Absorption‐Dominant Electromagnetic Shielding in Ultrathin <scp>PLA</scp> Composite Films Through Engineered <scp>MWCNTs</scp> @Ag and Multilayer Architecture

ABSTRACT Low‐thickness, eco‐friendly electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) are urgently needed to address escalating electromagnetic pollution in miniaturized electronic devices. Herein, we synthesized silver nanoparticle‐decorated multiwalled carbon nanotubes (MWCNTs@Ag) via a rapid solvent‐free method and integrated them into poly(lactic acid) (PLA) matrices to fabricate composite films through solution casting. The resulting PLA/MWCNTs@Ag composite film containing 10 wt% MWCNTs@Ag achieves an average EMI SE of 18.59 dB at a thickness of approximately 95 μm, with the shielding mechanism dominated by surface reflection. To strategically control EMI attenuation pathways, multilayered architectures were engineered using layer‐by‐layer solution casting while maintaining identical filler content. Systematic analysis reveals that both thickness and layer number significantly influence EMI shielding performance. Notably, a multilayer film with a thickness of approximately 155 μm and seven layers exhibits an average EMI SE of 24.43 dB with an absorption‐dominated mechanism, showing a 31.41% enhancement over single‐layer counterparts. This performance transition from reflection to absorption dominance originates from optimized impedance matching, enhanced interfacial polarization, multiple internal reflections, and reconstructed conductive networks enabled by structural design. The synergy between hierarchical structure engineering and hybrid filler incorporation provides new insights for developing sustainable high‐performance EMI shielding materials.