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 cMw for which the zero shear viscosity changes from proportionality with cM(W) to proportionality with (cM(W))3.4 is ca. 900.