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Industrial weaving yarn manufacturers explain the principle of yarn mercerization process


What is mercerization

Cotton products (yarn, fabric) are treated with concentrated caustic soda solution under tension, and then washed away under tension.


1、 Purpose of mercerization


1. The luster and brightness are improved after mercerization;

2. The adsorption capacity and chemical reaction capacity are enhanced, and the dye yield is improved;

3. Shrinkage, dimensional stability, and improved fabric flatness;

4. The mechanical properties such as strength and extensibility have changed.


2、 Mercerization process

Classification by process:

1. Bleaching before silk: good mercerizing effect, relatively clean waste alkali, but poor whiteness, easy to stain, suitable for colored cloth, especially heavy fabrics.

2. First silk and then bleaching: good whiteness, but poor gloss. The fabric is easy to be damaged during bleaching. It is suitable for bleached cloth and printed cloth.

3. Mercerization after dyeing: it is suitable for varieties that are easy to scratch or not easy to be leveled (after mercerization, the fabric feels hard and dyes faster). When dyeing dark colors, in order to improve the surface effect and dyeing fastness of the fabric, and some varieties that require high gloss, mercerization after dyeing can also be used.

4. Half mercerization before dyeing and conventional mercerization after dyeing: in order to improve the adsorption and chemical reactivity of dyes.


3、 Evaluation of mercerizing effect

1. Gloss: one of the main indicators to measure the appearance effect of mercerized fabrics.

It can be measured by variable angle photometry and polarized light, but there is no unified and ideal test method. At present, it is mostly evaluated by visual inspection.

2. The morphological changes of fibers were observed by microsection

3. Adsorption performance

(1) Barium value method: it is a common method to test the mercerization effect. Large barium value has good mercerization effect. Barium value of cotton cloth =100, barium value > 150 indicates full mercerization, generally 135 ~ 150.

(2) Iodine absorption method

(3) Iodine contamination and dyeing test method: samples with different barium values (100 ~ 160) are treated with a certain concentration of iodine solution h or direct blue 2B dye solution to make a color card, and then the iodine contamination and dyeing depth of unknown samples are compared with the color card to quantitatively evaluate the barium mercerization value.

4. Dimensional stability: the change of fabric length before and after treatment is measured by mechanical shrinkage method or impregnation shrinkage method, and the shrinkage is calculated by formula. Generally, the shrinkage in warp direction is often greater than that in weft direction, but some varieties with higher warp density produce negative shrinkage (large door width).





4、 Fiber changes after mercerization


1. Morphological structure


The fiber diameter Zeng becomes larger and rounder, the longitudinal natural twist rate changes (80% to 14.5%), the cross section changes from waist to oval, or even round, and the cell cavity shrinks to a little. If appropriate tension is applied, the fiber roundness Zeng becomes larger, the original wrinkles on the surface disappear, the surface smoothness, the optical properties are improved, the intensity of reflected light is increased, and the fabric shows a silky luster.



2. Microstructure

Crystallinity ↓ (70 → 50%) and amorphous area ↑ make the hydroxyl that was not accessible in water accessible, so the adsorption and chemical reaction properties of the fiber to the dye are improved. In addition, due to the change of fiber morphology after mercerization, the light scattering on the surface and inside is reduced, so the dyeing depth is also increased when dyeing with the same concentration of dye.


After the fiber swells, the hydrogen bonds between macromolecules are broken up. Under the action of tension, the arrangement of macromolecules tends to be neat, which improves the degree of orientation. At the same time, the uneven deformation of the fiber surface is eliminated, reducing the weak links.



The fiber can evenly share the external force, thereby reducing the fracture phenomenon caused by stress concentration. It also reduces the factors of fracture caused by macromolecular slip.










3. Changes in molecular structure






After the cotton fiber swells in the concentrated alkali solution, the hydrogen bonds between the macromolecular chains are disassembled, which relieves the internal stress stored in the fabric. Through stretching, the macromolecules are oriented and arranged, and new molecular bonds are established at new positions, and the intermolecular force is greater than that before swelling.










After Zui, the hydrogen bonds between the oriented fibers are fixed under tension, and the fibers are in a low energy state, so the size is stable.






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5、 Main factors of mercerization process






1. Alkali concentration: the main factor affecting mercerizing effect






(1) The changes of length and diameter of cotton fiber treated with different concentrations of caustic soda solution: when the concentration is > 8%, the diameter increases and the length shortens to Zui.










(2) Shrinkage and dyeing force of cotton yarn in NaOH solution with different concentrations








(3) The concentration requirements of cotton mercerization (relationship between C and shrinkage and barium value) when c=177g/l, barium value is 150, c=245g/l, barium value: Zui high. C=240~280g/l, and the shrinkage tends to be stable.








In actual production, it can be selected according to the quality of semi-finished products and the quality requirements of finished products.






2. Tension






(1) Influence of tension on fabric gloss: when cotton fabric is treated with concentrated alkali, only with appropriate tension can it show good gloss. From the influence of tension on the properties of cotton yarn after mercerization, it can be seen that high tension and good gloss.








(2) The influence of tension on the mechanical properties and adsorption properties of fabrics: that is, under weak conditions, the Qiang force of cotton yarn has been improved. If appropriate tension is applied, the Qiang force can be further improved, but the gloss is not increased much, and the fracture elongation and adsorption properties are decreased.










(3) The influence of tension on fabric shrinkage: during mercerization, the tension in warp and weft plays an important role in fabric shrinkage.






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3. Temperature






The effect of caustic soda and cellulose fiber is exothermic reaction, so increasing the temperature of caustic soda can weaken the swelling of fiber, thus reducing the mercerizing effect, which is manifested in the decrease of shrinkage and barium value. Therefore, the mercerizing caustic soda is better at low temperature. However, in actual production, considering the economic benefits and the low temperature, the viscosity of caustic soda is Zeng, which makes it difficult for the reducing solution to penetrate into the yarn and fabric, and then it is difficult to expand, Therefore, cold water is usually introduced into the interlayer of the rolling groove to cool the lye.








4. Time






Mercerization is to make caustic soda quickly, evenly and fully penetrate into the interior of cotton yarn or fabric and act on the fiber, so Bi must ensure a certain time.








The cotton yarn was mercerized with 280g/l NaOH under no tension. It was found that the yarn shrinkage and dye absorption could reach Zui value in 20s, and the extension of time did not significantly improve the mercerization effect.








5. Dealkalization






Alkali removal has a great impact on the setting effect of mercerization. If there is more than 5% alkali on the fabric after the tension is relaxed, the fabric will still shrink, thus affecting the gloss and weft shrinkage.










Alkali removal is carried out in two steps: ① in the case of expanding, use the flushing and suction device to wash the fabric with hot dilute alkali; ② After relaxing the weft tension, enter the alkali removal tank and wash and steam with light alkali.


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