Preformed particle toughening of epoxy-based film adhesive systems: The effect of particle size and chemistry

A new family of particulate modifiers was incorporated into an epoxy-based model film adhesive system and the performance was evaluated. The particulate modifiers were selected to include a range of particle sizes, chemistry, and functionality. Thermal analysis, lap shear, and fracture energy tests were performed to characterize the performance of the adhesives. The mechanisms of failure for the adhesives were analyzed in relation to the particle modifier characteristics. Significant differences were found for mode I fracture energy when comparing adhesively joined composite specimens in cocured and bonded situations. Large preformed particle modified adhesives had nearly the same G IC values for both cocured and bonded applications, while the G IC values for the much smaller core-shell particle modified adhesives differed significantly. All particle modified adhesives provided an improvement in mode II fracture toughness over that of the control such that the laminates failed either in compression (through-thickness direction) or through delamination of the prepreg plies.