Rheological properties of micro-/nanofibrillated cellulose suspensions: wall-slip and shear banding phenomena

The rheological properties of enzymatically hydrolyzed and TEMPO-oxidized microfibrillated/nanofibrillated cellulose (MFC/NFC) aqueous suspensions were investigated in oscillation and steady-flow modes and were compared with the morphology of the studied materials. The flow instabilities, which introduce an error in the rheological measurements, were discovered during flow measurements. A wall-slip (interfacial slippage on the edge of geometry tools and suspension) was detected at low shear rates for two types of NFC suspensions while applying cone-plate geometry. A roughening of the tool surfaces was performed to overcome the aforementioned problem. Applying to TEMPO-oxidized NFC, a stronger suspension response was detected at low shear rates with higher values of measured shear stress. However, a shear banding (localization of shear within a sample volume) became more pronounced. The use of serrated tools for enzymatically hydrolyzed NFC produced lower shear stress at the moderate shear rates, which was influenced by water release from the suspension.