Preparation And Properties Of Lignin-PAN Carbon Nanofibers

As global fossil energy shortages, while energy shortages occur, the shortage ofchemicals based on fossil energy also comes. Use of bio-based materials to supplementpetroleum-based materials is becoming increasingly important. Because lignin is apolyaromatic macromolecule and has a carbon content of55%-66%, it may fulfill many of therequirements for being a precursor to carbon fibers.Electrospinning is the only direct, continuous preparation method of a polymer nanofiber.This paper uses corn stalk lignin and polyacrylonitrile(PAN) as raw materials to produceLignin-PAN nanofibers by electrospinning. Then Lignin-PAN carbon nanofibers wereprepared by thermostabilization and carbonization. Its structure and properties have also beenstudied.Lignin-PAN nanofibers were prepared by electrospinning of lignin/PAN solutions indifferent blend concentrations. Effects of processing parameters including electrospinningvoltage, flow rate, tip-to-collector distance, and rotational speed on the morphology ofelectrospun lignin-PAN fibers were studied. Pure lignin solutions could not be processed intouniform fibers. The electrospinnability of lignin was improved by blending in a solution ofPAN. The beadless, uniform Lignin-PAN nanofibers with a diameter of200~300nm wereobtained when the weight ratio of polyacrylonitrile to lignin is4:1. The optimum processparameters were as follows: the voltage is25kV; the flow rate is1.5ml/h; the tip-to-collectordistance is17cm; the rotational speed is2000r/min.The Lignin-PAN nanofibers and PAN nanofibers were stabilized in air and carbonized innitrogen. The structure and properties of carbon nanofibers were investigated by scanningelectron microscope (SEM), Thermogravimetric Analyzer (TG), X-ray diffractometer (XRD),Fourier transform in frared (FT-IR), Raman spectroscopy (Raman) and X-ray PhotoelectronSpectrometer (XPS). Lignin added had no influence on the morphology and diameter ofcarbon nanofibers. The obtained carbon nanofibers were smooth and had a uniform diameterdistribution. The thermal stability of Lignin-PAN carbon nanofibers and PAN carbonnanofibers is not much difference. Both carbon nanofibers began to melt until550°C. The Lignin-PAN carbon nanofibers and PAN carbon nanofibers were turbostratic structure. Thegraphitization degree of carbon nanofibers increased slightly due to the addition of lignin. Thesurface carbon content of two kinds of carbon nanofibers were more than90%. Lignin addedhad little influence on structure and properties of carbon nanofibers, which can be used in thenext step.The Lignin-PAN nanofibers were carbonized at800°C,900°C,1000°C, and1100°C,respectively. Results showed that with increasing carbonization temperature from800to1100°C, the average diameter of carbon nanofibers gradually decreased. Fiber breakagestarted to occur when the carbonization temperature exceeded1000°C. The carbonnaonofibers were disordered, amorphous carbon structures regardless of the carbonizationtemperature. With the increase of carbonization temperature, the graphitization degree ofcarbon nanofibers increased. But when the temperature exceeded1000°C, carbon nanofibersshowed little change in graphitization. The surface carbon content of the carbon nanofibersincreased with the increase of carbonization temperature. When the temperature exceeded900°C, however, the surface carbon content was not significantly increased. The carbonationof nanofibers had been completed under900°C. Considering the cost and properties of carbonnanofibers, we chose900°C as the optimum carbonization temperature.PAN-TiO2nanofibers and Lignin-PAN-TiO2nanofibers were prepared viaelectrospinning and were characterized by SEM, XRD and EDS analysis. Photocatalyticactivities of nanofibers were investigated by observing degradation of Rhodamin B under UVirradiation. The results showed that lignin added had little influence on structure andproperties of nanofibers. The prepared Lignin-PAN-TiO2nanofibers showed goodphotocatalytic activity. The degradation rate was92.9%. After5times of use，the degradationrate was85.6%。...