Desizing knowledge

Why sizing?

In order to increase the abrasion resistance, smoothness and antistatic properties of the warp yarn in weaving, increase its strength and cohesion, and improve its weaveability, sizing processing must be carried out before weaving, also known as sizing (protective warp yarn), especially for This is especially true of the widely used high-speed looms (air-jet looms, water-jet looms).

The warp sizing rate is generally 4 to 8% of the cloth weight, and compact fabrics such as poplin will be higher, reaching 8 to 14%.

Note: Knitted fabrics are not sizing.

Why desizing?

After sizing, the slurry penetrates between the fibers and partially adheres to the surface of the warp. While improving the performance of the yarn, the slurry contaminates the dyeing and finishing liquid and hinders the chemical interaction between the fiber and the dyeing material, making it difficult to perform dyeing and finishing. .

Commonly used slurry for desizing

The pulp materials used for warp sizing include natural sizing agents such as starch, wild starch, seaweed gum, gums, etc., chemical sizing agents such as polyvinyl alcohol (PVA), polyacrylic acid (PAA), and cellulose preparations such as carboxymethyl cellulose (CMC). , Polyester, etc. Other ingredients such as preservatives, softeners, hygroscopic agents, and friction reducers are also added to the sizing liquid.

Starch pulp is mostly used for cellulosic fiber fabrics, such as cotton fabrics, hemp fabrics, etc., and chemical pulp is mostly used for synthetic fiber fabrics.

What are the methods of desizing?

The method of desizing of various fabrics varies with the size used for sizing. The following four methods are commonly used.

1. Alkali desizing

Principle of alkali desizing:

1) Under the action of hot lye, the slurry will swell, changing from a gel state to a sol state, and the adhesion to the fiber becomes loose, and it is easy to wash off.

2) The solubility of CMC and PA type slurries in hot lye increases, and they can be easily removed from the fabric after washing with water;

3) Hot caustic soda solution can remove part of natural impurities, especially suitable for cotton cloth containing more cotton seed hulls.

Suitable for all slurries, low desizing rate (50%～70%)

Note: The fabric must be fully washed after desizing, and the lotion must be constantly replaced

2. Enzymatic desizing

Principle of enzyme desizing:

Catalyzes the hydrolysis of starch macromolecular chains to generate low molecular weight compounds with lower molecular weight, lower viscosity and higher solubility, and then wash with water to remove the hydrolyzed product to achieve the purpose of desizing.

Amylase is a biochemical catalyst, and pancreatic amylase and bacterial amylase are commonly used. The main components of these two enzymes are α-amylase, which can promote the cleavage of the glycoside bonds of the long-chain starch molecules to produce dextrin and maltose, which can be easily washed off the fabric. The amylase desizing solution is preferably near neutral, and sodium chloride, calcium chloride, etc. are often added as activators in use to improve the activity of the enzyme. After the fabric is impregnated with amylase solution, the starch can be fully hydrolyzed by stacking it at 40～50℃ for 1～2 hours. Bacterial amylase is more heat-resistant than pancreatic amylase, so after the fabric is soaked with enzyme solution, a fast process of steaming for 3 to 5 minutes can also be used to create conditions for continuous desizing process.

Features: specificity, high efficiency, mild conditions, environmental protection

3. Acid desizing

Principle of desizing:

Acid can hydrolyze starch and other slurries to a certain extent and turn them into soluble products, which can easily fall off the fabric

There are not many domestic applications. Because it is easy to damage the fiber when used, it is not used alone, but used in combination with alkaline desizing or enzyme desizing.

4. Oxidant desizing

Principle of desizing:

The oxidant oxidizes the slurry and degrades until the molecular chain is broken, the solubility increases, and it is removed by washing with water

Especially suitable for PVA slurry

Oxidant:

Sodium bromite, hydrogen peroxide, sodium perborate, hypochlorite, etc. are all oxidants. Sodium bromite (NaBrO2) and hydrogen peroxide (H2O2) are commonly used in production.