Rheology of alginate from Azotobacter vinelandii in aqueous dispersions

Abstract

The rheological behaviour of a range of alginate-like polymers produced by Azotobacter vinelandii DSM 576 was determined at different alginate concentrations ( y), temperatures ( T) and shear rates (γ) in the ranges 0.3–1.5% w/v, 278.16–308.16 K, and 1.1–1400s −1, respectively. All aqueous dispersions exhibited the typical pseudoplastic behaviour, that was described by the well known Ostwäld-de Waele model. The consistency coefficient ( K ow ) was found to be a complex function of T, y, and number-average molecular mass ( M n ) of the biopolymer used. The flow behaviour index ( n) showed a hyperbolic reduction with y, thus tending to a limiting value progressively deviating from unity as M n increased from 40 to 193 kDalton. By maximising the least squares regression coefficient ( r 2) up to 0.99, it was possible to reconstruct the experimental apparent viscosities ( μ a ) of aqueous dispersions containing either bacterial or algal alginates with a mean standard error of ca. 15%, thus resulting in straightforward estimation of the thickening capability of any alginate, whatever is its algal or bacterial origin based only upon its number-average molecular mass.