What can cause yellowing of fabrics and how to deal with it

Yellowing, refers to white or light-colored material in external conditions such as light, heat, chemicals and other effects, the phenomenon of surface color is yellowed. When white and dyed textiles are yellowed, not only will their appearance be damaged, but their service life will also be greatly reduced. Therefore, the research on the causes of textile yellowing and anti-yellowing measures has been one of the hot topics in China and abroad.

Nylon, Elastomeric fiber, and their blends of white or light-colored textiles are especially susceptible to yellowing, which can happen in the dyeing process, in storage or hanging in store windows, or even at home. There are many reasons that may cause the phenomenon of yellowing, such as the fiber itself that is prone to yellowing (material-related), or the use of chemicals on the fabric, such as oil residues and softeners, etc. (chemical-related).

Further analysis is usually necessary to know the causes of yellowing, how to set the processing conditions, what chemicals should be used or only what chemicals can be used, what influencing factors can cause the interaction of yellowing, how the fabric is packaged and stored, etc.

Today, letZhejiang Dingyi New Materials Technology Co., Ltd.discuss with you the high heat yellowing and storage yellowing of nylon and polyester and elastic fiber blends, such as Lycra, Dorlastan, Spandex, etc.

Various causes of fabric yellowing:

1.Gas fading

2.Temperature

3.Packaging&Storage

4.Micro-organisms

5.Miscellaneous

Analysis of the sources of the problem and countermeasures:

1.Forming machine

There are several different types of forming machines used in the textile industry, including those directly heated by burning gas and fuel oil, or those not directly heated by hot oil. The combustion heating stereotypes will produce more harmful NOx, because of the direct contact of heated air with burning gas and fuel oil. While a forming machine heated by hot oil does not mix the burning gas with the hot air used to form the fabric. Avoid excess NOx created by direct heating of the forming machine during the high temperature setting process, which can usually be removed by using SPANSCOUR.

2.Fume fading and storage

Some fibers and packaging materials, such as plastic, foam, recycled paper, in the processing of these auxiliary materials added with phenolic antioxidants, such as BHT (Butylated Hydroxy Toluene), these antioxidants will react with NOx fumes in stores and warehouses, these NOx fumes from air pollution (including, for example, air pollution caused by traffic). Firstly, we can avoid using packaging materials containing BHT, and secondly, make the PH value of the fabric lower than 6 (fiber neutralizing acid can be used), which can avoid this problem. Besides, anti-phenolic yellowing treatment during the dyeing and finishing process can avoid the problem of phenolic yellowing.

3. Ozone fading

Ozone fading is a problem that occurs mainly in the garment industry because some softeners can cause yellowing of fabrics due to ozone, and special ozone-resistant softeners can minimize this problem.

4.High temperature

Exposure of textiles to high temperatures can cause yellowing due to oxidation of fibers, fiber and spinning lubricants, and impurities on the fibers.Other yellowing problems may happen when molding synthetic fabrics, especially for women's intimate underwear (e.g. PA/EL bras). Some anti-yellowing products can be extremely helpful in overcoming such problems.

5.Packaging material

The relationship between nitrogen oxide gas and the yellowing in storage has been proven. The traditional practice is to adjust the final pH of the fabric between 5.5 and 6.0, as storage yellowing only occurs under neutral to alkaline conditions, and this type of yellowing can be confirmed simply by pickling, as storage yellowing disappears under acidic conditions. This kind of yellowing is mainly due to the combination of phenol-containing substances such as (BHT) and NOx from air pollution, which produces yellowing substances. BHT may exist in plastic bags, recycled paper cartons, glue, etc., can try to use BHT-free plastic bags to reduce the occurrence of such problems.

6.Sunlight

In general, fluorescent brighteners have low sunlight fastness, fluorescent whitening of the fabric if exposed to sunlight for too long, will gradually turn yellow, it is recommended to use fluorescent brighteners with high daylight fastness for fabrics with high quality requirements. Sunlight, as an energy source, can degrade fibers; glass cannot filter all UV rays (only light waves below 320 nm). Nylon is a very easy to yellowing fiber, especially the semi-glossy or non-glossy fibers containing pigments, this kind of photo-oxidation will cause yellowing and loss of strength, if the fiber contains high water gas will make the problem more serious.

7.Microorganisms

Mildew and bacteria can also cause yellowing of the fabric, even turning brown or black. Mildew and bacteria need nutrients to grow, such as organic chemical residues on the fabric ( for example, organic acids, homogeneous dye, surfactants ). Humid environment and the surrounding temperature will accelerate the growth of microorganisms.

8.Miscellaneous

Cationic softener will interact with the anionic fluorescent whitening agent, and reduce the whiteness of the fabric value, the rate of reduction with the type of softener and the opportunity to contact the nitrogen atoms, the impact of PH value is also important, but also to avoid strong acid conditions. If the pH value of the fabric is below 5.0, it will also cause the color phase of the fluorescent brightener to become greenish. If the fabric must be in acidic conditions to avoid phenol yellowing, then the appropriate fluorescent whitening agent must be selected.