# NMR Relaxometry and IR Thermography to Study Ancient Cotton Paper Bookbinding
## 3 Results and Discussion  
### 2d \({}^{1}\)H-NMR-R Measurements and Processing  
Figure 2 shows the T\({}_{1}\)-T\({}_{2}\) correlation maps of some selected sections of the book cover, L\({}_{1}\)-, L\({}_{2}\)-, L\({}_{5}\)- and L\({}_{10}\)-, recorded after conditioning the book at 45% RH (first row) and 100% RH (second row). All the maps exhibit the typical features of pure cellulose paper [23; 24] and paper from a blank page of the inspected ancient book (see Supplementary Materials). Proton signal density forms over one separated cluster in the relaxation times space, more evidenced in the 100% RH maps rather than in those at 45% RH. This feature unambiguously confirms that in the amorphous cellulose domains there are different sites for water molecules in slow chemical exchange regime. The low-T\({}_{2}\) population (average T\({}_{2}\)-value of about 10\({}^{-4}\) s) is due to dynamically high restricted water molecules, fast exchanging with hydroxyl groups of the cellulose chains. The high-T\({}_{2}\) population with T\({}_{2}\approx\) 10\({}^{-3}\) s depicts few and more mobile water molecules, almost exclusively confined in the amorphous cellulose regions [11; 12]. Unlike low-T\({}_{2}\) values, independent from relative humidity degree, the high-T\({}_{2}\) values at 100% RH are well greater than those obtained at 45% RH. This implies that with higher relative humidity percentages, a larger amount of dynamically liquid-like water permeates the available cellulose interspaces. The dynamically different water populations, observable by T\({}_{2}\)'s, are not clear in the detected T\({}_{1}\)'s widespread (over three orders of magnitude). Anyway, in the 100% RH data set (reported in Figures 2 and 3), for the high-T\({}_{2}\)'s water molecule domain, a great spread of T\({}_{1}\)'s distribution to shorter T\({}_{1}\)'s can be observed. According to electron paramagnetic resonance studies on historical paper, such behavior may be due to low-to-moderate content of paramagnetic impurities. The latter may derive from natural or processing causes and are mostly limited in a significant fraction of the amorphous regions. [33]. For a proper description of the longitudinal relaxation data, the effects on the NMR relaxation, either from Fe\({}^{3+}\), Cu\({}^{2+}\), Mn\({}^{2+}\) ions or from other paramagnetic species eventually present in the paper, should, therefore, be considered. In each dataset, the average values of both relaxation times do not change on account of L\({}_{\rm n}\)-section. Then, no kind of noticeable decay process of the ancient cellulosic material is evidenced by changes in relaxation times [7; 19; 34]. In Figures 2 and 3, greyscale bars were set to the absolute maximum intensity of all maps of both series, i.e., L\({}_{5}\)-map collected at 100% RH, to compare the proton amounts in the areas under analysis. In both datasets, in fact, the L\({}_{5}\)-section turned out to be the one with the highest signal densities, showing the greatest presence of water in both its domains. The contours are equally spaced from 10% to 90% of the maximum intensity for each map. The dash-dot line indicates the water bulk reference T\({}_{1}\) = T\({}_{2}\). Figure 2: Two-dimensional nuclear magnetic resonance (2D \({}^{1}\)H-NMR) T\({}_{1}\)–T\({}_{2}\) maps of L\({}_{1}\)-, L\({}_{2}\)-, L\({}_{5}\)- and L\({}_{10}\)-sections collected at 45% (first row) and 100% (second row) relative humidity. The common greyscale bars are set to the highest intensity of both series, i.e., L\({}_{5}\)-map’s intensity acquired at 100% relative humidity (RH). The contours are equally spaced from 10% to 90% of the maximum intensity for each map. The dash-dot line corresponds to T\({}_{1}\) = T\({}_{2}\). As regards the intensities of the T\({}_{1}\)-T\({}_{2}\) correlation maps, the maximum intensities of the twelve maps at 100% RH resulted always higher than those at 45% RH.