Causes of yellowing of elastic fabrics
1. Common problems
Yellowing, especially yellowing of white or light-colored elastic fabrics during finishing, storage and transportation, 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, exposure to heat during molding, storage, 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 when formed (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
Preventing 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 finishing results focus on excellent protection against storage yellowing, the possibilities to meet other requirements (such as a neutral to slightly acidic product pH) are limited.
These effects and problems can only be controlled by selecting special textile auxiliaries and corresponding processes.
2. Heat Yellow
First, the gray fabric is heat-set on a gas-fired tenter, which causes severe yellowing due to contact with heat finishing (forming) and the bonding process. Made of polyamide and increasingly polyester. These problems are exacerbated when microfiber products exhibit their large surface area.
There are more and more problems caused by cotton/spandex blended knitted fabrics. Yellowing is prone to occur during the initial heat setting step to eliminate curling and obtain sufficiently stable dimensions. Usually, after finishing in this step, the fabric will become Brown, 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
The yellowing caused by the nitrogen oxidation reaction is affected by the fiber material used, and is similar to the yellowing of phenolics. When exposed to nitrogen oxide gas, during textile dyeing and finishing, elastic polyimide or polyester products, depending on Its spandex content shows a slightly yellowish to reddish color change.
The deposition of fiber lubricants and fabric additives have a negative impact on NO. Yellowing has additional effects. In actual operations, high concentrations of nitrogen oxides are often encountered, such as those produced in heat setting processes (gas stenter), warehouses (such as exhaust from loading and unloading trucks), and some atmospheric pollutants (smoke).
The effects of exposure to nitrogen oxides, depending on the degree of damage, are not apparent until weeks later, leading to complaints of yellowing. Common antioxidants generally used to prevent thermal yellowing and phenolic yellowing Not enough to resist the effects of nitrogen oxides
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