3D-printed PLA/CNT/pyrrhotite ash composites for absorption-dominated EMI shielding and improved flame retardancy

Combining EMI shielding with flame retardancy in a single lightweight composite remains a key requirement for next-generation electronics and communication hardware. This work reports multifunctional 3D-printed PLA composites built from hybrid CNT/pyrrhotite ash (PA) fillers, further enhanced through a CNT-based spray coating. The uncoated PLA/CNT/PA6 formulation (0.5 wt% CNT, 6 wt% PA) delivered a total shielding effectiveness ( SE T ) of 15.45 dB at 2 mm thickness across the X-band (8.2–12.4 GHz), governed mainly by absorption. CNT coating raised SE T to 23.52 dB, equivalent to roughly 99% attenuation and well above the 20 dB level typically needed for practical shielding. This gain tracked a steep rise in electrical conductivity, from 1.62 10 −4 to 1.57 10 3 S/m, consistent with a continuous conductive surface layer formed by the coating. Conductive, magnetic, and dielectric loss mechanisms reinforced by improved impedance matching and interfacial polarization jointly account for the shielding behavior. Beyond shielding, the hybrid filler system also raised thermal stability, flame resistance, crystallinity, and mechanical properties, with PLA/CNT/PA6 showing the best stiffness, tensile strength, and hardness of all formulations tested. Together, these results point to a practical strategy for producing lightweight, fire-safe, mechanically robust EMI shielding composites for next-generation electronic systems.