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 common problem. A big challenge for organizers.
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.
In general, 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 the 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:
High whiteness and high brightness of color;
Low yellowing during molding (color and luster) Match the original sample);
A phenolic yellowing evaluation mark of 4 is the minimum standard, which is used as the bottom line for storage yellowing;
The final pH value of a finished product is 4-7;
Preventing exposure to NOx
Fabric finishers often have to make compromises to achieve these goals. Preventing phenolic yellowing is often considered the most important aspect of finishing elastic polyamide fabrics, however this is only one of many interfering factors.
For example:
While the finishing results focus on excellent protection against storage yellowing, the possibility of meeting other needs (such as a neutral to slightly acidic product pH) will Restricted.
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-set on the gas tenter, which is caused by contact with heat finishing (forming) and the bonding process. Severe yellowing. Elastic fabrics made of polyamide and increasingly polyester are particularly sensitive. These problems are exacerbated when microfiber products exhibit their extremely large surface areas.
An increasing problem arises with cotton/spandex blended knitted fabrics, where yellowing tends to occur during the initial heat setting step to eliminate crimping and obtain sufficiently stable dimensions. This step is usually where the finished fabric is finished. It will turn brown and must undergo time-consuming and costly scouring and bleaching processes to achieve the required whiteness.
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 additional effects 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. </p
