Unexpected Rheological Behavior of a Hydrophobic Associative Shellac-Based Oligomeric Food Thickener

Area of Science:

• Rheology
• Materials Science
• Polymer Chemistry

Background:

• Sodium shellac, a natural polymer derivative, possesses unique surfactant properties.
• Understanding its rheological behavior under varying conditions is crucial for novel applications.

Purpose of the Study:

• To investigate the shear-thickening behavior of sodium shellac.
• To elucidate the role of pH and hydrophobic associations in its rheological properties.
• To explore its potential as a functional shear thickener.

Main Methods:

• Steady shear flow tests to observe fluid transitions.
• Dynamic oscillation tests to analyze viscoelastic properties (G' and G'').
• Introduction of hydrophilic polymer poly(ethylene oxide) (PEO) to disrupt hydrophobic associations.

Main Results:

• Sodium shellac exhibits continuous shear-thickening behavior, transitioning from Newtonian to non-Newtonian fluid under high shear rates.
• At low concentrations, it acts as a viscous fluid, while at high concentrations, it behaves as an elastic fluid.
• Shear-thickening properties were attributed to hydrophobic associations, which were disrupted by PEO, confirming the mechanism.
• Reaction with H+ solidifies hydroclusters, retaining high viscosity under shear.

Conclusions:

• Sodium shellac is a functional shear thickener with tunable rheological properties.
• Its shear-thickening behavior is reversible and dependent on pH and hydrophobic interactions.
• Demonstrates significant potential for use in food, medical gels, adhesives, and cosmetics.