Effects of Various Transition Metals on the Thermal Oxidative Stabilization of Polyacrylonitrile Nanofibers

Jung-Hun Lee,Siying Li,Young-Jun Kim,Ji-Beom Yoo

doi:10.1007/s10904-021-01954-x

Abstract

In this paper, the polyacrylonitrile (PAN) nanofibers and PAN nanofibers bonded with different transition metal (Fe, Co, Ni, and Cu) acetates were successfully prepared and their thermal oxidative stabilization process were analysed by Fourier-transform infrared spectra (FT-IR) and differential scanning calorimetry (DSC). The structural evolution of process was characterized by examining the FTIR spectral peaks generated at four different thermal oxidative stabilization temperatures. Based on the thermal oxidative stabilization rates obtained from each transition metal, Co-PAN and Cu-PAN are the only effective precursors for the thermal oxidative stabilization process and, according to differential scanning calorimetry, Co-PAN is the most effective and suitable precursor for the PAN with different transition metals. Although Co-PAN increased the exothermic reaction (ΔH) by approximately 140%, it alleviates the heat release rate (ΔH/ΔT) by approximately 44%.

Highlights

The conformation of PAN molecules bonded with various transition metal precursors were visualized to identify how the transition metal ions affect the stabilization of the polymer (Fig 1)
We examined the heat release rates of various thermal oxidative stabilization processes by dividing the amount of heat generated by the reaction temperature range (ΔH/ΔT)
The structural evolution of electrospun PAN nanofibers bonded with different transition metal precursors was investigated through Fourier-transform infrared (FTIR) and differential scanning calorimetry (DSC) analyses

Summary

Introduction

Polyacrylonitrile (PAN) is one of the most commonly used materials for the fabrication of carbon fibers.[1,2,3] To produce PAN-based carbon fibers, the polymer must first be converted to a flame-resistant structure (e.g., a ladder-like structure or a non-plastic cyclic structure) through a stabilization process[2] to prevent it from melting during carbonization.The stabilized PAN structure, which has a high rate of conversion to carbon fiber, is the reason why the PAN-based carbon fiber has outstanding properties compared with carbon fibers based on any other precursor material.[4, 5]When heated from 200 °C to 300 °C in air, PAN will be transformed into a ladder-like structure through cyclization, dehydrogenation, and oxidation processes[4,5,6] The cyclization process converts the nitrile groups to conjugated nitrogen double bonds, which in turn forms an aromatic ring together with five carbon atoms.[7]. Methylpropane acid (AMPS).[9,10,11,12,13,14,15,16,17,18] Among these co-monomers, IA resulted in a significant decrease in the stabilization temperature and alleviated the intense exothermic reaction.[14, 16,17,18] it decreased the cyclization rate, generating many beta-amino groups and conjugated nitrile groups, which caused point defects in the carbon fiber.[19, 20] Each transition metal resulted in a different cyclization rate, exothermic reaction, and enthalpy during the PAN stabilization process.

Results

Conclusion