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

## TL;DR

This paper studies how the length of carbon nanotubes affects the properties of buckypaper used for blocking electromagnetic interference.

## Contribution

The study systematically investigates how MWCNT aspect ratio influences buckypaper processing and EMI shielding performance.

## Key findings

- Short MWCNTs form flexible buckypapers without aids, while long MWCNTs require sacrificial mats.
- Short MWCNT buckypapers show higher porosity and surface area compared to long MWCNT ones.
- Short MWCNT buckypapers achieve up to 36 dB EMI shielding effectiveness at submillimeter thickness.

## Abstract

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.