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The Dielectric Properties Improvement of Cable Insulation Layer by Different Morphology Nanoparticles Doping into LDPE

Low density polyethylene (LDPE) doped with inorganic nano-MMT and nano-ZnO particles improved the dielectric properties of the cable insulation layer. In this article, nano-MMT/LDPE and nano-ZnO/LDPE composites were prepared by polymer intercalation and melt blending, respectively. The octadecyl quaternary ammonium salt and silane coupling agent were applied for surface modification in nano-MMT and nano-ZnO particles, and this then improved the compatibility of nanoparticles and polymeric matrix. These samples were characterized by FTIR, PLM, DSC and TSC, from which the effect of nanoparticles doping on polymer crystal habit and interface traps would be explored. In these experiments, the AC breakdown characteristics and space charge characteristic of different composites were studied. The experimental results showed that the interface bonding of nanoparticles and polymer was improved by coupling agents modifying. The dispersion of nanoparticles in matrix was better. When the mass fraction of nanoparticles doping was 3 wt.%, the crystallization rate and crystallinity of composites increased, and the crystalline structure was more complete. Besides, the amorphous regions in material decreased and the conducting channel was circuitous. At this time, the breakdown field strength of nano-MMT/LDPE and nano-ZnO/LDPE increased by 10.3% and 11.1%, compared to that of pure LDPE, respectively. Furthermore, the density and depth of interface traps in polymer increased with nanoparticles doping. Nano-MMT and nano-ZnO could both restrain the space charge accumulation, and the inhibiting effect of nano-ZnO was more visible.