The influence of nanoparticles and their functionalization on the dielectric properties of biaxially oriented polypropylene for power capacitors

Biaxially oriented silica–polypropylene nanocomposites for HVDC film capacitors: morphology-dielectric property relationships, and critical evaluation of the current progress and limitations

“…Interestingly, the 1.0 wt-% silica-BOPP nanocomposite prepared via the masterbatch route (dilution of 4.5 wt-% masterbatch during cast film extrusion step) exhibited a slightly higher breakdown strength in comparison to the 1.0 wt-% variant prepared via direct mixing route. It is remarked that even though HMDS-treated silica has been previously shown to result in small-area dielectric strength improvement of BOPP 33,37 , the large-area dielectric strength results presented herein can provide a more realistic picture of the breakdown performance in film capacitor operation due to the area effect. Several laboratory-scale compounding and film production trials were performed during which aspects related to mixing and de-agglomeration efficiency, cast film extrusion and biaxial stretching parameters were studied: these data are summarized for relative change of large-area DBS in Figure 12b, and for thickness-dependence of the Weibull 𝛽 parameter in Figure 12c.…”

“…The realized nanoparticle weight fractions ( φ ) in the nanocompounds were determined from cast film samples by burning the organic polymer and additives at 600 °C and weighing the residual ash in accordance with the ISO 3451-1 standard. The realized nanoparticle concentrations obtained by the ash method are typically slightly lower than the targeted concentrations, 33,37 being attributable to rate fluctuations and loss in the gravimetric feeding of low amounts of nanosilica during compounding.…”

“…The measured 𝜀 𝑟 values were generally within the expected range for BOPP 5,18 , showing a slightly decreasing trend with increasing temperature from -60 °C to 125 °C. Slight variation in 𝜀 𝑟 were noticed between the studied materials, which can be partly related to the HMDStreated silica 37 , however assessing the role of silica and silica-PP interface on the real permittivity is challenging, as the small differences in 𝜀 𝑟 observed in Figure 8a could also be attributed to film voids (see above) or thickness measurement inaccuracy 78 . With increasing silica content, the dielectric loss spectra (tan 𝛿 = 𝜀 𝑟 ′ /𝜀 𝑟 ) showed (i) a slight increase of tan 𝛿 below the glass transition temperature 𝑇 𝑔 (approx.…”

“…melt extrusion and biaxial orientation). This has been seldomly reported in a comprehensive manner 37,39,40 , thus leaving processingstructure-property relationships in BOPP nanocomposites largely non-established. Moreover, understanding the fundamental mechanisms for dielectric property enhancement as well as the current limiting factors for biaxially oriented PNC thin films is highly required for advancing the field 39 .…”

“…29,30 On the other hand, the latter approach, focusing on increasing the maximum permissible electric field stress of PP films via inclusion of permittivity-matching nanoparticles to tailor the charge trapping and transport properties at the nanometric level, has been shown to be a promising route towards practical film capacitor applications. Previously, pathways to the modification of the trap density of states and indications of bulk dielectric property improvement in BOPP films through incorporation of low amounts of surface-functionalized inorganic nanoparticles such as SiO 2 , Al 2 O 3 , TiO 2 and POSS have been demonstrated, 31–33 including decreased electrical conductivity and space charge accumulation, 34–36 increased short-term dielectric breakdown strength, 33,37,38 and increased resistance against partial discharges (PD), 38 for instance.…”