Electromagnetic Shielding Property of Low‐Temperature Toughened Polypropylene Composites With Conductive Networks Transition Based on Dielectric and Rheological Analysis

ABSTRACT Conductive polymer composites were used as electromagnetic interference (EMI) shielding materials owing to their advantages such as light weight and corrosion resistance. Polypropylene (PP)/ethylene propylene rubber (EPR)/high density polyethylene (HDPE)/nickel‐coated carbon fibers (NCF) composites with varying NCF contents were prepared via melt blending. Mechanical analysis indicated that with the addition of 25 wt% NCF, the PP/EPR/HDPE/NCF composites achieved a 172% increase in low‐temperature impact strength and a 21% improvement in bending strength. The transition of conductive networks was investigated through dielectric and rheological behaviors. Notably, a weakened low‐frequency power‐law dependence of the storage modulus occurred when NCF contents ≥ 15 wt%, and this phenomenon became more pronounced with denser conductive networks. The EMI shielding exhibited frequency selectivity: denser conductive networks significantly enhanced EMI shielding effectiveness (EMI SE) in low‐frequency waves, while sparse conductive networks achieved excellent shielding in high‐frequency waves. Remarkably, the composite with 25 wt% NCF achieved an optimal EMI SE of 79.7 dB at 3 GHz, maintaining 50–60 dB at higher frequencies. Furthermore, after aging tests, the EMI SE of composites remained stable, demonstrating exceptional durability. PP/EPR/HDPE/NCF composites functioned as lightweight frequency‐selective EMI shielding materials with potential applications in electronics and aerospace over a broad frequency range (1.5–30 GHz).