Fabric Bleaching

Bleaching powder may be used for bleaching cotton and linen. The fabric is soaked in a weak aqueous suspension of bleaching powder and exposed to the air when hypochlorous acid is liberated and causes bleaching by oxidation. The process is completed after repeated boiling, washing and exposure to sunlight for up till 6 months.

Chlorine can destroy silk and wool which contain proteins, of which the peptide group would be hydrolysed in acid, therefore commercial hypochlorite bleaches should never be used on silk fibres. Instead, hydantoin and cyanurate bleaches, which release chlorine slowly in water, are used. Hence there is less chance of damaging the fabrics. However they impart a hard –to-eliminate odor to fabrics.

Dichlorodimethlyhydantoin (a hydantoin bleach)

The blue spheres represent the ntrogen atoms

The red spheres represent the oxygen atoms

The grey spheres represent the carbon atoms

The white spheres represent the hydrogen atoms

The green spheres represnt the chlorine atoms

Bromine is not used for commercial bleaching.

The so called optical bleaches, also known as optical whitening/ brightening agents, are not really bleaches but fluorescent dyes (organic compounds) that convert invisible ultra-violet light of short wavelength into visible blue or blue-green light with a longer wavelength. Whites that are bluer in cast are perceived to being ‘purer’, thus fluorescent dyes have the potential for making fabrics and other materials appear brighter to the eye. Blancophors are the chemical names of these compounds. The safety of these chemicals is not yet known with certainty. They do not appear to harm human beings but they do cause minor mutations in microorganisms. They are also known to cause rashes in some people.

Blancophor R 

Blancophor R

The red spheres represent the oxygen atoms

The grey spheres represent the carbon atoms

The yellow spheres reprenet the sulphur atoms

The white spheres represent the hydrogen atoms

Blancophors are able to convert ultra-violet light into blue light and therefore hides yellowing in fabrics.