Abstract

The perfect inhibition of Cr6+ formation in Cr-tanned leather has been reported using combined inhibitors consisting 3(2)-t-butyl-4-hydroxyanisole (BHA), ascorbic acid (AsA), and collagen peptide (CP-9). In this study, the inhibitory mechanism of the combined inhibitors was investigated with respect to: (i) Inhibiting the conversion of Cr3+ to Cr6+ by scavenging lipid radicals and peroxy radicals in free lipid of Cr-tanned leather; (ii) strengthening the reductivity within Cr-tanned leather; and (iii) stabilising Cr3+ complexes by coordination with CP-9. Electron spin resonance (ESR) of free lipid extracted from the Cr-tanned leather treated with combined inhibitors showed that free radicals considerably reduced with BHA and AsA. AsA markedly depressed peroxide value (POV), indicating strong effectiveness of the reducing action of AsA. The CP-9-added extract with 0.1 mol/L potassium phosphate buffer (pH 5.5) of the Cr-tanned leather before changing from pH5.5 to 8.0 showed that the conversion of Cr3+ to Cr6+ showed concentration-dependent inhibition, suggesting stabilisation through CP-9 coordination. Therefore, perfect inhibition of Cr6+ formation in Cr-tanned leather using combined inhibitors was concluded to be caused by the multiple inhibitory actions of BHA, AsA, and CP-9, such as radical scavenging, radical scavenger regeneration, reducing action, and Cr3+ stabilisation.