OxyFile #348

September 2, 1995, New Scientist: Last Word Column

On your marks

Q: Does a bleaching agent really get rid of stains or does it just 
make them invisible?

A: Practically all bleaching products today contain oxidising 
agents capable of rapidly disrupting the delicate chromophoric 
balance of stain, making them invisible.  Then, given sufficient 
time and temperature, they fragment the whole stain structure into 
water-soluble pieces.  Then, given sufficient time and 
temperature, they fragment the whole stain structure into water-
soluble pieces, so guarding against any potentially embarrassing 
return of the offending colour.

Sodium hypochlorite (chlorine bleach) is the most powerful 
oxidising bleach familiar in the home and is capable of stain 
removal at ambient temperature, but it is not used in British 
laundries, being judged too damaging to fabrics, dyes, enzymes, 
perfumes and so on.  Laundry bleaches in Britain are based on 
hydrogen peroxide which is much less reactive and hence more 
discriminating.  It performs superbly in a long boil wash but, 
unaided, is insufficiently reactive to cope with today's short 
40oC washes.

Detergent companies have created ways of activating peroxide to 
improve performance while reducing its damaging effects.  The 
latest move is to convert the peroxide into peroxyacids during the 
laundry operation but the favoured approach in the future might be 
catalytic activation of the peroxide by transition metal ions.  
However this infant technology is suffering some teething 
problems.

Fred Hardy
Newcastle upon Tyne