强剪切流动下聚丙烯基复合材料介电性能和结构演变的研究

研究了多壁碳纳米管(MWCNT)、线型低密度聚乙烯(LLDPE)和强剪切流动场对聚丙烯(PP)/MWCNT/LLDPE复合材料的导电性能、结晶性能、力学性能和介电性能的研究。结果表明,PP/MWCNT复合材料随着MWCNT含量的提高,导电性能逐步改善,导电逾渗值约为1.8%,而第二分散相LLDPE的引入使复合材料的导电性能表现出了先降低后升高的现象,并且随着LLDPE含量的增加,MWCNT逐步向LLDPE内部迁移,构成了双连续结构。复合材料经过固态口模拉伸的强剪切流动场之后,随着拉伸速率从10 mm/min增加到300 mm/min的过程中,复合材料的融化温度逐渐向高温方向偏移,表现出了片层厚度增加的现象。复合材料内部分子链取向和纤维结构的形成,能够显著提高复合材料的拉伸强度和介电性能,拉伸强度提高从约50 MPa提高到了约240 MPa,提高了约380%。MWCNT和强剪切流动场的引入也使复合材料的介电常数大幅提升。

Dielectric Property and Structural Evolution of Polypropylene Matrix Composites under Strong Shear Flow

The effects of multi-wall carbon nanotubes(MWCNTs),linear low-density polyethylene(LLDPE)and strong shear flow field on the conductivity,crystallization,mechanical and dielectric properties of polypropylene(PP)/MWCNTs/LLDPE composites were investigated.The results show that the conductive performance of the composite is gradually improved with the increase of MWCNTs content,and the conductive percolation value is about 1.8%.The introduction of second dispersed phase LLDPE could make the conductive performance of the composite decrease firstly and then increase.Moreover,with the increase of LLDPE content,MWCNTs gradually migrates into LLDPE phase and forms a double-continuous structure.After applying the strong shear flow field by solid-die drawn machine,as the tensile rate increases from 10 mm/min to 300 mm/min,the melting temperature of the composite gradually shifts to the high temperature direction,showing the phenomenon that the lamellar thickness increases.The formation of molecular chain orientation and fiber structure inside the composite material can significantly improve the tensile strength and dielectric properties of the composite material,and the tensile strength increases from about 50 MPa to about 240 MPa,which has increased about 380%.The introduction of MWCNTs and strong shear flow field greatly increases the dielectric constant of the composite material.