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

The adsorption and degradation behavior of an epoxy/amidoamine system on th e surfaces of 1020 cold-rolled steel (CRS), 2024-aluminum (2024-Al), and zi nc (Zn) substrates was studied using reflection absorption infrared spectro scopy (RAIR), The epoxy resin was spin-coated on the polished metal substra tes from solutions with different amounts of the epoxy system and then aged at 130 degrees C for the RAIR analyses. From the relative intensities of a mide and amino hands shown in RAIR spectra it is concluded that the amidoam ine curing agent was preferentially adsorbed on the three metal oxide surfa ces, and the amount of the adsorbed amidoamine followed the order CRS > Zn > 2024-Al. Moreover, the CRS could attract more amide than amino groups, bu t vice versa for the Zn substrate. During the thermal exposure; amide and c arbonyl groups were formed in the epoxy film and the concentration varied i n 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 e poxy system, based on the amount of formed amide groups. The accelerated de gradation found found on the three metal substrates is attributed to the af orementioned referential adsorption of the curing agent.