What Is The Purpose of Scouring?

After the cotton cloth is desized, although most of the sizing and a small part of the natural impurities have been removed, there is still a small amount of sizing and most of the impurities. The presence of these impurities not only makes the cloth surface yellow, affects the appearance of the fabric, but also reduces the quality of the fabric. It affects the hygroscopicity of the fabric and affects the continuation of raw processing. Therefore, most of the desized cotton fabrics need to be boiled and bleached. Scouring is the process of chemically removing natural impurities from cotton fabrics and refining and purifying the cellulose. After scouring cotton cloth, its hygroscopicity and whiteness are improved.

The impurities contained in fabrics mainly include pectin and waxy substances, which are mainly distributed on the surface of the fiber; in addition, there are also nitrogen-containing substances and cottonseed hulls.

Scouring principles and ingredients

The cooking process is very complex, including hydrolysis, saponification, metathesis, solubilization, emulsification, dissolution and mechanical effects. These functions can be accomplished with the help of certain scouring agents. Caustic soda is used as the scouring agent in the scouring liquid; in addition, some auxiliaries such as penetrants, refining agents, dispersants, etc. are added.

1. Remove pectin

Under the action of hot alkali, the fabric hydrolyzes the calcium and magnesium salts of pectic acid and methyl pectate into sodium pectate, causing the molecular chain to break and be dissolved and removed.

2. Remove nitrogenous substances

Under the action of hot alkali, the amine chain in the nitrogen-containing substance molecules undergoes hydrolysis and cleavage, generating soluble sodium amino acid for removal.

3． Remove fatty acids from waxy substances

The fatty acids in the waxy substance are saponified and dissolved under the action of hot alkali, and then removed by washing with water. The remaining higher fatty alcohols and hydrocarbons are removed by emulsification. Commonly used emulsifiers are soap and flat fatty acids. It is also converted into soap during saponification and can be converted into an emulsifier during cooking.

4. Removing certain components from the cotton husk

The oil, protein, tannins and some polysaccharides in cotton shells can be dissolved and removed by certain chemical reactions with caustic soda. As for lignin, due to the presence of phenolic hydroxyl groups in its substructure, it may swell and become soft after reacting with caustic soda during the cooking process, and its adhesion to the fabric is reduced. In addition, part of the tissue dissolves and disintegrates, and the remaining parts are washed and rubbed. It falls off, but it is not easy to remove. There is still a large part attached to the fabric. During bleaching, the oxidant can oxidize it to achieve removal.

5. Remove some inorganic salts

Under the action of hot alkali, inorganic salts undergo chemical and physical reactions and are removed through emulsification, saponification, dispersion machinery, etc.

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