A Flexible Smart Sensor For Monitoring Humidity Inside Fruit And Vegetable Packaging

The humidity environment inside the package has a significant influence on the fruit and vegetable products during storage and transportation.When the humidity exceeds a certain value,bacteria and microorganisms will multiply and it accelerates the decay of the fruits and vegetables;when the humidity is too low,the moisture of the fruits and vegetables will be lost leading to quality degradation.Due to the complexity of humidity in the whole circulation process of packaging,it is necessary to monitor the humidity in the packaging in real time so as to take measures to control it in time.This subject prepared a flexible smart packaging that can be used to monitor the internal humidity of fruit and vegetable packaging.The research results obtained are as follows:?1?The preparation of the resistance type flexible humidity sensor mainly includes a three-layer structure of a substrate,an electrode and a sensitive layer.Through the performance comparison of PVA and PET films,PET is preferred as the base material of the sensor.Comb interdigitated silver electrodes with different line widths were made as metal electrodes.A mixture of carboxylated multi-walled carbon nanotubes?MWCNTs-COOH?,graphene oxide?GO?,and tungsten disulfide(WS₂)was prepared as sensitive layers.Then,a resistive flexible humidity sensor with a three-layer structure was prepared by screen printing,coating,etc.?2?A different humidity simulation test environment of 0⁹7.6%RH was constructed,and the impedance performance of the sensor was tested with LCR meter.Sensor test results of MWCNTs-COOH/WS₂ sensitive layer materials with different ratios show that:with the increase of relative humidity,the resistance has a clear increasing trend.The sensor with MWCNTs-COOH ratio of 80%has the best linearity and sensitivity.The test results of sensors with different ratios of MWCNTs-COOH/GO sensitive layer materials,different carbon nanotube sizes,and different ratios of interdigitated electrode line widths show that the linearity of the sensor with the electrode line width of 100?m and MWCNTs-COOH ratio of 20%is the best;The sensitivity of the sensor with a line width of 50?m and MWCNTs-COOH ratio of 20%is relatively highest.Sensors with higher carbon nanotube sizes in different groups have relatively high linearity,sensitivity and conductivity.?3?Under different humidity,the response characteristics of the flexible humidity sensor were studied.The results showed that from low humidity to high humidity environment,the test time increased from 15s to 85s.The humidity hysteresis characteristics of the flexible humidity sensor were studied under the conditions of low humidity-high humidity-low humidity,and the results showed that there was a certain hysteresis of hygroscopicity.In different groups,the hysteresis degree of MWCNTs-COOH content is relatively small.Under different humidity,the repeatability and stability of the flexible humidity sensor were studied.The results show that the repeatability and stability are better.In summary,the flexible humidity sensor has a resistance signal response that increases with humidity.The MWCNTs-COOH/GO sensor with 20%MWCNTs-COOH has relatively good linearity and sensitivity.The sensor response of MWCNTs-COOH/WS2 is faster and hysteresis is relatively small.