Rheological characterization of two viscosity grades of methylcellulose: an approach to the modeling of the thixotropic behaviour

Abstract

The rheological behavior of two viscosity grades of methylcellulose (MC) (M-0262 and M-0512) was determined based on the dispersions of different polymer concentrations (from 0.1 to 5% w/w). In order to analyze the possible thixotropic character of the dispersions, the up and down curves of rheograms for several agitation times were plotted. In all cases, the Ostwald-De Waele rheological model (or Power Law model) was used. For both grades of MC, preparations of concentrations in the range of 0.1–1.0% (w/w) exhibited Newtonian behavior, while at polymer concentrations from 2–5% (w/w), pseudoplastic behavior was observed. The lower viscosity grade MC (M-0262) showed no thixotropy, while the higher viscosity grade MC (M-0512) exhibited thixotropic behavior from 2–5% (w/w). To analyze and define thixotropic behavior, we propose an equation model obtained from the values of consistence, m, determined for each of the curves in a flow diagram $\tau\rightarrow\dot\gamma .$ The results obtained from the proposed equation model showed good correlation to those obtained with the thixotropic areas method, and thus could be used as an alternative model for analyzing thixotropy.