碳纳米纤维/高密度聚乙烯复合材料结晶行为和介电性能的研究

Crystallization and Dielectric Properties of Carbon Nanofiber/High-density Polyethylene Composites

利用新型纳米材料———碳纳米纤维(CNF)对高密度聚乙烯(HDPE)进行改性,采用转矩流变仪熔融共混和模压两步法制备1%～20%(质量分数,下同)CNF/HDPE复合材料。研究了CNF的分散特性及其对HDPE材料结晶行为和介电性能的影响。结果表明:CNF可良好分散于HDPE基体中,同时CNF会导致HDPE的结晶度和晶粒尺寸发生变化,并促进HDPE沿(110)晶面取向生长;另一方面,复合材料的介电常数随CNF含量增加而大幅度提高,当CNF含量为20%时,复合材料在103 Hz下的介电常数达到580,比HDPE提高～150倍;同时由于CNF的存在,与介电常数不随频率变化的HDPE不同,复合材料的介电常数表现出强烈频率依赖性。CNF对复合材料的AC导电率也有显著影响,当CNF含量达到10%以上时,AC导电率表现出明显的直流特性。

An attractive type of nanofiller-carbon nanofiber （CNF） was used to modify high-density polyethylene （HDPE）, in which the nanocomposites with 1%-20~//00 CNFs were prepared via a two- step process including melt mixing and hot press. The crystallization and dielectric properties of CNF/ HDPE composites, as well as the dispersion of CNFs, were investigated . The results showed that CNFs were well dispersed in HDPE. It was also demonstrated that the crystallinity and crystal size of HDPE were influenced by the introduction of CNFs. The （110） planes of HDPE was also enhanced as proved with the increased intensity of the characteristic peak. In addition, the dielectric constant of nanocomposites was dramatically improved with higher CNF contents. The highest dielectric con- stant, 580 at 10aHz, was achieved with 20~if0 CNFs, which was about 150 times higher than that of pure HDPE. Simultaneously, the dielectric constant of nanocomposites showed high dependence on the frequency due to the existence of CNFs, compared with the independent dielectric constant of pure HDPE. The AC conductivity of nanocomposites was also greatly affected by CNF,the characteristic of direct conductivity was obviously exhibited with the CNF concentration higher than 10%.