What is the purpose of cooking of cotton fabric?

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

The impurities in the fabric mainly include pectin and waxy substances, which are mainly distributed on the surface of the fibers; in addition, there are nitrogen-containing substances and cottonseed husks.

2. Cooking principle and ingredients

The scouring process is very complex, including hydrolysis, saponification, metathesis, solubilization, emulsification, dissolution and mechanical action in this process. These functions can be accomplished with the help of certain refining agents. Caustic soda is the scouring agent in the scouring liquid; in addition, some auxiliary agents such as penetrating agent, refining agent, dispersing agent, 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, so that the molecular chain is broken and dissolved and removed.

2. remove nitrogenous substances

Under the action of hot alkali, the amine chain in the nitrogen-containing substance molecule is hydrolyzed and broken, and soluble sodium amino acid is generated and removed.

3. Removes fatty acids from waxy substances

The fatty acid in the waxy substance is saponified and dissolved under the action of hot alkali, and then removed by washing, and the rest of the higher fatty alcohols and hydrocarbons are removed by emulsification. It is also converted into soap during saponification, and can be converted into an emulsifier during cooking.

4. Remove certain components from cotton husks

The oil, protein, tannin and some polysaccharides in the cotton husk can be dissolved and removed by some chemical action with caustic soda. As for lignin, due to the presence of phenolic hydroxyl groups in its substructure, it may swell and become soft after being reacted with caustic soda during the scouring process, and the adhesion to the fabric is reduced. It falls off, but it is not easy to clean, and a large part is still attached to the fabric. During bleaching, the oxidant can oxidize it to achieve the removal operation.

5. Remove some inorganic salts

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