Effect of Polyelectrolyte Molecular Weight and Structure on the Rheological Properties of Cellulose Nanofibril Suspensions

Abstract

The effect of polyelectrolyte addition on the rheological behavior of cellulose nanofibril (CNF) suspensions was examined at a CNF consistency of 1.5%. Cationic and anionic polyelectrolytes with different molecular weights and structures were employed, and rheological behavior was evaluated using steady shear and strain-controlled measurements, with particular emphasis on viscosity hysteresis and yield stress as indicators of network deformation and recovery. At this consistency, steady-state viscosity exhibited little response to polyelectrolyte addition. In contrast, viscosity hysteresis and yield stress showed strong dependence on polyelectrolyte molecular weight and structure, reflecting differences in CNF network deformation and reformation behavior. High molecular weight polyelectrolytes restricted nanofibril mobility and altered network recovery after shear, whereas low molecular weight polyelectrolytes acted through electrostatic interactions. Branched cationic polyelectrolytes enhanced network strength, as evidenced by increased yield stress, while linear and anionic polyelectrolytes reduced network strength by limiting effective inter-fibrillar contacts. These results indicate that, at a CNF consistency of 1.5%, rheological responses are governed predominantly by network-scale interactions associated with polyelectrolyte molecular weight and architecture rather than by surface charge alone. These findings clarify the deformation and recovery behavior of CNF suspensions under conditions relevant to practical handling and processing.