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Solutions for fabric yellowing

Solutions for fabric yellowing

  • Categories:技术专栏
  • Time of issue:2021-05-26 09:06:17
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Solutions for fabric yellowing

The yellowing problem of white or light bright-colored textiles in the process of finishing, storage and transportation is very difficult. Fabrics containing elastic spandex are yellowed by various factors, which seriously affect the appearance and use performance of textiles. At the same time, it causes textile finishing companies, clothing Claim disputes or frictions between manufacturers or end users.

Main factors of yellowing

Generally speaking, the following factors affect fabric yellowing:
(1) Light and heat (including heat setting and compression molding processing) cause the fiber bonds of the nylon fabric to break and decompose, thereby causing yellowing.
(2) The nitrogen oxide compound NOx in the air causes the amine oxidation of nylon fabric to produce yellow substance, which leads to yellowing.
(3) The fabric is alkalescent, which is more likely to cause yellowing, and pH<6 generally does not cause yellowing.
(4) There is an antioxidant in the polyethylene plastic film for packaging, the chemical name is 2, 6 diisobutyl phenol (BHT). Under certain conditions, the phenolic substance chemically reacts to form a yellow organic compound containing nitrate. Make the fabric yellow.
(5) Under high temperature environment, it will cause yellowing due to fiber oxidation, fiber and spinning lubricant, and impurities on the fiber. Other yellowing problems may occur when synthetic fabrics are stamped, especially lingerie (such as PA/EL bras).

 

 

Yellowing detection method

1. Assessment of potential phenol yellowing:
GB/T 29778—2013 "Textile color fastness test, evaluation of potential phenol yellowing"
Principle: Wrap the test sample and a piece of control fabric with test paper containing phenol and place them between glass plates and superimpose them to form a combined sample. After applying a certain pressure, wrap it with polyethylene film and place it in the specified In a constant temperature oven or oven for a period of time, remove the polyethylene film after cooling, take out the control fabric and the sample, and immediately evaluate the yellowing grade of the sample with a gray scale. If the staining of the control fabric reaches the predetermined value, the staining level of the sample is the test value, otherwise the test shall be repeated.

2. Evaluation of fastness to light yellowing
GB/T 30669—2014 "Textile color fastness test: color fastness to light yellowing"
Principle: After the sample has been irradiated under UV light for a certain period of time, it is compared with the unirradiated sample, and the degree of discoloration is evaluated by the gray scale for evaluating discoloration, so as to determine the ability of textile materials to resist light yellowing under UV light.

Determine the type of yellowing

There are several methods for judging yellowing:
(1) Use Saltzman reagent to test. If the reagent turns purple, it means that there is NOx, if there is no color change, it means that there is no NOx.
(2) Expose the yellowed part to acetic acid vapor. If the yellow color disappears, it is BHT yellowing, otherwise it is not BHT yellowing.
(3) Extract the part without yellowing with CHCl3, add 1 drop of HAc, if there is a change, it may be FBA yellowing, otherwise it is not FBA yellowing.
(4) Expose the yellowing part to sunlight without air pollution. If the yellowing disappears, it will be phenolic yellowing.
(5) Hang the yellowed product in a small box containing reducing powder. After 24 hours, the yellowing disappears, which is phenol yellowing.

 

 

Anti-yellowing measures

(1) Consumers should pay attention to maintenance during the wearing process.
(2) During production and processing, strictly control the amount of fluorescent whitening agent to avoid exceeding the yellowing point of the fluorescent whitening agent. The effect of improving the yellowing of the textile and increasing the whiteness of the textile can be achieved by increasing the blue light that can be reflected in the textile. According to chromaticity theory, a certain amount of blue light and yellow light are mixed to form white light, and blue light and yellow light are complementary colors. Therefore, the reason why textiles are yellow is that there is insufficient blue light in the reflected light. According to this, textiles with high yellowness have less blue light and low whiteness in reflected light; while light yellowness has more blue light and high whiteness in reflected light.
(3) In the finishing process, the setting temperature should not be too high. If the setting temperature is too high, the fabric will turn yellow after setting. For fabrics containing spandex, the setting temperature should be lower than 190℃.
(4) Prevent BHT from yellowing during the packaging process. Products with yellowing of phenols and BHT are sensitive to pH. 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) in the post-processing of the fabric will greatly reduce the probability of yellowing.
(5) Anti-yellowing treatment of packaged finished products. For packaged finished products or products stored in warehouses, if there is yellowing or the yellowing test is found to be unqualified, and the washing and tagging have been nailed, it is not easy to put into the water for disposal. At this time, consider using the reduction method.
Put a layer of white paper under 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 cardboard box, seal the cardboard box, and place it for 24h~48h After dispersing and placing it for more than 6 hours, repack it after it has 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 tag, but improper handling of the reducing powder may cause color changes.
Yuefa Textile's suggestions on yellowing:
Anti-phenol yellowing agent CT
【Use】
White and bright fabrics often produce yellowing due to the absorption of nitrophenol derivatives of butylated hydroxytoluene antioxidants. Such antioxidants are widely present in packaging materials (such as packaging films). Yellowing occurs. The application of this product on nylon can help prevent this yellowing.
[Group]
Manufactured products of aryl sulfonic acid, alkanolamine and polyol
【Performance】

External view: Transparent to light brown low-viscosity liquid pH value 7-8 (5% aqueous solution)
Isolation: Anionic Solubility: Easily soluble in water
General stability: set the acid, alkali and electrolyte in the general dosage of hard water below 170ppm and textile processing. ...
Compatibility: It can be used with anionic substances. Weak cationic substances will weaken the product's efficacy, and strong cationic substances will cause precipitation. To
Ecological/toxicity: The storage, operation and use of products should comply with the general health and safety regulations for chemical storage and transportation
Storage stability: It can be stored at least one year in a closed container at 20℃ in the dark

【Characteristic】

● Prevent the fiber from absorbing the nitrophenol derivative of butylated hydroxytoluene.
● It has affinity with fiber, and has good leveling and reproducibility.
● It can be processed in the same bath with the brightener without affecting the fastness performance
●Low foam is suitable for exhaustion processing of fabrics running at medium speed

【Application】

This product can be diluted with cold water or warm water in any proportion, or it can be directly added to the dyeing bath without dilution.
Dosage: 2-3% of this product
Recommended prescription
Nylon fabric bleaching-whitening and exhaustion processing
0.5-2 g/L Fluorescent brightener
0.5-3 g/L Insurance powder
0.1-2 g/L Chelating dispersant
0.5-1 g/L Degreaser
2--3 g/L This product
pH value 4-6 acetic acid or citric acid adjustment
Bath ratio 10:1-20:1
Temperature 120-80℃
Processing time 20-60 min
After the nylon fabric is whitened, it is processed by the padding method, and the dosage is 30-40g/L. At the same time, 0.25g/L citric acid or 2g/L optimizer AB-55 is added to the padding bath.

Contact details

Address: Building C, Fumao Industrial Park, No. 2456, Nansanhuan Road, Shengze Town, Wujiang, Jiangsu Province

Phone:86-0512-63556100

Fax:86-0512-63556200

Mailbox:Davis@yuefagroup.com

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