Defination of Bleaching | Objects of Bleaching | Selection of bleaching agent | Classification of Bleaching agent | Factor of peroxide Bleaching | H2O2 is called Universal bleaching agent

Defination of Bleaching:

Bleaching is chemical treatment employed for the removal of natural coloring matter from the substrate. The source of natural color is organic compounds with conjugated double bonds , by doing chemical bleaching the discoloration takes place by the breaking the chromophore , most likely destroying the one or more double bonds with in this conjugated system. The material appears whiter after the bleaching.

Objects of Bleaching:

• Removal of coloured impurities. 
• Removal of the seed coats. 
• Minimum tendering of fibre. 
• Low chemical & energy consumption. 
• Increasing the degree of whiteness.

Selection of bleaching agent according to fiber types:

Type of Fiber	Alkali	Sodium chloride	Sodium hypo chloride	H2O2	Reducing Agent
cellulose	++	++	++	++	++
Animal	-	-	-	++	++
Polyamide	+	++	-	(+)	++
Polyester	(+)	++	+	+	+
Polyacrylonitrile	-	++	+	(+)	+

++ ..............Process highly soluble.

+.................Process applicable without fiber damage but without achieving and whitening effect.

(+)................Process applicable only with special precaution.

- ...................Process Unsuitable

Classification of Bleaching agent:

Factor of peroxide Bleaching:

• Temperature:80-95 for cotton and Bust &75-80 for cellulose fibers 
• Time:18-24 Hours
• pH:9-10
• Water Quality:Soft water

Why H₂O₂  is called Universal bleaching agent:

• Because it can be employed for bleaching fibers like wool,silk, and jute also.
• It requires less handling of fabric and hence less labor.
• The loss of weight in bleaching is less.
• Less water is required.
• More absorbent.