Textile Bleaching | Object of Bleaching | Bleaching Agent | Recipe for 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.

Natural fibres, i.e. cotton, wool, linen etc. are off-white in colour due to colour bodies present in the fibre. The degree of off-whiteness varies from batch-to-batch. Bleaching therefore can be defined as the destruction of these colour bodies. White is also an important market colour so the whitest white has commercial value. Yellow is a component of derived shades. For example, when yellow is mixed with blue, the shade turns green. A consistent white base fabric has real value when dyeing light to medium shades because it is much easier to reproduce shade matches on a consistent white background than on one that varies in amount of yellow.

Textile bleaching
Fig: Textile bleaching
Bleaching may be the only preparatory process or it may be used in conjunction with other treatments, e.g. desizing, scouring and mercerizing. The combination of such treatments for an individual situation will depend on the rigorousness of the preparation standard and economic factors within the various options. Other chemicals will be used in addition to the bleaching agent. These serve various functions such as to activate the bleaching system, to stabilize or control the rate of activation, to give wetting and detergent action, or to sequester metallic impurities. This section gives consideration to the selection of bleaching agents and to the role of the various chemicals used in conjunction.

The purpose of bleaching is to remove coloured impurities from the fibre and increase the whiteness level of fabric.

The aim of bleaching can be described as following:

  • Removal of coloured impurities. 
  •  Removal of the seed coats. 
  •  Minimum tendering of fibre. 
  •  Technically reliable & simple mode of operation. 
  •  Low chemical & energy consumption. 
  •  Increasing the degree of whiteness.
Bleaching Agent
A bleaching agent is a substance that can whiten or decolorize other substances.Bleaching agents essentially destroy chromophores (thereby removing the color), via the oxidation or reduction of these absorbing groups. Thus, bleaches can be classified as either oxidizing agents or reducing agents.

Type of Bleaching Agents

  1. Oxidative Bleaching Agents
  2. Reductive Bleaching Agents
  3. Enzymatic Bleaching Agents

Typical Recipe for Bleaching:

NaOH ------------------------------------------17ml/kg

SOAP (DTC) ----------------------------------2ml/kg

STABILIZER --------------------------------- 5ml/kg

H2O2 -------------------------------------------30ml/kg

Reaction time -------------------------------- 25min.

Speed -----------------------------------------50-70m/min

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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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