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.
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