Uses of Nonionic Surfactants

 
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Many nonionic surfactants have the problem that they become insoluble in warmer water. This temperature is known as the cloud-point - all of a sudden the solution becomes cloudy and is the surfactant begins to precipitate. This places technical restrictions on their use.

Australia had a significant role in the commercial production of nonionic surfactants. The story starts with the large UK company ICI (Imperial Chemicals Industry) that had an Australian arm. In the mid-1990s, ICI Australia bought itself out and changed its name to Orica. Orica still exists today and is the world's largest explosives manufacturer; however, many of its other divisions have been sold to other companies. The surfactants division, which was one of the world's largest producers of nonionic surfactants, was sold in 1999 to Huntsman Chemicals. Huntsman Chemicals is a huge privately owned company based in the US.

Alcohol Ethoxylates and Alkylphenol Ethoxylates

These surfactants have been widely used in alkaline metal cleaning formulations, hospital cleaners, oil-well drilling fluids and emulsion polymerisation reactions. They have proved to be a robust and useful surfactant.

However, there have been fears about the environmental impacts of their use. It appears that there are two problems with these types of surfactants, particularly the alkylphenol ethoxylates (although more recent evidence suggests these fears may be misplaced, but their reputation is already tarnished):

  • It seems that some bacteria are able to digest the poly(ethylene oxide) chain, due to its chemical similarity to polysaccharides. The phenyl group in middle of molecule is toxic to the bacteria.
  • There is some evidence that these surfactants may be an estrogen mimic. (Such compounds are reponsible for malformed animal genetalia and low sperm counts.

As a result, surfactants such as the nonylphenyl ether poly(ethylene oxide) pictured above, are being phased out.

Alkyl Polyglucosides

The alkyl glucoside pictured above contains an ether linkage between the hydrophobic tale and the sugar. Although this is actually relatively easy to synthesise (you could do it in the lab), these have not proved to be cheap surfactants to produce. As a result, they are not widely used, except for a couple of niche markets and in a few dishwashing liquids.

The glucose ester is industrially useful and the focus of current research. Australia's CSIRO Molecular Science has a long-running project looking at the biodegradation of these surfactants.

Sorbitan Esters

The sorbitan esters are a large class of surfactants. The groups that are attached to the sorbitan (the central ring structure of the molecule shown) include oleate, palmitate, stearate and ethoxylated versions of each of these (the ethoxylated oleate is shown in the structure of Tween 85 above).

The ethoxylated sorbitan esters are water soluble and used as industrial emulsifiers, antistatic agents, fibre lubricants and solubilisers. The non-ethoxylated sorbitan esters are often water insoluble, but are useful as solublisers in the oil phase. These surfactants have been approved for human consumption and are widely used as emulsifiers in foods, drinks and pharamceuticals.

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