Abstract
The modification before the stabilization process could tune the exothermic behavior and the structural evolution of PAN fibers during stabilization. In this study, we demonstrate that a rapid thermal pretreatment in nitrogen can effectively mitigate the exothermic behavior of PAN fibers, such as decreasing the initial temperature, broadening the exothermal peak, and decreasing the nominal heat release during heating the fibers in air. The color of fibers has shown gradual changes from white to light yellow, yellow and brown during thermal pretreatment in nitrogen with the increase of pretreating temperature and time. The differential scanning calorimetry (DSC), Fourier Transform Infrared Spectrometer (FTIR), X-ray diffraction (XRD), and Thermogravimetric Analysis (TG) characterization have been applied to analyze the thermal properties, chemical and physical structural difference between PAN, and thermally pretreated PAN fibers. The thermal pretreatment of PAN fibers in nitrogen could induce cyclization, dehydrogenation, and cross-linking reactions, in which the cyclization play an important role on improving the cyclization index of stabilized PAN fibers. Meanwhile, the pretreatment can result in noticeable changes of the aggregation structure of PAN fibers, as indicated by the increase of crystallinity and crystalline size. These structural modifications can benefit the main cyclization reaction during stabilization and enhance the carbon yield in resultant carbon fibers. The rapid thermal pretreatment in nitrogen could increase efficiency of modification on PAN fibers, and that could save much time and energy. It is beneficial to manufacture low-cost carbon fibers and to spread the applications of carbon fibers.
Highlights
Carbon fibers have shown excellent properties such as high specific tensile strength, high specific young’s modulus, chemical resistance, corrosion resistance, and light weight [1,2,3]
Thermal modification in air has been researched [26], and the results indicate that chemical reactions and aggregation structure changes during modification are beneficial to the structure and mechanical properties of carbon fibers
The color changes during thermal pretreating PAN fibers in nitrogen can exhibit the changes
Summary
Carbon fibers have shown excellent properties such as high specific tensile strength, high specific young’s modulus, chemical resistance, corrosion resistance, and light weight [1,2,3]. During the manufacture of PAN-based carbon fibers, thermal stabilization in air atmosphere is indispensable [7]. Various reactions, such as cyclization, oxidation, dehydrogenation, and cross-linking reactions, initiated at elevated temperature during stabilization [8]. The linear PAN chains convert into cyclic structure or ladder-like structure, which could keep fibers infusible and nonflammable when carbonized at higher temperatures [9,10,11,12,13,14]. Thermal stabilization is a time-consuming and energy-consuming process, which retards the commercializing and broader application of carbon fibers
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