Effects of Bromination-Dehydrobromination on the Microstructure of Isotropic Pitch Precursors for Carbon Fibers.

Dingcheng Liang,Qiang Xie,Shuai Yang,Deqian Liu,Jinchang Liu,Changyu Lu

doi:10.3390/polym12123059

Dingcheng Liang, Qiang Xie + Show 4 more

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https://doi.org/10.3390/polym12123059

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Journal: Polymers	Publication Date: Dec 20, 2020
Citations: 10	License type: CC BY 4.0

Affiliation: China University of Mining and Technology

Abstract

In this work, isotropic pitch precursors are synthesized by the bromination-debromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and 13C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by bromination-debromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of bromination-dehydrobromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.

Highlights

Carbon fiber is an important material that is widely used in the automobile, aerospace, and sport industries, as well as other industries [1,2]
At 110 ◦ C, some of the bromine added to the ethylene bottom oil (EO) was converted into bromine free radicals, and the aliphatic side chains of polycyclic aromatic hydrocarbons (PAHs) in EO were substituted by these bromine radicals
As the amount of bromine added increased, the amount of hydrogen on the side chains of the aromatic rings substituted by bromine increased, which promoted the occurrence of the condensation reaction and increased the condensation degree of molecules in the EO

Summary

Introduction

Carbon fiber is an important material that is widely used in the automobile, aerospace, and sport industries, as well as other industries [1,2]. General-purpose carbon fibers (GPCFs) that are prepared with isotropic pitch as a precursor have the advantages of a low cost and appropriate mechanical properties. The properties of GPCFs are significantly affected by the qualities of raw materials and the properties of isotropic pitch precursors [7]. Raw materials used for the preparation of GPCFs mainly come from the byproducts of coal and petroleum processing, such as coal tar, anthracene oil, ethylene bottom oil (EO), and so forth to realize the low-cost preparation of GPCFs [8,9,10,11]. With a high carbon content and low ash content, EO is a cheap material that can be used for the potential preparation of isotropic pitch and carbon fiber materials. Starting from EO, the preparation methods of isotropic pitch precursors and GPCFs include thermal condensation [12,13], co-carbonization with PVC [14,15], and bromination-debromination [16]

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Conclusion