Studies on the effects of mixed light-thermal ageing on parchment by vibrational spectroscopy and micro hot table method

Abstract

The damaging effects of mixed light-thermal ageing on parchment were studied by exposing mock-ups to artificial light (162 W/m2 irradiance) at controlled temperature and relative humidity (52 °C, 30% RH) for up to 748 h, with testing being made during this time incrementally. The physical–chemical changes (deterioration) resulting from these conditions were analysed by applying FTIR-ATR and Raman spectroscopy, colorimetric measurements and MHT. The deterioration found includes the formation of collagen-destabilised intermediate states which then progressively convert to disorganised structures, e.g. pregelatinised collagen and gelatin. The process is characterized by molecular changes of collagen associated with its photo-oxidation. These are shown by changes in the position and intensity of the main FTIR absorption bands of collagen, namely those of Amide I, Amide II, and Amide III, as well as by the occurrence and the increase of a shoulder at 1740 cm−1. The shrinking activity of the collagen fibres in the parchment mock-ups was measured by the micro-hot-table (MHT) method, which revealed the presence of multiple collagen populations with distinct thermal stabilities and confirmed the deterioration pattern suggested by the molecular changes.