Why does cotton fabric always turn yellow? Composite fabric information

Analyzing the causes of yellowing of cotton fabrics, the main reasons are: 1. Fiber degradation: Fiber degradation occurs due to the effects of heat, light, other radiation, chemicals and biodegradation. 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 yellowing matter is transferred to the fabric from the contact paper, cardboard, plastic film or plastic bag and the pumice stone used for stone washing. 5. Consumer contaminants: such as sweat and residues from household washing and bleaching. During storage, yellowing of phenols is the most common. Raw yellow pigments such as phenolic compounds or butylated hydroxytoluene [BHT] are transferred to the fabric from packaging materials such as cardboard, paper or plastic film during storage, where they are retained by nitrogen, oxidation and The yellow product formed by nitrophenol compounds or 1,2-stilbene produced by the action of chemicals is more favorable in an alkaline environment. The yellowing of phenols has a pure bright yellow color, with maximum absorption characteristics at 420~450nm, and 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 with a pH of 5 or lower.
Measures to prevent yellowing caused by phenols include: 1. Avoid using brown paper, brown cardboard and plastic film containing phenol antioxidants to package finished products; 2. Avoid using plastic packaging based on heat shrinkage; 3. , Provide good ventilation conditions during storage; 4. Use less phenol derivatives as additives; 5. Prevent the finished product from being alkaline. In addition, after using citric acid as an acid treatment, the fabric will also tend to turn yellow. 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. It dehydrates to form anhydride when heated and baked. 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 influence of 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.
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