Thickening, shear thinning and thixotropic behavior of a new polysaccharide-based polyampholyte in aqueous solutions

An investigation was focused on the flow characteristics of aqueous solutions of a new polysaccharide-based polyampholyte, O-carboxymethyl-O-2-hydroxy-3-(trimethylammonio)propyl guar (CMHTPG), under different conditions of concentration, temperature, added salts and surfactant. In the range of measured shear rates of 3.0–1312 s−1, the CMHTPG solutions behaved as pseudoplastic shear-thinning fluids, which could be fairly well described by the power-law model with a consistency index (K) and a characteristic flow behavior index (n) lower than 1. When CMHTPG concentration (Cguar) increased from 0.1 to 4.0% (w/v), the K value increased while the n value decreased. Depending on the Cguar, the solution of this guar-based polyampholyte could exhibit a thixotropic behavior. By investigating the effect of temperature, it was found that the K value decreased with the temperature while the opposite trend was observed with the n value. In the range of salt concentrations investigated, the influence of added salts including NaCl, CaCl2 and MgCl2 on the n value was not obvious but their addition affected greatly the K value. Compared with its aqueous solution in the absence of added salts, the salt-containing solutions of amphoteric CMHPTG were characteristic of an increase in the K value, especially for divalent salts, showing an unusual salt-response behavior. As sodium dodecylsulfate having the concentrations of 0.3, 0.6 and 1.0% (w/w) was added respectively into aqueous 1.0% CMHTPG, the K value was found to have an increase and the n value to have a decrease.