Improved Electric Strength and Space Charge Characterization in LDPE Composites with Montmorillonite Fillers

Space charge distribution and breakdown strength were investigated in composites of low density polyethylene (LDPE) and various contents of montmorillonite (MMT). The disperse performance of MMT in LDPE was observed with scanning electron microscopy (SEM) and X-ray diffraction. For MMT concentration of 1？wt%, the better intercalation of LDPE into MMT interlayers and the tighter interface structure between polymer-filler were observed, relative to MMT concentration of 3 and 5？wt%. Space charge profiles were obtained using the pulsed electroacoustic (PEA) method. Less space charge accumulated in the LDPE/MMT with MMT content of 1？wt% than that in pure LDPE, and space charge in the central of LDPE/MMT was much more uniformly. On the other hand, when MMT concentration was up to 3 and 5？wt%, large amounts of heterocharges were accumulated in the sample bulk. In MMT doped samples the dielectric strength increased up to a maximum at 1？wt% loading, and then decreases at 3 and 5？wt%. 1. Introduction Polyethylene is well known for its excellent electrical and mechanical properties which makes it an attractive insulating material for cable. The performance of polyethylene is a subject that has presented an increased activity in the last two decades. The major advantages are excellent electrical properties such as high breakdown strength, extremely low conductivity, and low dielectric loss. However, space charge formation in polymeric materials as one of the main problems in the development of cables, which strongly affect the degradation process and breakdown strength, due to accumulated charges causes the distorting of electric field severely and initiates the electric tree growth to part of the material being overstressed [1]. In recent decades, nanomaterial modification has developed rapidly in the field of dielectric materials. These inorganic fillers have been found to have a beneficial effect in improving the dielectric properties [2–4]. Among these, fillers have been used to improve the breakdown strength and reduce the possibility of tree generation. It was shown that low density polyethylene (LDPE) mixed with nanofiller could enhance the resistivity and reduce space charge accumulation [5–7]. In polymer-layered silicate nanocomposite systems, the proper addition of layered silicates leads to a great improvement in the properties of the matrix such as thermal stability and mechanical performance [8, 9]. For insulating dielectric material, experiments have proven that the addition of an appropriate amount of montmorillonite (MMT) to silicone rubber,