The effects of hydration on the DC breakdown strength of polyethylene composites employing oxide and nitride fillers

Abstract

Particle dispersion, water absorption/desorption and electrical breakdown behavior were studied in a range of polyethylene composites having a common matrix morphology. Three different conditioning routes (dry, ambient and wet) were used to vary the absorbed water content. Systems employing oxide fillers (silica and alumina) were found to have poor or intermediate levels of particle dispersion and could absorb/desorb significant amounts of water. Consequently, they required drying to provide breakdown strengths comparable to that of the host matrix. Systems based on calcined silica exhibited reduced water absorption and provided improved breakdown strength after ambient conditioning, despite having an identical dispersion to those utilizing untreated silica. Composites employing nitride fillers (silicon nitride and aluminum nitride) were found to have good or intermediate levels of particle dispersion. These absorbed far less water and hence provided breakdown strength values comparable to that of the host matrix following ambient conditioning. Their breakdown strength was degraded after wet conditioning with both exhibiting similar breakdown strengths despite there being a large difference in the level of particle dispersion between the two fillers. In composites based upon a hydrophobic host matrix, water absorption is largely determined by particle surface chemistry and, although the above results are presented in terms of water absorption, we suggest that changes in this characteristic can be interpreted as a proxy for changed surface chemistry. The results suggest that surface chemistry is at least as important as particle dispersion in determining the electrical breakdown strength.

Effect of organoclay loading on the dielectric properties and charge dynamics of a PP‐rubber nanocomposite

“…Furthermore, the observation that increasing organoclay loading decreases the BDS aligns well with the literature for organoclay, silica, oxide and nitride‐based nanofillers [16, 34, 35]. Possible mechanisms for this occurrence relate to the thermal instability of the material due to the clay increasing the sample conductivity, a higher current making an avalanche to breakdown more likely, space charge accumulation over ∼2 min BDS measurement and/or the electric field enhancement due to agglomerations, specifically at higher filler loadings [5, 16, 34]. No matter the exact mechanism, taking the system holistically, it is reasonable to assume that organoclay, not being a polymer, has a detrimental effect on the DC dielectric BDS because it disrupts the homogeneous polymer.…”

Experimental demonstration of deep traps in silica-based polyethylene nanocomposites by combined isothermal surface potential decay and pulsed electro-acoustic measurements

“…from batch to batch specimen manufacturing. 8,9,12,13 In addition, nanosilica is a potential particle for industrial applications because it can be produced by flame hydrolysis or polymerization at low cost and is widely available in a range of nanometers from tens to hundreds. In this research, as-received nanosilica (Sigma-Aldrich 637238) was used.…”

High performance polymer blend systems for HVDC applications

“…In comparable AC tests [6][7][8] the breakdown strength was increased by around 20 % in a blend relative to a LDPE reference material; the DC values here are approximately 2.5 times the reported AC values. DC breakdown testing on analogous polyethylene blends yielded values of 480 kV/mm [22] and 425 kV/mm [23] with comparable β values. Thus, the same trends, seen previously under AC conditions, are reproduced here under DC conditions.…”