Lignin doped epoxy acrylate sandwich electromagnetic shielding material synergized with Fe3O4 and CNT

A kind of novel electromagnetic shielding sandwich coating material with excellent electromagnetic interference shielding and coating properties was explored in this work. The interlayer was obtained through the in situ reaction of lignin, epoxy and acrylate doped with modified Fe3O4 nanoparticles (Fe3O4) and multi-wall carbon nanotubes (CNT) (FCLBEA). The FCLBEA layer was coated by two layers of lignin-based epoxy acrylate (LBEA) on both sides, and the total thickness was only around 1 mm. The SEM image showed that the Fe3O4 and CNT are uniformly dispersed in the LBEA matrix. The electromagnetic interference shielding efficiency (EMI SE) of LBEA@FCLBEA@LBEA sandwich material (LFL) was tested in the frequency range of 8.2–18 GHz, and the EMI SE value was higher than 10 dB in the entire measurement range. When the content of Fe3O4 and CNT was both 5% and the lignin content was 15%, the maximum EMI SE reached 14.8 dB. The LFL showed excellent hardness (4H) and adhesion (standard 1). The lignin enhanced the mechanical properties of LFL due to its benzene ring skeleton structure. In addition, the benzene ring of lignin interacted with CNT through π-π bond, which enhanced the dispersion of carbon nanotubes and Fe3O4 in the matrix, and promoted a complete electronic network formed in the system. The most important, the benzene ring in lignin has certain electromagnetic shielding effect, and can also form a synergistic effect with Fe3O4 and CNT to enhance the electromagnetic shielding performance. It was illustrated that the LBEA@FCLBEA@LBEA sandwich material with excellent overall properties can be promising in wide applications, such as EMI coatings, dark room and military fields.