Study On Preparation Technology And Structural Properties Of PP-based Activated Carbon Fiber

Carbon fiber and its composites have attracted wide attention in recent years and are used in more and more industries.However,due to the complex manufacturing process and high production cost of carbon fiber,its large-scale application is still limited.A large part of the production cost of carbon fiber lies in the production of precursor.Taking polyacrylonitrile(PAN)based carbon fiber as an example,more than half of the production cost is used to prepare PAN fiber.Therefore,if a new low-cost carbon fiber precursor can be developed,it will greatly promote the development of the carbon fiber industry.Polypropylene(PP)is a promising precursor of carbon fiber with high carbon content,low cost and easy processing.At present,there has been systematic research on PP-based carbon fiber abroad,and is promoting industrialization,but there is a technical blockade to our country;Although a few laboratories in our country have made preliminary exploration of the preparation process of PP-based carbon fiber,the research is not thorough enough,and there are some doubts about the changes in the structure and properties of PP fiber in the process of sulfonation,carbonation and activation.Therefore,in this paper,low-cost PP-based active carbon fibers are prepared by the"sulfonation-carbonation-activation"route,and characterized by Fourier Transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),X-ray diffractometer(XRD),microscopic confocal Raman spectrometer(Raman)and X-ray photoelectron spectroscopy(XPS).The transformation law of the structure of PP fiber in the process of sulfonation,carbonization and activation were studied,and the influence of several technological conditions on the structure and properties of PP-based activated carbon fiber was explored,which provided the necessary basic research support for the preparation of low-cost activated carbon fiber.The main research conclusions are as follows:1.The effect of sulfonation technology on the structure and properties of PP fiber was studied by sulfonating PP fiber with concentrated sulfuric acid.Polypropylene molecules undergo sulfonation and desulfonation reactions under the action of concentrated sulfuric acid to form a cross-linked structure.The sulfonation process destroyed the crystal structure of PP fiber,greatly reduced the crystallinity,and the carbon structure was more disordered.With the increase of sulfonation time,hydroxyl group and carboxyl group appear successively on the surface of PP fiber,indicating that the sulfonation process is accompanied by strong oxidation reaction.The fiber with short sulfonation time will appear hollow structure after carbonization,and the hollow structure will disappear with the extension of sulfonation time,indicating that sulfonation is an outward to inside process.Increasing the temperature can accelerate the sulfonation reaction rate of PP fiber.With the increase of the sulfonation temperature,the damage degree of the original mesocrystalline structure of PP fiber is deepened,but the proportion of ordered carbon is increased.2.The sulfonated PP fiber was treated by high temperature carbonization,and the effect of carbonization on the structure and properties of PP-based carbon fiber was studied.With the increase of carbonization temperature,the fiber diameter decreases gradually,indicating that the removal of non-carbon elements is closely related to the carbonization temperature.With the increase of carbonization temperature or the extension of carbonization time,the carbon content of fiber gradually increases,the pore volume gradually increases,and the specific surface area first increases and then decreases.When carbonization temperature was 800℃and carbonization time was 1 h,the specific surface area and pore volume of PP-based carbon fiber reached 408.12 m~2/g and 0.31 cm~3/g.The PP based carbon fiber prepared under this condition can effectively save energy,and at the same time ensure high specific surface area and pore volume,which is suitable for practical production.3.PP-based carbon fibers were treated by steam activation,and the effect of activation process on PP-based activated carbon fibers was studied.After activation,there are obvious holes on the surface of PP-based carbon fiber,indicating that the activation can generate new pores and expand the original pores.After activation,carbon content and oxygen content of fiber decreased,and the degree of graphitization decreased.The pores of PP-based active carbon fibers are mainly composed of micropores and hollows.Increasing activation temperature,prolongating activation time and increasing deionized water flow are beneficial to the development of pore structure of PP-based carbon fibers in a certain range.The specific surface area and pore volume increase first and then tend to be stable.Considering the yield and adsorption efficiency,the optimal activation process is as follows:activation temperature800℃,activation time 2 h,deionized water flow 3 m L/min.In this case,the specific surface area and pore volume of PP-based activated carbon fibers can reach 633.78 m~2/g and 0.87cm~3/g,respectively.