The effect of ethylenediamine pretreatment on the molecular structure of thermally stabilized polyacrylonitrile fibers before carbonization

Abstract

Aqueous ethylenediamine (EDA) pretreatment followed by thermal stabilization of polyacrylonitrile (PAN) fibers in an oxygen rich air environment was carried out prior to the carbonization stage. The results show that the EDA pretreatment is very effective and efficient in promoting the cyclization of nitrile groups by shortening the time necessary for the development of thermally stable structure needed to withstand the high carbonization temperatures. A direct relationship between the values of density and the oxygen content is found which is believed to be due to the positive role played by the oxygen containing functional groups in the formation of ladder frame structures. Analysis of the equatorial X-ray diffraction traces shows the transformation of the original structure from a highly ordered phase to a totally disordered amorphous phase as indicated by the loss of the degree of order of the original PAN fiber. X-ray, Differential Scanning Calorimetry (DSC), and infrared conversion indices show the rapid conversion from the original open structure to highly cyclized and crosslinked polymer structure. Utilization of EDA pretreatment prior to the thermal stabilization is expected to significantly reduce the cost of the final carbon fiber manufacturing by reducing the time necessary for the thermal stabilization stage. POLYM. ENG. SCI.,

Molecular and thermal studies of carbon fiber precursor polymers with low thermal‐oxidative stabilization characteristics

“…The molecular parameters [average molecular weights, molecular weight distribution ( M w / M n )] were determined by size exclusion chromatography (SEC)‐TDA max instrument of Malvern Viscotek TDA 305 (Triple Detector Array) equipped with I‐MBHMW‐3078 column, a differential refractometer, a precision low angle light scattering detector, and a viscometer. The molecular weight parameters were computed using SEC data processing system (Omni SEC software), the instrument was operated at 50 °C with DMSO as solvent. A flow rate of 1 mL min −1 and injection volume of 100 μL was maintained.…”

“…Several types of pretreatments to the PAN‐based fibers have been employed to promote the cyclization . For example, pretreatments with plasma, Gamma ray, electron beam, and UV irradiation and chemical treatment with boron, bromide agents have been reported to promote the intermolecular cyclization as well as the crosslinking of the nitrilegroups . However, excessive irradiation could induce surface defects, which had negative impacts on the mechanical properties of the resulted fibers.…”

“…23,27 For example, pretreatments with plasma, Gamma ray, electron beam, and UV irradiation and chemical treatment with boron, bromide agents have been reported to promote the intermolecular cyclization as well as the crosslinking of the nitrilegroups. 28,29 However, excessive irradiation could induce surface defects, which had negative impacts on the mechanical properties of the resulted fibers. Many investigators attempted to produce acrylonitrile copolymers as CF precursors with enhanced thermal properties, but these candidate precursors suffer from the poor drawing characteristics during the heat treatment process due to high brittleness and causes a high frequency of fluff/loose filaments per meter of precursor.…”

Structural Characterization of Thermally Stabilized Poly(acrylonitrile) Fibers by Means of X-ray Diffraction, FT-IR Spectroscopy, and TGA Analysis

“…Because of the structural changes occurring during the thermal stabilization process, a new vibration at about 1585 cm -1 is observed in the IR spectrum of NH 4 Br impregnated and heat stabilized PAN sample. The infrared band positioned at 1585 cm -1 is thought to be an indication of intramolecular reactions as well as the transformation of nitrile (C≡N) group into nitrile (C=N) band due to the development of aromatization processes (Karacan and Erdogan, 2012). The spectrum develops further with increasing stabilization time (Fig.…”

Influence of air circulation on the structure and properties of melt-spun PAN precursor fibers during thermal oxidation

“…2,3 But high cost of PAN precursor bers, which accounts for almost 50% of the total cost, limits the potential widespread use of carbon bers in commercial application in comparison with other structural material like glass bers and steel. 11 Results indicated that these gases facilitated cyclization and oxidation reactions to shorten the stabilization time. Thus, it is necessary to develop a new spinning process or precursor bers in order to lower the cost of PAN-based carbon bers.…”