Shear rheology of micro-fibrillar cellulose aqueous suspensions

Abstract

Micro-fibrillar cellulose aqueous suspensions with different fiber lengths were prepared by mechanical refining of softwood pulp fiber suspensions at different specific refining energies. Effects of refining energy level, micro-fiber concentration and temperature on the rheological properties of these aqueous suspensions were studied. These microfibers form a three-dimensional network, which displays typical shear-thinning behavior with little thixotropic tendency, at concentrations as low as 0.5 wt%. A viscoelastic analysis showed that these micro-fibrillar cellulose suspensions at different concentrations (from 0.5 to 2 wt%) exhibit a viscoelastic gel-like behavior [G′ > G″ over an extended range of frequencies (ω) and a weak dependency of G′ on ω] at 25 °C. The storage modulus, G′, at 1 rad/s increased strongly upon increasing concentration from 0.5 to 2 wt% following a power law with an exponent of 3.2. However, increasing the temperature decreases the storage modulus, G′, due to weakening or disruption of intermolecular interactions at elevated temperatures. The viscoelastic behavior changes to liquid-like, with G″ > G′ at the investigated frequency range, for the suspensions at 85 °C.