| Carbon fibers perform excellent properties such as high specific strength and modulus, but the tensile strength of commercial carbon fibers is much lower than that of the therotic tensile strength. The tensile strength of carbon fibers is mainly limited by the surface and internal defects of fibers. Electrospun PAN fibers possess advantages of ultra slim diameter, higher crystallinity and density, as well as structural homogenization which can greatly reduce the internal defects of fibers during heat treatment. As PAN-based fibers being transformed into carbon fibers (CFs), stabilization and carbonization conditions have a significant effect on the formation of structure which could further affect the mechanical properties of carbon fibers.In this study, the electrospun PAN fibers were prepared through electrospinning and collected through a collection bath with flowing water. And the posttreatment of the electrospun PAN fibers is carried out. The better stabilization process of PAN fibers was explored. The effect of the applied tension and the maximum temperature during carbonization on the structure and properties of carbon fibers was studied. The structure and properties of electrospun PAN fibers, stabized fibers and carbon fibers were characterized by SEM, density tube, XRD, FT-IR, EA, Raman, etc.The results indicated that:(1) Compared to as-electrospun PAN nanofibers, the nanofibers via post-spinning treatment possessed smaller diameter and higher crystallinity, crystalline size and orientation. Meanwhile, the diameter, crystallinity, and crystalline size and orientation of the nanofibers prepared with different batches were very similar. This result indicated that the electrospinning process and the nanofiber quality were extremely stable. (2) The PAN nanofibers were stabilized at 260℃, 274℃ and 284℃ in air for 5 min. This was the excellent stabilization condition of the electrospun PAN nanofibers. The density and tensile of the corresponding carbon fibers reached a maximum value, which was 1.7581 g·cm-3,950.0 MPa, respectively. The stabilization time of PAN nanofibers is greatly shortened, which has important guiding significance for the research on reducing the cost of carbon fibers preparation. (3) With the increase of the maximum carbonization temperature, the graphitization degree, crystalline size (Lc), crystalline length (La‖) and crystaline width (La⊥) of carbon fibers increased gradually; the crystal plane spacing (d002) reduced; the porosity (Vp) and the orientation (fc) altered little; the density, tensile and modulus were increased significantly. The density, tensile and modulus of carbon fibers were reached a maximum value, which was 1.7581 g·cm-3,950.0 MPa and 121.3GPa, respectively, when the corresponding maximum temperature is 1350℃ during carbonization. In a certain temperature range, the increase of maximum temperature can is beneficial to the improvement of the structure and the mechanical properties of the carbon fiber during carbonization. (4) In a certain tension range, with the increase of tension, the diameter (between 120-130nm) and graphitization degree of CFs altered little; crystalline size (Lc), crystalline length (La‖) and orientation (fc) of carbon fibers showed a trend of first increasing and then decreasing; crystaline width (La⊥) and the porosity (Vp) showed a trend of first decreasing and then increasing; the crystal plane spacing (d002) did not change significantly;the density, tensile and modulus showed a trend of first increasing and then decreasing. The maximum density, tensile and modulus of carbon fibers were obtained, which was 1.7633 g·cm-3,1114.6 MPa and 194.5 GPa, respectively, when the corresponding tension is 20 cN during carbonization. Applying the appropriate tension in the carbonization process. Proper tension is applied during the carbonization, which is helpful to improve the structure and the mechanical properties of the carbon fiber. |
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