Microcellular foaming enabled nanoporous thermoplastic polyurethane/multi-walled carbon nanotubes composites with enhanced electromagnetic interface shielding and mechanical performance

A flexible and environmentally-friendly methodology is proposed to prepare microcellular and nanocellular thermoplastic polyurethane (TPU)/multi-walled carbon nanotubes (MWCNTs) nanocomposites. Thanks to the heterogeneous nucleating effect of MWCNTs, the TPU/MWCNT nanocomposite foam can achieve nanocellular morphology, while the pure TPU foam can merely show microcellular morphology. The significantly refined cellular morphology not only endows the TPU/MWCNT nanocomposites with lightweight and flexibility, but also significantly enhances their electromagnetic shielding performance. The electromagnetic interface (EMI) shielding effectiveness of the nanocellular TPU/MWCNT nanocomposite foam with 10 wt% MWCNT is up to 40 dB, while that of the solid nanocellular TPU/MWCNT nanocomposite with the same MWCNT content is only about 25 dB. The enhanced electromagnetic shielding capacity is due to the significantly enhanced electrical conductivity by the refined cellular morphology, meanwhile the porous morphology also creates more reflective interfaces, which increases the loss of electromagnetic waves by multiple reflections and absorptions. Moreover, the foamed TPU/MWCNT nanocomposites show absorption-dominated shielding behavior, while the solid TPU/MWCNT nanocomposites show reflection-dominated shielding behavior.