Effects of Oxidation on Electrical Conduction and Breakdown of Low-Density Polyethylene Films with Different Densities

Oxidation more greatly enhanced the conduction current in low-density polyethylene with a low density of 0.9172 g/cm3 (ℓ-LDPE) than that with a high density of 0.9255 g/cm3 ( h-LDPE). This result was attributed to the easier carrier transport in the unoxidized region of ℓ-LDPE. Both oxidized specimens had almost the same impulse breakdown strength (F Bimp), except when the absorbance of carbonyl groups (A) was higher than 0.6. At 30°C, the increase in the number of injected electrons which initiate an avalanche decreased F Bimp for A<0.1 but the carrier scattering effect due to carbonyl groups increased F Bimp for A>0.1. However, a thermal or electromechanical breakdown mechanism would take part in the breakdown process at higher temperatures. The dc breakdown strength (F Bdc) decreased with oxidation, and h-LDPE showed a higher F Bdc than ℓ-LDPE. These results suggested a contribution of the thermal mechanism to the breakdown. Space charge also seemed to play a role in the breakdown process.