Assembling Native Elementary Cellulose Nanofibrils via a Dynamic and Spatially Confined Functionalization

Selective surface modification of bio-sourced colloids affords effective fractionation and functionalization of polysaccharide-based nanomaterials, as shown by the classic TEMPO-mediated oxidation. However, such route leads to changes of the native surface chemistry, affecting interparticle interactions and limiting the full exploitation of the supermaterial properties associated with such nanomaterial assemblies. Here we introduce a methodology to extract elementary cellulose fibrils by treatment of biomass with N-succinylimidazole, achieving spatially confined (92% regioselectivity towards primary C6-OH) and dynamic surface functionalization, as elucidated by nuclear magnetic resonance, infrared spectroscopy, and gel permeation chromatography. No polymer degradation or crosslinking nor changes in crystallinity occur under the mild conditions of the process yielding elementary fibrils. The structure of the fibrils was validated by cross-corelating solid-state NMR, chromatographic analysis, and atomic force microscopy imaging. We demonstrate the fully reversible nature of the dynamic modification, which offers a significant opportunity for the reconstitution of the interfaces back to the native states, chemically and structurally. Consequently, access to 3D structuring of native elementary cellulose I fibrils is made possible, reproducing the supramolecular features of the native cellulosic supermaterials. Overall, we propose the reversible and regioselective surface succinylation as a suitable route to overcome current limitations in the production of cellulose nanomaterials, which is required to unlock the full potential of cellulose as a sustainable building block.