Preparation And Control Of Leather Antioxidants Microcapsules Hexavalent Chromium

Sexivalent chromium (Cr(VI)) in leather is systemic problem, which includes the formation, determination, and prevention of sexivalent chromium. Both raw hides or skins and leather chemicals may lead to the formation of sexivalent chromium. Tanning process of leather making may affect the formation of sexivalent chromium as well. The toxicity of sexivalent chromium is one hundred times more than of that of trivalent chromium (Cr(III)). Carcinogenesis and damage to the skins may be caused by sexivalent chromium. So the study on the formation, determination, and prevention of sexivalent chromium in finished leathers is one of the great problems facing the leather industry. In the recent years, more and more strict regulations are applied for the soluble chromium in leathers by Western Europe and Australia. Generally, the need for soluble chromium in leathers is less than 5 ppm. In some more strict regulations, the need may be less than 2 ppm.Formation cause of sexivalent chromium is studied in this article. The result of experiments shows: Content of sexivalent chromium increases more than three times when leathers are heated, and extending being heated time and rising the being heated temperature are equivalent in the formation of sexivalent chromium content in leathers. Content of sexivalent chromium rises as pH rises, and content of sexivalent chromium doesn't change obviously when pH is 7.5-8.0. Relative humidity also influences the content of sexivalent chromium and content of sexivalent chromium decreases greatly when relative humidity is 20%-40%.Three ways are used to prevent the formation of sexivalent chromium, which are using vegetable tannin to retan, adding Mg²⁺ into extracting liquor, and adding antioxidant into leathers. Such materials as vitamins, tea polyphenols, synthesized antioxidant, reducing agent, phytic acid and etc are used to prevent the formation of sexivalent chromium. Content of sexivalent chromium in leathers is reduced to 2.0ppm by vitamine C, and it is reduced to 2.9ppm by synthesized antioxidant, and falls to 1.0ppm after adding hyposulphite.Appeared in 1950s, microcapsules technique is a burgeoning technique. It can improve the physical character of matters, control releasing, reduce side-effect and shield odor. Microcapsules are made up of cyst core and cyst wall. Cyst core is made of synthesized antioxidant and cyst wall is made of polyacrylic acid-co-acrylamide. The products are white powder. Antioxidant microcapsules may extend the effect time of oxidantby controlling the release process of oxidant.