Hydrogels of polysaccharide carboxymethyl hydroxypropyl guar crosslinked by multivalent metal ions

Hydrogels of polysaccharide carboxymethyl hydroxypropyl guar crosslinked by chromium(III) ions are synthesized. The effect of crosslinker concentration on the mechanical behavior of the gels is studied, and the amount of chromium compounds able to interact with polymer chains and the amount of carboxyl groups of the polymer involved in crosslinking are compared. It is shown that the elastic modulus of the gels attains a constant value when not all but only about 10% functional groups interact with chromium compounds. At high concentrations, crosslinker molecules basically bind to one functional group; as a result, the gel recharges. This binding proceeds until all carboxyl groups are filled.