Electron Paramagnetic Resonance and 1H and 13C NMR study of paper

High quality antique sheets of paper have been characterized by H-1 NMR relaxation, C-13 CP MAS spectra, and Electron Paramagnetic Resonance spectroscopy. Paper can be regarded as a bi-component material made by cellulose and water plus a small amount of organic and inorganic additives and impurities. Semi-crystalline fibrous cellulose, rich in water, is present as polymorphs I alpha and I beta. Amorphous cellulose, with a lower water content, presents a higher amount of paramagnetic impurities and is characterized by quite short H-1 spin-lattice relaxation times and by C-13 resonances with noticeable chemical shifts. ''Ad hoc'' tailored sequences are able to produce C-13 CP MAS spectra in which the amorphous content of cellulose in paper is quite well observable. The nature of water as fully bound to the cellulose lattice has also been proved. Low-temperature EPR spectra have shown the presence of measurable amounts of different inorganic paramagnetic impurities, such as Fe3+, Mn2+, Cu2+ often found in different stereochemical environments. The spectra are all, qualitatively, closely similar. However, quantitative data have shown that in paper the state of conservation does not depend on the amount of pseudo-octahedral iron, but is strongly correlated to the concentration of this metal ion in a rhombic stereochemistry and to the presence of even very small amounts of copper.