# Effect of Environmental Temperature on the Insulating Performance of Epoxy/MgO Nanocomposites
## 1 Introduction  
Epoxy resins are widely used in electronics due to their good electrical, thermal, and processing properties, being one of the main materials used in electrical equipment [1; 2]. However, epoxy resins exhibit poor heat dissipation, which significantly shortens the service life of insulating equipment [3; 4]. In recent years, higher requirements have been demanded on the electrical and thermal properties of epoxy resins owing to the development of the power industry toward high voltage and large capacities [5; 6]. The improvement of the performance of polymer matrix composites using inorganic particles has been thoroughly investigated [7; 8]. In 1994, [PERSON] first proposed the concept of nanocomposite dielectrics, which refers to a material composed of organic particles with a diameter of 1-100 nm in the polymer matrix [9]. Since then, nanocomposite dielectrics have become an electricalinsulating material and a focus of extensive research for device applications and other fields. Studies have demonstrated that the thermal conductivity, dielectric, breakdown, and other main electrical properties of epoxy resins can be improved by doping with different kinds of nanoparticles, such as silicon dioxide, titanium dioxide, aluminum oxide, and magnesium oxide, among others. At present, the influence of nanoparticles on the thermal properties and dielectric performance of epoxy resins has been studied extensively [10; 11; 12; 13; 14; 15; 16; 17]. It has been demonstrated that the introduction of micron-modified particles can increase the dielectric constant of epoxy resins, because of the higher dielectric constant of the organic particles compared with the epoxy matrix. Furthermore, Maxwell-Wagner-type interfaces can be introduced by micro-particles to increase the dielectric constant [11]. [PERSON] et al. demonstrated that titanium dioxide epoxy composites exhibit better insulation performances than epoxy resins [12]. [PERSON] et al. have shown that the electrical strength of nano-TiO\({}_{2}\) and epoxy resin composites was much higher than that of the pure epoxy resin and the micro-doped samples, at a frequency of 60 Hz [13]. [PERSON] et al. found that the glass transition temperature of epoxy resins was higher than that of epoxy resins with nanolayered silicate at 20 \({}^{\circ}\)C, which effectively reduced the dielectric constant and dielectric loss at a high temperature [16]. [PERSON] et al. reported that the electrical strength of epoxy resins doped with nano-Al\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\) increased when the nanoparticle content was 1% [17]. [PERSON] et al. investigated the dielectric performance of nanotitanium dioxide epoxy resins, demonstrating that nanofillers can reduce the interface polarization characteristics of traditional materials and reduce the accumulation of internal electric fields [18]. [PERSON] et al. developed a method for obtaining nanofiller and micro-filler mixture composites, which improved their insulation properties while maintaining a low thermal expansion [19]. Nano-MgO is used in the field of high voltage insulation due to its high thermal conductivity, good thermal stability, and suppression of space charge accumulation. [PERSON] et al. investigated the effect of nano-MgO on the thermal conductivity and dielectric performance of epoxy and found that doped nano-MgO can effectively improve the relative dielectric constant, dielectric loss, and thermal conductivity and the improvement of the thermal conductivity was much greater than that of micron-doped Epoxy (EP) with the same mass fraction [20]. [PERSON] et al. proposed a thermal conductivity model for nanothermal conductive materials.