The Complete Guide To Desizing-1

 

desizing

In textile dyeing-finishing production, there are many factors influencing the dyeing-finishing result due to the multiple steps. Desizing is an important process before dyeing-finishing, the desizing results directly affect the inner and appearance quality of fabric dyeing and printing.Therefore, how to choose desizing agent and judge whether desizing process can meet the requirements is particularly important.

Sizing (process before desizing)

Weaving is a process of repeatedly forcing the yarn to move.In order to prevent or reduce yarn breakage during weaving and improve work efficiency, the yarn is treated with sizes to form a film on the yarn surface, so as to achieve the purpose of reducing hairiness, wear resistance and increasing strength.
In the past, it was generally believed that the purpose of warp sizing was to increase the yarn breaking strength, maintain the yarn breaking elongation and improve the wear resistance, so the main quality indexes for the inspection of warp sizing yarn in textile mills were the strengthening rate and elongation retention rate.However, in recent years, the objective of warp sizing is wear-resisting and hair-reducing, so adhesive force, wear-resisting times and hair-reducing rate have been used to evaluate warp sizing effect.
After sizing, the size penetrates into the fiber, and part of it is attached to the warp surface. While improving the yarn performance, the size contaminates the dyeing-finishing processing fluid, hinders the chemical interaction between fiber and dyeing chemicals, and makes dyeing-finishing processing difficult. Desizing process is required to remove the sizes.

Desizing

This is an important process before dyeing-finishing, the desizing results directly affect the inner and appearance quality of fabric dyeing and printing, such as soaping color fastness and color brilliance.In order to better understand the desizing process of fabric and evaluate the desizing degree, it is necessary to measure the desizing rate of fabric accurately as soon as possible.

Desizing agent

The role of desizing agent is to make the size on the fabric can be removed as far as possible to ensure the smooth progress of the following process. Fabric desizing process according to the sizes to decide which desizing agent to choose. Generally can be divided into alkali desizing, alkali acid desizing, enzyme desizing and oxidation desizing.

​Alkali desizing

PVA – based mixed sizes (containing starch) and PA type sizes with this method. A method for removing starch, polyvinyl alcohol and other sizing materials from fabric with dilute solution of caustic soda. Desizing rate is about 70%. This method is safe, reliable, low cost, wide applicability, is one of the commonly used desizing methods.Principle: starch, PVA and other sizes in alkali solution easy to expand, so that it becomes a sol state, reduce the adhesion with fiber, so as to facilitate water washing sizes removal.

Alkali-acid desizing

A method of removing size from fabric by treating it first with alkali and then with acid. After alkali desizing, fabric has to remove most of the sizes, but base sizes viscosity is higher, often part of the sizes will be attached on the fabric, processed with dilute acid solution at this moment, not only can decrease the residual starch hydrolysis, improve the effect of desizing, also can remove minerals on the fiber, improve the fabric whiteness and absorbent.

​​Enzyme desizing

​A method of removing starch size from fabric using amylase. Amylase commonly used for desizing malt amylase, pancreatic amylase and bacterial amylase, etc., each has the best use conditions, must strictly control pH value, temperature and other technological conditions.

Oxidant desizing

​Mainly used for desizing PVA and its mixed sizes. The size on the fabric is removed by oxidation decomposition of oxidant. Oxidant desizing efficiency is high, widely used, not only can return starch size, but also can return other chemical sizes and mixed sizes. However, attention should be paid to the control of process conditions, otherwise it will damage the fiber.
No matter what desizing process, its principle is to make the slurry polymer compound into low molecular compound, and make the slurry insoluble material into water soluble material, easy to remove. Desizing, in addition to the use of acid, alkali, enzyme and oxidizer, in order to speed up the desizing speed and improve the desizing effect. It is necessary to add auxiliary agents, this kind of additives known as desizing additives.

Due to space limitations, more details about Quantitative method for starch and PVA desizing rate will be posted on the next article.

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