Improvement of electrical treeing resistance in LDPE by mixed addition of nano-particles and azobenzoic compound

Polymer nano-composite was prepared by mixed addition of azobenzoic compound and Al₂O₃ nano-particle into LDPE to improve the electrical treeing resistance under ac voltage application. Three kinds of azobenzoic compound were tested: azobenzen (Az), nitro-azobenzen (Ni_Az) and aminoazobenzen (Am_Az). Any dispersant was not used. The test materials of the mixed addition were processed in our laboratory by the solution casting method. The experimental result showed that tree initiation voltage (TIV) was increased by the mixed addition. The increasing ratio of TIV for the mixed addition depends on the kind of azobenzoic compound. The highest increasing ratio of 300% was obtained in the mixed addition of Az and Al₂O₃ at the concentrations of 2.0 wt% and 3.0 wt%, respectively. The mixed addition was also effective in restriction of tree development. The control effect depended significantly on the concentration of the azobenzoic compound. When the concentrations of Az and Al₂O₃ were 1.0 wt% and 3 wt%, respectively and PD was induced by 5s of over voltage application, PD due to the treeing from the electrode tip was restricted to undetectable level, which continued more than 2000 min under the constant voltage application. However, in the case of 30s of the over-voltage application, the period of time to the breakdown for the mixed addition of above concentrations was almost the same as that for the single addition of the particle. The restriction of PD to the undetectable level was achieved by increasing the Az concentration to 2.0 wt% in the case of the overvoltage application of 30s.