| Guar gum is one of the best water-soluble compound of natural polymers presently known, be widely used as thickeners or protective colloids in the food, textile, petroleum and mining industries. However, it has a few shortcomings, such as slowly dissolving, the high content of insoluble residue and the instable viscosity , so it is often chemically modified to improve its physical and chemical properties and expend it application fields.In this work, Carboxylmethyl hydroxypropyl guar gum (CMHPG)is prepared in THF by the reaction of guar gum with propylene oxide and sodium chloroacetate . 1H-NMR and IR are used to characterize the structure of the modified guar gum . . 1H-NMR spectrometry is used to determine molar substitution of hydroxypropyl. The rheological characteristics of aqueous solutions of CMHPG were studied in terms of the effects of its concentration, added salts and temperature by means of Brookfield DV-III rotating rheometer. It was found that CMHPG solutions investigated behaved as non-Newtonian shear-thinning fluids. It could be expressed by a relation of the form of the Ostwald-Dewaele equation: Inηa=Ink+(n-1)1nt. With the increase of CMHPG concentration from 0.1% to 1. 0% , the consistency coefficient increased while the viscosity behavior index decreased. The obvious viscosity behavior of polyelectrolyte solution was observed in aqueous salt solutions containing sodium chloride.The zero shear viscosity(η0)could be obtained by using Spencer-Dillon equation, and the temperature dependence ofη0 could be expressed by Arrhenius equation:ηo =A·exp( Ea /RT)...
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