Multi-scale characterization of thermoplastic starch structure using Second Harmonic Generation imaging and NMR

Area of Science:

• Materials Science
• Polymer Science
• Biomaterials Science

Background:

• Thermoplastic starch (TPS) is derived from extruding starch granules into a continuous matrix.
• Significant breakdown of starch granular organization is typically required for TPS formation.
• Understanding starch microstructure is crucial for controlling material properties.

Purpose of the Study:

• To investigate the effect of glycerol plasticization and high humidity storage on potato starch microstructure.
• To analyze the recrystallization behavior and water interaction of thermoplastic starch.
• To correlate microstructural changes with the material's swelling behavior in water.

Main Methods:

• Extrusion of potato starch with and without glycerol.
• Storage of samples at high humidity to induce recrystallization.
• Multi-scale microstructural analysis using Wide-Angle X-ray Scattering (WAXS), solid-state Nuclear Magnetic Resonance (NMR), and Second Harmonic Generation (SHG) imaging.
• Assessment of material swelling and integrity in water.

Main Results:

• Glycerol-plasticized starch samples exhibited minimal swelling in water.
• Recrystallized samples contained numerous embedded granules with native-like structures.
• Glycerol limited granule and crystallite fragmentation during extrusion.
• Reduced proportion of constrained starch molecules in glycerol-treated samples facilitated polymer network formation.

Conclusions:

• Glycerol plasticization and controlled recrystallization can yield thermoplastic starch with improved water resistance.
• The formation of a robust polymer network, despite the presence of intact granules, is key to limiting water penetration.
• This study provides insights into tailoring starch-based materials for specific applications by controlling microstructure.