Over the past decade, cellulose nanofibrils, produced through a top-down approach using cellulose fibers, have made remarkable advancements in materials science. However, a significant hurdle in this research area has been developing a mild and efficient method for creating nanocelluloses with precise and selective modifications [1].
Here, we introduce a methodology to extract elementary C6-OH-succinylated cellulose nanofibrils (C6SA-CNFs) by treatment of dissolving pulp with N-succinylimidazole, which can be reverted using a mild post-treatment [2]. No polymer degradation, cross-linking, or changes in crystallinity occurred under the mild processing conditions, yielding negatively charged C6SA-CNFs decorated with carboxylate moieties. C6SA-CNFs are strongly shear-thinning and can be post-modified at the free C2,C3-OHs position to yield multifunctional C6SA-CNFs for various applications. They can be, e.g., used as inks in direct ink writing, enabling the preparation of hydrogels with functional and mechanical gradients. Alternatively, the native C6SA-CNFs can be processed into nanopaper and/or treated in alkali to remove the succinate groups. The latter offers the opportunity to reconstitute the chemical and structural interfaces associated with the natural states of cellulose microfibrils, which, for instance, do not exist anymore in the case of irreversibly modified TEMPO-oxidized materials.
In conclusion, regioselective succinylation offers new possibilities for post-modification, resulting in multifunctional C6SA-CNFs. Furthermore, the reversibility of these modifications enables the enhancement of interfibrillar interactions and the augmentation of mechanical properties.

Reversible and Spatioselective surface esterification.

Antje Potthast

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