Why Do Clothes Turn Yellow and How to Avoid It

Generally speaking, there two types of yellowing. One is yellow discoloration by light. This means the textile surface is becoming yellow because of sunlight or ultraviolet light. The other is yellow discoloration by phenol, which is caused by nitric oxide or phenolic compound.

White textiles will become yellow sometimes in storage. The yellow part will return to the original color after acid treatment. If alkali liquid is dropped on the recovered part, it will become yellow again. This is phenol yellowing.

The reasons for phenol yellowing is the antioxidant BHT(2,6-Ditert-butyl-4-methyl phenol) used widely in packing materials sparks chemical reaction with the nitrogen oxide in air and then produces DTNP(2,6 Di-Tert-buty-nitrophenol). DTNP is colorless in acid condition. But it sublimates easily and transfers in room temperature. When it meets alkaline, it becomes yellow immediately.

The yellow discoloration of textiles in storage, transportation, and wearing will cause financial loss directly.

Four detail reasons for yellow discoloration

1. Raw materials

Ordinary wool, viscose, chinlon, and spandex will cause yellowing easily. Chinlon and spandex are made from the same material called as toluene diisocynate(TDI). BTH is added into TDI to avoid light aging in storage and usage. When BTH meets nitrogen oxide in air and sparks chemical reaction, it causes yellow discoloration. This is BTH yellowing.

2. Yellowing in production

Textiles will turn yellow due to treatment process, usage of additive and PH level in treatment process. For example, residual hydrogen peroxide in textile will cause yellowing in appropriate reaction conditions. Concentration of fluorescent brightener also has effect. When the concentration of fluorescent brightener reaches to a certain degree, the white will reach the highest value. If the concentration surpasses the degree, the white value will go down with the concentration of fluorescent brightener going up.

The additive use after dyeing might also cause yellow discoloration. For example, the finishing agent of anti-bacteria and deodorization will make the textile yellow as the agent includes nitrogen-atoms.

3. Yellowing in storage and transportation

Materials such as polythene are used as packing materials for textiles. These packing materials contain phenolic compounds as antioxidant. Among the antioxidants, the most widely used and cheapest is BHT. The solubility of BHT in polythene is low and BHT is easy to volatilize. BHT in pe film will transfer to textiles and then has chemical reaction with the nitrogen oxide in air or in packing bag. Yellow substance will then grow on the textile.

4. Yellowing in wearing and washing

Yellow discoloration will form due to sunlight, temperature change, humidity. Avoid inappropriate use of bleacher in detergent and detergent with unbalanced PH level. Any tiny antioxidant of phenol will transfer to textile through volatilization or friction, which will lead to yellowing as time passes.

How to avoid yellowing

1. Keep the textiles in good maintenance.

2. Keep the fluorescent brightener in strict control while in production.

3. The temperature for shaping the clothes in final steps should not be too high. For textiles with spandex, the temperature should not exceed 150℃.

4. Avoid BHT yellowing in packing. Small amount of nonvolatile acid such as citric acid can be used in final treatment of textiles to reduce the probability of yellowing.

5. Treatment of yellowing after packing. Lay a white paper under carton and then dust some reduced powder and cover the powder with cardboard. Cut some holes on the cardboard. Put the textiles in the carton and seal the carton. After 24 hours to 48 hours, open the carton and keep it opening for over 6 hours. Repack the textiles after there is no smell. In this way, the textile products can remain the same shape and washing marks and taps are not needed to be removed. But the yellowing may also occur if the reduced powder is not used properly.

6. If clothes are tested to be yellowed, brown cardboard and plastic film containing antioxidants with phenol shall be avoided to pack the clothes. Store the products in ventilated place.

In a word, there are many reasons for causing yellowing in textiles. The reasons shall be analyzed and appropriate measures be taken. Therefore, the quality and performance of textile products can be improved.