Impact of MWCNT Aspect Ratio on the Processing and Functional Properties of Buckypaper for EMI Shielding Applications

Buckypaper (BP), a free-standing porous film composed of entangled carbon nanotube networks, is a promising material for lightweight and multifunctional electromagnetic interference (EMI) shielding. In this study, the effect of multiwalled carbon nanotube (MWCNT) aspect ratio on the processing, microstructure, electrical properties, and EMI shielding performance of buckypapers was systematically investigated. Two commercial MWCNTs with distinct geometries were used: short MWCNTs (S-MWCNT, aspect ratio ≈ 158) and long MWCNTs (L-MWCNT, aspect ratio ≈ 600). Buckypapers were fabricated by vacuum-assisted filtration with and without electrospun polyacrylonitrile (PAN) sacrificial mats. S-MWCNTs readily formed uniform, flexible, and self-supporting buckypapers without processing aids, whereas L-MWCNTs required sacrificial mats to enable film formation. Morphological and structural analyses (FEG-SEM, XRD, Raman spectroscopy, and N₂ adsorption) showed that higher-aspect-ratio MWCNTs promote agglomeration and denser networks, while S-MWCNT buckypapers exhibited higher porosity and surface area (up to 205 m².g^-1). Impedance spectroscopy revealed higher electrical conductivity for S-MWCNT buckypapers prepared without sacrificial mats (≈10^-1S.cm^-1), whereas residual PAN significantly reduced the conductivity. EMI shielding measurements in the X-band (8.2-12.4 GHz) demonstrated excellent shielding effectiveness for S-MWCNT buckypapers, reaching values up to 36 dB at submillimeter thickness, with reflection as the dominant attenuation mechanism. These results demonstrate that MWCNT aspect ratio is a key parameter governing buckypaper processability and functional performance, offering valuable guidelines for the design of lightweight EMI shielding materials.