Effect of association on rheological behaviors in the non-aqueous solutions of semi-flexible cellulose derivatives

The rheology of cellulose derivatives dissolved in highly viscous solvent was studied. Results demonstrated that a concentration-dependent transition occurred at ca. 10 vol% for ethyl cellulose, and at ca. 2.0 vol% for hydroxypropyl cellulose. Below the transition point, steady shear viscosity of solutions showed weak concentration dependency. The exponent of the power law model was about 3.7. Above the transition, the viscosity was strongly dependent on the concentration. Further studies showed that such a transition strongly depended on the association between chains. Above the transition point, their long-time dynamics were dominated by the hydrogen bonds acting as the transient cross-links between chains. While below this point, long-time dynamics were governed by the percolation statistics. As a result, their viscosities indicated different concentration dependence relationships. Our studies showed that the entanglement and association behaviors were different, for the flexible and semi-flexible chains.