Thixotropic properties of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound

Abstract

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena. With the increase of mass ratio ( R) of HTlc to CS, the equilibrium viscosity ( η eq ) and the consistency coefficient ( m) values of the suspensions increase in the range of neutral and alkaline pH (higher than 6.5) while decrease in the range of acid pH (lower than 6.5). With the increase of pH value, the η eq and m values of the suspensions in the R range of 0–0.08 studied increase initially and then decrease, appearing a maximum value at about pH 7.41 ± 0.25 . The CS/HTlc suspensions display viscid character and the yield point of the suspensions was not observed except the suspension with R = 0.08 in the pH range of 7.66–9.70, which showed a yield point and viscoelasticity. The CS/HTlc suspensions may display different thixotropic types: negative, complex or positive thixotropy, depending on pH and R value. The thixotropic type of the CS/HTlc suspension may be transformed from negative (pure CS solution), through complex ( R = 0.02 ), into positive thixotropy ( R = 0.05 and 0.08) with the increase of R in the studied R range of 0–0.08, and the thixotropic strength of the suspensions increases initially and then decreases with pH value in the pH range studied. The mechanism of the thixotropic phenomenon is discussed.