Ammonia is a natural substance in nature. Ammonia and water are also indispensable sources of life for human beings. Both animals and plants need natural ammonia to survive, and only ammonia can fix the natural ammonia source. on the contrary. Ammonia is excreted through the decomposition of animals or the decay of plants, and then returns to nature and circulates in nature. Liquid ammonia is to cool the gaseous ammonia at normal temperature to below -34°C to become liquid ammonia. Because the surface physical state of liquid ammonia is as easy to flow as water, its viscosity and surface tension are lower than water, and it is extremely permeable; therefore, liquid ammonia can easily penetrate into the fiber to change the crystallinity of the fiber without damaging it. fibers and seeps out quickly and easily. Fabrics finished with liquid ammonia have remarkable characteristics such as dimensional stability, good resilience, smooth cloth surface, clear texture, soft luster, fullness and smoothness, and less discoloration. The styles of chemical fiber and natural fiber fabrics have both, so the fabric’s Taking performance and added value are greatly improved. Liquid ammonia treatment has an irreplaceable role in other finishing methods.
1. Liquid ammonia finishing method
1. Intermittent liquid ammonia treatment Nitrogen finishing
The intermittent liquid ammonia finishing machine is a sealed pressure tank that can withstand pressures of 8~16 Pa. It is equipped with a pneumatic closing door and a mechanical starting device. The fabric enters the tank, and the vacuum pump removes the air in the tank to form a sufficient vacuum; then the fabric is impregnated with liquid ammonia and reciprocates on the cloth rolling shaft to evaporate the free liquid ammonia from the fabric; at the same time, the ammonia gas is condensed and recovered Treat to remove residual ammonia from the fabric and remove the fabric.
2. Continuous liquid ammonia finishing
For continuous liquid ammonia finishing In ammonia finishing equipment, the moisture in the fabric must be removed before feeding into the fabric. After drying in the drying drum, the fabric is blown and cooled, and then enters the box to be padded with liquid ammonia; the liquid level of the padding liquid must be constant to ensure even penetration of the ammonia and instantaneous ammonia absorption. . Entering the upper and lower cloth guide rollers installed in the reaction chamber prolongs the residence time of the fabric, fully reacts with nitrogen, and evaporates ammonia on the fabric at the same time. The fabric enters the heated drying drum to further remove ammonia remaining on the fabric. In order to prevent ammonia gas from escaping, strict sealing measures are taken at the entrance and exit of the cloth. Any working area with ammonia is always under negative pressure to prevent nitrogen from leaking.
2. The effect of liquid nitrogen finishing on textile fibers
Nitrogen molecules, as a polar, small molecule, low viscosity, medium dielectric constant non-aqueous fiber swelling agent, can penetrate into the fiber fibrils in a very short time, making the fiber molecule bundles and The hydrogen bonds between bundles are broken down, causing the cellulose fibers to assume a certain plastic state. When the ammonia that enters the inside of the fiber is removed, the fiber naturally retracts and the molecules are rearranged. The innate and acquired internal stress of the fiber is eliminated, so that the natural twist of the fiber disappears, and the cross-section becomes more oval, increasing the sensitivity to light. Uniform reflectivity and
toughness. Macroscopically, it reduces the sliding friction between fibers, increases strength and elasticity, and improves dimensional stability. This treatment has a mercerizing effect, but unlike traditional caustic soda mercerization, it will not cause caustic soda to corrode cellulose fibers and cause unevenness.
1. Effect on cotton fiber
Cotton fiber in liquid During ammonia treatment, ammonia can instantly penetrate into the fiber, causing the cotton fiber to expand from the core. The cross-section expands from flat to round, and the hollow part becomes smaller; at the same time, due to the change in the fiber crystal structure, the distortion stress inside the fiber decreases or disappears, making the internal stress of the cotton fiber tend to be uniform. The slipperiness between fibers is enhanced and the fiber surface becomes smooth, making the cotton fiber exhibit excellent softness. This improves the tensile strength and tearing strength of the fabric, maintains a good feel even after repeated washing, improves the dimensional stability of the fabric, and greatly improves the shrinkage of cotton fabrics when washed.
