The influence of moisture on the electrical performance of XLPE/silica nanocomposites

Abstract

Moisture is known to influence the electrical performance of polymers. The introduction of nano particulates creates numerous additional pathways which radically affect the migration of moisture in nanocomposite materials. In this paper, cross-linked polyethylene/silica nanocomposites at loadings of 5 wt% and 12.5 wt% of both unfunctionalized and vinylsilanefunctionalized nano silica were exposed to humid environments at elevated temperature. Nanocomposites were found to have a much higher moisture uptake compared to cross-linked polyethylene base resin. The dielectric properties of these hydrothermal conditioned samples were characterized by breakdown strength measurements, pulsed electro-acoustic analysis, and dielectric spectroscopy. A close relationship between particle loading, moisture uptake and dielectric properties was found, which provides important evidence that determining the optimal particle loading of nanodielectrics should take moisture influence into account.

On the effect of functionalizer chain length and water content in polyethylene/silica nanocomposites: Part I — Dielectric properties and breakdown strength

“…Whilst the addition of a nanofiller leads to two characteristic loss peaks and an increase in permittivity at low frequencies [8,9,12,16,18,21,22], in cases where the nanofiller is well dispersed, this is not observed. Instead, the dielectric loss increases in a similar manner to that in comparable micro-filled systems [15,[16][17]20].…”

“…Consequently, when the breakdown strength of a nanocomposite is compared with that of an identical polymer without nanofiller, examples can be found where the addition of the nanofiller reduced the breakdown strength [13,14], where no change in breakdown strength was seen [15] or where increased breakdown strength occurred [16,17]. A possible explanation for these apparent contradictions may be found in morphological data (where this is provided); poor nanofiller dispersion seems to lead to detrimental effects on breakdown strength [10,11,18] whilst well dispersed systems seem to show improved performance [15,16]. Poor nanoparticle dispersion and particle aggregation is a particular issue at high filler loadings, leading to poor breakdown strength even in otherwise well dispersed systems [15].…”

“…Such behavior can be explained by changes in nanofiller dispersion -poorly dispersed nanoparticles lead to increased dielectric loss since, then, they effectively behave as micrometric inclusions. However this is not the only variable, since dielectric data are also strongly influenced by water content; the associated loss peaks tend to shift towards higher frequencies and the permittivity increases in wetter samples [12,18,21,22].…”

“…While it is tempting to ascribe such effects to subtle variations in the materials used by different researchers, different processing conditions, etc., including the impact of such factors on nanoparticle dispersion, the final point raises an additional issue worthy of consideration, namely, environmental factors. Water is ubiquitous and it is well known that measured dielectric properties are sensitive to absorbed water [12,18,21,22]. Many researchers have already highlighted the crucial role of the nanoparticle/polymer interface [6,8,[16][17][18][21][22][23] and surface functionalization [11,12,16,17,24] in determining dielectric properties.…”

“…Water is ubiquitous and it is well known that measured dielectric properties are sensitive to absorbed water [12,18,21,22]. Many researchers have already highlighted the crucial role of the nanoparticle/polymer interface [6,8,[16][17][18][21][22][23] and surface functionalization [11,12,16,17,24] in determining dielectric properties. Consequently, it is easy to envisage how, for a hydrophilic system such as nanosilica, the nanofiller/matrix interface can be influenced by absorbed water and, consequently, the potentially critical role of surface functionalization in limiting or promoting water uptake.…”