Author(s):
1. Slavica Maletić, Univerzitet u Beogradu, Fizički fakultet, Studentski trg 12, Beograd, Serbia
2. Nataša Jović Orsini, VINČA Institute of Nuclear Sciences – National Institute of the Republic of Serbia, Department of Th, Serbia

Abstract:
Epoxy resins are the most widely used conventional thermosetting plastics with applications in many industries, including automotive, chemical, aerospace, military, electronics and computers. Most cured epoxy resins are amorphous, non-conducting thermosets that exhibit good mechanical strength, toughness, and resistance to corrosion and strong chemicals. Numerous epoxy-based composites have been created by doping an epoxy matrix with various fillers, such as ceramics, metal compounds, and carbon-based nanostructures. Carbon fillers, such as graphite, graphene, carbon nanotubes, carbon black, can be used to reinforce electrically insulating epoxy matrices in order to enhance mechanical strength, thermal conductivity and flame resistance, without compromising the insulating properties of polymer composites. Electrically insulating materials with high thermal conductivity performance are required for portable electronics and can also be usaed as thermal adhesives, flame retardants, and high-voltage insulators. A comparative analysis of the dielectric properties of composites based on a bisphenol A–epichlorohydrin (DGEBA) epoxy matrix loaded with two types of graphite with different degrees of exfoliation is presented here. Graphite flakes (GF) obtained by prolonged milling of bulk graphite, and exfoliated expanded graphite (EEG) sheets were used as fillers to obtain two series of composites. The loading amounts of the fillers ranged from 1 wt.% to 15 wt.% for GF flakes and 7 wt.% for EEG sheets. Dielectric measurements were carried out over a wide temperature range (170–350 K) and a low frequency range (30 Hz–120 kHz). We analyzed the morphology and microstructure of the composites using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Dielectric measurements revealed that all composites filled with graphite flakes (GF) are electrically insulating. Their dielectric losses are low (tanδ < 0.25). Composites loaded with exfoliated expanded graphite (EEG) sheets exhibit different dielectric performance. Only the epoxy/EEG-1 composite has a tan of less than 0.48 in the low-frequency range, whitch is acceptable for applications such as high-charge storage capacitors. Non-Ohmic conduction through the barrier-tunneling effect between EEG flakes separated by an epoxy layer was observed in the epoxy/EEG-3 and epoxy/EEG-5 composites. Significant increases in dielectric permittivity (εr=70), tangent loss (tanδ=40.1103 at 30 Hz) and AC conductivity (AC) were observed in the epoxy/EEG-7 composite with 7 wt.% EEG loading. Its AC conductivity at low frequencies was five orders of magnitude higher than that of pure epoxy and remained independent of frequency, suggesting the presence of long-range conductive pathways and an Ohmic conduction mechanism over macroscopic distances.

Key words:
composites, graphite nanosheets, dielectric properties, percolation treshold

Thematic field:
SYMPOSIUM A - Science of matter, condensed matter and physics of solid states

Date of abstract submission:
18.03.2026.

Conference:
Contemporary Materials 2026 - Savremeni Materijali

Applied paper from author