The effect of metal surfaces on the adsorption and degradation behavior of an epoxy/amidoamine system

Abstract

The adsorption and degradation behavior of an epoxy/amidoamine system on the surfaces of 1020 cold-rolled steel (CRS), 2024-aluminum (2024-Al), and zinc (Zn) substrates was studied using reflection absorption infrared spectroscopy (RAIR). The epoxy resin was spin-coiated on the polished metal substrates from solution with different amounts of the epoxy system and then aged at 130 °C for the RAIR analyses. From the relative intensities of amide and amino bands shown in RAIR spectra, it is concluded that the amidoamine curing agent was preferentially adsorbed on the three metal oxide surfaces, and the amount of the adsorbed amidoamine followed the order CRS > Zn > 2024-Al. Moreover, the CRS could attract more amide than amino groups, but vice versa for the Zn substrate. During the thermal exposure, amide and carbonyl groups were formed in the epoxy film and their concentration varied in dependence on the contacted substrate. The degradation rate of the epoxy resin on three metal surfaces was in the order CRS > 2024-Al > Zn > blank epoxy system, based on the amount of formed amide groups. The accelerated degradation found on the three metal substrates is attributed to the aforementioned preferential adsorption of the curing agent.