Rapid stabilization of polyacrylonitrile fibers achieved by plasma-assisted thermal treatment on electron-beam irradiated fibers

https://doi.org/10.1016/j.jiec.2018.10.008Get rights and content

Abstract

In the manufacturing process of polyacrylonitrile (PAN) based carbon fiber (CF), stabilization, is crucial to both process efficiency and the mechanical properties of CFs. Highly effective stabilization was successfully demonstrated by plasma-assisted thermal treatment (PT) on electron-beam irradiated PAN fibers. The method was remarkably efficient to prepare carbonizable fibers within a total stabilization time of 13.3 min, which includes electron beam irradiation (3.3 min) and PT time (10 min). We believe that such a fast stabilization was achieved by coaction of diffusive and reactive oxygen species from atmospheric plasma source with oxygen-favored radicals introduced by pre-treatment of electron-beam irradiation.

Introduction

Carbon fibers (CFs) are prepared by following processes: precursor synthesizing, fiber spinning, stabilization, carbonization, and surface treatment [1], [2], [3], [4]. For extensively wide applications of CFs, low cost CFs have been developed as important research projects around the world with various approaches such as a new precursor development for reducing fiber manufacturing cost [5], [6], shortening time in stabilization [7], [8], [9], and energy saving process in carbonization [10]. Commercially, polyacrylonitrile (PAN) [11] and pitch based CFs [12], [13], [14] are manufactured, classified by type of precursors. In the previous studies, we demonstrated new effective stabilizations such as plasma-assisted stabilization [15], [16] and electron beam (e-beam) irradiation prior to thermal treatment [17], [18], which can be compared to conventional thermal stabilization for preparing PAN based CFs. It was revealed that plasma in air atmosphere could generate very active species such as ozone, oxygen atoms, and oxygen related functional groups, which diffused into PAN fibers efficiently, because some of them are small and reactive enough to penetrate into fibers and oxidize them. Hence, stabilization was significantly reduced for 120 to 60 min while maintaining comparable tensile strength of resulting CFs [15], [16]. Recently, e-beam was irradiated on PAN fibers with doses of 200–1500 kGy at 25 °C, controlled by a water-cooled stage, which produced peroxy radicals in PAN molecules, and they started to induce cyclization when thermal treatment was applied at 150 °C as a relatively low temperature, leading to accelerating stabilization [17]. Therefore, e-beam exposure for 200 s or 200 kGy and an additional heat treatment for 30 min resulted in well stabilized PAN fibers [17].

In this study, we combined two methods to achieve extremely short stabilization. A tailor-made plasma assisted thermal convection oven was designed for this study and atmospheric plasma was applied at a given temperature on e-beam irradiated PAN fibers. A systematic investigation by various techniques revealed structural evolution in e-beam irradiated and plasma treated PAN fibers. Those fibers were carbonized at 1200 °C, and tensile properties were determined by a single filament test.

Section snippets

Materials

Commercial of PAN tows of 12k filaments (Jilin, China) were obtained from Sinosteel Jilin Carbon Co., Ltd.

Sample preparation

Electron-beam irradiation on fibers was carried out at EB Tech Co., Ltd (Daejeon, Republic of Korea). About a meter of tows was placed on the stage with water cooling system and was irradiated for 200 s. The beam energy and current were set at 1 MeV and 1 mA, respectively. The irradiated fibers were collected and stabilized by a tailor-made plasma-assisted thermal system for 10, 20, 30 min.

Thermal behavior of stabilized fibers

The scheme of experiments is represented in Fig. 1a. Commercial PAN fibers (Jilin, 12k, China) were firstly e-beam irradiated under cooling environment for 200 s and the fibers were thermally stabilized at 230 °C with atmospheric plasma source distanced by about 5 cm below providing reactive oxygen species. One of main purposes of stabilization in CF manufacture is to diminish residual reaction heat released during carbonization because a fiber bundle could experience fusion between filaments in

Conclusion

The total of 13.3 min of rapid stabilization was achieved using efficient stabilization method of EPT on e-beam irradiated PAN fibers. Comparative analyses between ET and EPT were conducted to elucidate the synergic effect between e-beam irradiation and atmospheric plasma source regarding the fast oxidation. It was evident that rapid and uniform oxidation of e-beam irradiated PAN fibers by EPT, which, in fact, allowed rapid preparation of thermally manageable stabilized fibers within short time

Acknowledgements

This work was supported by a grant from the Korea Institute of Science and Technology (KIST) Institutional program and the Industrial Core Technology Development Program (10052760) and the Civil-Military technology cooperation program funded by the Ministry of Trade, Industry and Energy, Republic of Korea.

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