Mechanisms on electrical breakdown strength increment of polyethylene by aromatic carbonyl compounds addition: a theoretical study

Abstract

A theoretical investigation is accomplished on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels. It is found that the addition of aromatic carbonyl compounds as voltage stabilizers is one of the important factors for increasing electrical breakdown strength of polyethylene, as the additives can trap hot electrons, obtain energy of hot electrons, and transform the aliphatic cation to relatively stable aromatic cation to prevent the degradation of the polyethylene matrix. The HOMO-LUMO energy gaps (E(g)), the ionization potentials (IPs), and electron affinities (EAs) at the ground states of a series of aromatic carbonyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The theoretical results are in good agreement with the available experimental findings, show that 2,4-dioctyloxybenzophenone (Bzo) and 4,4'-didodecyloxybenzil (Bd) molecules can effectively increase the electrical breakdown strength when they are doped into polyethylene because of their much smaller E g values than all the other studied aromatic carbonyl molecules and excellent compatibility with polymers matrix.

A New Application Area for Fullerenes: Voltage Stabilizers for Power Cable Insulation

“…The rich chemistry of C 60 permits a wealth of fullerene derivatives, [ 9 ] such as the widely studied [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM), [ 10 ] which carries a solubilizing side chain that greatly enhances the processability from common organic solvents.…”

Tailored side‐chain architecture of benzil voltage stabilizers for enhanced dielectric strength of cross‐linked polyethylene

“…It was shown that in particular Et 12 is an attractive voltage stabilizer, which can be easily prepared from the commercial precursor p ‐anisoin and features dodecyloxy side chains that offer increased miscibility with polyethylene. Moreover, the two side chains are attached at the para position of the two phenyl rings via ether linker groups, which due to their strong electron donating effect significantly reduce the IP from IP ∼ 9.2 eV for neat benzil to IP ∼ 7.6 eV for Et 12 , as modeled by Zhang et al using density functional theory calculations …”

Trap mechanism based on frontier molecular orbitals of additives in polyethylene insulators: A theoretical study and molecular design strategy

“…In addition, the acetphonene was demonstrated that keto‐enol tautomerism reactions focus on S 0 and T 1 . In previous works of our group, the tautomerism reaction potential barriers at S 0 and T 1 of acetophonene are 62.31 kcal/mol (2.7 eV) and 28.71 kcal/mol (1.24 eV), respectively, which are much smaller than the average CC bond energy(82.95 kcal/mol = 3.59 eV) of polyethylene . The discussion above indicates acetophoene can undergo isomerization reaction, absorbing and consuming the energies of “hot electrons.” As a result, it can play an important role on inhibiting the electric breakdown.…”

“…In theoretical and computational chemistry, the vertical EA and IP could also be obtained by formulas (5) and (6), where represents the energy of neutral molecule in their lowest energy geometry, represents the energy of anion with the neutral geometry, and represents the energies of cation with the geometries of neutral geometry. …”

“…So called “hot electrons” are formed during the process of charges transportation and accumulation as high voltage was stressed on the insulated cables for long time, and there is much energy released. The “hot electrons” could further excite the defect parts from ground state to excited state (the excited energy 6.01 eV of C 8 H 16 O calculated by TDDFT is given in Table ), or break CC bond of polyethylene (3.59 eV CC breaking energy). Obviously, CC breaking is easier and result in electric treeing initiated in the end.…”