Rheological behaviour of aqueous dispersions of algal sodium alginates

The rheological behaviour of a few commercial alginates of weed origin in aqueous dispersions was determined at different alginate concentrations (y) and temperatures (T) in the ranges 0.125-1.5% w/v and 278.16-308.16 K, respectively. lit all cases, the shear diagrams exhibited the typical pseudoplastic behaviour and were reconstructed by using the well-known Ostwald-de Waele model. The effect of temperature on the consistency index (K) at constant alginate concentration was better described by using a power-law model rather than the Arrhenius relationship. The changes in the flow behaviour index (n) with T were statistically negligible (at the 95% confidence level in about 80% of all experiments) as compared to those in K, while those with y were described by using an empirical hyperbolic model. All the regression coefficients of this model were then correlated to the average molecular weight of each alginate studied, the latter being estimated on the basis of the corresponding intrinsic viscosity via a Mark-Houwink regression. By maximising the least squares regression coefficient (r(2)) up to 0.99, it was possible to reconstruct the experimental apparent viscosities (mu(a)) with a mean standard error of ca. 12%, thus resulting in straight forward estimation of the thickening capability of any alginate whatever its weed origin based upon its average molecular weight only. (C) 1996 Elsevier Science Limited.