Preparation Of Lignin-based Carbon Fiber Precursors And Properties Of Carbon Fiber

Carbon fiber is a kind of special fiber which has a wide range of applications.The polyacrylonitrile is the most important precursor of carbon fiber.However,with the continuous reduction of fossil resources,the development of carbon fiber has been hindered and inhibited to some extent.The topic of preparing low-cost renewable biomass carbon fiber has attracted more and more attention of the society.Lignin is a kind of abundant and renewable natural polymer.If it can be applied to the preparation of carbon fiber,the cost of carbon fiber preparation can be reduced to a certain extent.However,lignin has a complex structure and is difficult to be used.In order to solve this problem,a series of methods were adopted in this paper.Firstly,the modification of lignosulfonate is divided into three steps.The first step is the amination of lignin,in order to improve the activity of lignin The second step is to use 2-chloro acrylonitrile on modification.The third step is the synthesis of poly(acrylonitrile/acrylonitrile-ammoniation lignin sulfonate)copolymer,and a series of characterization methods have been characterized for modified products,and studied the solubility and rheology in N,N-dimethyl formamide(DMF)solution for polyacrylonitrile and poly(acrylonitrile/acrylonitrile-ammoniation lignin sulfonic acid sodium).In contrast to previous studies,gel permeation chromatography showed that the molecular weight of the copolymer increased obviously(up to 203,944)due to the presence of lignin.Viscosity analysis shows that the addition of lignin reduced the viscosity of the copolymer solution.Thermogravimetric analysis shows that the degradation temperature increased and melt temperature decreased.These results indicate that the attachment of acrylonitrile to lignin molecules can control the molecular weight and molecular structure of poly(acrylonitrile / acrylonitrileammoniated lignosulfonate)copolymers,thus improving their solubility,spinnability and other molecular-weight related properties.Then the poly(acrylonitrile / acrylonitrile-sodium ammoniated lignosulfonate)copolymer was dissolved in N,N-dimethylformamide to prepare the spinning solution.The poly(acrylonitrile/acrylonitrile-sodium aminated lignosulfonate)nanofibers were prepared by high voltage electrospinning technology.The influences of various spinning parameters,consist of spinning voltage,spinning velocity,roller speed and receiving distance were analyzed on the morphology and diameter of carbon nanofibers.The optimal spinning process parameters are as follows: spinning voltage is 23 k V,spinning velocity is 1.0m L /h,roller speed is 1000 rpm,and receiving distance is 130 mm.Finally,carbon fiber was prepared by using poly(acrylonitrile / acrylonitrilesodium ammoniated lignosulfonate)copolymer as raw material and spinning under the optimum conditions of electrospinning.Then,the primordial fibers were preoxidized by a nine-stage process,and next the gradient temperature was raised to 700.At the same high temperature,the carbon fibers were carbonized by holding for 2 hours.Thus,poly(acrylonitrile/acrylonitrile-sodium aminated lignosulfonate)based carbon fibers were prepared and characterized.It can be seen from the scanning electron microscope that the morphology of carbon fiber is relatively regular,smooth surface,compact structure,almost no defects.However,the higher the lignin content,the more serious the distortion of the fiber.It can be seen from the diameter distribution histogram that with the increase of lignin content in the copolymer,the diameter of the fiber decreases first and then increases.The results of FTIR XPS and elemental analysis showed the carbonization of carbon nanofibers was relatively complete after the corresponding preoxidation and carbonization treatment.The results of TG and DSC showed the addition of lignin reduced the heat resistance of poly(acrylonitrile / acrylonitrile-ammonium lignosulfonate)based carbonization fibers.Raman spectroscopy results showed the addition of lignin makes the crystalline of poly(acrylonitrile/acrylonitrile-ammoniation lignin sulfonate)nanofibers lower,graphitization degree is reduced,but not big gap between the R value.XRD results show that the carbon of the poly(acrylonitrile/acrylonitrile-ammoniation lignin sulfonate)based carbon nanofibers were amorphous carbon.