Causes and solutions for yellowing of yarn after bleaching

　　Analysis of the causes of yellowing of yarn after bleaching

　　After the bleached and whitening yarn is placed for a certain period of time, one is to produce macula, and the other is to increase the whiteness over time.

　　Analysis of the causes; the macular production is caused by poor water quality for bleaching and high divalent iron ions. The divalent iron ions are oxidized to trivalent iron ions over time, so that they are on the yarn. Macular formation. This macula not only affects the appearance quality, but also causes the fiber to be brittle.

　　Attack: When the water quality is poor, use oxalic acid 1.5-2.0g/L before bleaching the yarn and pickled at 80-85℃. Because oxalic acid can form complex ions with iron ions and dissolve in water, the iron in the water can be removed to achieve the goal of not yellowing.

　The main reason why bleaching and whitening yarns decrease with time is due to insufficient cooking. If the yarn is not cooked thoroughly and the impurities in the cotton fibers are not completely removed, use this yarn to bleach and whiten immediately. Over time, the impurities and natural pigments inside the fibers will be exposed to cause a decrease in whiteness.

　　The way to overcome it: to ensure that the bleaching effect of the bleaching yarn reaches 13-375px/30min, and the bleaching effect must be uniform and consistent to ensure that the bleaching and whitening yarn does not turn yellow.

　　In addition, when bleaching with sodium hypochlorite and dechlorination, excessive amount of baking soda can also cause yellowing of the yarn. When the yarn is drying, the temperature of the drying room is too high and the drying time is too long, which will cause the yarn to turn yellow.

　　Remedy: First, rinse the white yarn, then put the white yarn in a basin with clear water, soak it with some dark blue ink, knead it gently for half a minute, and take out the white yarn and dry it directly. It’s OK. Because the blue ink ingot blue pigment can restore the fluorescent whitening agent in the white yarn, it can also be soaked in hot rice washing water, and it can also be boiled with orange peel and rubbed, which can also promote the fluorescent whitening in the white yarn. Recovery of agent.