Electrical Insulating Polymer Composite Foams: Achieving Improved EMI Shielding and Absorption through Double-Percolated Structures with Phase Coarsening and Selective Cell Distribution

Polymer composites with electrical insulation and electromagnetic interference (EMI) shielding have attracted a lot of interest. However, the introduction of conductive fillers in polymer composites inevitably leads to a dramatic decrease in electrical resistivity. Herein, double-percolated polycaprolactone (PCL)/polystyrene (PS)/multiwall carbon nanotube (MWCNT) foams with phase coarsening and selective distribution of cells were obtained through a combination of melt mixing, supercritical carbon dioxide (scCO2) annealing, and subsequent foaming. Annealed PCL/PS/MWCNT foams were found to have optimized filler dispersion in the PS phase and increased connectivity of the double-percolated network due to scCO2 annealing. Additionally, the cell structure specifically placed in the PCL phase reduced impedance mismatch and improved electrical insulation. A high electrical resistance of 4.6 × 1010 Ω·cm, an electromagnetic interference shielding effectiveness (EMI SE) of 48.0 dB, and an absorption coefficient of 0.65 were achieved for annealed PCL/PS/MWCNT foams. This study offers a sustainable and efficient method to create double-percolated foams with high electrical resistance, EMI SE, and electromagnetic wave absorption capacity.