Synthesis and microwave characterization of expanded graphite/novolac phenolic resin composite for microwave absorber applications

Chemical oxidation and thermal treatment method is used to synthesize expanded graphite from natural graphite flakes of size ∼2 μm. Novolac phenolic resin(NPR) is used as base matrix and mechanically mixed with expanded graphite (EG) in different weight ratios (30 wt.%, 40 wt.% & 50 wt.% of EG). The mixture is molded at 100–150 °C using compression molding technique to pellets of EG/NPR composite for electrical and microwave characterization. Surface morphology and structural characterization are investigated using scanning electron microscope and X-ray diffraction respectively. 50 wt% EG composite shows a maximum value of electrical conductivity ∼147 S/cm and thermal stability ∼350 °C. The composite is highly dissipating with (εr″/  εr′>1) over the entire X band. Reflection loss >−13 dB is observed throughout out the frequency range. The composite has a potential for broadband microwave absorber application.