2. Effect on ramie fiber
Ramie fiber has excellent properties such as smoothness, coolness, fast moisture absorption and release, and good breathability. However, due to its microstructure with high crystallinity and high orientation, the ramie fiber is relatively stiff, has small fracture extension, low softness and flexibility, and poor cohesion. This results in the ramie fabric having a lot of hairiness on the surface, a rough feel, and easy to peel off. Defects include wrinkles, poor wear resistance, and itching when worn. In order to overcome the shortcomings of ramie and maintain its advantages, ramie fabric can be treated with liquid ammonia. After treatment with liquid ammonia, the ammonia molecules interact with the warp groups in the cellulose molecules to form cellulose ammonia complexes that are easily decomposed. The ammonia-modified cellulose is obtained by steaming away the ammonia. This process causes the ramie fiber to expand, shrink and shape, reduce the crystallinity, loosen the microstructure, rearrange fiber molecules, redistribute internal stress, and increase its softness and fiber holding power; thus making the surface of the ramie fabric smooth, smooth, elastic, and wrinkle-resistant. The sex has been greatly improved, its rough feel and itchy feeling when worn have also been greatly improved, and the taking performance has been greatly improved.
3. Effect on hemp fiber
To improve hemp fabrics Liquid helium can be used to clean up cannabis by taking advantage of its shortcomings of being rough, not softening, easy to wrinkle, and having a large shrinkage rate, and give full play to its advantages to meet people’s needs. After being treated with liquid ammonia, the cannabis mat not only maintains its original advantages of antibacterial health care, moisture absorption and rapid heat dissipation, but also gives the product a good luster, a smooth and plump feel, good dimensional stability, and flexibility and wear resistance.The good appearance fully reflects the rough and primitive style of linen fabrics.
4. Effect on viscose fiber
Viscose fiber Although regenerated cellulose fiber has the same chemical structure as cotton fiber, its physical structure is quite different from cotton fiber. Viscose fiber fabric has the characteristics of moisture absorption, breathability, softness, no static electricity, and comfortable wearing, but its dimensional stability, wrinkle resistance and wear resistance are poor. This can be solved by liquid ammonia finishing method. After the viscose fabric is treated with liquid ammonia, the fibers in the fabric are deeply and uniformly expanded, causing obvious changes in the morphological structure and supramolecular structure of the fibers. Liquid nitrogen treatment can significantly reduce the shrinkage of viscose fabrics and improve the dimensional stability and elasticity of the fabrics. After the viscose fabric is treated with liquid ammonia, the dyeing performance of reactive dyes and some direct dyes on the fabric is improved.
5. Effect on wool fiber
There are reports abroad that liquid ammonia affects the fineness of wool fiber. , the influence of scale structure. After liquid ammonia treatment, wool fibers with rough surfaces become smooth and rounded. Therefore, liquid ammonia treatment can change the surface structure of wool fibers, thereby improving the feel and luster of wool. Domestic experiments have also been carried out on the liquid ammonia treatment of wool fabrics. The experiments have proved that liquid nitrogen can break up some of the cross-links in wool fibers and form new cross-links at the same time, which can improve the stability of the yarn’s bending state and improve its tensile recovery. It partially eliminates the internal stress in the fabric and stabilizes the fabric structure; the tensile recovery rate of the fabric is improved, and the strength loss is not large. After the wool fiber is treated with liquid ammonia, the dye adsorption rate of the fiber and the binding basin of the dye are increased, and the dyeing rate and dyeing percentage are increased.
3. Conclusion
Flax fiber contains more hydrophilic group, so it has better moisture absorption and heat dissipation functions, and the linen fabric has a crisp appearance and is not close-fitting, making it an ideal fabric for summer clothing. However, because flax fiber has a thicker feel, higher brittleness, and poor knitability, the flax yarn is stiff, stiff, and hairy, and some problems often occur when it is directly used on the machine. That is to say, before weaving on the machine, the linen yarn must be softened to improve the softness of the linen yarn and improve its knitting performance on the machine. In order to improve the many shortcomings of flax fibers, yarns and fabrics and retain and give more excellent characteristics to flax, it is necessary to conduct modification research on flax fibers and fabrics. Textile liquid ammonia finishing, as an advanced, efficient, pollution-free processing technology, has been applied in the modification treatment of a variety of natural fibers, especially the treatment effect on hemp fibers is more significant. Therefore, it is conceivable that using liquid nitrogen finishing technology to functionalize and modify flax fibers and their fabrics will be a research point in the future. </p
