A study of the rheological behavior of scleroglucan weak gel systems

Abstract

This study deals with the rheological behavior of aqueous systems of scleroglucan, the neutral polysaccharide secreted exocellularly by certain fungi of the genus Sclerotium. We investigated several aqueous systems under different temperatures and polymer concentrations by means of continuous and oscillatory flow procedures. Continuous shear flow tests revealed that a transition exists between a sol-like and a weak gel behavior for those scleroglucan systems in a polymer concentration range between 0.2 and 0.3% w/w. All systems exhibit marked non-Newtonian properties, which change from shear-thinning in the solution domain to plastic in the gel domain; however, the shear-dependent behavior of all systems can be satisfactorily described by a modified Cross equation. As far as the time-dependent properties are concerned, all scleroglucan aqueous systems exhibit a thixotropic response; stress transient experiments show that a delay time of approximately 4–5 min is necessary to remove shear history and to reconfigure the unperturbed state. Both classical dynamic measurements and parallel superposed continuous and oscillatory shear tests confirm the sol-gel transition for scleroglucan aqueous systems, and highlight the weak, transient nature f this microbial polysaccharide gel state.