Quantitative diagnostics of ancient paper using THz time-domain spectroscopy

In this work we have studied the terahertz spectra of modern artificially aged and ancient paper samples using terahertz time-domain spectroscopy. Hydrothermal artificial aging was performed in closed and open reactors. Ancient paper samples were produced during the 15th century in European countries. The main aim of the work is the quantitative assessment of spectral feature observed by terahertz spectroscopy as a function of degradation. To this goal, the state of degradation of paper samples was characterized by crystallinity measurements obtained by using X-ray diffraction and by the degree of polymerization of cellulose polymers obtained by size exclusion chromatography. The behavior of the terahertz spectra was formerly investigated as a function of the hydration of paper samples. This allowed discriminating between the spectral features induced by the presence of water and those induced by degradation of paper. Results indicate clear dependences of spectral parameters from the evolution of crystallinity and the degree of polymerization. They can be used as a nondestructive analytical method to assess the state of degradation of ancient paper by terahertz spectroscopy.