Aspect Ratio of TEMPO-Oxidized Nanocellulose and Rheological Analysis of Aqueous Suspensions

From dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) measurements, the aspect ratio f of two types of TEMPO-oxidized nanocellulose (TOCN) with different fiber lengths was quantitatively calculated. As a result, the aspect ratios f of the normal length N-type and the short fiber length S-type were 243 and 77, respectively. Rheological analysis was carried out in the diluted to semi-dilute concentration regions of two types of TOCN aqueous suspensions. The viscosity of suspensions increased linearly with TOCN concentration in the dilute region, but increased exponentially above the critical concentration C*. Both C* and intrinsic viscosity [η] can be described as a function of f, which is in agreement with those of Tanaka et al. Furthermore, storage modulus G′ in the semi-dilute region showed an elastic gel with a quasi-flat elastic modulus Gp′ independent of frequency. Since Gp′ is proportional to the TOCN concentration raised to the power of 1.9-2.3, we speculate that the development of elasticity is due to the entanglement between nanofibers. However, S-type Gp′ increased sharply with TOCN concentration exceeded 1.5 wt%, deviating from the power law. This seems to suggest that there is a new elastic mechanism other than entanglement.