Mercerization: When textiles are under a certain tension, with the help of concentrated caustic soda and maintaining the required size, they can obtain a silk-like luster. This process is called mercerization.
Mercerized purpose
1. Improve the surface gloss and feel of the fabric
Due to the puffing of the fibers, the fibers are more neatly arranged and the reflection of light is more regular, thus increasing the gloss.
2. Improve dyeing color yield
After mercerizing , the crystalline area of the fiber is reduced and the amorphous area is increased, so the dye is easier to enter the inside of the fiber, the coloring rate is 20% higher than that of unmercerized fiber cotton cloth, and the brightness is improved, while the covering power of the dead surface is increased.
3. Improve dimensional stability
Mercerization has a shaping effect. It can eliminate rope-like wrinkles and better meet the quality requirements of dyeing and printing semi-finished products. The most important thing is that after mercerization, the stability of the fabric’s expansion and contraction deformation has been greatly improved, thus greatly reducing the shrinkage of the fabric.
Principle of mercerization
The fiber swells irreversibly, Na + water The degree of oxidation is very strong, and a large amount of water is brought into the fiber, causing the fiber to swell violently.
During the mercerization process, natural cellulose, also called cellulose I, reacts with caustic soda to produce alkali cellulose. Alkaline cellulose is extremely unstable. It is hydrolyzed after washing with water and generates hydrated (hydrated) cellulose. It is then dehydrated and dried to obtain mercerized cellulose, namely cellulose II.
The main factors that affect the mercerizing effect are the concentration, temperature, action time of the alkali solution and the tension exerted on the fabric.
Concentrated caustic soda solution (about 18~25%) is mainly used to treat cotton, fiber/cotton or polyester/cotton fabrics, so the fundamental reason for obtaining good mercerization effect is that Concentrated alkali can cause irreversible and violent swelling of cotton fibers. In addition, it must be matched with appropriate tension.
When the cotton fiber swells violently in concentrated alkali solution, the cross-section of the fiber changes from a flat waist or ear shape to a round shape, and the cell cavity also shrinks. For completely mercerized fibers it shrinks almost to a point. Moreover, the natural torsion in the longitudinal direction disappears. If appropriate tension is applied to stretch the fiber or prevent it from shrinking, the wrinkles on the surface of the fiber disappear and become a very smooth cylinder, which reflects light regularly and shows luster.
After the cotton fiber is subjected to the action of concentrated alkali, it swells violently, which is not only reflected in the change of the lattice parameters, but also the transformation of some crystal areas into amorphous areas. After being washed with water After de-alkali removal and drying, although there will still be a certain degree of shrinkage in the diameter direction of the fiber, it cannot return to its original state. Instead, it basically preserves the shape during swelling and becomes irreversible swelling, so that the luster obtained It is durable, and at the same time, due to the increased content of the amorphous zone, the adsorption performance of the fiber is improved.
As for the reason why cotton fiber will swell irreversibly in concentrated alkali solution, it is mainly believed that cotton fiber will swell in concentrated alkali solution. It can form cellulose sodium salt (cellulose-ONa) with sodium hydroxide in the liquid. Since sodium ions are ions with strong hydration ability, when it combines with cellulose, a large amount of water will be brought into the fiber. Internally, it causes violent swelling of the fiber, and can also provide an appropriate explanation for the reason why the concentration of the alkali solution is too high or the alkali solution contains electrolytes such as salt, which causes the fiber swelling to decrease. In fact, in addition to this explanation, there are some other explanations. For example, applying the membrane balance principle can also provide a satisfactory explanation for the fiber swelling performance. A brief explanation is as follows.
Using membrane balance to illustrate the principle of mercerization is to regard the inside of the fiber as the intramembrane system and the external alkali solution as the extramembrane system. When fiber is combined with alkali, there will be cellulose-O-, Na+, OH- and other ions. If there is salt, there will also be Cl-. Among them, cellulose-O- can only be inside the membrane and cannot diffuse outside the membrane, while other ions are mobile and establish a balance inside and outside the membrane according to certain conditions.
If the internal and external volumes of the membrane are equal and unchanged during the equilibrium process, when equilibrium is reached, the concentration of (I) and external (O) ions in the membrane can be expressed as follows:
If the concentration of NaOH before the action is C2 and the concentration of NaCl is C3, the cellulose after equilibrium [Cellulose-O-] formed by the interaction with alkali is C1, and x and y are respectively the concentrations of Na+ and OH- in the membrane after equilibrium. During equilibrium, electrical neutrality must be maintained inside and outside the membrane, so [Cl-]1 is C3-x+y+C1, and [Cl-].
At the same time, for any mobile monovalent cation (such as Na+), the ratio of the concentration inside and outside the membrane should be equal, and inversely proportional to the anion concentration, that is:
<img width=100% height=auto data-preview-src=""data-preview-group="1"src="http://pic.168tex.com/Upload/News/image/202Itcanbecombinedwiththescouringprocesstoshortentheprocessroute,reducecosts,andimproveeconomicbenefits(beforecooling,steamthefabricsoakedinhotalkalifor10′atnormalpressure)
Mercerizingequipment
Commonlyusedmercerizingmachinesincludeclothclipmercerizing,bentrollermercerizingandstraightrollermercerizingmachines.Theclothmercerizingmachinehasthebesteffectandisthemostwidelyused.
1.Clothmercerizingmachine
Itconsistsofafrontrollingalkalitank,aclothstretchingroller,arearrollingalkalitank,andaclothmercerizingmachine.Itconsistsofwebdevice,alkaliremovalbox,flatwashingmachineandotherparts.
Advantages: Tension is easy to control, fabric shrinkage and alkali removal effect are better than other mercerizing machines ideal. Disadvantages: The cloth clip part is prone to mechanical defects, and the equipment occupies a large area.
2. Straight roller cloth mercerizing machine
By feeding the cloth It consists of device, alkali rolling tank, heavy pressure roller, alkali removal tank, alkali removal box and flat washing tank.
Features: Often carried out in double layers, the output is high, the mercerization is uniform, and there will be no Broken edges; the fuselage is short, the transmission is simple, and the operation is convenient, but the expansion effect is poor (the weft shrinkage rate is difficult to reach the national standard), which is its main shortcoming. Some domestic factories use cloth clips and straight rollers together to better solve this problem.
</p
