Causes, Testing and Solutions for Phenolic Yellowing in Textiles
September 26, 2025
Textile Yellowing
Yellowing refers to the phenomenon where white or light-colored materials turn yellow on the
surface under conditions such as light, ultraviolet rays, heat, oxygen, stress, and chemicals, also
known as yellowing. The causes of material yellowing vary, and it cannot be detected by a single
method. It is only possible to identify the cause of yellowing based on actual conditions and then
take targeted measures to solve it.
In general, the common types of yellowing in textiles mainly include light-induced yellowing and
phenolic yellowing. The former refers to the yellowing of the textile surface caused by sunlight or
ultraviolet radiation, while the latter refers to the yellowing of the textile surface caused by nitrogen
oxides or phenolic compounds.
Phenolic Yellowing
Phenolic yellowing is a type of yellowing. It occurs because phenolic compounds are used as
antioxidants during the production and processing process. Among them, 2,6-di-tert-butyl-4-
methylphenol (BHT) is the most widely used antioxidant due to its strong antioxidant capacity
, stable performance, and low price. However, BHT can react with nitrogen oxides to form new
compounds, which causes the material to turn yellow.According to the standard GB/T 29778-2013 Textiles - Testing for Color Fastness - Evaluation
of Potential Phenolic Yellowing, the scope of phenolic yellowing testing specifies the method
for evaluating the potential phenolic yellowing of textile materials. It only targets the phenolic
yellowing of textile materials and does not involve yellowing caused by other reasons. The
testing principle of phenolic yellowing is as follows: clamp each test sample and control fabric
between test papers containing 2,6-di-tert-butyl-4-nitrophenol, place them between glass plates
and stack them together, wrap them tightly with a polyethylene film free of BHT (2,6-di-tert-butyl
-4-methylphenol) to form a test package, and place it in a constant temperature oven or drying
oven for a certain period of time under specified pressure. Use the gray scale for assessing staining
to evaluate the yellowing grade of the test samples, so as to assess the possibility of phenolic
yellowing of the test samples. (Note: 2,6-di-tert-butyl-4-nitrophenol is formed by the reaction of
BHT (2,6-di-tert-butyl-4-methylphenol) with nitrogen oxides.)
Figure 1: Schematic diagram of fabric yellowing
Testing of Phenolic Yellowing
For the phenomenon of phenolic yellowing, both ISO and GB standards have specified the same
testing methods.
◦ ISO 105-X18
◦ GB/T 29778
The specific testing process is as follows:
1. Prepare a sealed test package. Inside each test package, six test papers, five test samples, and one
control fabric are clamped with seven glass slides.
2. Fold the test paper along the 100mm edge, and place each sample and control fabric separately
in the middle of the test paper, resulting in a total of six combined samples. Clamp the combined
samples with glass slides, and separate each combined sample with a glass slide.
If the number of test samples is less than five, seven glass slides should still be used, and seven
glass plates should be used in the package. Ensure that when the number of samples is insufficient
, the control fabric can still be tested normally.
3. Wrap the glass slides, test papers, test samples, and control fabric tightly with BHT-free
polyethylene film for three layers, and seal them with tape.
4. Place the test package on a testing device and apply a pressure of (5 ± 0.1) kg. A maximum of three
test packages can be stacked one on top of another on each testing device.
5.Place the testing device into a constant temperature oven/drying oven at (50 ± 3) °C for 16 h ± 5
min in the specified manner.
6. Remove the testing device from the constant temperature oven/drying oven, take out the test
package, and allow it to cool.
7. Conduct the grading within 30 minutes after opening the test package; otherwise, the samples of
some materials may fade when exposed to air. First, check the control fabric. Use the gray scale
for assessing staining to evaluate the yellowing of the control fabric. If it reaches at least grade 3,
it indicates that the test is normal. If the yellowing of the control fabric does not reach grade 3, re
test with new samples and materials.
