Testing portable NMR to monitor the effect of paper exposure to UV-light

Paper-based works of art can be considered the most important carrier of information about culture, science, business, politic and history. Therefore, it is highly important to preserve the integrity of the paper these objects are made of. Paper is an organic material mainly made of cellulose fibers, whose durability depends on pH, heat, humidity, oxygen, pollution, metal ions, lignin, and UV-visible light. Cellulose absorbs more in the near UV region, therefore radiation with wavelength of 300–550 nm produces most of the paper damage. The aim of this work was to test the potential of single-sided portable NMR to highlight the effect of UV light on paper. To this end, the longitudinal relaxation time (T1) and the transversal relaxation time (T2) of structural-known filter paper before and after the exposure to UV light were measured and supported by Raman spectroscopy. The decrease of both T1 and T2 parameters with the increase of the UV exposure time indicates a modification of the cellulose chains, which was confirmed by Raman spectra. Moreover, this study presents a preliminary non-invasive protocol for assessing the effect of artificial UV irradiation on paper by using a portable NMR sensor.