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Anionic surfactant

The workhorse of most laundry and dishwashing products, and the reason hard water used to ruin a wash.

In detail

An anionic surfactant carries a negative charge on the water-loving end of the molecule. That charge is what makes the class such an effective remover of oily and particulate soil, and it is also the class's one structural weakness: a negative head group is attracted to the positive calcium and magnesium ions in hard water, and the resulting compound is insoluble. That is the whole history of the soap-versus-detergent question in one sentence. Traditional soap is an anionic surfactant, and its calcium salt is the grey curd that used to line baths and stiffen laundry. Synthetic anionics were developed to keep the cleaning power and lose the curd, and builders and chelating agents were added to take the hardness ions out of play entirely. On a label the class is declared by name — the law requires the weight band where it is present above 0.2% — so a reader can tell how much of a product is surfactant, though never which one.

Why

Sources for this page

Sources

  1. Regulation (EC) No 648/2004 on detergents, Annex VII — labelling and ingredient data sheet

    European Parliament and Council, as retained in UK law (legislation.gov.uk), 2004 · Government or regulator

    Relied on for: That the class is one of the constituents a detergent label must declare, in weight bands above 0.2%. (states this directly)

    Verification: a person has read the passage relied on.

    Read on — Annex VII section A, the weight-range list and the declare-regardless list. Supports the claim as stated. Enumerates the ingredient-class family completely, and supplies the vocabulary a reader is actually confronted with on the back of a bottle.

  2. Handbook of Detergents (Surfactant Science Series)

    CRC Press / Taylor & Francis · Reference work

    Relied on for: That anionic surfactants are the principal detersive class in laundry and dishwashing formulations and that their calcium salts are insoluble. (background and mechanism only)

    Verification: the work exists and is described correctly. Nobody has yet read the specific passage.

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