Figure 2: Phenolic yellowing testing equipment
Causes and Countermeasures of Phenolic Yellowing
Phenolic yellowing occurs when 2,6-di-tert-butyl-4-methylphenol (BHT), which acts as an
antioxidant in materials, reacts with nitrogen oxides to form 2,6-di-tert-butyl-p-nitrophenol (DTNP
). DTNP itself is highly sublimable and can migrate to other materials even at room temperature.
DTNP is colorless under acidic conditions but turns yellow immediately under alkaline conditions.
Considering the characteristics of BHT, we should pay attention to and take the following measures
.
1. Avoid contact with materials containing BHT
BHT is widely used in various industries. Therefore, during the processing, packaging, and
transportation of products, contact with materials containing BHT should be avoided, especially
packaging materials. The yellow DTNP substance generated on the packaging materials will
migrate to the products, causing them to turn yellow. This is also the most common cause of
phenolic yellowing.
2. Improve the protection of the products themselves
If it is difficult to avoid contact with materials containing BHT during packaging and transportation
, anti-phenolic yellowing treatment can be applied to the products in advance. Adding
corresponding additives can effectively prevent the materials from absorbing derivatives.
Reducing powder can also be used to prevent or treat some yellowing phenomena.
3. Avoid using BHT as an antioxidant
As a cost-effective antioxidant, BHT is widely used in many fields, including the synthetic rubber
and plastic fields, although it may not be used as the main antioxidant.Therefore, in the shoemaking industry, phenolic yellowing is not limited to textiles such as
shoelaces and fabric uppers. For example, if the drop-molded parts of shoes turn yellow when
stored in a warehouse without light and at normal temperature, it is necessary to check whether it
is phenolic yellowing. It may be that the shoes have come into contact with materials containing
BHT, or the drop-molded materials themselves contain BHT, and the poor air circulation in the
warehouse leads to a high content of nitrogen oxides, which causes a chemical reaction.
4. Pay attention to the impact of the environment
In addition to providing good ventilation conditions, it is also necessary to prevent the products
from being in an alkaline environment considering the characteristics of DTNP.
Phenolic yellowing can be prevented and controlled, and its chemical reaction itself is reversible.
Therefore, as long as we attach importance to this problem, it can be avoided.
5. Use anti-phenolic yellowing agents
This product has a good effect on preventing the discoloration of nylon and nylon fluorescent dyed
fabrics caused by long-term storage or atmospheric NOX and SOX, as well as the yellowing caused
by BHT-containing packaging materials and BHT/NOX mixed gas. Theoretically, it is also effective
for other fluorescent dyed fabrics such as cotton and polyester.
1. Performance
（1）. It has a good preventive effect on the discoloration of nylon fluorescent white fabrics caused by
NOX and SOX, and the yellowing caused by BHT-containing packaging materials after treatment.
（2）. Prevents phenolic yellowing caused by BHT, which is used as an antioxidant in packaging films.
（3）. Prevents yellowing caused by ultraviolet rays, etc.
（4）. Does not reduce the color fastness.
2. Application
This product is a high-concentration product, and it is recommended to dilute it by 2-3 times before
use.
Dilution method: Stir with normal temperature water until it is completely dissolved and uniform.
This product is suitable for the padding process and also for the exhaust dyeing method. For
bleaching, it can be treated with a bleaching agent in the same bath at a high temperature during
exhaust dyeing, or it can be added when the temperature is lowered to about 70°C after dyeing. For
dyeing, it is recommended to add it after draining the water at the end of dyeing.Recommended processes:
（1）. Padding method:
Anti-phenolic yellowing agent: 15-30g/L, Citric acid: 2.0-5.0g/L. Pad at room temperature with a
liquid carrying rate of 80-85%, and dry at 120-140°C.
（2）. Exhaust dyeing method:
For bleaching, it can be added in the same bath or when the temperature is lowered to 60-70°C; for
dyeing, it can be added after draining the water:
Anti-phenolic yellowing agent: 2-3%; Citric acid: 0.5-1.0g/L; Treat at 70°C for 20-30 minutes and
then dry.