Synthesis and Testing of β-Diketone Coupling Agents for Improved Durability of Epoxy Adhesion to Steel

Abstract

Epoxide resins are used extensively for the adhesive bonding of metal substrates. Their poor performance in the presence of water seriously limits the use of these resins to non-critical applications. Introducing coupling agents at the metal/resin interface which are capable of chemically bonding to the surface of the substrate can markedly improve the durability of the adhesive joint. β-diketone chelators have been synthesized and evaluated as potential coupling agents for epoxy/steel adhesion. The adhesive system has been evaluated by subjecting torsional joints to shear failure after accelerated immersion testing in distilled water. The presence of an oxide layer was found to be detrimental to the effectiveness of the coupling agent. An ammonium citrate pretreatment has been developed which effectively removes or greatly reduces the oxide layer. Subsequent treatment with the β-diketone coupling agent has a beneficial effect on the durability of the adhesive system.