Comprehensive Explanation Of Mercerizing Technology Principle

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

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 drift after silk: mercerizing effect is good, waste alkali is more net, but whiteness is poor, easy to stain, suitable for color cloth, especially heavy fabric.

2. First silk and then bleach: good whiteness, but poor luster. Fabrics are easy to be damaged during bleaching.

Printed cloth.

3. After dyeing mercerizing: it is suitable for varieties that are easy to scratch or not to be leveled. (after mercerizing, the fabric feels hard and dyed fast). In order to improve the surface effect and color fastness of fabrics and some varieties which require high gloss, dyed mercerizing can also be used.

(PS:) mercerized dyes are selective.

4. Semi mercerizing before dyeing and conventional 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. It can be measured by means of variable angle spectrophotometry and polarized light. However, there is no uniform and ideal testing method.

2. Microscopical observation of fiber morphology.

3. Adsorption properties

(1) barium method is a commonly used method to test mercerizing effect. The barium value is large and mercerizing effect is good.

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

(2) iodine absorption method

(3) iodine staining and staining test method: different barium value (100~160) sample, with a certain concentration of iodine liquid h or direct blue 2B dye treatment, made color card, and then the iodine stain of unknown samples and dyeing depth and color card comparison, quantitative evaluation of the value of barium mercerization value.

Use

The shrinkage of the fabric before and after treatment is measured by impregnation shrinkage method. The shrinkage rate is usually larger than the zonal direction by formula, but the negative shrinkage rate of some varieties with higher density is higher than that of the zonal.

Four. Changes in fiber after mercerizing

1. Morphological structure

Fiber diameter increased and round, and longitudinal 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 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), which increased the intensity of reflected light, and the fabric showed a silk 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.

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

1. Lye Concentration: the main factor affecting mercerizing effect.

(1)

The change of length and diameter after treatment with different concentrations of caustic soda solution: the concentration >8%, the diameter increased, and the length shortened to the maximum.

(2)

Shrinkage and dyeing strength in different concentrations of NaOH solution

(3) cotton silk mercerization on the concentration requirements (C and contraction and barium value) C=177g/L, the barium value is 150, C=245g/l, barium value: 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 lustre: 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: tension is large and gloss is good.

(2) tension.

The influence of mechanical properties and adsorption properties: the strength of cotton yarn has been improved under the condition of inability, and the tensile strength can be further improved if the suitable tension is applied, but the gloss increases little, and the fracture elongation and adsorption properties decrease.

(3) the effect of tension on the shrinkage of fabrics: when the mercerization is applied, the warp and weft tension plays a very important role in the shrinkage of fabrics.

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 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 solution, which makes it difficult for the liquid to penetrate into the yarn and fabric, and the expansion is more difficult.

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.