Emna Helal

Evaluation of dielectric behavior of polyethylene/thermoplastic elastomer blends containing zinc oxide (ZnO) nanoparticles for high voltage insulation

The dielectric performance of nanocomposites made of Polyethylene (PE) and a master batch of Styrene-Ethylene/Butylene-Styrene grafted maleic anhydride (SEBS-MA) triblock copolymer containing individually dispersed zinc oxide (ZnO) nanoparticles, was investigated in comparison with conventional PE/ZnO nanocomposites and correlated to the difference in nanoparticles dispersion. The presence of agglomerations in conventional PE/ZnO nanocomposites, typically attributed to poor compatibility, was confirmed by microscopy and consistent with rheological properties. By contrast, no agglomerations were observed in PE/SEBS-MA/ZnO blend nanocomposites, indicating that the nanoscale dispersion featured in SEBS-MA/ZnO master batch was successfully transferred to the blend. Although the unfilled PE/SEBS-MA blend is less performant compared to neat PE in terms of breakdown strength and resistance to surface erosion, the blend nanocomposite featured the best properties compared to PE/ZnO, due to the improved dispersion. In particular, the dielectric losses were considerably reduced. Besides, the addition of 5 wt% ZnO nanoparticles to neat PE resulted in around 9% decrease in breakdown strength while PE/SEBS-MA/ZnO blend nanocomposite maintained nearly the same breakdown strength of the unfilled blend. The resistance to surface erosion measurements revealed that the blend nanocomposite featured the highest resistance with a reduction in eroded volume equal to 63% compared to unfilled PE/SEBS-MA, 58% compared to neat PE and 18% compared to PE/ZnO.

Dielectric properties of thermoplastic elastomer/zinc oxide (ZnO) nanocomposites with controlled nanoparticles dispersion

In this study, the rheological and dielectric properties of two sets of nanocomposites prepared respectively from Styrene-Ethylene-Butylene-Styrene (SEBS) and SEBS grafted maleic anhydride (SEBS-g-MA) block copolymer matrices and surface functionalized zinc oxide nanoparticles have been investigated. The interaction at the polymer-nanoparticle interface was tuned through the MA graft in order to tailor the nanoparticles dispersion in the block copolymer nanostructure and to highlight its effect on the dielectric performance. Small Amplitude Oscillatory Shear (SAOS) measurements revealed highly improved solid-like behavior and a low frequency independent storage modulus in SEBS-g-MA based nanocomposite which indicates good dispersion and formation of a network between the nanoparticles and the polymer chains. This result was supported by a reduction in the adsorbed carbonyl peak in Fourier Transformed Infrared (FTIR) spectra attributed to an interaction between MA graft and the functional groups on the surface of ZnO nanoparticles. The dielectric spectroscopy revealed a limited increase of both real and imaginary parts of the dielectric permittivity and absence of interfacial relaxation peak, in the case of SEBS-MAZnO nanocomposite. Besides, the AC short term breakdown strength was slightly improved in the SEBS-MA-ZnO nanocomposite compared to the pure matrix while it decreased by 18% in SEBS-ZnO nanocomposite due to the presence of agglomerations.

Polyethylene/styrenic block copolymer blends: Morphology and dielectric properties

In this work, a polymer blend of High Density Polyethylene HDPE and Styrene-Ethylene-Butylene-Styrene SEBS triblock copolymer has been prepared. The composition of the blend was tailored to control the morphology from a state of dispersed droplets of SEBS in a PE matrix to a fiber-like morphology. The microstructure of the blends has been assessed by means of Scanning Electron Microscopy SEM. The Thermal Gravimetric Analysis TGA has been performed on the samples to evaluate their thermal stability. The materials dielectric response was evaluated using Broadband Dielectric Spectroscopy BDS and the AC dielectric strength has been estimated by means of short-term breakdown tests. Overall, an improvement of the thermal stability of HDPE has been induced in the blend containing respectively 10 and 20 wt% of SEBS in droplets form. Moreover, the AC breakdown strength and the dielectric loss of this blend configuration remained in the same range of the pure HDPE. However, a consistent decrease of the AC dielectric strength, by approximately 13%, has been induced in the blend with a fiber-like morphology.

Dielectric properties of various metallic Oxide/LDPE nanocomposites compounded by different techniques

Metallic oxide reinforced thermoplastics are good candidates as insulating material for HVDC cables because of their ability to limit or suppress space charges injection and accumulation. In this paper, LDPE based nanocomposites reinforced by Magnesium Oxide (MgO), Polyhedral Oligomeric Silsesquioxanes (POSS) or Zinc Oxide (ZnO) were prepared either by mechanical alloying or by melt mixing and their dielectric properties were investigated for low loadings from 0 to 5 wt% in order to assess the efficiency of the compounding procedure in producing enhanced dielectric properties. The thermal step method was used to investigate the space charge behavior of the various samples. The space charge measurements have shown differences between the different nanocomposites reinforced by different kind of nanofillers and made by different preparation protocols, just after manufacturing and also after different conditions of DC poling. None of the prepared nanocomposites showed significant increases in their dielectric losses in a broad range of frequencies and temperatures and no significant increase in their DC conductivity.