Impact of the Paper Degradation State and Constituents on Its Behavior During and After X-ray Exposure

Abstract Paper is a complex biopolymer material which contains papermaking additives and often bears inks and other graphic media. Cultural heritage paper-based artefacts are most often deteriorated to some extent. This research explores how intrinsic factors such as constituents and degradation state can impact the modifications incurred in aged papers during and after X-ray examination. To this end laboratory model papers, artificially aged, and 18th and 19th century archival documents, with and without additives (gelatin, calcium carbonate) and iron gallate ink, were exposed to Synchrotron X-ray radiation at doses that were previously shown to incur damage in unaged cotton papers (0.7 to 4 kGy). Glycosidic scissions, hydroxyl free radicals, UV luminescence and yellowing were measured immediately after the irradiation, and were monitored over a period of three years. The depolymerization of cellulose was lower in the aged papers, as well as in the papers containing calcium carbonate and gelatin, than in the unaged fully cellulosic papers. Compared to the papers with no additives, there were more hydroxyl free radicals in the papers with calcium carbonate and slightly less in the gelatin sized papers. UV luminescence and yellowing both appeared post-irradiation, with a delay of several weeks to months, while the intensity of the responses was impacted by the various paper constituents. The papers with iron gallate ink showed limited degradation in the low doses range, most probably due to recombination of the free radicals produced. Doses below 4 kGy did not cause yellowing or UV luminescence of the archival papers within the whole monitoring period. At higher doses (26 to 36 kGy), a slight UV luminescence appeared after 21 months, as well as a slight yellowing after three years, in some of them. No clear correlation between the degradation induced by the irradiation and the constituents in the paper nor its conservation state could be made. The archival papers in good conservation state depolymerized to the same extent as the model papers, while the most degraded archival papers were less impacted than the latter.