Causes, Testing, and Solutions for Textile Yellowing

Introduction

The phenomenon of white or light-colored substances turning yellow on the surface due to external conditions such as light or chemicals is known as "yellowing."

When white textiles and dyed textiles turn yellow, not only is their appearance affected, but their lifespan is also significantly reduced. Therefore, the study of the causes of textile yellowing and prevention measures has always been a popular topic both domestically and internationally.

I. What causes textile yellowing?

1. Light Yellowing:

Light yellowing refers to textiles turning yellow due to exposure to sunlight or ultraviolet light, causing molecular oxidative cleavage reactions. Light yellowing is most common in light-colored garments, bleached textiles, and whitened textiles. After exposure to light, the energy is transferred to the fabric dye, causing the dye conjugate to split, leading to photofading and making the textile surface appear yellow. Visible light and ultraviolet light are the main factors causing azo dyes and phthalocyanine dyes to fade, respectively.

2. Phenolic Yellowing:

Phenolic yellowing is generally caused by the contact transfer of NOX and phenolic compounds, leading to textile surface yellowing. The primary reactive substance is usually the antioxidant present in packaging materials, such as butylated hydroxytoluene (BHT). After leaving the factory, garments, and shoes are often transported in packaging for extended periods. The BHT in the packaging materials reacts with NOX in the air, causing the garments to yellow.

3. Oxidative Yellowing:

Oxidative yellowing refers to the yellowing of textiles due to oxidation by the atmosphere or other substances. During dyeing and finishing, textiles typically use reductive dyes or auxiliaries. When these come into contact with oxidizing gases, oxidative reduction occurs, causing yellowing.

4. Optical Brightener Yellowing:

Optical brightener yellowing mainly occurs in light-colored textiles. When residual optical brighteners on the garment surface migrate after long-term storage, it leads to an overconcentration of brighteners in certain areas, causing the garment to yellow.

5. Softener and Other Finishing Agent Yellowing:

During the finishing process, the softening agents used on garments can cause yellowing in treated areas when exposed to heat or light conditions, due to the oxidation of cations present in the softeners.

II. What are the standards for testing textile yellowing?

1. Natural Light-Induced Yellowing Test Method:

GB/T 8427—2008 "Textiles—Tests for Colorfastness—Colorfastness to Artificial Light: Xenon Arc" describes the principle of placing the sample together with a set of blue wool standard samples in a box and exposing them under artificial light conditions. The color change of the sample and the blue wool standard samples is then rated to assess colorfastness.

2. Ultraviolet Light-Induced Yellowing Test Method:

GB/T 30669—2014 "Textiles—Tests for Colorfastness—Colorfastness to Light Yellowing" describes the principle of exposing the sample to ultraviolet light for a specific time and comparing it to an unexposed sample. A grayscale card for color change is used to rate the degree of color change.

3. Phenolic Substance-Induced Yellowing Test Methods:

• GB/T 29778—2013 "Textiles—Tests for Colorfastness—Assessment of Potential Phenolic Yellowing
• SN/T 2468—2010 "Test Method for Phenolic Yellowing of Imported and Exported Textiles" describes the principle of placing each sample and a control fabric between papers containing 2,6-di-tert-butyl-4-nitrophenol (BHT), stacking them between glass plates, and tightly wrapping the stack with polyethylene film free from BH to form a test package. This is then placed in an incubator or oven at a defined pressure and time. A grayscale card for staining is used to rate the degree of yellowing, assessing the potential for phenolic yellowing.

4. Chlorine Bleaching-Induced Fabric Yellowing Test Method:

FZ/T 01078—2009 "Test Method for Yellowing due to Chlorine Absorption of Fabrics" describes the principle of evaluating the yellowing grade of the sample after chlorine bleaching, washing, and drying in a washing machine compared to the original sample.

III. How to prevent textile yellowing?

1. For varieties that require the use of fluorescent brighteners, select brighteners that exhibit minimal yellowing under various conditions.

2. During fabric finishing and setting, the temperature should not be too high, as high temperatures can cause oxidative cleavage of the dye or auxiliaries on the textile surface, leading to yellowing.

3. Test the yellowing performance of softeners and other finishing auxiliaries before use, and choose auxiliaries with low yellowing potential.

4. During packaging and storage, use packaging materials with low BHT content, and maintain ambient temperature and ventilation to prevent phenolic yellowing.

5. Use anti-yellowing agents based on the specific causes of yellowing, generally categorized into anti-oxidative yellowing agents and anti-phenolic yellowing agents.

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