Influence of morphology, irradiation and prestressing on the breakdown of LDPE

It is a well-known fact that the breakdown of low density polyethylene (LDPE) depends on the space charge (SC) accumulation in the polymer bulk. In turn, above mentioned process is governed by a submicroscopic structure of polymers, the contact conditions on the interface electrode-polymer and the charge carrier´s injection from electrodes. It is shown that the surface modification of the LDPE samples by the proton irradiation allows the number of pulses to breakdown to be increased. One more a way for the increase in the lifetime and the breakdown strength of LDPE is the so-called prestressing, i.e., previous polarization of LDPE under DC voltage. It is found that the number of impulses to breakdown is increased more than by a factor of 2.6 and 1.6 at the probability P= 0.05 and P= 0.632 respectively, when an impulse voltage of the same polarity is applied after prestressing of the DC voltage. The number of pulses to breakdown for the irradiated samples is increased by a factor of 9.4 and 3.6 at P=0.05 and P=0.632 respectively, when an impulse voltage of the same polarity is applied after prestressing of the DC voltage. This phenomenon is related with the homo-charge accumulation near the electrodes.