Manipulating a novel epoxy‐based composite with core–shell rubber particles for designing a structural adhesive in aluminum–aluminum bonded joints

Abstract

Epoxy adhesives become very brittle after curing due to their high‐crosslinking degree. For increasing the toughness of epoxy adhesives, the addition of different toughening agents has been proposed. In this study the diglycidyl ether of bisphenol A (DGEBA)/dicyandiamide epoxy network has been modified by adding an emulsion latex containing core–shell rubber particles (CSPs) prepared by means of seeded emulsion polymerization. The CSPs consist of poly (butyl acrylate) (PBA) as core and methyl methacrylate (MMA) copolymerized with glycidyl methacrylate (GMA) as shell. The effects of adding various amounts of the emulsion latex on the mechanical properties, thermal stability, adhesion, and microstructure of the cured epoxy resin were investigated. The CSPs were analyzed by transmission electron microscopy (TEM), Fourier‐transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The mechanical properties, thermal stability, adhesion to aluminum plates, and microstructure of the cured epoxy resin were investigated by stress–strain, thermal gravimetric analysis (TGA), single lap shear test, and field emission scanning electron microscopy (FESEM), respectively. The addition of 7 wt.% emulsion latex to epoxy enhanced the tensile strength and the toughness of the dumbbell‐shaped samples by 421% and 4388% with respect to neat epoxy, respectively. Furthermore, the single lap shear strength increased in 33% and an increase of 71°C in the initial decomposition temperature of the epoxy was obtained by adding 7 wt.% CSP, without affecting the maximum decomposition temperature. The FESEM micrographs of the fractured surfaces indicated that the major toughening mechanisms were CSP de‐bonding, plastic void growth, and shear bond yielding.