Causes of yellowing of elastic fabrics
1. Common problems
Yellowing, especially the yellowing of white or light-colored elastic fabrics during the finishing, storage and transportation processes, is a major challenge faced by fabric finishers.
The yellowing problem may cause complaints and conflicts between organizers, clothing manufacturers and even customers. Additionally, finishing to avoid or eliminate fabric yellowing is time-consuming and costly. Therefore, this issue cannot be ignored.
Generally speaking, textile manufacturers must deal with yellowing caused by temperature and storage. But yellowing of elastic fabrics is a more complex phenomenon that must be considered to avoid. Some degree of yellowing may be caused by heat setting of fabrics, molding and storage exposed to heat, heat setting and storage in nitrogen oxides, and molding of foam-lined fabrics (such as women’s corsets).
The yellowing tendency of elastic fabrics varies based on different materials and fiber additives used. The problem of yellowing has been discussed by many people without borders.
On the contrary, the diversity and high demand of customers include:
One-color high white High strength and high brightness;
Low yellowing upon molding (color matches the initial sample);
A phenolic yellowing evaluation mark of 4 is the low standard, which is used as the bottom line for storage yellowing;
A final pH value of the finished product is 4-7;
Preventing exposure to NOx
Fabric finishers often have to make compromises to achieve these Target. Prevention of phenolic yellowing is often considered an important aspect in the finishing of elastic polyamide fabrics, however this is only one of many interfering factors.
For example:
When the sorting results focus on excellentWhen protecting against storage yellowing, the possibility of meeting other requirements (such as a neutral to slightly acidic product pH) is limited.
These effects and problems can only be controlled by selecting special textile auxiliaries and corresponding processes.
2. Heat yellowing
First of all, the gray fabric is Heat setting on gas stenter will cause serious yellowing due to contact with heat finishing (forming) and bonding process. Elastic fabrics made of polyamide and increasingly polyester are particularly sensitive. These problems are exacerbated when microfiber products exhibit their extremely large surface areas.
There are more and more problems caused by cotton/spandex blended knitted fabrics, which are prone to occur during the initial heat setting step to eliminate curling and obtain sufficiently stable dimensions. Yellowing O Usually the fabric will turn brown after finishing in this step, so it must go through time-consuming and costly scouring and bleaching processes to achieve the required whiteness.
In order to prevent thermal yellowing, special additives have been designed to prevent or minimize yellowing under thermal stress.
3. Yellowing caused by nitrogen oxides
Yellowing caused by nitrogen oxidation reaction is affected by the fiber material used and is similar to phenolic yellowing. When exposed to nitrogen oxide gas, during textile dyeing and finishing, elastic polyimide or polyester products, depending on their spandex content, will show a more or less yellowish to reddish color change.
Deposition of fiber lubricants and fabric additives have an additional impact on NO yellowing. In actual operations, high nitrogen oxide concentrations are often encountered, such as those produced in the heat setting process (gas tenter), warehouses (such as exhaust gas from loading and unloading trucks), and some atmospheric pollutants (smoke).
The effects of exposure to nitrogen oxides, depending on the extent of the damage, are not apparent until weeks later, leading to complaints of yellowing. Common antioxidants commonly used to prevent thermal yellowing and phenolic yellowing are not sufficient to combat the effects of nitrogen oxides.
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