Rheological behavior of cyanoethyl celluloses in aqueous solutions

Water-soluble cyanoethyl cellulose (CEC) samples were synthesized by homogeneous reaction of cellulose with acrylonitrile in LiOH/urea aqueous solutions. The dynamic viscoelastic property of CEC with different degree of substitution (DS) in water at different temperatures and concentrations were investigated. At low concentrations, the CEC solutions displayed liquid-like behavior with G' smaller than G'' at low frequencies; while the curves of G' and G'' intersected at the middle of the frequency range at higher concentration, indicating an existence of chain aggregation and entanglement network. The gelation temperature (T (gel)) was determined from the point of intersection in tan delta versus temperature (T) at different frequencies, indicating the validity of Winter-Chambon criteria. It was found that T (gel) increased with increasing DS, and that the exponent (n) values at the gel point decreased with increasing DS. The heating-cooling process proved that the sol-gel transition for CECs in water was thermally irreversible. The AFM images revealed that the particles packed loosely together to form gel aggregates. Moreover, the Maxwell model with four elements was used to describe the frequency dependencies of G' and G'' for CEC in aqueous solution.