Why are azo dyes forbidden in textile printing and dyeing process?

After using azo dyes containing banned aromatic amines in textiles and clothing, they may be absorbed by the skin and diffuse in the human body during long-term contact with the human body. These dyes may undergo reduction reactions under the conditions of biochemical reactions that occur in normal human metabolism, thereby decomposing carcinogenic aromatic amines. After the activation of carcinogenic aromatic amines, it will change the structure of human DNA, and eventually cause human diseases and induce cancer.

In July 1994, the German government for the first time banned the production, use and sale of azo dyes that reduce carcinogenic aromatic amines and products using these dyes. Subsequently, the Dutch and Austrian governments also promulgated corresponding laws. In 2003, my country promulgated GB18401-2003 "National Basic Safety Technical Specifications for Textile Products", which officially included the banned azo dyes. At present, the monitoring of banned azo dyes has become one of the most important quality control items in the international textile and garment trade, and it is also one of the most basic quality indicators of ecological textiles.

An overview of azo dyes

1.1 Development History

As early as 1834, Mitseherlich prepared azobenzene using potassium hydroxide and nitrobenzene in ethanolic solution. However, azo dyes were produced and used after 1858, and azo dyes were prepared by diazotization reaction.

In 1863, the first commercial azo dye Bismarck Brown came out. Azo dyes began industrial production.

The synthesis of Congo red in 1884 can be said to be a milestone in the development history of azo dyes. 1. Congo red is used as the dye, and no catalyst is added, which greatly simplifies the printing and dyeing process; second, this azo dye can obtain different colors through its different structures; third, its synthesis process is simpler. Lower cost and better dyeing performance.

1.2 Carcinogenic problems of azo dyes

In the 1930s, Japanese Yoshida discovered that solvent yellow can cause hepatocellular carcinoma in mice. People only realize the harm of azo dyes and their intermediates in the process of production and use. In fact, some aromatic amines in dyes such as magenta, auramine and naphthylamine have been shown to be carcinogenic as early as 1905 by the German health authorities. This situation is further exacerbated with the rapid development of dye chemical industry. According to incomplete statistics, by the 1960s, due to the work of dye chemical industry, more than 3,000 cases of bladder cancer occurred all over the world.

Started in the 1970s. The world's major dye producers have voluntarily signed an agreement to stop the sale of benzidine and benzidine-based azo dyes on the market. The German government established the MAK (Maximum Arbeitplaz Konzentrations (Maximum Arbeitplaz Konzentrations) committee on the maximum permissible concentrations of chemicals known to pose a threat to human health in the workplace) in 1958. Since then, 1 MAK table has been published every year. According to the different carcinogenicity to humans, the MAK table is divided into three different levels: MAK (III) Al: According to experience, this class of substances can cause human malignant tumors. MAK(III)A2: So far, there has been clear evidence that these substances can cause cancer, but this evidence is obtained by simulating the human working environment and animal experiments. MAK(Ⅲ)A3: Suspected as a potential carcinogen, further investigation is needed urgently; and it is pointed out that the azo dyes synthesized with these carcinogenic aromatic amines are prone to coupling reaction due to the action of human intestinal bacteria and azoreductase. Nitrogen gas is reductively cleaved and re-releases carcinogenic aromatic amines, resulting in carcinogenic effects.

Most (about 60%) synthetic dyes on the market today are based on azo chemistry. The problem of carcinogenicity is that the reducible aromatic amines in some azo dyes have been proved to be potentially carcinogenic to humans or animals through long-term research and clinical trials. Azo dyes on textiles will be transferred from textiles to human skin under some special conditions, especially in the case of poor color fastness, and long-term contact with the skin. Through the normal metabolic process of the human body, secretions are decomposed and reduced under the biocatalysis of secretions, releasing certain carcinogenic aromatic amines. After these aromatic amines are absorbed by the human skin, they deoxygenate the cells through metabolism in the body. Changes in ribonucleic acid (DNA) have potential carcinogenic sensitization effects.

1.3 Classification of azo dyes

Azo dyes are dyes containing azo groups (-N="N-) in their molecular structure. They are the most versatile and most widely used synthetic dyes. According to the number of azo groups, they can be divided into: (1) Monoazo Nitrogen dyes, such as Acid Scarlet G; (2) disazo dyes, such as Direct Scarlet 4B; (3) polyazo dyes, such as Direct Black BN. According to different solubility, they can be divided into: (1) Soluble azo dyes refer to Generally water-soluble dyes; (2) Insoluble azo dyes, including ice dyes and other water-insoluble azo dyes.

Azo dyes are used for dyeing and printing of various fibers, dyeing of leather, paper, soap, candles, wood, straw, feathers, etc., and coloring of paints, inks, plastics, rubber, food, etc.