Effect of a reactive interfacial agent on the properties of a nitrile-rubber-modified epoxy film adhesive

Reactive interfacial agents are often used to homogenise the morphology of immiscible polymer blends and to improve the level of adhesion between the phases to achieve enhanced properties. This paper demonstrates the ability of hydroxyl methyl bisphenol A (HMBPA) to function as a reactive interfacial agent (compartibilizer) in a nitrile-epoxy film adhesive made from nitrile rubber (NBR) and solid epoxy resin blend. The curing of the adhesive film was achieved at 170° C by adding dicyandiamide, a latent curing agent for epoxy resin, and rubber vulcanising agents. Hydroxyl methyl bisphenol A resins with different hydroxyl methyl content, synthesised by the base-catalysed reaction of bisphenol A and formaldehyde in various mole ratios, were used to compatibilize a blend of nitrile rubber (NBR) and epoxy resin 50/50wt/wt. The effect of addition of HMBPA on the morphology, adhesive, thermal, and mechanical properties of the adhesive film was investigated. The nitrile-epoxy adhesive films were characterised by measurements of adhesive joint strength, stress-strain properties, DSC, TGA, TMA, DMA, and SEM. Results revealed that significant improvement in joint strength occurred at low levels of HMBPA, and the optimum strength was obtained at about 15 wt% of HMBPA in the blend. The hydroxyl methyl content in HMBPA was found to influence the properties of the adhesive film. The concept of strengthening the interphase between NBR and epoxy through the coupling reactions of HMBPA was used for interpreting the results. The effect of addition of silica, alumina, and aluminium fillers on the properties of the nitrile-epoxy adhesive film was also studied, and a comparison of properties with and without HMBPA is presented.