Do You Know The Principle Of Mercerizing Technology?

The difference between mercerization and alkali shrinkage is:

Mercerizing:

Cotton products (yarns, fabrics) are treated with concentrated caustic soda under tension conditions, and then wash the caustic soda under tension.

Alkali shrinkage:

Cotton products are treated with concentrated caustic liquor in loose state, so that yarn or fabric can be contracted arbitrarily, and then wash away the caustic soda process, also known as tension-free mercerizing.

First, the purpose of mercerization.

1, gloss and brightness increase after mercerization.

2, adsorption capacity, chemical reaction ability increased, dye dye yield increased.

3. Shrinkage, dimensional stability and fabric smoothness.

4, mechanical properties such as strength and elongation have changed.

Two. Mercerizing process

Classification by process:

1, first bleed after silk:

Mercerizing effect is good, waste alkali is net, but whiteness is poor, easy to stain, suitable for color cloth, especially heavy fabric.

2, first silk and then drift:

The whiteness is good, but the luster is poor. The fabric is easy to be damaged during bleaching. It is suitable for bleached cloth and printed cloth.

3. After dyeing mercerizing:

Suitable for easy scratching or unevenness of varieties (mercerized, fabric feels hard and fast dyed). When dyed dark, in order to improve fabric surface effect and color fastness, as well as some varieties of high gloss requirements, can also be used after dyeing mercerizing.

4. Semi mercerized before dyeing, regular mercerization after dyeing.

In order to improve the adsorption and chemical reactivity of dyes.

Three. Mercerizing effect evaluation

1, gloss

One of the main indexes to measure the appearance effect of mercerized fabric.

We can use variable angle spectrophotometry and polarized light method, but there is no unified ideal testing method.

2. Microscopical observation of fiber morphology.

3. Adsorption properties

(1) barium method is a commonly used method to test mercerizing effect.

Cotton barium value =100, barium value >150 indicates full mercerization, usually 135~150.

(2) iodine absorption method

(3) iodine contamination and staining test method:

Different barium (100~160) samples were treated with iodine solution h or direct blue 2B dye solution to make color cards. Then the iodine contamination of unknown samples and dyeing depth were compared with color cards, and the mercerizing barium value was quantitatively evaluated.

4. Dimensional stability

The shrinkage of the fabric before and after treatment is measured by mechanical shrinkage or impregnation shrinkage. The shrinkage rate is usually calculated by the formula, and the shrinkage rate is usually larger than the zonal direction. However, some of the varieties with higher density have negative shrinkage.

Four. Changes in fiber after mercerizing

1. Morphological structure

The diameter of the fiber increased and the natural twist rate changed (80% to 14.5%). The cross section was deformed to oval or even round by the waist, and the cell cavity contracted to a point. If the proper tension was applied, the fiber roundness increased, the original wrinkles on the surface disappeared, the surface smoothness and optical properties were improved (the reflection of light was changed from diffuse reflection to more directional reflection), and the reflected light was increased. The fabric shows a silky luster.

The change of fiber morphology is the main cause of luster, and tension is the main factor to enhance gloss.

2. Microstructure

Crystalline degree (70% to 50%), amorphous region, so that the original hydroxyl which is not accessible in water becomes accessible. Therefore, the adsorption and chemical properties of the dye are improved. In addition, because of the change of fiber morphology after mercerization, the light scattering between the surface and the interior decreases, so the dyeing depth increases with the concentration of dyes.

After swelling, the hydrogen bonds between macromolecules are disintegrated. Under tension, the arrangement of macromolecules tends to be orderly, and the orientation degree is improved. Meanwhile, the uneven deformation of fiber surface is eliminated, and the weak links are reduced. The fiber can share the external force evenly, thereby reducing the fracture caused by stress concentration. With the addition of extruded rearrangements, the fibers cling to each other and join forces, and also reduce the factors causing breakage due to macromolecule slipping.

3. Changes in molecular structure

After swelling of the cotton fiber in concentrated lye, the hydrogen bonds between the macromolecular chains are dismantled and the internal stress stored in the fabric is relieved. Through stretching, the macromolecules are aligned and new molecular bonds are established in the new position, and the intermolecular force is larger than that before the swelling. Finally, the hydrogen bonds between the aligned fibers are fixed (in a more natural and stable state) when the tension is down, and the fibers are in a lower energy state, so the size is stable.

Four, the main factors of mercerizing Technology

The basic condition of mercerizing is the concentration, temperature, time, tension and alkali removal of NaOH solution.

