Page 27 - HPIC India

Cover Story

Bleaching Agents: Chemicals that ensure stain-free

clothes

The human race since early times
has considered whiteness to be an
embodiment of purity and cleanli-
ness, and the quest for cleaner and
purer fabrics led to the invention of
several different types of cleaning
and bleaching processes. Fabrics
are cleaned satisfactorily only if the
interactions of the wash components
in the entire washing process are
optimised. The major components in
this context would be the nature of
the soil to be washed, the fibre to be
cleaned, the chemicals present in the
detergent used, and so in the wash
liquor, and the type of equipment used
for cleaning. Removal of soil from the
fabric during the washing process
also depends on the mechanical ac-
tion, the wash duration and the tem-
perature of washing. contribute to dislodge and remove or change of pigmented soils adher-
the oily and coloured pigmented soils ing to the fibre. During washing all
The cleaning achieved during a from textile fibres or solid substrates. the above processes occur simultane-
washing procedure is a combination ously at varying levels. The impor-
of washing and bleaching. Washing Bleaching implies the destruc- tance of the process depends on the
or cleansing in an aqueous medium is tion of the chromophore system of a nature and class of the soil present
a complex process involving several coloured soil that cannot be removed on the fibre. Soils like carbon black,
different types of physical and chemi- from the fibres by simple washing. inorganic oxides, carbonates & sili-
cal forces. Washing, broadly, can be The resulting colourless reaction cates, fats & waxes, higher hydrocar-
defined as the removal of soil and product of a bleached soil is either bons, and denatured proteins are dif-
the dissolution of any water-soluble left, as is, in the cleaned fibre, or is ficult to remove from fabrics. Removal
impurities present on the fabric, by subsequently washed off the fabric of bloodstains from fabrics can also
use of water or an aqueous surfactant during rinsing. Bleaching, as a part present problems during washing.
solution. The physical removal of the of the cleaning process, is usually
soil from the fabric substrate occurs carried out by oxidising chemicals Staining in fibres is normally due
due to non-specific adsorption of sur- and sometimes by reducing agents. to the result of either a chemical inter-
factants on different interfaces pre- Bleaching induces a change from a action between the soil and the gar-
sent and through specific adsorption darker shade to a lighter shade in the ment, or the soil sticking superficially
of chelating agents on certain polar colour of the soil, thereby increasing to the surface to the fabric. It depends
soil components present on the fab- the reflectance of visible light and re- on the chemistry of the stain and the
ric. Added to above, the indirect ef- ducing absorption. The overall effect type of the substrate it is present on.
fect caused by calcium ion exchange, obtained on the washed fabric as a In most cases, the staining reaction
results in the freeing of calcium ions result of the cleaning process in tota- is not instantaneous, which is the
from the soil deposits and fibres, dis- lity is the most important aspect to reason fresh stains are easier to re-
lodging any remaining residue. Elec- be considered. move. Physical and mechanical forces
trolytes present in detergents, and, are effective in removing pigmented
in turn, in the wash liquor, signifi- Generally, bleaching occurs by and greasy soils. Chemical bleaching
cantly compresses the double layer at mechanical, physical and/or chemical is used to remove non-washable soil
boundary surfaces. All these effects methods, specifically by the removal stains adhering to fibres. In an actual
Home, Personal & Institutional Care India November 2020 27