The morphology and flowing behaviors of TEMPO-oxidized cellulose nanofibers dispersed in non-aqueous solutions

Cellulose nanofibers (CNF), sustainable and possessing good mechanical properties, is a good reinforcement agent for polymer composites. However, pure CNF is hard to disperse in common organic solvents due to the strong inter-fibrillar H-bondings and van der Waals interactions. In this study, we investigated the dispersion behavior of CNFs having different charged density, prepared by the TEMPO-oxidation and nitro-oxidation methods, in two different non-aqueous solvents: ethylene glycol and propylene glycol. The morphologies of CNF was first characterized by combined AFM, TEM and solution SAXS methods, whereby the results showed that the fiber cross-section dimensions were closely related to the oxidation conditions that also led to different charge density. The rheological results indicated that the overlap concentration of the suspension is solvent independent. Moreover, the CNF/glycol suspensions behave very similarly to polymer solutions, exhibiting shear thinning behavior beyond the overlap concentration. We postulate that the solvent exchanging method could also be used to disperse CNF into other non-aqueous solvent for better mixing with hydrophobic polymers.