Influence of concentration and mannuronate/gluronate ratio on steady flow properties of alginate aqueous systems

Steady flow properties were measured at various concentrations for aqueous systems of alginates with different mannuronate/gluronate (M/G) ratios using a cone-plate type rheometer. The flow curve (a plot of shear stress vs. shear rate) shows a plateau region, which is ascribed to a heterogeneous structure, at low shear rate. This plateau region is more noticeable in the G-rich systems than in the M-rich systems. On the other hand, the flow curves for the systems with the same molecular weight but different M/G ratios are congruent in the high shear rate region. The zero shear viscosity can be reduced by the segment contact parameter, cM_w, for the alginates with the same M/G ratio but different molecular weights. The zero shear viscosity is proportional to cM_w in a low concentration region and is proportional to (cM_w)^3.4 at relatively high concentrations. The critical value of cM_w for which the zero shear viscosity changes from proportionality with cM_w to proportionality with (cM_w)^3.4 is ca. 900.