Mercerizing

Mercerization is the processing technology of cellulose fiber textiles treated with concentrated caustic soda solution under the condition of tension.

There are two forms ：fabric mercerization and yarn mercerization

Mechanism: Changes of supramolecular structure and morphological structure of cotton fiber

Purpose: To get a good shine

I. Mercerizing equipment and process types

Basic equipment type：Clip mercerizing machine，Straight roll mercerizing machine，and bending roll mercerizing machine

according to the temperature of alkali immersion: Cold mercerizing (15 ~ 20℃) and Thermal mercerizing (60 ~ 70℃)

According to fabric input: Dry cloth mercerizing (dry into) and Wet cloth mercerizing (wet into)

wet mercerizing reduce one drying process, and with strong lye penetration, uniform treatment, low shrinkage rate, good dyeing uniformity, however Fabric moisture will dilute lye and increase the recycling burden. That’s why during the production, it is mainly dry mercerizing.

According to the process: grey cloth mercerizing, mercerizing before bleaching, mercerizing after bleaching, mercerizing after dyeing

1. Caustic soda concentration

1.1 Only when the concentration of caustic soda reaches a certain critical value, it can cause significant irreversible swelling of cotton fiber

1.2 According to the test, when the concentration of lye is more than 8%, the diameter of the fiber will increase, and length of cotton fiber will shorten, with the increase of the concentration of lye

1.3 The patch of fiber contraction and diameter increase is similar

First, the fiber continue to swell in lye, then dip into water and begin to contract, and finally completely dry

1.4 Cotton fiber in the concentrated lye will gradually swelling after washing and drying, the diameter will be reduced, the length will increase, but cannot return to the original state

1.5 If the treatment effect of barium is 150, 170g/L concentration is required. However, considering the luster and certain amount of caustic soda absorbed by the cotton itself, 260 ~ 280g/L is used in production

2. Tension

2.1 The application of tension will improve the luster, it is obviously better than the relaxation treatment, and it also will increase cotton yarn strength;

2.2 The breaking elongation of cotton yarn decreases with the increase of tension

2.3 With too large tension, the luster of the product does not increase much, while the fracture elongation decreases;

2.4 Relaxation treatment on the fabric luster and strength is small, but it can improve the elasticity of the fabric, the fracture elongation has a greater increase

2.5 Mercerizing can eliminate the original stress in the fiber and increase the dimensional stability of the fabric

2.6 Elongation has an important influence on the zonal dimensional stability of finished products

2.7 Elongation rate also needs to be considered

2.8 The zonal tension is controlled by the stretching distance between the clip chains, and the meridional tension is controlled by adjusting the linear speed of the front and back alkali groove rolling mill

3. Temperature

3.1 The reaction between caustic soda and cellulose is exothermic reaction, reducing the temperature is conducive to the swelling of fibers

3.2 Under the condition of the same lye concentration, the higher the temperature, the smaller the shrinkage rate and barium value of the product, which will reduce the mercerization effect

3.3 Low temperature, the need for strong cooling capacity; The concentration of lye increases significantly, which makes it difficult for the lye to penetrate into the inner part of the yarn, resulting in opaque mercerization and surface mercerization

4. Time

4.1 Lye uniform penetration takes time, mainly affected by temperature and fabric wettability (pretreatment quality), but also by fabric structure and lye concentration

4.2 Wetting agent can be added to speed up the penetration, but it will increase the recovery of mercerizing liquid waste, so it is rarely used

4.3 properly raise the temperature of lye and repeated dipping lye is an option too.

Mercerizing process flow

Clip mercerizing machine

1. The fabric can be expanded, and the warp tension and expanding range can be adjusted

2. The luster of the treated fabric is good and the shrinkage rate of the fabric is small

3. When the wide fabric expands, it will cause the cloth edge to be dense and the middle to be loose

4. Process: alkali rolling tank → stretching cloth roller (extend alkali time) → after alkali rolling tank → clip stretching device (4 ~ 5 sets of washing and vacuum water absorption) → alkali removing box → plain washing machine

Straight roll mercerizing machine

1. Rely on friction force, prevent contraction, no expansion effect

2. Process: feeding → bending roll expansion → straight roll penetration zone (lye dipping tank) → rolling mill → straight roll stabilization zone (washing to remove alkali tank) → removing alkali steaming box → flat washing and drying

Cold and hot mercerizing process comparison

1. Swelling behavior of cotton fiber in concentrated lye

1.1 Balanced swelling — the maximum swelling of cotton fiber

At low temperature (5℃), the equilibrium swelling value is the highest. The equilibrium swelling decreases obviously with the increase of temperature. When the temperature reaches 60 ℃, the equilibrium swelling almost does not decrease with the increase of temperature

2. Swelling speed

2.1 In industrial practice, the swelling time of mercerizing alkali immersion is generally limited to 30 ~ 60s, so the swelling of the fiber cannot reach the maximum swelling. Temperature is the most important factor affecting the swelling speed of cotton fiber

3. Uniformity of swelling

3.1 Cold mercerizing, when the concentrated alkali first adsorbed on the yarn surface fiber, due to the intense swelling of the fiber, yarn surface layer density increases, thus hindering the concentrated alkali from the yarn surface layer to the core layer penetration, resulting in the core layer of mercerization degree reduced. The high viscosity of cold NaOH also increases the barrier to diffusion into the core layer

4. Dyeing performance, strength and dimensional stability

4.1  Hot mercerizing and cold mercerizing improve the dyeing performance of cotton fiber, so that the shrinkage rate of cotton fabric decreases, fabric size stability increases, the strength of hot mercerizing is slightly higher,

5. Feel

5.1 Hot mercerizing feels softer than cold mercerizing