Abstract
Affected by ambient oxygen and thermal diffusion mechanism, the radial structural distribution of polyacrylonitrile (PAN) fiber during the pre-oxidation process will be inherited to the carbon fiber, which had a remarkable effect on the mechanical properties of carbon fiber. It is important to understand the evolution mechanism of radial structure evolution of PAN fiber during the pre-oxidation process to manufacture the high-performance carbon fiber. In this paper, a series of fine denier model fibers were prepared by adjusting the oxygen concentration to describe the structural characteristics at different radial regions of pre-oxidized fibers. The evolution mechanism of the radial structure of pre-oxidized fiber, with the increase of heat treatment temperature, was studied by the methods of optical microscope, C13 nuclear magnetic resonance (13C-NMR), and thermogravimetric analyzer (TGA). The results showed that along the radial direction of pre-oxidized fiber from skin to core layer, the degree of cyclization changed little while the dehydrogenation and oxygen-containing structure gradually decreased. Specifically, the oxygen-containing functional groups in the core decreased to the lowest level or even disappeared. A moderate increase of temperature in the initial and middle pre-oxidation processes could effectively promote the formation of cyclized structure and stabilize cross-linked ladder structure in the skin region of the fiber. With it, the thermal stability of obtained pre-oxidation fiber was improved.
Highlights
Polyacrylonitrile (PAN) based carbon fiber has excellent mechanical and functional properties, which made it an irreplaceable material in aerospace, energy transportation, civil and construction engineering, bridge structures, and other fields [1,2,3,4]
A fine denier model fiber was prepared in the laboratory, which was beneficial to form more homogeneous pre-oxidation structures owing to the full diffusion beneficial to form more homogeneous pre-oxidation structures owing to the full diffusion of ambient oxygen into the fiber
The radial structure distribution fiber for during the pre-oxidation process was optimized, which provided an effectiveofmethod during pre-oxidation process was optimized, thethe preparation of high-performance carbonwhich fiber. provided an effective method for the preparation of high-performance carbon fiber
Summary
Polyacrylonitrile (PAN) based carbon fiber has excellent mechanical and functional properties, which made it an irreplaceable material in aerospace, energy transportation, civil and construction engineering, bridge structures, and other fields [1,2,3,4]. The preparation technology of high-performance carbon fiber was always the main task for the researchers. Compared with the ideal graphite, PAN-based carbon fiber has a “pseudo-graphite”. In 1974, Johnson et al [10,11] proposed the skin-core structure model of PAN-based carbon fiber, as shown, including the skin structure and core structure. The arrangement of a “pseudo-graphite” structure was relatively regular in the skin, while it was arranged disorderly in the core. 1. Skin-core structure of PAN (a) of skin-core structural modelmodel of carbon fiber [10]
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