Design, preparation and characterization of a high-performance epoxy adhesive with Poly (butylacrylate-block-styrene) Block Copolymer and Zirconia nano particles in aluminum- aluminum bonded joints

Background: Epoxy adhesives are one of the polymers used as high performance matrix in adhesives. However, the high brittleness and low toughness due to their high-crosslinking degree are critical problems during their service in structural applications. The lack of appropriate thermal stability at high temperature is another drawback of these valuable materials. In this study, the effect of hybrid reinforcement comprising zirconium oxide nanoparticles (NPs), phenolic resin (resol type) and poly (butyl acrylate-block-styrene) copolymer (BCP) on mechanical, adhesion, thermal and morphological properties of the epoxy adhesive was studied. Methods: Mechanical properties, thermal stability, and microstructure of the epoxy adhesive was assessed using tensile test, TGA, and FESEM tests, respectively. To investigate the adhesion features, the formulated adhesive was applied in lap joint bonding of an aluminum to aluminum. Significant findings A new approach was developed for designing advanced adhesives with high mechanical, adhesion and thermal properties by adding hybrid additives. Based on the tensile test results, adding 5 phr of zirconium oxide nanoparticles to the epoxy adhesive increased the tensile strength, modulus, and the toughness of the dumbbell-shaped samples by 69%, 33% and 175% as compared with the neat epoxy adhesive, respectively. Furthermore, the highest improvement of shear strength in the single lap joint was observed in the sample containing 10 phr phenolic resin, 5 phr zirconia NPs, and 2.5 phr block copolymer, showing a 420% increment compared to the pure epoxy, reflecting the synergistic impact of these compounds at the mentioned percentage. The TGA results indicated the highest initial degradation temperature in the sample containing 5 phr zirconia NPs which was 54.4 o C higher than that of the pure epoxy. The images of the fracture surface of the optimal samples in the tensile test showed that the cavitation, shear band formation, crack deviation, and crack tip blunting are among the major mechanisms in the increase of the toughness of the samples.