Full-Temperature Range Relaxation Analysis of Ternary Epoxy Composites Doped With Second-Phase Fillers

Analyzing the dielectric relaxation process is essential for further optimization and application of the formulated system. To clarify the impact of two excellent second-phase toughening fillers, liquid rubber and polyethersulfone, on the dielectric relaxation process of epoxy resins, we measured the broadband dielectric spectroscopy of the composite material from −40 °C to 200 °C. Various dielectric relaxation models (Havriliak-Negami model, complex AC conductivity, complex electric modulus) are rationally used to analyze through the in-depth understanding of the dielectric spectrum information in each temperature range. The results indicate that incorporating hydroxyl-terminated liquid nitrile rubber (HTBN) introduces the α relaxation process in the low temperature region and the interfacial polarization process in the medium temperature region. In contrast, the hydroxyl-terminated polyethersulfone (PES), which has strong interfacial bonding ability with epoxy resin, does not introduce any new relaxation process. Further analysis and fitting of the dielectric spectrum data across the full-temperature range were performed. In the low temperature region, the β relaxation intensity decreased with the introduction of PES. In the medium temperature region, both the relaxation time and activation energy of the interfacial polarization increase with higher PES doping, owing to the introduction of the highly polar sulfone group. In the high temperature region, the introduction of fillers increases the contribution of electrode polarization. Additionally, the carrier transport process is suppressed as PES content increases in the ternary formulation system. This study investigates the dielectric relaxation process of ternary composites, which may facilitate the application of this formulation system in electrotechnical equipment.