Research On DC Dielectric Properties Of Crosslinking Polyethylene Grafted Chloroacetic Acid Allyl Ester

Crosslinking polyethylene(XLPE)is easily led to form the phenomenon of space charge accumulation in the interior by the effect of high voltage direct electric field,which may distort the electric field in the material and cause the insulation failure.The space charge characteristic of XLPE can be improved by the composite modification technology of inorganic nanoparticles in the polymer,but the effectiveness of this method depends largely on the dispersion of nanoparticles.The compatibility of inorganic nanoparticles and polyethylene is not steady and the agglomeration phenomenon often appears,which has an adverse effect on the property of material.In order to improve the space charge characteristic of XLPE and overcome the agglomeration of nanoparticles in polyethylene,grafting polar compounds is used to introduce polar groups into the material.Meanwhile deep traps are introduced to suppress the formation and accumulation of space charge.Chloroacetic acid allyl ester(CAAE)with polar groups is grafted on molecular chain of crosslinking polyethylene(XLPE)during the crosslinking reaction by taking dicumyl peroxide as initiator.XLPE-g-0.5wt%CAAE,XLPE-g-1.0wt%CAAE and XLPE-g-1.5wt% CAAE are prepared to explore whether grafting CAAE can improve the DC dielectric properties of XLPE.In this paper,XLPE is compared with 3 kinds of XLPE-g-CAAE with different grafting content of CAAE in material characterization,crystallization property,mechanical property and DC dielectric properties.Infrared spectrogram proves that CAAE has been grafted successfully on molecular chain of XLPE.The heat extension and the gel extraction experiment show that grafting CAAE has no obvious influence on the crosslinking degree of the material.The heat resistance and cracking resistance of the material are still stable.The results of DSC test show that grafting CAAE has little effect on the crystallization properties of the material.The tensile test and DMA test results show that mechanical property of XLPE-g-CAAE is slightly lower than that of XLPE,but the difference is little.Compared with XLPE in the DC dielectric performance tests,XLPE-g-CAAE shows excellent ability to suppress space charge and has lower conductivity current and higher breakdown strength.The breakdown strength of XLPE-g-CAAE is still higher than that of XLPE in high temperatures.The effect of DC dielectric performance improvement of materials is the best when content of CAAE is 1.5wt%.Grafting polar groups introduces position fixed,uniformly and dense distributed deep traps in material.Electrons or holes may be trapped and forming the charge distribution like lattice and Coulomb force field,which could effectively suppress further injection of electrons or holes from electrode and migration of charge carrier in the bulk of material.Therefore,the purpose of restraining the formation and accumulation of space charge and improving DC dielectric properties is achieved.This research may provide an idea for the development of HVDC power cable insulation materials.