Uses of Anionic surfactants

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Soaps

The most common soaps are the ones shown previously. Since soaps are quite closely derived from natural products, they are quite impure. The typical composition of a couple of common classes of commercial soap are:

Tallow soaps:
40-45% oleate,
25-30% palmitate,
15-20% stearate
Coconut oil soaps (even more impure):
45-50% various C12 carboxylates,
16-20% various C14 carboxylates,
8-10% various C16 carboxylates,
5-6% oleate,
10-15% various C12 or shorter carboxylates

You might be interested to know that a common brand of soap was named because it was derived from palm oil and olive oil (think about it...). The company that started as Palmolive, a soap manufacturer, has now grown to be a large multinational in the personal care industry, having merged with Colgate.

In the 1940s, many applications that used to use soaps were altered to use the new synthetic detergents. The synthetic detergents were much better behaved in hard water than the soaps and gave superiour performance. Unfortuately, the detergents needed a small amount of phospate added to them to achieve this performance in many commercial applications (e.g. laundry detergents). The large amounts of phosphates that ended up in waterways in developed countries led to eutrophication (an algal explosion that consumes all the oxygen in the water leading to large-scale fish and plant death). Phosphates have largely been replaced in laundry detergents with other builders such as zeolites or polymers.

Soaps are still used in small amounts in most laundry detergents to control the amount of suds produced and to reduce the transfer of dyes.

Alkyl Sulfates

The alkyl sulfates (like sodium dodecyl sulfate, SDS, shown previously) are commonly used surfactants. They have been found to have similar feel and emolliency properties to soaps. The applications of these surfactants are principally in shampoos, textile processing, emulsion polymerisation, laundry products and in carpet cleaners. (Their use in carpet cleaners is because many of them can make a rich foam that is low in water content.)

Alkyl Sulfonates

The alkyl sulfonates offer reasonable performance in hard water, although they do tend to form some complexes with calcium and magnesium ions. These surfactants are widely used in some industrial processes requiring anionic surfactants and are also used in low levels in some hand-dishwashing detergents.

Sulfosuccinates

Sulfosuccinates like AOT (pictured before) have proved to be quite useful surfactants. While ester linkage can be hydrolysed in harsh conditions, these surfactants are generally regarded as being mild and versatile. They are used when strong wetting, detergency penetration and solubilisation characterics are needed. (AOT is a good emulsifier and wetting agent.)

Alkyl Benzenesulfonates

The alkyl benzenesulfonates have the heaviest usage of the non-soap surfactants. These surfactants have almost entirely replaced soaps in household laundry products. Unfortunately, these surfactants are only slowly biodegradable, leading to a significant build-up of these surfactants in the environment (some water bodies had foam on top of them...).

The commercial and industrial success of the alkyl benzenesulfonates is due in part to their performance and part to the low manufacturing cost. Apart from laundry products, they are widely used in hand-dishwashing and in hard surface cleaners.

Alkyl Phosphates

The calcium and magnesium salts of these surfactants are insoluble, so their performance in hard water is poor, and the ester linkage makes them unstable in acids. There are a number of applications for these surfactants, although they are normally only used in industrial processes where it is known that the water quality is sufficiently good.

Their most common uses are in textile mills, industrial cleaning, dry-cleaing fluids and in the emulsion polymerisation of vinyl acetate. These surfactants have also been used as corrosion inhibitors in pesticides and in papermaking processes.

[Source: Bartolo, R.G., Soap, in Encyclopedia of Chemical Technology, 4th ed, J.I. Kroschwitz, Editor. 1993, Wiley Interscience. p. 297-326.]