Study On Dielectric Properties Of Nano-SiO₂/PP/SEBS Composites

Polypropylene itself has excellent dielectric properties,but its disadvantages such as brittle fracture at low temperature,poor toughness,and high mold shrinkage severely restrict its application in power cables.By adding thermoplastic elastomer SEBS to PP,the mechanical properties can be significantly improved,but the electrical properties are also significantly reduced.The addition of nano-SiO₂ can effectively improve the electrical resistance of PP/SEBS,while the different nano-dispersion properties have a certain impact on dielectric properties.In this paper,the influence of the crystallization characteristics of polypropylene on its electrical properties was studied firstly.Then the nanocomposites with different dispersion characteristics were obtained by different preparation methods,and the DC and AC resistance performance tests were carried out.Studies have shown that the crystal morphology of PP is different under different preparation methods.The lower melting and crystallization temperature makes the number of PP spherulites increase,the spherulite size decreases,and the small spherulites can reduce the PP storage modulus.The higher melting and crystallization temperatures can be formed into a large and sparse spherulites.During the growth process,the large spherulites crowd out more structural defects into the amorphous region,and the space charge is significantly increased,the breakdown process can be developed along a shorter path,thereby the breakdown strength is significantly reduced.SiO₂/PP/SEBS composites with different nano-dispersion properties were prepared by different preparation methods.The dispersion characteristics of nano-silica were observed by scanning electron microscopy?SEM?.It was found that with PP/SiO₂ as the masterbatch,most of the nanoparticles are uniformly dispersed in the PP phase;with SEBS/SiO₂ as the masterbatch,the nanoparticles are mostly dispersed at the interface between PP and SEBS,and the dispersion is poor.When PP/SEBS is used as the masterbatch,the nanoparticles are in the PP and SEBS phases.Both are scattered and the dispersion is between the two.The DC resistance test results show that the PP will cause structural defects during processing,which will cause the DC performance to decrease.The filling of nano-SiO₂ can effectively improve the DC performance,and there are some differences in the nano-dispersion characteristics.When the nano-SiO₂ is mostly dispersed in the PP phase,The composite material can have better DC performance,and the nano-particles are mostly dispersed at the interface between PP and SEBS,and the DC performance improvement effect is poor.The results of AC electric test show that the doping of nanoparticles effectively improves the AC breakdown strength of composites,and the AC breakdown strength of nanocomposites with different dispersion characteristics is different.The improvement rule is similar to DC breakdown;It is found that the addition of SEBS will aggravate the initiation and growth of PP electric branches,and the doping of nano-SiO₂ can improve the ability of PP/SEBS to suppress electric branches,and the law of suppressing electric branches by different nano-dispersion characteristics is similar to that of AC and DC breakdown.