Preparation and characterization of isotactic polypropylene/MgO composites as dielectric materials with low dielectric loss

Abstract

The dielectric and thermal properties of isotactic polypropylene/magnesium oxide (0–30 vol %) composites were investigated. The dielectric constant of the composite material increased from 2.3 to 3.2 on increasing the MgO content and the observed variation of the dielectric constant with the MgO fraction was in good agreement with the Bruggeman mixing model. Low dielectric losses at microwave frequencies, on the order of 10⁻⁴, were obtained using highly crystalline MgO as the filler, and it was also found that the use of larger MgO particle sizes led to further reductions in the dielectric loss. The absolute value of temperature coefficient of the dielectric constant as well as the coefficient of thermal expansion decreased with increasing MgO content, while thermal conductivity increased with increasing MgO content in a manner which could be predicted using the Maxwell-Garnett mixing model.