Why does cotton fabric always turn yellow?

Analyze the causes of yellowing of cotton fabrics, mainly including:

1. Fiber degradation: The fiber is degraded due to heating, light, other radiation, chemicals and biodegradation.

2. Additives: such as 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 transmitted to the fabric from the contacted paper, cardboard, plastic film or plastic bag and the pumice used for stone washing.

5. Consumer pollutants: such as sweating and residues from household washing and bleaching.

During storage, yellowing with phenols is the most common. During storage, the original yellow pigments such as phenol compounds or butylated hydroxytoluene [BHT] that are transferred from packaging materials such as cardboard, paper or plastic film to the fabric, and due to nitrogen, oxidation and The yellow product formed by the nitrophenol compound or 1,2-stilbene produced by the action of the substance, the alkaline environment is more favorable for this. The yellowing of phenols has a pure bright yellow color and has the largest absorption characteristics at 420~450nm. It 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 an acidic medium with a pH of 5 or lower.

Measures to prevent yellowing caused by phenols include:

1. Avoid using brown paper containing phenol antioxidants, brown cardboard paper and plastic film 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. Avoid the alkalinity of the finished product after finishing.