The vane method and kinetic modeling: shear rheology of nanofibrillated cellulose suspensions

From colloidal spheres to nanofibrils: Extensional flow properties of mineral pigment and mixtures with micro and nanofibrils under progressive double layer suppression

“…As reported earlier, two types of MNFC materials are used, [18,19,31,34,25,55] with MFC being produced by grinding birch kraft pulp with an ultra-fine friction grinder (Masuko Supermasscolloider, MKZA 10-15 J) and NFC produced in a pilot process by oxidising the birch kraft pulp using TEMPO catalyst to induce fibrillation 20. Detailed specifications of MNFC materials have been presented earlier [18,19,31,34,24,25].…”

“…geometry is prone to wall-slip and shear inhomogeneities, in particular for complex shear thinning fluids, such as coating colours and MNFC-containing suspensions [15,31,32,63]. The following measurement procedures were designed to mitigate as far as possible such effects when using this geometry.…”

“…The gap for coating colour measurements was set to 1 mm to account for the presence of larger fibrous material. In order to avoid any memory effect in the sample, derived from previous deformations, all samples were pre-sheared at an angular frequency of 10 rad s À1 and strain deformation of 0.1% for 10 min, followed by a rest stationary state time of 10 min [31,32]. To prevent evaporation of water, plate edges were sealed with silicone oil [64][65][66][67].…”

“…The apparent effective yield stress depends on the determination method and the flow geometry [59][60][61][62][63], as well as potential wall slip in gel-like materials, which is a major factor adding to the difficulties of its estimation for gel-like MFC/NFC suspensions [31,32,58,60]. Beyond the dynamic yield stress (s d 0 ) the rheological property of the suspension is considered to be in the fully flowing condition.…”

“…MNFC suspensions are usually found to form a gel network at rest with the rheological response of the suspension being predominantly elastic (G 0 ) G 00 ) and largely independent of the angular frequency of oscillation (x) [15,28,29]. Under steady state conditions MNFC suspensions are both shear thinning and thixotropic [30][31][32] due to the prevailing fibril-fibril packing organisation and subsequent break-down of the gel network upon shearing. The flow curves of MNFC suspensions at low shear rates exhibit constant shear stress, but after reaching a certain threshold, the shear stress rises as a function of shear rate, due to spatial organisation of flowing agglomerates at higher shear [15,28,29,33].…”