Introducing Chlorine Into Epoxy Resin to Modulate Charge Trap Depth in the Material

Abstract

The epoxy insulators in DC gas insulated transmission lines (GIL) tend to accumulate surface charges, which causes insulation flashover. Increasing the surface conductivity of epoxy resin, which can restrain the accumulation of surface charges on the epoxy insulator, is a potential method to improve the insulation performance of DC GIL insulators. The conductivity of polymer dielectric is strongly influenced by the charge trap characteristics of the polymer. In this work, we introduce chlorine with strong electronegativity and a larger atomic radius into the epoxy group segment of epoxy resin to improve the distributed energy level structure, which in turn reduces the electron trap depth, so as to increase the surface conductivity of epoxy insulating material without affecting its intrinsic dielectric strength. Based on the results of quantum chemistry calculation, the modulation laws of introduced chlorine (including the chlorine in form of hydrolyzable chlorine atom and non-hydrolyzable chlorine atom) on distributed energy levels of epoxy resin molecule are anticipated. These laws are explained from the microscopic perspectives of electron energy structure and electron cloud offset. Both the inductive effect of the chlorine atom and the conjugation effect of 2p electron orbital of oxygen atom in epoxy group impact the distributed energy levels through changing the spatial distribution of electron cloud density between and on valence bonds.

Methyl and carbon–carbon double bond in anhydride molecules modulated surface charge trap depth of epoxy materials

“…When the orbital electrons between the valence bonds are attracted by the group, the orbital electrons shift towards the positively charged center of the group, and the electron cloud density between the positively charged center and the atom whose orbital electrons have shifted increases. This makes the electron orbital system between the valence bonds in the segment more stable, so the energy of the orbital electrons (conduction band electrons) moving between the valence bonds decreases, the LUMO energy level of the segment decreases [20]. When the orbital electrons on the valence bonds are attracted by the electron-absorbing group, the orbital electrons shift towards the positively charged center of the group.…”

“…In this way, the electron cloud density on the valence bonds decreases, and the overlap of the electron cloud is reduced. This makes the covalent bonds formed between the bonding atoms more unstable, so the energy of the orbital electrons (valence band electrons) moving on the valence bonds increases, the HOMO energy level of the segment increases [20].…”

“…In the resin segment of the DGEBA/Me-HHPA molecule, the 2p orbital of the oxygen atom in the ether oxygen group connected with the benzene ring forms a p-π conjugation with the large π orbitals of the benzene rings, which makes the electron cloud density between the conjugated atoms lower and the internal energy of the conjugated system lower, thus forming a more stable conjugated system [20]. In contrast to those of the DGEBA/Me-HHPA molecule, the anhydride segments of the DGEBA/Me-THPA molecule are curled toward the resin segment in three-dimensional space, as can be seen in figure 3(c).…”

High thermal conductivity insulating AlN/poly(m-phenylenedicarbonyl-m-phenylenediamine) paper realized by enhanced compatibility: a selection of appropriate coupling agent

“…Figure 7(a) exhibits the carrier trap distribution of different samples. During the carrier transport process, carriers driven by the external electric field are continuously refracted in the insulating paper, consuming their kinetic energy, and carriers are thus more easily to be trapped by traps [26,27]. This characteristic of composite paper is a clear mirror that indicates its interface defects generated between the inorganic fillers and organic matrix.…”