Preparation Of Materials Based On Cellulose Nanofibers And The Study On Its Electromagnetic Shielding Performance

The development of communications,artificial intelligence and advanced manufacturing fields bring great convenience to people’s daily life,while these electronic and electrical equipment in the work process will also produce a large amount of electromagnetic radiation,which will not only affect electronic devices and military strategic equipment,resulting in equipment failure and degradation,affecting information security,but also cause harmful electromagnetic radiation pollution,and thus endanger human health and production life.Electromagnetic interference shielding technology（Electromagnetic Interference,EMI）has an important role in suppressing electromagnetic radiation,and the preparation of flexible,light and durable,comprehensive performance and green non-polluting electromagnetic shielding materials is the key to achieve electromagnetic wave shielding.Cellulose is one of the most abundant and sustainable natural biopolymers on the earth.Cellulose nanofibers（CNFs）have high aspect ratio,reliable stability,excellent flexibility and lightweight properties,which can effectively enhance the mechanical strength and toughness of materials,and their low density and large specific surface area can be used as dispersants in composite materials to improve the agglomeration problem.Besides its abundant resources in nature,renewable and degradable,it is ideal for the preparation of green electromagnetic shielding materials.The aim of this study is to use cellulose nanofibers as matrix and dispersant,and some other functional materials（such as reduced graphene oxide,silver nanowires,polypyrrole and carbon materials,etc.）as fillers to regulate the structure of the composites by simple vacuum filtration and freeze-drying methods to achieve ordered assembly of cellulose nanofibers and functional materials.Thus,lightweight,ultra-thin,and flexible electromagnetic shielding materials with ordered structure,high porosity,high resilience and excellent mechanical strength are prepared,and the influence of the structure on the electromagnetic shielding performance and the mechanism of electromagnetic shielding are explored.The main study and research results are as follows:（1）The composite conductive films were prepared by adjusting the amount of polypyrrole,cellulose nanofibers and graphene oxide.The conductive films prepared by reduction,freeze-drying and compression have a conductivity of up to 0.45 S cm^-1 at a thickness of 1 mm and an electromagnetic shielding of up to 26.79 d B,which meets the commercial standard,and can block 99.79%of electromagnetic waves with an absorption loss of 70%,showing an absorption-based electromagnetic wave shielding mechanism.（2）An ultrathin conductive composite paper was prepared by alternate extraction and reduction with Ag NWs/GO of different mass ratios using cellulose nanofibers as the basic raw material.The thickness of the composite paper is only 34μm and its electrical conductivity is 7.2 S cm^-1.Due to the improvement of the sandwich structure,the tensile strength of the composite paper is 26.7 MPa,the elongation at break is 2.87%,and the electromagnetic shielding performance is 24 d B,which can block 99.6%of the incident electromagnetic waves,and the absorption loss accounts for 64%,showing an absorption-based electromagnetic shielding mechanism.In addition,the resistance did not change significantly under 100times of bending.（3）Carbon aerogel with regular,porous lamellar structure was prepared by targeted freeze-drying and carbonization using cellulose nanofibers and graphene oxide as the backbone materials.The carbon aerogel exhibited excellent mechanical properties and electromagnetic shielding performance.The height retention after 90%release of compressive strain was 97.5%,and effective rebound was achieved.The height retention was 88%and stress retention was 90.9%after 100 cycles of strain 70%and compression release.The electromagnetic shielding effectiveness of the carbon aerogel can reach 67.52 d B,which can block 99.999%of electromagnetic waves,and demonstrates an absorption-based electromagnetic shielding mechanism with a 97.5%absorption loss ratio.The carbon aerogel has good linear sensitivity(S=2.11 KPa^-1)and can be used as a sensor to accurately capture biological signals.