Study on foamability and electromagnetic interference shielding effectiveness of supercritical CO ₂ foaming epoxy/rubber/MWCNTs composite

The functional multi-walled carbon nanotubes (fMWCNTs) and liquid carboxy-terminated butadiene-acrylonitrile copolymer (CTBN) were incorporated into epoxy (EP) resin to fabricate thermosetting composites, which were foamed using supercritical carbon dioxide (SCCO ₂ ). The foamability, electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) of foams were discussed. Owing to the heterogeneous nucleation caused by carbon nanotube, the average cell size of ∼400nm and cell density of ∼10 ¹² cells/cm ⁻³ were obtained, resulting in the excellent foamability of EP-CTBN-fMWCNTs systems. The biaxial stretching during cell growing facilitates fMWCNTs to align, forming 2D conductive networks, and resulting in the improvement of electrical property. The composite foam with fMWCNTs content of 5.0 wt% possesses EMI SE of 22.90 dB and specific EMI SE of 37.54 dB/(g cm ³ ), which attributes to its high electrical conductivity of 0.43 S/m and cellular morphologies that made electromagnetic microwaves multi-reflect from one cell to another and then be attenuated by conductive filler.