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/cm(3) (l-LDPE) than that w ith a high density of 0.9255 g/cm(3) (h-LDPE). This result was attribu ted to the easier carrier transport in the unoxidized region of l-LDPE . Both oxidized specimens had almost the same impulse breakdown streng th (F-Bimp), except when the absorbance of carbonyl groups (A) was hig her than 0.6, At 30 degrees 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 mechan ism would take part in the breakdown process at higher temperatures. T he dc breakdown strength (F-Bdc) decreased with oxidation, and h-LDPE showed a higher F-Bdc than l-LDPE, These results suggested a contribut ion of the thermal mechanism to the breakdown. Space charge also seeme d to play a role in the breakdown process.