Answer 1:
Washing Bleach contains Hypocloric acid,
which
acts as a very strong oxidizer. It works by
oxidizing dye agents in the stains so that they
become colorless. It preferentially attacks dyes
since strongly colored (or odorous) organic
chemicals often have conjugated double carbon
bonds. These bonds have easily moved electrons
which allow selective interaction with visible
light, hence they absorb some frequencies and not
others, inducing color.
Bleach interacts with
the organic molecules by adding chlorine or oxygen
to the compound which removes the bonds or even
breaks up the molecule. This serves two purposes:
the color is removed or greatly reduced, and the
new sites increase the water solubility of the
material, so it can often be removed by
washing.
Commercial dyes are rated by a
'fugitive' rating which describes how they will
break down in UV or due to chemical attack.
Typically, they are much more stable than typical
stain dyes, so although the bleach attacks
everything, they often survive. However, it is
often the case that clothing vendors over-dye some
cloths to create very heavily saturated colors. In
such cloth, the excess dye is not really bound to
the fiber, but usually to a bonding agent (called
a fixative). Both the excess dye and the
fixative are attacked by bleach, often with quite
odd results. (I had a green shirt on which red
wine was spilled. After bleaching, the red wine
stain was gone, but I had a yellow/tan shirt...).
This isn't completely the fault of the cloth
manufacturers. Dyes are all relatively active
compounds, some of the prettiest are the most
fugitive... Similar problems happen in paints
watercolor is particularly troublesome) where
artist colors are known to decompose in a few
weeks in moderate sunlight... This is why
toxic cadmium compounds are still used in artist
paints, they are very stable over time. One could
not use such dyes in cloth for obvious reasons. |
