73 / 2021-06-08 10:25:43

Wood-derived Nanostructured Hybrid for Efficient Flame Retarding and Electromagnetic Shielding

nanostructured wood,PANI,flame retardancy,photothermal conversion,electromagnetic shielding

In recent years, electromagnetic pollution has become a serious environmental problem due to the rapid development of mobile phones, computers, wireless devices and other electronic products, which has seriously affected human health and the stability of the communication system. Traditional electromagnetic interference shielding materials are usually metals and metal composite materials, which achieve electromagnetic shielding effectiveness by reflecting electromagnetic radiation from free electrons (this shielding mechanism can easily cause secondary electromagnetic pollution). With the increasing development of human society, the demand for renewable and sustainable materials continues to increase. In this case, many works use biomass materials (cellulose, chitosan, collagen, etc.) combining with conductive polymers, carbon-based materials, magnetic or metal nanoparticles to build electromagnetic shielding materials. At present, most of the research on cellulose electromagnetic shielding materials is based on the bottom-up method where nanocellulose or its derivatives were prepared first and then integrated with metal nanoparticles, conductive polymers, etc. Wood is an endless natural material with a unique and orderly structure. After removing lignin and hemicellulose, the cellulose in wood retains a perfect porous 3D skeleton, which can be used as an ideal platform for electromagnetic shielding materials. Here, a top-down method was implemented to selectively remove lignin and hemicellulose to prepare wood aerogel composed almost entirely of cellulose, which were used as substrates for loading aniline monomers. Then, aniline was polymerized in situ with mixed acid (H₃PO₄ and HCl) as dopant. The obtained polyaniline-wood aerogel (PANI-WA) with a thickness of 2-3 mm showed a good electromagnetic interference (EMI) shielding effectiveness of 27.63 dB in the X band (8.2-12.4GHz). Moreover, the material simultaneously possessed excellent flame retardancy, which could self-extinguish and retained its original shape after repeated ignition. PANI-WA also exhibited the ability of photothermal conversion under near-infrared (NIR) irradiation. To sum up, the PANI was introduced through in-situ polymerization to develop a non-carbonized nanostructured wood with a porous structure and high conductivity, which can be used for electromagnetic interference shielding, while also having flame retardancy and photothermal conversion capability. The conductive nanostructured wood is a promising future research direction for the development of renewable, environmentally friendly, and lightweight electromagnetic shielding materials. What is more, it also solves the problem of flammability of cellulose in applications. Hence, as a multifunctional electromagnetic shielding material, PANI-WA has broad application prospects in construction, military and other fields.