Construction of a Fully Biobased Plastic from a Starch Tung Oil Acid Ester

Renewable and biodegradable starch-based materials offer attractive alternatives to petroleum-based plastics, yet their processing and performance require optimization. This study employed starch (ST) and tung oil (TO) to synthesize a starch tung oil acid ester (ST-TO) via esterification in a CO 2 -switchable solvent, followed by thermal cross-linking of conjugated double bonds. By systematically controlling the degree of substitution ( DS, from 1.42 to 2.40), the hydroxy groups were progressively replaced, which weakened hydrogen bonding and reduced the glass transition temperature to as low as 88.99 °C, thereby imparting thermal processability. The resulting cross-linked bioplastics exhibited tunable mechanical properties, with optimal performance at DS of 1.82 (SP3): tensile strength of 16.1 ± 3.3 MPa, pencil hardness of 9H, water contact angle exceeding 90°, and gel content up to 98.98%. SP3 maintained dimensional stability in acids, bases, and organic solvents over 30 days, withstood thermal exposure up to 250 °C without deformation, and achieved approximately 90% mass loss in soil within 90 days. This work demonstrates that precise control over substitution and cross-linking yields starch-based plastics with integrated thermal processability, robust mechanical performance, exceptional chemical resistance, and natural biodegradability, offering a viable pathway toward sustainable alternatives to conventional petroleum-based materials.