Fly ash cenospheres as sustainable carriers for enhanced dispersion of carbon nanotubes in composites

This study introduces a novel and scalable method for improving the dispersion of carbon nanotubes (CNTs) in composite materials by utilizing hollow aluminosilicate fly ash cenospheres (FACs) as micro-scale carriers. The fabrication process leverages cohesion of the FACs and CNTs in an aqueous suspension, leading to the formation of a hybrid CNT-FAC filler. This approach mitigates CNT agglomeration and ensures their uniform distribution within the composite matrix. Two types of composites were fabricated and characterized: a transformer oil-based system to investigate pressure-dependent conductivity and a polyurethane (PU)-based system to evaluate electromagnetic (EM) shielding properties. The oil-based composites containing single-walled CNTs (SWCNTs) demonstrated a reproducible and reversible increase in electrical conductivity above a pressure threshold of 1 MPa, attributed to the formation of a percolating conductive network. In contrast, anisotropic compression caused an irreversible conductivity enhancement due to matrix densification. The PU-based composites with 20 wt% of the SWCNT-FAC filler exhibited a superior EM shielding performance, with a minimum return loss of −17 dB at ∼5 GHz, significantly outperforming composites with conventionally dispersed CNTs. The findings demonstrate that using FACs as CNT carriers is an effective and sustainable strategy for developing lightweight, multifunctional composites with tunable electrical and EM properties for applications in sensing and EMI shielding.