Bleaching: This is a
process of whitening-fibers, yarns, fabrics or garments having natural colour. Bleaching can be carried out by oxidative bleaching and reductive bleaching agents.
1. Oxidative bleaching agents: These can be divided in to two system- peroxide system & chlorine system.
Peroxide system: Hydrogen peroxide, sodium peroxide, sodium perborate, potassium permangnate, peracetic acid, ozone
Chlorine system: Bleaching powder, sodium hypochlorite, lithium hypochlorite, sodium chlorite, chloramine, isocynual trichloride
2. Reductive bleaching agents: Sulhur dioxide, sodium hyposulphite, sulphoxylates, acidic sodium sulphite, sodium bisulpphites
The most popular bleaching agents used in the textile industry are:
It is important to optimize the whitening of fibre using these oxidative bleaching agents as they may also degrade cellulose.
Action of Oxidative and Reductive bleaching agents:
Oxidative bleaching agent is a chemical reagent which decomposes in alkali solution and produce active oxygen. The active oxygen in fact the intrinsic bleaching agent as it will further destroy partly or completely the coloring matter present in the textile materials.
In the case of reductive bleaching agent destroy the colouring matter by reductive reaction of SO2. Whenever bleaching is carried out following auxiliaries are used:
Stablizers, activators, wetting agents, sequestering agent etc.
Colour producing agents:
1. Oxidative bleaching agents: These can be divided in to two system- peroxide system & chlorine system.
Peroxide system: Hydrogen peroxide, sodium peroxide, sodium perborate, potassium permangnate, peracetic acid, ozone
Chlorine system: Bleaching powder, sodium hypochlorite, lithium hypochlorite, sodium chlorite, chloramine, isocynual trichloride
2. Reductive bleaching agents: Sulhur dioxide, sodium hyposulphite, sulphoxylates, acidic sodium sulphite, sodium bisulpphites
The most popular bleaching agents used in the textile industry are:
•Sodium hypochlorite (NaOCl)
•Hydrogen peroxide (H2O2)
•Sodium Chlorite (NaClO2)
It is important to optimize the whitening of fibre using these oxidative bleaching agents as they may also degrade cellulose.
Action of Oxidative and Reductive bleaching agents:
Oxidative bleaching agent is a chemical reagent which decomposes in alkali solution and produce active oxygen. The active oxygen in fact the intrinsic bleaching agent as it will further destroy partly or completely the coloring matter present in the textile materials.
In the case of reductive bleaching agent destroy the colouring matter by reductive reaction of SO2. Whenever bleaching is carried out following auxiliaries are used:
Stablizers, activators, wetting agents, sequestering agent etc.
The colour
producing agents in natural fibers are often organic compounds containing conjugated double bonds. (Conjugated double
bonds in a molecule, mean that the single and double bonds alternate.)
It is
known in dye chemistry that conjugation is necessary for an organic molecule to
perform as a dyestuff.
Discolouration can
occur by breaking up the chromophore, most
likely destroying one or more of the double bonds within the conjugated system.
(A chromophore is the part of a molecule responsible for its colour. The colour arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. It is a Greek word: Chroma= "colour" and Phoros =Bearer)
(A chromophore is the part of a molecule responsible for its colour. The colour arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. It is a Greek word: Chroma= "colour" and Phoros =Bearer)
How does bleaching agents works? Oxidative
bleaches oxidize color bodies into colourless compounds. For example, double
bonds are known to be oxidize into epoxides which
easily hydrolyse into diols.
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