The effect of temperature and voltage on polymer chain scission in high-field region

The treeing resistance of polyethylene was improved drastically in an oxygen-free condition, and a deteriorated region was found in the high-field region before tree initiation started. This paper describes the effect of temperature and applied voltage on the formation of the deteriorated region at the tip of a needle electrode. Chemical analysis suggests that chain scission of polyethylene takes place in the deteriorated region. The chain scission is considered to be caused by injected carriers. At low temperature, the formation of the deteriorated region is suppressed. The most probable cause is either the relaxation of the electric field by carrier accumulation around the tip of needle electrode, or the recombination of broken chains. The deteriorated region increases in size with applied voltage. It also increases at first with the duration of voltage application, but saturates after 3 to 4 h. The voltage dependence of the size may be explained by the field distribution around the needle tip