Research On Space Charge Properties Of Micro-,Nano-,Micro/Nano-SiO₂/LDPE Composites

The addition of inorganic nano filler in the polymer can effectively inhibit the accumulation of space charge, as well as improve the level of its insulation and compression capacity. But So easily happened in the process of preparation,storage and use due to the tiny nanoparticles size, specific surface area and high surface activity, But it easily happened to agglomerate in the process of preparation, storage and use due to the tiny size, specific surface and high activity, which makes it loses its superior performance. However, the size of micron particle is relatively large, owning small specific surface, so micron material is not born with the same characteristics like nanoparticles. But micron particle has excellent property of resistance to electro corrosion. If the micron particles and nano particles are blended into the polymer together, by adjusting the ratio of micron particles and nano particles, because of the synergy, the dielectric properties of composites might be more superior than the only nanocomposites which has the same content, while maintaining the excellent performance of nano particles.First of all, the neat low density polyethylene samples were prepared. Then Micro-SiO₂ and Nano-SiO₂ of the same content were added into the polyethylene respectively, to prepare micro-composite and nano-composite. After that, MicroSiO₂ and Nano-SiO₂ were added to polyethylene at the same time, to prepare micro/nano-composite. At last, the micro-composite was mixed as master batch with nano-filler, and the nano-composite was mixed as master batch with microfiller, so two different kinds of micro/nano-composites were prepared in addition.Finally we have six kinds of samples. Those samples were grouped into two groups. The first four is classified as a group to investigate the influence of micro-filler, nano-filler and synergistic effect on the dielectric properties ofLDPE. The other group consisting of the latter three samples shows the influence of the adding order of micro-filler and nano-filler on the dielectric properties of LDPE.From the measurement about the chemical structure, crystallization morphology, and space charge distribution, conductivity, DC breakdown of the two groups of samples, the phenomenon was shown up that Micro- and NanoSiO₂ could be combined with LDPE molecular chain after they were mixed with LDPE. Micro-filler and Nano-filler could homogenize and decrease the cell size,as well as improve the crystallinity of composites, by acting nucleation centre.And then through the modulation of the interface traps, the carrier mobility will be reduced, the accumulation of space charge will be inhibited, and the DC breakdown strength will be enhanced. Among them, the best modification effect to LDPE is Nano-SiO₂, the addition of both Micro-SiO₂ and Nano-SiO₂ takes second place, but Micro-SiO₂ is the worst. This may have relationship with the specific surface size. The cell size of Nano-SiO₂/PE composite reduces by half,the conductivity reduces by 94.2%, The remnants amount of space charge by70%, but the DC breakdown strength is improved by 20.1% compared with neat LDPE.The insulating properties of the materials can be influenced seriously by the adding order of the micro-filler and nano-filler in the micro/nano-composites.The cell size of the sample made in the order that Micro-SiO₂ before Nano-SiO₂ reduces by 47.4%, the conductivity reduces by 91%, and the remnants amount of space charge by 67%, but the DC breakdown strength is improved by 17.4%compared with nest LDPE. This may be because that the PE molecular chain can be split by Micro-SiO₂, so Nano-SiO₂ can enter the molecular and combine with it, inhibiting agglomeration.