Abstract
The quality of polyacrylonitrile (PAN) precursor has a great influence on the properties of the resultant carbon fibers. In this paper, a novel comonomer containing the sulfonic group, 2-acrtlamido-2-methylpropane acid (AMPS), was introduced to prepare P(AN-co-AMPS) copolymers using itaconic acid (IA) as the control. The nanofibers of PAN, P(AN-co-IA), and P(AN-co-AMPS) were prepared using the electrospinning method. The effect of AMPS comonomer on the carbon nanofibers was studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman spectrum. The structural evolutions of PAN-based nanofibers were quantitatively tracked by FTIR and XRD during the thermal oxidative stabilization (TOS) process. The results suggested that P(AN-co-AMPS) nanofibers had the lower heat release rate (ΔH/ΔT = 26.9 J g−1 °C−1), the less activation energy of cyclization (Ea1 = 26.6 kcal/mol and Ea2 = 27.5 kcal/mol), and the higher extent of stabilization (Es and SI) during TOS process, which demonstrated that the AMPS comonomer improved the efficiency of the TOS process. The P(AN-co-AMPS) nanofibers had the better thermal stable structures. Moreover, the carbon nanofibers derived from P(AN-co-AMPS) precursor nanofibers had the better graphite-like structures (XG = 46.889). Therefore, the AMPS is a promising candidate comonomer to produce high performance carbon fibers.
Highlights
Due to their high strength and modulus, low weight, and excellent heat resistance, carbon fibers have been extensively used as a versatile reinforcing material of composites applied in the fields of aerospace, automotive industries, and civil engineering [1,2,3,4]
In our previous work [23], we found that ethylenesulfonic acid (ESA) containing a sulfonic group is more effective for PAN-based carbon fiber precursor than itaconic acid (IA) in the theoretical calculation and experimental results, including activation energy of cyclization, heat release, and char yielding
The incorporation of IA and AMPS comonomers into the PAN macromolecular chains reduces the values of molecular weights (Mw), which can be attributed to the inhibition effect caused by the larger molecular volume of the comonomers
Summary
Due to their high strength and modulus, low weight, and excellent heat resistance, carbon fibers have been extensively used as a versatile reinforcing material of composites applied in the fields of aerospace, automotive industries, and civil engineering [1,2,3,4]. During the manufacturing process of PAN-based carbon fibers, thermal oxidative stabilization (TOS) at 200–300 ◦ C is a key stage undergoing cyclization, dehydrogenation, oxidation, and tautomerization reaction [8,9]. PAN homopolymer undergoes an uncontrollable exothermic reaction because of the radical cyclization mechanism during the TOS process, which results in macromolecular chain scission, voids and defects in the final carbon fiber [12,13]. It is unfavorable for the high performance of carbon fiber and for the manufacturing costs [14]
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