Properties of tree propagation from a simulated tree channel in LLDPE prepared by metallocene catalyst

Abstract

In this paper, properties of tree propagation from a simulated tree channel in linear low density polyethylene (LLDPE) prepared by metallocene catalyst are compared with those in low density polyethylene (LDPE) prepared by Ziegler catalyst. The inception voltage of the tree propagation is obtained when AC ramp voltage is applied. The inception voltage of the tree propagation for the LLDPE is higher than that for the LDPE. The time required for the tree propagation and the shape parameter m in the time Weibull probability distribution are also obtained under application of AC constant voltage. In the LDPE, the tree propagation characteristics are divided into three different types according to applied voltage; early/random failure type (m/spl les/1) in the low voltage range, fatigue failure type (m>1) in the moderate voltage range and early/random failure type (m/spl les/1) in the high voltage range. However, the tree propagation characteristics in the LLDPE are divided into only two different types; fatigue failure type (m>1) in the low and moderate voltage ranges and early/random failure type (m/spl les/1) in the high voltage range. These differences in the tree propagation properties are because the LLDPE has few structural weak points which act as the starting point of the tree propagation, and also has a great number of tie molecules.