Preparation Of Light Wood Based Carbon Sponge Composite Flexible Sensor And Its Piezoresistive/Electromagnetic Shielding Performance

In recent years,flexible pressure sensors with three-dimensional mesh structure show high reversible compressibility and good sensitivity,and their complex network shape is also conducive to the construction of stable conductive networks,showing great application prospects in wearable electronic devices,medical diagnosis,human health monitoring and other aspects.The construction of 3D conductive network and the optimization of sensing performance have become a research difficulty of flexible pressure sensors.At the same time,with the arrival of the flexible electronic age and the continuous expansion of human needs,the development direction of flexible sensors in the future will focus on multi-functions.In this paper,aiming at building a stable three-dimensional conductive network and optimizing sensing performance,natural light wood with a hierarchical structure of vertically arranged microchannels was used as the original material,and it was chemically treated to build a three-dimensional layered network structure.Then,by regulating catalytic carbonization process,a carbonized wood sponge（CWS）with compressive elasticity was obtained and composite with TPU elastomer material.A composite pressure sensor was designed and its mechanical properties and pressure sensing properties were investigated.Further,magnetic Fe₃O₄ material was prepared by hydrothermal method,and CWS/Fe₃O₄/TPU composite was obtained.The shielding performance and mechanism of electromagnetic interference were explored.Finally,the composite pressure sensor was successfully used in human health monitoring,flexible contact and non-contact switch,and the sensor also possessed joule heating function and mobile phone signal shielding function.The main research contents and conclusions are as follows:（1）The effects of catalytic treatment and carbonization process on the structural properties of CWS were studied;According to the pyrolysis mechanism of cellulose and thermogravimetric analysis,the carbonization process of wood sponge（WS）was designed.It was found that after the catalytic treatment,the carbonized CWS had a stable three-dimensional conductive network structure,and its carbonization yield was significantly improved.Further,Raman spectroscopy and XPS spectroscopy were used to study the structure difference of CWS obtained under different catalytic treatment conditions and carbonization temperatures.It was found that after catalytic treatment with phosphoric acid-glycine mixed solution,the graphitization degree of CWS was significantly increased and the content of C element was 93.46%.The ratio of sp² hybrid carbon was 61.06%,and the initial resistance was only 61.66Ω,indicating that a more perfect six-membered carbon ring structure was formed.（2）The mechanical properties and sensing properties of the CWS/TPU composite pressure sensor were explored;CWS/TPU composite pressure sensor with excellent performance was successfully prepared by combining CWS with TPU elastomer.The sensor presented a highly reversible compressibility,the compression strain raised up to 60%,and the pressure range can be up to 60k Pa;With sensitivity up to 12.87k Pa^-1（pressure range up to 22k Pa）,low detection limit of10Pa,fast response time of 360ms and sensing stability of more than 5000 cycles,and environmental stability,the resulting sensor can be applied to different scenarios detection.（3）Preparation of CWS/Fe₃O₄/TPU composites and their electromagnetic interference shielding properties;Fe₃O₄ magnetic nanoparticles were successfully prepared by hydrothermal method with a saturation magnetization of 49.51emu/g.The CWS/Fe₃O₄/TPU composites with good magnetic properties and mechanical properties were obtained by the composite of different mass fractions of Fe₃O₄ nanoparticles with CWS and TPU elastomers.When the mass fraction of Fe₃O₄ is 15wt%,the saturation magnetization was 28.52emu/g,and the compression stress raised up to 93.13k Pa under 60%compression strain.In the Ku band（12-18GHz）,the EMI shielding SE_T value can reach 30.13d B,which was mainly due to the synergistic effect of the three-dimensional conductive carbon layer structure of CWS and the magnetic nanoparticles Fe₃O₄.This caused electromagnetic absorption loss and multiple reflection,thus significantly improving the total EMI shielding performance.（4）Application and multi-functional exploration of composite pressure sensors;CWS/TPU composite pressure sensor can not only be applied to the detection of human joint motion of knuckles and wrists,but also can real-time monitor the changes of plantar pressure,pulse,arterial and other subtle physiological signals during human walking.The low resistance of CWS was also used to realize the function of joule heating.At the same time,due to the piezoresistive response of CWS/TPU sensors and the magnetic response of CWS/Fe₃O₄/TPU sensors,the flexible contact and non-contact switches were respectively designed.Finally,the practical application of CWS/Fe₃O₄/TPU composite in mobile phone signal shielding was successfully realized.A composite pressure sensor with high reversible compressibility and excellent sensitivity has been successfully fabricated by using CWS with three-dimensional conducting carbon layer structure,and good electromagnetic interference shielding performance has been obtained by composite Fe₃O₄ magnetic nanoparticles,thus realizing multi-functional applications.This simple and effective preparation strategy and excellent sensing performance are expected to provide a new research idea for the development of multifunctional flexible pressure sensors.