Interactions of BTESPT silane and maleic anhydride grafted polypropylene with epoxy and application to improve adhesive durability between epoxy and aluminium sheet

For improvement of adhesive strength and durability of adhesion between epoxy and aluminium sheet bis-(triethoxysilylpropyl)tetrasulfide (BTESPT) silane and maleic anhydride grafted polypropylene (PP-g-MAH) are chosen for surface pretreatment of the aluminium sheet respectively. Fourier transform infrared (FTIR) spectroscopy was used for characterization of the structure and the interactions in the systems. It is shown that BTESPT silane and the anhydride on PP-g-MAH take part in the curing reactions of the epoxy/polyamide system. The adhesive shear strength of the samples, prepared under different curing temperatures, and after immersion in boiling water and 3.5% NaCl water solution respectively, was tested. The features of the shear fractured surfaces were examined by scanning electron microscope (SEM). For the aluminium sheet pretreated by BTESPT silane, the maximum adhesive shear strength is 22.2 MPa, which is higher than that of 17.5 MPa for aluminium sheet without pretreatment by the silane. After immersion in boiling water for 80 h and in NaCl water solution at 50 °C for 180 h the adhesive shear strengths are 13.39 MPa and 18.4 MPa respectively, which are higher than these (below 6 MPa) for aluminium sheet without pretreatment by the silane. As for the aluminium sheet pretreated by PP-g-MAH, the maximum adhesive shear strength is 13.17 MPa. After immersion in boiling water for 80 h and in NaCl water solution at 50 °C for 180 h the adhesive shear strengths decline to 10.67 MPa and 8.1 MPa respectively.