Rheology of scleroglucan dispersions

The rheological properties of a scleroglucan, industrially produced by Sclerotium rolfsii, either in aqueous or dimethylsulfoxide (DMSO) dispersions at concentrations (c) ranging from 0.01% to 1.5% (w/w) were determined by using Cannon-Fenske capillary viscometers and a dynamic stress rheometer with plate-and-cone geometry under steady shear flow, small amplitude oscillatory shear and creep. The intrinsic viscosity [n] in water and DMSO was found to be equal to 12.1 +/-0.3 and 4.6 +/-0.3 dl/g, respectively. Despite the creep and oscillatory tests pointed out the presence of more or less strong molecular entanglements resulting in a three-dimensional network for c greater than or equal to0.35% (w/w), the steady shear flow ones using a stress increasing exponentially with time showed a Newtonian behaviour at low enough shear rates, a pseudo-plastic one in the middle shear rate range and a second Newtonian plateau at very high shear rates. The Cross equation was capable of describing the theological behaviour of the aqueous scleroglucan dispersions both in the sol and gel domain for shear rates (gamma )over dot and scleroglucan concentrations in the ranges 5 x 10(-5) -3.5 x 10(3) s(-1) and 0.15-1.5% (w/w), respectively; while the Ostwald-de-Waele model well fitted the apparent viscosity of the scleroglucan dispersion in DMSO at c=1% (w/v) and (gamma )over dot ranging from 2.5 to 180 s(-1). (C) 2001 Elsevier Science Ltd. All rights reserved.