Some mechanical aspects of the propagation of water trees in polyethylene

In a previous communication [1] we have given a new idea to account for the propagation of water trees in polyethylene: the propagation of a channel of a water tree would be a fracture phenomenon similar to the propagation of a crack in a mechanically stressed material. Due to the presence of water in the channels, the parallel phenomenon would be the so-called environmental stress-cracking (ESC); but, unlike ESC, the stress, originated from electrostatic pressure, would be directly exerted at the tips of the channels. The electric field being alternating, the phenomenon should be compared with fatigue ESC. A theoretical model for the propagation of a channel [1, 2], based on an energy criterion, has shown that in usual conditions the forces at the tip of a thin water-filled channel can cause fracture of the polymer. Other authors have also considered water treeing to be related to ESC [3]. Up to the present time, no convincing experimental proof for such an interpretation has been given.