Synergistic viscosity characteristics of aqueous mixed solutions of hydroxypropyl- and carboxymethyl hydroxypropyl-substituted guar gums

The viscosity characteristics of aqueous mixed solutions of two important guar gum derivatives, hydroxypropyl-substituted guar (HPG) and carboxymethyl hydroxypropyl-substituted guar (CMHPG), were studied at different mixing ratios, shear rates and temperatures. For all the mixed solutions investigated, the measured viscosity values are higher than the calculated viscosity values determined by the additivity rule for ideal two-component solution mixture, showing an interesting synergistic viscosity property. This viscosity synergism may be attributed to the formation of interpolymer complex between the mixed CMHPG and HPG components, as confirmed by UV spectroscopy measurements, and its degree depends on the compositions of the mixed polysaccharide solutions and the shear rates. At same temperature, the zero-shear viscosity of the mixed solution is larger than that of any component solution. For aqueous CMHPG, HPG component solutions with same concentrations of 1.0% (w/v), and their mixed solution with a 0.50 weight fraction of HPG, the activation energies of the apparent viscosity were determined to be 30.1, 27.9 and 14.0 kJ/mol, respectively. In contrast, the mixed CMHPG/HPG solution showed improved temperature tolerance with respect to the viscosity.