Mechanical And Electrical Properties Of Polypropylene-based Insulating And Semi-conductive Shielding Materials

Polypropylene(PP)has a high melting point and electrical strength,and is a potential environmentally friendly cable insulation material.However,its low-temperature brittleness is poor and cannot be directly applied to cable manufacturing.The toughening modification of PP will lead to a decline in electrical properties.How to balance the relationship between mechanical properties and electrical properties is a difficult point in the development of insulating materials.In addition,PP has poor resistance to heat and oxygen aging,and the reasonable configuration of antioxidants is still to be studied.Moreover,when PP is used as a cable shielding layer,it is still a challenge to disperse carbon black uniformly in PP and maintain high mechanical strength and melting temperature.In summary,the study of PP-based insulating materials and semi-conductive shielding materials suitable for industrial applications has engineering value,and it is of scientific significance to study the influence of modified fillers on the properties of PP insulation and semi-conductive shielding materials.In this paper,copolymer polypropylene is used as the base material,and ethylene-octene copolymer(POE)and styrene-ethylene/butylene-styrene triblock copolymer(SEBS)are used as toughening modified fillers,systematic analysis of the influence of elastomer fillers on the electrical and mechanical properties of polypropylene-based insulation and shielding layers,the main conclusions are as follows.By comparing the inhibitory effects of different types of antioxidants on the thermal oxidative aging of materials,an antioxidant formulation system suitable for polypropylene insulation is selected.The study found that when the antioxidant 1035 and the antioxidant 168 are compounded at a ratio of 1:1,the oxidation induction period is the longest,the mechanical properties decline the least after thermal aging,and the oxidation resistance is the best.The order of antioxidant capacity of antioxidants is: antioxidant 1035 and antioxidant 168 compound> antioxidant 1010 and antioxidant 168 compound> antioxidant 1035> antioxidant 1010> antioxidant300.The melting crystallization curve shows that the compound system of antioxidant 1035 and antioxidant 168 can make the crystallization melting temperature of the material not change significantly after aging.After the elastomer is incorporated,the crystallinity of the composite material is reduced,the yield stress of the material is reduced,the toughness of the material is improved,and the composite material still has good heat resistance,and the maximum thermal elongation deformation is only 6.5%;The melt index test results show that the fluidity of the system decreases after the elastomer is incorporated,and the electrical performance test shows that the space charge accumulation of the composite material increases,the electrical strength decreases,the electrical conduction current increases,and the dielectric loss increases.Among them,when SEBS is used as a modified filler,the insulation performance is less reduced,which is better than the POE composite system.The performance difference of materials prepared by different mixing processes is mainly due to the fact that the shear stress of the twin-screw extruder is stronger than that of the torque rheometer.On the one hand,strong shear stress will make the distribution of elastomers more uniform;on the other hand,it will also degrade part of the PP macromolecular chains into small molecular chains.A more uniform distribution of the elastomer will increase the crystallinity of the material,increase the electrical strength,and decrease the electrical conduction current.The degradation of part of PP macromolecular chains into small molecular chains will lead to more structural defects,and increased space charge injection and electric field distortion.In the research of semi-conductive shielding materials,the dispersibility of carbon black in the polypropylene matrix is greatly improved by grafting maleic anhydride with polypropylene as a compatibilizing filler.The study found that the maleic anhydride graft rate of the compatibilized filler is positively correlated with the uniformity of carbon black distribution.After the dispersibility of carbon black is improved,the volume resistivity of the shielding material decreases significantly.The insulating materials and shielding materials prepared in this study meet the requirements of 35 k V cross-linked polyethylene standards and have industrial application value.