Preparation And Properties Of Biomass-based Capacitive Humidity Sensing Material

With the continuous development of social science and technology,sensors have been widely used.Cellulose and lignin resources are extensive,and have the advantages of low cost,renewable,good biocompatibility and harmless to the environment.In this paper,the humidity sensor materials with fast response,low hysteresis,good stability and high signal intensity were successfully prepared from biomass.Through the analysis of the capacitance signal response and the chemical structure of the material,we clarified the correlation between the chemical composition and the linear response of the humidity sensitive material.The results provides a new idea for the preparation of new humidity sensitive materials and a new scheme for high value utilization of biomass.The main conclusions are as follows:（1）The humidity sensitive composite film was prepared by mixing the suspension of microcrystalline cellulose（MCC）in N,N-Dimethylformamide（DMF）solution of Polyvinylidene fluoride（PVDF）with carboxymethyl cellulose sodium（CMC-Na）、N-Hydroxy succinimide（NHS）or Acrylamide（AM）.The moisture-sensitive sensing material added with CMC-Na has a signal mutation phenomenon in response,which is suitable for switch circuit design.By coating the gel made of N-hydroxysuccinimide（NHS）/acrylamide（AM）to PVDF+MCC suspension,the cellulose based humidity sensitive membrane materials（MNP and MAP）with the characteristic of high sensitivity,low hysteresis,excellent repeatability and short response time were successfully prepared.The best performance have been achieved at the contents of 100%NHS and 80%of AM in the material and R²>0.98 after the linear fitting of the response signal to humidity.In the range of relative humidity from 11%RH to 97%RH,the prepared membrane material has stable response and good repeatability.The moisture absorption response time of MNP₁₀₀ is 50s,the dehumidification time is 20s,and the humidity hysteresis is 4.25%RH;the moisture absorption response time of MAP₈₀ is 150s,the dehumidification time is 20s,and the humidity hysteresis is 7.76%RH.（2）A new type of lignin humidity sensitive membrane material（LAP）was prepared by copolymerization of lignin and acrylamide.When the addition of lap is 60%,the humidity sensitive material has the best performance in response speed,hysteresis,stability and sensitivity to humidity.The moisture absorption response time is 70s,dehumidification time is 10s,and humidity hysteresis is3.52%RH.（3）Biomass based sensing materials were used in human respiration monitoring and soil moisture monitoring.The results showed that the humidity sensing materials could quickly and accurately monitor the change of respiration signal.The response to soil moisture content was accurate and the signal was strong.The prepared materials had rapid response,low hysteresis,good stability and high signal strength.It should have broad applications in the fields of medicine,industry and agriculture industry.