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 CO2-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