Zinc chloride aqueous solution is a non‐derivatizing solvent for starch, and can be used as a media for homogeneous starch modification. Here, the rheological properties of starch in ZnCl2 aqueous solution under different conditions are considered. Specifically, a large number (120) of viscosity–shear‐rate curves for starch–ZnCl2 solutions with different starch contents, ZnCl2 concentrations, and temperatures were obtained and modeled using a master curve method. In particular, the power‐law index (n) from the modeling could accurately classify the starch molecules in ZnCl2 aqueous solutions into an insoluble state, a dilute state, a semi‐dilute state, and a sticky state, reflecting the different degrees of chain interactions in the solution. In particular, the sticky state would be mostly likely be controlled by the zinc–starch complex, which made the rheological behavior entirely different from that at low ZnCl2 concentrations. The knowledge obtained from this study can be used to guide the homogeneous modification of starch and the fabrication of starch‐based materials using green solvents such as aqueous ZnCl2 with desired properties.

Starch and cellulose are two typical natural polymers from plants that have similar chemical structures. The blending of these two biopolymers for materials development is an interesting topic, although how their molecular interactions could influence the conformation and properties of the resultant materials has not been studied extensively. Herein, the rheological properties of cellulose/starch/ZnCl2 solutions were studied, and the structures and properties of cellulose-starch hybrid films were characterized. The rheological study shows that compared with starch (containing mostly amylose), cellulose contributed more to the solution’s viscosity and has a stronger shear-thinning behavior. A comparison between the experimental and calculated zero-shear-rate viscosities indicates that compact complexes (interfacial interactions) formed between cellulose and starch with ≤50 wt % cellulose content, whereas a loose structure (phase separation) existed with ≥70 wt % cellulose content. For starch-rich hybrid films prepared by compression molding, less than 7 wt % of cellulose was found to improve the mechanical properties despite the reduced crystallinity of the starch; for cellulose-rich hybrid films, a higher content of starch reduced the material properties, although the chemical interactions were not apparently influenced. It is concluded that the mechanical properties of biopolymer films were mainly affected by the structural conformation, as indicated by the rheological results.