Effect of epoxy resin reactivity on adhesion strength of metal-epoxy joint (poster)

In this work, the effect of epoxy resin reactivity on the adhesion strength of metal-epoxy joint was been studied for steel and aluminum substrates. Three resin combinations (a faster, medium and slower reactive system) were used for this study. The reactivity of the resins was compared at 20°C by microcalorimetry (TAM III, TA Instruments), comparing the time to reach the maximum heat flow of the reaction exotherm. The adhesion strength was measured by pull-off tests (dolly testing) 1. All dolly samples were prepared following the same method, using curing cycles established by DSC measurements of the three resin systems. The adhesion strength results show that for both steel and aluminum, the slower reactive system shows higher adhesion strength while the faster reactive system shows lower adhesion strength. The difference in adhesion strength is more pronounced in case of steel substrates than for aluminum substrates. A slower reactive system gives more time for diffusion of epoxy and/or amine from the bulk to the interphasial region and the metal surface (before they are consumed by the curing reaction). Consequently, compared to a faster reactive system, the formation of the interphase will be different and also might lead to different physical-chemical metal/polymer interactions and interaction strength. This might be the reason for this observed adhesion strength difference2.

Reference:
1. L. L. Zhai, G. P. L., Y. W. Wang (2007). "Effect of nano-Al2O3 on adhesion strength of epoxy adhesive and steel." International Journal of Adhesion & Adhesives 28: 6.
2. S. Maeda (1996). "Surface chemistry of galvanized steel sheets relevant to adhesion performance." Progress in organic coatings 28: 12.