Fluorination effects on polypropylene membrane for enhanced transformer oil purification

Abstract In this study, a multi-scale approach is employed to systematically investigate the improvement mechanism of surface fluorination treatment on the performance of polypropylene membrane for filtering transformer insulation oil impurities. The multi-physics field simulation results indicate that the insulation oil outlet temperature reaches 323 K under the transformer’s rated working conditions, thereby providing boundary conditions for the filtration process. Density functional theory calculations reveal that fluorination reduces the HOMO and LUMO energy levels of polypropylene, narrows the energy gap, and significantly enhances the dipole moment and polarizability. This improvement leads to an enhanced charge storage density and stability, thus improving the electret characteristics as well as the electrostatic adsorption capability of the membrane. Molecular dynamics simulations demonstrate that the absolute value of interaction energy between polypropylene and H 2 O, DBDS, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">SO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> </mml:math> , and Cu 2+ increases after fluorination, particularly at 323 K, where the adsorption performance is optimal. The surface fluorination experiment optimized the fluorination process parameters to prevent material damage and verified that the initial surface potential of the fluorinated polypropylene membrane increased by 5.7%, with the charge half-life extended by 1.8 times, thus confirming the simulation results. The multi-scale systematic study reveals that fluoride modification significantly enhances the filtration efficiency of polypropylene membrane by strengthening the synergistic effect of electret characteristics and impurity adsorption capacity. Furthermore, it establishes the feasibility of in situ filtering of insulation oil under actual working conditions, offering theoretical and technical support for the development of high-performance insulation oil purification membrane.