Effect Of Maleic Anhydride Graft Modification On The Mechanical And DC Dielectric Properties Of Polypropylene Based Composite

Polypropylene(PP)has excellent electrical and heat resistance properties.Compared to traditional cable insulation material cross-linked polyethylene(XLPE),PP does not require cross-linking during cable manufacturing and use,resulting in reduced production energy consumption,significantly shortened processing cycles,and retired cables that can be recycled,meeting the national "dual carbon" development goals,and has great industrial application value.However,the bending modulus of polypropylene is too large and its flexibility is poor,making it unsuitable for direct application in cable manufacturing.To improve the above problems,it is generally necessary to add highly flexible elastomer materials to PP,in order to achieve the goal of increasing flexibility and toughness of the PP material.However,due to the low melting temperature and crystallinity of conventional elastomers,their insulation performance is poor.Although the flexibility of the material is improved,the electrical properties of the material at high temperatures are significantly reduced.In order to improve the direct current performance of PP/elastomer composite materials,especially the space charge and conductivity characteristics above 70 ℃,this thesis selects an elastomer with high melting temperature and high crystallinity as a flexible modification filler,and grafts maleic anhydride(MAH)molecules carrying polar groups onto polypropylene and high melting temperature elastomers.The deep trap effect generated by polar groups is utilized to suppress carrier migration,Thus improving the direct current performance of the material.This article first uses diisopropylbenzene peroxide as the initiator and styrene derivatives as degradation inhibitors,and uses melt grafting technology to graft MAH polar groups onto PP and elastomer macromolecular chains.The infrared spectrum absorption experiment shows that this method can achieve a high grafting rate and reduce the degradation of the material due to grafting.The DC breakdown strength,space charge,and conductivity current characteristics of PP-g-MAH were tested under different grafting amounts of MAH.The experiment found that the direct current performance of PP was significantly improved after grafting MAH.When the amount of MAH was 1%,the direct current performance of PP-g-MAH was optimal at different temperature ranges.Prepare samples by blending PP-g-MAH with low melting temperature elastomers and high melting temperature elastomers without grafting or grafting modification,respectively.Various modified polypropylene based composite materials have been prepared.Scanning electron microscopy(SEM)experiments have shown that the dispersion of the elastic phase in the composite material is improved after PP grafting treatment.Among them,the high crystallinity elastomer without grafting modification shows obvious phase separation characteristics with PP,and there is an incompatible zone at the interface.After both PP and elastomer have undergone grafting modification,the two phase interfaces fuse with each other,exhibiting good compatibility.The results of differential scanning calorimetry(DSC)showed that the crystallinity of PP decreased after blending with elastomer,and the crystallinity of the composites could further decrease after both phases were grafted.The hot extension experiment shows that the composite material has a deformation rate of less than 15%at 165 ℃ and has good heat resistance performance.The dynamic thermal mechanical analysis(DMA)experimental results show that the two types of elastomers have a significant softening effect on PP,and the elastic modulus of the composite material has significantly decreased compared to PP.After biphasic grafting,the elastic modulus of the composite material further decreases.The stress-strain experiment shows that two-phase grafting can better improve the fracture elongation and tensile strength of composite materials compared to single-phase grafting.The DC breakdown experiment,conductivity characteristic experiment,and space charge characteristic experiment show that the DC performance of the composite material has been improved after grafting at various temperatures.However,when using low crystallinity elastomer for composite modification,due to its low melting temperature,even grafting modification cannot achieve the ideal DC performance improvement effect in the high-temperature region;By using high crystallinity elastomers and grafting them with PP-g-MAH,excellent DC performance improvement can be achieved in the high-temperature region,significantly suppressing space charge accumulation,and reducing the electric field distortion amplitude of the composite material in high temperature and strong fields.The research results of this article indicate that blending high crystallinity and high melting temperature elastomers with PP is beneficial for improving the DC performance of the composite material at high temperatures,but it will significantly decrease the mechanical and physical properties due to the incompatibility of the two phases.Graft modification technology can improve the compatibility between PP and high melting temperature elastomers,significantly enhance the DC performance of composite materials,and achieve synergistic optimization of material mechanics and DC performance.