formulations are also more difficult to thicken than products based on alkyl sulphates or alkyl ether sulphates but use of alkanolamides or sarcosinates as secondary surfactants can overcome both problems and give a product more acceptable to the consumer. 

In manual dishwash, a high-SME product (such as Alpha-Step MC48 from Stepan, SME SFA 5 1) based on a distilled coconut methyl ester is used as a partial replacement for LAS and alkyl ether sulphate. Substitution of SME for LAS/AES can give enhanced... 

Figure 4.20 Salt response of alkyl ether sulphates.

Applications. Alkyl ether sulphates are almost ubiquitous in cleaning products but are rarely found as the primary surfactant as they bring only some detergency but mainly contribute to foaming and viscosity building. 

Alkyl ether sulphates are used relatively little in laundry products, especially in solid ones. The surfactant has a very poor solid form, the pure product being amorphous, somewhat hygroscopic and sticky. Commercial dry ether sulphates are unknown other than as blends of 50% with carrier solids, such as sodium carbonate. In liquid formulations, 3-mol ether sulphates can be used to give improved solubility and hard water tolerance in unbuilt liquids and amine salts are occasionally used. 

Sources and properties of alcohol ethoxylates are covered in more detail under alkyl sulphates and alkyl ether sulphates. 

Simulsol Series Ethoxylated fatty alcohols and acids Alkyl ether sulphates... 

Environmental Data Review of Alkyl Ether Sulphates (AES), a report compiled by BKH Consulting Engineers, Delft, The Netherlands for the NVZ and European surfactant industry, October 1994. 

Ammonium hydroxide is used for the neutralisation of alkyl hydrogen sulphates (R-O-SO3H) and alkyl ether sulphates (R-(OCH2CH2) OS03H). 

Alternatively, a method is described for alkyl ether sulphates, which would also be applicable to alcohol ethoxylates, in which the equilibrium head-space is analysed on a 3 m x 1.8 mm i.d. column of 0.8% THEED/ Carbopack C (80-100 mesh) [14]. A detection limit with FID of 0.1 ppm is claimed. For improved quantitation, both methods can be adapted to a method of standard additions. 

Alkyl ether sulphates can be analysed on a 2.5 cm x 2 mm i.d. column of CIS reverse phase material with a water/tetrahydrofuran gradient system [20]. In this example the detector was the evaporative light scattering detector, as a gradient system was being used with a molecule with no strong chromophore. Alternatively, to obtain more detailed distributions, the molecule could be desulphated and analysed as described for alcohol ethoxylates. 

The analysis of alkyl sulphates and alkane sulphonates using similar conditions to those given previously is described in [41]. Separation of alkyl sulphates and alkyl ether sulphates using a silica gel layer with acetone tetrahydrofuran (9 1, v/v) and visualisation with Pinakryptol yellow is described in [42]. 

Alkyl ether sulphates feature bands characteristic of ethoxy groups (see section 10.6.2) and alkyl sulphate functionality, with additional bands at 1030 and 780 cm ... 

Similar groups of ions to those described above (L , L Na -iL Na Jj. i) are seen in the spectra of a-olefin sulphonates, alkyl ether sulphates, sarcosinates and sulphosuccinates. Fatty acid salts do not give rise to strong positive ions but do give good anion signals in negative-ion spectra. 

Sodium alkyl ether sulphate/ carboxylate/phosphate... 

Typical anionic siirfactants. (a) Sodium alkyl sulfate (R = SOj /phosphate (R = POj -) (b) sodium alkyl ether sulphate(R = SO3 )/phosphate (R = P03 ) sodium bis (2-ethylhexyl)sulfo-... 

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