Paper Title
VISCOELASTICITY AND ELECTRIC PROPERTY OF CELLULOSE NANOFIBER AQUEOUS SOLUTIONS UNDER SHEAR FLOW

Abstract
Cellulose nanofiber (CNF) is a fiber extracted from wood and it is defibrated to the nano levelby mechanically or chemically defibration. The CNF demonstrates various advantages such as high mechanical strength, high elasticity, low thermal expansion etc., and it has been widely used recently as functional materials. 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidized cellulose nanofiber (TOCN)is obtained by the TEMPO mediated oxidation. The TOCN is a polyelectrolyte which has carboxyl groups on the main chain and their counterions dissociated. Thus, TOCN has an interesting ionic structure in water which is a long nanofiber with negative charges is covered with counterions with positive charges. In this study, we investigated the effect of the alignment of long nanofibers by steady shear flow on the ion transportation in water. Sodium salt of TOCN (TOCN-Na; RHEOCRYSTA® C-2SP, DKS) was used for viscoelastic and electric measurements. The length and the diameter of TOCN-Na were 827 nm and 3.4 nm, respectively. The shear viscosity was measured at shear rates from 0.01 to 100 s-1 by using a rheometer (MCR301, Anton Paar) at 25.0 ºC. In-situ measurement of the electric conductivity was carried out by an ac two-terminals method using an LCR meter with a dielectrical measuring cell (P-PTD200, Anton Paar). The frequency was kept at 100 Hz and the applied voltage was 0.1 V. The viscosity at a shear rate of 0.01 s-1 was approximately 2×104 Pa•s and it decreased depending on the shear rate, indicating that the nanofibers align in the flow direction. The electric conductivity at a shear rate of 0.01 s-1 was approximately 3.4×10-5 S/cm and it decreased depending on the shear rate. This strongly indicates that the electric conduction of free counterions is disrupted by the orientation of TOCN-Na fibers.