Preparation Of Lignin Carbon Nanofibers By Electrospinning

Lignin, the second largest natural polymer except cellulose, has not been well utilized. Because of its high carbon content lignin can be used to prepare carbon fibers.Acetic acid lignin-based carbon nanofibers were prepared by electrospinning, thermostabilization and carbonization process. Three kinds of solvents (N,N-dimethylformamide, tetrahydrofuran, acetic acid) were used to prepare lignin solution for electrospinning. Scanning electron microscopy was used to examine the surface morphology of the lignin nanofibers. Lignin+DMF solution and lignin+THF solution can not be electrospun into fibers. Fibers were obtained by electrospinning lignin+acetic acid solution. To keep fiber morphology, thermostabilization process is needed before carbonization process. It was found that the AAL fibers were needed to be thermostabilized at heat rate lower than 1℃/min and carbonized at temperature lower than 700℃. The crystal structure and surface elemental composition of the AAL carbon fibers were characterized by WAXD and XPS, respectively. The carbon is amorphous. The carbon element content is 86.707% and the oxygen element content is 13.293%.Alkali lignin nanofibers were obtained by electrospinning. The impacts of solution conductivity, concentration, voltage, feed rate, and spinneret-collector distance on the morphology and diameter of electrospun lignin nanofibers were systematically investigated. The morphology of lignin nanofiber was investigated by scanning electron microscopy. It was found that the morphology and diameter of the nanofibers strongly depended upon conductivity and concentrations of lignin solution. Spheres were obtained when using DMF as the solvent because the solution conductivity was low. Spheres were obtained at the concentration of 20% and 30%. Fibers were obtained at the concentration of 35%, 40%, 45%. The fiber diameter increased with increasing of solution concentration. The fiber diameter first increased and then decreased when the voltage increased from 10kV to 60kV, and the fiber diameter touched bottom at the voltage of 60kV. The fiber diameter increased with increase in feed rate. At the polar distance of 15cm, the fiber diameter was least compared with the polar distance of 10cm and 20cm. The alkali lignin fibers were thermostabilized and carbonized at 500℃,600℃,700℃, respectively. The crystal structure and the degree of the graphitization of the alkali lignin carbon fibers were characterized by WAXD and raman spectra. It was found that the carbon is amorphous and the degree of the graphitization increased with increase in carbonization temperature.