Theoretical study on the mechanisms of polyethylene electrical breakdown strength increment by the addition of voltage stabilizers

AbstractA theoretical investigation on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels is accomplished. The addition of aromatic carbonyl and carboxyl compounds as voltage stabilizers may increase the electrical breakdown strength of polyethylene. The HOMO-LUMO energy gaps, the ionization potentials, the electron affinities, and the reorganization energies at the ground states of a series of aromatic carbonyl and carboxyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The 24 isomerization reactions at the S0 and T1 states, including the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path (MEP) by the intrinsic reaction coordinate (IRC) theory, are obtained at the same level. The results show that 4,4'-didodecyloxybenzil (Bd) molecule, which has much smaller HOMO-LUMO energy gap, much larger reorganization energy than others, and excellent compatibility with polymers matrix, can increase the electrical breakdown strength effectively. This result is in good agreement with the available experimental findings. FigureThe addition of acetophenone as voltage stabilizer can increase the alternate current breakdown strength of cross-linking polyethylene (XLPE). Potential energy surface of keto-enol isomerization reaction of acetophenone has been investigated. The mechanism of voltage stabilizer for increasing electrical breakdown strength of XLPE has been suggested. It is expected to provide reliable information for preparation of the insulation material of high-voltage cable exceeding 500 kV.