Mercerization is a process in which cotton fabrics are treated with concentrated caustic soda solution under a certain tension and maintained at the required size, so that the fabrics obtain a silky luster.
Mechanism of mercerization process
When mercerized cotton fiber is treated with concentrated caustic soda, because of the small size of sodium ions, it can enter the fiber at the same time The amorphous region and crystalline region, the water molecules surrounding the sodium ions form a hydration layer. When the sodium ions enter the interior of the fiber and combine with the fiber, water molecules are also brought in at the same time, causing violent swelling of the fiber and forcing the cotton fiber to The diameter increases, the length shortens, the longitudinal curl of the fiber almost disappears, the cross-section of the fiber changes from kidney-shaped to nearly round, and the entire fiber changes from a flat ribbon to a cylindrical shape. At this time, a certain tension is applied, and the fiber is stretched. Afterwards, the uniformity and surface smoothness are improved, and the diffuse reflection of light by the fiber before mercerization is transformed into more directional reflection, which increases the intensity of the reflected light, so that the fabric shows a silky luster; the cotton fiber is crystallized after mercerization The density dropped from about 70% before mercerization to 50-60%. Due to the decrease in fiber crystallinity, good dyeing performance was produced. It also improved the dyeing performance of dead cotton and improved the quality of dyed products. Improve the dimensional stability of the fabric, eliminate stress within the fabric and remove wrinkles.
The main agents used in mercerization are: caustic soda, alkali-resistant penetrant, acetic acid, etc. The function of the alkali-resistant penetrant: accelerates the wetting and penetration of the mercerizing alkali solution, improves the mercerizing effect, and improves the dyeing depth, brightness, fullness and gloss.
Types of mercerizing machines: straight roller mercerizing machine, cloth clip mercerizing machine, straight roller cloth clip mercerizing machine, knitted fabric cylinder mercerizing machine, knitted fabric split width mercerizing machine, short process straight roller mercerizing machine Machine etc.
1. Mercerization of woven fabrics: padding with concentrated alkali → ventilation → padding with concentrated alkali → ventilation → (Preheating washing) → Expanding cloth clips to flush and absorb alkali → Straight roller flushing to remove alkali → Steaming and washing → Neutralization → Water washing → Drying
2. Mercerizing of knitted fabrics: Open-width feeding → Photoelectric Weft straightening device → Straight roller groove → Two-roller re-rolling car → Five-roller large cylinder alkali rolling machine → Two-roller re-rolling car → Cloth clip expansion punch and suction to remove alkali → Two-roller re-rolling car → High-efficiency drum rinsing box → Two Roller light rolling car → High-efficiency drum rinse box → Two-roller light rolling car → High-efficiency drum rinse box → Two-roller light rolling truck → High-efficiency drum rinse box → Two-roller light rolling truck → High-efficiency drum rinse box → Two-roller light rolling car → High-efficiency drum rinse box → Two-roller heavy rolling car → Open-width doffing.
3. Mercerizing process conditions The main process technical parameters of mercerizing include: caustic soda concentration, rolling residue rate, alkali action time, warp tension, weft tension, number of alkali leaching, alkali removal temperature, cloth drop Width, drop cloth pH value, etc.
1. The degree of dryness and wetness of the fabric before mercerization must be uniform. When mercerizing the wet fabric, the water-gathering rate is 60% for cotton fabrics and linen fabrics, and 50% for polyester-cotton fabrics. Ensure that the left, middle and right parts of the fabric are evenly soaked with liquid.
2. When dry cloth is mercerized, the fabric must be fully cooled by a ventilation rack before padding with alkali solution to keep the temperature of the mercerizing concentrated alkali solution stable.
3. When the fabric is mercerized, it must bear a certain amount of tension in the warp and weft directions. The greater the tension, the better the luster of the fabric and the higher the size and temperature resistance.
4. During the mercerization process, the fabric must be kept flat to prevent curling, wrinkles, etc. Once tested, the mercerization must be repeated and repaired.
