Rheological characterization of schizophyllan aqueous solutions after denaturation-renaturation treatment

Schizophyllan (SPG) with a molecular weight of 2.6 x 10(6), designated SPG-1, is denatured and then renatured at a concentration of 1.8 wt % by alkalization-neutralization. The prepared denatured-renatured samples (DRSPG-1) are diluted to various concentrations and equilibrated for 10 days before rheological and intrinsic viscosity measurements. When concentration (C-p) is above 0.75 wt %, DRSPG-1 aqueous systems have weak gel-type rheological properties. However, for 0.28 wt % less than or equal to C-p less than or equal to 0.65 wt % and C-p less than or equal to 0.19 wt %, DRSPG-1 aqueous systems behave as power law fluids and Newtonian fluids, respectively, which are attributed to the moderate isotropy degree of DRSPG-1 chains. Furthermore, a critical overlap parameter of c*[eta] = 1.2 is determined for DRSPG-1 in aqueous solutions, which is close to that of I for intact SPG in water while far smaller than that of 4.3 for SPG in DMSO. This is considered to be due to the strong interactions of DRSPG-1 chains in water, further confirmed by the intrinsic viscosity measurements in which the DRSPG-1 aqueous solution shows an abnormally large value of Huggins constant. Regarding the structure of DRSPG-1 weak gels, multiruns of dynamic strain sweep measurements suggest that the dominant structures are aggregates formed by hydrogen-bonding associations of DRSPG-1 chains rather than the permanent three-dimensional network. In addition, the step-shear rate tests are performed to study the thixotropic properties of DRSPG-1 aqueous systems. (D 2004 Wiley Periodicals, Inc.