Fracture behavior of a self-healing, toughened epoxy adhesive

A self-healing, toughened epoxy adhesive is demonstrated based on a commercial structural adhesive film. Self-healing is achieved via embedded microcapsules containing dicyclopentadiene monomer and solid particles of bis(tricyclohexylphosphine)-benzylidine ruthenium (IV) dichloride (Grubbs') catalyst. Recovery of fracture toughness is assessed through fracture testing of width tapered double cantilever beam (WTDCB) specimens. Healing efficiencies as high as 58% were achieved for 6.6 wt% DCPD microcapsules and 10 mg Grubbs’ catalyst. However, virgin fracture toughness is reduced with the addition of ca. 117 μm diameter microcapsules as a result of suppression of the damage zone as revealed by transmission optical micrographs. The uniform dispersal of microcapsules throughout a rubber toughened epoxy adhesive formulated using EPON 828, piperidine and CTBN alleviated the suppression effect and demonstrated retention of virgin fracture toughness of adhesives.