Cross‐Linked Epoxy Microspheres and Its Effect on Mechanical, Thermo‐Mechanical and Interface Properties of Ambient Cured Epoxy Adhesives

ABSTRACT Highly cross‐linked epoxy adhesives in its pristine form are unamenable for structural applications as they lose their strength and toughness under various mechanical stresses. In this paper, epoxy microspheres based on a tri‐functional epoxy and an aromatic amine were synthesized and characterized. They were incorporated into an ambient cured two‐part epoxy adhesive formulation based on di‐functional epoxy resin and polyether‐amine curing agent. The modified adhesive was evaluated for mechanical, interfacial, viscoelastic properties, and failure morphology. Microsphere modified formulations exhibited an improved tensile strength of 75 MPa and an adhesive Lap Shear Strength of 18 MPa on standard aluminum substrates with an elongation of 4.5% at room temperature, which was superior to the unmodified system. The epoxy microspheres showed improved miscibility and a uniform distribution within the adhesive matrix, which caused plastic deformation and shear yielding of the matrix. The inclusion of epoxy microspheres reduced the modulus and glass transition temperature associated with the reduced crosslink density of the matrix.