Structural viscoelasticity of a water-soluble polysaccharide extract.

Two structural changing processes are incorporated into a traditional viscoelastic model to characterize and predict the shear thickening rheological behaviors of a polysaccharide mucilage of black tree fern. The shear-dependent structure effect could cause varying linear viscoelasticity, and the relaxation spectrum in the model was modified by an empirical sigmoidal function and a structure parameter. The steady shear viscosity of the mucilage was fitted to obtain the parameters in the empirical function. The step rate experimental data was fitted to obtain the structural formation and disruption information. According to the varying spectrum in steady shear state, the extract shows slight shear strengthening of linear viscoelasticity at low shear rate, then steep strengthening in 3-6 s-1, and last large strengthening at the shear rate higher than 10 s-1. Both the time-dependent shear thickening viscosity and the shear hysteresis behavior of the mucilage can be predicted using the developing structure.