Synergetic Effect of Ni@MWCNTs and Hybrid MWCNTs on Electromagnetic Interference Shielding Performances of Polyurethane–Matrix Composite Foams

Polyurethane/multiwalled carbon nanotube (PU/MWCNT) composite foams containing MWCNTs with long length (MWCNT-L and Ni@MWCNT-L) and MWCNTs with short length (MWCNT-S) were prepared using an environmentally friendly water-blown method. The influence of different MWCNTs on the foaming process, morphologies, electrical conductivity, and mechanical and electromagnetic interference (EMI) shielding performances has been studied. The PU foams with MWCNT-L and MWCNT-S hybrid fillers (PU/MWCNT-L-S) display a more uniform cell structure compared with PU/MWCNT-L foams at the same filler loading because the short rod of MWCNT-S with mechanical sensitivity can help MWCNT-L eliminate the physical barrier during the foaming process. Conductance, polarization, and magnetic losses in PU/Ni@-2L-CNT-2L-4S foam can scatter and reflect electromagnetic waves inside the cellular microstructure and eventually transform into heat in the conductive networks. PU/Ni@-2L-CNT-2L-4S exhibited a density of 0.30 g/cm3 and excellent specific EMI shielding efficiency of 102.7 dB/(g/cm3) over the X-band.