Epoxy-rich carbon-based composites are well recognized materials in industries
owing to their good mechanical properties and thermal stability. Here,
dielectric properties of composites based on bisphenol-A-epoxy resin loaded
with 5, 6, 10, and 15 wt% of graphite flakes (GF) have been studied. The frequency
and temperature dependence of the dielectric permittivity, dielectric
loss, and ac conductivity have been examined in temperature ( 103 to 97 C)
and frequency (20 Hz–200 kHz) range. Influence of the filler surface chemistry
have been studied for composites loaded with 5 wt% GF obtained: (i) under
wet milling, without or with adding Triton-100x as a surfactant, or (ii) under
dry milling in the presence of KOH. The composite made of epoxy loaded with
5 wt% exfoliated expanded graphite flakes (EEG), was also prepared. The surface
treatment with KOH notably increased dielectric constant of the composite,
keeping low dielectric loss, while treatment with Triton-100x significantly
increased tanδ. The composite loaded with exfoliated expanded graphite shows
higher ac conductivity than those obtained with flaky graphite, GF. Possibility
to change dielectric properties of the composites without changing the loading
content can be used as an approach in tailoring one with desired dielectric
properties.

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