The most important degradation mechanism of cellulose is the acid-catalyzed hydrolysis of glycosidic bonds, which results in the decrease of cellulose degree of polymerization (DP) and, macroscopically, in the loss of the original mechanical properties. Therefore, in the case of acidic and strongly mechanically-degraded cellulosic works of art, both a deacidification and a strengthening treatment are required, so to grant the preservation of these materials that constitute a large part of the global patrimony of mankind. Alkaline nanoparticles are known to be effective in neutralizing acidity, while cellulose nanocrystals have the potential to be used as compatible and effective strengthening agents. To this aim, we have grafted cellulose nanocrystals with oleic acid using a 1’1-carbonyldiimidazole mediated procedure, to increase their dispersibility in organic solvents. Grafted CNSs were characterized using Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Thermogravimetric Analysis (TGA) and Atomic Force Microscopy (AFM), showing that cellulose nanocrystals were effectively grafted and stably dispersed in ethanol. Grafted nanocellulose and alkaline nanoparticles, obtained via a solvothermal process, were used to prepare ethanol-based <i>hybrids</i>. Prior to the application, the physico-chemical properties of nanocellulose dispersions and <i>hybrids</i> were studied by rheology and Small-Angle X-ray Scattering (SAXS). Changes in the mechanical behavior of systems have been related to the changes in the composition: interactions between cellulose nanocrystals are the driving force behind the gelation of the systems that can be either due to the surface grafting, to the use of a less polar solvent or to the introduction of cations from alkaline nanoparticles in the system. The formation of cluster of nanocellulose crystals of increased size depending on the composition of the system was shown by SAXS, confirming the results obtained from the rheological characterization. These dispersions are thixotropic, a behavior particularly appealing to conservation purposes, since they can be applied in the liquid state, or, when a more confined application is required, they can be applied in a gel-like state. As a result of the application, an improvement in the mechanical properties of paper and an increase of pH were obtained.

Grafted nanocellulose for the conservation of works of art: Synthesis, characterization and interactions with alkaline nanoparticles

ACS Spring Meeting 2021

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