Deconstruction of microfibrillated cellulose into nanocrystalline cellulose rods and mesogenic phase formation in concentrated low-modulus sodium silicate solutions

This work demonstrates for the first time the deconstruction of microfibrillated cellulose (MFC) into rod-like cellulose nanocrystals (CNCs) in concentrated low modulus sodium silicate solutions. To this aim, MFC suspensions at different concentrations were first treated in sodium hydroxide solutions and then amorphous silica powder was added. Optical microscopy and transmission electron microscopy observation showed how MFC was efficiently deconstructed into CNCs, evidencing the occurrence of a phase separation into an isotropic and mesogenic phase. The extracted CNCs were characterized by a remarkably higher length (600–1200 nm) in comparison with the plant-derived ones commonly reported in literature. FT-IR spectroscopy and ²⁹Si MAS NMR confirmed that the Qⁿ equilibrium of the suspended silicate species was affected, proportionally to the amount of MFC. It was also shown, that due to the excluded volume effect exerted by silicate anions, nematic or smectic ordering could be achieved for CNC concentrations far below the critical rod concentration predicted by the Doi-Edwards model.