Characterisation and modelling of time-independent and time-dependent flow behaviour of sodium alginate dispersions

The time-independent and time-dependent rheological behaviour of sodium alginate dispersions were
determined. The concentration of sodium alginate in the dispersions and temperature of measurement were
between 1% and 3%, and 25 and 55 �C, respectively. Shear-thinning behaviour was observed for these
alginate dispersions when subjected to progressively increasing shear stresses. The Cross power indices (m)
were between 0.57 and 0.82. The time-dependent studies were conducted by loop experiments at constant
shear rates of 25, 125 and 625 s)1. The thixotropic loop and the different time-dependent parameters were
sensitive to the concentration of alginate and temperature of measurement. The models of Weltman,
Mangelsdorf and the three-parameter non-linear model were suitable to predict the shear stresses at constant
shear rates, as judged by root mean square error values. The coefficient of thixotropic breakdown with
shearing (M) could be obtained from forward curve while it gave an indication of structural build-up when
shear rate was progressively decreased.