(698d) Highly Conductive Polyolefin Nanocomposites: Controlled Dispersion of the Mixed Solid Nanofillers

Carbon nanotube is commonly used as conductive nanofiller to improve the electric conductivity of hosting polymer matrix.¹ However, the conductivity of the polymer nanocomposite depends on the net work formation of carbon nanotube in the polymer matrix, and high CNTs content was required to accomplish the conduction network in polymer matrix. To enhance the conductivity, additional treatments including chemical functionalization² and heating were have been reported to improve the dispersion of CNTs in polymer matrix. However, these treatments would cause negative effect on the conductivity of the pristine CNTs. In order to make a more efficient network formation of CNTs in polymer matrix, the conductive polypropylene (PP) nanocomposites were prepared by innovatively coating carbon nanotubes (CNTs) on the surface of gelated/swollen soft polypropylene (PP) pellets. The brand new processing method ensures the CNTs network formation in the polyer matrix and the electrical conductivity (σ) studies revealed a percolation value of only 0.3 wt% CNTs. At lower processing temperature, the CNTs formed network structure more easily in the polymer matrix resulting in a higher σ. Compared with the mixed α and γ crystal phases for pure PP, more γ phase PP (0.2533 at 160 °C) was observed in the polymer nanocomposites (PNCs) and the fraction of γ phase increased with increasing the pressing temperature. In addition, the CNTs at lower loading (0.1 wt%) served as the nucleating sites and promoted the crystallization of PP by reducing the surface free energy barrier towards nucleation. The CNTs were observed to favor the shear thinning behavior of the polymer matrix and at high shear rates, the CNTs serving as the branches of polymer chains favored the disentanglement of polymer chains and thus caused an even lower viscosity of PNCs than that of pure PP. The calculated optical band gap of CNTs from Tauc plot was observed to increase with increasing the processing temperature, i.e., 1.55 eV for PNCs prepared at 120 °C and 1.70 eV for PNCs prepared at 160 and 180 °C. Both Drude model and interband transition phenomenon have been used for theoretical analysis of the observed real permittivity variation from negative to positive (also called plasma frequency) and from positive to negative, respectively.

1.         Y. Li, J. Zhu, S. Wei, J. Ryu, Q. Wang, L. Sun and Z. Guo, Macromolecular Chemistry and Physics, 2011, 212, 2429-2438.

2.         H. Gu, S. Tadakamalla, X. Zhang, Y.-D. Huang, Y. Jiang, H. A. Colorado, Z. Luo, S. Wei and Z. Guo, Journal of Materials Chemistry C, 2013, 1, 729-743