Preparation Method And Dielectric Properties Of Polypropylene Modified By UV-initiated Grafting MAH

Polypropylene(PP)has excellent electrical and heat resistance properties,the rigidity,brittleness and low-temperature impact resistance of PP have been solved with the emergence of high-elastic polypropylene.Based on this,PP has become the first choice for a new generation thermoplastic cable insulation materials.Despite that,as HVDC cable insulation material,PP still faces the coupling filed of intense electrical stress and elevated-temperature generated by the electric power and conductor heating.Accordingly,the in-depth development of the PP modification for HVDC is of great significance to further increase the operating voltage and current carrying capacity of the cable.In order to obtain excellent performance PP insulation materials,inspired by the principle of improving the DC dielectric properties by the deep trap introduced in polymer,the high grafting rate masterbatch inherited the mechanical properties and processability of PP,PP-g-(St*-co-MAH)has been prepared with ultraviolet light irradiation technology and anti-degradable material styrene derivatives.After adjusting the MAH content of the polar group in PP to an appropriate level by diluting the masterbatch,the grafted material was tested for DC dielectric properties in a wide temperature range under the cable operating conditions.The optimal grafting process was explored and PP-g-(St*-co-MAH)was prepared grafting masterbatch through tensile test,melt flow rate and gel content test of grafts prepared under different irradiation doses and grafting systems.The results of hydrogen nuclear magnetic resonance spectroscopy analysis and grafting rate determination of the grafting masterbatch showed that MAH and St*were successfully grafted onto the PP macromolecular chain with a superior level.Space charge distribution in a wide temperature range shows that the grafted MAH can significantly inhibit the accumulation of space charges in the PP body,restrain electric field distortion under strong fields,and avoid charge packet migration phenomenon in PP.The PP-g-0.57wt%(St*-co-MAH)shows the most excellent charge suppression properties at elevated temperature,and overlap polar groups will increase the depth of charge injection;Thermal stimulated depolarization current spectra shows that the introduction of MAH can bring PP with deeper and higher density deep traps distribute to improve its DC dielectric properties;The calculation results of the electron energy state density show that the grafting(St*-co-MAH)can introduce the electron bound state into the PP as a charge trap,which is in line with the TSDC test result;The electrical conduction current test shows that the introduction of the polar group MAH can greatly reduce the electrical conduction current in the PP material,and weaken its dependence on temperature and electric field;The DC breakdown test results further verified the excellent dielectric properties of PP-g-(St*-co-MAH).The calculation results of the 3D electrostatic potential distribution show that the MAH group can form a large area of high electrostatic potential,effectively trapping charges and reducing the carrier mobility,but the introduction of excessive MAH will reduce the formed electrostatic potential energy and the charge trapping ability.