Tuning electromagnetic absorption for EMI shielding in PBSA composites with Fe3O4-decorated carbon nanotubes

This study investigates the electromagnetic interference (EMI) shielding behavior of bio-based poly(butylene succinate-co-adipate) (PBSA) composites filled with magnetite (Fe 3 O 4 )-grafted single-walled (SWCNT) and multi-walled carbon nanotubes (MWCNT). Hybrid fillers were synthesized via one-step aqueous co-precipitation onto non-functionalized CNTs, yielding nominal Fe 3 O 4 contents of 15 and 30 wt.% (actual: 12.1-26.9 wt.%), expressed as a fraction of the total filler mass. They were then incorporated into PBSA at 0.10-2.0 vol.% via solvent casting. Microscopy revealed two distinct hybrid filler morphologies: individual Fe 3 O 4 nanoparticles dispersed along CNT sidewalls and agglomerates concentrated at CNT junctions. Magnetometry showed that the deposited Fe 3 O 4 was superparamagnetic, with specific magnetization calculated to range from 4.7 to 65 emu/g depending on crystallite size. Tensile testing revealed up to a 2.2-fold increase in elastic modulus and a 1.4-fold increase in ultimate tensile strength. Sheet resistance indicated percolation at ~ 0.1 vol.%, increasing to ~ 0.5 vol.% after Fe 3 O 4 co-precipitation. The composites were analyzed by electromagnetic spectroscopy in the frequency ranges of 0.1-3 GHz and 8.4-12.6 GHz. CNT incorporation produced shielding in which dissipation carried the larger share of the shielding effectiveness, with ⟨SE A ⟩/⟨SE T ⟩ ratios of up to 0.78. Fe 3 O 4 -grafted MWCNT composites at 1.0 vol.% exhibited a broadband absorption plateau below 3 GHz (⟨SE A ⟩/⟨SE T ⟩ ratio of 0.70), which the SWCNT-based composites did not develop in this range. Unmodified SWCNT composites at 2.0 vol.% transitioned to reflection-dominated shielding at 8.4 to 12.6 GHz. This work indicates that CNT morphology is an important design variable for absorption-based EMI shielding.