The natural fibre and fabrics
even after scouring still contain naturally occuring colouring matter. This
yellowish and brown discolouration may be related to flavone pigments of the
cotton flower. The climate, soil, drought and frost can also cause various
degrees of yellowness. Tips of leaves or stalks coming in contact with the
moist ball after opening will cause dark spots and discolouration. Discolouration
may also come from dirt, dust, insects or from harvesting or processing
equipment in the form of oils and greases. The object of bleaching is to produce
white fabrics by destroying the colouring matter with the help of bleaching agents
with minimum degradation of the fibre. The bleaching agents either oxidise or
reduce the colouring matter which is washed out and whiteness thus obtained is of
permanent nature. Chemical bleaching of textile fibres is further aided by addition
of optical brighteners.
When fibres are to be dyed to very dark shades, where fibres brightness is not so important bleaching is not required. For light and medium shades , fibre brightness is important, bleaching is an essential operation before dyeing and printing.
Object of bleaching
¨The natural coloring material can be destroyed in two types:
When fibres are to be dyed to very dark shades, where fibres brightness is not so important bleaching is not required. For light and medium shades , fibre brightness is important, bleaching is an essential operation before dyeing and printing.
Object of bleaching
- To remove the natural colouring material
- Any other colouring material from natural fibres or man-made fibres
¨The natural coloring material can be destroyed in two types:
- Oxidation
- Reduction
- Chlorine
- Hydrogen Peroxide
- Sodium sulphite
- Sodium hydrosulphite
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