Effect of degassing and low temperature on electrical treeing in ethylene based copolymers

Experiments using EVA and EAA with different monomer contents have been performed. The effects of degassing and cooling to 77 K on electrical treeing have been examined as a function of monomer contents. The degassed sample shows a higher AC tree initiation voltage than the untreated sample because of oxygen removal. AC tree initiation voltage of degassed copolymers decreases with monomer contents. Oxygen in the molecular chain is probably released by a high field process and causes autoxidation. The 77 K sample shows the highest tree initiation voltage. The main reason for this may be freezing of oxygen, although other factors should also be taken into account. The AC tree at 77 K starts from a microcrack at the side portion of the electrode interface. The tree initiation voltage of copolymers at 77 K decreases with monomer contents, possibly due to decrease of crystallinity