Research On DC Dielectric Properties Of CPP-g-MAH/iPP/SEBS Composite

As a recyclable thermoplastic material,polypropylene has many advantages like chemical stability,good heat resistance,strong tensile and bending resistance,high breakdown strength,etc.It is a potential DC power cable insulation material,but its existing disadvantages such as modulus of presence is high,rigid and low temperature brittleness,and the insulating material is easy to accumulate space charge under DC electric field,resulting in local field strength distortion inside the material,it is easy to make the material aging,partial discharge or even breakdown,therefore,we need to improve two aspects of properties include the mechanical properties and dielectric properties of polypropylene.In this paper,thermoplastic elastomer SEBS was used as the toughening modified filler,cPP-g-MAH material with grafting group was used as the dielectric property modifying filler,and isotactic polypropylene,cPP-g-MAH/iPP/SEBS composite was prepared by melt blending,as well as iPP/SEBS composites used for comparison,were compared,and analyzed in terms of material characterization,crystallization properties,mechanical properties and DC dielectric properties.SEM experiments show that PP phase and SEBS in cPP-g-MAH/iPP/SEBS composite are presented as “island structure”,cPP-g-MAH improves the compatibility of PP phase with SEBS,and the dispersion of SEBS phase is obviously improved.DSC test results show that the crystallization and melting temperatures of cPP-g-MAH/iPP/SEBS composite is very different from iPP,which retains the high temperature resistance of iPP.The mechanical properties test showed that the elastic modulus of cPP-g-MAH/iPP/SEBS composite was reduced by 58% compared with iPP at room temperature.Although the thermal elongation was doubled,it was still better than the heat of XLPE under the same experimental conditions.The elongation shows that the mechanical properties of the composite meet the requirements of power cable production.In the field of DC dielectric performance test,the spacecharge test results show that the incorporation of grafted materials significantly enhances the ability of cPP-g-MAH/iPP/SEBS composite to suppress space charge accumulation,and its high field at home temperature.There is almost no accumulation of space charge during intense polarization.Conductivity characteristics experiments show that the conductivity of cPP-g-MAH/iPP/SEBS composite is significantly lower than that of iPP/SEBS composite at the same temperature and field strength,although its short-time DC breakdown strength is better than iPP/SEBS composite.The blend was slightly lower but still reached 255kV/mm at 90?.In order to study the influence of MAH on the trap characteristics of composite materials,the electronic energy density of polypropylene grafted maleic anhydride was calculated by simulation software according to the first principle method of full electronic numerical orbit.The calculations show that maleic anhydride grafted onto polypropylene will produce two electron-bound states in the band gap of polypropylene with trap levels of about 1.2 eV and 1.6 eV.It is considered that the deep trap of dense distribution can effectively suppress the migration of carriers and block the injection of space charge,thereby improving the DC performance of the material.The research in this paper shows that cPP-g-MAH/iPP/SEBS composite has excellent DC performance under the premise of obviously improving mechanical properties,and can be applied to the manufacture of polypropylene insulated high voltage DC cable.