1, alkali concentration

Main factors affecting mercerizing effect

(1) the length and diameter of cotton fibers treated with different concentrations of caustic soda solution:

Concentration >8%, diameter increased, length shortened to maximum.

Shrinkage and dyeing of cotton yarn in different concentrations of NaOH solution

3. Concentration requirement of cotton mercerizing (C and shrinkage and barium value)

When C=177g/L, the barium value is 150, C=245g/l and barium are the highest.

C=240~280g/l, the shrinkage tends to be stable.

Therefore, the best caustic soda concentration for mercerizing is about 245g/l. Considering the alkali absorption of fabric and alkali consumption in the air, the mercerizing soda concentration of cotton cloth is 260 ~ 280g/l. 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) the effect of tension on fabric gloss.

When cotton fabric is treated with strong alkali, only proper tension is added to show good luster. The effect of tension on the properties of cotton yarn mercerization can be seen: the tension is large and the gloss is good.

2) the effect of tension on the mechanical properties and adsorption properties of fabrics.

The strength of cotton yarn has been improved under the condition of inability. If the appropriate tension is applied, its strength can be further improved, but the gloss increases little, and the fracture elongation and adsorption properties decrease.

3) the effect of tension on shrinkage of fabric.

In the mercerizing process, the warp and weft tension plays an important role in fabric shrinkage.

In actual production, the shrinkage ratio of warp and weft fabrics of various specifications is unbalanced. Khaki, Fu tune and other fabrics with higher density have a higher shrinkage rate than the zonal shrinkage, so the meridional tension is preferred.

3, temperature

The role of caustic soda and cellulose fiber is exothermic reaction, so increasing the temperature of alkali solution can weaken the swelling effect of fiber, thereby reducing the mercerizing effect. It shows that the shrinkage rate and the barium value decrease, so the mercerizing lye is better at low temperature, but in actual production, the economic benefits are taken into account, and the viscosity of liquid is too low to increase the viscosity of the alkali liquor, so that the liquid can hardly penetrate into the yarn and fabric. It is difficult to expand, so it is usually used to pass cold water into the sandwich layer to cool the lye.

4, time

The mercerizing action is to make caustic soda rapidly and evenly penetrate into the inner part of cotton or fabric and produce fiber. Therefore, a certain time must be guaranteed.

When the cotton yarn is used for 280g/lNaOH under the condition of no tension, it is found that the yarn shrinkage rate and the dye absorption rate reach the maximum value at 20s time. The prolonging time is not significant to enhance the mercerizing effect. In addition, the time is related to the alkali concentration and temperature. When the concentration is low, the action time should be appropriately extended; generally 50 ~ 60s.

5. Remove alkali.

Alkali removal has a great effect on the shaping effect of mercerizing. If the tension is relaxed, more than 5% alkali is still on the fabric, the fabric will shrink, which will affect the gloss and the weft shrinkage rate. De alkali is divided into two steps: (1) under the condition of enlargement, the hot and dilute alkali is used to rinse the fabric with flushing device.

Five. Mercerizing equipment

Commonly used mercerizing machines include cloth mercerizing, bending roll mercerizing and straight roller mercerizing machine. The cloth mercerizing machine has the best effect and the most extensive application.

1, cloth mercerizing machine

It is composed of pre rolling base tank, cloth roller, post rolling alkali bath, cloth expanding device, alkali removing box, horizontal washing machine and so on.

Advantages: tension is easy to control, fabric shrinkage and alkali removal are better than its mercerizing machine.

Disadvantages: cloth parts are prone to mechanical defects, and the equipment occupies a large area.

2. Bending roller mercerizing machine

The difference between the mercerizing machine and the cloth mercerizing machine is mainly in the enlarging and initial washing parts, and the enlarging part is composed of a shallow flat step iron groove and 10~12 pairs of bending rollers. The enlarging effect is widened by the zonal force generated by the fabric around the curved camshaft of the curved sleeve. In the process of bending roll mercerizing machine, two layers of fabric are often folded together, and the output is higher, but the efficiency of alkali washing is low and the expansion effect is poor. Although it has the advantages of short fuselage and single tube structure, it is easy to produce uneven density, and the weft yarn is curved and moon shaped.

3. Straight roller mercerizing machine

Unlike the first two, there are no rollers and rollers, nor expansion devices.

Features: double deck, high yield, uniform mercerization, no break edge, short fuselage, simple transmission and easy operation, but the expansion effect is poor (the drawback shrinkage rate is difficult to reach the national standard), which is the main drawback. Some factories in China use cloth and straight roller to solve this problem.