Redispersion Strategies for Dried Cellulose Nanofibrils

The potential for large-scale applications of cellulose nanofibrils (CNFs) is limited by the high water content of the starting material, which leads to high transportation costs and undesirable environmental impact. However, drying of CNFs results in loss of their nanoscopic dimensions leading to deterioration of their unique inherent mechanical properties. Herein, thorough redispersion studies of both fundamental and applied nature have been conducted in order to evaluate the effect of charge, redispersing agent, and drying method. Freeze-dried CNF dispersions were successfully redispersed by either increasing the charge density or adding redispersing agents. The greatest effect on redispersibility was achieved with fractionated LignoBoost lignin as redispersing agent, and this is attributed to steric repulsion during water removal and reduced CNF adhesion. Furthermore, the results unexpectedly show that redispersion is easier when the CNFs are dried in the form of nanopapers. By using this approach, excellent redispersibility was achieved even without a redispersing agent. Nanopapers formed from the redispersed CNFs was found to have essentially the same mechanical properties as those made from never-dried CNFs. Hence, this work suggests solutions for making CNFs viable for large-scale application while maintaining their nanoscale dimensions and their ability to create nanopapers with excellent mechanical properties.