Self-healing is triggered by crack propagation through embedded microcapsules in an epoxy matrix, which then release
the liquid healing agent into the crack plane. Subsequent exposure of the healing agent to the chemical catalyst initiates
ring-opening metathesis polymerization (ROMP) and bonding of the crack faces. In order to improve self-healing
functionality, it is necessary to enhance adhesion of polymerized healing agent within the crack to the matrix resin. In
this study, shear bond strength between different norbornene-based healing agents and an amine-cured epoxy resin was
evaluated using the single lap shear test method (ASTM D3163, modified). The healing agents tested include endodicyclopentadiene
(endo-DCPD), 5-ethylidene-2-norbornene (ENB) and DCPD/ENB blends. 5-Norbornene-2-methanol
(NBM) was used as an adhesion promoter, containing hydroxyl groups to form hydrogen bonds with the amine-cured
epoxy. A custom synthesized norbornene-based crosslinking agent was also added to improve adhesion for ENB by
increasing the crosslinking density of the adhesive after ROMP. The healing agents were polymerized with varying
loadings of the 1st generation Grubbs' catalyst at different reaction times and temperatures.
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