Reconditioning acidic and artificially aged cellulose with alkaline nanoparticles: an NMR diffusometry study

The prominent degradation mechanism of cellulose is the acid-catalyzed hydrolysis of glycosidic bonds, which results in the decrease of the degree of polymerization (DP) and, macroscopically, in the dramatic decay of the mechanical resistance of cellulose-based materials. Alkaline nanoparticles in organic solvents have been recently proposed for the deacidification of cellulose-based artworks. Their effectiveness has been demonstrated in previous studies, by pH and DP measurements, colorimetric and thermal analyses. Herein, the changes in the cellulosic network following an acidification bath and a consequent deacidification treatment using Ca(OH)2 nanoparticles, have been investigated by NMR self-diffusion dynamics of water and related to the changes of samples’ DPs. The deacidification treatment modifies intra- and inter-chain interactions, leading to a buffered cellulose network configuration similar to that characterizing the untreated reference sample in terms of diffusive parameters and confining environment. Such results are plausibly due to a rearrangement in connectivity of the cellulosic network, even though with a different physical fingerprint with respect to the reference sample. The analysis of tortuosity of the cellulosic network in acidic and deacidified samples confirms this conclusion, further corroborating the idea that calcium hydroxide nanoparticles are an effective tool to hamper the degradation of cellulose induced by acids and aging in strong environmental conditions, even from the standpoint of cellulose network arrangement.