Flexible Polyethylene Matrix Carbon-based Nanocomposites for Electromagnetic Compatibility

The feasibility of carbon nanofibers (CNF) to impart transport properties to a flexible and ductile polyethylene matrix for electromagnetic compatibility (EMC) was assessed in contrast to traditional carbon fibers (CF). Raman spectroscopy and electrical resistivity measurements of the bulk of the carbon fillers showed that commercial Pyrograf-III, PR-19 grade CNF were significantly more amorphous with lower transport properties than Thornel P-55 CF. A range of CNF/polyethylene nanocomposites (concentrations 0-40 wt %) were prepared via twin-screw extrusion and their electrical, dielectric, electrostatic dissipation, electromagnetic shielding, and mechanical properties were investigated. Good dispersion was revealed by electron microscopy, demonstrating the dispersibility of CNFs. PR-19 CNF led to superior surface conductivity and electrostatic dissipation at low concentrations. Nevertheless, the microcomposites prepared with P-55 pitch-based CF led to higher electromagnetic shielding (similar to 11 dB), electrical conductivities (i.e., surface resistivity of 1.4 x 10(3) Omega/sq), and relative permittivity (72.2-81.5j) at larger concentrations, displaying an in-plane anisotropic behavior. The microcomposites, though, displayed a stiff (modulus similar to 1.4 GPa at 40 wt %), weak (breaking strength of only similar to 3 MPa at 40 wt %), and brittle behavior (<3% at 40 wt %), whereas the nanocomposites retained acceptable flexibility (modulus similar to 1 GPa), strength (similar to 10 MPa), and ductility (similar to 30%) at comparable concentrations. This study points out the feasibility of pristine CNFs for flexible thin-wall materials for EMC applications.