Production of highly substituted cationic cellulose nanofibrils through disk milling/high-pressure homogenization

The cationic cellulose nanofibrils demonstrate outstanding properties and have garnered extensive attention as sustainable materials. However, the large-scale preparation of cationic cellulose nanofibrils was limited since the high crystallinity of plant fibers made them harder to disintegrate and nanofibrillate. In this study, cationic cellulose nanofibrils, HKCF, were produced from softwood bleached kraft pulp (SWBK) with 2,3-epoxypropyltrimethylammonium chloride (EPTAC) by disk milling, followed by high-pressure homogenization. Morphologies and structures of cationic fibers (KCF and CCF) and homogenized products were characterized. The influence of cationization combined with high mechanical shear on the degree of substitution (DS) of cationic fibers was studied. At the same molar ratios of EPTAC to anhydroglucose units and holding time, the DS of KCF was higher than that of CCF. Compared with simple mixing induced by conventional stirring, the high mechanical shear induced by disk milling could increase the cationic efficiency of EPTAC by at least 50%. After high-pressure homogenization, KCF was completely fibrillated to HKCF with nano-scaled dimensions. HKCF dispersion showed a Bingham flow behavior and viscosity-dominating fluid-like behavior. Our study provides a facile and effective industrialized approach for producing highly substituted cationic cellulose nanofibrils.