Direct diazotization of graphite nanoplatelets with melamine and their favorable application in epoxy resins

The ease of undesirable agglomeration and a low efficiency are two problems that restrict the application of graphite nanoplatelets (GNPs) in epoxy resins (EP). Herein, a new strategy with melamine (MEL) as the precursor to functionalize GNPs chemically, which form a bonding layer that is compatible with epoxy matrix, is reported. The MEL fragments with secondary amine groups were grafted uniformly on the GNPs surface by covalent junctions to exploit the diazonium chemistry. This behavior led to a better dispersion and a stronger interaction with the epoxy matrix and resulted in an enhanced glass transition temperature and bending strength, compared with the pure EP. When only 1 wt% functionalized GNPs (f-GNPs) was used, the Tg of the modified EP raised of about 15°C compared with pure EP, and the bending strength increased by approximately 39%. The dielectric constant of the EP with f-GNPs was impacted slightly, and the dielectric loss decreased. At 10⁵ Hz, the dielectric loss of the EP with 1 wt% f-GNPs decreased by approximately 11% compared with pure EP. Therefore, diazotization modification of the GNPs is a useful approach to improve the compatibility in nanoparticle networks.