Abstract
An electron beam was irradiated on polyacrylonitrile (PAN) fibers prior to thermal stabilization. The electron-beam irradiation effectively shortened the thermal stabilization process by one fourth compared with the conventional thermal stabilization process. A comprehensive mechanistic study was conducted regarding this shortening of the thermal stabilization by electron-beam irradiation. Various species of chain radicals were produced in PAN fibers by electron-beam irradiation and existed for a relatively long duration, as observed by electron spin resonance spectroscopy. Subsequently, these radicals were gradually oxidized to peroxy radicals in the presence of oxygen under storage or heating. We found that these peroxy radicals (CO) enabled such an effective shortcut of thermal stabilization by acting as intermolecular cross-linking and partial aromatization points in the low temperature range (100–130 °C) and as earlier initiation seeds of successive cyclization reactions in the next temperature range (>130–140 °C) of thermal stabilization. Finally, even at a low irradiation dose (200 kGy), followed by a short heat treatment (230 °C for 30 min), the PAN fibers were sufficiently stabilized to produce carbon fibers with tensile strength and modulus of 2.3 and 216 GPa, respectively, after carbonization.
Highlights
Of their energy to the covalent bond electrons in the polymers, which is sufficient to break these covalent bonds and produce various radicals
The color change of polymeric materials by irradiation with ionizing radiation is caused by the formation of conjugated double bonds (C=C)n or color centers associated with radical species trapped within glassy polymer matrices, as previously reported in the literature[27,28]
It is well known that energetic electron irradiation can cause bond cleavage of polymeric materials, no significant changes were observed by Fourier transform infrared (FT-IR) spectroscopy until an electron dose of 1500 kGy
Summary
Of their energy to the covalent bond electrons in the polymers, which is sufficient to break these covalent bonds and produce various radicals. Dietrich in 199617, which showed that electron-beam irradiation can significantly reduce the thermal stabilization time of polyacrylonitrile (PAN) fibers, no studies have been reported on the electron irradiation of PAN fibers with low beam current and low dose in air conditions. Several reports have described electron irradiation of PAN fibers in which the irradiation induced cross-linking and cyclization reactions[16,20,21,22,23,24] These reports are commonly conducted at high beam current, which may cause local temperature rise within the fiber even though the irradiation was conducted at room temperature. Electron-beam irradiation was performed on PAN fibers to reduce the thermal stabilization time. The effects of electron irradiation on thermal stabilization of PAN fibers were carefully and thoroughly analyzed, and a reasonable mechanism was deduced based on the analysis results
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