New technology: mercerizing technology

Mercerizing is a new technology that makes cotton fabrics have a silky luster by treating them with concentrated caustic soda solution under a certain tension and maintaining the required size. 1. Mercerizing process mechanism When mercerized cotton fiber is treated with concentrated caustic soda, because the sodium ion is small in size, it can enter the amorphous area and crystalline area of ​​the fiber at the same time. The water molecules surrounding the sodium ion form a hydration layer. When the sodium ion enters the fiber and combines with the fiber, the water molecules are also brought in at the same time, causing the fiber to swell violently, forcing the cotton fiber diameter to increase, the length to shorten, the longitudinal curl of the fiber almost disappears, the fiber cross section changes from kidney-shaped to nearly circular, and the whole fiber changes from flat ribbon to cylindrical. At this time, a certain tension is applied. After the fiber is stretched, the uniformity and surface smoothness are improved, and the diffuse reflection of the fiber to light before mercerization is changed to more directional reflection, which increases the intensity of the reflected light, so that the fabric shows a silk-like luster; the crystallinity of cotton fiber after mercerization is reduced from about 70% before mercerization to 50-60%. Due to the decrease in fiber crystallinity, good dyeing performance is produced, and the dyeing performance of dead cotton is also improved, and the quality of dyed products is improved. Improve the dimensional stability of the fabric, eliminate the stress in the fabric and remove wrinkles. (1) The main mercerizing agents are: caustic soda, alkali-resistant penetrant, acetic acid, etc. (2) The role of alkali-resistant penetrant: accelerate the wetting and penetration of mercerizing alkali solution, improve the mercerizing effect, and improve the dyeing depth, brightness, fullness and gloss. (3) Types of mercerizing machines: direct roller mercerizing machine, clip mercerizing machine, direct roller clip mercerizing machine, knitted fabric cylindrical mercerizing machine, knitted fabric slitting mercerizing machine, short-process direct roller winding mercerizing machine, etc. 2 Mercerizing process (1) Mercerizing of woven fabrics: Dip and roll in concentrated alkali → Ventilate → Dip and roll in concentrated alkali → Ventilate → (Preheating and washing) → Cloth clip expansion and rinsing to remove alkali → Straight roller rinsing to remove alkali → Steam washing → Neutralization → Water washing → Drying (2) Mercerizing of knitted fabrics: Open-width cloth feeding → Photoelectric weft straightening device → Straight roller groove → Two-roller heavy rolling mill → Five-roller large drum alkali rolling mill → Two-roller heavy rolling mill → Cloth clip expansion and rinsing to remove alkali → Two-roller heavy rolling mill → High-efficiency drum rinsing box → Two-roller light rolling mill → High-efficiency drum rinsing box → Two-roller heavy rolling mill → Open-width cloth dropping. (3) Mercerizing process conditions The main process technical parameters of mercerizing include: caustic soda concentration, rolling ratio, alkali action time, warp tension, weft tension, alkali rinsing times, alkali removal temperature, cloth drop width, cloth drop pH value, etc. 3 Mercerizing precautions (1) The wetness of the fabric before mercerizing must be uniform. When mercerizing with wet cloth, the water pressing rate of cotton and linen fabrics is 60%, and that of polyester and cotton fabrics is 50%. Ensure that the liquid is uniform in the left, middle and right parts of the fabric. (2) When mercerizing with dry cloth, the fabric must be fully cooled on a ventilation rack before being dipped into the alkali solution to keep the temperature of the mercerized concentrated alkali solution stable. (3) When mercerizing, the fabric must be subjected to a certain tension in the warp and weft directions. The greater the tension, the better the gloss of the fabric and the higher the dimensional temperature resistance. (4) During the mercerizing process, the fabric must be kept flat to prevent curling and wrinkling. Once tested, the mercerization must be repeated and repaired. (5) The mercerizing process of knitted fabrics generally uses grey cloth mercerizing or mercerizing after singeing. Because the fabric has poor water absorption, a penetrant must be used to enhance the penetration of concentrated caustic soda solution and improve the mercerizing effect. (6) Frequently use a broad indicator or test paper to test the pH value of the mercerized fabric, try to keep the fabric neutral, and neutralize it with acid during the washing process if necessary. (7) Concentrated caustic soda (concentrated acid) has a severe corrosive and burning effect on human skin. People who come into contact with concentrated alkali solution (concentrated acid solution) should be equipped with necessary protective equipment. If the alkali solution (or acid solution) splashes onto the skin or eyes, they should be rinsed with plenty of water before seeking medical attention. 4 Mercerization effect evaluation (1) Gloss: It is one of the main indicators for measuring the appearance effect of mercerized fabrics, but there is no unified ideal testing method. Currently, it is mostly evaluated by visual inspection. (2) Microscopic sectioning to observe microscopic morphological changes. (3) Adsorption performance A Barium value method: It is a test method for measuring the absorption performance of cotton fibers. It is often used to test the increase in the absorption capacity of fabrics after the mercerization process. Take one piece of mercerized and one piece of unmercerized fabric, wash them with hot water and cold water, and then dry them at 100-105°C for 1 hour. Take out and keep constant weight. Accurately weigh 2 grams of each piece, cut into small pieces, and place them in 100 ml conical bottles with lids. Pipette 30 ml of 0.25 mol/L barium hydroxide into the bottles, cover the bottles immediately, and shake them from time to time. After 2 hours, take 10 ml and titrate with 0.1 mol/L hydrochloric acid standard solution using phenolphthalein as an indicator to calculate the barium value. B Iodine staining and dyeing 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. Then compare the iodine staining and dyeing depth of the unknown sample with the known color card to quantitatively evaluate the mercerized barium value. (4) Fabric dimensional stability: Use the fabric shrinkage method to test the change in the warp and weft length of the fabric before and after mercerization. The smaller the fabric shrinkage, the better the mercerization effect. 5 Common mercerizing problems and solutions (1) Color difference between left, middle and right A. The wool effect of the left, middle and right in the pre-treatment is inconsistent, resulting in inconsistent alkali content in different parts of the fabric. B. The alkali concentration in different parts of the alkali rolling tank is inconsistent. C. The wear of the rolling car and the inflexibility of the cylinder lead to inconsistent liquid content in the left, middle and right parts of the fabric. D. The alkali absorption and leaching are inconsistent on the left, middle and right during expansion, resulting in inconsistent alkali content in different parts of the fabric. E. Insufficient washing. (2) Too much shrinkage in the warp and weft of the fabric A. The alkali concentration is too high. (Thin fabrics have a large shrinkage in the weft). B. Insufficient expansion (excessive tension when feeding the cloth clip), resulting in difficulty in weft expansion. C. The warp tension of the cloth stretching roller between the two alkali rolling tanks is too small, the warp mercerization setting effect of the fabric is poor, and the warp shrinkage of the fabric is large. D. The alkali absorption effect is poor and the fabric carries too much alkali when it leaves the cloth clip. 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. (3) Broken edges and holes A. The cloth clip is worn or inflexible. B. The cloth clip track is out of adjustment, and the tension on the left and right sides of the fabric is inconsistent. C. The cloth clip outlet width is too wide. D. The expansion range is too large or the expansion is too rapid. E. The edge detection or expansion device is inflexible. (4) Auxiliary spots During the bleaching and boiling, the residual surfactant on the fabric is destroyed by alkali, and the lipophilic bases gather and stain the fabric, causing the fabric to reject dye locally and form light spots; direct repair after post-processing is easy to form color spots.