# Effect of Environmental Temperature on the Insulating Performance of Epoxy/MgO Nanocomposites
## 3 Results and Discussion
### Dielectric Performance  
The dielectric constant and dielectric loss of the pure epoxy resin and the MgO/epoxy composites with different mass fractions at environmental temperatures of 20, 80, and 150 \({}^{\circ}\)C were measured. As shown in Figure 4, the dielectric constant of the epoxy composites gradually increased with the increase in MgO nanofillers. It was hypothesized that as the content of MgO nanofillers increased, the distribution of the MgO nanofillers in the epoxy-matrix became denser, and the degree of cross-linking in the matrix system increased, which enhanced the polarity effect of the interface, thereby increasing the dielectric constant of the composites. Comparing the dielectric constants at different temperatures, it was found that the dielectric constant of the epoxy composites increased with temperature because the positive and negative ions inside the material migrate in opposite directions under the action of an electric field, resulting in a non-zero average dipole moment. As the temperature increased, the decrease in the binding force between the positive and negative ions led to an increase in its polarization, and the dielectric constant increased. In addition, as the frequency increased, the dielectric constant of the epoxy composites decreased. This may be due to the action of the electric field, where the dipoles were deflected by the electrostatic force and arranged regularly along the direction of the electric field, showing polarity to the outside. As the frequency increased, the steering of dipoles may not keep up with the change in the direction of the electric field [17]. Figure 3: Volume resistivity of MgO/epoxy composites. As shown in Figure 5 the dielectric loss first decreased and then increased with the MgO nanoparticle content. When the content of MgO nanoparticles was 1%, the dielectric loss reached the minimum value, indicating that a small amount of nano-doping can reduce the epoxy resin. The dielectric loss of the composite dielectric then decreased, which may be because the nano-MgO and epoxy resin were tightly bonded in the interaction zone, making it difficult to turn the molecular chains in the composite dielectric, which inhibited the turning polarization process and reduced the steering polarization loss. When the content of MgO nanoparticles was greater than 1%, the dielectric loss increased with the increase in MgO nanoparticle content. This may be due to the overlap in the interaction zone, which formed a local conduction channel inside the material and increased the conductive. On the other hand, as the doping concentration increased, the agglomeration effect of MgO nanoparticles led to an increase in dielectric loss. At low temperatures, the dielectric loss of the epoxy composites increased with the increase in frequency. At high temperatures, the dielectric loss decreased sharply with an increasing frequency. This may be because composites mainly exhibit a relaxation polarization and conductive loss in the electric field. At lower temperatures, composite dielectric loss consists mainly of relaxation polarization loss, and conductive loss is inversely proportional to frequency, which has a smaller effect at low temperatures. The dielectric loss thus increased with frequency. At high temperatures, the kinetic  
Figure 4: Dielectric constant of nano-MgO/epoxy composites as a function of frequency at (**a**) 20 \({}^{\circ}\)C; (**b**) 80 \({}^{\circ}\)C; (**c**) 150 \({}^{\circ}\)C.  
energy of the carriers inside the composite material increased, thereby improving carrier mobility, and the main body consisted of a conductive loss. With an increase in frequency, the change time of the electric field direction and the composite dipoles turn. When such a time is similar, the relaxation polarization loss gradually increases, causing the dielectric loss of composites to increase rapidly.