Self-Conversion of Hexavalent Chromium Formed in Chrome-Tanned Leather during Long-term Storage and Perfect Inhibition with a Combination of Inhibitors

摘要

Complete inhibition of Cr6+ formation from chrome-tanned leather can be achieved by treatment with a three-component inhibitor containing 1.0mmol 3(2)-t-butyl-4-hydroxyanisole, 0.01mmol ascorbic acid, and 0.001mmol collagen peptide. In the present paper, chrome-tanned leather was heat-aged at 80 degrees C for 24 hours and then stored at relative humidity of 33%, 65% or 97% for 12 months to investigate spontaneous conversion of Cr6+ to Cr3+ and to clarify availability of these inhibitors over long-term storage. The amount of Cr6+ decreased as the storage period increased, and was undetectable after 8 months. However, a second reheat-ageing resulted in reformation of Cr6+. This conversion to Cr3+ increased with the water content of the leather. Chrome-tanned leather treated with the three-component inhibitor maintained perfect inhibition of Cr6+ formation for 12 months, even if heat-aged again.