Study on the Influence of Organic–Inorganic Interface Properties on Breakdown Strength and Thermal Properties of MgO/PLA Composites

Polylactic acid (PLA) is expected to be widely used in green power equipment manufacturing due to its good mechanical properties and biodegradability. In this paper, the effects of MgO with different particle sizes and mass fractions on the thermal and electrical properties of PLA composites were studied. The experiment found that with the increase in MgO particle sizes and mass fractions, the thermal conductivity of MgO/PLA composites showed a rising trend, which was up to 165.4% higher than that of pure PLA. However, the heat resistance first increases and then decreases. For the electrical properties of MgO/PLA composites, the breakdown strength and volume resistivity decrease with an increase in MgO particle size and mass fraction. In order to further study the influence mechanism of the introduction of MgO with different particle sizes and mass fractions on the thermal and electrical properties of MgO/PLA composites, molecular dynamics simulation was used to simulate the glass transition temperature (Tg) of PLA composites doped with MgO of different particle sizes, and it was found that MgO doping weakened the movement of the PLA molecular chain segment. Using density functional theory (DFT) calculations, it was found that in the MgO and PLA system, electrons have a tendency to migrate from the PLA matrix to MgO, which causes the formation of electron traps at the inorganic–organic interface and affects its electrical properties. The purpose of this study is to provide a theoretical reference for PLA composites in the manufacture of power equipment.