Why Does Elastic Fabrics Turn Yellow?

1. Common problems

Yellowing, especially yellowing of white or light-colored elastic fabrics during finishing, storage and transportation, is a major challenge for fabric finishers.

Yellowing problems may cause complaints and conflicts between finishers and clothing manufacturers and even customers. In addition, finishing to avoid or eliminate yellowing of fabrics is time-consuming and costly. Therefore, this problem 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 and avoided. A certain degree of yellowing may be caused by heat setting of the fabric, forming with contact heat, storage, heat setting and storage in nitrogen oxides, and forming of fabrics with foam linings (such as women's corsets).

The tendency of elastic fabrics to yellow varies based on the different materials and fiber additives used. The problem of yellowing has been discussed a lot by dyers without borders.

On the contrary, the diversity and high demands of customers are:

- High whiteness and brightness of the color;

- Low yellowing during molding (color matches the initial sample);

- Phenolic yellowing assessment mark 4 as a minimum standard, as a baseline for storage yellowing;

- Final pH value of 4-7 in the finished product;

- Protection against exposure to NOx

Textile finishers often have to make compromises to achieve these goals. Protection against phenolic yellowing is often considered the most important aspect in the finishing of elastic polyamide fabrics, but it is only one of many interfering factors.

For example:

When the finishing result focuses on excellent protection against storage yellowing, the possibility of meeting other requirements (such as neutral to slightly acidic product pH) is limited.

These results and the problems involved can only be controlled by selecting special textile auxiliaries and corresponding processes.

2. Thermal yellowing

First, the grey fabric is heat-set on a gas-fired tenter frame, which produces severe yellowing due to contact with hot finishing (molding) and bonding processes. Elastic fabrics made of polyamide and increasingly polyester are particularly sensitive. These problems are exacerbated when microfiber products present their greatest surface area.

An increasing number of problems arise with cotton/spandex blended knitted fabrics, which are susceptible to yellowing during the initial heat setting step to eliminate curling and obtain sufficiently stable dimensions. The fabric usually turns brown after this step, and must go through time-consuming and costly scouring and bleaching steps to achieve the required whiteness.

To prevent heat yellowing, special auxiliaries are designed to prevent or minimize yellowing under thermal stress.

3. Yellowing caused by nitrogen oxides

Yellowing caused by nitrogen oxidation reactions is affected by the fiber material used, similar to phenolic yellowing. When exposed to nitrogen oxide gases, elastic polyimide or polyester products, depending on their spandex content, show a more or less slightly yellowish to reddish color change during textile dyeing and finishing.

Deposition of fiber lubricants and fabric additives have an additional impact on NO yellowing. In practice, high concentrations of nitrogen oxides are often encountered, for example in heat setting processes (gas-fired stenters), in warehouses (e.g. exhaust gases from loading and unloading vehicles) and in some atmospheric pollutants (smog).

The effects of exposure to nitrogen oxides, depending on the degree of damage, are only apparent after several weeks, which can lead to yellowing complaints. Common antioxidants, which are generally used to prevent heat and phenolic yellowing, are not sufficient to combat the effects of nitrogen oxides.

To combat the yellowing challenges faced by elastic fabrics,Sylic FU5610/CY-737 Anti-phenol Yellowing Agent offers an effective solution. Specifically designed to prevent phenolic and nitrogen oxide-induced yellowing, this agent is ideal for maintaining the whiteness and brightness of polyamide and polyester fabrics. It works by stabilizing the fabric during heat setting and storage, offering protection against discoloration caused by exposure to NOx gases and high-temperature processing.

This product is highly recommended for elastic fabrics such as spandex blends, which are prone to yellowing during heat treatment and storage. By using Sylic FU5610/CY-737, textile finishers can ensure a consistent and high-quality finish, meeting the strict demands of colorfastness, brightness, and anti-yellowing performance required by today's fashion industry.

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