Investigation of the mechanical and electrical properties of polypropylene-titanium oxide composites

Abstract

Titanium dioxide (Ti02)-filled isotactic polypropylene (iPP) composites with various contents of Ti02 were prepared by a locally fabricated extrusion molding machine. The extrudates were melt-pressed at 180°C and produced as plane sheets of nearly equal thickness by rapid cooling. The iPP sample shows the smoothest surface in comparison to other two composites, and the composite surface of 20 wt% TiOz seems to be slightly smoother and becomes less white than that of.40 wt% filler. The composite of 40 wt% TiOz contains more agglomerates or larger particles, which seem to form lumps on the surface, than the composite of 20 wt% TiOz. Increasing Ti02 content develops slight roughness and whiteness on the ECM composite surfaces but does not show any noticeable gap or sharp boundary between filler and polymer matrix. Gaps are significantly notable in the EM composite of 40 wt% TiOz. Small particles are seen to disperse inhomogeneously in the :pp matrix ill the composite samples. While the surface of the neat iPP shows a few .:racks, terraces and voids, a considerable amount of voids appear .in the composites indicating different fracture processes in the neat iPP and the composites. Scanning electron micrographs taken 011 the fractured surface of the samples show increasing amount of voids with increasing filler content. Tensile strength, elongation-atbreak (%) and glass transition temperature of the samples are found to decrease .:onsiderably with the increase in TiOz content, whereas mictohardness decreases slightly with the filler content. The thermal behavior of iPP-TiOz composites was analyzed by thermogravimetric, differential thermal analyses and differential scanning calorimetry. It is seen that the melting temperature does not show any noticeable change but the degradation temperature increases with the increase of filler. Glass transition temperature decreases as TiOz content increases in the composites. It is observed that the ac conductivity increases with the increase of frequency but very weakly dependent on temperature. The dielectric constant decreases with the increase in' frequency and not much dependent on temperature. As the frequency increases the dipoles in the composite can not follow the field and thus lag behind the applied field. So