Effect Of Deep Mixing On Dispersion And DC Electrical Properties Of SiO₂/LDPE Nanocomposites

Due to its excellent DC dielectric properties,nanocomposite media have great engineering application value.The key to influence the dielectric properties of nanocomposite is the dispersion of nanoparticles in the matrix.In this paper,SiO₂/LDPE nanocomposite media with different dispersibility were prepared by repeated mixing with a parallel twin screw extruder.The physical and chemical properties and DC electrical properties of SiO₂/LDPE nanocomposite media after deep mixing were tested.The study shows that with the increase of mixing times,the particle size of nanoparticles dispersed in pure LDPE decreases and the distribution is more uniform.FTIR,XRD and DSC tests showed that with the increase of mixing times,the nanocomposite medium showed slight oxidation.When the mixing times were greater than three times,the crystallinity of the nanocomposite medium began to decrease.The variation of tensile strength is also consistent with the variation of crystallinity.The above experimental results show that the mechanical shear of repeated long time leads to and promotes the process of thermal oxygen aging.The results of DC breakdown and conductance at variable temperature indicate that the DC breakdown strength increases and conductivity decreases with the increase of mixing times,but when the mixing times are greater than three times,the breakdown strength changes little,and the conductivity increases slightly.The variable temperature space charge test shows that with the increase of mixing times,the nanocomposite medium has a strong ability to inhibit space charge at room temperature,but the ability of space charge suppression is significantly worse when the temperature reaches 60?.The above results show that the negative effect of impurities caused by slight thermal oxygen aging does not change the DC breakdown strength and electrical conductivity of composite medium,but leads to the deterioration of space charge performance above 60?.The trap distribution in nanocomposite media was measured by thermally stimulated current.It was found that compared with pure LDPE,a new current emission peak appeared at 90?,indicating that there existed deep trap level in the nanocomposite media.At the same time,it is found that the thermally stimulated current peak of the intrinsic structural defects of polyethylene,which is in the vicinity of 60?,is obviously suppressed in the nanocomposite.However,when the mixing frequency is greater than three times,the charge release peak of the nanocomposite medium at 60 is increasing,and the ?variation of space charge is basically the same with that above 60?.The above results indicate that the slight thermal oxygen aging increases the structural defects in the nanocomposite medium,and the space charge is very sensitive to this,so that the space charge performance of the nanocomposite medium at the temperature above 60 becomes worse after multiple mixing.?The research in this paper confirms that although multiple mixing can effectively improve the dispersion of nanoparticles and increase the electrical strength of the system,but when mixing too many times,the molecular degradation slightly although not significantly affect the dielectric strength and mechanical properties,it will significantly affect the system of the space charge inhibition ability at a higher temperature.