Research On Microstructure And Electrical Properties Of Nano-TiO₂/PP Composites

Cross-linked polyethylene has been used as a traditional cable insulation material for decades,but it suffers from a high number of by-products,complex processes,and the inability to recycle.Polypropylene cable materials are already in use on the market,but elastomers tend to lose some of their electrical properties while ensuring their mechanical properties.Therefore,it is necessary to optimize the AC/DC electrical properties of the substrate specimens by utilizing suitable modification methods,while maintaining their mechanical properties.In this thesis,P90-PP and NKT90-PP nanocomposites with different mass fractions（0.5wt%,1.0wt%,1.5wt%,2.0wt%）were prepared using polypropylene（PP）cable material as the matrix and untreated and surface-modified Ti O₂nanoparticles as fillers,respectively,using the melt blending method.The effects of Ti O₂ nanoparticles at different levels on the microstructure,electrical properties,and mechanical properties of the composites were investigated.The microscopic morphology was observed by SEM and PLM;the crystallization and melting process and crystallization characteristics of the composites were characterized by DSC and XRD;the trend of conductivity current with the electric field and the dynamic process of space charge accumulation and dissipation in the composites under DC electric field were analyzed;the electric breakdown characteristics of the composites under AC and DC electric field were studied and the insulation performance of different components of the composites was compared;the dielectric properties at different frequencies were tested and the internal interfacial polarisation behavior of the materials was analyzed;the effect of Ti O₂ nanoparticles on the toughness of the matrix was investigated by tensile experiments.The experimental results show that the P90-PP composite has a larger spherical crystal size;the NKT90-PP composite has a smaller and more regular crystalline size.Both Ti O₂ slightly improved the heat resistance of PP,advancing the crystallization process and increasing the crystallinity at contents of 1.0wt%and1.5wt%.NKT90 enhanced the tensile strain at break and tensile strength of the matrix PP.Ti O₂ nanoparticles introduce interfacial regions and traps in PP that restrict carrier movement and suppress the conductive current density and space charge accumulation;as the content increases,the distance between Ti O₂ particles decreases to produce low resistance paths for carrier transport,the current density begins to increase and charge accumulation occurs at the same time,and NKT90 is more effective in suppressing space charge accumulation.The NKT90 content of1.0wt%significantly increased the AC-DC breakdown field by 5.5%and 20.8%respectively;the hydrophilic P90 resulted in an overall lower AC-DC breakdown field than the matrix due to agglomeration.The overall increase in the dielectric constant of the composite is between 2.2 and 2.5 for Ti O₂ nanoparticles.In summary,the composite at 1wt%of NKT90 improves both the mechanical properties of the matrix and the AC/DC electrical properties,providing a reference for the development of new high-performance,green cable insulation materials.