A DSC study of deterioration caused by environmental chemical pollutants to parchment, a collagen-based material

A DSC study of new parchments exposed at 25 °C for 1–16 weeks to controlled atmospheres containing 50 ppm of gaseous chemical pollutants (NO2, SO2, NO2 + SO2) and 50% relative humidity (RH) was performed. Samples were exposed to chemical pollutants alone, as well as after previous heating at 100 °C for 2–16 days and/or irradiating with visible light (1.7 × 105 lx) for 4–16 h. DSC measurements were performed in both sealed crucibles in static air atmosphere at 25–200 °C and open crucibles under gas flow (nitrogen, oxygen, synthetic air) at 25–280 °C. Analysis of DSC curves provided the variation induced by ageing on the thermodynamic parameters associated with both parchment denaturation and softening of collagen crystalline fraction. All the ageing procedures decreased both temperature and enthalpy of denaturation and increased broadness of DSC peak in function of ageing time. The occurrence of thermal oxidation peaks and/or lower temperature endothermic peaks was observed. The temperature of the first softening peak always indicated a general tendency to decrease as a function of ageing time. Shrinkage temperature of collagen fibres measured by thermomicroscopy also decreased as a result of accelerated ageing treatments.