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What is the reason why nylon fabric often yellowing ?

September 06,2023

Nylon fabric  yellowing, also known as "yellowing", refers to the phenomenon of white or light colored substances turning yellow on the surface under external conditions such as light, heat, chemicals, etc. After yellowing of white and dyed textiles, not only is their appearance damaged, but their service life will also be greatly reduced.

Therefore, the research on the causes of textile yellowing and the measures to prevent yellowing has always been one of the hot topics at home and abroad.

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The white or light colored textiles of nylon, elastic fibers, and their blends are particularly prone to yellowing. Yellowing of  nylon fabrics  may occur during the dyeing and finishing process, during storage or hanging in store windows, or even at home. There are many reasons that may cause yellowing of nylon fabrics, such as the fiber itself being prone to yellowing (material related), or chemicals used on fabrics such as residual oil and softeners (chemical related).

Further analysis is usually necessary to understand the causes of yellowing of nylon fabrics

How to set processing conditions, what chemicals should be used or only what chemicals can be used, and what influencing factors can cause the interaction of yellowing of nylon fabrics, as well as the packaging and storage conditions of fabrics.

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1. Sizing machine

There are several different types of molding machines used in the textile industry, including those that are directly heated by burning gas and fuel, or those that are not directly heated by hot oil. The stereotype of combustion heating generates more harmful NOx, as the heated air comes into direct contact with the combustion gas and fuel; The shaping machine heated with hot oil will not mix the burning gas with the hot air used to shape the fabric.

To avoid excess NOx generated by direct heating during the high-temperature setting process, we can usually use our SPANSCOUR to remove it.

2. Smoke fading and storage

Some fibers and packaging materials, such as plastic, foam, and recycled paper, are processed with phenolic antioxidants, such as BHT (Butylated Hydroxy Toluene), which react with NOx smoke in stores and warehouses. These NOx smoke comes from air pollution (such as air pollution caused by traffic).

Generally, we have two ways to prevent this yellowing phenomenon. One is to avoid using packaging materials containing BHT, and the other is to keep the pH value of the fabric below 6 (fibers can be used to neutralize acids), which can avoid this problem. In addition, anti phenol yellowing treatment can be carried out during the dyeing and finishing process to avoid the problem of phenol yellowing.

3. Ozone fading

Ozone fading mainly occurs in the garment industry, as certain softeners can cause yellowing of nylon fabrics due to ozone. Special ozone resistant softeners can minimize this problem.

Especially cationic amino aliphatic softeners and some amine modified silicone softeners (with high nitrogen content) are highly sensitive to high-temperature oxidation, resulting in yellowing. The selection of softeners and the required final results must be carefully considered in conjunction with the drying and finishing conditions to reduce the probability of yellowing.

4. High temperature

Textile fabrics exposed to high temperatures can cause yellowing due to fiber oxidation, fiber and spinning lubricants, and impurities on the fibers. The yellowing problem of other nylon fabrics may occur during the molding of synthetic fiber fabrics, especially for women's intimate underwear (such as PA/EL bras). Some anti yellowing products are of great help in overcoming such problems.

5. Packaging material

The relationship between gases containing nitrogen oxides and yellowing during storage has been confirmed. The traditional approach is to adjust the final pH value of the fabric to between 5.5 and 6.0, as yellowing only occurs under neutral to alkaline conditions. This type of yellowing can be easily confirmed through acid washing, as yellowing disappears under acidic conditions. Some companies' anti phenol yellowing products can effectively prevent the occurrence of stored phenol yellowing.

The main reason for this type of yellowing is because phenolic substances such as (BHT) combine with NOx from air pollution to produce yellowing substances. BHT may exist in plastic bags, recycled paper boxes, and medium glue. Plastic bags without BHT can be used as much as possible to reduce such problems.

6. Daylight

Generally speaking, fluorescent whitening agents have low light fastness. If fluorescent whitening fabrics are exposed to sunlight for too long, they will gradually turn yellow. It is recommended to use fluorescent whitening agents with high light fastness for fabrics with high quality requirements. Sunlight, as an energy source, can cause fiber degradation; Glass cannot filter all ultraviolet rays (it can only filter light waves below 320 nm). Nylon is a fiber that is very prone to yellowing, especially for semi light or matte fibers containing pigments. This type of photooxidation can cause yellowing and loss of strength. If the fiber has high moisture content, the problem will be more serious.

7. Microorganisms

Mold and bacteria can also cause fabric yellowing, even browning or black pollution. Mold and bacteria require nutrients to grow, such as residual organic chemicals on fabrics (such as organic acids, dyes, and surfactants). A humid environment and surrounding temperature can accelerate the growth of microorganisms.

8. Other reasons

Cationic softeners will interact with anionic fluorescent brighteners, reducing the whiteness value of the fabric. The rate of decrease is related to the type of softener and the opportunity to come into contact with nitrogen atoms. The influence of pH value is also important, but strong acid conditions should also be avoided. If the pH of the fabric is lower than pH 5.0, it will also cause the color phase of the fluorescent whitening agent to become greenish. If the fabric must be under acidic conditions to avoid phenol yellowing, an appropriate fluorescent whitening agent must be selected.

9. Phenol yellowing test ( Edida method )

There are many reasons for the yellowing of phenols. The most important reason is the antioxidants used in packaging materials. In most cases, BHT ( Butylated Hydroxy Toluene ) is used as an antioxidant for packaging materials. During storage, BHT and nitrogen oxides in the air will form yellow 2,6-di-tert-butyl-1,4-quinone methide, which is one of the most likely causes of storage yellowing.


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