Thermoplastic adhesive bonding of galvanized steel to polypropylene composite and its durability

A thermoplastic adhesive bonding process with a high-density polyethylene (HDPE)-based adhesive has been developed for galvanized steel to polypropylene (PP) composite. The processing temperature significantly affects the strength of the adhesively bonded lap joints. Melting of the surface of the PP composite prior to bonding was found helpful for interdiffusion between adhesive and PP composite during the bonding process. Cataplasma aging tests showed that use of a polyester–melamine-based primer on the galvanized steel before preparation of the PP composite/galvanized steel joints reduced durability. However, the primer did not cause significant adhesion loss under cyclic moisture/temperature condition. It was established that the loss in adhesion of joints made from galvanized steel treated with primer was due to the blistering of the primer in Cataplasma environment.