Enhancement of Hydrophobic Properties in Starch‐Based Composites via Reactive Blending With Epoxidized Soybean Oil and Citric Acid

ABSTRACT The hydrophilic nature and limited mechanical performance of thermoplastic starch (TPS) restrict its applicability compared with conventional plastics. This study improves the hydrophobicity and tensile properties of starch‐based composites by incorporating epoxidized soybean oil (ESO) as a natural hydrophobic component through a reactive blending approach. Citric acid (CA) was used to promote crosslinking between starch and ESO. The molar ratio between carboxylic groups of CA and oxirane groups of ESO was varied from 0.2 to 1.0 to investigate its effects on phase dispersion and final performance. The reactive blending process enhanced hydrophobicity by up to 55% and improved compatibility through controlled crosslinking, as confirmed by FTIR mapping and DSC. Among all compositions, R0.6 demonstrated the most balanced crosslink network, resulting in the highest tensile strength at 4.4 MPa. These results demonstrate an effective strategy for preparing starch‐based composites with improved hydrophobicity for food packaging applications.