The emergence of nano dielectrics for specialized high voltage applications sparked off a variety of research activities, which proved that nano-fillers are capable of improving the electrical, thermal and mechanical properties of polymers. This paper primarily investigates the effect of addition of hBN (hexagonal boron nitride) nanoparticles into an epoxy polymer base by increasing fill-grade, from 0.2 to 5 % by volume, from two different standpoints: (a) characterizing the electrical space charge (S.C.) accumulation threshold under DC electrical fields, and, (b) demonstrating the alterations in material properties of the modified polymeric materials, from the unfilled polymer. Objective (a) is experimentally investigated by the pulsed electro-acoustic (PEA) technique, well known for determining spatial charge distribution in dielectrics. Objective (b) is investigated by determining the ultrasonic velocity response of the modified composites and unfilled polymer. The obtained results suggest a relation between electrical threshold fields for S.C. accumulation fill-grades, as well as the fact that incorporating stiff filler materials into brittle polymer bases leads to a tougher composite (capable of withstanding greater breaking stress levels), but with reduced ductility.

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Many researchers have reported an improvement of the properties of polymer dielectrics by introducing nanofillers. However, the influence of ambient conditions and sample storage under different conditions are often not taken into account. The epoxy matrix itself is a polar polymer susceptible to water absorption, and the presence of hydrophilic nanofillers such as silica will enhance the uptake of moisture from the environment. The dielectric response both of neat epoxy resin and an epoxy-based nanocomposite under an electrical stress greatly depends on the amount of absorbed water. This study investigates the effect of water absorbance on the dielectric spectrum of epoxy-silica nanocomposites containing different concentrations of nanoparticles.

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Poly(2-nonyl-2-oxazoline)80-stat-poly(2-dec-9′-enyl-2-oxazoline)20 and poly(2-dec-9′-enyl-2-oxazoline)100 can be synthesized from the cationic ring-opening polymerization of monomers that can be derived from fatty acids from renewable resources. These (co)poly(2-oxazoline)s can be crosslinked with di- and trifunctional mercapto compounds using the UV-induced thiol-ene reaction. The complex permittivity of the corresponding networks increases with the temperature and decreases with the network density. In a frequency range from 10−2 to 106 Hz and at temperatures ranging from −20 to 40 °C, the changes of the real part of the complex permittivity as well as the loss factor can be explained by interfacial polarization within the material. At a temperature of 20 °C and a frequency of 50 Hz, the permittivity of the crosslinked (co)poly(2-oxazoline)s covers a range from 4.29 to 4.97, and the loss factors are in the range from 0.030 to 0.093. The electrical conductivities of these polymer networks span a range from 5 × 10−12 to 8 × 10−9 S/m, classifying these materials as medium insulators. Notably, the values for the permittivity, loss factor and conductivity of these copoly(2-oxazoline)s are in the same range as for polyamides, and, hence, these copoly(2-oxazoline)-based networks may be referred to as “green” alternatives for polyamides as insulators in electronic applications.@en