Hexavalent chromium release from leather over time natural ageing vs accelerated ageing according to a multivariate approach.

European restriction limits the hexavalent chromium content to not more than 3 mg/kg in leather products. Owing to the evolution of hexavalent chromium content in leathers over time, it's difficult to guarantee the products will be harmless for consumers. The designing of an accelerated and representative artificial ageing procedure is therefore highly desirable. This article proposes a thorough study of the influence of storage conditions on the formation of hexavalent chromium in 4 bovine leathers. A factorial design of experiment was built with the following factors: temperature of 40-80 °C, relative humidity of 20-50%, presence or not of UV and exposure duration of 24-48 h. The results of these artificial ageings demonstrate that a high temperature, a dry atmosphere and the presence of light favor the formation of hexavalent chromium and that synergistic effects operate between temperature/humidity, temperature/UV and humidity/UV. At the same time, the leathers were subjected to a natural ageing for 12 months with a weekly hexavalent chromium analysis. The principal component analysis of the artificial ageing tests combined with the natural ageing tests, show that the artificial ageings 40 °C-50%RH-UV-48 h and 40 °C-20%RH-UV-24 h best simulate a natural ageing in the tannery, whatever the leather studied.