Structure, Viscoelasticity and Electrical Conductivity of PMMA/HDPE/Carbon Nanofiber Composites

Abstract

In slow melt-blending and annealing of poly(methyl methacrylate) (PMMA) and carbon nanofibers (vapor grown carbon fibers, VGCFs) with very small amount of high density polyethylene (HDPE), the flexible HDPE chains adsorb onto the rough surface of the VGCF ends and behave like a glue between VGCFs. After 4 h annealing, the percolation threshold of VGCF is determined as 1.15 vol% from dynamic viscoelastic behavior of the PMMA/HDPE/VGCF composites at 200 °C. Applying the percolation theory for gel systems to the composites, the fractal dimension d f is found to be 1.8 -2.0, reflecting very effective connectivity of VGCFs facilitated by the selective adsorption of HDPE. The dimension d f is found to be smaller for the composite with smaller molecular weight of HDPE, while the threshold does not change. The addition of HDPE and annealing at 200 °C for 4 hours also lead to the prominent reduction in the critical concentration of VGCF to 0.71 vol% at the insulator-conductor transition (1×10 -7 S/m). When the VGCF content exceeds the viscoelastic threshold (1.15 vol%), the electrical conductivity of the composite approaches up to 10 S/m.