Extraction And Humidity Sensing Properties Of Nano Cellulose Based On Deep Eutectic Solvent

Humidity regulation plays an important role in environmental monitoring,health monitoring and intelligent identification.Cellulose is a renewable,biodegradable and non-toxic biopolymer with strong water enrichment ability.It is considered to be an ideal humidity sensing material.With the in-depth development of electronic equipment,the development of paper-based humidity sensor using cheap,easily available and flexible cellulose has attracted extensive attention of researchers.However,the existing paperbased humidity sensors still have many shortcomings,such as poor conductivity,limited sensitivity of paper sensors,incompatibility and weak affinity between rigid conductive filler and flexible paper,which may lead to cracking or peeling in the process of deformation.To solve the above problems,firstly,cellulose nanofibers(CNF)were prepared by the combination of betaine/oxalic acid deep eutectic solvent(DES)treatment and ultrasonic treatment,and used to disperse the cellulose nanofibers/graphene dispersion(CNF/Gr)obtained from graphene.Further,CNF/Gr dispersion was vacuum filtered onto cellulose nanofiber film(CNFF)to obtain CNF based humidity sensor(CNFF-CNF/Gr).The introduction of CNF not only improves the water enrichment ability of sensing materials,but also enhances the adhesion of graphene conductive materials on the surface of CNFF.This paper systematically investigated the sensitivity,responsiveness and stability of the sensing material under different mass ratios of CNF/Gr in CNF/Gr dispersion,and further discussed the application potential of the sensor in non-contact sensing.The specific research contents and results are as follows:(1)Controllable preparation and physicochemical properties of nano cellulose: the pulp cellulose was pretreated by DES and assisted by ultrasound to effectively regulate the yield and particle size structure of nano cellulose.The CNFF was successfully prepared by vacuum suction filtration.Through orthogonal test and particle size regulation,it was found that the optimal process of nano cellulose was betaine / oxalic acid molar ratio 1:4,treatment time 6 h,treatment temperature 110 ℃,the yield was76.5%,and the particle size length diameter ratio of nano cellulose was regulated between10.5-24.6.The CNFF prepared by vacuum suction filtration showed strong tensile stress(50-70 MPa).In addition,the CNFF showed good hydrophilicity and water absorption.Its moisture absorption and moisture regain were as high as(2.34 ± 0.04)g/g and(0.14 ±0.01)g/g,and the water contact angle was as low as 73.19 °.(2)Preparation of cellulose nanofiber/graphene and its humidity sensing performance: cellulose nanofiber/graphene dispersion(CNF/Gr)was obtained by dispersing graphene with CNF as dispersant and stabilizer.The effects of CNF/Gr mass ratio on the adhesion of conductive medium graphene and its humidity sensitivity,responsiveness and stability of CNFF-CNF/Gr humidity sensor were systematically investigated.The results show that CNF has good dispersibility to Gr,and CNFF-CNF/Gr shows good adhesion to graphene conductive materials(i.e.there is almost no trace when dragged under 1 kg weight).The mechanism analysis shows that the introduction of CNF can improve the regularity of graphene arrangement on the base film CNFF,and the interaction force with graphene(hydrogen bond,van der Waals force)improves its surface adhesion.The sensing performance of CNFF-CNF/Gr sensor is also studied.The results show that the introduction of CNF provides rich adsorption sites for capturing water molecules and improves the water enrichment ability of graphene.At the same time,the prepared CNFF-CNF/Gr humidity sensor shows 45 s fast response and 29 s fast recovery performance,as well as wide relative humidity detection range(15-99%)and long-term stability(15 d).In addition,the sensor can monitor the humidity of human skin and respiration,and display a multi-functional non-contact humidity sensing function by changing the component ratio of CNF to Gr as needed.In this work,nano cellulose was prepared by combining DES with ultrasonic assistance,and CNFF-CNF/Gr films with rich hydroxyl groups were prepared by depositing nano cellulose dispersed graphene on CNFF.Based on the polyhydroxy structure of CNF,CNFF-CNF/Gr shows excellent graphene adhesion and hydrophilicity.At the same time,CNFF-CNF/Gr has excellent humidity sensitivity and humidity response.The research of this paper provides a new method for the green production of nano cellulose and the preparation of fast response and high stability humidity sensitive materials,and provides new materials with great application prospects in the fields of medicine and electronics industry.