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Highlights • Hydroxypropylmethylcellulose (HPMC) were hybridised with hydroxypropyl starch (HPS). • The rheological, gel and film properties were tailored by HPMC/HPS contents. • HPS displayed reduced viscosity and increased compatibility with HPMC. • HPS exhibited less chain rearrangement and lower film crystallinity and rigidity. • Starch hydroxypropylation reduced film density and oxygen permeability in blends. Abstract This work investigates the rheology, structure, and properties of novel thermal/cooling-gel biphasic systems formed by hybridization of hydroxypropyl methylcellulose (HPMC) as a thermal gel and hydroxypropyl starch (HPS) as a cooling gel. Due to the different gelation properties, HPS became the dispersed phase in the other continuous phase at low temperatures, and so did HPMC at high temperatures. However, the dispersed phase could play a dominant role in the viscosity, thixotropy, and gel properties of the blends, and subsequently affect the crystalline structure, fractal structure, mechanical properties, oxygen permeability, and thermal stability of the blend films. Moreover, the rheological properties and the film structure and performance could also be varied by the chemical modification of starch. Hydroxypropylation could break the starch intermolecular hydrogen bonding, disrupt its ordered structure, inhibit the molecular rearrangement, and result in a softer gel texture that was more compatible with HPMC. With a higher degree of hydroxypropyl substitution, the resultant blend films were more amorphous and flexible but exhibited decreased mechanical properties and oxygen permeability. The knowledge obtained from this work could provide guidance to further developing various thermal/cooling-gel multi-phasic systems with desired properties and functionality. [ABSTRACT FROM AUTHOR]

• Hydroxypropyl methylcellulose (HPMC) was blended with hydroxypropyl starch (HPS) • The continuous phase of HPMC-HPS mixed hydrocolloid changed with HPMC/HPS ratio. • Hydroxypropylation promoted HPMC gelation. • Good compatibility between HPMC and HPS enhanced the HPMC-HPS gel strength. • HPMC hydroxypropylation improved the oxygen barrier effect of HPMC-HPS film. This work investigates the structure, processability, and film performance of hydroxypropyl methylcellulose (HPMC) hydrocolloids affected by hydroxypropy substitution degree and blending with hydroxypropyl starch (HPS). The hydroxypropylation of HPMC could increase inter-chain hydrogen bonding, thereby promoting its gelation, and improve film-forming, but reduce the mechanical properties of the films. HPMC-HPS mixed hydrocolloid system showed a typical "sea-island" morphology with the continuous phase changing with blend ratio. The content of hydroxypropy groups of HPMC affected the compatibility between HPMC and HPS, the morphology of the discrete phase, and the rheological properties of the blends. The fluid-like HPS enhanced the gel strength of HPMC when they had better compatibility. With a higher degree of hydroxypropy substitution, blend films exhibited a much denser structure, better oxygen barrier property, and appropriate mechanical properties. The knowledge obtained from this work could guide the development of edible packaging materials with desired properties and functionality. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hydroxypropylene grafted on both cellulose and starch improved their compatibility. [•] PEG acted as both a plasticizer and a compatibilizer for the blends. [•] Viscosity of starch at lower temperature improved viscosity balance of the system. [ABSTRACT FROM AUTHOR]

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. Image 1 • Hydroxypropyl methylcellulose (HPMC) and hydroxypropyl starch (HPS) mixture studied. • Strong rheological and gelation effects on the phase structure of HPMC/HPS shown. • HPMC/HPS blend ratio and temperature controls continuous/discrete phase change. • Phase structure correlated to zero-shear viscosity and Arrhenius coefficient α. • A schematic model to describe the temperature-induced conformational change. [ABSTRACT FROM AUTHOR]