(522h) Depletion and Electrostatic Forces in Shear Rheology of Cellulose Nanofiber Suspensions

Suspensions of cellulose nanofibers (CNF) in water exhibit thixotropy. CNFs also undergo shear-induced flocculation at even very low solids ~0.1 wt.%. In this work, we use a rheo-microscope to observe the floc formation as a function of shear rate for different CNF suspensions. We further studied the effect of different depletants, namely carboxy methyl cellulose (CMC) and polyethylene oxide (PEO), as well as ionic strength on the shear-induced flocculation of CNF. The depletion forces from CMC and PEO were quantified using Asakura−Oosawa potential for different depletant molecular weights and concentrations. Moreover, the electrostatic forces between CNF particles were quantified using the Debye length in the DLVO theory as a function of ionic strength. Also, using the CNF surface potential (estimated via Zeta potential measurements) in the DLVO theory, the effect of pH on electrostatic repulsions, and thereafter shear-induced flocculation of CNF, was examined.