Fourier transform infrared spectroscopy to detect thermal degradation of vegetable and chrome-tanned leather

Abstract

The present experimental study determined the thermal degradation stages for vegetable and chrome-tanned leathers (goat and sheep) at 90, 100, and 130?°C by using Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis. Infrared spectra revealed that a temperature of 90?°C affected the adsorbed water band at 3400?cm^?1. Moreover, this temperature slightly reduced the vibrations of amide II and amid III (1340?cm^?1) confirming the preliminary decomposition of protein folds, but it is worth noting that the aliphatic side chains remained stable at this stage of aging. At 100?°C, there was a sharp rupturing in the phenolic-OH bond and side-by-side N–H vibrations decreased dramatically. The peak decomposition occurred at 130?°C, where the amide I and amide III intensities significantly increased, which can be considered indicative of protein unfolding. Those changes are substantiation of protein denaturation. Thermal analysis demonstrated that thermal aging significantly reduced the required temperature for the process of oxidation. The oxidation occurred at 217?°C in goat sample aged at 90?°C. Nevertheless, the reference sample suffered from oxidation at about 220?°C, while with increasing aging temperatures (at 100 and 130?°C), endothermic reactions were observed. Such reactions are usually associated with protein denaturation.