Regioselective and Water-Promoted Surface Esterification of Never-Dried Cellulose Fibers Towards Nanofibers with Adjustable Surface Energy

A new regioselective route is introduced for surface modification of biological colloids in the presence of water. Taking the case of cellulose nanofibers (CNFs), we demonstrate a site-specific (93% selective) reaction between the primary surface hydroxyl groups (C6-OH) of cellulose and acyl imidazoles. CNFs bearing C6-acetyl and C6-iso-butyl groups, with a degree of substitution up to 1 mmol·g^–1 were yielded upon surface esterification, affording nanofibers of adjustable surface energy. The morphological and structural features of the nanofibers remained largely unaffected, but the regioselective surface reactions enabled tailoring of interfacial interactions, as demonstrated in oil/water Pickering emulsions. Our method precludes the need for drying or solvent exchange to organic solvents for surface esterifications, which are otherwise demanded in the fabrication of esterified colloids and polysaccharides and can be potentially implemented into reactive extrusion and compounding of high-solid content colloids. The proposed acylation is expected to open new and sustainable approaches that benefit from the presence of water and the high selectivity.