The study of rheological properties and microstructure of carboxylated nanocellulose as influenced by level of carboxylation

Abstract

In this work, carboxylated nanocellulose had been prepared by using TEMPO-periodate oxidized reaction, in which the level of carboxylation was controlled by adjusting sodium hypochlorite (NaClO) concentration. The effects of the level of carboxylation on the rheological behavior and microstructure for the carboxylated nanocellulose dispersion had been investigated. It indicated that the nanocellulose dispersion exhibited sol state with low storage (G′) and loss (G″) modulus when NaClO concentration controlled to 2 mmol/g. But nanocellulose dispersion presented a form of gel at high NaClO concentration (6–12 mmol/g) and a critical state (similar values of G′ and G″) was obtained with the NaClO concentration of 4 mmol/g. In addition, both the G′ and G″ of nanocellulose dispersion were increased and then decreased with the increase of NaClO concentration. The highest modulus obtained when NaClO concentration controlled to 8 mmol/g, and a high fractal dimension (Df) was also obtained at this concentration, indicating a compact network structure. The large amplitude oscillation shear (LAOS) suggested that nanocellulose dispersion exhibited Ⅰ behavior (strain thinning) but had a trend of III behavior (weak strain overshoot). The Fourier transform rheology, Chebyshev coefficient, and Lissajous curves were used to analyze the nonlinear behavior, implying a correlation between the nonlinear behavior and the network structure of the nanocellulose dispersion. This work would provide some guidance for regulating the properties of nanocellulose dispersion.