Using gas-assisted electrospinning to design rod-shaped particles from starch for thickening agents and Pickering emulsifiers

Starch's large particle size and compact semi-crystalline structure limit its effectiveness as an emulsifier and shear-reversible thickener. To address this, we used gas-assisted electrospinning to convert large starch granules into thin fibers and then into rod-shaped particles for use as starch-based thickeners and emulsifiers. Manipulating the starch concentration in formic acid, and the electrospinning parameters, caused the jetted polymers to form different shapes. At low starch content (<5 w/w%), electrospraying produced smaller particles (0.4–3.0 μm diameter). At higher concentrations, the polymers tangled and favored the formation of fibers (0.5–3.9 μm diameter). The starch's morphological behavior was fine-tuned by adjusting flow rate, coaxial airflow pressure, voltage, needle gauge, and jetting distance. Extensive formic acid treatment (> 4 days) caused a fiber-to-bead transition. Fiber suspensions exhibited ∼10⁶-times higher viscosity (3215 Pa·s at a shear rate of 0.002 s⁻¹) than unmodified starch. High-shear and ultrasonication were used post-spin to chop the fibers into rod-shaped particles (4, 6 and 8 μm length), which were used as effective emulsifiers. The longest rods (8 μm) stabilized emulsions with the smallest droplets (12 μm). Using food-safe polymers, this study demonstrated that the shape of particles plays important roles in modulating the material functionalities.