Channarong Banmongkol

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

In this study, the effect of blending on physical and electrical properties of low-density polyethylene (LDPE) was investigated. Two kinds of LDPEs whose densities are evaluated to be 0.9179 g/cm3 and 0.9192 g/cm3, respectively, were used and blended according to different blend ratios. The LDPE with a blend ratio of 50 wt% had the lowest impulse breakdown strength, FBImp, at 30°C. However, the LDPE with a blend ratio of 50 wt% also had the highest FBImp at 90°C among all specimens. The DC breakdown strength, FBDC, decreased with the increase of the blend ratio at 30°C but increased at 60°C and 90°C. However, the FBDC did not depend on the blend. The current densities for all specimens were almost the same at 30°C, but decreased with a blend ratio up to 75 wt% at 90°C. By analyzing X-ray diffraction (XRD) patterns, we found that the crystal size in the (020) plane increased with a blend ratio up to 50 wt%, and the LDPE with a blend ratio of 50 wt% had the largest crystal size in the (020) plane among all specimens. It was found that the FBImp was strongly related to the crystal size in the (020) plane.

High-field electrical properties of new LDPE films prepared using metallocene catalyst

Now low-density polyethylene (M-LDPE) prepared using metallocene catalyst has narrower composition distribution and molecular weight distributions than linear low-density polyethylene (LLDPE) using Ziegler catalyst. The authors 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 high-field current was much reduced in M-LDPE with a low melting point. The impulse breakdown strength of M-LDPE increased 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 the fact that M-LDPE with a low melting point includes more low-molecular-weight components. We also discuss the effects of antioxidant on the electrical properties of M-LDPE. We compared the electrical conduction and breakdown strength of undoped M-LDPE and antioxidant-doped M-LDPE. Differences in their electrical properties were minor. It was found that the excellent properties of M-LDPE do not depend on the effects of antioxidant.

High-field electrical properties of LDPE films prepared using new catalyst

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 high-field current was much suppressed in m-LDPE with a low melting point. The impulse breakdown strength of m-LDPE increased with the decrease of temperature. The insulating properties of m-LDPE with a low melting point were improved at 30/spl deg/C. These results were explained by a fact that m-LDPE with a low melting point includes more low-molecular-weight components.

Breakdown and space charge of LDPE films prepared using metallocene catalyst

Polyethylene (PE) has been widely used as electrical insulation for power cables because of its excellent electrical and mechanical properties. Low density PE (LDPE) prepared using a high pressure process has been widely used as insulating polymer of power cables. In this paper, the authors have investigated the performance of new LDPE prepared using metallocene catalyst (m-LDPE) as electrical insulating material. m-LDPE has narrower composition and molecular-weight distributions than LDPE. High-field electrical properties of m-LDPE at 90/spl deg/C were compared with those of the other LDPEs. In addition, the prestress effect and the effect of space charge on breakdown strength were discussed.

High-field phenomena in LDPE with various physical and chemical properties

The high-field phenomena in low-density polyethylene (LDPE) with various physical and chemical properties have been investigated at 90/spl deg/C. The objective of this paper is to present the influence of film density and carbonyl groups. The high-field conduction and the electrical breakdown were found to strongly depend upon the film density. It was also shown that not only the concentration but also the type of carbonyl groups affect the high-field conduction.

Effects of oxidation on electrical conduction and breakdown of LDPE films with different densities

The effects of oxidation on electrical conduction and breakdown strength were studied in two kinds of LDPE films with different densities. Oxidation enhanced more the conduction current in the LDPE film with density of 0.9172 g/cm/sup 3/ (l-LDPE) than that with density of 0.9255 g/cm/sup 3/ (h-LDPE). This result was attributed to the easier carrier transport in unoxidized region of l-LDPE. Both oxidized specimens had almost the same impulse breakdown strength (F/sub Bimp/) except when the absorbance of C=O groups (A) is higher than 0.6. At 30/spl deg/C, it was considered that the increase in the number of injected electrons which initiate avalanche decreased F/sub Bimp/ for A<0.1, but the carrier scattering due to C=O groups increased F/sub Bimp/ for A>0.1. However, thermal or electromechanical breakdown mechanism would take part in the breakdown process at higher temperatures. The dc breakdown strength (F/sub Bdc/) decreased with oxidation and h-LDPE showed a higher one. These results suggested a contribution of thermal mechanism to the breakdown.

Effect of oxidation and space charge on high-field phenomena of low-density polyethylene prepared by metallocene catalyst

We used low-density polyethylene (LDPE) prepared using metallocene catalyst (m-LDPE) and linear-LDPE prepared using Ziegler catalyst (LLDPE). The current density of slightly oxidized m-LDPE and LLDPE films is lower than that of unoxidized ones. The breakdown strength of m-LDPE and LLDPE films decreases with the progress of oxidation. In addition we consider the effect of space charge by the pre-stress method. It is found that m-LDPE has lower current density than LLDPE, but the sum of space charge of m-LDPE is larger than that of LLDPE.

Influence of molecular structure on high-field phenomena in LDPE films

The authors have investigated the high-field phenomena in low-density polyethylene (LDPE). The objective of this paper is to study the relationship between molecular structure and the high-field phenomena at high temperature near the melting point of LDPE. The results can be summarized as follows. (1) The high-field current and the breakdown strength strongly depend upon film density determined by the concentration of methyl group. (2) The breakdown strength can be qualitatively estimated from the measurement of the high-field current. This incident as well as the above result suggests that a thermal process takes part in the dielectric breakdown of LDPE film at 90/spl deg/C. (3) Both the type and the concentration of carbonyl groups affect the high-field current of LDPE.