Kinetics of dextran crosslinking by epichlorohydrin: a rheometry and equilibrium swelling study.

Curing behavior and gel properties of dextran are investigated during its crosslinking by epichlorohydrin (ECH) using rheometry and equilibrium swelling studies. Each ECH/anhydroglucose unit of different molar ratio (0.16-0.99) was added to a known volume of aqueous dextran solution (25%, w/w) in the presence of sodium hydroxide (1.2-3.6 M) as a catalyst. Gel point was investigated as a function of the reactants concentration. The rheological behavior of the curing gels was evaluated using a rheokinetic model. Swelling behavior of the cured, cylindrical specimens was also studied gravimetrically. Increasing NaOH and ECH concentrations significantly increased the crosslinking reaction rate leading to shorter gel points, which was attributed to more ionization of hydroxyl functional groups of dextran due to higher NaOH concentrations. Degree of swelling vs. the reaction time was decreased sharply as a direct function of increasing NaOH and ECH concentrations up to certain levels, which then leveled off. In contrast, higher NaOH concentrations increased the swelling ratio probably due to the alkaline induced degradation of dextran chains.