Research On DC Dielectric Properties Of Multifunctional Group Modified SEBS/PP Composite

The traditional cross-linked polyethylene(XLPE)cable insulation material has problems such as large production energy consumption,long processing cycle,and inability to recycle after the cable reaches its service life when manufacturing and using the cable.Driven by the recent interest in thermoplastic environmentally friendly cable insulation materials,polypropylene(PP),with its high melting temperature and excellent insulating properties,is widely regarded as the future replacement of XLPE.However,polypropylene is too hard and has poor flexibility,so it is not suitable for cable engineering applications.In order to improve these problems,the method of adding high-toughness elastomer materials to PP is usually used to achieve flexibility and toughness of PP materials.However,due to the poor insulation performance of thermoplastic elastomers,although the flexibility of the material is improved,the overall insulation performance is significantly reduced.In this thesis,in order to solve the problem that the flexibility and insulating properties of materials are difficult to synergize,maleic anhydride(MAH)and acetophenone units were modified in elastomer SEBS by grafting reaction and FriedelCrafts acylation reaction,and co-polymerized with PP.The PP-based thermoplastic cable insulation material was prepared by mixing.The acid anhydride functional group in MAH is used to form deep trap energy levels in polyolefin materials,which can effectively suppress space charges;the acetyl functional group carried by acetophenone molecules is used to suppress the generation of high-energy electrons through keto-enol conversion,which significantly improves the impact of the material.Wear strength.The study found that the elastomer material modified with bifunctional groups still has the function of toughening and flexibility,realizing the synergistic improvement of the flexibility and insulation performance of PP-based thermoplastic cable insulation materials.Infrared absorption data showed that the method adopted in this thesis successfully modified MAH unit and acetophenone unit in SEBS.Scanning electron microscopy experiments show that the grafting of maleic anhydride groups improves the compatibility of PP phase and SEBS phase,and significantly improves the dispersibility of elastomer phase.In the PP composite material,the PP phase and the elastomer phase present a uniform "island structure".DSC test results show that when the degree of acetylation is appropriate,the crystallization and melting temperatures of AC-SEBS-g-MAH/PP composites have little difference compared with pure PP,which retains the high temperature resistance of pure PP.The stress-strain performance test shows that AC-SEBS-g-MAH/PP has the effect of enhancing the toughness of pure PP,increasing the elongation at break and increasing the tensile stress at break at room temperature,indicating that the mechanical properties of the composite material meet the use of power cables Require.In order to study the effect of maleic anhydride group and acetophenone group on the trap characteristics of composites,according to the first-principles method of all-electron numerical orbital,the simulation software was used to calculate the SEBS grafted maleic anhydride group and acetophenone group.The density of electronic energy states,the calculation results show that the two groups grafted onto SEBS have two spatial structures respectively,which will generate two electronic bound states in the SEBS energy band gap,and the two groups can synergistically introduce deep trap pairs,which can effectively suppress the migration of carriers and reduce the injection of space charges,thereby improving the DC dielectric properties of the material.In terms of DC dielectric performance test,the space charge test results show that the appropriate amount of grafted material can significantly improve the ability of ACSEBS-g-MAH/PP composite to suppress space accumulation,and its high field strength at room temperature and 50 degrees Celsius The accumulation of space charges in the polarization process is smaller than that of pure PP.At 80 degrees Celsius,the accumulation of space charges is still smaller than that of pure PP.The electrical conductivity characteristics experiments show that the electrical conductivity of AC-SEBS-g-MAH/PP composites with appropriate acetylation is significantly lower than that of SEBS/PP,SEBS-g-MAH/PP,pure PP composites at the same temperature and field strength.the conductivity of the material.Appropriate amounts of acetophenone groups and maleic anhydride groups at different temperatures have a synergistic effect on improving the breakdown strength of the composite system,and an appropriate amount of acetylated AC-SEBS-g-MAH/PP improves the breakdown strength of SEBS/PP by 26 %,also higher than pure PP.The research in this thesis shows that the AC-SEBS-g-MAH/PP composite material has excellent DC performance under the premise of significantly improving the mechanical properties,and can be used in the manufacture of polypropylene insulated high-voltage DC cables.