Study of Dielectric Behavior of Titanium Dioxide-Filled Polypropylene Composites

Abstract

Titanium dioxide (TiO2)-filled isotactic polypropylene (iPP) composites with various contents of TiO2 were prepared using an extrusion molding machine. Scanning electron micrograph shows that the surface of iPP is smoother in comparison to those of iPP/ TiO2 composites with varying TiO2 concentration. The composite of 40 wt% TiO2 contains more agglomerates or larger particles, than the composite of 20 wt% TiO2. With increasing filler content amount of voids and holes is increased on the composite surfaces. The DTA shows two endothermic peaks that represent melting temperatures at 169, 167, 163 and 167°C and thermal degradation temperatures at 435, 437, 448, 462°C of various TiO2 concentrations. While the melting peak of the neat iPP is sharp, the TiO2-loaded composites rather show diffuse melting peaks along with a shift of peaks towards lower temperatures. In AC electrical measurement it is demonstrated that with the increase of frequency, conductivity (σ) increases but dielectric constant (ɛ′) decreases of these composites. With varying TiO2 concentration, there is no noticeable change observed in σ where as ɛ′ value is decrease of these composites. Both σ and ɛ′ are weakly dependent on temperature. At lower frequency region loss tangent (tanδ) increases with frequency and attains a maximum peak after that tanδ decreases rapidly at higher frequency region. This reverse and usual behavior of tanδ at high frequency can be explained in accordance with Koop’s theory.