Scouring is the pretreatment process of wet processing technology. Scouring is the first stage of pretreatment. Before dyeing or printing of textile materials natural fibers must pass scouring process. Scouring process bears an impotency in wet processing.
Scouring is the process by which natural (oil, wax, gum, fat etc) as well as added (during fabrication process) impurities are removed completely as possible. Especially hydrophobic character which is present in the fiber of fabric is removed by this process.
Objectives of Scouring: Scouring process has some important objectives. The objectives of scouring process are given bellow:
- The main purpose of the scouring is to remove impurities from the textile materials.
- The textile materials are leave in a highly absorptive condition without undergoing any chemical or physical damage significantly.
- After scouring process materials become suitable for next bleaching process.
Effects of Scouring: Followings changes occurred during scouring process:
- Saponifiable oils and free fatty acids are converted into soaps.
- Pectose and pectin are changed into soluble salts of pectic acid.
- Proteins are hydrolysed into soluble degradation products.
- Mineral matters are dissolved in the water.
- Unsaponifiable oils and waxes are emulsified by the soaps formed from saponification.
- Dust particles are removed and held in suspension.
In above I have written about Saponification. So, the reaction by which the insoluble and water immiscible materials are converted into water soluble products is called saponification. The reaction is as follows:
Oil + Caustic soda + Water = Soap + glycerin
Methods of Scouring: Scouring process is done by the following two ways. They are:
- Continuous process: In this process scouring of the fabric is done continuously in a J-Box. In this machine pretreatment and dyeing process are done continuously. This type of application is very limited.
- Discontinuous process: This type of process also called batch process. Here scouring is done discontinuously in Kier Boiler, Jigger or Winch dyeing machine. Before dyeing different batch or lot is created.
In the dyeing machine different controlling parameters are controlled strictly. I like to give a sample recipe of scoring process of cotton in kier boiler.
Caustic Soda = 0.5 to 3% on the weight of fabric (owf)
Sodium-bi-Carbonate = 0.5 to 1% owf
Wetting Agent = 0.5 to 1% owf
Materials: Liquor = 1: 6/8/10/12 (as required)
Temperature = 100 to 140 degree Celsius
Pressure = 10 to 30 PSI
Time = 60 to 90 minutes
Material forms = Rope or Open width
Scouring is generally done for natural fiber. Better dyeing or printing performance depends on better scouring of the materials. Otherwise different types of dyeing or printing faults are appearing on the face of the fabric. So, it needs to take care on scouring process. It also depends on the shade of the fabric. Generally it is important for light shade dyeing.
So, Scouring agent is supplied by different textile chemical manufacturing companies. Before use the scouring agent one should ensure the properties of scouring agent.