# Effect of Environmental Temperature on the Insulating Performance of Epoxy/MgO Nanocomposites
## 1 Introduction
The model states that if the conductive block formed by the filler particles and the polymer conductive block is parallel to the direction of the heat flow, the thermal conductivity is the highest if the filler particles are distributed in parallel with the polymer matrix, and if the filler particles are distributed in series with the polymer matrix, the thermal conductivity is the lowest [21]. [PERSON] et al. focused on the effect of nano-MgO on the space charge, Direct Current (DC) conductance, and dielectric properties of epoxy resins [22]. [PERSON] et al. found that nano-MgO can improve the DC tracking resistance of the epoxy matrix [23]. Moreover, [PERSON] et al. demonstrated that the addition of MgO nanoparticles can improve the tracking resistance of epoxy resins, and the best improvement was obtained when the nanoparticle content was 5 wt% [24]. [PERSON] et al. conducted a broadband dielectric response test in a wide temperature range (-20 to 120 \({}^{\circ}\)C) and found that the relative dielectric constant of nano-doped epoxy was lower than that of pure EP. When the content of MgO nanoparticles was 2%, the relative dielectric constant was the smallest [25]. [PERSON] et al. cured an MgO/EP composite at 160 \({}^{\circ}\)C for two days and measured its dielectric properties. It was found that the dielectric loss of the samples decreased to varying degrees [26]. [PERSON] et al. studied the dielectric performance of Low Density Polyethylene/MgO (LDPE/MgO) nanocomposites under a high Alternating Current (AC) voltage and estimated the content of MgO nanoparticles under an application of 50 and 200 Hz LDPE based on the dissipation current waveform under a high electric field. It was observed that the MgO nanoparticle content was dependent on the volume resistivity and relative dielectric constant under 50 and 200 Hz AC electric fields [27]. [PERSON] et al. studied the space charge behavior of LDPE/nano-MgO composites containing MgO particles of different particle sizes at a high temperature and electric field. The results showed that between 30 and 60 \({}^{\circ}\)C, the electric field increased with an increasing amount of MgO nanoparticles. In terms of suppressing the injection of packet-like charges and reducing electric field distortion, MgO nanoparticles have a better effect than MgO micro-particles, especially when they contain a small amount of MgO nanoparticles [28]. [PERSON] et al. studied the electrical properties of LDPE/MgO nanocomposites under DC voltage, including volume resistivity and breakdown strength, and found that the DC breakdown strength and volume resistivity of the composites increased when adding MgO nanofillers [29]. [PERSON] et al. studied the electrical properties of magnesium oxide nanocomposites under DC voltage. Due to the addition of MgO nanofillers, the space charge of the composites under high electric fields was reduced. The mechanism by which MgO nanofillers improve the DC characteristics of LDPE has also been discussed [30]. At present, there is an urgent need for high-temperature and high-pressure insulating materials, and there are few reports on the insulation properties of nano-MgO/EP composites at different environmental temperatures. The insulation performance of nano-MgO/EP composite dielectrics at different temperatures has important practical applications. Therefore, this article studied the dielectric and breakdown characteristics of nano-MgO/epoxy composites at different temperatures. A blended solution method was used to prepare nano-MgO/epoxy composites (named epoxy-MgO composites) with different mass fractions, and the thermal conductivity and volume resistivity performance were analyzed. The influence of temperature on the electrical performance of nano-MgO/epoxy composites (epoxy-h-BN composites) with different mass fractions, including the dielectric performance and breakdown performance, was studied.