Studies of Structure Changes of Archeological Leather by FTIR Spectroscopy

Fourier transform infrared spectroscopy was used to investigate protein structures in new vegetable-tanned and artificially aged leather as well as in waterlogged archaeological leather dating from the Warring State Period (475BC-221BC). The obtained quantitative and qualitative information on protein structure changes was useful to characterize the deterioration of the archaeological leather during ageing in the buried environment. Compared with those in new vegetable-tanned leather, the amide A and amide II bands in the artificially aged and archaeological leather shifted to lower wavenumbers, suggesting hydrogen bonding in the collagen in the artificially and naturally aged leather was weakened. The estimation of the relative percentages of collagen secondary structures based on the peak area of component bands in the amide Ill showed that a-helix structure of collagen converted into a random coil structure in the artificially aged and archaeological leather. Besides, the characteristic absorption peaks of tannins appeared in the spectra of all archaeological leather samples, but the tannins content decreased, indicating that tannins present in the archaeological leather could be degraded or detanned. The results showed that there was an increase in disorder structures in the collagen molecular structure and that the cross-linking between the tannins and collagen was disrupted in archaeological leather. This study will help us to elucidate the deterioration mechanism and guide the conservation of archaeological leathers.