Influence of substitution on the rheological properties and gelation of hydroxyethyl cellulose solution in NaOH-water solvent

The rheological properties of hydroxyethyl cellulose (HEC) with a low molar substitution (MS) dissolved in 8 wt% NaOH-water were studied as a function of solution temperature, polymer concentration and molar substitution. Special attention was paid to gelation kinetics. Similar to cellulose dissolved in alkali or ionic liquids, the intrinsic viscosity of HEC decreased with temperature increase, indicating a decrease of solvent thermodynamic quality. The gelation time of HEC solutions decreased exponentially with temperature but the kinetics is much slower than the gelation of microcrystalline cellulose solutions in the same solvent. Higher molar substitution leads to slower gelation. The small amount of introduced hydroxyethyl groups prevented cellulose aggregation thus increasing solution stability.