What are the anti-yellowing measures?

1 During the wearing process, consumers themselves pay attention to maintenance

2 During production and processing, strictly control the amount of fluorescent whitening agent to avoid exceeding the yellowing point of fluorescent whitening agent

The effect of improving textile yellowing and increasing textile whiteness can be achieved by increasing the blue light that can be reflected in textiles. According to the theory of chromaticity, a certain amount of blue light and yellow light are mixed into white light, and blue light and yellow light are complementary colors of each other, so the reason why the textile is yellow is the lack of blue light in the reflected light. Accordingly, the reflected light of textiles with high yellowness has less blue light and low whiteness; the reflected light with small yellowness has more blue light and high whiteness.

3 During the finishing process, the setting temperature should not be too high

If the setting temperature is too high, it will cause the fabric to yellow after setting. For fabrics containing spandex, the setting temperature should be lower than 150 ℃.

4 During the packaging process, prevent the yellowing of BHT

Phenolic and BHT yellowed products are pH sensitive. In terms of anti-yellowing, the fabric should be slightly acidic after dyeing. According to the test, when the pH value of the fabric is <5, the yellowing time will be longer; when the pH value is >6, the yellowing time will be shorter. Adding a small amount of non-volatile acid (such as citric acid) to the fabric post-treatment will greatly reduce the chance of yellowing.

5 Anti-yellowing treatment of packaged finished products

For the packaged finished products or the products stored in the warehouse, if there is yellowing or the yellowing test is found to be unqualified, and the washing marks and tags have been nailed, it is not easy to deal with it. At this time, the reduction method can be considered. Put a layer of white paper at the bottom of the carton, sprinkle a certain amount of reducing powder, and then cover the reducing powder with a layer of cardboard, make small holes in the cardboard, stack the products in the carton, seal the carton, and leave it for 24h ~ 48h After dispersing and placing for more than 6 hours, repacking after no smell. This method does not require water treatment, can maintain the original shape of the product, and does not need to remove the washing mark and hang tag, but improper treatment of the reducing powder may cause color changes.

In addition, if there is yellowing on the garment, avoid using brown cardboard and plastic film packaging fabrics containing phenolic antioxidants, and require good ventilation during storage.

In a word, yellowing is a common old problem in textiles, and there are many reasons for yellowing. By analyzing the causes of yellowing, judging the yellowing, and taking effective measures to prevent the yellowing, the quality level and performance of the product can be better improved.

6 Factors and preventive measures that cause fabric yellowing

Analysis of the causes of yellowing of cotton fabrics mainly include:

(1) Fiber degradation

Fibers are degraded by heat, light, other radiation, chemicals and biodegradation.

(2) Additives

Such as yellowing and discoloration caused by the addition of softeners, oils, lubricants, resins, optical brighteners and metal compounds.

(3) Air pollutants

Yellowing caused by effects such as nitrogen oxides, sulfur dioxide and ozone.

(4) Transmission of pollutants

The original yellow pigment of the yellowed material is transferred to the fabric from the contact paper, cardboard, plastic film or plastic bag and pumice stone used for stonewashing.

(5) Pollutants of consumers

Such as sweat and residues from household washing and bleaching.

During storage, yellowing of phenols is the most common. Original yellow pigments such as phenolic compounds or butylated hydroxytoluene [BHT] transported to the fabric during storage from packaging materials such as cardboard, paper or plastic film, and on them due to nitrogen, oxygen The nitrophenol compound produced by the action of the compound, or the yellow product formed by 1,2-stilbene, the alkaline environment is more favorable for this.

The yellowing of phenols has a pure bright yellow color and has the maximum absorption characteristics at 420-450nm, which will fade when exposed to light or ozone. The yellow product dissolves in hot water and polar solvents such as alcohol, and becomes colorless in acidic media at pH 5 or lower. Measures to prevent phenols from causing yellowing include:

(1) Avoid using brown paper, brown cardboard and plastic film containing phenol antioxidants to package finished products;

(2) Avoid plastic packaging based on heat shrinkage;

(3) Provide good ventilation conditions during storage;

(4) Use less phenol derivatives as additives;

(5) Avoid the finished product being alkaline.

In addition, after finishing with citric acid as an acid agent, the fabric is also prone to yellowing. The reason: citric acid is easily dehydrated to form anhydride when heated. Because citric acid has one more hydroxyl group than general polyacids in structure, it belongs to hydroxy acid, and it is dehydrated to form acid anhydride during heating and baking. At the same time, the hydroxyl group in the molecule and the hydrogen on the ortho position may also be further removed by the influence of heat and external environment to generate unsaturated acid (acrylic acid), and it is possible to remove water and CO2 to form itaconic acid. These unsaturated acids are easy to make the cloth yellow, so it is best not to use citric acid as an acid agent for white cloth.

Analysis of the yellowing of the bleached yarn:

After the bleached and whitened yarns are placed for a certain period of time, firstly, macula will be produced, and secondly, the whiteness will decrease with time. According to the analysis of the reasons, the macular is caused by the poor water quality for bleaching and the high content of divalent iron ions. The divalent iron ions are oxidized or trivalent iron ions over time, so that the macular is formed on the yarn. This macular not only affects the quality of appearance, but also makes the fibers brittle. The way to overcome it is: in case of poor water quality, pickle the yarn with 1.5~2.0g/L of oxalic acid at 80~85℃ before bleaching. Because oxalic acid can form complex ions with iron ions and dissolve in water, iron in water can be removed to achieve the purpose of not yellowing.

The main reason for the decrease in whiteness of bleached and whitened yarns over time is due to insufficient scouring. If the scouring of the yarn is not sufficient and the impurities in the cotton fiber are not completely removed, the yarn will be bleached and whitened immediately. Over time, the impurities and natural pigments inside the fiber will be exposed, resulting in a decrease in whiteness.

The way to overcome it is to ensure that the wool effect of the bleached yarn reaches 13-15cm/30min, and the wool effect must be uniform, so as to ensure that the bleached and whitened yarn does not turn yellow.

In addition, when bleaching with sodium hypochlorite and dechlorination, the amount of baking soda is too much or the yarn is not washed, which can also make the yarn yellow. When the yarn is dried, the temperature of the drying room is too high, and the drying time is too long, which will also cause the yarn to turn yellow.