Effect of ethylene glycol-based plasticizers on the properties of zein-based biopolymers processed by extrusion and injection molding

This study aims to advance protein-based materials toward industrial scale manufacturing using extrusion and injection molding processes. The incorporation of plasticizers improved zein processability and performance, and ethylene glycol derivatives with different ethylene glycol repeating units. Ethylene glycol (1EG), diethylene glycol (2EG), triethylene glycol (3EG), and tetraethylene glycol (4EG) were introduced as plasticizers. Mechanical characterization showed that lower molecular weight plasticizers promoted more ductile behavior, whereas higher molecular weight plasticizers increased material strength. Thermal and thermomechanical analyses indicated that the glass transition temperature shifted to lower values as the plasticizer chain length decreased, reflecting higher plasticization efficiency. Plasticized zein samples disintegrated under composting conditions within 7 weeks, independently of the plasticizer used. Increasing the ethylene glycol chain length increased the ratio of methylene units to hydroxyl groups, which reduced plasticizer polarity and promoted more hydrophobic behavior. These results demonstrate ethylene glycol-based plasticizers with different chain lengths enable effective control of the mechanical, thermal and wetting properties of protein-based materials while preserving their compostability.