Melamine resin/graphite nanoflakes hybrids and its vacuum-assisted prepared epoxy composites with anisotropic thermal conductivity and improved flame retardancy

Melamine resin/graphite nanoflakes hybrids (MGNH) were synthesized by in situ polymerization. The SEM and TEM demonstrate that melamine resin was self-deposited on the surface of the flakes. MGNH is uniform sheeted hybrids which exhibits excellent dispersiveness. MGNH/epoxy composite (MGNH/EP) is prepared via vacuum-assisted method. The special prepared method endows MGNH/EP with interesting anisotropic thermal conductivity. The coefficient of thermal conductivity of the composite in normal direction is 0.4024 W m−1 K−1, while that of MGNH/EP in horizontal direction is 1.5596 W m−1 K−1. The optical microscope image of the composite suggests that the nanoflake is arranged as a parallel conduction medium, it is demonstrated that direct flake-flake conduction can form heat-transfer passages, which contributes to the higher thermal conductivity of the composite in horizontal direction. Also, MGNH/EP shows excellent flame retardant properties, evidenced by the dramatically reduced peak heat release rate and 51% of total heat release values compared with neat EP obtained from a microcombustion calorimeter. The reduced fire hazard can mainly attributed to the synergistic effects of melamine resin and graphite nanoflakes.