Short- and Long-Term Effects of X-ray Synchrotron Radiation on Cotton Paper

Abstract

X-ray analytical techniques are increasingly being used to study manuscripts and works of art on paper, whether with laboratory equipment or synchrotron sources. However, it is difficult to anticipate the impact of X-ray photons on paper- and cellulose-based artifacts, particularly due to the large variety of their constituents and degradation levels, and the subsequent material multiscale heterogeneity. In this context, this work aims at developing an analytical approach to study the modifications in paper upon synchrotron radiation (SR) X-ray radiation using analytical techniques, which are fully complementary and highly sensitive, yet not frequently used together. At the molecular scale, cellulose chain scissions and hydroxyl free radicals were measured using chromatographic separation techniques (size-exclusion chromatography–multiangle laser light scattering–differential refractive index (SEC–MALS–DRI) and reversed-phase high-performance liquid chromatography–fluorescence detector–diode array detector (RP-HPLC–FLD–DAD)), while the optical properties of paper were characterized using spectroscopy (UV luminescence and diffuse reflectance). These techniques showed different sensitivities toward the detection of changes. The modifications in the cellulosic material were monitored in real time, within a few days, and up to 2 years following the irradiation to define a lowest observed adverse effect dose (LOAED). As paper is a hygroscopic material, the impact of the humidity in the environment was studied using this approach. Three levels of moisture content in the paper, achieved by conditioning the samples and irradiating them at different relative humidities (RHs), were studied (0, 50, 80% RH). It was shown that very low moisture content accelerated molecular and optical modifications.

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

“…S6 in the Supplementary data file), indicating that no macromolecular degradation took place during the irradiation, whether the dose was delivered at once or in several stages. This is consistent with the lowest observable adverse effect dose (LOAED) for glycosidic scissions of 0.21 kGy defined in our previous work (Gimat et al 2020).…”

“…S7 in the Supplementary data file). The model samples W and R exhibited a luminescence maximum λmax at 432 nm, which is consistent with previous data (Gimat et al 2020). The intensity varied depending on the degradation state, luminophores being produced during the aging, and on the type of additive.…”

“…Carbonyl groups in the artificially aged Whatman n1 papers increased the glycosidic scissions in the low doses range, below 0.5 kGy. Confirming previous results (Gimat et al 2020), the optical changes appeared with considerable delay, often one year after the irradiation, and could not be directly correlated to the initial DP nor to the glycosidic scissions concentration that grew steadily during this postirradiation period (dark storage, room temperature). As expected, the archival papers made of linen rags had an overall more complex X-ray exposure behavior than the model papers.…”

“…Yet because they are ionizing, Xrays induce changes in organic (as well as inorganic) materials. Cellulose depolymerization, oxidation and changes in the optical properties have been observed under gamma-ray (Ershov 1998;Bouchard et al 2006;Henniges et al 2013;Bicchieri et al 2016) and X-ray exposures (Mantler and Klikovits 2004;Kozachuk et al 2016;Gimat et al 2020). In quasi-pure cellulose paper, the impact of X-rays has been shown to be proportional to the dose (Gimat et al 2020).…”

“…The papers, some of which had been previously artificially aged, were irradiated at doses in the range 0.7-4 kGy. The samples were characterized immediately after the exposure using a multiscale analytical procedure developed in a previous study (Gimat et al 2020), which encompasses the macroscopic (yellowing and UV luminescence) and the microscopic scales (glycosidic scissions and formation of hydroxyl radicals). The changes were monitored over a period of three years.…”