9. What are the better ways to prevent silk from yellowing?
Answer: Refined and bleached silk and pure silk will turn yellow and discolor during storage or consumption, which will reduce the commodity value. The main reason for the yellowing of silk is that the amino acid residues such as tryptophan and tyrosine in the silk protein are oxidized and colored in the air. The existence of perfection can promote the occurrence of this phenomenon.
There are generally several methods to prevent silk from yellowing.
① “Foreign Dyestuff Digest” reported that the bleached silk was soaked in 0.5% NaOH aqueous solution for 3 seconds, and after padding (padding rate 80%), 1% thiourea and 1% l,3 , soak in an aqueous solution of 5-triacryloyl hexahydro-s-triazine at 70°C for 30 minutes, and then wash with water. Then treat with 0.3% HCl at 70°C for 30 minutes, wash with water, and dry. The initial yellowing index of silk treated with the above method is 2.8. The yellowing index after 180 days is 3.8.
②Treat with chitosan. In 300 mL of 1% acetic acid aqueous solution, add 0.3 to 1.5 g of chitosan to prepare a 0.1% to 0.5% chitosan solution. Put silk (10cm × 10cm) in this solution. After padding and drying at 80°C, a chitosan film is formed on the surface of the silk fiber. The treated silk was fully irradiated with a carbon arc lamp (20h, 40h), and the degree of yellowing was measured with an automatic Henkel whiteness tester. As a result, chitosan-treated silk showed less yellowing compared to untreated silk.
③Treat with anti-yellowing agent HN-200. Anti-yellowing agent HN-200 is an antioxidant produced by Japan Hydrazine Industrial Co., Ltd. Its function is to provide electrons to vivid free radicals or serve as a hydrogen atom donor to terminate the chain autocatalytic oxidation reaction, thereby providing an effective anti-yellowing effect on silk. The method is to treat the silk with 0.2% HN-200 at 80°C for 5 to 10 minutes and then dry it. The yellowing index increase (ΔY1) of the treated silk after 100 Ohm xenon lamp irradiation is only about half of that of the untreated silk. However, this type of anti-yellowing agent has high water solubility and little affinity with fibers, so its washing resistance is not ideal.
④ Use dimethylol vinyl urea resin and polyurethane lamination finishing process. Silk is laminated and finished with dimethylolethylene urea resin (DMEU) and polyurethane 105 resin to achieve an anti-yellowing effect. The method is: soak the whitened 07 silk crepe de chine in a working solution composed of DMEU 100g/L, polyurethane 105 40g/L, 20% magnesium chloride (weight to the resin), and 5% citric acid (weight to the resin) at room temperature. 15min, two immersions and two rollings (match rate 90%, liquor ratio 1:50), pre-bake at 80°C for 4min, 140. Bake for 3 min at The anti-yellowing effect is: △Y1 after 200 hours is 8.69, and the untreated sample is 15.06. For this process, if you add 0.5% UV-284 (anti-UV finishing agent) and 1% HN-200 to the laminating resin working fluid, the effect will be better.
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