To investigate the long-term effects of electro- thermal-mechanical multi-physical fields on the performance and space charge characteristics of biaxially oriented polypropylene (BOPP) films used in dry-type DC capacitors

this study examines a 5.8 μm thick BOPP film aged under conditions of 150 kV/mm

80 °C

and 10 N for durations of 0

168

360

and 720 hours. The physicochemical properties

electrical properties

space charge

and trap characteristics are analyzed. The results show that under long-term multi-physical field action

the molecular weight of the polypropylene film decreases

and molecular chains break; the surface crystal ring density and diameter distribution remain unchanged

while the surface defect size

grain boundary defects

crystallinity

and lamellar thickness gradually increase. As the aging time increases

the breakdown field strength of the film decreases rapidly at first and then slowly; the dielectric constant first decreases and then increases; the dielectric loss and volume conductivity both increase significantly. Positive and negative charge injections appear successively inside the film

and the electric field distribution during polarization changes from anode enhancement and cathode reduction to simultaneous enhancement at both anode and cathode. The breakdown performance of the film is closely related to charge behavior and internal structural changes. At the nanoscale

increased space charge injection leads to an increase in internal defect size and trap density at the microscale

resulting in a decrease in breakdown field strength of the BOPP film at the macroscale. This study provides theoretical basis and experimental data reference for improving the preparation process of BOPP films for dry-type DC capacitors.