Polyelectrolytes from polysaccharides: selective oxidation of guar gum- a revisited reaction

The aim of this work was to study the properties of the carboxylated polyelectrolyte obtained from guar gum. The C-6 alcohol functions of galactose units side chains were oxidized first by GO-ase to aldehyde groups and then to carboxylic groups by halogen oxidation. The enzymic oxidation step was followed by the Dische method, by viscosity and light scattering measurements. With regard to previous reports, some changes were introduced in the two-step reaction, in order to prevent polymer degradation. Several characteristics of the carboxylated polyelectrolyte have been studied, such as molecular weight distribution, degree of substitution, viscosity, intrinsic viscosity determined by the isoionic method, radius of gyration, charge parameter and apparent intrinsic persistence length. The charged macromolecule formed from native guar showed all the typical characteristics of a polyelectrolyte. The viscometry results indicate that carboxylated guar has a much higher viscosity in low salt content than the native polymer, which improves its thickening properties.