Preparation Of Polyacrylonitrile/Lignin Carbon Nanofibers By Electrospinning

As the only renewable biological resource with benzene ring structure in nature,lignin is rich in reserves and high in carbon content.At present,the application of lignin is mainly concentrated in some low-value industries,such as fuels,cement,ceramics etc.With the increasing shortage of fossil energy,the high value utilization of lignin has gradually attracted the attention of various researchers,one of the most important application is used as a raw material for carbon fiber preparation.Carbon nanofibers not only have the excellent comprehensive properties of carbon fiber,but also have the advantages of high porosity,large specific surface area,etc.,and have good applications in the fields of filter materials,adsorbent materials,hydrogen storage materials etc.At present,most carbon nanofibers are prepared by electrospinning polyacrylonitrile(PAN),and electrospinning is the only spinning process capable of continuously preparing nanofibers.In this paper,polyacrylonitrile /lignin composite nanofibers were prepared by electrospinning which device has been optimized with sisal lignin and PAN as raw materials,and they were pre-oxidized and carbonized to obtain polyacrylonitrile/lignin composite carbon nanofibers.The main research contents are as follows:1)Lignin was extracted with High-temperature alkali-cooking method which optimum process conditions is 17% alkali content,20% sulfidation degree,and cooking temperature 160 °C.and then modified.The structural properties of lignin and the electrospinning test of lignin were carried out.It is found that the main structural units of the extracted lignin are syringyl-based and guaiac-based structural units,and the thermal weight loss mainly occurs at 200-450 ° C,and the maximum weight loss temperature is 341 ° C.The final amount of residual carbon can reach 46%,and lignin is more difficult to electrospinning on its own.2)Optimized design the electrospinning device through understanding of the electrospinning principle,and electric field intensity was simulated.Used the electrospinning molding PAN,this paper discusses the electrospinning process parameters on the influence of the fiber morphology diameter,it found the electrospinning conditions of forming good fibre morphology is solution concentration of 8% ~ 14%,spinning voltage of 9 kV ~ 18 kV,spinning distance of 12 cm ~ 18 cm,and get the minimum fibre diameter of electrospinning conditions as follows: solution concentration is 10%,spinning voltage is15 kV,spinning distance is 16 cm,the average fiber diameter can be up to 237 nm.3)Polyacrylonitrile/lignin composite nanofibers were prepared by electrospinning,and the influence of lignin and its modification on polyacrylonitrile/lignin composite nanofibers was discussed.The experimental results show that the increase of lignin can enhance the conductivity of the solution,affect the spinnability of the blend solution,reduce the average diameter of the fiber,lose the fiber morphology,and weaken the thermodynamic properties of the fiber.After the modification of lignin,the morphological characteristics and thermodynamic properties of polyacrylonitrile/lignin composite fiber were improved to a certain extent,which was beneficial to the utilization of lignin,the preparation of carbon fiber with high porosity and good thermodynamic properties.4)Polyacrylonitrile fiber and polyacrylonitrile/lignin composite fiber was peroxided and carbonized,and the peroxidation process was discussed to investigate the influence of preoxidation process conditions of the fibers,using Fourier transform infrared spectroscopy(FT IR),scanning electron microscope(SEM),thermogravimetric analyzer(TG),Raman spectroscopy(Raman),X-ray diffraction(XRD)techniques to characterize the structure of preoxidation fiber and carbon fiber properties.Results show that under the condition of the rate of 10 ℃ / min preoxidation temperature and maximum temperature of 250 ℃,good morphology peroxided fiber can be obtained,and the peroxided fiber has lower shrinkage,higher oxidation degree,good heat resistance;The addition and modification of lignin can reduce the fiber diameter of carbon nanofibers,but have no significant effect on the formation of amorphous carbon in the carbonization process.Moreover,carbon nanofibers with good carbonization degree and high strength and low modulus have been formed.The carbon nanofibers prepared can also be used in the next step.