Introducing a new approach for designing advanced epoxy film adhesives with high mechanical, adhesion, and thermal properties by adding hybrid additives for structural bonding

Epoxy-based adhesives are widely used in different industries in various forms. Among them, epoxy film adhesives are particularly applicable in constructing honeycomb structures in aerospace systems. However, these adhesives suffer from brittleness, low flexibility, and thermal stability. In the current paper, the effect of pure and functionalized SiO2 and ZrO2 nanoparticles (NPs), the addition of a block copolymer (butyl acrylate-block-styrene), and Novolac resin on the mechanical, thermal, and adhesive properties of the epoxy film adhesive were thoroughly studied. The mechanical properties, thermal stability, and surface morphology of the epoxy adhesive samples were evaluated using tensile, thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FE-SEM) images, respectively. More importantly, the Lap shear and Peel tests were utilized to investigate the adhesive properties. Pure and functionalized NPs were added to the prepared epoxy adhesive samples. Intriguingly, compared to the non-functionalized NPs, by only adding 1 phr of each functionalized NPs to the formulation, the tensile modulus, tensile strength, and toughness increased to 66 %, 197 %, and 553 %, respectively. More importantly, the single lab shear and T-peel strength were increased as high as 121 % and 101 %, respectively, indicating a synergistic effect. After optimizing the parameters effective on the properties, FE-SEM images of the fractured surface of optimized samples were used to study the possible fracture mechanisms, including crack deflection, crack pinning, nanoparticle debonding, and shear band formation. Also, this synergistic effect was observed in the thermal stability where the only addition of 1 phr of functionalized NPs increased the decomposition onset temperature up to 40 ℃ higher than the neat one. This simple and applicable method can pave the way for using functionalized NPs in modifying epoxy adhesives.