Abstract
Paper has been widely used as convenient vehicle for the acquisition, storage and dissemination of human knowledge. For centuries, a growing number of cellulose-based manuscript and printed book have been accumulating in archives, libraries and museums. The progressive transformation leading to an increased fragility and yellowing -commonly observed in the ancient paper-based artefacts- have been connected to the fragmentation of cellulose polymers (depolymerisation) and their oxidation [1,2]. The establishment and improvements of models of preservation for often-irreplaceable items is in many ways connected to the development of techniques (possibly in-situ and standoff, in light of the practical constraints in moving and handling some of those items), to assess in non-destructive ways the state of degradation of cellulose compounds [3]. Our investigation demonstrates that microscopy techniques based on Terahertz-Time Domain Spectroscopy (TDS) [4] are competitive with state-of-the-art solutions and have the potential to outperform them. Resonances in the THz region are dominated by collective atomic vibrational modes (Fig. 1). These modes are directly correlated to cellulose crystallinity and can give information on the state of the depolymerisation of cellulose polymers. In addition TDS provides access to the average optical density spectrum, information in general not available in other frequency ranges. The investigation approach undertaken here highlights specific spectral markers of degradation with remarkably high contrast for practical sample thicknesses.
© 2015 IEEE
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