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Method of bleaching for wool

Method of bleaching for wool

Bleaching of wool is carried out in stainless steel or wooden vessel contacting a solution of hydrogen peroxide and 0.5 % sodium silicate or stabilizer C at 50 °C.



Hydrogen peroxide

2 volume

Sodium silicate or stabilizer



50 °C

The process sequence of wool bleaching - 
Wool bleaching sequence
Wool bleaching sequence 

  • Bleaching with the above recipe for 20-30 min > Cooling for 3 - 4 hours > rinsing > Treat with dilute acetic acid (CH3COOH) > rinsed 
  • After steeping, the scoured material is removed, rinsed, and scoured with Dilute carboxylic acid before being allowed to cool down for 3 to 4 hours or overnight. 
  • After steeping, the fabric is removed, rinsed, and scoured with Dilute ethanoic acid before being rinsed again.
  • Heavy textiles, like worsted, may require a 6-volume peroxide solution. 
  • When fabric contains stripe-effect treated using Acid dyes, it's occasionally preferable to avoid alkaline peroxide bleach.
  • In such conditions, prolonged immersion in alkaline solutions will end in staining of the nearby undyed parts. 
  • These colours, on the opposite hand, are sensitive to acidic environments.
  • When peroxide bleaching is completed under acidic conditions, wool degrades less and has better handling. 
  • When using the above strategy, the extent of degradation is sort of non-existent.
  • The acid Bleaching with Peroxide stabilizer KN (based on acid fluoride) was designed specifically for acid Bleaching. 
  • It's utilized at a degree of 0.8 to 1%, which is enough to stay the pH between 3.9 and 4.0. 
  • Acid Bleaching is best for blankets since it leaves the perfect high handle and therefore the bright-coloured threads don't stain neighbouring areas. 
  • Bleaching wool or cotton unions may also be done using this procedure. 
  • Bleaching can even be finished with sodium peroxide and sodium perborate, in additionally to peroxide. 
  • Optical Brighteners may additionally be applied to the fabric, looking at the wants. 
Bleaching machines
Bleaching machines

Hydrogen peroxide decomposition - 

There are two reasons the decomposition of peroxide takes place one is Metals and the other is Mildew or micro-organisms.

(i) Metals - Metal traces, like iron and copper, produce quick decomposition of peroxide, which ends up in fibre disintegration, or tendering, which can not be visible until the things are within the consumer's hands.

(ii) Mildew or Micro-organisms - Mildew or microorganism growth occurs when wool is stored in an exceedingly alkaline environment in a warm environment, leading to rapid peroxide decomposition. The peroxide decomposes when a load is soaked in a very bleach bath for 20 to half-hour.

Stabilizer - For the controlled decomposition of oxide stabilizers are used.

The following stabilizers are used for wool Bleaching- 

1. water glass
2.  builder
3.  Stabiliser C 

Peroxide bleaching, like cellulosic fibres, needs the utilization of a Stabiliser to limit oxide breakdown. Sodium silicate, tetrasodium pyrophosphate, and stabilizer C are the foremost often used stabilizers in wool bleaching. 

Effect of pH -
The most suitable pH range for wool Bleaching is 5 to 8.

  1. If pH is just too high then - Rapid decomposition of oxide takes place. Oxygen evolution takes place before per hydroxyl ion (HO2-) has a chance to exert bleaching action. Degradation of wool in the course of loss of strength.
  2. During the Bleaching process, it's preferable to test and adjust the pH regularly.
  3. In theory, any alkali is often used, but in practice, hydroxide (NaOH) and salt (Na2CO3) aren't used because delicate pH adjustments don't seem to be possible. 
  4. Liquor ammonia is employed for bleaching, but it's no stabilizing properties and tends to cause excessive peroxide loss.
  5. Soluble glass is the most typically used for bleaching and has no harmful effects on wool fibres. 
  6. In the soluble glass, residues of silicate remain, leading to harsh cloth handling, necessitating thorough washing after bleaching. 

Difference between bleached fabric and unbleached fabric

Questions -

  1. What is the method of bleaching wool fabric?
  2. What is the sequence of wool bleaching?
  3. Why does the decomposition of peroxide happen in bleaching?
  4. What is the role of a stabiliser in the bleaching process?
  5. Describe the effect of pH in the wool bleaching process.


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Further read,

Part Bleaching process of wool fibres

Part 2 Method of bleaching for wool

Introduction to bleaching processing

Bleaching types - Sodium Hypochlorite Bleaching

Bleaching types - Using Hydrogen peroxide

Bleaching types - Using Sodium chlorite

 - Rushikesh Patil (Textile Engineer)
(DKTE Society textile engineering college Ichalkaranji)

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