Investigation On Crystalline Morphology And Tree Discharge Characteristic Of PE/MMT Nanocomposites

Polyethylene doesn't contain polar groups, and its molecules structure is symmetric, so it has excellent insulation properties, and it is one of the most widely used plastic in electrical insulation field. But electrical trees will be initiated easily under long-term high electric field, leading to insulation aging. For improving its treeing-resistance properties, scholars worldwide have researched many methods to modify polyethylene, and this paper used the montmorillonite with the layer-structure of 2:1 type to modify polyethylene.Polyethylene/montmorillonite composites were prepared by melting intercalation process. Crystalline morphology of polyethylene was observed by polarizing microscope, and microstructure of polyethylene/montmorillonite materials was characterized by atomic force microscope, the results showed that composites obtained are nanocomposites.The electrical treeing and partial discharge signals corresponding to growing process of electrical tree of polyethylene and polyethylene/montmorillonite nanocomposites were respectively studied by the combined test system of electrical tree initiation and partial discharge measurement. The results showed that: under the same condition, compare to polyethylene samples, in polyethylene/montmorillonite nanocomposites, dispersion of electrical trees was small, and most of electrical trees were bush-shaped, at the voltage applied to the samples for 360min the length of electrical trees were shorter, the fractal dimensions of electrical trees during electrical treeing were larger, and partial discharge was smaller and sparser, and the phenomenon of discharge extinction happened in polyethylene/montmorillonite nanocomposites. These results showed that polyethylene/montmorillonite nanocomposites can effectively restrain the electrical tree to grow, and improve the properties of treeing-resistance of polyethylene. Furthermore, this paper studied the effect of voltage level to initiate electrical trees in polyethylene and polyethylene/montmorillonite nanocomposites, and the results showed that voltage level was higher, the electrical trees would grow faster in the two materials, but the tree structures were different.For futher investigation on treeing-resistance mechanism of polyethylene/montmorillonite nanocomposites, thermally stimulated current spectrum and energy level were tested on polyethylene and polyethylene/montmorillonite nanocomposites. The results showed that: compare to polyethylene, polyethylene/montmorillonite nanocomposites has shallow traps of bigger level density and deep traps of smaller level density, therefore, the nanocomposite can restrain the growth of electrical tree through modulating the thickness and mobility of charge carriers and reducing electron formation.