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Bleaching of weft knitted and woven fabric


Bleaching of cotton (weft) knitted material

The bleaching process completely depends on the fabric types (Fibers used for fabric formation). With the different materials of the fabric, bleaching agents are changed. 

In the case of silk fibre material, the following processes are followed.

Bleaching machine for weft knitted cotton material
Bleaching machine for weft-knitted cotton material

Warp knits typically require filament yarns that are 100 percent synthetic and do not require bleaching.

Weft fabrics made of 100 percent cotton or a cotton-synthetic hybrid might also be utilised Weft knit is a comfortable fabric to wear.

An alternative is to use a peroxide solution including mild alkali detergent and soluble glass as a stabiliser for a one-stage combined scouring and bleaching.

The Bleaching of fabric, such as that of woven fabrics blanching agent, is generally not suitable for Bleaching of cloth due to the alkaline nature of the bleaching process and the restriction on AOX generation, but Hypochlorite can be used at pH =11 and at temperatures not exceeding 30 to 35°C. 

After 3 to 4 hours in the presence of effective wetting agents, the material is treated with antichlor. 

The sodium chlorite Bleaching process' acidic nature makes it ideal for knitting.

Low tension machinery is generally suitable for Bleaching cotton knitted fabrics. 

The combined Hypochlorite and Peroxide i.e. hypo-peroxide process generally provides the best witness on knitted cotton fabric. 

Bleaching of coloured woven goods - 

It's commonly used for cloth with colour threads as borders in dhotis and sarees, or as a check effect. 

Bleaching for the undyed component of this kind of cloth should be done carefully to not influence the coloured portion. 

There could be a risk of colour change within the dyed portion of the material during the bleaching process because of over-oxidation. 

The following methods are used for coloured woven goods: 

(i)Desizing with a powerful desizing agent 
(ii)Enzymatic agent 
(iii)Washing to get rid of solubilized starch 
(iv) Mild Alkali 
(v)then wash to get rid of solubilized contaminants 
(vi)Mild checking with chloride of lime or sodium Hydrosulphite or Peroxide followed by souring with Dilute acid.

Finally, undergo washing to get rid of residual acid completely 

Process sequence - 

Desize > kier boil > Chemick > kier boil > Chemick (bleach) > souring > wash. 

Bleaching machine

Evaluation of the efficiency of Bleaching - 

(A) Whiteness
(B) Chemical or physical damage (Qualitative & Quantitative test )
(C) Absorbancy
(D) Freedom from impurities 

Questions -

  1. Describe bleaching for weft-knitted cotton material.
  2. Describe bleaching for coloured woven fabric.
  3. What is the evaluation used to measure the efficiency of the bleaching process?


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Further reading,

Part 1 Introduction to bleaching processing

Part 2 Bleaching types - Sodium Hypochlorite Bleaching

Part 3 Bleaching types - Using Hydrogen peroxide

Part 4 Bleaching types - Using Sodium chlorite

Part 5 Bleaching process of Polyester materials

Part 6 Bleaching process of wool fibres

Part 7 Bleaching process of synthetic fibres

Part 8 Bleaching process of silk and cotton blend fibres

Part 9 Weft-knitted and woven fabric bleaching process

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

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