Study On Space Charge Characteristics And Dielectric Properties Of SiO₂/LDPE Micro/Nano-Composites Under Tensile Condition

Polyethylene is a cable insulation material with good electrical properties,cable will inevitably be affected by tensile force in the process of production,transportation and laying operation.The existence of tensile stress may affect the electrical properties of insulating materials.It is significant to study the influence of tensile on the electrical properties of composite materials.In this paper,the effect of tension on the electrical insulation properties of composites is discussed through different tension treatments of composites.In this paper,LDPE was used as matrix,Micron-SiO₂ and Nano-SiO₂ were used as fillers respectively,and the composites with different content of micron and Nano SiO₂ were prepared by melt blending method.The mechanical properties of the composites were tested by tensile test,the structure of the composites was characterized by PLM and FTIR,and then the space charge and conductivity of the composites were tested by PEA the conductivity current test relative permittivity and loss test and DC breakdown strength test.The experimental results show that in the PLM test,the cells under tension are compact,the area of amorphous region is small,the cell spacing increases after tension,the area of amorphous region increases,and the internal structure becomes loose.As a result of tension,the molecular chain spacing increases,the polar intermolecular binding decreases,and the relative dielectric constant and dielectric loss factor increase.With the increase of tensile strength,the conductive currents of LDPE and micron composites increase in varying degrees.The conductive currents of nano-composites decrease gradually,and the conductive currents of nano-composites are always lower than those of LDPE.The conductive currents of micro-and nano-composites increase first and then decrease.When measuring the space charge distribution,the accumulation of space charge in LDPE is more,and the accumulation of space charge in nano-SiO₂/LDPE composite is the least,which indicates that the addition of nano-SiO₂can effectively inhibit the accumulation of space charge in LDPE.Under different stretching conditions,the accumulation of space charge in LDPE,nanocomposites,micro-composites and micro-nanocomposites increases with the increase of tensile rate.Compared with other composites,nano-SiO₂ particles are joined together in the matrix molecular chain through the role of interfacial layer,and SiO₂ particles play a cross-linking role.When the composite is stretched by external force,the stress will be evenly distributed by the crosslinking point,which reduces the stress concentration and destroys the whole structure.The increase of space charge in nano-SiO₂/LDPE composite is the least,which shows that nano-SiO₂/LDPE composite has a strong ability to inhibit the accumulation of space charge,indicating that nano-SiO₂/LDPE composite has a higher tensile property.