Study And Performance Of Lignin-based Electromagnetic Shielding Material

With the development of science and technology,people's life is increasingly dependent on electronic products.In addition,the development of electronic products is also very rapid.However,this also brings about serious electromagnetic interference,which not only affects the performance and reliability of electronic equipment,but also affects the human health.Therefore,the development of shielding materials is imminent.Lignin is an important biological material with biodegradability and renewability.It is rich in active sites and functional groups,such as hydroxyl,carboxylic acid,etc.,and thus can be modified through physical and chemical reactions.On the other hand,lignin contains many benzene rings,which is supposed to present certain electromagnetic shielding performance.In this paper,lignin was introduced to prepare electromagnetic shielding materials,and three kinds of flexible lignin-based electromagnetic shielding materials were prepared.Firstly,the lignin-based polyurethane electromagnetic shielding materials?FeGLPU?with excellent electromagnetic shielding properties were prepared and studied.KH550 was used to modify the reduced iron powder,and then the obtained modified reduced iron powder was mixed with lignin,polyethylene glycol?PEG200?,hexamethylene diisocyanate?HDI?and graphite to in-situ synthesize FeGLPU.The thermal stability,mechanical properties,and electrical conductivity of FeGLPU were described in detail.The electromagnetic shielding effectiveness?EMI SE?of FeGLPU was tested in the frequency range of 8.2-26.5 GHz.When the content of reduced iron powder and graphite was fixed at 10%and the content of lignin was 5%,the maximum EMI SE was 21.6 dB,and the frequency width of EMI SE greater than 10dB was 18.3 GHz.The electrical conductivity was 4.27×10^-4 S/m,and the tensile strength of Fe10G10L5PU reached 11.7 MPa.When the lignin content was 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 electrical conductivity was 1.06×10^-2 S/m,and the thermal decomposition temperature T₅?5%weight loss?reached 234?.It can be seen from the SEM observation that graphite and reduced iron powder are uniformly dispersed in the PU matrix.The graphite dispersed in PU matrix because of the conjugation interaction between the bezene group and the graphite.The excellent electromagnetic shielding effect obtained should be attributed to the synergistic effect between reduced iron powder,graphite and lignin.In this work,a new type of flexible lignin-based polyurethane?FCLPU?electromagnetic shielding materials with excellent properties was further prepared and studied.Carbon nanotubes?CNT?in lignin-based polyurethanes and aminated ferric oxide nanoparticles?Fe₃O₄?were used together as additives to improve electromagnetic shielding performance.KH550-modified Fe₃O₄ was mixed with lignin,PEG200,HDI and multi-walled CNT to in-situ synthesize FCLPU.When the content of Fe₃O₄ and CNT were both 10%and the content of lignin was 15%,the maximum EMI SE reached 37.5 dB,and the EMI SE value in the entire measurement range was greater than 20 dB.This excellent electromagnetic shielding effect was attributed to the synergistic effect between Fe₃O₄,CNT and lignin.FCLPU has an electrical conductivity of 0.48 S/m and a tensile strength of 7.25 MPa,which was sufficient for most applications.Finally,a new type of layered lignin-based epoxy acrylate resin electromagnetic shielding material?FCLBEA?with excellent properties was prepared and studied.CNT and Fe₃O₄ were used as additives and added to lignin-based epoxy acrylic resin.The synthesized FCLBEA was used as an intermediate layer.Then,a layer of lignin-based epoxy acrylate resin?LBEA?were coated on both sides of FCLBEA to obtain the film with a thickness of only 1 mm.The EMI SE of FCLBEA was tested in the frequency range of 8.2-18 GHz.When the content of Fe₃O₄ and CNT were both5%and the lignin content was 15%,the maximum EMI SE reached 14.8 dB,and the EMI SE value exceeded 10 dB in the entire measurement range.This excellent electromagnetic shielding effect was attributed to the synergistic effect between Fe₃O₄,CNT and lignin.The study illustrated that the lignin-based electromagnetic shielding material prepared in this paper was not only low-cost and eco-friendly,but also has excellent electromagnetic shielding properties,mechanical properties and high thermal stability.It is expected to be widely applied in the military and civilian fields.