Development of optimized autonomous self-healing systems for epoxy materials based on maleimide chemistry

Maleimide chemistry involving amines and thiols is presented and evaluated for the design of autonomous self-healing epoxy materials. Model reactions show that amines react rapidly with maleimide compounds at room temperature via the Michael addition reaction. Moreover, thiols and maleimides react readily in the presence of tertiary amines that are present in the epoxy material. The maleimide conjugation reaction with residual amines in the epoxy material ensures chemical bonding of the newly formed network with the original materials during crack healing, while in the crack plane, multifunctional thiols react with difunctional maleimides to fill the crack area. Healing efficiencies are evaluated using the tapered double cantilever beam (TDCB) test method with manual injection of the healing agents, revealing a maximum healing efficiency up to 121% for EPON 828 epoxy material. Furthermore, the use of maleimide chemistry has also been evaluated for self-healing applications towards a cold-curing resin that is currently used for infusion of wind turbine blades (RIM resin). While the healing efficiency is strongly dependent on the type of epoxy material, the average maximum peak load for fracture after healing is roughly the same for all tested epoxy materials.