Why Does Pre-treatment Require Desizing?

Speaking of desizing, we have to mention the three major sizing materials in the textile sizing industry: starch and derivatives, polyvinyl alcohol (PVA), and acrylic sizing. PVA has been gradually phased out due to environmental issues, and most of them are now used in combination with starch and acrylic slurry.

Four commonly used desizing methods: hot water desizing, alkali desizing, enzyme desizing, and oxidative desizing. Enzyme desizing and alkali desizing are currently used more frequently, and enzyme desizing (amylase) is mainly targeted at starch sizing. The desizing effect is generally evaluated by the desizing level. Among the three major slurries, acrylic slurry is easier to remove, while starch slurry and PVA both have simple and fast test methods (such as iodine/potassium iodide method.)

Insufficient desizing will affect the coloring rate of the dye during dyeing, or cause the fabric's feel to deteriorate.

Sizing basics

Sizing is a very important process. The sizing machine produces for one minute and the loom runs for one shift. From this, it can be seen that the quality of the sizing is closely related to the realization of high quality, high yield and low consumption in the weaving process. Therefore, in the sizing process, the selection of sizing materials, the performance of sizing and sizing machinery, process conditions and operating techniques are all important links. A slight negligence will cause a factory-wide disaster.

Before the warp is weaved, the warp must be sized with sizing material to increase the wear resistance of the warp and the strength of the single yarn so that the weaving can proceed smoothly. This process is called sizing.

For warp yarns that have not been sized, since the heads and tails of many fibers are exposed on the surface of the yarn, hairiness is formed, and the cohesion between the fibers is not strong enough. During the weaving process, due to thousands of repeated stretching (caused by shedding, beating, and winding), friction (warp yarns and warp yarns, warp yarns and weft yarns, warp yarns and reeds, drop pieces, back beams and other components) and bending Due to the mechanical action, the warp yarns will become loose and fluffy, causing ends to break, affecting the production efficiency of the loom and the quality of the fabric. Therefore the warp yarns need to be sized.

The task of sizing is to adsorb the slurry on the surface of the yarn and form a smooth and tough film after drying, so that the hairiness is close to the surface and the surface is smooth, thereby improving the wear resistance of the yarn. In addition, some of the slurry penetrates into the interior of the yarn, making the yarn The fibers adhere to each other, increasing the cohesion between fibers and improving the breaking strength of the warp yarns. Practice has proved that the warp strength after sizing is increased by 10% to 30% than before sizing.

Appropriately increasing the warp strength can reduce warp yarn breakage on the loom, but if the strength is too large, the yarn will be brittle and hard, easy to break, and the process performance will be reduced. Appropriately increasing the strength of the warp yarn (reinforcement), maximizing the elasticity of the warp yarn (maintaining stretch), reducing the hairiness of the warp yarn and reducing the friction coefficient (friction reduction) are the basic requirements for sizing. Wear resistance and adhesion hairiness are particularly important for new shuttleless looms.

The performance changes of warp yarns after sizing, under certain conditions, depend on the ratio of "covering" and "soaking" of the yarns with the sizing liquid during sizing. The ideal sizing should be that part of the sizing liquid penetrates into the yarn, filling the gaps between fibers and serving as a solid foundation for the sizing film; part of the sizing liquid forms a smooth and tough film on the surface of the yarn. If the amount of penetration is too little, the sizing film will not be resistant to friction and will easily fall off; if the amount of penetration is too much, the elasticity of the yarn will be lost too much and breakage will easily occur.

Sizing is a very important process. It is one of the most important factors in reducing warp breakage during weaving and improving product quality. If the sizing work is slightly neglected, it will seriously affect the weaving production; conversely, if the sizing is handled properly, poor quality warp yarns can also be improved to a certain extent. Weavers have a saying: "One minute of sizing, one shift of cloth machine." It shows the importance of the sizing process in the weaving process, and workers call the sizing process the "tiger's mouth".

Usually single yarn must be sized, depending on the warp type, density and yarn characteristics. The starch sizing rate of cotton single yarn is generally 7% to 17%, the mixed sizing rate is 4% to 12%, and the chemical sizing rate is 2.5 %~9%. Strand sizing or otherwise depends on the specific situation. Medium and special strands, such as 14texX2, generally do not need to be sized or only dehydrated and axially processed. For example, for corduroy fabrics with larger weft density (669 threads/10cm) (due to repeated mechanical action) and thin special strands with lower strength, such as 9.5texX2, the sizing rate is generally controlled at about 2%.

The sizing process is divided into two parts: sizing (preparing slurry and cooking the slurry) and sizing (making the slurry stick to the warp yarns and drying them, and then winding the warp yarns onto the pulp shaft).

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