Fabric yellowing has always been a problem. In recent years, the yellowing problem has been extensively studied. Analysis of the causes of cotton fabric yellowing mainly includes the following points:
1. Fiber degradation: fiber degradation due to the effects of heat, light, other radiation, chemicals and biological degradation.
2. Additives: Yellowing and discoloration caused by adding softeners, oils, lubricants, resins, fluorescent whitening agents and metal compounds.
3. Atmospheric pollutants: yellowing caused by the influence of nitrogen oxides, sulfur dioxide and ozone.
4. Transmitted pollutants: The original yellow pigment of the yellowed matter is transmitted from the paper, cardboard, plastic film or plastic bag in contact with it and the pumice used for stone washing. Fabric.
5. Consumer contaminants: such as sweat and residues from household washing and bleaching.
6. Yellowing of phenols: During storage, yellowing of phenols is the most common. Original yellow pigments such as phenolic compounds or butylated hydroxytoluene that are transferred to the fabric from packaging materials such as cardboard, paper or plastic film during storage and where they are produced by the action of nitrogen oxides and The produced nitrophenol compound or the yellow product formed by 1,2-stilbene is more favorable in an alkaline environment. The yellowing of phenols has a pure bright yellow color, with maximum absorption characteristics at 420nm ~ 450nm, and will fade when exposed to light or ozone. The yellow product dissolves in polar solvents like hot water and alcohol, and becomes colorless in acidic media with a pH of 5 or lower.
Measures to prevent phenols from causing yellowing include:
1 , Avoid using brown paper, brown cardboard paper and plastic film containing phenol antioxidants to package finished products;
2. Avoid using heat shrink-based plastic packaging;
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3. Provide good ventilation conditions during storage;
4. Use less phenol derivatives as additives;
5. Prevent the finished product from being alkaline.
In addition, fabrics tend to turn yellow after being treated with citric acid.
The reason: citric acid is easily dehydrated to form anhydride when heated. Because citric acid has one more hydroxyl group than ordinary polybasic acids in its structure, it is a hydroxy acid. When heated and baked, Dehydration produces acid anhydride. At the same time, the hydroxyl group and the hydrogen in the ortho position in the molecule may also be further removed by heat and the external environment to generate unsaturated acid (acrylonic acid), and may remove water and CO2 to form itaconic acid. These unsaturated acids tend to make the cloth yellow, so it is best not to use citric acid as an acid agent for white cloth. </p
