The invention relates to a grafted guar gum obtainable by a method for grafting an unsaturated monomer selected from a vinyl monomer having a carboxylate group, a sulfonate group, a phosphonate group or a quarternary ammonium group to guar gum and depolymerizing the guar gum, said method comprising the steps of a) mixing the unsaturated monomer and the guar gum； and b) irradiating the guar gum and monomer mixture of step a) with a dose of electron beams effective to graft the monomer to the guar gum and depolymerize the grafted guar gum to a pre-selected molecular weight of below 700,000 Daltons.
