Origin of low dielectric permittivity in crosslinked cellulose/ Kevlar fiber composites as revealed via molecular dynamics simulation

Abstract

The mismatch of the dielectric constant of oil-paper insulation mainly affects the unreasonable field strength distribution of oil-paper insulation under alternating current conditions. Reducing the dielectric constant of insulation paper by using low dielectric constant Kevlar is an effective way to modify natural fibers. However, the bonding capability of Kevlar and natural fibers is poor. Based on the molecular simulation method, the influence mechanism of different butanetetracarboxylic acid (BTCA) contents on the dielectric constant of cellulose-Kevlar composite structures is analyzed from the perspective of free volume, bond length and angle distribution, and glass transition temperature. The bonding performance of Kevlar and cellulose molecular chains is strengthened when BTCA content is increased and the fractional free volume of the composite structure is reduced. Such a reduction restricts the movement of polar groups and decreases the dielectric constant of the composite structure. Further increasing the BTCA content will raise the number of polar groups and gaps in the system, which is conducive to the establishment of the turning polarization, leading to an increase in the dielectric constant. Within the range of BTCA content selected in the paper, the dielectric constant of the composite structure first decreases, then rises with an increase in BTCA content, and finally reaches the minimum value (3.53) when the BTCA content is 3%. The crosslinking modification method achieves the purpose of improving the dielectric properties of the composite structure and provides a certain theoretical basis for the study of low dielectric constant insulating paper.