Significant reduction in stabilization temperature and improved mechanical/electrical properties of pitch-based carbon fibers by electron beam irradiation

https://doi.org/10.1016/j.jiec.2016.03.040Get rights and content

Highlights

  • An E-beam irradiation was introduced in the stabilization during production of carbon fibers.

  • The E-beam irradiated pitch fibers were stabilized at a lower temperature and its SI was more than 90%.

  • The mechanical property of carbon fibers treated with E-beam in their stabilization process was improved by 2.5 times.

Abstract

Carbon fibers are produced using an electron beam, which can reduce the temperature and time in their stabilization processes compared with the existing processes that use heat treatment. Pitch fibers with a stabilization index (SI) of more than 90% are obtained under a lower heat treatment temperature after an electron beam irradiation of 3000 kGy. It is contributed that electron beam irradiation facilitates dehydrogenation and the introduction of oxygen. Carbon fibers stabilized under the conditions of 3000 kGy and 250 °C show 563 MPa and 69 GPa for tensile strength and Young's modulus, respectively. In addition, the electrical conductivity of carbon fibers is approximately 600 S/cm with SI of more than 84%. Therefore, the electron beam reduces the time and energy required to stabilize the pitch fibers, and electron beam-treated carbon fibers show excellent tensile strength and electrical conductivity.

Graphical abstract

An E-beam increases radicals formation that provide oxygen to stabilize pitch fibers with more reactive sites, which showed a higher stabilization index and physical properties of carbon fibers.

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Introduction

Carbon fibers consist of six-membered crystallite carbon in a stacked structure. Carbon fibers have excellent properties, such as tensile strength, modulus, chemical stability, electrical conductivity [1], and a low coefficient of thermal expansion, due to the sp2 hybridization of the carbon bond and the orientation of the crystallite due to the heat treatment [2], [3]. High-performance carbon fibers are used as a reinforcement for composites due to their mechanical characteristics, such as tensile strength and modulus. Carbon fibers have been widely used in civil and architectural engineering, energy, automobile, and aerospace industries, as well as in sports and leisure industries. For this reason, the production yield of carbon fibers has increased from 15,000 tons to 40,000 tons over the past ten years [4], [5]. Carbon fibers can be prepared from polyacrylonitrile (PAN), petroleum- or coal-based pitch, and rayon, among these, PAN-based carbon fibers have been the most highly produced until now [6]. However, the use of PAN-based carbon fibers in bulk goods, such as in the sports and leisure industries, has been limited because their unit price is high [7]. Therefore, pitch-based carbon fibers with inexpensive raw materials and high productivity have recently been shown as a promising alternative [8], [9].

An important part of the production process of pitch-based carbon fibers is the stabilization of the pitch fibers before a high heat treatment. Stabilization prohibits the melting of pitch fibers during carbonization and maintains the fiber morphology, providing oxygen on the inside and on the surface of the pitch fibers. In addition, this process is key factor for determining the mechanical properties of the final carbon fibers [10], [11]. The present stabilization process is performed using heat, which is cost prohibitive considering the slow heating rate and the high stabilization temperature [12], [13]. Thus, the stabilization process using heat treatment must be improved.

Electron beam (E-beam) irradiation is an effective method because of various advantages, such as low operating costs, clean operation, and the possibility of using at room temperature. E-beam irradiation has already been used in polymer technology, such as polymerization, crosslinking, and setting without an initiator [14], [15]. Studies on the stabilization of pitch fibers using E-beam irradiation are lacking although the stabilization of PAN fibers (the formation of a ladder structure by cyclization) using E-beam irradiation has been studied [16], [17], [18], [19]. In addition, it is possible to reduce the heat-treatment temperature and the stabilization time of pitch fibers if E-beam irradiation is used, which also reduces the operation cost and provides a simple process.

In this study, we aimed to determine the effect of E-beam irradiation on the stabilization of pitch fibers during carbon fiber production. Pitch fibers were treated with heat and E-beam irradiation, and then the stabilized pitch fibers were carbonized. The characteristics of the stabilized carbon fibers were investigated to evaluate the stabilization level. The physical properties of the carbon fibers prepared under the stabilization conditions were also investigated.

Section snippets

Materials

Pitch fibers used in this stabilization experiment were prepared from a pitch reforming pyrolysis fuel oil (PFO), which was a petroleum-based residue and was obtained from GS Caltex. Co., Korea. The PFO contained more than 90 wt% carbon and more than 6 wt% hydrogen, as shown in Table 1. Additionally, nitrogen and sulfur impurities were present at 2.19 and 0.1 wt%, respectively, in the PFO. 500 g of the PFO was heated from room temperature to 360 °C at a heating rate of 2 °C/min under a 2 L/min

Changes in the chemical structure of the stabilized pitch fibers

Stabilization induces crosslinking between the inner molecules of the pitch fibers during the heat treatment. This process provides a proper structure, which has an excellent thermal stability, and prohibits melting of the pitch fibers during carbonization. To maintain the fiber morphology of the pitch fibers, oxygen is supplied during stabilization. If the stabilization is not well conducted, then the fibers will fuse and congeal. In the case of pitch fibers, dehydrogenation and the

Conclusions

The comparative studies presented here demonstrated that the introduction of electron-beam irradiation in the stabilization of pitch fibers reduced the heat-treatment temperature. The electron beam enabled dehydrogenation and the formation of oxygen functional groups, such as carbonyls and ethers, at lower temperatures. This is attributed to a higher degree of oxygen diffusion into the pitch fibers, forming more reactive sites for oxygen attack by electron beam irradiation. A stabilization

Acknowledgement

This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (No. 2013M2A2A6043697).

References (35)

  • Q. Yang et al.

    Mater. Des.

    (2014)
  • B.J. Kim et al.

    Int. J. Hydrogen Energy

    (2008)
  • D.I. Chukov et al.

    Composites B

    (2015)
  • B.J. Kim et al.

    Carbon

    (2014)
  • S. Arbab et al.

    Polym. Degrad. Stab.

    (2013)
  • I.C. Lewis

    Carbon

    (1980)
  • F. Vautard et al.

    Composites A

    (2013)
  • B. Schlemmer et al.

    J. Chromatogr. A

    (2009)
  • H.K. Shin et al.

    J. Ind. Eng. Chem.

    (2014)
  • M. Park et al.

    J. Ind. Eng. Chem.

    (2014)
  • Y.-S. Lee et al.

    Carbon

    (2003)
  • E. Vilaplana-Ortego et al.

    Fuel Process Technol.

    (2007)
  • Y. Zhang et al.

    Electrochim. Acta

    (2009)
  • Y. Choi et al.

    Mater. Lett.

    (2014)
  • R.B. Mathur et al.

    Carbon

    (1991)
  • M.J. Yu et al.

    Mater. Lett.

    (2007)
  • E. Mora et al.

    Carbon

    (2002)
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