Study On Electrospun Polyacrylonitrile (PAN) Nanofibers And Carbonization

Because carbon nanofibers have fine diameter and high electrical conductivity, it has a great application value in the area such as catalyst and carrier of catalyst, the lithium battery anode materials, double electricity layers capacitor electrode, efficient adsorbent, structure-strengthen material, field electrons transmit material and so on. It is an essential new material in the field of spaceflight, aviation and sophisticated technique of national defence and Military industry. Today, there has many ways to manufacture carbon nanofibers. Electrospinning is the single way to produce polymer nanofibers directly and continuously. With the electrospinning maturing, it becomes real that manufacture large quantities of carbon nanofibers by electrospinning. Electrospun carbon nanofiber is a new carbon material, there is little research about its structure and electrical conductivity. There is little research about the relation of electrical capability and its microstructure.Electrospinning method was used to fabricate PAN nanofiber. The diameter and morphology of electrospun nanofibers were investigated by scanning electron microscopy (SEM) . SEM images showed that the fiber diameter and the nanostructured morphology depended on processing parameters such as concentration, applied electric field intensity, solution feeding rate and ionic salt addition. By orthogonal testing analytical method, concentration and salt addition were found to have relatively larger effects on the fiber diameter than the other parameters. The best process had been found to fabricate fine diameter and low dispersion degree of electrospun nanofibers.Polyacrylonitrile (PAN) nanofiber web was pre-oxdated in electrothermal blowing dry box. Effects of the temperature and pre-heating rate on the structure and property of pre-oxidation web were discussed in this paper. The results showed that the tensile properties and moisture content gradually increased with the increasing temperature. Mass loss rate and cyclization index were also found to qucikly increase in the range 220～250℃. With the increasing heating rate , mass loss rate and breaking strength gradually increased and the moisture content reached its maximum 5℃/min.The morphology of electrospun nanofibers, pre-oxidized nanofibers and carbon nanofibers was studied by scanning electron microscope (SEM) , and their tensile and elongation , and conductivity were compared. It was found that the conductivity of the carbon nanofibers enhanced significantly. Characterization of the microstructure of PAN powder, electrospun nanofibers, pre-oxidized nanofibers and carbon nanofibers was performed by X-ray diffractometry and infrared spectroscopy.At the end of the paper, the electrical conductivity of carbon nanofibers web was comprehensively and systematically studied. The electrical conductivities of carbon nanofibers webs were measured by the four-point probe method. By orthogonal testing analytical method, carbonization temperature was found to have relatively larger effects on the electrical conductivity. X-ray diffraction and Raman spectroscopy were used to investigate structure of carbon nanofibers. The research results indicate that the crystallite dimensions (Lc) and the graphite mole fraction (La) gradually increase and the conductivity of carbon nanofiber webs become better with the temperature rising. There is a linear relationship between the graphite mole fraction (La) and electrical conductivity of carbon nanofiber web.