Scouring and Bleaching of cotton fabrics

Scouring and Bleaching Process for Yarn in package form:

The following process sequence may be used for Scouring and Bleaching of yarn in package form:

yarn scouring and bleaching

Recipe:
Demineralization:
Demineralizing Agent = 0.5 %
Non-ionic & anionic admixtures = 0.5 %

Scouring & Bleaching:
Sequestering Agent = 0.5%
Organic Stabilizer = 0.6 % (0.4 gpl)
Soda Ash =2.4% (3 gpl)
Hydrogen Peroxide (50%) = 1.6% (2 gpl)

Peroxide Killer Treatment:
Organic Peroxide killer =0.4%
Acetic Acid = 2 gpl

Conventional Knit Goods Bleaching Process:

The current problem that mostly worries the modern dyers could be short-listed as
Shade-matching in buyer defined illuminants.
Shade tolerance limits for shade passing.
Strict limits of various Color-fastness properties.
Lowest Processing cost.
Lowest load in effluent water
Meeting the various buyer-defined pre-requisites like Oko-Tex standards
The survival of the modern dyer would therefore lie in the ability to
Prepare Right Fabric for dyeing
Select Right Dyes and Chemicals for various fastness requirements.
Maximize the Right First Time (RFT) dyeing both in lab and bulk dyeing.
The “Garbage in, Garbage out?, “what we sow that we reap? – all these sayings would be proved true in the case of quality pretreatment. It has been told that dyeing is the mirror image of preparatory treatment. Unless the preparatory fabric is excellent, one cannot achieve proper dyeing and finishing.

Bleaching Technique:
The main aim of preparatory process is,
To remove natural pectin, wax, protein, coloring matter and unwanted minerals from the fiber,
To make the substrate uniformly absorbent throughout its length and breadth,
To make the substrate uniformly white for pure white finishes with optical brighteners or for subsequent dyeing, mercerizing etc.
The ideal process of combined Scouring and Bleaching for cotton knits and yarn should have the following contents.

Recipe
1. Non-Ionic detergent with high cloud point, low foaming and good rewetting property or a nofoaming Anionic wetting agent 0.5 to 0.75% (o.w.f.)
2. crease lubricating-agent 0.3 to 0.50% (o.w.f.)
3. Soda Ash 0.5 to 1.0% (o.w.f.)
4. Hydrogen Peroxide (50%) 2.0 to 4.0gms/liter
5. Peroxide Stabilizer 0.5 to 1.0 gm/liter
6. Caustic Soda flakes 0.7 to 1.0% (o.w.f.)

If the water hardness is above 100ppm, then a suitable sequestering agent should also be added to the above recipe (0.5 to 1.0g/l).
Check the pH of the bleach bath. It should be 10.5~11.0

A treatment at 85°C is given for 45~60 minutes, followed by
Hot wash at 80°C for 15 minutes
Treatment with 0.5% peroxide-killer at the pre-defined temperature
Hot wash at 80°C for 15 minutes
Neutralize with 2 gms/liter Acetic Acid.
So, this is the optimum process requirement for good quality fabric/yarn.

Continuous Bleaching:

The desized fabric was taken for continuous bleaching in BEN EXTRACTA, Beninger Bleaching range with the following recipe:

Recipe

Remarks

Hydrogen Peroxide (50%) = 35 gpl
Caustic Flakes = 25 gpl
Nustabilize NI = 7 gpl
Nuseq = 3 gpl
Nunon-WET = 3 gpl

The recipe was reformulated to avoid pin- hole damages without affecting the RFD properties.

Conditions maintained:

  • Speed = 60 meters/minute
  • Reaction Time : 12 minutes
  • Pickup % (approx) = 140
  • Temperature in reaction chamber = 89°C
  • Total quantity processed = 3500 mtrs.

Observations:

  • This fabric is a blend of cotton and lycra; lycra being a synthetic fiber, it needs to be  HEAT SET at about 185 to 190°C for 30 seconds. But since it has not been pre heat set, we noticed a lot creases while bleaching.
  • The whiteness was a little bit dull.
  • The absorbency of the fabric was good.
  • Width after desize wash and before bleaching = 57 inches.
  • Width after bleaching = 54 inches

Bleaching Machines:
Jigger, winch, soft-flow, cabinet and continuous bleaching ranges such as Beninger are some of the routine machines used for textile bleaching.

Some useful hints in Hydrogen Peroxide bleaching:
The maximum bleaching activity from hydrogen peroxide is obtained generally at about pH 11.5. In practice this alkalinity level is altered to suit fiber sensitivity and bleaching process requirements; e.g. wool, cotton, amount of seed etc. Selection of the alkali to be used in peroxide bleaching is dependent therefore on the fibers or the blend being bleached. Sodium Hydroxide and Sodium carbonate will be used generally on cellulose fibers, whilst ammonia and tetra sodium pyrophosphate are used when bleaching protein fibers.

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