Yellowing of textiles refers to the surface yellowing of white or light-colored materials under environmental conditions such as light and chemicals. Textiles may produce yellowing during storage, transportation, and wearing. There are many reasons for the yellowing of textiles, but the common yellowing reasons are mainly light yellowing and phenolic yellowing.
Photoyellowing refers to the yellowing of the surface color of textiles caused by sunlight or ultraviolet light, and is a photoaging phenomenon of polymer materials. Usually, adding suitable anti-yellowing agents in the fabric post-treatment process can greatly improve its yellowing resistance.
Phenolic yellowing refers to the phenomenon that nitrogen oxides react with phenolic substances to form yellow substances, which cause yellowing of textile materials, that is, phenolic yellowing. White fabrics sometimes turn yellow during storage. After acid treatment, the yellow color disappears and returns to the original white. If the lye is added and the yellow color returns, this yellowing is phenol yellowing. The main cause of phenol yellow is the chemical reaction between BHT (2,6-di-tert-butyl-p-cresol), an antioxidant commonly used in packaging materials, and nitrogen oxides (NOx) in the air to generate 2,6-di-tert-butyl Butyl-p-nitrophenol and 2,6-di-tert-butyl-p-nitrophenol are colorless in acidic state, easily sublimated and transferred at room temperature, and turn yellow immediately when encountering alkaline substances.
The main reasons for the yellowing of textile fabrics are:
1. Yellowing caused during the production process. During the production process, the treatment process, the use of additives and the pH value during the treatment can all cause yellowing of the fabric. The concentration of fluorescent whitening agent has an effect on the yellowing of textiles. The appropriate concentration of fluorescent whitening agent will make the fabric whiteness reach the optimum; but when the concentration exceeds this concentration, the fabric whiteness will decrease with the increase of concentration, resulting in fabric flooding. Yellowing; in fabric finishing, hydrogen peroxide is often used, and the residual hydrogen peroxide on the fabric will make the fabric yellow under the appropriate reaction conditions; steam ironing or setting drying may also cause the whitening agent to migrate, resulting in excessive local concentration High causes local yellowing; additives used in the post-dyeing process, such as cationic softeners, antibacterial and deodorant finishing agents (finishing agents contain nitrogen atoms), etc., these additives may cause yellowing of fabrics; used in fabric dyeing The direct dyes can form complexes with heavy metal ions, resulting in a decrease in dye solubility and a change in dyeing shade. Even a small amount of copper or iron ions can inhibit fluorescence, reduce the whiteness of fluorescently whitened fiber materials, and cause yellowing.
2. Yellowing caused by the fabric itself. Generally, organic fabrics such as wool, viscose fiber, nylon, and spandex are prone to yellowing. Both nylon and spandex require the same raw material – toluene diisocyanate (TDI), and TDI manufacturers will add antioxidant BHT to it to prevent oxidative yellowing of the finished product during storage and use. The BHT in these raw materials reacts chemically with nitrogen oxides (NOx) in the air, resulting in yellowing, which is called BHT yellowing, that is, phenol yellowing.
3. Yellowing during packaging and storage. The packaging materials of various textiles are mostly polyolefin materials, and hindered phenolic antioxidants are added to these materials during processing, among which the antioxidant BHT is widely used because of its low cost. However, BHT has low solubility in polyolefin materials and is easy to volatilize, so BHT in packaging materials will gradually migrate to the surface of packaging materials. Polyamide fabrics are packaged with polyethylene film containing BHT. During storage, BHT can be transferred to the fabric or clothing, and have complex interactions with nitrogen oxides (mainly NO2) absorbed or stored in the air and packaging materials. A chemical reaction forms a yellow substance, causing yellowing visible to the naked eye.
4. Yellowing in the process of wearing and washing, that is, yellowing in the process of consumption. Exposure to sunlight and changes in temperature may cause yellowing of fabrics. During the washing process, it is necessary to pay attention to whether the washing powder is completely removed, and whether bleaching agent or detergent with unbalanced pH value is used inappropriately in the cleaning agent. In the presence of nitrogen oxides, any traces of phenolic antioxidants are transferred to the surface of the fabric through volatilization or friction, all of which will cause yellowing over time.
Currently, the national standard for assessing the light yellowing of textiles is GB/T 30669-2014 “Textile Color Fastness Tests for Color Fastness to Light Yellowing”, and the national standard for assessing phenolic yellowing is GB/T 29778-2013 “Evaluation of potential phenolic yellowing in textile color fastness tests”.
If the cause of the yellowing of the fabric is found, the effective measures to prevent the yellowing of the fabric are:
1. Strictly control the amount of fluorescent whitening agent during production and processing to avoid exceeding the fluorescent Yellowing point of whitening agent.
2. During the finishing process, the setting temperature should not be too high, and the setting temperature of the fabric containing spandex should be lower than 150°C; if the setting temperature is too high, the fabric will turn yellow after setting.
3. Prevent the yellowing of BHT during the packaging process, and require good ventilation during storage. alkaline. Products with phenolic and BHT yellowing are pH sensitive. According to the test, when the pH value of the fabric is 6, the time for yellowing will be relatively short. Adding a small amount of non-volatile acid (such as citric acid) to fabric post-treatment will greatly reduce the chance of yellowing.
4. Anti-yellowing of packaged productsIf you want to solve it, you can consider using reducing powder to deal with it.
Label:   Anti-yellowing agent
