Some Factors Effecting on the Dielectric Strength for (PVC- Kaolin) Composites


This research includes the effect of kaolin additions to the polymer matrix (PVC)and study some factors affecting to dielectric strength.The kaolin powder was added as percentage by weight (1,2,3 and 4%) to PVC,and the specimens formed by hot pressing method, with different thickness (0.8-2mm). Some of the results was showed decrease in the electrical strength with kaolinadditives, especially for large thickness due to presence of lattice water, which hashigh dielectric constant but in the same time has high dielectric loss factor, where theelectrical strength decrease when dielectric loss factor increases. Thus the influence ofleakage currents is evident in the large thickness as a result of the electro-thermaleffects.Electrical strength was decreased when the time rate of raising voltage increases.The effect of the cycles number of breakdown for composite specimens was studded.Also the dielectric strength decreased with temperature increases.Optical microscopy images for breakdown region was shown thecarbonization in the breakdown points as a result of crashing polymers chains.Also, micro cracks occurring for specimens that has large amount of kaolin andthis cracks extend directly from the breakdown region.