Hydroxypropyl methylcellulose and hydroxypropyl starch: Rheological and gelation effects on the phase structure of their mixed hydrocolloid system

It is common to hybridize biopolymers for developing materials with combined properties or functionality. However, biopolymers are usually not fully compatible despite their chemical similarity, posing challenges to create mixed systems. Herein, we investigated how the gelation behavior and rheological properties of hydroxypropyl methylcellulose (HPMC), a thermal gel, and hydroxypropyl starch (HPS), a cooling gel, affect their miscibility and the phase structure of their mixed system. The dependence of the zero-shear viscosity for HPMC/HPS paste on biopolymer concentration in a double-logarithmic coordinate can be divided into two parts with the slopes being 11.9 and 2.8 respectively, indicating different degrees of intermolecular entanglement. A typical “sea-island” morphology was shown in the blends, and the phase structure (continuous or discrete) changed with varying HPMC/HPS blend ratio and temperature. This phase structure change can be well correlated to rheological parameters such as zero-shear viscosity, loss tangent, complex viscosity, and the Arrhenius equation correction coefficient (α). Biopolymer concentration, HPMC/HPS ratio, and temperature together controlled rheological properties and phase distribution for the mixed system. The relationship between rheological behavior and phase structure for HPMC/HPS understood from this work provides an insight into designing mixed biopolymer systems with desirable processability, structure, and properties.