5. The mercerization process of knitted fabrics generally adopts mercerization of gray cloth or mercerization after singeing. Because the fabric has poor water absorption, penetrant must be used to enhance the penetration performance of concentrated caustic soda solution and improve the mercerization effect.
6. Frequently use a wide range of indicators or test paper to detect the pH value of mercerized fabric. Try to keep the fabric neutral. If necessary, use acid to neutralize it during the washing process.
7. Concentrated caustic soda (concentrated acid) corrodes and burns human skin severely. Personnel who come into contact with concentrated alkali (concentrated acid) should be equipped with necessary protective equipment. In case of alkali (or acid) liquid) splashed on the skin or eyes, flush with plenty of water before seeking medical advice.
Evaluation of mercerized effect
1. Gloss: It is one of the main indicators to measure the appearance effect of mercerized fabrics, but there is no unified The ideal testing method is currently mostly used for visual evaluation.
2. Observe microscopic morphological changes through microscopic sections.
3. Adsorption performance
A Barium value method: It is a test method to measure the absorption performance of cotton fibers. It is commonly used to test the increase in the absorption capacity of fabrics after mercerization. Take one piece of mercerized and unmercerized cloth sample, wash it with hot water and cold water and dry it at 100-105 for 1 hour. Take out the constant weight, accurately weigh 2 grams of each, cut into small pieces, and place them in 100 ml. In a covered Erlenmeyer flask, absorb 30mL of 0.25mol/L barium hydroxide and inject it into the flask. Cover the lid immediately and shake it from time to time. After 2 hours, absorb 10Ml, use phenolphthalein as indicator, titrate with 0.1mol/L hydrochloric acid standard solution, and calculate the barium value.
B Iodine staining and staining method: Treat samples with different barium values (100 150) with a certain concentration of iodine solution or direct blue 2B to make a color card, and then add the iodine of the unknown sample to The liquid contamination and dyeing depth are compared with known color cards to quantitatively evaluate the mercerized barium value.
4. Fabric dimensional stability: Use the fabric shrinkage method to test the changes in the warp and weft length of the fabric before and after mercerization. The smaller the fabric dimensional shrinkage, the better the mercerization effect.
Silk��Common problems and overcoming methods
1. Color difference between left, middle and right
A The wool effect of left, middle and right pre-treatment is inconsistent, resulting in alkali content in various parts of the fabric Inconsistent.
B The alkali concentration in various parts of the alkali rolling tank is inconsistent.
C The wear of the pad car and the inflexibility of the cylinder lead to inconsistent liquid amounts in the left, middle and right parts of the fabric.
D When expanding, the alkali absorption is inconsistent on the left, middle and right, resulting in inconsistent alkali absorption in various parts of the fabric.
E Insufficient washing.
2. The shrinkage rate of the fabric in the warp and weft directions is too large.
A The alkali concentration is too high. (Thin fabrics have a large shrinkage in the weft direction).
B Insufficient expansion (the tension is too high when feeding the cloth clip), resulting in difficulty in weft expansion.
C The warp tension of the cloth roller between the two alkali rolling tanks is too small, the fabric’s warp mercerization setting effect is poor, and the fabric’s warp shrinkage is large.
D The effect of leaching alkali is poor. The amount of alkali contained in the fabric when it comes out of the cloth clip is too large. The fabric shrinks greatly when washed with high alkali and high temperature.
E The equipment tension is too high and the fabric shrinks greatly in the weft direction.
3. Broken edges and holes
A The cloth clips are worn or inflexible.
B The cloth clip track is out of balance, and the tension on the left and right sides of the fabric is inconsistent.
C The door width of the cloth clip outlet is too wide.
D The expansion is too large or the expansion is too rapid.
E The edge detection or amplification device is not flexible.
4. Additive spots
When boiling and bleaching, the surfactant remaining on the fabric is destroyed by alkali, and the lipophilic group The collection of stained fabrics will cause local dye rejection and light spots on the fabrics; direct repair after post-processing and softening will easily cause colored spots. </p