When defects dominate: Rheology of nanofibrillated cellulose suspensions

Conventional rheological tests can be difficult to carry out in the case of suspensions of nanofibrillated cellulose (NFC). Such suspensions tend to migrate away from the walls of a rheometer device, leaving a low-viscosity layer. The very high aspect ratio of typical nanofibrillated cellulose particles favors formation of tangled clusters. But application of hydrodynamic shear can cause fragmentation of those clusters. It is proposed in this essay that some focus be placed on the fragments of entangled clusters of NFC and interactions between them at their fractured surfaces. The condition of near-uniform, defect-free structures of nanocellulose spanning the volume within a sheared suspension might be regarded as an unlikely circumstance. Isaac Newton started with a very simple equation to start to understand rheology. It is proposed that a similarly bold and simplified approach may be needed to account for the effects of broken entangled clusters of NFC on flow phenomena, their assessment, and their consequences related to industrial processes.