Study on crystalline morphology and breakdown property of micro-, nano-, micro-/nano- composites

In order to investigate the effect of adding micro- and nano- inorganic particles in the polymer on the morphology and dielectric properties, the low density polyethylene (LDPE) was used as the matrix, the inorganic micro and nano silicon dioxide (SiO₂) were selected as inorganic fillers, origin LDPE and M-SiO₂ and N-SiO₂ and MN-SiO₂ composite materials were respectively prepared by melt blending, and the influence of preparation process of M/N-SiO₂ and N/M-SiO₂ in different ratio and adding sequence on composites were also discussed. The crystalline morphology and breakdown properties of the composites were investigated. The experimental results show that the crystal grain size of the composites with inorganic fillers obviously reduces and the distribution is more uniform comparing with LDPE. The average crystal grain size of N-SiO₂ is 23.1μm which is the smallest among all samples and that of origin LDPE is the biggest about 46.5μm in size. The DC breakdown field strength of the composites with SiO₂ in different size and contain was significantly higher than that of LDPE, the breakdown strength of N-SiO₂ composites is the highest, which is 338.8 kV/mm and 20.1% higher than LDPE. The results of comparative experiments show that the preparation process of the micro- and nano-composites has obvious influence on their properties.