Controlled Electromagnetic Shielding And Electrically Induced Elastic Wood Construction And Its Properties

The purpose of this study is to use renewable natural wood as raw material,combined with hydrothermal reaction and in-situ nano-loading technology,to regulate the internal pore and wall microstructure of wood,regulate the growth and adhesion effect of nanomaterials,and develop wood-based force-electric induction and controllable electromagnetic shielding dual smart materials.The effects of the microstructures,mechanical properties,types and loads of active nano-substances on the mechanical sensing properties and electromagnetic shielding switch properties of smart elastic wood were revealed,and the rules of action were provided for further development of biomass-based smart materials.The main results are as follows:（1）Natural balsa wood was used as the base material.After 24h hydrothermal reaction with alkaline aqueous solution of sodium hydroxide and sodium sulfite at 100℃,and then hydrothermal treatment with hydrogen peroxide solution at 100℃for 4h,the lignin and hemicellulose in natural wood were removed,and white elastic wood（DW）was obtained after freeze drying.The DW exhibits a low elastic modulus（175 k Pa）and can recover completely without plastic deformation residue under the condition of strainε=60%and 100 compression and release cycles.（2）With the DW as the base material,ferric oxide was synthesized in situ on the wood surface by hydrothermal reaction in the solution of Fe Cl₂·4H₂O and Fe Cl₃·6H₂O mixed with iron ions at 150℃,and dark brown magnetically elastic wood（Fe W）was prepared.VSM magnetic property testing revealed that Fe W had good soft magnetic properties and a sensitive magnetic response,with a saturation magnetization intensity of 18 emu·g^-1.Under the condition of strainε=40%and 100compression and release cycles,it can still recover completely without plastic deformation.However,the electromagnetic shielding performance of Fe W is poor,which decreases from 7.1-12.1 d B before compression to 2.6-3.8 d B after compression at 8.2-12.4 GHz.（3）With the DW as the base material,soaked in ferric chloride solution,freeze-dried,and then deposited by pyrrole cryogenic vapor deposition to obtain the black conductive elastic wood（PW）loaded with polypyrrole,which was labeled PW0.5h,PW1h and PW2h according to the deposition time of pyrrole,respectively.Under the condition ofε=40%and 100 compression and release cycles,PW can recover completely without plastic deformation residual.Piezoresistive performance tests show that PW0.5h and PW1h show higher strain sensitivity（εin 16%GF=2.42-4.62）,while PW2h shows better linearity（εin 40%GF=1.87）.PW2h can be used as an intelligent branch electronic control system to control the switching operation of different electronic components.In addition,the electromagnetic shielding performance of PW2h before and after compression is 28.4-37.6d B,while the electromagnetic shielding performance of PW1h before and after compression is up or down 20 d B,which can be used as an electromagnetic shielding mode sensor and electromagnetic shielding switch.