A Study on Structural Characterization of Thermally Stabilized PAN Precursor Fibers Impregnated with Ammonium Bromide before Carbonization Stage

Demirel, Tuba; Rahman, Md. Mahbubor; Tunçel, Kemal Şahin; Karacan, İsmail

doi:10.1007/s12221-022-4901-x

Cited by 5 publications

(1 citation statement)

References 48 publications

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“…This is attributed to the prominent cyclization reaction that occurs in this stage, leading to intermolecular or intramolecular cross-linking of the molecular chains in PAN fibers. As a result, the distance between PAN fiber molecular chains decreases [ 46 ], leading to an increase in the average chord length of the micropores. Additionally, the generation of new, small molecular gases after the cyclization reaction contributes to the increase in the relative micropore volume.…”

Section: Resultsmentioning

confidence: 99%

In Situ Study and Improvement of the Temperature Increase and Isothermal Retention Stages in the Polyacrylonitrile (PAN) Fiber Pre-Oxidation Process

Cui,

Liu,

Song

et al. 2024

Polymers

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The pre-oxidation process of Polyacrylonitrile (PAN) fibers is a complex procedure involving multiple stages of temperature increase and isothermal temperature retention. However, the impact of the temperature increase stage on PAN fiber has often been overlooked. To address this, samples were collected before and after the temperature increase and isothermal retention stages, treating them as separate influencing factors. Therefore, the pre-oxidation process can be divided into four distinct stages: (1) A temperature increase stage before the cyclization reactions: the PAN fiber’s small-size crystals melt, and the crystal orientation changes under fixed tension, leading to shrinkage and increased orientation of the micropore. (2) An isothermal retention stage before the cyclization reactions: The crystal structure maintains well, resulting in minimal micropore evolution. The PAN fiber’s crystal orientation and micropore orientation increased under fixed tension. (3) A temperature increase stage after the cyclization reactions: The PAN fiber’s crystal melts again, reducing the average chord length and relative volume of the micropore. However, the PAN fiber can recrystallize under fixed tension. (4) An isothermal retention stage after the cyclization reactions: Significant crystal melting of the PAN fiber occurs, but the highly oriented crystals are maintained well. The average chord length and relative volume of the micropore increase. Recommendations for improving the pre-oxidation process are made according to these stages.

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Section: Resultsmentioning

confidence: 99%

In Situ Study and Improvement of the Temperature Increase and Isothermal Retention Stages in the Polyacrylonitrile (PAN) Fiber Pre-Oxidation Process

Cui,

Liu,

Song

et al. 2024

Polymers

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Multi‐step heating strategy during thermal stabilization of polyacrylonitrile multi‐filament bundle before carbonization

Hariri,

Tunçel,

Karacan

2024

Polymer International

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A polyacrylonitrile (PAN) multi‐filament bundle underwent a multi‐step heat treatment following impregnation with a solution of ammonium bromide, phosphoric acid and urea (A‐P‐U). The multi‐step thermal stabilization process was conducted in an air atmosphere at temperatures ranging from 200 to 245 °C for various stabilization times spanning from 10 to 70 min. Comprehensive analysis of physical and mechanical properties, infrared (IR) spectroscopy, X‐ray diffraction (XRD) and thermal analysis (DSC and TGA) revealed the significant influence of stabilization time on the structure and properties of thermally stabilized PAN multi‐filament bundle. The fiber thickness and linear density of the stabilized fibers decreased by approximately 29.5% and 10.6%, respectively, after 70 min of heat treatment. However, the fiber density value increased from 1.18 to 1.38 g cm−3 during the same stabilization time. Additionally, the carbon yield value obtained using TGA increased from 31% to 73% at 850 °C. The presence of A‐P‐U markedly reduced the time needed for the conversion of the PAN polymer into a cyclized structure through its nitrile groups, thereby accelerating the stabilization reactions. Furthermore, the IR spectra exhibited the appearance of CC bonds, signaling the creation of a crosslinked ladder‐like structure. The XRD traces confirmed the decrease in crystallinity with increasing stabilization time, consistent with the findings from IR spectra. The findings showed that the A‐P‐U integrated system is notably successful and proficient in promoting the cyclization of nitrile groups, thereby decreasing the time needed to establish a thermally stable structure capable of withstanding elevated carbonization temperatures. © 2024 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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Accelerated multistep thermal stabilization of polyacrylonitrile fibers using an ethylenediamine pretreatment

Tunçel,

Demirel,

Karacan

2024

J Mater Sci

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The polyacrylonitrile multifilament yarn underwent a multistep heat treatment process including stabilization times ranging from 5 to 75 min following impregnation with a 30% ethylenediamine (EDA) aqueous solution. A series of measurements were employed to determine the structure and properties of thermally stabilized PAN samples. These included fiber thickness, fiber density, flame testing, tensile testing, X-ray diffraction, thermal analysis (differential scanning calorimetry and thermogravimetric analysis), and infrared spectroscopy. The results from XRD and IR spectroscopy indicated that the rate of aromatization reactions increased with longer stabilization times. A detailed examination of the XRD curves obtained through curve-fitting procedures suggested a rapid transformation of the original structure into a disordered amorphous phase containing pre-graphitic domains, evidenced by a gradual reduction in the degree of apparent crystallinity of the original PAN sample. The integration of EDA before the thermal stabilization stage significantly reduced the cyclization time of nitrile groups in the PAN polymer structure, thereby accelerating the stabilization reactions. This chemical pretreatment also improved the thermal stability of the samples by promoting oxidative cross-linking of the PAN polymer chains. After a 75 min multistep stabilization, the carbon yield at 1000 °C was 70.5%. Conversion index values, calculated using IR, XRD, and DSC methods, were 98.3%, 94.8%, and 89.5% respectively for the 75 min sample. These findings highlight the importance of EDA in accelerating the formation of an aromatic structure, which is critical for withstanding the high temperatures of subsequent carbonization stages. Graphical abstract

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A Study on Structural Characterization of Thermally Stabilized PAN Precursor Fibers Impregnated with Ammonium Bromide before Carbonization Stage

Cited by 5 publications

References 48 publications

In Situ Study and Improvement of the Temperature Increase and Isothermal Retention Stages in the Polyacrylonitrile (PAN) Fiber Pre-Oxidation Process

In Situ Study and Improvement of the Temperature Increase and Isothermal Retention Stages in the Polyacrylonitrile (PAN) Fiber Pre-Oxidation Process

Multi‐step heating strategy during thermal stabilization of polyacrylonitrile multi‐filament bundle before carbonization

Accelerated multistep thermal stabilization of polyacrylonitrile fibers using an ethylenediamine pretreatment

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