In our experiments, the greatest solubility was obtained using 65.0 wt% ZnCl₂ aqueous solution, while cellulose was insoluble in ZnCl₂ aqueous solution, below 65.0% (wt%) , which supports the fact that the cellulose molecules are in competition to the water molecules in the coordination sphere of zinc ion. With higher salt concentration of cellulose/ ZnCl₂ aqueous solution, the fluidity of solution has declined (see Figure 1).

With higher DP, the solubility of cellulose in 65.0% ZnCl₂ aqueous solution is decreasing. Solutions containing up to 15.0 wt% avicel (DP=200) can be formed as viscous pastes in 65.0% ZnCl₂ aqueous solution, while the cellulose (DP=600)/65.0% ZnCl₂ aqueous solution can be highest to 10.0%. Then to improve the dissolving ability of ZnCl₂ aqueous solution, we adopt the ways by reducing the water or adding the urea, which indicates that with the same weight ratio of cellulose to ZnCl₂ adding urea could increase the fluidity of cellulose solution and decreasing the water could enhance the dissolving ability of solution as well as the its viscosity.

Acknowledgment

We gratefully acknowledge the financial support from the NSFC (project 20436020 and 50573025).

Figure 1 The solutions of cellulose (DP=200) in ZnCl₂ aqueous solution

Left: 8% cellulose/ ZnCl₂ (65.0%); right: 11% cellulose/ ZnCl₂ (76.5%)