Dielectric properties of epoxy/graphite flakes composites: Influence of loading and surface treatment

Abstract

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.

Electrical properties of epoxy/graphite flakes microcomposite at the percolation threshold concentration

“…Epoxy/carbon nanocomposites are used in many modern applications such as sodium-ion batteries and fuel cells and in both cases, the filler concentration is at least 80% [5,6]. However, there are other applications for epoxy/carbon nanocomposites when the filler concentration is less than 15%, such as overcurrent and overtemperature protection of electrical circuits, supercapacitors, and biosensors [7,8]. Therefore, it is necessary to study the percolation threshold of fillers to understand the changes in electrical properties in epoxy/carbon compounds and their derivatives.…”

“…Therefore, it is necessary to study the percolation threshold of fillers to understand the changes in electrical properties in epoxy/carbon compounds and their derivatives. GFs exhibit significant potential as a nano/microfiller due to their relatively large size which plays an important role in interfacial charge, high strength, excellent thermal, electrical conductivities, and cost-effectiveness compared to its alternatives like graphite nanoparticles and graphite nanotubes [8,9].…”

“…In polymers with dipolar groups, the mechanism of orientation of dipolar side groups or dipolar segments corresponds to Debye relaxation polarisation [10]. The dielectric properties of composites depend largely on several factors, including the nature of the filler/matrix interface, the surface area of the filler, and the inherent conductivity of the filler [8]. At low electric field frequencies, free charges accumulate at the filler/matrix interfaces due to the difference in electrical conductivity in such composites; this is called interfacial polarization.…”

“…The dielectric behaviour is governed by Maxwell-Wagner (MW) interfacial polarisation when one component has a higher electrical conductivity than the other [11,12]. Above the percolation threshold at which the transition between insulation and electrical conductivity can be observed, the dielectric response of MW materials is additionally affected by the electron conduction process [8].…”

“…GFs exhibit significant potential as a nano/microfiller due to their large size which plays an important role in interfacial charge, high strength, excellent thermal and electrical conductivities, and cost-effectiveness compared to alternatives like graphite nanoparticles and graphite nanotubes [8,9]. Several literatures have studied composite materials based on epoxy/graphite composite or their functional analogues.…”