Crystallization morphology and space charge property of silica/low density polyethylene composites

The accumulation of space charge in polymer insulation limits the development of high-voltage direct current transmission and reduces the service lifetime of power equipment. The electrical properties of polymers are affected greatly by their crystalline morphology. In order to study the effect of silica on the crystalline morphology and space charge characteristics of low density polyethylene (LDPE), nano-SiO2/LDPE composites, micro-SiO2/LDPE composites, and nano-/micro-SiO2/LDPE composites were prepared by melt blending. The silica distributions were characterized by scanning electron microscopy. Fourier transform infrared spectrophotometry was used to determine the chemical structure of the silica, LDPE, and silica/LDPE composites. The crystalline morphology of the LDPE and composites was investigated with an atomic force microscope and by differential scanning calorimetry. The space charge distribution of the LDPE and composites was measured with a pulsed electro-acoustic system. The results show that the introduction of silica particles did not evolve the chemical structure of LDPE. Compared with that of pure LDPE, the crystallinity of the composites increases with the decrease in the grain size. Moreover, the silica/LDPE composites exhibit the ability to inhibit the space charge. The improvement of space charge in the composites was attributed to the traps existing on the interfaces between the silica particles and LDPE (crystalline and amorphous).