Epoxy Vitrimers: Effect of Thermal Cycling on Stress Relaxation and Self-Healing Properties

Epoxy vitrimers have emerged as promising materials due to their dynamic covalent networks, enabling reprocessability, self-healing, thermal stability, and stress relaxation. This study investigates the effects of thermal cycling on the stress-relaxation and self-healing behavior of epoxy vitrimers incorporating dynamic disulfide bonds. Vitrimers were synthesized by curing the epoxy monomer diglycidyl ether of bisphenol A (DGEBA) with 2,2’-dithiodibenzoic acid (DTBA) in the presence of an imidazole initiator. The samples underwent 10, 20, and 30 thermal cycles between 30 °C and 100 °C to evaluate changes in thermal stability, dynamic behavior, and self-healing performance. Results revealed that thermal cycling initially enhances the material’s properties. After 20 cycles, the storage modulus increased by up to 130%, and the thermal degradation temperature (Td5%) rose by ∼26 °C, indicating enhanced crosslink density and thermal stability. Self-healing efficiency peaked at 92.5% in the vitrimer with 2 wt% DTBA after 20 cycles. However, after 30 cycles, a decline in these properties was observed due to network degradation and increased chain mobility. This led to reduced storage modulus and healing efficiency. Overall, the study highlights the significant influence of thermal cycling on the viscoelastic and healing properties of epoxy vitrimers, supporting their potential in aerospace, automotive, and wind energy applications.