Direct Bonding of Polypropylene to Aluminum Using Molecular Connection and the Interface Nanoscale Properties

Because of the ever increasing demand for high precision and high reliability adhesions, interest in the investigation and development of direct adhesion and interface bonding between different materials is growing rapidly. We report here a direct adhesion method for polymer/metal bonding via grafting of a triazine molecular layer. Polypropylene (PP) and aluminum (Al) are the bonding polymer and metal, respectively, in our study. The surface and interface characteristics at the nanoscale were studied through nanoscale thermal analysis (nano-TA) and atomic force microscopy + nanoscale infrared spectroscopy (AFM nano-IR) to evaluate the thermal properties and chemical structure of the bonding substances. It was found that the triazine molecular agent reacted with the plasma-treated PP and Al surfaces, leading to a covalent bond on the surfaces. The adhesion interface of PP and Al has revealed that the adhesion strength approached the cohesive failure stress of PP when the adhesion temperature exceeded the surface transition temperature (Tt) of PP (i.e., 127 °C ± 3 °C). The AFM-nanoIR spectra displayed crystal peaks of PP at 1164 cm–1 along the interface. The results revealed the effect of surface nanoscale thermal properties and covalent bonding on the resin adhesion bonding. The findings from this study should be particularly valuable in the precision adhesion applications of industrial resins.