Structure–Property Correlation of <scp>MWCNT</scp> @Polyurethane Foams: Mechanical Reinforcement, Electrical Conductivity, and <scp>EMI</scp> Shielding Effectiveness

ABSTRACT Electromagnetic interference (EMI) threatens the reliability of modern electronic systems, creating a demand for lightweight, absorption‐dominated shielding materials. In this work, multifunctional polyurethane (PU) foams reinforced with multi‐walled carbon nanotubes (MWCNTs) were fabricated via in situ polymerization and systematically evaluated in terms of microstructure, mechanical performance, electrical conductivity, and EMI shielding behavior. SEM analysis revealed a strong morphology–property correlation, where moderate MWCNT loading (1 wt%) refined the pore structure (average pore size ≈ 160 μm) and increased pore density, resulting in enhanced mechanical reinforcement (compressive modulus ≈ 4.1 MPa) and improved conductive pathways. EMI shielding measurements in the X‐band (8–12 GHz) demonstrated absorption‐dominated behavior, with the 1 wt% composite achieving an optimal total shielding effectiveness of approximately −16 dB. Although increasing the MWCNT content to 2 wt% further improved shielding effectiveness to −23 dB, it caused severe pore collapse and mechanical degradation due to nanotube agglomeration. Electromagnetic parameter analysis based on NRW‐derived relations confirmed strong dielectric losses and favorable impedance matching, explaining the effective attenuation achieved with only 6 mm thickness. Overall, this study establishes a structure–property optimization strategy for MWCNT/PU foams, highlighting their potential for lightweight EMI shielding applications.