Lignin Based Flexible Electromagnetic Shielding PU Synergized with Graphite

In this paper, lignin (L)-based polyurethane (FeGLPU) with excellent electromagnetic shielding properties was prepared and studied. The modified reduced iron powder was modified with KH550, and then the obtained modified reduced iron powder (Fe) was mixed with lignin, polyethylene glycol 200 (PEG200), hexamethylene diisocyanate (HDI) and graphite (G) to in-situ synthesize the FeGLPU. The thermal stability, mechanical properties, electronic conductivity, and morphology of the composite FeGLPU were characterized in detail. The electromagnetic interference shielding effectiveness (EMI SE) of FeGLPU was tested in the frequency range of 8.2–26.5 GHz. When the content of Fe and G was fixed at 10% and the lignin content was 5%, the maximum EMI SE was 21.6 dB, and the frequency width of EMI SE greater than 10 dB was 18.3 GHz. The conductivity was 4.27×10−4 S/m, and the tensile strength of Fe10G10L5PU reached 11.7 MPa. When the lignin content increased to be 20%, the maximum EMI SE was 22.5 dB, and the frequency width of EMI SE greater than 10 dB was 18.3 GHz. The conductivity was 1.06×10−2 S/m, and the thermal decomposition temperature T5 (5% weight loss) reached 234 °C. The obtained excellent EMI SE should be due to the synergistic effect of Fe, G and lignin. It can be observed from the SEM observation that the G and Fe are uniformly dispersed in PU matrix with strong interfacial interaction. It was illustrated that the prepared FeGLPU was with efficient electromagnetic shielding properties, good mechanical properties, and high thermal stability. This lignin based electromagnetic shielding PU was proposed to have broad application prospects due to its low expenses and ecology friendliness.