Key Takeaways & Executive Findings
- •• L-SP with lower polymerization degree and longer alkyl side chains exhibits viscous-dominant rheology, promoting uniform stretching and maximizing carbon fiber properties. • H-SP with larger PAHs and higher branching shows balanced viscous-elastic behavior, leading to die swelling and surface irregularities despite better physical properties. • Both pitches yield carbon fibers with similar tensile strength and modulus, indicating that rheological properties critically influence fiber quality. • Optimal spinnable pitch should have high aromatic carbon content, small PAH size, and low C=O/O-C=O content to ensure viscosity-dominated flow and reduce defects.
Abstract
The structure and composition of a spinnable pitch determine the properties of the carbon fibers produced from it. Spinnable pitches with low and high softening points (L-SP and H-SP) were prepared by air-blowing thermal polymerization of coal tar pitch. The polymerization mechanism, structural composition, properties of the pitch, and the carbon fiber properties were investigated by fluorescence excitation-emission spectroscopy with parallel factor analysis, EPR, 13C-NMR, dynamic shear rheometry, XRD, Raman, etc. L-SP had the lower degree of polymerization, longer alkyl side chains, and a higher proportion of C―O―C groups. At its spinning temperature, the molten L-SP had viscous-dominant rheological characteristics. H-SP had larger polycyclic aromatic hydrocarbon rings, a higher degree of branching, and a higher polarity. The molten H-SP had a high storage and loss moduli, and a rheological behavior with nearly balanced viscous and elastic properties. Although carbon fibers prepared from H-SP had the better physical properties, their inferior rheological properties could lead to melt die swelling, the formation of surface particles and an increased number of irregularities. The superior viscoelasticity of L-SP promoted uniform stretching, maximizing the properties of carbon fibers. This ultimately resulted in similar tensile strengths and moduli of the carbon fibers prepared from the two pitches. The high-quality spinnable pitch had a high aromatic carbon content, a small size of its PAHs, and a low C＝O/O―C＝O content, which ensured viscosity-dominated rheological behavior, thereby reducing die swelling and melt fracture, and the spinning stability and properties of the carbon fibers produced were improved.
1. Introduction
Carbon fiber plays an important role in aerospace, defense, and new energy transportation fields due to its excellent performance[1−2]. In contrast to the superior mechanical performance of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber exhibits typical characteristics of a functional material, particularly in thermal protection and oxidation resistance[3–5]. Various heavy products derived from coal and petroleum, and polycyclic hydrocarbons, are suitable raw materials for preparing pitch-based carbon fiber[6−7]. Among them, coal tar pitch is an excellent precursor due to its high content of polycyclic aromatic hydrocarbons, readily polymerized, cross-linked, graphitized, as well as a high carbon yield[4,8−9].
The quinoline-insoluble components and impurities in coal tar pitch have to be removed, as they affect the rheological properties and spinnability of the spinnable pitch, and ultimately degrade the performance of the resultant carbon fibers[10−11]. It was reported that pitch-based carbon fiber prepared from coal tar pitch (refined by washing oil extraction) showed good mechanical properties[12]. An ideal spinnable pitch should possess a narrow molecular weight distribution, low impurity, heteroatom content, and excellent melt rheological properties[13−14].
Spinnable pitch with suitable softening point, favorable thermal stability, and rheological properties could be obtained by physical or chemical modification[15–18]. Spinnable pitch prepared by the co-carbonization of coal tar pitch with methylnaphthalene or petroleum pitch exhibited a linear molecular structure, which facilitated extrusion from spinnerets and enhanced spinnability[16]. The bromomethylation reaction facilitated the formation of linear molecular structure with methylene cross-linked bridges in spinnable pitch. Moreover, the tensile strength and modulus of resultant carbon fibers were...
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LI Qian, ZHANG Bingfeng, YANG Yan, ZUO Pingping, QIN Fangfang, QU Shijie, SHEN Wenzhong (2025). The effect of the chemical structure of spinnable pitches on their rheological properties and spinnability and the properties of carbon fibers produced from them. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2026-41-03-14)
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What is the effect of chemical structure on the rheological properties of spinnable pitches?
The chemical structure, such as the degree of polymerization, alkyl side chain length, and PAH size, directly influences the rheological behavior. Pitches with lower polymerization and longer alkyl chains exhibit viscous-dominant flow, while those with larger PAHs and higher branching show balanced viscous-elastic properties.
How does the rheological behavior of spinnable pitch affect carbon fiber properties?
Viscous-dominant rheology promotes uniform stretching during spinning, reducing defects like die swelling and melt fracture, leading to improved fiber tensile strength and modulus. In contrast, elastic-dominant behavior can cause surface irregularities and inferior spinning stability.
What are the key characteristics of a high-quality spinnable pitch?
A high-quality spinnable pitch should have high aromatic carbon content, small PAH size, and low C=O/O-C=O content. These features ensure viscosity-dominated rheological behavior, reducing die swelling and melt fracture, and improving spinning stability and final fiber properties.
Why do carbon fibers from L-SP and H-SP have similar tensile strengths despite different physical properties?
Although H-SP-derived fibers have better physical properties, their inferior rheological properties lead to defects. L-SP's superior viscoelasticity allows uniform stretching, maximizing fiber properties, resulting in similar tensile strengths and moduli for both.
What methods were used to investigate the pitch structure and properties?
The study employed fluorescence excitation-emission spectroscopy with parallel factor analysis, EPR, 13C-NMR, dynamic shear rheometry, XRD, and Raman spectroscopy to analyze the polymerization mechanism, structural composition, and rheological properties of the pitches.
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