Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Epoxy microspheres (EMs) were successfully synthesized from a trifunctional epoxy resin and an aromatic amine hardener and extensively characterized. EMs were incorporated into an ambient curable epoxy adhesive system, and its effect on interfacial, mechanical, thermo-mechanical, and fracture morphological properties was investigated. The addition of EMs has improved the mechanical properties of the adhesive, with a 40% improvement in the tensile strength and improved toughness properties. The Lap Shear Strength increased to a maximum of 63% compared to the neat formulation. The glass transition temperature reduced with the incorporation of epoxy microspheres, attributed to the reduced cross-link density of the epoxy adhesive.


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.