Degradation markers of fibroin in silk through infrared spectroscopy

Infrared spectroscopy (FTIR) is a commonly available tool in laboratories dealing with both degradation of materials and conservation of art objects to evaluate their condition. In this paper FTIR was engaged to study degradation of fibroin included in silk samples (Bombyx mori) artificially aged at various conditions (oxygen, water vapor and volatile organic products) at temperature of 150 °C. The results collected by Attenuated Total Reflectance/Fourier Transform Infrared Spectroscopy (ATR/FTIR) were validated by UV/Vis, XRD and SEC analyses. Based on the results, the degradation estimators were verified and classified as: (1) crystallinity defined as ratio of absorbance at 1620 and at 1656 cm−1, A1620/A1656[1], or at 1620 and 1699 cm−1, A1620/A1699[2]; or ratio of areas under fitted curves of band at 1261 and 1230 cm−1, P1261/P1230[3], (2) oxidation - A1620/A1514 and (3) depolymerization - P1318/P1442. Degradation gauges defined in such a way indicate that upon artificial aging water vapor and oxygen has the most profound impact on the progress of silk degradation. It also indicates that oxygen-lean conditions stabilize silk at elevated temperature.