Micro-mechanics of electrostatically stabilized suspensions of cellulose nanofibrils under steady state shear flow

Abstract

In this study, we characterized and modeled the rheology of TEMPO-oxidized cellulose nanofibril (NFC) aqueous suspensions with electrostatically stabilized and unflocculated nanofibrous structures. These colloidal suspensions of slender and wavy nanofibers exhibited a yield stress and a shear thinning behavior at low and high shear rates, respectively. Both the shear yield stress and the consistency of these suspensions were power-law functions of the NFC volume fraction. We developed an original multiscale model for the prediction of the rheology of these suspensions. At the nanoscale, the suspensions were described as concentrated systems where NFCs interacted with the Newtonian suspending fluid through Brownian motion and long range fluid-NFC hydrodynamic interactions, as well as with each other through short range hydrodynamic and repulsive colloidal interaction forces. These forces were estimated using both the experimental results and 3D networks of NFCs that were numerically generated to mimic the nanostructures of NFC suspensions under shear flow. They were in good agreement with theoretical and measured forces for model colloidal systems. The model showed the primary role played by short range hydrodynamic and colloidal interactions on the rheology of NFC suspensions. At low shear rates, the origin of the yield stress of NFC suspensions was attributed to the combined contribution of repulsive colloidal interactions and the topology of the entangled NFC networks in the suspensions. At high shear rates, both concurrent colloidal and short (in some cases long) range hydrodynamic interactions could be at the origin of the shear thinning behavior of NFC suspensions.

Ice-Templated Porous Nanocellulose-Based Materials: Current Progress and Opportunities for Materials Engineering

“…The solid-like properties of nanocellulose suspensions can also be observed from steady-state flow curves (e.g., Figure 4b). As shown in Figure 4b, CNF suspensions exhibit a macroscale yield stress at low strain-rates [100,[104][105][106]. This regime is then followed by a shear-thinning behaviour, where the suspension viscosity decreases with increasing the strain-rates [107].…”

“…To be printable in a 3D printer, the fluid needs to flow in the printer and have the ability to become like a "solid" on a substrate after being dispensed (Figure 8b) [130]. As mentioned in Section 3.1, nanocellulose suspensions are yield stress fluids that are characterised by a pronounced shear thinning behaviour at high strain-rates [100,107]. Hence, these suspensions are particularly suitable for this type of processing route.…”

“…Using gas absorption experiments, Munier et al [120] also observed that the density of the foam cell walls increased with increasing CNF concentration. The decrease in the foam pore size could be related to the increase with the CNF concentration in the rheological properties of the suspensions, namely the yield stress τ 0 [100]. Higher yield stress would restrain ice crystal growth, so that nucleation sites would be induced, resulting in the formation of numerous small pores.…”

“…The rheological properties of the suspensions, namely the dynamic modulus G', the yield stress τ 0 and the viscosity µ of the suspensions are power-law functions of the nanofibre concentration [104,105,108]. These macroscale rheological properties, which are of great importance in materials forming, are closely related to the current microstructure of the fibrous reinforcement and its evolution during flow, and to a combination of nanoscale fluid-particles and particles-particles interaction forces [35,100,109]. More information related to the rheology of nanocellulose suspensions can be found in recent review articles [97,98].…”

Steady-shear and viscoelastic properties of cellulose nanofibril–nanoclay dispersions

“…Previous work has shown that aqueous dispersions of slender and kinked CNFs display non-Newtonian rheological behavior characterized by shear thinning and pronounced viscoelastic behavior at concentrations above the gelation threshold (de Kort et al 2016;Jowkarderis and van de Ven 2015;Martoia et al 2016). Recent studies have investigated the effects of pulp source (Tanaka et al 2016), fibril dimension and concentration (Agoda-Tandjawa et al 2010), mechanical treatments (Pääkkö et al 2007), ionic strength (Dong et al 2013), pH (Fall et al 2013), as well as addition of amphiphilic molecules (Quennouz et al 2016) on the rheology of CNF dispersions.…”