Why do fabrics have yellowing ?

Environmental protection / Date: /

First, the analysis of the causes of cotton fabric yellowing mainly include:

  • Fiber degradation: due to heating, light, other radiation, chemicals and bio-degradation of the role of fiber degradation.

  • Additives: such as adding softeners, oils, lubricants, resins, fluorescent whitening agents and metal compounds caused by yellowing and color change.

  • Air pollutants: such as nitrogen oxides, sulfur dioxide and ozone caused by the impact of yellowing.

  • Transmission of pollutants: the original yellow pigment of the yellowing material is transmitted to the fabric from contact paper, cardboard board, plastic film or plastic bag and pumice stone used for stone washing.

  • Consumer contaminants such as perspiration and residues from household washing and bleaching.

Phenolic yellowing is most common during storage.During storage from cardboard, paper or plastic film sort of transport packaging material on the fabric such as phenol compounds or butyl hydroxy toluene (butylated hydroxytoluene) of the original yellow pigment, and on it due to the effect of nitrogen, oxidation and the content of styrene nitro phenol compounds or 1, 2-2 yellow product, which is formed by the alkaline environment better.Phenolic yellowing has a pure bright yellow color, with maximum absorption at 420~450nm and fades 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:

  • Avoid using brown paper, brown cardboard and plastic film containing phenol antioxidant to package finished products.

  • Avoid plastic packaging based on heat shrinkage.

  • Storage to provide good ventilation conditions.

  • To the north of less phenol derivatives as additives.

  • Avoid finishing the finished product is alkaline.

In addition, after using citric acid as an acid finishing agent, the fabric is also easy to yellowing.

The reason is that citric acid is easily dehydrated to form anhydride when heated, because citric acid has one more hydroxyl group than general polyacids in structure, which belongs to hydroxyl acid, and it is dehydrated to form anhydride when heated and baked.At the same time, the hydroxyl group and the ortho hydrogen in the molecule may be further removed by the influence of heat and external environment to generate unsaturated acid (triallic acid), and may be removed from water and CO2 to form conic acid.These unsaturated acids are easy to make the cloth yellowing, so it is best not to use citric acid as an acid for white cloth.