Oxidation and bleaching
Bleaches do not lift stains out — they destroy the part of the molecule that carries the colour. Nothing is removed, so nothing is selective.
In detail
A stain is visible because the molecules in it contain a chromophore: a structural feature, usually a system of alternating double bonds, that absorbs some wavelengths of light and reflects others. Oxidising bleaches attack that structure. When the chromophore is broken, the molecule stops absorbing visible light and the stain stops being visible, even though the molecule itself is still present on the fabric. This explains behaviour that is otherwise puzzling. Bleaching is not removal, so a bleached stain can sometimes reappear if the residue is later altered. It is not selective either: a chromophore in a fabric dye is chemically no different from a chromophore in a wine stain, which is why chlorine bleach strips colour from garments as readily as it removes marks from them. The difference between chlorine and oxygen bleaches is one of strength and of what else they do — hypochlorite is the more aggressive oxidant and also attacks protein fibres, while peroxide-based bleaches are milder and generally spare fabric dyes.
Why
- Sodium hypochlorite (chlorine bleach) is explained by Oxidation and bleaching
- Sodium percarbonate (oxygen bleach) is explained by Oxidation and bleaching
- Hydrogen peroxide is explained by Oxidation and bleaching
- Hydrogen peroxide is explained by Oxidation and bleaching
- Cotton is explained by Oxidation and bleaching
Ten chlorine washes did more damage to the cellulose than one hundred ordinary ones.
- Calcium hypochlorite is explained by Oxidation and bleaching
- Sodium dichloroisocyanurate is explained by Oxidation and bleaching
- Laundry detergent is explained by Oxidation and bleaching
- Dishwasher detergent is explained by Oxidation and bleaching
- Mould remover is explained by Oxidation and bleaching
- Hair dye is explained by Oxidation and bleaching
- Oil-based paint is explained by Oxidation and bleaching
- Pyrolytic (self-clean) cycle is explained by Oxidation and bleaching
- Sodium chlorite is explained by Oxidation and bleaching
- Chlorine dioxide is explained by Oxidation and bleaching
- Phosphonate is explained by Oxidation and bleaching
- Polyurethane foam is explained by Oxidation and bleaching
The agent of destruction is the air. Nothing in a cleaning cupboard slows it.
Sources for this page
Sources
Kirk-Othmer Encyclopedia of Chemical Technology
John Wiley & Sons · Reference work
Relied on for: That bleaching agents act by oxidising chromophores, and that hypochlorite and peroxide bleaches differ in oxidising strength.