Electrical strength in ramp voltage AC tests of LDPE and its nanocomposites with silica and fibrous and laminar silicates

The electrical strength of a set of LDPE micro and nanocomposites with silica, laminar silicates and fibrous silicates has been studied. A significant 60% increase of the breakdown electrical field is shown by the microsized microdispersed LDPE/montmorillonite composites while only a 20% increase is obtained with a nanosized laminar silicate. Nanosized nanodispersed composites of the spherical silica and fibrous silicate with LDPE show a lower increase of the breakdown electrical field. The data point scatter in repeated tests is very high in the case of the microcomposites, indicating strong morphological heterogeneity, while it is very low in the nanocomposites. This implies that these nanocomposites are remarkably defect-free as regards electrically weak sites. An analysis of the crystalline structure, semicrystalline morphology and inorganic particle size and distribution evidences the importance of the role played not only by the inorganic particles but also by the semicrystalline morphology in the final dielectric performance of the composite. (C) 2008 Wiley Periodicals.