Interfacial coupling of pitch- and PAN-based carbon fibers with carbon nanotubes in polyethersulfone for electromagnetic interference shielding

Abstract Lightweight thermoplastic polymer shields to suppress electromagnetic interference (EMI) exhibit a trade-off between processability and performance. In this study, we introduced a co-processing step in polyethersulfone (PES) to enrich the perimeter of short carbon fibers (CFs) with single-walled carbon nanotubes (CNTs). Scanning electron microscopy images of fracture surfaces revealed a continuous interphase along the fiber–matrix boundary. A CNT masterbatch with a polyol ester carrier, integrated via twin-screw extrusion and injection molding, improved dispersion and promoted direct linking at the fiber boundary to yield a percolated network. This interphase governed the shielding and mechanical responses of the composites, with electrical conductivity enhancement being the most pronounced in the coupled pitch-based fibers. With 3.2 mm plates in the X-band, the coupling increased the total shielding; at 10 GHz in the vertical orientation, the total shielding reached 44.3 and 54.6 dB for pitch- and polyacrylonitrile (PAN)-based composites, respectively, exceeding those in the horizontal orientation. S-parameter analysis indicated that the improvement from coupling was higher for absorption than for reflection, although the reflective fraction remained substantial. Coupling also increased the storage modulus across the measured temperature range, with the coupled specimen maintaining the highest modulus through the glass transition temperature. At equal filler contents, the Young’s modulus increased by 15.4 and 9.8% for pitch- and PAN-based composites, respectively, without compromising strength. These results indicate that interfacial coupling via PES and standard processing routes can enhance EMI shielding and preserve overall mechanical integrity, to facilitate the practical adoption of CF–CNT composites.