Epoxy nanocomposites for enhanced fire retardancy and metal-to-metal bonding properties of aircraft aluminum alloys

Abstract

Epoxy adhesives have a wide range of applications in aerospace, automotive, marine, and construction industries. Epoxies reduce the weight of a structure by minimizing fasteners. By application of epoxy adhesive, a structure can achieve uniform stress distribution, structural integrity, durability and cost effectiveness. A mechanical weakness of epoxy adhesives is their lack thermal stability and failure at post-curing-cycle temperatures. Fire retardancy can be improved by incorporating graphene nanomaterials as reinforcements. These graphene additions have potential to improve the epoxy's thermal, mechanical and electrical properties. The epoxy nanocomposites of different weight percentages of graphene nanomaterials were prepared using a three-roll milling machine, Single-lap, shear-strength tests were carried out for evaluating the mechanical properties of the epoxy using a tensile test method. The flame retardancy values for the epoxy nanocomposites were determined using the ASTM UL-94 vertical burn tests. The thermal characterization of the epoxy nanocomposites was carried out using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Surface morphology analysis was carried out for epoxy nanocomposites by using scanning electron microscopy. The test results showed that fire retardancy was improved by 3wt% and 5wt% with graphene nanomaterial inclusions when compared with pristine epoxy. The DSC results, when compared to 0.5wt and 5wt% graphene inclusions showed the glass transition temperatures increased by 6.2%. The TGA results showed a decrease in mass reduction by 6.2%, due to inclusion of graphene nanomaterials. The lap shear strength when tested under tensile tests were improved by 27%, compared to pristine epoxy. Thus, graphene nanomaterial inclusions improved both mechanical and thermal properties while increasing thermal stability of the epoxy when compared to pristine epoxy.