Preparation Of Conductive Paper By In-situ Polymerization Of Aniline In Pulp Fiber System

The conductive paper is a kind of functional paper which can be widely used as antistatic packaging material, electromagnetic shielding material, facial heating material, new energy and electrochemical material, sensor and driven material. Manufacturing methods of conductive paper include papermaking with mixture of conductive material and pulp fiber, electroless plating, and so on. However, conductive papers manufactured by these methods above mentioned have some defects. In order to overcome shortages from the methods above mentioned, the author stroke out in another direction and tried to probe a new technical line to produce conductive paper, which aniline was polymerized into pulp fibers under the action of oxidant and dopant by in-situ absorption polymerization process.The conditions of absorption polymerization (the type and dosage of oxidant, reaction temperature and time), the doping conditions (dopant species and concentration, secondary doping time, secondary doping temperature and co-doping), pulp fibers (pulp species, sulfonation degree, delignification degree and beating degree) were investigated to obtain suitable conditions of absorption polymerization, doping conditions and suitable pulp fibers. The relationships of the conditions of absorption polymerization, doping conditions and pulp species with surface resistivity of conductive paper were defined. The results showed that the optimum conditions of absorption polymerization are as follows: ammonium persulfate used as oxidant, mass ratio of oxidant to aniline 3:4, polymerization time 105 minutes and reaction temperature 5°C;the optimum doping conditions are as follows: p-toluene sulphonic acid and sulphuric acid as dopants, concentration 0.6 mol/L, doping for 5 h under 23 °C. The surface resistivity of conductive paper is 108 Ω? cm^-2 and 95 Ω ? cm^-2 when sulphuric acid and p-toluene sulphonic acid were used as dopants respectively. When p-toluene sulphonic acid and sulphuric acid were blended to co-dope, the best doping effect was obtained and the surface resistivity was up to 87 Ω ? cm^-2 under the mole ratio 2:1. It was also found that type of pulp fiber, sulfonation degree of CTMP, delignification degree of chemical pulp have great influences on the surface resistivity of conductive paper. And sulfonic groups in pulp fibers can promote absorption polymerization of aniline and possibly have self-doping effect on polyaniline. However, lignin in pulp fibers can impede absorption polymerization of aniline. The effects of beating degree on absorption polymerization of aniline and the surface resistivity of conductive paper are negligible.Percolation behavior of conductive paper was studied based on the above research. Top threshold of conductive paper is at the range of 3.6% to 4.2%. And bottom threshold can be closely related to oxidant species very nearly but dopant very little. Its electric and mechanicalproperties were evaluated. The conductive paper in this study has been up to electrostatic dissipation material and close to electrostatic conductor material. The surface resistivity increased no more than 20 fi-cm"2 within 5 months which indicates the electric performance of the conductive paper is relatively stable. It was found that the strength of pulp fiber itself in conductive paper decreased a little but bonding strength decreased more which the reason is that the deposition of polyaniline on pulp fiber surface covered hydroxyl group and impeded hydrogen bond forming. The structures of conductive paper were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electrical microscope (SEM). Crystallinity degree of pulp fibers decreased after treated. Polyaniline deposited on pulp fibers is spheroidal and granular. Its particle diameter is in the range from 100 to 200 nm and it distributes on the surface of pulp fibers mainly. Doping ratio of polyaniline on the surface of conductive paper is about 0.3, which is less than theory value 0.5. And doping first takes place on N atom of quinoneimine in polyaniline.Conductive paper manufactured in this study has low cost and can be easily produced on a large scale by using modern papermaking technique. Polyaniline is too hard melt and dissolved to process in machine shaping. The conductive paper successfully manufactured in this research will expand the use range of polyaniline.