Hexavalent chromium (Cr VI) is recognized worldwide as a hazardous substance. It is not only a carcinogen but also causes allergic dermatitis, as well as digestive and respiratory system diseases when humans are exposed to it for a long time via skin and mucous membranes, digestive tract, or respiratory tract.
Annex 17 of the EU REACH regulation stipulates that Cr VI content in leather shall not be higher than 3 mg/Kg. China’s mandatory national standard GB 30585-2014 “Safety technical specifications for children’s footwear” stipulates that Cr VI in leather and fur shall not exceed 10 mg/kg. In recent years, “Safety Gate” in Europe reported substandard footwear consumer products, with more than 50% of the products exceeding the Cr VI standards. Therefore, preventing excessive hexavalent chromium content has become a key control point for quality control in the leather and footwear industry.
Causes of excessive Cr VI in leather products can be attributed to several factors.
Chromium powder, used as a chromium tanning agent, is the largest and most direct source of chromium element in leather. Due to poor management of some leather chemical plants, chromium powder produced by them often contains a small amount of Cr VI.
Additionally, some metallic complexing dyes and certain chemical auxiliaries, catalysts, and other chemicals used can contain Cr VI ions.
Oxidizing bleaching with agents such as sodium hypochlorite and sulfuric acid treatment during chrome tanning can also cause Cr III to be oxidized to Cr VI. The use of fat fillers containing certain iodine values, such as sulfite oil, can promote the conversion of Cr III to Cr VI.
Prevention scheme for hexavalent chromium exceeding the standard
To prevent excessive Cr VI content, leather processing should use chrome-free tanning agents such as vegetable tanning agents or wet blue skin retanning.
Pigments and additives containing chromium, such as yellow or orange inorganic pigments, and fat additives with high unsaturated value should be avoided.
Alkaline conditions during leather and footwear production should also be avoided, which allows for the oxidation of Cr III to Cr VI.
In the drying and finishing stage, high temperatures and ultraviolet rays should be avoided, and washing should be sufficient.
Rational use of reducing agents, antioxidants, and treatment agents can also help reduce Cr VI to Cr III.
Proper storage and transportation conditions of leather products should be maintained, such as maintaining a weak acid environment, controlling the temperature and humidity, and avoiding exposure to oxidizing gases.
In conclusion, preventing excessive Cr VI content in leather products requires comprehensive measures to ensure compliance with standards. Feel free to talk with our experts for effective solutions.