Investigating the Effect of Fixation Tension on the Thermal Analysis Process and Crystal Structure of Polyacrylonitrile (PAN) Fibers

Abstract

Thermal analysis of polyacrylonitrile (PAN) fibers is commonly employed to assess the chemical and physical changes occurring during the pre-oxidation stage. However, in actual pre-oxidation processes, PAN fibers are stretched to a certain extent (approximately 5%) to prevent fiber shrinkage. Consequently, the pre-oxidation process of PAN fiber is influenced not only by temperature and atmosphere but also by the stretching tension. In this study, two types of PAN fiber samples with different crystal structures were utilized alongside four different processing methods (PAN powder, unfixation, physical fixation, and chemical fixation) to generate three degrees of fixed stretching. These included PAN powder and unfixed PAN fiber samples (without fixation tension), physically fixed PAN fiber with relatively weak fixation tension, and chemically fixed PAN fiber with strong fixation. Through a comparison of these samples, it was observed that the fixation tension aided in preserving the crystal structure during the heating process, significantly reducing the cyclization rate of the PAN fibers. The cyclization reaction rate of PAN fiber A, initially at 85% without any fixation, decreased to 66% after physical fixation and dropped to 56% after chemical fixation. For PAN fibers with distinct crystal morphologies, the impact of the fixation tension was more prominent for PAN fibers with larger crystal sizes and lower orientation. Additionally, the presence of crystal orientation facilitated the occurrence of the cyclization reactions.

Keywords:

• Differential scanning calorimetry (DSC)
• fixation tension
• polyacrylonitrile
• wide-angle X-ray diffraction (WAXD)

Acknowledgments

Thanks to the Shanghai Synchrotron Radiation Facility (SSRF) and the Beijing Synchrotron Radiation Facility (BSRF) for their assistance and support in analyzing the WAXD data in this study. The authors express gratitude for the assistance of the beamline scientists at BSRF and SSRF, especially Guang Mo and Zhihong Li.

Ethical approval

We certify that this manuscript is original and has not been published and will not be submitted elsewhere for publication while being considered by Journal of Macromolecular Science, Part B. In addition, the study is not split up into several parts to increase the quantity of submissions and submitted to various journals or to one journal over time. No data have been fabricated or manipulated (including images) to support conclusions. This article does not contain any studies with human participants or animals performed by any of the authors.

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Informed consent was obtained from all individual participants included in the study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Liaoning Pandeng Scholar program.