Synergistic Effects of Hybrid Single-Walled Carbon Nanotube/Carbon Black Fillers in 3D-Printable Polyamide 6 Nanocomposites: Balancing Electrical Conductivity and Mechanical Performance

Abstract

Conductive polymer nanocomposites for additive manufacturing face a persistent trade-off, as achieving electrical conductivity requires filler loadings that impair processability and mechanical integrity. While PA6 provides superior thermal and mechanical properties compared to PLA and ABS, conductive PA6 systems remain severely understudied. This study addresses the gap by systematically investigating asymmetric SWCNT/CB hybrid ratios (1:3) in PA6 matrices. Compositions spanning 0.25-1 wt% SWCNT and 1.5-3 wt% CB were characterized, revealing that asymmetric hybrids significantly outperform both single-filler and balanced hybrid systems. The optimized PA6/1% SWCNT/3% CB composite achieved 80 Omega cm resistivity in compression-molded samples and 7 x 10(6) Omega cm in 3D-printed parts, representing a 2.4-fold improvement over single-filler systems and nearly two orders of magnitude over balanced hybrids, while maintaining melt viscosities suitable for printing (<= 5 x 10(4) Pa s at 270 degrees C). Improved conductivity was attributed to geometric complementarity between high-aspect-ratio SWCNTs and spherical CB particles, enabling efficient interparticle bridging. Mechanical testing revealed trade-offs: intermediate loadings (0.5% SWCNT/1.5% CB) enhanced tensile strength by 60% (37 MPa), whereas electrically optimized formulations sacrificed strength (14 MPa). Processing effects increased resistivity by two orders of magnitude in 3D-printed specimens, quantifying layer-by-layer deposition impacts for PA6 hybrids. These findings establish structure-property-processing relationships critical for advancing PA6-based conductive composites in additive manufacturing.