Adhesion Strength of Block Copolymer Modified Epoxy Adhesives

Epoxies are widely used as coatings and structural adhesives in the aerospace, automotive, and consumer goods industries. Prior studies have shown that the addition of block copolymers (BCPs) to epoxy resins can increase bulk fracture toughness, but little work has been done to understand the adhesive properties of these modified epoxy systems. In this work, the influence of self-assembled BCP nanostructures on the adhesion strength of epoxy thermosets was evaluated. Poly(ethylene-alt-propylene)-b-poly(ethylene oxide) BCP modifiers of various molecular weights and weight fractions were mixed into an epoxy resin, forming well dispersed nanoscale structures. Two self-assembled morphologies were studied: spherical micelles and bilayer vesicles. For both nanostructure morphologies, the modified epoxies exhibited significant improvements in bulk fracture toughness, with no reduction in elastic modulus. Single-lap-joint shear tests showed a significant (~50%) increase in the adhesion strength when spherical micelle modified epoxies were used on surface roughened aluminum. In contrast, vesicle-forming modifiers were detrimental, with a 36% reduction in adhesion strength. Possible mechanisms for the adhesion strength results will be discussed.