Effect of additives on treeing initiation as a function of oxygen concentration in polyethylene

The effect of additives on treeing initiation was studied in low-density and cross-linked polyethylene (LDPE and XLPE) under various conditions. The additives suppress the initiation of the deteriorated region, which is a precursor of the tree initiation, and increase the tree starting voltage. This effect was found to be a function of oxygen concentration absorbed in PE; observable when the sample is equilibrated with atmospheres with a range of oxygen from 1 ppm to 10%. Also the effect of additives is not as clear at 77 K as it is at room temperature, and differs for impulse and AC voltage. These results can be explained by the following model. (1) Free radicals are generated in the high field region by carriers injected from the electrode. (2) The free radicals react with oxygen to produce chain scission of the PE molecule, especially if no additives are present. (3) Additives stabilize the free radicals against reaction with oxygen molecules.<
>