What is Scouring? [Get A Comprehensive Look]

Scouring is an important step in the pre-treatment process. It is a preparatory process that prepares the fabric for subsequent dyeing process. If scouring is not carried out properly, it will lead to uneven dyeing.

If you want to know what is scouring and more information about it, you are on the right track. Look no further!

Let’s dive in…….

What is scouring?

Scouring is a process in which the natural impurities of cellulosic fibers are normally removed by boiling off in a strong alkaline solution. The natural impurities such as mineral matters, oils, waxes, ashes hinder the penetration of dyes and chemicals to the interior of fiber which results in the huge wastage of dyes and chemicals. Again improper scouring leads to uneven dyeing. Alkali ( Caustic & soda Ash ) treatment with auxiliaries at high temperature removes the inherent and added impurities from cotton and other cellulosic fibers such as hemp, ramie, kenaf, linen, jute.

Reaction Occurs During Scouring

Raw cotton contains impurities in it and has a cuticle layer of pectins, oils or waxes around it which makes in quite hydrophobic. These are high molecular fatty acid such as steeric acid. During scouring process, concentrated caustic soda solution reacts with steeric acid by removing all these impurities and the goods become more absorbent.

Objectives of Scouring

  • Main purpose is to remove all impurities from the fabrics
  • To make the fabric highly absorbent
  • To facilitate dye and chemical penetration
  • To remove non-cellulosic materials form cotton
  • To leave the fabric in super absorptive state without any significant chemical or physical damage
  • To improve the fabric handle
  • To prepare the fabric for subsequent process

Impacts of Scouring On Cotton

  • Saponification of oils and fatty acids leads to the conversion of water soluble soaps
  • Protiens are hydrolyzed into water soluble amino acids or ammonia
  • Pectin and pactose are solubilized and converted into soluble salts of pectic acid
  • Extraction of mineral matter
  • Unsaponifiable natural oils and waxes are emulsified
  • Dirt particles are removed by detergent and alkali
  • Dissolution of amino compounds
  • Sizing materials are broken down.

Scouring Depends On the Following Parameters

  • Fabric construction
  • Twist and count of yarn
  • Fabric color
  • Fabric type
  • Cleanliness of fabric

Chemical Requirement & Their Functions for Scouring Process

Based on the type and form of materials a series of chemicals are used in scouring bath. Usually, the scouring bath consists essentially of a caustic material and a surfactant, at least 0.01% by weight, based on the total weight of the scouring bath, of a solubilizing agent which is amino tri (methylene phosphonic acid). The key chemicals used for scouring process of different fibers and their functions are given below:

Chemicals

Functions

Caustic Soda

·       Neutralizes acidic materials

·       Saponify glycerides (waxes & oils)

·       Solubilizes silicate

Soda ash

·       Neutralizes acidic materials

·       Saponify glycerides (waxes & oils)

·       Solubilizes silicate

Sodium silicate

·       Penetrate & brake-down lignin in motes

·       These are added when fabric has large amount of motes and other assorted materials.

Surfactant

·       Reduce surface tension

·       Reduce interfacial tension

·       Helps to wet out the materials with liquid

Detergents

·       Emulsify fats, oils and waxes

·       Remove oil borne stains

·       Suspend materials after they have been removed

Sequestering agent

·       Deactivate metal ions

Builder (salt)

·       Cause detergents to become increasingly effective

Solvent

·       Assists emulsification by dissolving oily materials

A typical Recipe for Scouring:

Chemicals used

Amounts needed

·       Wetting agent

·       Detergent

·       Sequestering agent

·       Caustic soda (36°Be)

·       pH

·       M:L

·       0.5-1.0 g/L

·       1.0-2.0 g/L

·       1.0-3.0 g/L

·       2.0-4.0 g/L

·       10-11

·       1:10

Form of Scouring

Scouring can be carried out both in yarn and fabric stage. Again, this process can be carried out in different forms. They are discussed below:

·       Scouring of Yarn

Ø  Hank form

Ø  Package form

Ø  Continuous warp sheet form

·       Scouring of Fabric

Ø  Open form: J-box, Pad-batch, Progressive Jigger

 

Ø  Rope Form: Kier boiler, Washer

Scouring Methods

Scouring process is done mainly in two methods-

  • Continuous process- In continuous process, fabric is scoured continuously in J-box where dyeing process is also carried out after pre-treatment. But in our industry, it has very limited use.
  • Discontinuous Process- In this case, scouring is carried out in kier boiler, winch or jigger dyeing machine. As the name implies, it is carried out in discrete manner. Different lots or batches are created before dyeing. This process is also called Batch process.

Assessment of Scouring

For estimation of scouring effect two types of methods can be carried out:

  • Determination of weight loss
  • Absorbency test
  • Immersion test or Wicking test

Determination of weight loss

Absorbency test

  • Drop test

Water is taken in a pipette and a drop of water is dropped on the scoured sample. Time for the absorption of that water drop is observed visually.

The standard time for absorption is 0.5-0.8 to 1 second.

  • Spot test

1% direct or congo red solution is taken in a pipette. Then droplet of the solution is put on the different places of the scoured sample. The shape of the absorption area is then observed.

 

Wicking or Immersion test

  • Sample preparation: 18cm × 5cm size sample is cut from the scoured sample. A mark is drawn above 1 cm from the sample bottom.

·       Procedure:

Ø  1% direct red solution is taken in a pipette.

Ø  Sample is hung from a wood-stick in such a way that 1 cm portion of that sample is immersed in the dye solution.

Ø  Then the point up to which the solution is absorbed straight above the way in just 5 min.

 

·       The standard range is 30-50 mm.

Difference Between Scouring & Souring

  • Don’t confuse with this two terms- Scouring and Souring. Both of the process are completely different from each other.
  • Scouring is the process of removing impurities with strong alkali at boiling temperature.
  • Whereas souring is the alkali neutralization process by using dilute acidic solution without any application of heat.

Main 2 Types of Scouring Process

  • Chemical or alkaline scouring- In this type, chemicals are used to conduct scouring process. This process need a lot of chemicals and not eco-friendly at all.
  • Bio-scouring- this process use enzyme for scouring and completely eco-friendly process.

Bio-scouring

  • Alkaline stable pectinase enzyme is used to remove pectin, wax or oil from the fabris.
  • Bio-scouring is eco-friendly process
  • Leave a soft handle on the fabric
  • No core alkali neutralization is needed thus less washing cycle.
  • Less TDS, COD, BOD
  • Find out difference between bio-scouring and alkaline scouring.

Without pre-treatment, dyeing process can’t be carried out. Scouring helps in proper dyeing process.

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