Indicators for evaluation of progress in thermal stabilization reactions of polyacrylonitrile fibers

Oxidative stabilization is a key process for polyacrylonitrile (PAN)-based carbon materials. During this process, oxygen has a significant influence on the formation of cyclization structure and crosslinking structure of PAN matrix. Here, graphene oxide (GO) was used as filler in PAN matrix, the structure evolution of GO/PAN composite was studied during oxidative stabilization. Solubility measurement revealed that the crosslinking degree increased, while the cyclization degree of stabilized films decreased after GO incorporation. The effect of GO on the structure of PAN film was characterized by XRD, DSC, DMA, FTIR, and XPS. These results verified that GO could initiate the cyclization reaction of PAN at a lower temperature. The carboxylic groups on GO sheets might take part in the cyclization reactions during the heat treatment. Moreover, the oxygen-containing molecules released from GO decomposition during the heat treatment were beneficial to the formation of crosslinking structure. The possible mechanism of the structure evaluation was proposed in this article.

Section: Resultssupporting

confidence: 68%

Structure evolution mechanism of polyacrylonitrile films incorporated with graphene oxide during oxidative stabilization

Chen

et al. 2019

“…ATR‐FTIR spectra of PAN‐ co ‐PSSA, PAN, and PAN‐ co ‐PVTz were shown in Figure . Bands corresponding to CN stretching vibration, and CH bending vibration of PAN were shown at 2248 and 1458 cm −1 , respectively . Asymmetric and symmetric stretching vibrations of SO in sulfonic acid of PSSA were at 1223, 1046, and 1001 cm −1 .…”

Section: Resultsmentioning

confidence: 93%

Polyacrylonitrile‐based proton conducting membranes containing sulfonic acid and tetrazole moieties

Sangthumchai

Youngme

Martwiset

2017

Proton conducting membranes based on polymers containing sulfonic acid and tetrazole moieties were developed. Successful syntheses of poly(acrylonitrile-co-styrene sulfonic acid) (PAN-co-PSSA), poly(acrylonitrile-co-5-vinyl tetrazole) (PAN-co-PVTz), and poly(acrylonitrile-co-5-vinyl tetrazole-co-styrene sulfonic acid) (PAN-co-PVTz-co-PSSA) were confirmed by 1 H-nuclear magnetic resonance spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy. Two approaches were performed to study the effects of molar ratio of sulfonic acid to tetrazole and tetrazole content on membrane properties. In the first approach, PAN-co-PSSA was blended with PAN-co-PVTz at three molar ratios. The second approach focused on PAN-co-PVTz-co-PSSA membranes with various tetrazole contents. PAN-co-PSSA membrane was also prepared. All solution-cast membranes were hydrolytically stable, except for PAN-co-PVTz-co-PSSA with 71% tetrazole. Surface morphologies of blend membranes were studied using scanning electron microscopy, and no phase separation was observed. Water uptake was shown to increase with increasing tetrazole. All membranes exhibited high thermal stability (up to 250 8C) and high storage moduli. Proton conductivity was found to depend significantly on relative humidity. The influences of sulfonic acid to tetrazole ratio and tetrazole content on proton conduction were observed and discussed. A maximum proton conductivity of 7.1 3 10 23 S/cm at 26 8C was obtained from PAN-co-PSSA membrane. In addition, all tested membranes showed relatively good oxidative stability after treatment in Fenton's reagent. V C 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45411.

“…1,15 Stabilization process is very complex especially in the oxidizing atmosphere. According to the previous studies on the extent of stabilization by FTIR, [16][17][18] the nitrile groups were gradually decreased as the stabilization proceeding and were not totally reacted. That is to say the stabilized PAN must be composed of two parts differing in chemical structure, the heat-resistant aromatic ring and the heat-labile polymer chain.…”

Section: Resultsmentioning

confidence: 95%

The conjugated plane formed in polyacrylonitrile during thermal stabilization

Shuai

Cao

2016

The formation process and mechanism of the pseudo‐graphite sheets of polyacrylonitrile (PAN) during thermal treatment in inert atmosphere were investigated by thermo‐gravimetry (TG) and X‐ray diffraction (XRD). According to the results, the conjugated plane originally formed during stabilization was proposed as the basic planar structure of the pseudo‐graphite sheets, and it was connected and stacked to form pseudo‐graphite microcrystal through chain scission reaction and non‐carbon atoms elimination reaction in 280–450 °C and 800–1300 °C respectively. The in situ measurements for time dependence of ultraviolet‐visible (UV‐vis) and Fourier transform infrared spectra (FTIR) were applied to study the conjugated plane of PAN during isothermal stabilization. It was found that with the higher temperature the conjugated plane forms more rapidly, and it has higher conjugated extent with the extending of heating time. The FTIR data showed that both cyclization and dehydrogenation are beneficial to the evolution of conjugated plane in the first 3 h, but only cyclization continues after 3 h at 250 °C. Further investigation indicated that stabilized PAN with large quantity and high conjugated extent of the conjugated plane would contribute to get large size of pseudo‐graphite microcrystal after carbonization, which is consistent with the former assumption. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43890.