RHEOLOGICAL BEHAVIOR 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 concentra tions (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 t he typical pseudoplastic behaviour and were reconstructed by using the well-known Ostwald-de Waele model. The effect of temperature on the c onsistency index (K) at constant alginate concentration was better des cribed by using a power-law model rather than the Arrhenius relationsh ip. The changes in the flow behaviour index (n) with T were statistica lly negligible (at the 95% confidence level in about 80% of all experi ments) 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 ma ximising the least squares regression coefficient (r(2)) up to 0.99, i t was possible to reconstruct the experimental apparent viscosities (m u(a)) with a mean standard error of ca. 12%, thus resulting in straigh t forward estimation of the thickening capability of any alginate what ever its weed origin based upon its average molecular weight only. (C) 1996 Elsevier Science Limited.