Aging resistance and adhesion strength of cold plasma treated aluminum-polypropylene joints: The role of surface treatments and curing agents

With the developing technology, Aluminum (Al) - Polypropylene (PP) composite materials, which combine lightness and high durability, are widely used especially in the aviation and automotive sectors. In this study, different combinations of surface treatment methods such as; sanding, sandblasting, chemical etching, anodization and cold vacuum plasma, were applied to the surface of PP and Al plates. After treatment procedures, these surfaces bonded with epoxy adhesives prepared with Triethylenetetramine (Teta), m-Xylenediamine (Mx) and Phenalkamine (PA) curing agents. The effect of the aging process on the bonding strength was investigated on various samples kept in a hot water bath for 2 months. Contact angle measurement, topography analyses, FTIR and tensile test measurements were conducted for evaluation of the given effects. In the experiments, the highest strength was obtained by bonding of sanded/plasma-treated PP plates with the chemical etched/ anodized/plasma-treated Al plates. Compared to the non-surface treatment plates, an increase of 558.72 % was achieved and a tensile strength of 1840 N (9.2 MPa) was handled. According to the aging results, it was determined that the greatest decrease in adhesion strength occurred in the plates bonded with Teta, while the least decrease occurred with PA curing agent. More resistant structures to the aging were obtained by first sandblasted, then anodized and then plasma applied aluminum plates bonded with sanded and plasma activated PP surfaces. It was determined that especially plasma-treated surfaces were more resistant to the aging than nonplasma activated surfaces.