Study on the Changes of Structures and Properties of PAN Fibers during the Cyclic Reaction in Supercritical Carbon Dioxide.

Mengmeng Qiao,Luwei Zhang,Xiaoma Ding,Haijuan Kong,Yuanzhi Cao,Muhuo Yu,Zhifeng Hu

doi:10.3390/polym11030402

Mengmeng Qiao, Luwei Zhang + Show 5 more

Open Access

https://doi.org/10.3390/polym11030402

Copy DOI

Abstract

Thermal pre-oxidation of polyacrylonitrile (PAN) fibers is a time-consuming and energy-consuming step in the production of PAN-based carbon fibers. In this paper, the effect of temperature on the structures and properties of PAN fibers cyclized in the supercritical carbon dioxide (Sc-CO2) medium was studied. The thermal behaviors of the PAN fibers were investigated by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The cyclization reaction was sensitive to the heating temperature and gas atmosphere. The FT-IR results of the PAN fibers treated in the Sc-CO2 confirmed that the degree of cyclization increased with the increase of the cyclization temperature. Compared with the PAN fibers treated in the air, the PAN fibers treated in the Sc-CO2 showed a higher degree of cyclization even at the same temperature. These findings might be related to the osmotic action of Sc-CO2 causing the fibers to be further arranged in a regular manner, which was favorable for the cyclization reaction. Moreover, as one kind of high diffusion and high heat transfer media, the heat release during the cyclization of PAN fibers could be quickly removed by Sc-CO2, which achieved the progress of the rapid-entry cyclization reaction.

Highlights

Carbon fibers (CFs), as one of the new materials of lightweight high-performance fibers for composites, are defined as fibers containing at least 92 wt % carbon [1,2]
The reactor was heated to a certain temperature, and the PAN fibers were fixed on a stirrer in the reaction vessel
Fourier transform infrared spectra (FT-IR) Evolution Analysis of the PAN Fibers Heated at Different Temperatures showed a reduction for PAN fibers treated at 140 °C in Sc-CO2, matching with an increase in the

Summary

Introduction

Carbon fibers (CFs), as one of the new materials of lightweight high-performance fibers for composites, are defined as fibers containing at least 92 wt % carbon [1,2]. Owing to the advantages of excellent tensile properties, low densities, and high thermal and chemical stabilities, CFs are widely used in various fields [3,4,5,6,7]. [8,9,10], among which PAN-based CFs are the preferred reinforcements for structural composites owing to their excellent strength and stiffness combined with the fact they are lightweight and cost less. PAN-based CFs are not easy to commercialize due to the time-consuming pre-oxidation step, which will significantly increase the manufacturing cost.

Objectives

Methods

Results

Conclusion