Study Of Structure And Properties Of Polyacrylonitrile-Based Carbon Fibers During Low Temperatur Carbonization

In this thesis, stabilized PAN fibers were treated at 500-1000℃for 2.25 to 18min. Nuclear magnetic resonance (NMR), Element Analysis, X-ray diffraction (XRD) and Raman Spectroscopy were applied to study the structures evolution of the fibers. Thermal gravity Analysis (TG), Infrared spectroscopy (FTIR) and Pyrolysis Gas Chromatography (PyGC) were used to study the composition of fiber.It was found that with the increasing of temperature, the content of C became more and more, and the contents of H and N became little and little in the fibers. The ejections of H and N by means of alkanes, alkenes, nitriles, amides, acyl-aniline, aromatic substitutions, pyrimidine, quinoline substances and gases (HCN, CH4, NH3, CO, CO2 and H2O).With the increasing of temperature, SP2 complex C=C structures in fiber became more and more during low temperature carbonization, while SP3 complex structures became little and little. And the degree of symmetry became higher and higher. Width of microcrystalline (La) and thickness of layers stacked (Lc) had a slow growth from 500 to 800℃. With the carbonization time rising at 500℃, the number of SP2 complex structure of C=C in the polycyclic aromatic structures became more and more, while the number of SP3 complex structure decreased. The chemical structures of fiber at 700℃had a same change with chemical structures at 500℃.With the increasing of temperature, the conjugated -HC=C< and> C=N- groups decreased, while the conjugated>C=C< groups increased in the skeleton structures of the fiber. The number of layers of polycyclic aromatic structure increased with temperature in the fibers reached to 1.29, 2.17,2.81 and 3.42 for fibers carbonized at 500,600,700 and 800℃, respectively. The N element was mainly in the way of conjugated -C=N- in the skeleton structures of the fiber. Enlarge the carbonization time did well to the growth of layers of polycyclic aromatic structure. The number of layers of polycyclic aromatic structure increased with carbonization time in the fibers reached to 1.29 and 6.67 for fibers carbonized at 500and 700℃, respectively. The strength and modulus of fiber had relationships with layer of polycyclic aromatic structure at low temperature carbonization. With the growth of layer of polycyclic aromatic structure, the strength and modulus of fiber enlarged.