High adhesion between aluminum and unsaturated polyester through hierarchical surface patterning

The main target in this study was to increase adhesion of unsaturated polyester (UP) adhesive to aluminum by structuring the aluminum surface on the microscale and nanoscale as well as by functionalizing the surface with 3-methacryloxypropyltrimethoxysilane. The micrometer-level surface structures were produced with micro-mesh printing and sandblasting techniques, while a nanoscale pseudoboehmite surface structure was obtained with a boiling water treatment. These modifications were combined to form different hierarchical surface structures. The adhesion strength of polyester to aluminum was assessed with a tensile-shear test. The micro-mesh printed pattern increased the tensile-shear strength of the joint from 2.3 MPa to 5.8 MPa, while the micro-micro-hierarchical joint specimen possessed a high shear strength of 14.5 MPa. Further, adhesion of UP adhesive with three-level hierarchical micro-micro-nanostructured specimens increased so high that the joints started to deform plastically during the shear strength measurement, preventing the evaluation of their maximum strength. The silane-treated specimens also displayed significantly higher shear strengths and a more cohesive failure than the corresponding untreated specimens. Silanization was also observed to improve interaction of the UP adhesive with the aluminum nanostructure. The results demonstrate that adhesion of polyester to aluminum can be significantly enhanced utilizing readily available and environmentally friendly methods.