Rheology of alginate from Azotobacter vinelandii in aqueous dispersions

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 (gamma) in the ranges 0.3-1.5% w/v, 278.16-308.16 K, and 1.1-1400 s(-1) respectively, All aqueous dispersions exhibited the typical pseudoplastic behaviour that was described by the well known Ostwald-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 inner (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 appal ent viscosities (mu(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. (C) 1998 Elsevier Science Limited. All rights: reserved.