Conductive Filament Composites from Waste Battery Rod-Derived Exfoliated Graphite for Fused Deposition Modeling 3D Printing: A Two-Level Factorial Design Optimization Study

Abstract

This study used carbon rods from spent zinc-carbon batteries as a source of exfoliated graphite (EG) to produce conductive filament composites for fused deposition modeling 3D printing. The EG filler was prepared through microwave irradiation, while the resulting 3D printable electroconductive EG composites were prepared using polylactic acid (PLA) and polyethylene glycol (PEG) as the polymer matrix and compatibilizer, respectively, via a sonication-assisted solution blending and melt extrusion process. A two-level full factorial design was employed to fully investigate the influence of filament production parameters such as EG loading, PEG:PLA ratio, and sonication time on the resistivity (i.e., conductivity-1) of the prepared composites. Analysis of variance showed that both EG loading and sonication time had significant effects on the resistivity of the composites. The optimum electrical resistivity of the new EG filament composites was found to be 916.418 Ω-cm (maximum conductivity = 1.091 x10-3 S/cm) at EG loading = 45 % w/w, PEG:PLA ratio = 1:10, and sonication time = 2 hours. The conductivity of the 3D printed composites was also correlated with EG amount by the power law model of percolation theory, resulting in an electrical percolation threshold at around 35 % w/w of EG. Our filament composites enable the fabrication of high-value conductive materials from waste resources for sustainable additive manufacturing in the electronics industry.