The Chemistry of Clothes Washing #6: Bleaches


There are several approaches to stain removal.

One of them is to destroy the stain.  That is, if you are unable to remove the stain from the garment, you destroy it where it stands.  That’ll learn it!

Now, in this sense buy “destroy” all I mean is that we have to alter one part of the molecule so that we can’t see it any more.  Most food-based stains are dyes, which are large complex organic molecules.  To alter the molecule so that it loses its colour, the easiest approach is simply to oxidise it, and this is where bleaches come in.

By “bleach”, we are normally referring to swimming pool bleach, sodium or calcium hypochlorite.  But, in fact, the term “bleach” is a generic term, and refers to any chemical that can have a whitening effect.  In this sense, it is referring to oxidising chemicals.

Swimming pool bleach is a very useful chemical as it is just about the strongest oxidiser in existence (which makes it a great disinfectant) but also because it is very cheap to make.

Unfortunately, because it is so aggressive, it’s a bit over the top when it comes to use on clothes, as it tends to destroy them.  I remember my mother used to clean my cricket whites in bleach, and they didn’t last long.  The material in the pockets fell apart first, followed by the rest of the garment.

In this sense, synthetic fibres are more resilient, and will cope with bleach more so than natural fibres, but it’s still not a good approach.

This is why laundry detergents contain gentler bleachers, and these are perborates, percarbonates, and (more recently) peroxides.

These have a more gentle oxidising effect on the stain then the chlorine bleach does.  The use of peroxides are a more recent addition, and I think this is what is referred to by the phrase “active oxygen” that some Reckitt Benckiser products are now advertising.

Peroxides fall between chlorine and the other bleachers in terms of strength.  They are not as aggressive as the chlorine is, but are more aggressive than the perborates and percarbonates.

Laundry bleachers are and integral part of any premium washing detergent, and tomorrow will will look at another one – enzymes.

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