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.
MI
M2M3 M4 M5 New Low Density Polyethylene (m-LDPE) prepared using metallocene catalyst has a narrower composition distribution and a molecular weight distribution than Linear-Low Density Polyethylene (LLDPE) using Ziegler catalyst. We compared the electrical insulating properties of m-LDPE films and conventional LLDPE films. The high-field current of m-LDPE was found to be lower than that of LLDPE. The difference in current increased with the decrease of temperature. The highfield current was much suppressed in m-LDPE with a low melting point. The impulse breakdown strength of m-LDPE raised with the decrease of temperature. The insulating properties of m-LDPE with a low melting point were improved at 30°C. These results were explained by a fact that m-LDPE with a low melting p o i n t i n c l u d e s m o r e l o w -m o l e c u l a r -w e i g h t components. 5.54 0.904 99.0 5.75 0.900 97.3 5.74 0.896 90.9 5.56 0.9 18 116.4 10.3 0.912 111.4
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