Preparation And Gas-sensing Properties Of Conducting Cellulose Composite

Gas-sensing materials are widely used in the field of industry, agriculture, medicine, national defense and so on. The study about them has a very important significance in theory and practice. Gas-sensing materials include inorganic materials, organic materials and inorganic/organic composite materials, and the last ones are the most widely used.In this thesis, we choose cellulose as the matrix of the gas-sensing material, and prepared the gas-sensing materials filled with carbon materials, such as carbon nanotubes, graphite particles in ionic liquids. The composite based on graphite/cellulose was prepared by grafting method, the composite based on MWCNTs/chitosan/cellulose and the composite based on MWCNTs/HPMC/cellulose were prepared by physical method, respectively. Then characterize these composites and explored the percolation phenomenon of them. Also the gas-sensing behaviors of them to different vapors in different conditions were detected. The main conclusions were listed below.(1) A type of conductive graphite/cellulose composite film used for chemical vapor-sensing material was prepared at room temperature in ionic liquid 1-butyl-3-methylimidazolium chloride([BMIm]Cl). Graphite was pretreated with both oxidation and reduction processes. Due to the use of N, N-carbonyldiimidazole(CDI), as a covalent cross-linking agent in [BMIm]Cl, there were limited chemical bonds between the graphite and cellulose. When these conducting films were exposed to certain organic vapors, their electrical resistances quickly changed, showing gas sensitivity. The percolation threshold of the conducting film was about 5 wt%. The gas-sensing behaviors of these films in solvent were the opposite of those gas-sensing materials based on a non-polar polymer matrix. A typical negative vapor coefficient(NVC) was observed when the film was placed in polar organic solvents such as methanol, ethanol, and acetone. After crosslinking, the crystallization index of the cellulose fiber decreased from 0.46 to 0.32.(2) The composite based on MWCNTs/chitosan/cellulose was prepared by physical method in ionic liquid [BMIm]Cl system. Modification of the MWCNTs and chitosan can both improve the dispersion of MWCNTs in matrix. When the material ratio of chitosan and cellulose was 1:7, the responsiveness and repeatability were all best in chloroform and acetone. When the content of MWCNTs was 2.8wt%, the responsiveness and repeatability of the composite film were all best in polar organic vapors, such as methanol, ethanol, acetone and chloroform. While there was nearly no response to the nonpolar vapors, like benzene and carbon tetrachloride. Also the composite was sensitive to ammonia. There were three reasons to the sensitivity of the composite: Physical adsorption, similar dissolve mutually theory, “NVC effect”(3) A type of chemical vapor-sensing materials made from MWCNTs/HPMC/cellulose composite films were prepared in the room temperature ionic liquid 1-butyl-3-methylimidazolium chloride([BMIm]Cl). The gas-sensing behavior was observed when the film was placed in the polar organic solvents such as methanol, ethanol and etc. Compared with the addition of chitosan, the Young’s modulus of the composite based on MWCNTs/HPMC/cellulose increased from 28.84 MPa to 58.93 MPa. At the same time, the composite had a certain sensitive to the vacuum environment. When the vacuum degree was in the range of 0.02 to 0.12, the resistance of film increased almost linearly with the decrease of the vacuum and the changes of resistance with the vacuum show a good repeatability. This composite was also sensitive to formaldehyde.