Development of self-healing epoxy/COC adhesives for potential use in wind turbine blades

• EP/COC blends were developed as thermally, self-healable adhesives. • EP-30 wt% COC repaired at 175 °C achieved fracture toughness recovery of 81 % • Bonded joints recovered up to 43 % of their lap shear strength. In this work, epoxy (EP)/cyclic olefin copolymer (COC) blends were investigated as a new type of thermally, self-healable adhesives. Blends, containing 15 and 30 wt% of COC, were formulated, characterized and then applied to epoxy/carbon fiber laminated joints, to evaluate their structural performance and self-healing capabilities. Rheological measurements on uncured blends revealed that storage modulus, loss modulus and complex viscosity of the blends increased with COC content, without compromising the processability of the blends. FTIR and FESEM analyses confirmed the formation of an immiscible morphology of discrete COC domains distributed and weakly bonded to the matrix. Thermal analysis revealed that the adhesives had good thermal stability, while mechanical tests showed a moderate reduction in tensile strength and fracture toughness upon COC introduction, due to the limited EP/COC interfacial adhesion. During the self-healing process at 175 °C, the COC phase softened and flowed into the damaged area and the blend containing 30 wt% of COC achieved a recovery in fracture toughness (K IC ) of 81 %. In the bonded joints, the application of the adhesive with 30 wt% of COC allowed to recover about 43 % of the original lap shear strength. This adhesive effectively achieved a balance between mechanical performance and self-healing capability.