Significant Improvement in Dielectric Properties and Energy Density of Polypropylene Films Based on Surface Modification

Biaxially oriented polypropylene (BOPP) is a polymer material that has been widely used in the field of film dielectric capacitors, but its low energy storage density limits its further applications. In this paper, we propose a method for functionalizing the molecular structure of the surface layer of the BOPP film to improve the breakdown strength and energy density. The introduced polar group can provide more deep traps to capture the charge injected by the electrode, which can inhibit the transport of charge and avoid the destruction of the polymer molecular chain, thereby improving the breakdown strength and energy storage density of the film. The experimental results show that the $D C$ breakdown strength of the film modified by hydroxyl reaches $717 \mathrm{kV} / \mathrm{mm}$, which is about 1.1 times that of pure BOPP, and the maximum discharge energy density of it reaches $5.46 \mathrm{~J} / \mathrm{cm}^{3}$ at $750 \mathrm{kV} / \mathrm{mm}$, which is 14.8 % higher than that of pure BOPP $\left(4.76 \mathrm{~J} / \mathrm{cm}^{3}\right)$ at $700 \mathrm{kV} / \mathrm{mm}$.