Oxidation dependence of breakdown strength of XLPE

It has been shown in a previous study (P. Rohl, 1982) that the breakdown strength of polyethylene increases with increasing oxidation levels. The purpose of the research reported here is to verify this somewhat surprising result. Unlike the earlier work, cross-linked polyethylene (XLPE), the principal insulation used in extruded cables, is utilized. The authors correlate dielectric breakdown measurements with oxidation, monitored by Fourier transform infrared (FTIR) spectroscopy, and the results are interpreted using the modified free-volume theory. It is found that the breakdown strength E _b indeed shows a slight tendency to increase with the oxidation level. In particular, the authors found a correlation between E_b and the degree of oxidation, expressed in terms of the carbonyl band (1741 cm^-1) absorption. The exact reasons for this behavior are not clear at this time, but appear to be compatible with the modified free-volume theory breakdown