Study of electrical conductivity in epoxy-based adhesives and polyurethane adhesives through the addition of graphene nanoplatelets before and after thermal aging

This study investigates the electrical conductivity of two commercial adhesives—epoxy-based and polyurethane-based—reinforced with varying concentrations of graphene nanoplatelets (GNPs) (0–30 % by volume) and evaluates the influence of thermal aging on this property. Using a custom-designed two-prong uniaxial measurement method that accounts for specimen volume and current pathways, the results reveal a consistent increase in conductivity with higher GNP concentrations. Across all concentrations, the polyurethane adhesive exhibited superior conductivity compared to the epoxy-based adhesive. Notably, the addition of 30 % GNPs doubled the conductivity in both adhesives relative to their unreinforced counterparts. Thermal aging, performed at 70 °C for 16 h, further enhanced conductivity for both adhesives, particularly at lower GNP concentrations for epoxy and across nearly all concentrations for polyurethane, with increases of up to 200 %. These improvements are attributed to more complete polymerization during aging, optimizing the conductive pathways. The findings highlight the potential of GNP-reinforced adhesives for applications requiring enhanced electrical properties.