# NMR Relaxometry and IR Thermography to Study Ancient Cotton Paper Bookbinding
## 4 Conclusions  
In this study, we performed two-dimensional nuclear magnetic resonance relaxometry and infrared thermography, both NDT techniques, to put in evidence defects related to degradation of an ancient book cover. The non-destructive and non-invasive approach of NMR surface apparatus makes it suitable for research on library heritage. Moreover, it allows performing measurements of proton relaxation times and moisture content on specific sections of the inspected item. Although it is not easy to mark directly relaxation time constants as unique structure anomalies of the cellulose network, some conclusions on its aging can be drawn by referring the results to the typical ranges of a good quality cellulosic material or comparing the data from areas of the same item with a different conservation status. The NMR relaxation and IRT results can be summarized as follows:  
* The 2D \({}^{1}\)H NMR-R measurements (Figures 2 and 3) performed on the twelve L\({}_{n}\) sections showed the typical T\({}_{1}\)- and T\({}_{2}\)-values of water molecules confined in a good quality cellulose paper. In particular, the two-component T\({}_{2}\)-distribution refers to water molecules trapped among cellulose chains, both as connections set up by one or two molecules (T\({}_{2}\)-low) or as domains of few molecules, acting like free water (T\({}_{2}\)-high). Figure 5: Kurtogram result pointed out by a segmentation procedure. White grid lines indicate the L\({}_{n}\)-sections used for performing NMR measurements. * The influence of increasing the environmental relative humidity from 45% up to 100% on the shape evolution of the T\({}_{2}\)-distribution (Figure 4), confirms that water molecules, besides being adsorbed on cellulose surfaces, can diffuse into the macromolecular network, swell the structure, and form new hydrogen bonds. * Contrary to T\({}_{2}\)'s, the two water domains have a similar T1-value that is quite unrelated to RH. However, for the high-T2's water molecule domain, we could detect a bimodal T1's distribution, especially in the 100% RH dataset (Figure 3), apparently caused by paramagnetic impurities in the water clusters. * For both RH datasets, an evaluation of the moisture content in different areas of the front cover (Table 1) put in evidence the high hydration capacity of L\({}_{1}\) and L\({}_{5}\) sections compared to others. This behavior seems to be a common aspect for both water phases in the amorphous cellulose network. In our opinion, the larger amount of signal in L\({}_{1}\) and L\({}_{5}\) could be the effect of biological/chemical degradation phenomena that led to an increase of the amorphous phase. Though crystalline and amorphous domains are always present in cellulose, the crystalline regions are almost unavailable to moisture. Then, the amorphous structure is the sole responsible for the amount of humidity inside the cellulosic network. * The evaluation of kurtosis value for every pixel in the thermogram matrix provided to get the kurtogram in Figure 5. This displayed a sign of the sub-surface defects and of their thermal diffusivity. * To explain the spatial inhomogeneity of thermal diffusivity, we took into account not only the presence of air but also of water. In the cellulose-water system, it is reasonable to assume that thermal diffusivity gets higher because of a great water amount. In conclusion, NMR moisture content evaluations and the statistical analysis of the IRT data, show a large matching area on the left of the inspected book cover where it is reasonable to assume that the defective areas are both sub-surface and structurally dysfunctional. Looking at the L\({}_{1}\)-and L\({}_{5}\)-sections, the highest moisture contents and thermal diffusivities support the hypothesis of crystalline-amorphous interface modification that increases the accessible sites for water molecules within the cellulose network.