Synthesis and characterization of carboxymethyl guar gum and rheological properties of its solutions

Carboxymethyl guar gum was synthesized with a simple dry and multi-step method for the first time as a product of the reaction of guar gum and monochloroacetic acid in the presence of sodium hydroxide. The influences of a variety of reaction parameters for degree of substitution were evaluated. The product was characterized by a variety of material characterization techniques. FTIR showed new bonds at 1618, 1424 and 1325 cm−1 after carboxymethylation. SEM showed that the surface of guar gum particles was mostly ruptured. XRD revealed that guar gum crystallinity was reduced. The rheological properties of product pastes were studied using a rotational viscometer. The viscosity of products’ solution decreased with increasing temperature and increased with increasing concentration. With the increase of storage time, the viscosity increased at first, and then decreased. In addition, a shear thinning pseudoplastic behavior was observed at all concentrations, temperatures and storage times.