The Study Of PAN Stabilized Fibers' Production And Structure

The production of carbon fibers is an important project in the development of science and technology,which is more and more widely used in many areas such as national defense,military,civil and commercial application,causes much attention of the countries and the organization all over the world.It has many excellent mechanical and chemical properties,such as low density,high corrosion resistance,low thermal expansion,heat inertia,creep resistant,higher strength and modulus,which is a kind of ideal functional material and structural material.The carbon fiber has many defects inside,whose actual strength and modulus is far away from the theoretical value,whose mechanical properties is affected a lot by its crystal structure,hole structure,surface structure and skin-core structure and so on.The polyacrylonitrile?PAN?precursor turns into the carbon fiber through stabilization,carbonization and graphitization process,during which the stabilization process is the key process.Three treatment process variables including the heating temperature,tensile stress and holding time,significantly affect the quality of stabilized PAN fibers,as well as the performance and production ratio of carbon fibers.This paper mainly studies the influence of heating temperature on the crystal structure,pore structure,surface structure and skin-core structure,we design a new type of stabilization device,which greatly improves the efficiency of the stabilization progress and the quality of stabilized PAN fibers.1?After the cyclization,dehydrogenation and oxidation reactions,precursor fibers with linear structure convert to stabilized fibers with intermediate cyclic structure.The PAN fibers are first stabilized at 180? in air through a constant stress,then stabilized at different temperature?200?,220?,240?,250?,260?,270? and280??for a specific period of time to get eight stabilized PAN fibers samples.We use X-ray wide-angle diffraction?XRD?,Fourier infrared spectrum?FTIR?,X-ray photoelectron spectroscopy?XPS?and Differential scanning calorimetry?DSC?to characterize the samples'structure,we find that the cyclization reaction,dehydrogenation reaction and oxidation reaction has its own drastic temperature range.2?We use the Small Angle X-ray Scattering?SAXS?to characterize the size,shape and distribution of micropores in the eight stabilized PAN fibers samples,fitting out four levels of micropores according to the angle scattering theory.We find that different levels of micropores are sensitive to different kinds of chemical reactions according to their axis ratio,volume fraction and the fractal dimension at different temperature range.After the mechanical tensile test,we find that the mechanical properties of stabilized PAN fibers samples are mainly affected by the biggest micropores,then secondly affected by the number,shape and distribution of the smallest micropores as the heating temperature change.3?The results show that 200?,220?,250?,and 280? are the key temperatures for the preparation of the stabilized PAN fibers.So,different thermal treatment procedures have been employed to study their impacts on the surface structure of the stabilized PAN fibers.We use the Solid carbon nuclear magnetic(¹³C{¹H}CP/MAS NMR spectra),XPS,Raman spectroscopy and Scanning electron microscope?SEM?to characterize the surface structure.In the analysis process,we try to give the possible chemical formula for the normal stabilized PAN fibers firstly.4?In order to reduce the skin-core structure of stabilized PAN fibers,we improve the traditional stabilization device.We use the moving microwave heating furnace with a funnel to titration the PAN fibers with hydrogen peroxide?H₂O₂?solution.The O atoms in the solution permeate the PAN fibers to react with the microwave polarization motion.The characterization of XRD,XPS and SEM results all show that the skin-core structure of the stabilized PAN fibers is significantly reduced.In addition,the device not only reduce the heat dissipation of side reactions,but also avoid the damage to the surface of the PAN fibers owing to the soaking and taking,which improves the efficiency and quality of the stabilization process.