Dielectric properties of multi-phase carbon nanofiber/polyethylene composites

An attractive type of nanofiller-carbon nanofiber (CNF) was used to modify High-density Polyethylene (HDPE) and polymer blends (UH-HDPE) of HDPE and ultra-high molecular weight polyethylene (UHMWPE), and two-phase and three-phase nanocomposites were prepared via a two-step process including melt mixing and hot press. The effects of CNF addition and their dispersion on the dielectric properties of nanocomposites were investigated. The results show that CNFs are well dispersed in HDPE matrix, while they are not permeated into the UHMWPE. It is demonstrated that CNFs are distributed homogenously in two-phase CNF/HDPE composites and heterogeneously in three-phase CNF/UH-HDPE composites. The dielectric constant of nanocomposites is dramatically improved with higher CNF content. The highest dielectric constant in CNF/HDPE composites, 190 at 102 Hz, is achieved with CNFs above 10% (mass fraction, the same as below), which is about 50 times higher than that of pure HDPE. Simultaneously, the dielectric constant of CNF/HDPE composites shows high dependence on the frequency due to the existence of CNFs, compared with the independent dielectric constant of pure HDPE. The influence of CNFs on the dielectric constant of CNF/UH-HDPE composites is similar to that of CNF/HDPE composites. However, the dielectric constant of three-phase composites is higher than that of two-phase counterparts with the same CNF addition. Additionally, no obvious dielectric loss is exhibited in both nanocomposites with CNF concentration under 5%.