Abstract
This article describes a quantitative evaluation method proposed to quickly identify the deterioration degree of hardened leather relics unearthed in China. We used three kinds of artificial aging samples, dry-heat aging (DH)、UV-aging (UV)、and alkali-thermal aging (AT) as the research objects. The degradation mechanism was studied by Thermal gravimetry/Differential thermal gravimetry (TG/DTG) and Fourier transform infrared—Attenuated Total Reflectance spectroscopy (FTIR-ATR). Combined with amide III band deconvolution and second derivative fitting, we constructed a method for evaluating the degree of degradation by the relative content of random coil (referred to as R) in the secondary structure of the protein. The results show that with the extension of aging time, the macrostructures and microstructures of leather changed to varying degrees. Based on the deterioration characteristics and fitting results, we divided hardened leather into the following four levels. Micro-degradation: R = 0, the leather is dry and hard, but the collagen structure is stable. Mild deterioration: 0 ≤ R ≤ 15%, a variety of collagen structures coexist, and some hydrogen bonds are broken. If 5 ≤ R ≤ 15%, the periodic change of hydrogen bonds may be affected by ultraviolet irradiation; Moderate deterioration: R ≥ 17%, β-sheet disappeared, the leather is seriously deformed and gelatinized due to the disintegration of the protein triple helix structure. Severe deterioration: R = 0, β-sheet disappeared, and the protein has undergone irreversible degeneration. The quantitative analysis method was suitable for the study of the deterioration mechanism and the evaluation of its degree of the Heishanling leather relics, which also provides a new practical scheme for collagen structure to evaluate the degree of leather hardening disease.