Ageing, yielding, and rheology of nanocrystalline cellulose suspensions

This paper investigates yielding and flow of nanocrystalline cellulose (NCC) suspensions by combining rheological measurements with light scattering echo (LS-echo). The NCC samples are characterized using static and dynamic light scattering as well as polarized optical microscopy coupled with a rotational rheometer. The storage modulus of the NCC suspensions is found to increase with waiting time after shear rejuvenation. The microscopic particle rearrangements of the NCC spindles are followed by LS-echo at both short and long waiting times under oscillatory shear flow. We find that the onset of shear-induced irreversible microscopic particle rearrangements, coincide with the strain at which storage and loss moduli cross over in the nonlinear viscoelastic regime identified by the macroscopic yield point of the sample. The yielding transition is found to occur at a higher strain as the frequency of oscillation increases. (C) 2013 The Society of Rheology. [http://dx.doi.org/10.1122/1.4764080]