Assessing the Reaction Kinetics and Solid Viscoelastic Behavior of Limonene Dioxide Epoxy Resin

ABSTRACT This study examines the relationship between limonene dioxide's (LDO) curing degree and glass transition temperature with methyltetrahydrophthalic anhydride (MTHPA) and triethylamine. Using isothermal and non‐isothermal differential scanning calorimetry (DSC) analyses, the curing behavior and degree of conversion were mapped on a time–temperature‐transformation (TTT) diagram. At 50°C, the isothermal curing required approximately 1000 min to reach a significant conversion level, indicating a slow reaction rate for LDO. The curing process likely progresses in multiple stages. The initial stage, within 50°C–100°C, is a first‐order reaction with an activation energy of 63.3 kJ/mol. Subsequent stages involve reactions associated with the reactivity of cis‐LDO and trans‐LDO isomers, acting as parallel autocatalytic reactions with activation energies around 60 kJ/mol, increasing to 80 kJ/mol due to diffusion limitations. Viscosity and dynamic‐mechanical analyses were used to assess the viscoelastic properties of the cured polymer. The isomer mixture formed a resin with low crosslink density and thermoplastic behavior, limiting high‐temperature applications but aiding recyclability. This aligns with previous findings, noting the resin's low reactivity in its oxirane ring to nucleophilic opening.