Thermoplastic zein/dextran blends plasticized and compatibilized with diethylene glycol: Scalable processing and functional properties for sustainable food packaging

This work reports, for the first time, the development of thermoplastic zein/dextran (zein/DEX) blends processed by extrusion and injection molding using diethylene glycol (DEG) as a dual plasticizer and compatibilizer. Zein, a hydrophobic protein, and dextran, a hydrophilic polysaccharide, were successfully combined to yield homogeneous and processable blends with tunable properties. Low dextran content (2.5 wt%) increased tensile strength and modulus from ∼8 MPa and ∼140 MPa (zein/DEG) to ∼14 MPa and ∼180 MPa, while higher dextran loadings (20 wt%) promoted ductility and toughness, reaching elongation at break of ∼82% and impact strength exceeding 6 kJ m⁻². Morphological analyses confirmed improved miscibility at high dextran contents, whereas thermomechanical data indicated increased chain mobility (β-relaxation shifting from −55 °C to −65 °C). Although thermal stability slightly decreased (T max 357 → 345 °C), blends showed enhanced hydrophilicity (contact angle 33° → 23°) and high water absorption (∼256% after four weeks for 20 wt% dextran). All formulations achieved complete disintegration under controlled compost conditions within seven weeks, with > 90% mass loss for 20 wt% dextran after five weeks. These results demonstrate zein/dextran/DEG systems as scalable, fully biodegradable materials with strong potential for sustainable food packaging applications.