Desizing Process in Textile Industry

Desizing Process: One of the Most Significant Procedures in Pretreatment of Dyeing

Sanjida Mehrin
B.Sc. in Textile Engineering
Textile Engineering College, Zorargonj, Chattogram

Abstract:
One of the most important steps in the pretreatment of grey cotton cloth is desizing. It is imperative to eliminate the size coating from the fabric before dyeing and printing. Cotton fabric is desized utilizing greener production techniques that replace harmful materials with the environmentally suitable substance like amylase. Hydrolytic desizing is a human and eco-friendly technique. The features and outcomes of hydrolytic desizing were examined using four different kinds of equipment. In the context of the textile wet processing sector, this article describes the advantages, methods, and outcomes of environmentally friendly desizing methods.

Definition of Desizing:
Desizing is the process by which size or sizing materials can be removed from the textile or fabrics. Although desizing is more crucial for cotton fibers, synthetic fabrics also require the removal of additions made during spinning before proceeding with latter procedures. The most common sizes include polyacrylates, cellulose ethers, natural starch, and starch ethers. Affordable starch-based mixtures work well for cotton fibers. Based on the variety of sizing agent that needs to be removed, several desizing processes exist.

Purpose behind Desizing:
The procedure of desizing involves taking the sizing materials out of the warp threads of the fabrics that are weaved. Size agents are applied to warp yarns before they weaved in order to lessen their frictional characteristics, reduce yarn breaks on the loom, and boost weft insertion speeds. The operations of dying, printing, and finishing could be hampered if the sizes are present. Performing desizing is the basis for the subsequent wet operations of bleaching, mercerizing, dying, printing, or finishing. The kind of sizing agent employed determines the desizing techniques and materials.

Types of Desizing Methods:
Mainly there are two types of desizing methods. They are given below:

A. Hydrolytic method:

Rot steeping
Alkali steeping
Acid steeping
Enzymatic steeping

B. Oxidative method:

Brometic desizing
Chlorite desizing
Ammonium per sulphate desizing

Above desizing methods are described below:

Rot steeping:
The earliest and least expensive method of desizing without the use of a specific chemical is rot steeping. Cloth is immersed in 40-60°C warm water throughout the rot steeping process to extract 100% of its expression. In this process, the fabric has to be socked in the warm water for at least 12-24hours. Even though this approach is the least expensive, its biggest drawback is how lengthy it is—it cannot be guaranteed that the material will be removed in the allotted amount of time. Moreover the fabric can be degraded and face shrinkage.

Acid steeping:
Cotton material is treated with diluted sulfuric acid of 0.5-1% or HCl for three to four hours at a temperature of approximately 40-60°C. This procedure is known as acid desizing. Little water soluble or soluble chain segments are created when diluted acid assaults the starch polymer chain, causing chain cleavage. There is always a possibility that sulphuric acid concentrations over ten g/1 and temperatures exceeding 50°C will weaken the fabric or create holes. Cotton degeneration will happen at the dried area if the treated cloth is left to dry on its own.

Enzymatic steeping:
Among the various sorts, it ranks as one of the more significant desizing. Using enzymes, the enzymatic desizing breaks down the starch size in cotton fibers. Enzymes are intricate, soluble, organic biocatalysts that are produced by living things and are employed to catalyze chemical reactions in biological processes. Enzymes work on a given substance in a very specific way. A significant amount of material can be broken down by a tiny amount of the enzyme. The grey cloth is normally pre-washed (0.5 g/l non-ionic wetting agent) at 90°C before undergoing an enzyme desizing procedure. The enzymes known as amylases hydrolyze, lower the molecular weight of the starch’s amylose and amylopectin molecules, making the starch sufficiently soluble in water to be removed from fabric .Strict control over the pH level, temperature, mineral content of the water, electrolyte addition, and surfactant selection is necessary for effective enzymatic desizing. At 50-60°C temperature the fabric are socked for 3-4 hours. The pH level is usually 6-7.5. Shrinkage doesn’t occur though the fabric may degrade by some extent.

Alkali steeping:
Applying alkaline hydrolysis, size material is extracted from the cloth in this approach. It is kept for eight to ten hours at 60 to 70 degrees Celsius in a 0.4-0.6% sodium hydroxide solution. Following that, use water to wash the fabric to get rid of the size materials. To ensure that the fabric doesn’t dry out while desizing, however, caution must be taken. It’s an extremely affordable and popular method.

Oxidative method:
Since oxidative desizing carries a very significant risk of damaging the cellulose fiber, it is rarely used for desizing. As oxidizing agent potassium, sodium persulphate or sodium bromite are used in oxidative desizing. By reducing the number of cloth preparation steps, oxidative desizing lowers the total energy usage. It is possible to add the oxidant to the hot caustic scour liquor without much or no need for magnesium silicate or natural stabilizer. More stringent control over alkali and oxidant ratios is necessary for rapid desizing treatments. The extent of chemical damage tends to rise with increasing alkalinity for a specific oxidant concentration and with increased oxidant above what is required for effective desizing. Compared to hydrogen peroxide Spersulphate stimulates desizing over whitening and requires more precise concentration control.

FAQs:

1. What are the goals behind the desizing process of the woven fabric?
Ans: The purpose of desizing is to take the size out of the warp strands in woven fabrics. A sizing agent is applied to warp yarns to lessen their frictional qualities, minimize yarn breakage, and increase weaving output. When wet processing, the sizing material acts as a resist to chemicals and dyes.

2. What type of enzyme is used for enzymatic steeping?
Ans: Enzyme is a highly molecular weighted living organism mainly consists of protein which also acts as a catalyst in chemical reaction. There are mainly two varieties of enzymes. They are cellulase enzyme and amylase enzyme. Here cellulase enzymes participate in the breakdown of cellulose and turn it into glucose. For this reason, this type of enzyme is not suitable for enzymatic steeping as it will degrade the fabric and dissolve it. As a result various types of amylase enzyme are used for this desizing process.

3. Which desizing method is more suitable for industrial purposes?
Ans: Out of all the desizing procedures, enzymatic steeping is the more suitable for using in industry. Because the enzymatic desizing process is easy to use, has a high rate of desizing, appropriate for continuous production which helps to decrease the production costing. It also doesn’t harm fiber. It is also good for the environment than the other methods of desizing as the wastage is biodegradable and the starch slurry can be effectively removed by BBT enzyme amylase A32.

4. What are the disadvantages of oxidative method?
Ans: The use of harsh chemicals, the potential of fiber attack and the limited range of application techniques are some drawbacks of oxidative desizing.