Properties of linear low-density polyethylenesilicone rubber nanocomposites for high voltage insulation application
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Date
2016-09-01
Authors
Nurul Hidayah Ismail
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Abstract
This study investigated the performance of thermoplastic elastomer nanocomposites based on linear low density polyethylene (LLDPE) and silicone rubber (SR) blends filled with different types of inorganic nanofillers such as silica (Si), boron nitride (BN) and zinc oxide (ZO) for the application of high voltage insulators. The first part of the study investigated the effect of different mixing sequences on the properties of LLDPE/SR/BN nanocomposites. 5 vol% of nano-BN was introduced into 70/30 LLDPE/SR by using three different sequences; LLDPE + SR + BN (mixed in single processing step), LLDPE + (masterbatch-SR/BN) and SR + (masterbatch-LLDPE/BN), where the samples with masterbatch were prepared by two processing steps. The samples with masterbatch-SR/BN exhibited encapsulation structure and showed the highest dielectric breakdown strength and the lowest permittivity and loss tangent compared to the other two mixing sequences which generated separated dispersion structure. Later, by adapting the optimum mixing sequence, various types of LLDPE/SR nanocomposites were prepared. The effect of three formulation parameters such as SR content (10, 20 and 30 wt%), type of nanofiller (Si, BN and ZO) and nanofiller loading (2, 5 and 8 vol%) on the properties of LLDPE/SR nanocomposites was investigated statistically by using design of experiment (DOE). Based on DOE analysis, it was found that the nanocomposites with 10 wt% of SR
and 2 vol% of BN exhibited optimum properties for high voltage insulators. In the third part of the study, the optimized nanocomposite sample was exposed to electron beam (EB) irradiation at varied doses (20, 40, 50 and 100 kGy). The results indicated that 20 kGy EB irradiation was enough to selectively crosslink the SR phases and improve interfacial adhesion in the nanocomposite system giving rise to the improved dielectric breakdown strength, volume resistivity, tensile strength and modulus. Investigation on the effects of ultraviolet (UV), heat and water ageing (varied to three different ageing times) on the unirradiated- and 20 kGy irradiated-LLDPE/SR/BN nanocomposites indicated that water ageing showed the most severe effect on the dielectric breakdown strength, followed by UV and heat ageing. It was found that increasing ageing time further reduced the dielectric breakdown strength. The hydrophobicity for the unirradiated samples reduced in all aged samples, but in the case of irradiated samples, the hydrophobicity showed insignificant effect on ageing.